1 @c Copyright (C) 1988-2017 Free Software Foundation, Inc.
2 @c This is part of the GCC manual.
3 @c For copying conditions, see the file gcc.texi.
6 @chapter Target Description Macros and Functions
7 @cindex machine description macros
8 @cindex target description macros
9 @cindex macros, target description
10 @cindex @file{tm.h} macros
12 In addition to the file @file{@var{machine}.md}, a machine description
13 includes a C header file conventionally given the name
14 @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}.
15 The header file defines numerous macros that convey the information
16 about the target machine that does not fit into the scheme of the
17 @file{.md} file. The file @file{tm.h} should be a link to
18 @file{@var{machine}.h}. The header file @file{config.h} includes
19 @file{tm.h} and most compiler source files include @file{config.h}. The
20 source file defines a variable @code{targetm}, which is a structure
21 containing pointers to functions and data relating to the target
22 machine. @file{@var{machine}.c} should also contain their definitions,
23 if they are not defined elsewhere in GCC, and other functions called
24 through the macros defined in the @file{.h} file.
27 * Target Structure:: The @code{targetm} variable.
28 * Driver:: Controlling how the driver runs the compilation passes.
29 * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}.
30 * Per-Function Data:: Defining data structures for per-function information.
31 * Storage Layout:: Defining sizes and alignments of data.
32 * Type Layout:: Defining sizes and properties of basic user data types.
33 * Registers:: Naming and describing the hardware registers.
34 * Register Classes:: Defining the classes of hardware registers.
35 * Stack and Calling:: Defining which way the stack grows and by how much.
36 * Varargs:: Defining the varargs macros.
37 * Trampolines:: Code set up at run time to enter a nested function.
38 * Library Calls:: Controlling how library routines are implicitly called.
39 * Addressing Modes:: Defining addressing modes valid for memory operands.
40 * Anchored Addresses:: Defining how @option{-fsection-anchors} should work.
41 * Condition Code:: Defining how insns update the condition code.
42 * Costs:: Defining relative costs of different operations.
43 * Scheduling:: Adjusting the behavior of the instruction scheduler.
44 * Sections:: Dividing storage into text, data, and other sections.
45 * PIC:: Macros for position independent code.
46 * Assembler Format:: Defining how to write insns and pseudo-ops to output.
47 * Debugging Info:: Defining the format of debugging output.
48 * Floating Point:: Handling floating point for cross-compilers.
49 * Mode Switching:: Insertion of mode-switching instructions.
50 * Target Attributes:: Defining target-specific uses of @code{__attribute__}.
51 * Emulated TLS:: Emulated TLS support.
52 * MIPS Coprocessors:: MIPS coprocessor support and how to customize it.
53 * PCH Target:: Validity checking for precompiled headers.
54 * C++ ABI:: Controlling C++ ABI changes.
55 * Named Address Spaces:: Adding support for named address spaces
56 * Misc:: Everything else.
59 @node Target Structure
60 @section The Global @code{targetm} Variable
62 @cindex target functions
64 @deftypevar {struct gcc_target} targetm
65 The target @file{.c} file must define the global @code{targetm} variable
66 which contains pointers to functions and data relating to the target
67 machine. The variable is declared in @file{target.h};
68 @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
69 used to initialize the variable, and macros for the default initializers
70 for elements of the structure. The @file{.c} file should override those
71 macros for which the default definition is inappropriate. For example:
74 #include "target-def.h"
76 /* @r{Initialize the GCC target structure.} */
78 #undef TARGET_COMP_TYPE_ATTRIBUTES
79 #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
81 struct gcc_target targetm = TARGET_INITIALIZER;
85 Where a macro should be defined in the @file{.c} file in this manner to
86 form part of the @code{targetm} structure, it is documented below as a
87 ``Target Hook'' with a prototype. Many macros will change in future
88 from being defined in the @file{.h} file to being part of the
89 @code{targetm} structure.
91 Similarly, there is a @code{targetcm} variable for hooks that are
92 specific to front ends for C-family languages, documented as ``C
93 Target Hook''. This is declared in @file{c-family/c-target.h}, the
94 initializer @code{TARGETCM_INITIALIZER} in
95 @file{c-family/c-target-def.h}. If targets initialize @code{targetcm}
96 themselves, they should set @code{target_has_targetcm=yes} in
97 @file{config.gcc}; otherwise a default definition is used.
99 Similarly, there is a @code{targetm_common} variable for hooks that
100 are shared between the compiler driver and the compilers proper,
101 documented as ``Common Target Hook''. This is declared in
102 @file{common/common-target.h}, the initializer
103 @code{TARGETM_COMMON_INITIALIZER} in
104 @file{common/common-target-def.h}. If targets initialize
105 @code{targetm_common} themselves, they should set
106 @code{target_has_targetm_common=yes} in @file{config.gcc}; otherwise a
107 default definition is used.
110 @section Controlling the Compilation Driver, @file{gcc}
112 @cindex controlling the compilation driver
114 @c prevent bad page break with this line
115 You can control the compilation driver.
117 @defmac DRIVER_SELF_SPECS
118 A list of specs for the driver itself. It should be a suitable
119 initializer for an array of strings, with no surrounding braces.
121 The driver applies these specs to its own command line between loading
122 default @file{specs} files (but not command-line specified ones) and
123 choosing the multilib directory or running any subcommands. It
124 applies them in the order given, so each spec can depend on the
125 options added by earlier ones. It is also possible to remove options
126 using @samp{%<@var{option}} in the usual way.
128 This macro can be useful when a port has several interdependent target
129 options. It provides a way of standardizing the command line so
130 that the other specs are easier to write.
132 Do not define this macro if it does not need to do anything.
135 @defmac OPTION_DEFAULT_SPECS
136 A list of specs used to support configure-time default options (i.e.@:
137 @option{--with} options) in the driver. It should be a suitable initializer
138 for an array of structures, each containing two strings, without the
139 outermost pair of surrounding braces.
141 The first item in the pair is the name of the default. This must match
142 the code in @file{config.gcc} for the target. The second item is a spec
143 to apply if a default with this name was specified. The string
144 @samp{%(VALUE)} in the spec will be replaced by the value of the default
145 everywhere it occurs.
147 The driver will apply these specs to its own command line between loading
148 default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
149 the same mechanism as @code{DRIVER_SELF_SPECS}.
151 Do not define this macro if it does not need to do anything.
155 A C string constant that tells the GCC driver program options to
156 pass to CPP@. It can also specify how to translate options you
157 give to GCC into options for GCC to pass to the CPP@.
159 Do not define this macro if it does not need to do anything.
162 @defmac CPLUSPLUS_CPP_SPEC
163 This macro is just like @code{CPP_SPEC}, but is used for C++, rather
164 than C@. If you do not define this macro, then the value of
165 @code{CPP_SPEC} (if any) will be used instead.
169 A C string constant that tells the GCC driver program options to
170 pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
172 It can also specify how to translate options you give to GCC into options
173 for GCC to pass to front ends.
175 Do not define this macro if it does not need to do anything.
179 A C string constant that tells the GCC driver program options to
180 pass to @code{cc1plus}. It can also specify how to translate options you
181 give to GCC into options for GCC to pass to the @code{cc1plus}.
183 Do not define this macro if it does not need to do anything.
184 Note that everything defined in CC1_SPEC is already passed to
185 @code{cc1plus} so there is no need to duplicate the contents of
186 CC1_SPEC in CC1PLUS_SPEC@.
190 A C string constant that tells the GCC driver program options to
191 pass to the assembler. It can also specify how to translate options
192 you give to GCC into options for GCC to pass to the assembler.
193 See the file @file{sun3.h} for an example of this.
195 Do not define this macro if it does not need to do anything.
198 @defmac ASM_FINAL_SPEC
199 A C string constant that tells the GCC driver program how to
200 run any programs which cleanup after the normal assembler.
201 Normally, this is not needed. See the file @file{mips.h} for
204 Do not define this macro if it does not need to do anything.
207 @defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
208 Define this macro, with no value, if the driver should give the assembler
209 an argument consisting of a single dash, @option{-}, to instruct it to
210 read from its standard input (which will be a pipe connected to the
211 output of the compiler proper). This argument is given after any
212 @option{-o} option specifying the name of the output file.
214 If you do not define this macro, the assembler is assumed to read its
215 standard input if given no non-option arguments. If your assembler
216 cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
217 see @file{mips.h} for instance.
221 A C string constant that tells the GCC driver program options to
222 pass to the linker. It can also specify how to translate options you
223 give to GCC into options for GCC to pass to the linker.
225 Do not define this macro if it does not need to do anything.
229 Another C string constant used much like @code{LINK_SPEC}. The difference
230 between the two is that @code{LIB_SPEC} is used at the end of the
231 command given to the linker.
233 If this macro is not defined, a default is provided that
234 loads the standard C library from the usual place. See @file{gcc.c}.
238 Another C string constant that tells the GCC driver program
239 how and when to place a reference to @file{libgcc.a} into the
240 linker command line. This constant is placed both before and after
241 the value of @code{LIB_SPEC}.
243 If this macro is not defined, the GCC driver provides a default that
244 passes the string @option{-lgcc} to the linker.
247 @defmac REAL_LIBGCC_SPEC
248 By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the
249 @code{LIBGCC_SPEC} is not directly used by the driver program but is
250 instead modified to refer to different versions of @file{libgcc.a}
251 depending on the values of the command line flags @option{-static},
252 @option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On
253 targets where these modifications are inappropriate, define
254 @code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the
255 driver how to place a reference to @file{libgcc} on the link command
256 line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified.
259 @defmac USE_LD_AS_NEEDED
260 A macro that controls the modifications to @code{LIBGCC_SPEC}
261 mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be
262 generated that uses @option{--as-needed} or equivalent options and the
263 shared @file{libgcc} in place of the
264 static exception handler library, when linking without any of
265 @code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}.
269 If defined, this C string constant is added to @code{LINK_SPEC}.
270 When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects
271 the modifications to @code{LIBGCC_SPEC} mentioned in
272 @code{REAL_LIBGCC_SPEC}.
275 @defmac STARTFILE_SPEC
276 Another C string constant used much like @code{LINK_SPEC}. The
277 difference between the two is that @code{STARTFILE_SPEC} is used at
278 the very beginning of the command given to the linker.
280 If this macro is not defined, a default is provided that loads the
281 standard C startup file from the usual place. See @file{gcc.c}.
285 Another C string constant used much like @code{LINK_SPEC}. The
286 difference between the two is that @code{ENDFILE_SPEC} is used at
287 the very end of the command given to the linker.
289 Do not define this macro if it does not need to do anything.
292 @defmac THREAD_MODEL_SPEC
293 GCC @code{-v} will print the thread model GCC was configured to use.
294 However, this doesn't work on platforms that are multilibbed on thread
295 models, such as AIX 4.3. On such platforms, define
296 @code{THREAD_MODEL_SPEC} such that it evaluates to a string without
297 blanks that names one of the recognized thread models. @code{%*}, the
298 default value of this macro, will expand to the value of
299 @code{thread_file} set in @file{config.gcc}.
302 @defmac SYSROOT_SUFFIX_SPEC
303 Define this macro to add a suffix to the target sysroot when GCC is
304 configured with a sysroot. This will cause GCC to search for usr/lib,
305 et al, within sysroot+suffix.
308 @defmac SYSROOT_HEADERS_SUFFIX_SPEC
309 Define this macro to add a headers_suffix to the target sysroot when
310 GCC is configured with a sysroot. This will cause GCC to pass the
311 updated sysroot+headers_suffix to CPP, causing it to search for
312 usr/include, et al, within sysroot+headers_suffix.
316 Define this macro to provide additional specifications to put in the
317 @file{specs} file that can be used in various specifications like
320 The definition should be an initializer for an array of structures,
321 containing a string constant, that defines the specification name, and a
322 string constant that provides the specification.
324 Do not define this macro if it does not need to do anything.
326 @code{EXTRA_SPECS} is useful when an architecture contains several
327 related targets, which have various @code{@dots{}_SPECS} which are similar
328 to each other, and the maintainer would like one central place to keep
331 For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
332 define either @code{_CALL_SYSV} when the System V calling sequence is
333 used or @code{_CALL_AIX} when the older AIX-based calling sequence is
336 The @file{config/rs6000/rs6000.h} target file defines:
339 #define EXTRA_SPECS \
340 @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
342 #define CPP_SYS_DEFAULT ""
345 The @file{config/rs6000/sysv.h} target file defines:
349 "%@{posix: -D_POSIX_SOURCE @} \
350 %@{mcall-sysv: -D_CALL_SYSV @} \
351 %@{!mcall-sysv: %(cpp_sysv_default) @} \
352 %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
354 #undef CPP_SYSV_DEFAULT
355 #define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
358 while the @file{config/rs6000/eabiaix.h} target file defines
359 @code{CPP_SYSV_DEFAULT} as:
362 #undef CPP_SYSV_DEFAULT
363 #define CPP_SYSV_DEFAULT "-D_CALL_AIX"
367 @defmac LINK_LIBGCC_SPECIAL_1
368 Define this macro if the driver program should find the library
369 @file{libgcc.a}. If you do not define this macro, the driver program will pass
370 the argument @option{-lgcc} to tell the linker to do the search.
373 @defmac LINK_GCC_C_SEQUENCE_SPEC
374 The sequence in which libgcc and libc are specified to the linker.
375 By default this is @code{%G %L %G}.
378 @defmac POST_LINK_SPEC
379 Define this macro to add additional steps to be executed after linker.
380 The default value of this macro is empty string.
383 @defmac LINK_COMMAND_SPEC
384 A C string constant giving the complete command line need to execute the
385 linker. When you do this, you will need to update your port each time a
386 change is made to the link command line within @file{gcc.c}. Therefore,
387 define this macro only if you need to completely redefine the command
388 line for invoking the linker and there is no other way to accomplish
389 the effect you need. Overriding this macro may be avoidable by overriding
390 @code{LINK_GCC_C_SEQUENCE_SPEC} instead.
393 @hook TARGET_ALWAYS_STRIP_DOTDOT
395 @defmac MULTILIB_DEFAULTS
396 Define this macro as a C expression for the initializer of an array of
397 string to tell the driver program which options are defaults for this
398 target and thus do not need to be handled specially when using
399 @code{MULTILIB_OPTIONS}.
401 Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
402 the target makefile fragment or if none of the options listed in
403 @code{MULTILIB_OPTIONS} are set by default.
404 @xref{Target Fragment}.
407 @defmac RELATIVE_PREFIX_NOT_LINKDIR
408 Define this macro to tell @command{gcc} that it should only translate
409 a @option{-B} prefix into a @option{-L} linker option if the prefix
410 indicates an absolute file name.
413 @defmac MD_EXEC_PREFIX
414 If defined, this macro is an additional prefix to try after
415 @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
416 when the compiler is built as a cross
417 compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
418 to the list of directories used to find the assembler in @file{configure.ac}.
421 @defmac STANDARD_STARTFILE_PREFIX
422 Define this macro as a C string constant if you wish to override the
423 standard choice of @code{libdir} as the default prefix to
424 try when searching for startup files such as @file{crt0.o}.
425 @code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
426 is built as a cross compiler.
429 @defmac STANDARD_STARTFILE_PREFIX_1
430 Define this macro as a C string constant if you wish to override the
431 standard choice of @code{/lib} as a prefix to try after the default prefix
432 when searching for startup files such as @file{crt0.o}.
433 @code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler
434 is built as a cross compiler.
437 @defmac STANDARD_STARTFILE_PREFIX_2
438 Define this macro as a C string constant if you wish to override the
439 standard choice of @code{/lib} as yet another prefix to try after the
440 default prefix when searching for startup files such as @file{crt0.o}.
441 @code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler
442 is built as a cross compiler.
445 @defmac MD_STARTFILE_PREFIX
446 If defined, this macro supplies an additional prefix to try after the
447 standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
448 compiler is built as a cross compiler.
451 @defmac MD_STARTFILE_PREFIX_1
452 If defined, this macro supplies yet another prefix to try after the
453 standard prefixes. It is not searched when the compiler is built as a
457 @defmac INIT_ENVIRONMENT
458 Define this macro as a C string constant if you wish to set environment
459 variables for programs called by the driver, such as the assembler and
460 loader. The driver passes the value of this macro to @code{putenv} to
461 initialize the necessary environment variables.
464 @defmac LOCAL_INCLUDE_DIR
465 Define this macro as a C string constant if you wish to override the
466 standard choice of @file{/usr/local/include} as the default prefix to
467 try when searching for local header files. @code{LOCAL_INCLUDE_DIR}
468 comes before @code{NATIVE_SYSTEM_HEADER_DIR} (set in
469 @file{config.gcc}, normally @file{/usr/include}) in the search order.
471 Cross compilers do not search either @file{/usr/local/include} or its
475 @defmac NATIVE_SYSTEM_HEADER_COMPONENT
476 The ``component'' corresponding to @code{NATIVE_SYSTEM_HEADER_DIR}.
477 See @code{INCLUDE_DEFAULTS}, below, for the description of components.
478 If you do not define this macro, no component is used.
481 @defmac INCLUDE_DEFAULTS
482 Define this macro if you wish to override the entire default search path
483 for include files. For a native compiler, the default search path
484 usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
485 @code{GPLUSPLUS_INCLUDE_DIR}, and
486 @code{NATIVE_SYSTEM_HEADER_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR}
487 and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
488 and specify private search areas for GCC@. The directory
489 @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
491 The definition should be an initializer for an array of structures.
492 Each array element should have four elements: the directory name (a
493 string constant), the component name (also a string constant), a flag
494 for C++-only directories,
495 and a flag showing that the includes in the directory don't need to be
496 wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of
497 the array with a null element.
499 The component name denotes what GNU package the include file is part of,
500 if any, in all uppercase letters. For example, it might be @samp{GCC}
501 or @samp{BINUTILS}. If the package is part of a vendor-supplied
502 operating system, code the component name as @samp{0}.
504 For example, here is the definition used for VAX/VMS:
507 #define INCLUDE_DEFAULTS \
509 @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \
510 @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \
511 @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \
518 Here is the order of prefixes tried for exec files:
522 Any prefixes specified by the user with @option{-B}.
525 The environment variable @code{GCC_EXEC_PREFIX} or, if @code{GCC_EXEC_PREFIX}
526 is not set and the compiler has not been installed in the configure-time
527 @var{prefix}, the location in which the compiler has actually been installed.
530 The directories specified by the environment variable @code{COMPILER_PATH}.
533 The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed
534 in the configured-time @var{prefix}.
537 The location @file{/usr/libexec/gcc/}, but only if this is a native compiler.
540 The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
543 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
547 Here is the order of prefixes tried for startfiles:
551 Any prefixes specified by the user with @option{-B}.
554 The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined
555 value based on the installed toolchain location.
558 The directories specified by the environment variable @code{LIBRARY_PATH}
559 (or port-specific name; native only, cross compilers do not use this).
562 The macro @code{STANDARD_EXEC_PREFIX}, but only if the toolchain is installed
563 in the configured @var{prefix} or this is a native compiler.
566 The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
569 The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
573 The macro @code{MD_STARTFILE_PREFIX}, if defined, but only if this is a
574 native compiler, or we have a target system root.
577 The macro @code{MD_STARTFILE_PREFIX_1}, if defined, but only if this is a
578 native compiler, or we have a target system root.
581 The macro @code{STANDARD_STARTFILE_PREFIX}, with any sysroot modifications.
582 If this path is relative it will be prefixed by @code{GCC_EXEC_PREFIX} and
583 the machine suffix or @code{STANDARD_EXEC_PREFIX} and the machine suffix.
586 The macro @code{STANDARD_STARTFILE_PREFIX_1}, but only if this is a native
587 compiler, or we have a target system root. The default for this macro is
591 The macro @code{STANDARD_STARTFILE_PREFIX_2}, but only if this is a native
592 compiler, or we have a target system root. The default for this macro is
596 @node Run-time Target
597 @section Run-time Target Specification
598 @cindex run-time target specification
599 @cindex predefined macros
600 @cindex target specifications
602 @c prevent bad page break with this line
603 Here are run-time target specifications.
605 @defmac TARGET_CPU_CPP_BUILTINS ()
606 This function-like macro expands to a block of code that defines
607 built-in preprocessor macros and assertions for the target CPU, using
608 the functions @code{builtin_define}, @code{builtin_define_std} and
609 @code{builtin_assert}. When the front end
610 calls this macro it provides a trailing semicolon, and since it has
611 finished command line option processing your code can use those
614 @code{builtin_assert} takes a string in the form you pass to the
615 command-line option @option{-A}, such as @code{cpu=mips}, and creates
616 the assertion. @code{builtin_define} takes a string in the form
617 accepted by option @option{-D} and unconditionally defines the macro.
619 @code{builtin_define_std} takes a string representing the name of an
620 object-like macro. If it doesn't lie in the user's namespace,
621 @code{builtin_define_std} defines it unconditionally. Otherwise, it
622 defines a version with two leading underscores, and another version
623 with two leading and trailing underscores, and defines the original
624 only if an ISO standard was not requested on the command line. For
625 example, passing @code{unix} defines @code{__unix}, @code{__unix__}
626 and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
627 @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
628 defines only @code{_ABI64}.
630 You can also test for the C dialect being compiled. The variable
631 @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
632 or @code{clk_objective_c}. Note that if we are preprocessing
633 assembler, this variable will be @code{clk_c} but the function-like
634 macro @code{preprocessing_asm_p()} will return true, so you might want
635 to check for that first. If you need to check for strict ANSI, the
636 variable @code{flag_iso} can be used. The function-like macro
637 @code{preprocessing_trad_p()} can be used to check for traditional
641 @defmac TARGET_OS_CPP_BUILTINS ()
642 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
643 and is used for the target operating system instead.
646 @defmac TARGET_OBJFMT_CPP_BUILTINS ()
647 Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
648 and is used for the target object format. @file{elfos.h} uses this
649 macro to define @code{__ELF__}, so you probably do not need to define
653 @deftypevar {extern int} target_flags
654 This variable is declared in @file{options.h}, which is included before
655 any target-specific headers.
658 @hook TARGET_DEFAULT_TARGET_FLAGS
659 This variable specifies the initial value of @code{target_flags}.
660 Its default setting is 0.
663 @cindex optional hardware or system features
664 @cindex features, optional, in system conventions
666 @hook TARGET_HANDLE_OPTION
667 This hook is called whenever the user specifies one of the
668 target-specific options described by the @file{.opt} definition files
669 (@pxref{Options}). It has the opportunity to do some option-specific
670 processing and should return true if the option is valid. The default
671 definition does nothing but return true.
673 @var{decoded} specifies the option and its arguments. @var{opts} and
674 @var{opts_set} are the @code{gcc_options} structures to be used for
675 storing option state, and @var{loc} is the location at which the
676 option was passed (@code{UNKNOWN_LOCATION} except for options passed
680 @hook TARGET_HANDLE_C_OPTION
681 This target hook is called whenever the user specifies one of the
682 target-specific C language family options described by the @file{.opt}
683 definition files(@pxref{Options}). It has the opportunity to do some
684 option-specific processing and should return true if the option is
685 valid. The arguments are like for @code{TARGET_HANDLE_OPTION}. The
686 default definition does nothing but return false.
688 In general, you should use @code{TARGET_HANDLE_OPTION} to handle
689 options. However, if processing an option requires routines that are
690 only available in the C (and related language) front ends, then you
691 should use @code{TARGET_HANDLE_C_OPTION} instead.
694 @hook TARGET_OBJC_CONSTRUCT_STRING_OBJECT
696 @hook TARGET_OBJC_DECLARE_UNRESOLVED_CLASS_REFERENCE
698 @hook TARGET_OBJC_DECLARE_CLASS_DEFINITION
700 @hook TARGET_STRING_OBJECT_REF_TYPE_P
702 @hook TARGET_CHECK_STRING_OBJECT_FORMAT_ARG
704 @hook TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE
706 @defmac C_COMMON_OVERRIDE_OPTIONS
707 This is similar to the @code{TARGET_OPTION_OVERRIDE} hook
708 but is only used in the C
709 language frontends (C, Objective-C, C++, Objective-C++) and so can be
710 used to alter option flag variables which only exist in those
714 @hook TARGET_OPTION_OPTIMIZATION_TABLE
715 Some machines may desire to change what optimizations are performed for
716 various optimization levels. This variable, if defined, describes
717 options to enable at particular sets of optimization levels. These
718 options are processed once
719 just after the optimization level is determined and before the remainder
720 of the command options have been parsed, so may be overridden by other
721 options passed explicitly.
723 This processing is run once at program startup and when the optimization
724 options are changed via @code{#pragma GCC optimize} or by using the
725 @code{optimize} attribute.
728 @hook TARGET_OPTION_INIT_STRUCT
730 @hook TARGET_OPTION_DEFAULT_PARAMS
732 @defmac SWITCHABLE_TARGET
733 Some targets need to switch between substantially different subtargets
734 during compilation. For example, the MIPS target has one subtarget for
735 the traditional MIPS architecture and another for MIPS16. Source code
736 can switch between these two subarchitectures using the @code{mips16}
737 and @code{nomips16} attributes.
739 Such subtargets can differ in things like the set of available
740 registers, the set of available instructions, the costs of various
741 operations, and so on. GCC caches a lot of this type of information
742 in global variables, and recomputing them for each subtarget takes a
743 significant amount of time. The compiler therefore provides a facility
744 for maintaining several versions of the global variables and quickly
745 switching between them; see @file{target-globals.h} for details.
747 Define this macro to 1 if your target needs this facility. The default
751 @hook TARGET_FLOAT_EXCEPTIONS_ROUNDING_SUPPORTED_P
753 @node Per-Function Data
754 @section Defining data structures for per-function information.
755 @cindex per-function data
756 @cindex data structures
758 If the target needs to store information on a per-function basis, GCC
759 provides a macro and a couple of variables to allow this. Note, just
760 using statics to store the information is a bad idea, since GCC supports
761 nested functions, so you can be halfway through encoding one function
762 when another one comes along.
764 GCC defines a data structure called @code{struct function} which
765 contains all of the data specific to an individual function. This
766 structure contains a field called @code{machine} whose type is
767 @code{struct machine_function *}, which can be used by targets to point
768 to their own specific data.
770 If a target needs per-function specific data it should define the type
771 @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
772 This macro should be used to initialize the function pointer
773 @code{init_machine_status}. This pointer is explained below.
775 One typical use of per-function, target specific data is to create an
776 RTX to hold the register containing the function's return address. This
777 RTX can then be used to implement the @code{__builtin_return_address}
778 function, for level 0.
780 Note---earlier implementations of GCC used a single data area to hold
781 all of the per-function information. Thus when processing of a nested
782 function began the old per-function data had to be pushed onto a
783 stack, and when the processing was finished, it had to be popped off the
784 stack. GCC used to provide function pointers called
785 @code{save_machine_status} and @code{restore_machine_status} to handle
786 the saving and restoring of the target specific information. Since the
787 single data area approach is no longer used, these pointers are no
790 @defmac INIT_EXPANDERS
791 Macro called to initialize any target specific information. This macro
792 is called once per function, before generation of any RTL has begun.
793 The intention of this macro is to allow the initialization of the
794 function pointer @code{init_machine_status}.
797 @deftypevar {void (*)(struct function *)} init_machine_status
798 If this function pointer is non-@code{NULL} it will be called once per
799 function, before function compilation starts, in order to allow the
800 target to perform any target specific initialization of the
801 @code{struct function} structure. It is intended that this would be
802 used to initialize the @code{machine} of that structure.
804 @code{struct machine_function} structures are expected to be freed by GC@.
805 Generally, any memory that they reference must be allocated by using
806 GC allocation, including the structure itself.
810 @section Storage Layout
811 @cindex storage layout
813 Note that the definitions of the macros in this table which are sizes or
814 alignments measured in bits do not need to be constant. They can be C
815 expressions that refer to static variables, such as the @code{target_flags}.
816 @xref{Run-time Target}.
818 @defmac BITS_BIG_ENDIAN
819 Define this macro to have the value 1 if the most significant bit in a
820 byte has the lowest number; otherwise define it to have the value zero.
821 This means that bit-field instructions count from the most significant
822 bit. If the machine has no bit-field instructions, then this must still
823 be defined, but it doesn't matter which value it is defined to. This
824 macro need not be a constant.
826 This macro does not affect the way structure fields are packed into
827 bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
830 @defmac BYTES_BIG_ENDIAN
831 Define this macro to have the value 1 if the most significant byte in a
832 word has the lowest number. This macro need not be a constant.
835 @defmac WORDS_BIG_ENDIAN
836 Define this macro to have the value 1 if, in a multiword object, the
837 most significant word has the lowest number. This applies to both
838 memory locations and registers; see @code{REG_WORDS_BIG_ENDIAN} if the
839 order of words in memory is not the same as the order in registers. This
840 macro need not be a constant.
843 @defmac REG_WORDS_BIG_ENDIAN
844 On some machines, the order of words in a multiword object differs between
845 registers in memory. In such a situation, define this macro to describe
846 the order of words in a register. The macro @code{WORDS_BIG_ENDIAN} controls
847 the order of words in memory.
850 @defmac FLOAT_WORDS_BIG_ENDIAN
851 Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
852 @code{TFmode} floating point numbers are stored in memory with the word
853 containing the sign bit at the lowest address; otherwise define it to
854 have the value 0. This macro need not be a constant.
856 You need not define this macro if the ordering is the same as for
860 @defmac BITS_PER_WORD
861 Number of bits in a word. If you do not define this macro, the default
862 is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
865 @defmac MAX_BITS_PER_WORD
866 Maximum number of bits in a word. If this is undefined, the default is
867 @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
868 largest value that @code{BITS_PER_WORD} can have at run-time.
871 @defmac UNITS_PER_WORD
872 Number of storage units in a word; normally the size of a general-purpose
873 register, a power of two from 1 or 8.
876 @defmac MIN_UNITS_PER_WORD
877 Minimum number of units in a word. If this is undefined, the default is
878 @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
879 smallest value that @code{UNITS_PER_WORD} can have at run-time.
883 Width of a pointer, in bits. You must specify a value no wider than the
884 width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
885 you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
886 a value the default is @code{BITS_PER_WORD}.
889 @defmac POINTERS_EXTEND_UNSIGNED
890 A C expression that determines how pointers should be extended from
891 @code{ptr_mode} to either @code{Pmode} or @code{word_mode}. It is
892 greater than zero if pointers should be zero-extended, zero if they
893 should be sign-extended, and negative if some other sort of conversion
894 is needed. In the last case, the extension is done by the target's
895 @code{ptr_extend} instruction.
897 You need not define this macro if the @code{ptr_mode}, @code{Pmode}
898 and @code{word_mode} are all the same width.
901 @defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
902 A macro to update @var{m} and @var{unsignedp} when an object whose type
903 is @var{type} and which has the specified mode and signedness is to be
904 stored in a register. This macro is only called when @var{type} is a
907 On most RISC machines, which only have operations that operate on a full
908 register, define this macro to set @var{m} to @code{word_mode} if
909 @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
910 cases, only integer modes should be widened because wider-precision
911 floating-point operations are usually more expensive than their narrower
914 For most machines, the macro definition does not change @var{unsignedp}.
915 However, some machines, have instructions that preferentially handle
916 either signed or unsigned quantities of certain modes. For example, on
917 the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
918 sign-extend the result to 64 bits. On such machines, set
919 @var{unsignedp} according to which kind of extension is more efficient.
921 Do not define this macro if it would never modify @var{m}.
924 @hook TARGET_C_EXCESS_PRECISION
926 @hook TARGET_PROMOTE_FUNCTION_MODE
928 @defmac PARM_BOUNDARY
929 Normal alignment required for function parameters on the stack, in
930 bits. All stack parameters receive at least this much alignment
931 regardless of data type. On most machines, this is the same as the
935 @defmac STACK_BOUNDARY
936 Define this macro to the minimum alignment enforced by hardware for the
937 stack pointer on this machine. The definition is a C expression for the
938 desired alignment (measured in bits). This value is used as a default
939 if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
940 this should be the same as @code{PARM_BOUNDARY}.
943 @defmac PREFERRED_STACK_BOUNDARY
944 Define this macro if you wish to preserve a certain alignment for the
945 stack pointer, greater than what the hardware enforces. The definition
946 is a C expression for the desired alignment (measured in bits). This
947 macro must evaluate to a value equal to or larger than
948 @code{STACK_BOUNDARY}.
951 @defmac INCOMING_STACK_BOUNDARY
952 Define this macro if the incoming stack boundary may be different
953 from @code{PREFERRED_STACK_BOUNDARY}. This macro must evaluate
954 to a value equal to or larger than @code{STACK_BOUNDARY}.
957 @defmac FUNCTION_BOUNDARY
958 Alignment required for a function entry point, in bits.
961 @defmac BIGGEST_ALIGNMENT
962 Biggest alignment that any data type can require on this machine, in
963 bits. Note that this is not the biggest alignment that is supported,
964 just the biggest alignment that, when violated, may cause a fault.
967 @hook TARGET_ABSOLUTE_BIGGEST_ALIGNMENT
969 @defmac MALLOC_ABI_ALIGNMENT
970 Alignment, in bits, a C conformant malloc implementation has to
971 provide. If not defined, the default value is @code{BITS_PER_WORD}.
974 @defmac ATTRIBUTE_ALIGNED_VALUE
975 Alignment used by the @code{__attribute__ ((aligned))} construct. If
976 not defined, the default value is @code{BIGGEST_ALIGNMENT}.
979 @defmac MINIMUM_ATOMIC_ALIGNMENT
980 If defined, the smallest alignment, in bits, that can be given to an
981 object that can be referenced in one operation, without disturbing any
982 nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
983 on machines that don't have byte or half-word store operations.
986 @defmac BIGGEST_FIELD_ALIGNMENT
987 Biggest alignment that any structure or union field can require on this
988 machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
989 structure and union fields only, unless the field alignment has been set
990 by the @code{__attribute__ ((aligned (@var{n})))} construct.
993 @defmac ADJUST_FIELD_ALIGN (@var{field}, @var{type}, @var{computed})
994 An expression for the alignment of a structure field @var{field} of
995 type @var{type} if the alignment computed in the usual way (including
996 applying of @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
997 alignment) is @var{computed}. It overrides alignment only if the
998 field alignment has not been set by the
999 @code{__attribute__ ((aligned (@var{n})))} construct. Note that @var{field}
1000 may be @code{NULL_TREE} in case we just query for the minimum alignment
1001 of a field of type @var{type} in structure context.
1004 @defmac MAX_STACK_ALIGNMENT
1005 Biggest stack alignment guaranteed by the backend. Use this macro
1006 to specify the maximum alignment of a variable on stack.
1008 If not defined, the default value is @code{STACK_BOUNDARY}.
1010 @c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}.
1011 @c But the fix for PR 32893 indicates that we can only guarantee
1012 @c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not
1013 @c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported.
1016 @defmac MAX_OFILE_ALIGNMENT
1017 Biggest alignment supported by the object file format of this machine.
1018 Use this macro to limit the alignment which can be specified using the
1019 @code{__attribute__ ((aligned (@var{n})))} construct. If not defined,
1020 the default value is @code{BIGGEST_ALIGNMENT}.
1022 On systems that use ELF, the default (in @file{config/elfos.h}) is
1023 the largest supported 32-bit ELF section alignment representable on
1024 a 32-bit host e.g. @samp{(((uint64_t) 1 << 28) * 8)}.
1025 On 32-bit ELF the largest supported section alignment in bits is
1026 @samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts.
1029 @defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
1030 If defined, a C expression to compute the alignment for a variable in
1031 the static store. @var{type} is the data type, and @var{basic-align} is
1032 the alignment that the object would ordinarily have. The value of this
1033 macro is used instead of that alignment to align the object.
1035 If this macro is not defined, then @var{basic-align} is used.
1038 One use of this macro is to increase alignment of medium-size data to
1039 make it all fit in fewer cache lines. Another is to cause character
1040 arrays to be word-aligned so that @code{strcpy} calls that copy
1041 constants to character arrays can be done inline.
1044 @defmac DATA_ABI_ALIGNMENT (@var{type}, @var{basic-align})
1045 Similar to @code{DATA_ALIGNMENT}, but for the cases where the ABI mandates
1046 some alignment increase, instead of optimization only purposes. E.g.@
1047 AMD x86-64 psABI says that variables with array type larger than 15 bytes
1048 must be aligned to 16 byte boundaries.
1050 If this macro is not defined, then @var{basic-align} is used.
1053 @defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
1054 If defined, a C expression to compute the alignment given to a constant
1055 that is being placed in memory. @var{constant} is the constant and
1056 @var{basic-align} is the alignment that the object would ordinarily
1057 have. The value of this macro is used instead of that alignment to
1060 The default definition just returns @var{basic-align}.
1062 The typical use of this macro is to increase alignment for string
1063 constants to be word aligned so that @code{strcpy} calls that copy
1064 constants can be done inline.
1067 @defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
1068 If defined, a C expression to compute the alignment for a variable in
1069 the local store. @var{type} is the data type, and @var{basic-align} is
1070 the alignment that the object would ordinarily have. The value of this
1071 macro is used instead of that alignment to align the object.
1073 If this macro is not defined, then @var{basic-align} is used.
1075 One use of this macro is to increase alignment of medium-size data to
1076 make it all fit in fewer cache lines.
1078 If the value of this macro has a type, it should be an unsigned type.
1081 @hook TARGET_VECTOR_ALIGNMENT
1083 @defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align})
1084 If defined, a C expression to compute the alignment for stack slot.
1085 @var{type} is the data type, @var{mode} is the widest mode available,
1086 and @var{basic-align} is the alignment that the slot would ordinarily
1087 have. The value of this macro is used instead of that alignment to
1090 If this macro is not defined, then @var{basic-align} is used when
1091 @var{type} is @code{NULL}. Otherwise, @code{LOCAL_ALIGNMENT} will
1094 This macro is to set alignment of stack slot to the maximum alignment
1095 of all possible modes which the slot may have.
1097 If the value of this macro has a type, it should be an unsigned type.
1100 @defmac LOCAL_DECL_ALIGNMENT (@var{decl})
1101 If defined, a C expression to compute the alignment for a local
1102 variable @var{decl}.
1104 If this macro is not defined, then
1105 @code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))}
1108 One use of this macro is to increase alignment of medium-size data to
1109 make it all fit in fewer cache lines.
1111 If the value of this macro has a type, it should be an unsigned type.
1114 @defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align})
1115 If defined, a C expression to compute the minimum required alignment
1116 for dynamic stack realignment purposes for @var{exp} (a type or decl),
1117 @var{mode}, assuming normal alignment @var{align}.
1119 If this macro is not defined, then @var{align} will be used.
1122 @defmac EMPTY_FIELD_BOUNDARY
1123 Alignment in bits to be given to a structure bit-field that follows an
1124 empty field such as @code{int : 0;}.
1126 If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
1129 @defmac STRUCTURE_SIZE_BOUNDARY
1130 Number of bits which any structure or union's size must be a multiple of.
1131 Each structure or union's size is rounded up to a multiple of this.
1133 If you do not define this macro, the default is the same as
1134 @code{BITS_PER_UNIT}.
1137 @defmac STRICT_ALIGNMENT
1138 Define this macro to be the value 1 if instructions will fail to work
1139 if given data not on the nominal alignment. If instructions will merely
1140 go slower in that case, define this macro as 0.
1143 @defmac PCC_BITFIELD_TYPE_MATTERS
1144 Define this if you wish to imitate the way many other C compilers handle
1145 alignment of bit-fields and the structures that contain them.
1147 The behavior is that the type written for a named bit-field (@code{int},
1148 @code{short}, or other integer type) imposes an alignment for the entire
1149 structure, as if the structure really did contain an ordinary field of
1150 that type. In addition, the bit-field is placed within the structure so
1151 that it would fit within such a field, not crossing a boundary for it.
1153 Thus, on most machines, a named bit-field whose type is written as
1154 @code{int} would not cross a four-byte boundary, and would force
1155 four-byte alignment for the whole structure. (The alignment used may
1156 not be four bytes; it is controlled by the other alignment parameters.)
1158 An unnamed bit-field will not affect the alignment of the containing
1161 If the macro is defined, its definition should be a C expression;
1162 a nonzero value for the expression enables this behavior.
1164 Note that if this macro is not defined, or its value is zero, some
1165 bit-fields may cross more than one alignment boundary. The compiler can
1166 support such references if there are @samp{insv}, @samp{extv}, and
1167 @samp{extzv} insns that can directly reference memory.
1169 The other known way of making bit-fields work is to define
1170 @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
1171 Then every structure can be accessed with fullwords.
1173 Unless the machine has bit-field instructions or you define
1174 @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
1175 @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
1177 If your aim is to make GCC use the same conventions for laying out
1178 bit-fields as are used by another compiler, here is how to investigate
1179 what the other compiler does. Compile and run this program:
1198 printf ("Size of foo1 is %d\n",
1199 sizeof (struct foo1));
1200 printf ("Size of foo2 is %d\n",
1201 sizeof (struct foo2));
1206 If this prints 2 and 5, then the compiler's behavior is what you would
1207 get from @code{PCC_BITFIELD_TYPE_MATTERS}.
1210 @defmac BITFIELD_NBYTES_LIMITED
1211 Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
1212 to aligning a bit-field within the structure.
1215 @hook TARGET_ALIGN_ANON_BITFIELD
1217 @hook TARGET_NARROW_VOLATILE_BITFIELD
1219 @hook TARGET_MEMBER_TYPE_FORCES_BLK
1221 @defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
1222 Define this macro as an expression for the alignment of a type (given
1223 by @var{type} as a tree node) if the alignment computed in the usual
1224 way is @var{computed} and the alignment explicitly specified was
1227 The default is to use @var{specified} if it is larger; otherwise, use
1228 the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
1231 @defmac MAX_FIXED_MODE_SIZE
1232 An integer expression for the size in bits of the largest integer
1233 machine mode that should actually be used. All integer machine modes of
1234 this size or smaller can be used for structures and unions with the
1235 appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
1236 (DImode)} is assumed.
1239 @defmac STACK_SAVEAREA_MODE (@var{save_level})
1240 If defined, an expression of type @code{machine_mode} that
1241 specifies the mode of the save area operand of a
1242 @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
1243 @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
1244 @code{SAVE_NONLOCAL} and selects which of the three named patterns is
1245 having its mode specified.
1247 You need not define this macro if it always returns @code{Pmode}. You
1248 would most commonly define this macro if the
1249 @code{save_stack_@var{level}} patterns need to support both a 32- and a
1253 @defmac STACK_SIZE_MODE
1254 If defined, an expression of type @code{machine_mode} that
1255 specifies the mode of the size increment operand of an
1256 @code{allocate_stack} named pattern (@pxref{Standard Names}).
1258 You need not define this macro if it always returns @code{word_mode}.
1259 You would most commonly define this macro if the @code{allocate_stack}
1260 pattern needs to support both a 32- and a 64-bit mode.
1263 @hook TARGET_LIBGCC_CMP_RETURN_MODE
1265 @hook TARGET_LIBGCC_SHIFT_COUNT_MODE
1267 @hook TARGET_UNWIND_WORD_MODE
1269 @hook TARGET_MS_BITFIELD_LAYOUT_P
1271 @hook TARGET_DECIMAL_FLOAT_SUPPORTED_P
1273 @hook TARGET_FIXED_POINT_SUPPORTED_P
1275 @hook TARGET_EXPAND_TO_RTL_HOOK
1277 @hook TARGET_INSTANTIATE_DECLS
1279 @hook TARGET_MANGLE_TYPE
1282 @section Layout of Source Language Data Types
1284 These macros define the sizes and other characteristics of the standard
1285 basic data types used in programs being compiled. Unlike the macros in
1286 the previous section, these apply to specific features of C and related
1287 languages, rather than to fundamental aspects of storage layout.
1289 @defmac INT_TYPE_SIZE
1290 A C expression for the size in bits of the type @code{int} on the
1291 target machine. If you don't define this, the default is one word.
1294 @defmac SHORT_TYPE_SIZE
1295 A C expression for the size in bits of the type @code{short} on the
1296 target machine. If you don't define this, the default is half a word.
1297 (If this would be less than one storage unit, it is rounded up to one
1301 @defmac LONG_TYPE_SIZE
1302 A C expression for the size in bits of the type @code{long} on the
1303 target machine. If you don't define this, the default is one word.
1306 @defmac ADA_LONG_TYPE_SIZE
1307 On some machines, the size used for the Ada equivalent of the type
1308 @code{long} by a native Ada compiler differs from that used by C@. In
1309 that situation, define this macro to be a C expression to be used for
1310 the size of that type. If you don't define this, the default is the
1311 value of @code{LONG_TYPE_SIZE}.
1314 @defmac LONG_LONG_TYPE_SIZE
1315 A C expression for the size in bits of the type @code{long long} on the
1316 target machine. If you don't define this, the default is two
1317 words. If you want to support GNU Ada on your machine, the value of this
1318 macro must be at least 64.
1321 @defmac CHAR_TYPE_SIZE
1322 A C expression for the size in bits of the type @code{char} on the
1323 target machine. If you don't define this, the default is
1324 @code{BITS_PER_UNIT}.
1327 @defmac BOOL_TYPE_SIZE
1328 A C expression for the size in bits of the C++ type @code{bool} and
1329 C99 type @code{_Bool} on the target machine. If you don't define
1330 this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
1333 @defmac FLOAT_TYPE_SIZE
1334 A C expression for the size in bits of the type @code{float} on the
1335 target machine. If you don't define this, the default is one word.
1338 @defmac DOUBLE_TYPE_SIZE
1339 A C expression for the size in bits of the type @code{double} on the
1340 target machine. If you don't define this, the default is two
1344 @defmac LONG_DOUBLE_TYPE_SIZE
1345 A C expression for the size in bits of the type @code{long double} on
1346 the target machine. If you don't define this, the default is two
1350 @defmac SHORT_FRACT_TYPE_SIZE
1351 A C expression for the size in bits of the type @code{short _Fract} on
1352 the target machine. If you don't define this, the default is
1353 @code{BITS_PER_UNIT}.
1356 @defmac FRACT_TYPE_SIZE
1357 A C expression for the size in bits of the type @code{_Fract} on
1358 the target machine. If you don't define this, the default is
1359 @code{BITS_PER_UNIT * 2}.
1362 @defmac LONG_FRACT_TYPE_SIZE
1363 A C expression for the size in bits of the type @code{long _Fract} on
1364 the target machine. If you don't define this, the default is
1365 @code{BITS_PER_UNIT * 4}.
1368 @defmac LONG_LONG_FRACT_TYPE_SIZE
1369 A C expression for the size in bits of the type @code{long long _Fract} on
1370 the target machine. If you don't define this, the default is
1371 @code{BITS_PER_UNIT * 8}.
1374 @defmac SHORT_ACCUM_TYPE_SIZE
1375 A C expression for the size in bits of the type @code{short _Accum} on
1376 the target machine. If you don't define this, the default is
1377 @code{BITS_PER_UNIT * 2}.
1380 @defmac ACCUM_TYPE_SIZE
1381 A C expression for the size in bits of the type @code{_Accum} on
1382 the target machine. If you don't define this, the default is
1383 @code{BITS_PER_UNIT * 4}.
1386 @defmac LONG_ACCUM_TYPE_SIZE
1387 A C expression for the size in bits of the type @code{long _Accum} on
1388 the target machine. If you don't define this, the default is
1389 @code{BITS_PER_UNIT * 8}.
1392 @defmac LONG_LONG_ACCUM_TYPE_SIZE
1393 A C expression for the size in bits of the type @code{long long _Accum} on
1394 the target machine. If you don't define this, the default is
1395 @code{BITS_PER_UNIT * 16}.
1398 @defmac LIBGCC2_GNU_PREFIX
1399 This macro corresponds to the @code{TARGET_LIBFUNC_GNU_PREFIX} target
1400 hook and should be defined if that hook is overriden to be true. It
1401 causes function names in libgcc to be changed to use a @code{__gnu_}
1402 prefix for their name rather than the default @code{__}. A port which
1403 uses this macro should also arrange to use @file{t-gnu-prefix} in
1404 the libgcc @file{config.host}.
1407 @defmac WIDEST_HARDWARE_FP_SIZE
1408 A C expression for the size in bits of the widest floating-point format
1409 supported by the hardware. If you define this macro, you must specify a
1410 value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
1411 If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
1415 @defmac DEFAULT_SIGNED_CHAR
1416 An expression whose value is 1 or 0, according to whether the type
1417 @code{char} should be signed or unsigned by default. The user can
1418 always override this default with the options @option{-fsigned-char}
1419 and @option{-funsigned-char}.
1422 @hook TARGET_DEFAULT_SHORT_ENUMS
1425 A C expression for a string describing the name of the data type to use
1426 for size values. The typedef name @code{size_t} is defined using the
1427 contents of the string.
1429 The string can contain more than one keyword. If so, separate them with
1430 spaces, and write first any length keyword, then @code{unsigned} if
1431 appropriate, and finally @code{int}. The string must exactly match one
1432 of the data type names defined in the function
1433 @code{c_common_nodes_and_builtins} in the file @file{c-family/c-common.c}.
1434 You may not omit @code{int} or change the order---that would cause the
1435 compiler to crash on startup.
1437 If you don't define this macro, the default is @code{"long unsigned
1442 GCC defines internal types (@code{sizetype}, @code{ssizetype},
1443 @code{bitsizetype} and @code{sbitsizetype}) for expressions
1444 dealing with size. This macro is a C expression for a string describing
1445 the name of the data type from which the precision of @code{sizetype}
1448 The string has the same restrictions as @code{SIZE_TYPE} string.
1450 If you don't define this macro, the default is @code{SIZE_TYPE}.
1453 @defmac PTRDIFF_TYPE
1454 A C expression for a string describing the name of the data type to use
1455 for the result of subtracting two pointers. The typedef name
1456 @code{ptrdiff_t} is defined using the contents of the string. See
1457 @code{SIZE_TYPE} above for more information.
1459 If you don't define this macro, the default is @code{"long int"}.
1463 A C expression for a string describing the name of the data type to use
1464 for wide characters. The typedef name @code{wchar_t} is defined using
1465 the contents of the string. See @code{SIZE_TYPE} above for more
1468 If you don't define this macro, the default is @code{"int"}.
1471 @defmac WCHAR_TYPE_SIZE
1472 A C expression for the size in bits of the data type for wide
1473 characters. This is used in @code{cpp}, which cannot make use of
1478 A C expression for a string describing the name of the data type to
1479 use for wide characters passed to @code{printf} and returned from
1480 @code{getwc}. The typedef name @code{wint_t} is defined using the
1481 contents of the string. See @code{SIZE_TYPE} above for more
1484 If you don't define this macro, the default is @code{"unsigned int"}.
1488 A C expression for a string describing the name of the data type that
1489 can represent any value of any standard or extended signed integer type.
1490 The typedef name @code{intmax_t} is defined using the contents of the
1491 string. See @code{SIZE_TYPE} above for more information.
1493 If you don't define this macro, the default is the first of
1494 @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
1495 much precision as @code{long long int}.
1498 @defmac UINTMAX_TYPE
1499 A C expression for a string describing the name of the data type that
1500 can represent any value of any standard or extended unsigned integer
1501 type. The typedef name @code{uintmax_t} is defined using the contents
1502 of the string. See @code{SIZE_TYPE} above for more information.
1504 If you don't define this macro, the default is the first of
1505 @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
1506 unsigned int"} that has as much precision as @code{long long unsigned
1510 @defmac SIG_ATOMIC_TYPE
1516 @defmacx UINT16_TYPE
1517 @defmacx UINT32_TYPE
1518 @defmacx UINT64_TYPE
1519 @defmacx INT_LEAST8_TYPE
1520 @defmacx INT_LEAST16_TYPE
1521 @defmacx INT_LEAST32_TYPE
1522 @defmacx INT_LEAST64_TYPE
1523 @defmacx UINT_LEAST8_TYPE
1524 @defmacx UINT_LEAST16_TYPE
1525 @defmacx UINT_LEAST32_TYPE
1526 @defmacx UINT_LEAST64_TYPE
1527 @defmacx INT_FAST8_TYPE
1528 @defmacx INT_FAST16_TYPE
1529 @defmacx INT_FAST32_TYPE
1530 @defmacx INT_FAST64_TYPE
1531 @defmacx UINT_FAST8_TYPE
1532 @defmacx UINT_FAST16_TYPE
1533 @defmacx UINT_FAST32_TYPE
1534 @defmacx UINT_FAST64_TYPE
1535 @defmacx INTPTR_TYPE
1536 @defmacx UINTPTR_TYPE
1537 C expressions for the standard types @code{sig_atomic_t},
1538 @code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t},
1539 @code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t},
1540 @code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
1541 @code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
1542 @code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
1543 @code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
1544 @code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
1545 @code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}. See
1546 @code{SIZE_TYPE} above for more information.
1548 If any of these macros evaluates to a null pointer, the corresponding
1549 type is not supported; if GCC is configured to provide
1550 @code{<stdint.h>} in such a case, the header provided may not conform
1551 to C99, depending on the type in question. The defaults for all of
1552 these macros are null pointers.
1555 @defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
1556 The C++ compiler represents a pointer-to-member-function with a struct
1563 ptrdiff_t vtable_index;
1570 The C++ compiler must use one bit to indicate whether the function that
1571 will be called through a pointer-to-member-function is virtual.
1572 Normally, we assume that the low-order bit of a function pointer must
1573 always be zero. Then, by ensuring that the vtable_index is odd, we can
1574 distinguish which variant of the union is in use. But, on some
1575 platforms function pointers can be odd, and so this doesn't work. In
1576 that case, we use the low-order bit of the @code{delta} field, and shift
1577 the remainder of the @code{delta} field to the left.
1579 GCC will automatically make the right selection about where to store
1580 this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
1581 However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
1582 set such that functions always start at even addresses, but the lowest
1583 bit of pointers to functions indicate whether the function at that
1584 address is in ARM or Thumb mode. If this is the case of your
1585 architecture, you should define this macro to
1586 @code{ptrmemfunc_vbit_in_delta}.
1588 In general, you should not have to define this macro. On architectures
1589 in which function addresses are always even, according to
1590 @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
1591 @code{ptrmemfunc_vbit_in_pfn}.
1594 @defmac TARGET_VTABLE_USES_DESCRIPTORS
1595 Normally, the C++ compiler uses function pointers in vtables. This
1596 macro allows the target to change to use ``function descriptors''
1597 instead. Function descriptors are found on targets for whom a
1598 function pointer is actually a small data structure. Normally the
1599 data structure consists of the actual code address plus a data
1600 pointer to which the function's data is relative.
1602 If vtables are used, the value of this macro should be the number
1603 of words that the function descriptor occupies.
1606 @defmac TARGET_VTABLE_ENTRY_ALIGN
1607 By default, the vtable entries are void pointers, the so the alignment
1608 is the same as pointer alignment. The value of this macro specifies
1609 the alignment of the vtable entry in bits. It should be defined only
1610 when special alignment is necessary. */
1613 @defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
1614 There are a few non-descriptor entries in the vtable at offsets below
1615 zero. If these entries must be padded (say, to preserve the alignment
1616 specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
1617 of words in each data entry.
1621 @section Register Usage
1622 @cindex register usage
1624 This section explains how to describe what registers the target machine
1625 has, and how (in general) they can be used.
1627 The description of which registers a specific instruction can use is
1628 done with register classes; see @ref{Register Classes}. For information
1629 on using registers to access a stack frame, see @ref{Frame Registers}.
1630 For passing values in registers, see @ref{Register Arguments}.
1631 For returning values in registers, see @ref{Scalar Return}.
1634 * Register Basics:: Number and kinds of registers.
1635 * Allocation Order:: Order in which registers are allocated.
1636 * Values in Registers:: What kinds of values each reg can hold.
1637 * Leaf Functions:: Renumbering registers for leaf functions.
1638 * Stack Registers:: Handling a register stack such as 80387.
1641 @node Register Basics
1642 @subsection Basic Characteristics of Registers
1644 @c prevent bad page break with this line
1645 Registers have various characteristics.
1647 @defmac FIRST_PSEUDO_REGISTER
1648 Number of hardware registers known to the compiler. They receive
1649 numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
1650 pseudo register's number really is assigned the number
1651 @code{FIRST_PSEUDO_REGISTER}.
1654 @defmac FIXED_REGISTERS
1655 @cindex fixed register
1656 An initializer that says which registers are used for fixed purposes
1657 all throughout the compiled code and are therefore not available for
1658 general allocation. These would include the stack pointer, the frame
1659 pointer (except on machines where that can be used as a general
1660 register when no frame pointer is needed), the program counter on
1661 machines where that is considered one of the addressable registers,
1662 and any other numbered register with a standard use.
1664 This information is expressed as a sequence of numbers, separated by
1665 commas and surrounded by braces. The @var{n}th number is 1 if
1666 register @var{n} is fixed, 0 otherwise.
1668 The table initialized from this macro, and the table initialized by
1669 the following one, may be overridden at run time either automatically,
1670 by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
1671 the user with the command options @option{-ffixed-@var{reg}},
1672 @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
1675 @defmac CALL_USED_REGISTERS
1676 @cindex call-used register
1677 @cindex call-clobbered register
1678 @cindex call-saved register
1679 Like @code{FIXED_REGISTERS} but has 1 for each register that is
1680 clobbered (in general) by function calls as well as for fixed
1681 registers. This macro therefore identifies the registers that are not
1682 available for general allocation of values that must live across
1685 If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
1686 automatically saves it on function entry and restores it on function
1687 exit, if the register is used within the function.
1690 @defmac CALL_REALLY_USED_REGISTERS
1691 @cindex call-used register
1692 @cindex call-clobbered register
1693 @cindex call-saved register
1694 Like @code{CALL_USED_REGISTERS} except this macro doesn't require
1695 that the entire set of @code{FIXED_REGISTERS} be included.
1696 (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
1697 This macro is optional. If not specified, it defaults to the value
1698 of @code{CALL_USED_REGISTERS}.
1701 @cindex call-used register
1702 @cindex call-clobbered register
1703 @cindex call-saved register
1704 @hook TARGET_HARD_REGNO_CALL_PART_CLOBBERED
1707 @findex call_used_regs
1710 @findex reg_class_contents
1711 @hook TARGET_CONDITIONAL_REGISTER_USAGE
1713 @defmac INCOMING_REGNO (@var{out})
1714 Define this macro if the target machine has register windows. This C
1715 expression returns the register number as seen by the called function
1716 corresponding to the register number @var{out} as seen by the calling
1717 function. Return @var{out} if register number @var{out} is not an
1721 @defmac OUTGOING_REGNO (@var{in})
1722 Define this macro if the target machine has register windows. This C
1723 expression returns the register number as seen by the calling function
1724 corresponding to the register number @var{in} as seen by the called
1725 function. Return @var{in} if register number @var{in} is not an inbound
1729 @defmac LOCAL_REGNO (@var{regno})
1730 Define this macro if the target machine has register windows. This C
1731 expression returns true if the register is call-saved but is in the
1732 register window. Unlike most call-saved registers, such registers
1733 need not be explicitly restored on function exit or during non-local
1738 If the program counter has a register number, define this as that
1739 register number. Otherwise, do not define it.
1742 @node Allocation Order
1743 @subsection Order of Allocation of Registers
1744 @cindex order of register allocation
1745 @cindex register allocation order
1747 @c prevent bad page break with this line
1748 Registers are allocated in order.
1750 @defmac REG_ALLOC_ORDER
1751 If defined, an initializer for a vector of integers, containing the
1752 numbers of hard registers in the order in which GCC should prefer
1753 to use them (from most preferred to least).
1755 If this macro is not defined, registers are used lowest numbered first
1756 (all else being equal).
1758 One use of this macro is on machines where the highest numbered
1759 registers must always be saved and the save-multiple-registers
1760 instruction supports only sequences of consecutive registers. On such
1761 machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
1762 the highest numbered allocable register first.
1765 @defmac ADJUST_REG_ALLOC_ORDER
1766 A C statement (sans semicolon) to choose the order in which to allocate
1767 hard registers for pseudo-registers local to a basic block.
1769 Store the desired register order in the array @code{reg_alloc_order}.
1770 Element 0 should be the register to allocate first; element 1, the next
1771 register; and so on.
1773 The macro body should not assume anything about the contents of
1774 @code{reg_alloc_order} before execution of the macro.
1776 On most machines, it is not necessary to define this macro.
1779 @defmac HONOR_REG_ALLOC_ORDER
1780 Normally, IRA tries to estimate the costs for saving a register in the
1781 prologue and restoring it in the epilogue. This discourages it from
1782 using call-saved registers. If a machine wants to ensure that IRA
1783 allocates registers in the order given by REG_ALLOC_ORDER even if some
1784 call-saved registers appear earlier than call-used ones, then define this
1785 macro as a C expression to nonzero. Default is 0.
1788 @defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno})
1789 In some case register allocation order is not enough for the
1790 Integrated Register Allocator (@acronym{IRA}) to generate a good code.
1791 If this macro is defined, it should return a floating point value
1792 based on @var{regno}. The cost of using @var{regno} for a pseudo will
1793 be increased by approximately the pseudo's usage frequency times the
1794 value returned by this macro. Not defining this macro is equivalent
1795 to having it always return @code{0.0}.
1797 On most machines, it is not necessary to define this macro.
1800 @node Values in Registers
1801 @subsection How Values Fit in Registers
1803 This section discusses the macros that describe which kinds of values
1804 (specifically, which machine modes) each register can hold, and how many
1805 consecutive registers are needed for a given mode.
1807 @defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
1808 A C expression for the number of consecutive hard registers, starting
1809 at register number @var{regno}, required to hold a value of mode
1810 @var{mode}. This macro must never return zero, even if a register
1811 cannot hold the requested mode - indicate that with
1812 @code{TARGET_HARD_REGNO_MODE_OK} and/or @code{CANNOT_CHANGE_MODE_CLASS}
1815 On a machine where all registers are exactly one word, a suitable
1816 definition of this macro is
1819 #define HARD_REGNO_NREGS(REGNO, MODE) \
1820 ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \
1825 @defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode})
1826 A C expression that is nonzero if a value of mode @var{mode}, stored
1827 in memory, ends with padding that causes it to take up more space than
1828 in registers starting at register number @var{regno} (as determined by
1829 multiplying GCC's notion of the size of the register when containing
1830 this mode by the number of registers returned by
1831 @code{HARD_REGNO_NREGS}). By default this is zero.
1833 For example, if a floating-point value is stored in three 32-bit
1834 registers but takes up 128 bits in memory, then this would be
1837 This macros only needs to be defined if there are cases where
1838 @code{subreg_get_info}
1839 would otherwise wrongly determine that a @code{subreg} can be
1840 represented by an offset to the register number, when in fact such a
1841 @code{subreg} would contain some of the padding not stored in
1842 registers and so not be representable.
1845 @defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode})
1846 For values of @var{regno} and @var{mode} for which
1847 @code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression
1848 returning the greater number of registers required to hold the value
1849 including any padding. In the example above, the value would be four.
1852 @defmac REGMODE_NATURAL_SIZE (@var{mode})
1853 Define this macro if the natural size of registers that hold values
1854 of mode @var{mode} is not the word size. It is a C expression that
1855 should give the natural size in bytes for the specified mode. It is
1856 used by the register allocator to try to optimize its results. This
1857 happens for example on SPARC 64-bit where the natural size of
1858 floating-point registers is still 32-bit.
1861 @hook TARGET_HARD_REGNO_MODE_OK
1863 @defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to})
1864 A C expression that is nonzero if it is OK to rename a hard register
1865 @var{from} to another hard register @var{to}.
1867 One common use of this macro is to prevent renaming of a register to
1868 another register that is not saved by a prologue in an interrupt
1871 The default is always nonzero.
1874 @hook TARGET_MODES_TIEABLE_P
1876 @hook TARGET_HARD_REGNO_SCRATCH_OK
1878 @defmac AVOID_CCMODE_COPIES
1879 Define this macro if the compiler should avoid copies to/from @code{CCmode}
1880 registers. You should only define this macro if support for copying to/from
1881 @code{CCmode} is incomplete.
1884 @node Leaf Functions
1885 @subsection Handling Leaf Functions
1887 @cindex leaf functions
1888 @cindex functions, leaf
1889 On some machines, a leaf function (i.e., one which makes no calls) can run
1890 more efficiently if it does not make its own register window. Often this
1891 means it is required to receive its arguments in the registers where they
1892 are passed by the caller, instead of the registers where they would
1895 The special treatment for leaf functions generally applies only when
1896 other conditions are met; for example, often they may use only those
1897 registers for its own variables and temporaries. We use the term ``leaf
1898 function'' to mean a function that is suitable for this special
1899 handling, so that functions with no calls are not necessarily ``leaf
1902 GCC assigns register numbers before it knows whether the function is
1903 suitable for leaf function treatment. So it needs to renumber the
1904 registers in order to output a leaf function. The following macros
1907 @defmac LEAF_REGISTERS
1908 Name of a char vector, indexed by hard register number, which
1909 contains 1 for a register that is allowable in a candidate for leaf
1912 If leaf function treatment involves renumbering the registers, then the
1913 registers marked here should be the ones before renumbering---those that
1914 GCC would ordinarily allocate. The registers which will actually be
1915 used in the assembler code, after renumbering, should not be marked with 1
1918 Define this macro only if the target machine offers a way to optimize
1919 the treatment of leaf functions.
1922 @defmac LEAF_REG_REMAP (@var{regno})
1923 A C expression whose value is the register number to which @var{regno}
1924 should be renumbered, when a function is treated as a leaf function.
1926 If @var{regno} is a register number which should not appear in a leaf
1927 function before renumbering, then the expression should yield @minus{}1, which
1928 will cause the compiler to abort.
1930 Define this macro only if the target machine offers a way to optimize the
1931 treatment of leaf functions, and registers need to be renumbered to do
1935 @findex current_function_is_leaf
1936 @findex current_function_uses_only_leaf_regs
1937 @code{TARGET_ASM_FUNCTION_PROLOGUE} and
1938 @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
1939 specially. They can test the C variable @code{current_function_is_leaf}
1940 which is nonzero for leaf functions. @code{current_function_is_leaf} is
1941 set prior to local register allocation and is valid for the remaining
1942 compiler passes. They can also test the C variable
1943 @code{current_function_uses_only_leaf_regs} which is nonzero for leaf
1944 functions which only use leaf registers.
1945 @code{current_function_uses_only_leaf_regs} is valid after all passes
1946 that modify the instructions have been run and is only useful if
1947 @code{LEAF_REGISTERS} is defined.
1948 @c changed this to fix overfull. ALSO: why the "it" at the beginning
1949 @c of the next paragraph?! --mew 2feb93
1951 @node Stack Registers
1952 @subsection Registers That Form a Stack
1954 There are special features to handle computers where some of the
1955 ``registers'' form a stack. Stack registers are normally written by
1956 pushing onto the stack, and are numbered relative to the top of the
1959 Currently, GCC can only handle one group of stack-like registers, and
1960 they must be consecutively numbered. Furthermore, the existing
1961 support for stack-like registers is specific to the 80387 floating
1962 point coprocessor. If you have a new architecture that uses
1963 stack-like registers, you will need to do substantial work on
1964 @file{reg-stack.c} and write your machine description to cooperate
1965 with it, as well as defining these macros.
1968 Define this if the machine has any stack-like registers.
1971 @defmac STACK_REG_COVER_CLASS
1972 This is a cover class containing the stack registers. Define this if
1973 the machine has any stack-like registers.
1976 @defmac FIRST_STACK_REG
1977 The number of the first stack-like register. This one is the top
1981 @defmac LAST_STACK_REG
1982 The number of the last stack-like register. This one is the bottom of
1986 @node Register Classes
1987 @section Register Classes
1988 @cindex register class definitions
1989 @cindex class definitions, register
1991 On many machines, the numbered registers are not all equivalent.
1992 For example, certain registers may not be allowed for indexed addressing;
1993 certain registers may not be allowed in some instructions. These machine
1994 restrictions are described to the compiler using @dfn{register classes}.
1996 You define a number of register classes, giving each one a name and saying
1997 which of the registers belong to it. Then you can specify register classes
1998 that are allowed as operands to particular instruction patterns.
2002 In general, each register will belong to several classes. In fact, one
2003 class must be named @code{ALL_REGS} and contain all the registers. Another
2004 class must be named @code{NO_REGS} and contain no registers. Often the
2005 union of two classes will be another class; however, this is not required.
2007 @findex GENERAL_REGS
2008 One of the classes must be named @code{GENERAL_REGS}. There is nothing
2009 terribly special about the name, but the operand constraint letters
2010 @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
2011 the same as @code{ALL_REGS}, just define it as a macro which expands
2014 Order the classes so that if class @var{x} is contained in class @var{y}
2015 then @var{x} has a lower class number than @var{y}.
2017 The way classes other than @code{GENERAL_REGS} are specified in operand
2018 constraints is through machine-dependent operand constraint letters.
2019 You can define such letters to correspond to various classes, then use
2020 them in operand constraints.
2022 You must define the narrowest register classes for allocatable
2023 registers, so that each class either has no subclasses, or that for
2024 some mode, the move cost between registers within the class is
2025 cheaper than moving a register in the class to or from memory
2028 You should define a class for the union of two classes whenever some
2029 instruction allows both classes. For example, if an instruction allows
2030 either a floating point (coprocessor) register or a general register for a
2031 certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
2032 which includes both of them. Otherwise you will get suboptimal code,
2033 or even internal compiler errors when reload cannot find a register in the
2034 class computed via @code{reg_class_subunion}.
2036 You must also specify certain redundant information about the register
2037 classes: for each class, which classes contain it and which ones are
2038 contained in it; for each pair of classes, the largest class contained
2041 When a value occupying several consecutive registers is expected in a
2042 certain class, all the registers used must belong to that class.
2043 Therefore, register classes cannot be used to enforce a requirement for
2044 a register pair to start with an even-numbered register. The way to
2045 specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK}.
2047 Register classes used for input-operands of bitwise-and or shift
2048 instructions have a special requirement: each such class must have, for
2049 each fixed-point machine mode, a subclass whose registers can transfer that
2050 mode to or from memory. For example, on some machines, the operations for
2051 single-byte values (@code{QImode}) are limited to certain registers. When
2052 this is so, each register class that is used in a bitwise-and or shift
2053 instruction must have a subclass consisting of registers from which
2054 single-byte values can be loaded or stored. This is so that
2055 @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
2057 @deftp {Data type} {enum reg_class}
2058 An enumerated type that must be defined with all the register class names
2059 as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS}
2060 must be the last register class, followed by one more enumerated value,
2061 @code{LIM_REG_CLASSES}, which is not a register class but rather
2062 tells how many classes there are.
2064 Each register class has a number, which is the value of casting
2065 the class name to type @code{int}. The number serves as an index
2066 in many of the tables described below.
2069 @defmac N_REG_CLASSES
2070 The number of distinct register classes, defined as follows:
2073 #define N_REG_CLASSES (int) LIM_REG_CLASSES
2077 @defmac REG_CLASS_NAMES
2078 An initializer containing the names of the register classes as C string
2079 constants. These names are used in writing some of the debugging dumps.
2082 @defmac REG_CLASS_CONTENTS
2083 An initializer containing the contents of the register classes, as integers
2084 which are bit masks. The @var{n}th integer specifies the contents of class
2085 @var{n}. The way the integer @var{mask} is interpreted is that
2086 register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
2088 When the machine has more than 32 registers, an integer does not suffice.
2089 Then the integers are replaced by sub-initializers, braced groupings containing
2090 several integers. Each sub-initializer must be suitable as an initializer
2091 for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
2092 In this situation, the first integer in each sub-initializer corresponds to
2093 registers 0 through 31, the second integer to registers 32 through 63, and
2097 @defmac REGNO_REG_CLASS (@var{regno})
2098 A C expression whose value is a register class containing hard register
2099 @var{regno}. In general there is more than one such class; choose a class
2100 which is @dfn{minimal}, meaning that no smaller class also contains the
2104 @defmac BASE_REG_CLASS
2105 A macro whose definition is the name of the class to which a valid
2106 base register must belong. A base register is one used in an address
2107 which is the register value plus a displacement.
2110 @defmac MODE_BASE_REG_CLASS (@var{mode})
2111 This is a variation of the @code{BASE_REG_CLASS} macro which allows
2112 the selection of a base register in a mode dependent manner. If
2113 @var{mode} is VOIDmode then it should return the same value as
2114 @code{BASE_REG_CLASS}.
2117 @defmac MODE_BASE_REG_REG_CLASS (@var{mode})
2118 A C expression whose value is the register class to which a valid
2119 base register must belong in order to be used in a base plus index
2120 register address. You should define this macro if base plus index
2121 addresses have different requirements than other base register uses.
2124 @defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{address_space}, @var{outer_code}, @var{index_code})
2125 A C expression whose value is the register class to which a valid
2126 base register for a memory reference in mode @var{mode} to address
2127 space @var{address_space} must belong. @var{outer_code} and @var{index_code}
2128 define the context in which the base register occurs. @var{outer_code} is
2129 the code of the immediately enclosing expression (@code{MEM} for the top level
2130 of an address, @code{ADDRESS} for something that occurs in an
2131 @code{address_operand}). @var{index_code} is the code of the corresponding
2132 index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise.
2135 @defmac INDEX_REG_CLASS
2136 A macro whose definition is the name of the class to which a valid
2137 index register must belong. An index register is one used in an
2138 address where its value is either multiplied by a scale factor or
2139 added to another register (as well as added to a displacement).
2142 @defmac REGNO_OK_FOR_BASE_P (@var{num})
2143 A C expression which is nonzero if register number @var{num} is
2144 suitable for use as a base register in operand addresses.
2147 @defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
2148 A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
2149 that expression may examine the mode of the memory reference in
2150 @var{mode}. You should define this macro if the mode of the memory
2151 reference affects whether a register may be used as a base register. If
2152 you define this macro, the compiler will use it instead of
2153 @code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for
2154 addresses that appear outside a @code{MEM}, i.e., as an
2155 @code{address_operand}.
2158 @defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode})
2159 A C expression which is nonzero if register number @var{num} is suitable for
2160 use as a base register in base plus index operand addresses, accessing
2161 memory in mode @var{mode}. It may be either a suitable hard register or a
2162 pseudo register that has been allocated such a hard register. You should
2163 define this macro if base plus index addresses have different requirements
2164 than other base register uses.
2166 Use of this macro is deprecated; please use the more general
2167 @code{REGNO_MODE_CODE_OK_FOR_BASE_P}.
2170 @defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{address_space}, @var{outer_code}, @var{index_code})
2171 A C expression which is nonzero if register number @var{num} is
2172 suitable for use as a base register in operand addresses, accessing
2173 memory in mode @var{mode} in address space @var{address_space}.
2174 This is similar to @code{REGNO_MODE_OK_FOR_BASE_P}, except
2175 that that expression may examine the context in which the register
2176 appears in the memory reference. @var{outer_code} is the code of the
2177 immediately enclosing expression (@code{MEM} if at the top level of the
2178 address, @code{ADDRESS} for something that occurs in an
2179 @code{address_operand}). @var{index_code} is the code of the
2180 corresponding index expression if @var{outer_code} is @code{PLUS};
2181 @code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses
2182 that appear outside a @code{MEM}, i.e., as an @code{address_operand}.
2185 @defmac REGNO_OK_FOR_INDEX_P (@var{num})
2186 A C expression which is nonzero if register number @var{num} is
2187 suitable for use as an index register in operand addresses. It may be
2188 either a suitable hard register or a pseudo register that has been
2189 allocated such a hard register.
2191 The difference between an index register and a base register is that
2192 the index register may be scaled. If an address involves the sum of
2193 two registers, neither one of them scaled, then either one may be
2194 labeled the ``base'' and the other the ``index''; but whichever
2195 labeling is used must fit the machine's constraints of which registers
2196 may serve in each capacity. The compiler will try both labelings,
2197 looking for one that is valid, and will reload one or both registers
2198 only if neither labeling works.
2201 @hook TARGET_PREFERRED_RENAME_CLASS
2203 @hook TARGET_PREFERRED_RELOAD_CLASS
2205 @defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
2206 A C expression that places additional restrictions on the register class
2207 to use when it is necessary to copy value @var{x} into a register in class
2208 @var{class}. The value is a register class; perhaps @var{class}, or perhaps
2209 another, smaller class. On many machines, the following definition is
2213 #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
2216 Sometimes returning a more restrictive class makes better code. For
2217 example, on the 68000, when @var{x} is an integer constant that is in range
2218 for a @samp{moveq} instruction, the value of this macro is always
2219 @code{DATA_REGS} as long as @var{class} includes the data registers.
2220 Requiring a data register guarantees that a @samp{moveq} will be used.
2222 One case where @code{PREFERRED_RELOAD_CLASS} must not return
2223 @var{class} is if @var{x} is a legitimate constant which cannot be
2224 loaded into some register class. By returning @code{NO_REGS} you can
2225 force @var{x} into a memory location. For example, rs6000 can load
2226 immediate values into general-purpose registers, but does not have an
2227 instruction for loading an immediate value into a floating-point
2228 register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
2229 @var{x} is a floating-point constant. If the constant cannot be loaded
2230 into any kind of register, code generation will be better if
2231 @code{TARGET_LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
2232 of using @code{TARGET_PREFERRED_RELOAD_CLASS}.
2234 If an insn has pseudos in it after register allocation, reload will go
2235 through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS}
2236 to find the best one. Returning @code{NO_REGS}, in this case, makes
2237 reload add a @code{!} in front of the constraint: the x86 back-end uses
2238 this feature to discourage usage of 387 registers when math is done in
2239 the SSE registers (and vice versa).
2242 @hook TARGET_PREFERRED_OUTPUT_RELOAD_CLASS
2244 @defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
2245 A C expression that places additional restrictions on the register class
2246 to use when it is necessary to be able to hold a value of mode
2247 @var{mode} in a reload register for which class @var{class} would
2250 Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
2251 there are certain modes that simply cannot go in certain reload classes.
2253 The value is a register class; perhaps @var{class}, or perhaps another,
2256 Don't define this macro unless the target machine has limitations which
2257 require the macro to do something nontrivial.
2260 @hook TARGET_SECONDARY_RELOAD
2262 @defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2263 @defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2264 @defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
2265 These macros are obsolete, new ports should use the target hook
2266 @code{TARGET_SECONDARY_RELOAD} instead.
2268 These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD}
2269 target hook. Older ports still define these macros to indicate to the
2270 reload phase that it may
2271 need to allocate at least one register for a reload in addition to the
2272 register to contain the data. Specifically, if copying @var{x} to a
2273 register @var{class} in @var{mode} requires an intermediate register,
2274 you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
2275 largest register class all of whose registers can be used as
2276 intermediate registers or scratch registers.
2278 If copying a register @var{class} in @var{mode} to @var{x} requires an
2279 intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
2280 was supposed to be defined be defined to return the largest register
2281 class required. If the
2282 requirements for input and output reloads were the same, the macro
2283 @code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both
2286 The values returned by these macros are often @code{GENERAL_REGS}.
2287 Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
2288 can be directly copied to or from a register of @var{class} in
2289 @var{mode} without requiring a scratch register. Do not define this
2290 macro if it would always return @code{NO_REGS}.
2292 If a scratch register is required (either with or without an
2293 intermediate register), you were supposed to define patterns for
2294 @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
2295 (@pxref{Standard Names}. These patterns, which were normally
2296 implemented with a @code{define_expand}, should be similar to the
2297 @samp{mov@var{m}} patterns, except that operand 2 is the scratch
2300 These patterns need constraints for the reload register and scratch
2302 contain a single register class. If the original reload register (whose
2303 class is @var{class}) can meet the constraint given in the pattern, the
2304 value returned by these macros is used for the class of the scratch
2305 register. Otherwise, two additional reload registers are required.
2306 Their classes are obtained from the constraints in the insn pattern.
2308 @var{x} might be a pseudo-register or a @code{subreg} of a
2309 pseudo-register, which could either be in a hard register or in memory.
2310 Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
2311 in memory and the hard register number if it is in a register.
2313 These macros should not be used in the case where a particular class of
2314 registers can only be copied to memory and not to another class of
2315 registers. In that case, secondary reload registers are not needed and
2316 would not be helpful. Instead, a stack location must be used to perform
2317 the copy and the @code{mov@var{m}} pattern should use memory as an
2318 intermediate storage. This case often occurs between floating-point and
2322 @defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
2323 Certain machines have the property that some registers cannot be copied
2324 to some other registers without using memory. Define this macro on
2325 those machines to be a C expression that is nonzero if objects of mode
2326 @var{m} in registers of @var{class1} can only be copied to registers of
2327 class @var{class2} by storing a register of @var{class1} into memory
2328 and loading that memory location into a register of @var{class2}.
2330 Do not define this macro if its value would always be zero.
2333 @defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
2334 Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
2335 allocates a stack slot for a memory location needed for register copies.
2336 If this macro is defined, the compiler instead uses the memory location
2337 defined by this macro.
2339 Do not define this macro if you do not define
2340 @code{SECONDARY_MEMORY_NEEDED}.
2343 @defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
2344 When the compiler needs a secondary memory location to copy between two
2345 registers of mode @var{mode}, it normally allocates sufficient memory to
2346 hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
2347 load operations in a mode that many bits wide and whose class is the
2348 same as that of @var{mode}.
2350 This is right thing to do on most machines because it ensures that all
2351 bits of the register are copied and prevents accesses to the registers
2352 in a narrower mode, which some machines prohibit for floating-point
2355 However, this default behavior is not correct on some machines, such as
2356 the DEC Alpha, that store short integers in floating-point registers
2357 differently than in integer registers. On those machines, the default
2358 widening will not work correctly and you must define this macro to
2359 suppress that widening in some cases. See the file @file{alpha.h} for
2362 Do not define this macro if you do not define
2363 @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
2364 is @code{BITS_PER_WORD} bits wide is correct for your machine.
2367 @hook TARGET_CLASS_LIKELY_SPILLED_P
2369 @hook TARGET_CLASS_MAX_NREGS
2371 @defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
2372 A C expression for the maximum number of consecutive registers
2373 of class @var{class} needed to hold a value of mode @var{mode}.
2375 This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact,
2376 the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
2377 should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
2378 @var{mode})} for all @var{regno} values in the class @var{class}.
2380 This macro helps control the handling of multiple-word values
2384 @defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
2385 If defined, a C expression that returns nonzero for a @var{class} for which
2386 a change from mode @var{from} to mode @var{to} is invalid.
2388 For example, loading 32-bit integer or floating-point objects into
2389 floating-point registers on Alpha extends them to 64 bits.
2390 Therefore loading a 64-bit object and then storing it as a 32-bit object
2391 does not store the low-order 32 bits, as would be the case for a normal
2392 register. Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
2396 #define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
2397 (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
2398 ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
2401 Even if storing from a register in mode @var{to} would be valid,
2402 if both @var{from} and @code{raw_reg_mode} for @var{class} are wider
2403 than @code{word_mode}, then we must prevent @var{to} narrowing the
2404 mode. This happens when the middle-end assumes that it can load
2405 or store pieces of an @var{N}-word pseudo, and that the pseudo will
2406 eventually be allocated to @var{N} @code{word_mode} hard registers.
2407 Failure to prevent this kind of mode change will result in the
2408 entire @code{raw_reg_mode} being modified instead of the partial
2409 value that the middle-end intended.
2413 @hook TARGET_IRA_CHANGE_PSEUDO_ALLOCNO_CLASS
2417 @hook TARGET_REGISTER_PRIORITY
2419 @hook TARGET_REGISTER_USAGE_LEVELING_P
2421 @hook TARGET_DIFFERENT_ADDR_DISPLACEMENT_P
2423 @hook TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P
2425 @hook TARGET_LEGITIMIZE_ADDRESS_DISPLACEMENT
2427 @hook TARGET_SPILL_CLASS
2429 @hook TARGET_ADDITIONAL_ALLOCNO_CLASS_P
2431 @hook TARGET_CSTORE_MODE
2433 @hook TARGET_COMPUTE_PRESSURE_CLASSES
2435 @node Stack and Calling
2436 @section Stack Layout and Calling Conventions
2437 @cindex calling conventions
2439 @c prevent bad page break with this line
2440 This describes the stack layout and calling conventions.
2444 * Exception Handling::
2449 * Register Arguments::
2451 * Aggregate Return::
2456 * Shrink-wrapping separate components::
2457 * Stack Smashing Protection::
2458 * Miscellaneous Register Hooks::
2462 @subsection Basic Stack Layout
2463 @cindex stack frame layout
2464 @cindex frame layout
2466 @c prevent bad page break with this line
2467 Here is the basic stack layout.
2469 @defmac STACK_GROWS_DOWNWARD
2470 Define this macro to be true if pushing a word onto the stack moves the stack
2471 pointer to a smaller address, and false otherwise.
2474 @defmac STACK_PUSH_CODE
2475 This macro defines the operation used when something is pushed
2476 on the stack. In RTL, a push operation will be
2477 @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
2479 The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
2480 and @code{POST_INC}. Which of these is correct depends on
2481 the stack direction and on whether the stack pointer points
2482 to the last item on the stack or whether it points to the
2483 space for the next item on the stack.
2485 The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
2486 true, which is almost always right, and @code{PRE_INC} otherwise,
2487 which is often wrong.
2490 @defmac FRAME_GROWS_DOWNWARD
2491 Define this macro to nonzero value if the addresses of local variable slots
2492 are at negative offsets from the frame pointer.
2495 @defmac ARGS_GROW_DOWNWARD
2496 Define this macro if successive arguments to a function occupy decreasing
2497 addresses on the stack.
2500 @defmac STARTING_FRAME_OFFSET
2501 Offset from the frame pointer to the first local variable slot to be allocated.
2503 If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
2504 subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
2505 Otherwise, it is found by adding the length of the first slot to the
2506 value @code{STARTING_FRAME_OFFSET}.
2507 @c i'm not sure if the above is still correct.. had to change it to get
2508 @c rid of an overfull. --mew 2feb93
2511 @defmac STACK_ALIGNMENT_NEEDED
2512 Define to zero to disable final alignment of the stack during reload.
2513 The nonzero default for this macro is suitable for most ports.
2515 On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
2516 is a register save block following the local block that doesn't require
2517 alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
2518 stack alignment and do it in the backend.
2521 @defmac STACK_POINTER_OFFSET
2522 Offset from the stack pointer register to the first location at which
2523 outgoing arguments are placed. If not specified, the default value of
2524 zero is used. This is the proper value for most machines.
2526 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2527 the first location at which outgoing arguments are placed.
2530 @defmac FIRST_PARM_OFFSET (@var{fundecl})
2531 Offset from the argument pointer register to the first argument's
2532 address. On some machines it may depend on the data type of the
2535 If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
2536 the first argument's address.
2539 @defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
2540 Offset from the stack pointer register to an item dynamically allocated
2541 on the stack, e.g., by @code{alloca}.
2543 The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
2544 length of the outgoing arguments. The default is correct for most
2545 machines. See @file{function.c} for details.
2548 @defmac INITIAL_FRAME_ADDRESS_RTX
2549 A C expression whose value is RTL representing the address of the initial
2550 stack frame. This address is passed to @code{RETURN_ADDR_RTX} and
2551 @code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable
2552 default value will be used. Define this macro in order to make frame pointer
2553 elimination work in the presence of @code{__builtin_frame_address (count)} and
2554 @code{__builtin_return_address (count)} for @code{count} not equal to zero.
2557 @defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
2558 A C expression whose value is RTL representing the address in a stack
2559 frame where the pointer to the caller's frame is stored. Assume that
2560 @var{frameaddr} is an RTL expression for the address of the stack frame
2563 If you don't define this macro, the default is to return the value
2564 of @var{frameaddr}---that is, the stack frame address is also the
2565 address of the stack word that points to the previous frame.
2568 @defmac SETUP_FRAME_ADDRESSES
2569 A C expression that produces the machine-specific code to
2570 setup the stack so that arbitrary frames can be accessed. For example,
2571 on the SPARC, we must flush all of the register windows to the stack
2572 before we can access arbitrary stack frames. You will seldom need to
2573 define this macro. The default is to do nothing.
2576 @hook TARGET_BUILTIN_SETJMP_FRAME_VALUE
2578 @defmac FRAME_ADDR_RTX (@var{frameaddr})
2579 A C expression whose value is RTL representing the value of the frame
2580 address for the current frame. @var{frameaddr} is the frame pointer
2581 of the current frame. This is used for __builtin_frame_address.
2582 You need only define this macro if the frame address is not the same
2583 as the frame pointer. Most machines do not need to define it.
2586 @defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
2587 A C expression whose value is RTL representing the value of the return
2588 address for the frame @var{count} steps up from the current frame, after
2589 the prologue. @var{frameaddr} is the frame pointer of the @var{count}
2590 frame, or the frame pointer of the @var{count} @minus{} 1 frame if
2591 @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is nonzero.
2593 The value of the expression must always be the correct address when
2594 @var{count} is zero, but may be @code{NULL_RTX} if there is no way to
2595 determine the return address of other frames.
2598 @defmac RETURN_ADDR_IN_PREVIOUS_FRAME
2599 Define this macro to nonzero value if the return address of a particular
2600 stack frame is accessed from the frame pointer of the previous stack
2601 frame. The zero default for this macro is suitable for most ports.
2604 @defmac INCOMING_RETURN_ADDR_RTX
2605 A C expression whose value is RTL representing the location of the
2606 incoming return address at the beginning of any function, before the
2607 prologue. This RTL is either a @code{REG}, indicating that the return
2608 value is saved in @samp{REG}, or a @code{MEM} representing a location in
2611 You only need to define this macro if you want to support call frame
2612 debugging information like that provided by DWARF 2.
2614 If this RTL is a @code{REG}, you should also define
2615 @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
2618 @defmac DWARF_ALT_FRAME_RETURN_COLUMN
2619 A C expression whose value is an integer giving a DWARF 2 column
2620 number that may be used as an alternative return column. The column
2621 must not correspond to any gcc hard register (that is, it must not
2622 be in the range of @code{DWARF_FRAME_REGNUM}).
2624 This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a
2625 general register, but an alternative column needs to be used for signal
2626 frames. Some targets have also used different frame return columns
2630 @defmac DWARF_ZERO_REG
2631 A C expression whose value is an integer giving a DWARF 2 register
2632 number that is considered to always have the value zero. This should
2633 only be defined if the target has an architected zero register, and
2634 someone decided it was a good idea to use that register number to
2635 terminate the stack backtrace. New ports should avoid this.
2638 @hook TARGET_DWARF_HANDLE_FRAME_UNSPEC
2640 @defmac INCOMING_FRAME_SP_OFFSET
2641 A C expression whose value is an integer giving the offset, in bytes,
2642 from the value of the stack pointer register to the top of the stack
2643 frame at the beginning of any function, before the prologue. The top of
2644 the frame is defined to be the value of the stack pointer in the
2645 previous frame, just before the call instruction.
2647 You only need to define this macro if you want to support call frame
2648 debugging information like that provided by DWARF 2.
2651 @defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
2652 A C expression whose value is an integer giving the offset, in bytes,
2653 from the argument pointer to the canonical frame address (cfa). The
2654 final value should coincide with that calculated by
2655 @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
2656 during virtual register instantiation.
2658 The default value for this macro is
2659 @code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size},
2660 which is correct for most machines; in general, the arguments are found
2661 immediately before the stack frame. Note that this is not the case on
2662 some targets that save registers into the caller's frame, such as SPARC
2663 and rs6000, and so such targets need to define this macro.
2665 You only need to define this macro if the default is incorrect, and you
2666 want to support call frame debugging information like that provided by
2670 @defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl})
2671 If defined, a C expression whose value is an integer giving the offset
2672 in bytes from the frame pointer to the canonical frame address (cfa).
2673 The final value should coincide with that calculated by
2674 @code{INCOMING_FRAME_SP_OFFSET}.
2676 Normally the CFA is calculated as an offset from the argument pointer,
2677 via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is
2678 variable due to the ABI, this may not be possible. If this macro is
2679 defined, it implies that the virtual register instantiation should be
2680 based on the frame pointer instead of the argument pointer. Only one
2681 of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET}
2685 @defmac CFA_FRAME_BASE_OFFSET (@var{fundecl})
2686 If defined, a C expression whose value is an integer giving the offset
2687 in bytes from the canonical frame address (cfa) to the frame base used
2688 in DWARF 2 debug information. The default is zero. A different value
2689 may reduce the size of debug information on some ports.
2692 @node Exception Handling
2693 @subsection Exception Handling Support
2694 @cindex exception handling
2696 @defmac EH_RETURN_DATA_REGNO (@var{N})
2697 A C expression whose value is the @var{N}th register number used for
2698 data by exception handlers, or @code{INVALID_REGNUM} if fewer than
2699 @var{N} registers are usable.
2701 The exception handling library routines communicate with the exception
2702 handlers via a set of agreed upon registers. Ideally these registers
2703 should be call-clobbered; it is possible to use call-saved registers,
2704 but may negatively impact code size. The target must support at least
2705 2 data registers, but should define 4 if there are enough free registers.
2707 You must define this macro if you want to support call frame exception
2708 handling like that provided by DWARF 2.
2711 @defmac EH_RETURN_STACKADJ_RTX
2712 A C expression whose value is RTL representing a location in which
2713 to store a stack adjustment to be applied before function return.
2714 This is used to unwind the stack to an exception handler's call frame.
2715 It will be assigned zero on code paths that return normally.
2717 Typically this is a call-clobbered hard register that is otherwise
2718 untouched by the epilogue, but could also be a stack slot.
2720 Do not define this macro if the stack pointer is saved and restored
2721 by the regular prolog and epilog code in the call frame itself; in
2722 this case, the exception handling library routines will update the
2723 stack location to be restored in place. Otherwise, you must define
2724 this macro if you want to support call frame exception handling like
2725 that provided by DWARF 2.
2728 @defmac EH_RETURN_HANDLER_RTX
2729 A C expression whose value is RTL representing a location in which
2730 to store the address of an exception handler to which we should
2731 return. It will not be assigned on code paths that return normally.
2733 Typically this is the location in the call frame at which the normal
2734 return address is stored. For targets that return by popping an
2735 address off the stack, this might be a memory address just below
2736 the @emph{target} call frame rather than inside the current call
2737 frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
2738 been assigned, so it may be used to calculate the location of the
2741 Some targets have more complex requirements than storing to an
2742 address calculable during initial code generation. In that case
2743 the @code{eh_return} instruction pattern should be used instead.
2745 If you want to support call frame exception handling, you must
2746 define either this macro or the @code{eh_return} instruction pattern.
2749 @defmac RETURN_ADDR_OFFSET
2750 If defined, an integer-valued C expression for which rtl will be generated
2751 to add it to the exception handler address before it is searched in the
2752 exception handling tables, and to subtract it again from the address before
2753 using it to return to the exception handler.
2756 @defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
2757 This macro chooses the encoding of pointers embedded in the exception
2758 handling sections. If at all possible, this should be defined such
2759 that the exception handling section will not require dynamic relocations,
2760 and so may be read-only.
2762 @var{code} is 0 for data, 1 for code labels, 2 for function pointers.
2763 @var{global} is true if the symbol may be affected by dynamic relocations.
2764 The macro should return a combination of the @code{DW_EH_PE_*} defines
2765 as found in @file{dwarf2.h}.
2767 If this macro is not defined, pointers will not be encoded but
2768 represented directly.
2771 @defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
2772 This macro allows the target to emit whatever special magic is required
2773 to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
2774 Generic code takes care of pc-relative and indirect encodings; this must
2775 be defined if the target uses text-relative or data-relative encodings.
2777 This is a C statement that branches to @var{done} if the format was
2778 handled. @var{encoding} is the format chosen, @var{size} is the number
2779 of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
2783 @defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs})
2784 This macro allows the target to add CPU and operating system specific
2785 code to the call-frame unwinder for use when there is no unwind data
2786 available. The most common reason to implement this macro is to unwind
2787 through signal frames.
2789 This macro is called from @code{uw_frame_state_for} in
2790 @file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and
2791 @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
2792 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
2793 for the address of the code being executed and @code{context->cfa} for
2794 the stack pointer value. If the frame can be decoded, the register
2795 save addresses should be updated in @var{fs} and the macro should
2796 evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded,
2797 the macro should evaluate to @code{_URC_END_OF_STACK}.
2799 For proper signal handling in Java this macro is accompanied by
2800 @code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
2803 @defmac MD_HANDLE_UNWABI (@var{context}, @var{fs})
2804 This macro allows the target to add operating system specific code to the
2805 call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive,
2806 usually used for signal or interrupt frames.
2808 This macro is called from @code{uw_update_context} in libgcc's
2809 @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
2810 @var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi}
2811 for the abi and context in the @code{.unwabi} directive. If the
2812 @code{.unwabi} directive can be handled, the register save addresses should
2813 be updated in @var{fs}.
2816 @defmac TARGET_USES_WEAK_UNWIND_INFO
2817 A C expression that evaluates to true if the target requires unwind
2818 info to be given comdat linkage. Define it to be @code{1} if comdat
2819 linkage is necessary. The default is @code{0}.
2822 @node Stack Checking
2823 @subsection Specifying How Stack Checking is Done
2825 GCC will check that stack references are within the boundaries of the
2826 stack, if the option @option{-fstack-check} is specified, in one of
2831 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
2832 will assume that you have arranged for full stack checking to be done
2833 at appropriate places in the configuration files. GCC will not do
2834 other special processing.
2837 If @code{STACK_CHECK_BUILTIN} is zero and the value of the
2838 @code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume
2839 that you have arranged for static stack checking (checking of the
2840 static stack frame of functions) to be done at appropriate places
2841 in the configuration files. GCC will only emit code to do dynamic
2842 stack checking (checking on dynamic stack allocations) using the third
2846 If neither of the above are true, GCC will generate code to periodically
2847 ``probe'' the stack pointer using the values of the macros defined below.
2850 If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
2851 GCC will change its allocation strategy for large objects if the option
2852 @option{-fstack-check} is specified: they will always be allocated
2853 dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes.
2855 @defmac STACK_CHECK_BUILTIN
2856 A nonzero value if stack checking is done by the configuration files in a
2857 machine-dependent manner. You should define this macro if stack checking
2858 is required by the ABI of your machine or if you would like to do stack
2859 checking in some more efficient way than the generic approach. The default
2860 value of this macro is zero.
2863 @defmac STACK_CHECK_STATIC_BUILTIN
2864 A nonzero value if static stack checking is done by the configuration files
2865 in a machine-dependent manner. You should define this macro if you would
2866 like to do static stack checking in some more efficient way than the generic
2867 approach. The default value of this macro is zero.
2870 @defmac STACK_CHECK_PROBE_INTERVAL_EXP
2871 An integer specifying the interval at which GCC must generate stack probe
2872 instructions, defined as 2 raised to this integer. You will normally
2873 define this macro so that the interval be no larger than the size of
2874 the ``guard pages'' at the end of a stack area. The default value
2875 of 12 (4096-byte interval) is suitable for most systems.
2878 @defmac STACK_CHECK_MOVING_SP
2879 An integer which is nonzero if GCC should move the stack pointer page by page
2880 when doing probes. This can be necessary on systems where the stack pointer
2881 contains the bottom address of the memory area accessible to the executing
2882 thread at any point in time. In this situation an alternate signal stack
2883 is required in order to be able to recover from a stack overflow. The
2884 default value of this macro is zero.
2887 @defmac STACK_CHECK_PROTECT
2888 The number of bytes of stack needed to recover from a stack overflow, for
2889 languages where such a recovery is supported. The default value of 4KB/8KB
2890 with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and
2891 8KB/12KB with other exception handling mechanisms should be adequate for most
2892 architectures and operating systems.
2895 The following macros are relevant only if neither STACK_CHECK_BUILTIN
2896 nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
2897 in the opposite case.
2899 @defmac STACK_CHECK_MAX_FRAME_SIZE
2900 The maximum size of a stack frame, in bytes. GCC will generate probe
2901 instructions in non-leaf functions to ensure at least this many bytes of
2902 stack are available. If a stack frame is larger than this size, stack
2903 checking will not be reliable and GCC will issue a warning. The
2904 default is chosen so that GCC only generates one instruction on most
2905 systems. You should normally not change the default value of this macro.
2908 @defmac STACK_CHECK_FIXED_FRAME_SIZE
2909 GCC uses this value to generate the above warning message. It
2910 represents the amount of fixed frame used by a function, not including
2911 space for any callee-saved registers, temporaries and user variables.
2912 You need only specify an upper bound for this amount and will normally
2913 use the default of four words.
2916 @defmac STACK_CHECK_MAX_VAR_SIZE
2917 The maximum size, in bytes, of an object that GCC will place in the
2918 fixed area of the stack frame when the user specifies
2919 @option{-fstack-check}.
2920 GCC computed the default from the values of the above macros and you will
2921 normally not need to override that default.
2925 @node Frame Registers
2926 @subsection Registers That Address the Stack Frame
2928 @c prevent bad page break with this line
2929 This discusses registers that address the stack frame.
2931 @defmac STACK_POINTER_REGNUM
2932 The register number of the stack pointer register, which must also be a
2933 fixed register according to @code{FIXED_REGISTERS}. On most machines,
2934 the hardware determines which register this is.
2937 @defmac FRAME_POINTER_REGNUM
2938 The register number of the frame pointer register, which is used to
2939 access automatic variables in the stack frame. On some machines, the
2940 hardware determines which register this is. On other machines, you can
2941 choose any register you wish for this purpose.
2944 @defmac HARD_FRAME_POINTER_REGNUM
2945 On some machines the offset between the frame pointer and starting
2946 offset of the automatic variables is not known until after register
2947 allocation has been done (for example, because the saved registers are
2948 between these two locations). On those machines, define
2949 @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
2950 be used internally until the offset is known, and define
2951 @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
2952 used for the frame pointer.
2954 You should define this macro only in the very rare circumstances when it
2955 is not possible to calculate the offset between the frame pointer and
2956 the automatic variables until after register allocation has been
2957 completed. When this macro is defined, you must also indicate in your
2958 definition of @code{ELIMINABLE_REGS} how to eliminate
2959 @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
2960 or @code{STACK_POINTER_REGNUM}.
2962 Do not define this macro if it would be the same as
2963 @code{FRAME_POINTER_REGNUM}.
2966 @defmac ARG_POINTER_REGNUM
2967 The register number of the arg pointer register, which is used to access
2968 the function's argument list. On some machines, this is the same as the
2969 frame pointer register. On some machines, the hardware determines which
2970 register this is. On other machines, you can choose any register you
2971 wish for this purpose. If this is not the same register as the frame
2972 pointer register, then you must mark it as a fixed register according to
2973 @code{FIXED_REGISTERS}, or arrange to be able to eliminate it
2974 (@pxref{Elimination}).
2977 @defmac HARD_FRAME_POINTER_IS_FRAME_POINTER
2978 Define this to a preprocessor constant that is nonzero if
2979 @code{hard_frame_pointer_rtx} and @code{frame_pointer_rtx} should be
2980 the same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM
2981 == FRAME_POINTER_REGNUM)}; you only need to define this macro if that
2982 definition is not suitable for use in preprocessor conditionals.
2985 @defmac HARD_FRAME_POINTER_IS_ARG_POINTER
2986 Define this to a preprocessor constant that is nonzero if
2987 @code{hard_frame_pointer_rtx} and @code{arg_pointer_rtx} should be the
2988 same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM ==
2989 ARG_POINTER_REGNUM)}; you only need to define this macro if that
2990 definition is not suitable for use in preprocessor conditionals.
2993 @defmac RETURN_ADDRESS_POINTER_REGNUM
2994 The register number of the return address pointer register, which is used to
2995 access the current function's return address from the stack. On some
2996 machines, the return address is not at a fixed offset from the frame
2997 pointer or stack pointer or argument pointer. This register can be defined
2998 to point to the return address on the stack, and then be converted by
2999 @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
3001 Do not define this macro unless there is no other way to get the return
3002 address from the stack.
3005 @defmac STATIC_CHAIN_REGNUM
3006 @defmacx STATIC_CHAIN_INCOMING_REGNUM
3007 Register numbers used for passing a function's static chain pointer. If
3008 register windows are used, the register number as seen by the called
3009 function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
3010 number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
3011 these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
3014 The static chain register need not be a fixed register.
3016 If the static chain is passed in memory, these macros should not be
3017 defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used.
3020 @hook TARGET_STATIC_CHAIN
3022 @defmac DWARF_FRAME_REGISTERS
3023 This macro specifies the maximum number of hard registers that can be
3024 saved in a call frame. This is used to size data structures used in
3025 DWARF2 exception handling.
3027 Prior to GCC 3.0, this macro was needed in order to establish a stable
3028 exception handling ABI in the face of adding new hard registers for ISA
3029 extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
3030 in the number of hard registers. Nevertheless, this macro can still be
3031 used to reduce the runtime memory requirements of the exception handling
3032 routines, which can be substantial if the ISA contains a lot of
3033 registers that are not call-saved.
3035 If this macro is not defined, it defaults to
3036 @code{FIRST_PSEUDO_REGISTER}.
3039 @defmac PRE_GCC3_DWARF_FRAME_REGISTERS
3041 This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
3042 for backward compatibility in pre GCC 3.0 compiled code.
3044 If this macro is not defined, it defaults to
3045 @code{DWARF_FRAME_REGISTERS}.
3048 @defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
3050 Define this macro if the target's representation for dwarf registers
3051 is different than the internal representation for unwind column.
3052 Given a dwarf register, this macro should return the internal unwind
3053 column number to use instead.
3056 @defmac DWARF_FRAME_REGNUM (@var{regno})
3058 Define this macro if the target's representation for dwarf registers
3059 used in .eh_frame or .debug_frame is different from that used in other
3060 debug info sections. Given a GCC hard register number, this macro
3061 should return the .eh_frame register number. The default is
3062 @code{DBX_REGISTER_NUMBER (@var{regno})}.
3066 @defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh})
3068 Define this macro to map register numbers held in the call frame info
3069 that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that
3070 should be output in .debug_frame (@code{@var{for_eh}} is zero) and
3071 .eh_frame (@code{@var{for_eh}} is nonzero). The default is to
3072 return @code{@var{regno}}.
3076 @defmac REG_VALUE_IN_UNWIND_CONTEXT
3078 Define this macro if the target stores register values as
3079 @code{_Unwind_Word} type in unwind context. It should be defined if
3080 target register size is larger than the size of @code{void *}. The
3081 default is to store register values as @code{void *} type.
3085 @defmac ASSUME_EXTENDED_UNWIND_CONTEXT
3087 Define this macro to be 1 if the target always uses extended unwind
3088 context with version, args_size and by_value fields. If it is undefined,
3089 it will be defined to 1 when @code{REG_VALUE_IN_UNWIND_CONTEXT} is
3090 defined and 0 otherwise.
3095 @subsection Eliminating Frame Pointer and Arg Pointer
3097 @c prevent bad page break with this line
3098 This is about eliminating the frame pointer and arg pointer.
3100 @hook TARGET_FRAME_POINTER_REQUIRED
3102 @defmac ELIMINABLE_REGS
3103 This macro specifies a table of register pairs used to eliminate
3104 unneeded registers that point into the stack frame.
3106 The definition of this macro is a list of structure initializations, each
3107 of which specifies an original and replacement register.
3109 On some machines, the position of the argument pointer is not known until
3110 the compilation is completed. In such a case, a separate hard register
3111 must be used for the argument pointer. This register can be eliminated by
3112 replacing it with either the frame pointer or the argument pointer,
3113 depending on whether or not the frame pointer has been eliminated.
3115 In this case, you might specify:
3117 #define ELIMINABLE_REGS \
3118 @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
3119 @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
3120 @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
3123 Note that the elimination of the argument pointer with the stack pointer is
3124 specified first since that is the preferred elimination.
3127 @hook TARGET_CAN_ELIMINATE
3129 @defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
3130 This macro returns the initial difference between the specified pair
3131 of registers. The value would be computed from information
3132 such as the result of @code{get_frame_size ()} and the tables of
3133 registers @code{df_regs_ever_live_p} and @code{call_used_regs}.
3136 @hook TARGET_COMPUTE_FRAME_LAYOUT
3138 @node Stack Arguments
3139 @subsection Passing Function Arguments on the Stack
3140 @cindex arguments on stack
3141 @cindex stack arguments
3143 The macros in this section control how arguments are passed
3144 on the stack. See the following section for other macros that
3145 control passing certain arguments in registers.
3147 @hook TARGET_PROMOTE_PROTOTYPES
3150 A C expression. If nonzero, push insns will be used to pass
3152 If the target machine does not have a push instruction, set it to zero.
3153 That directs GCC to use an alternate strategy: to
3154 allocate the entire argument block and then store the arguments into
3155 it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
3158 @defmac PUSH_ARGS_REVERSED
3159 A C expression. If nonzero, function arguments will be evaluated from
3160 last to first, rather than from first to last. If this macro is not
3161 defined, it defaults to @code{PUSH_ARGS} on targets where the stack
3162 and args grow in opposite directions, and 0 otherwise.
3165 @defmac PUSH_ROUNDING (@var{npushed})
3166 A C expression that is the number of bytes actually pushed onto the
3167 stack when an instruction attempts to push @var{npushed} bytes.
3169 On some machines, the definition
3172 #define PUSH_ROUNDING(BYTES) (BYTES)
3176 will suffice. But on other machines, instructions that appear
3177 to push one byte actually push two bytes in an attempt to maintain
3178 alignment. Then the definition should be
3181 #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
3184 If the value of this macro has a type, it should be an unsigned type.
3187 @findex outgoing_args_size
3188 @findex crtl->outgoing_args_size
3189 @defmac ACCUMULATE_OUTGOING_ARGS
3190 A C expression. If nonzero, the maximum amount of space required for outgoing arguments
3191 will be computed and placed into
3192 @code{crtl->outgoing_args_size}. No space will be pushed
3193 onto the stack for each call; instead, the function prologue should
3194 increase the stack frame size by this amount.
3196 Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
3200 @defmac REG_PARM_STACK_SPACE (@var{fndecl})
3201 Define this macro if functions should assume that stack space has been
3202 allocated for arguments even when their values are passed in
3205 The value of this macro is the size, in bytes, of the area reserved for
3206 arguments passed in registers for the function represented by @var{fndecl},
3207 which can be zero if GCC is calling a library function.
3208 The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself
3211 This space can be allocated by the caller, or be a part of the
3212 machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
3215 @c above is overfull. not sure what to do. --mew 5feb93 did
3216 @c something, not sure if it looks good. --mew 10feb93
3218 @defmac INCOMING_REG_PARM_STACK_SPACE (@var{fndecl})
3219 Like @code{REG_PARM_STACK_SPACE}, but for incoming register arguments.
3220 Define this macro if space guaranteed when compiling a function body
3221 is different to space required when making a call, a situation that
3222 can arise with K&R style function definitions.
3225 @defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype})
3226 Define this to a nonzero value if it is the responsibility of the
3227 caller to allocate the area reserved for arguments passed in registers
3228 when calling a function of @var{fntype}. @var{fntype} may be NULL
3229 if the function called is a library function.
3231 If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
3232 whether the space for these arguments counts in the value of
3233 @code{crtl->outgoing_args_size}.
3236 @defmac STACK_PARMS_IN_REG_PARM_AREA
3237 Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
3238 stack parameters don't skip the area specified by it.
3239 @c i changed this, makes more sens and it should have taken care of the
3240 @c overfull.. not as specific, tho. --mew 5feb93
3242 Normally, when a parameter is not passed in registers, it is placed on the
3243 stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
3244 suppresses this behavior and causes the parameter to be passed on the
3245 stack in its natural location.
3248 @hook TARGET_RETURN_POPS_ARGS
3250 @defmac CALL_POPS_ARGS (@var{cum})
3251 A C expression that should indicate the number of bytes a call sequence
3252 pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
3253 when compiling a function call.
3255 @var{cum} is the variable in which all arguments to the called function
3256 have been accumulated.
3258 On certain architectures, such as the SH5, a call trampoline is used
3259 that pops certain registers off the stack, depending on the arguments
3260 that have been passed to the function. Since this is a property of the
3261 call site, not of the called function, @code{RETURN_POPS_ARGS} is not
3265 @node Register Arguments
3266 @subsection Passing Arguments in Registers
3267 @cindex arguments in registers
3268 @cindex registers arguments
3270 This section describes the macros which let you control how various
3271 types of arguments are passed in registers or how they are arranged in
3274 @hook TARGET_FUNCTION_ARG
3276 @hook TARGET_MUST_PASS_IN_STACK
3278 @hook TARGET_FUNCTION_INCOMING_ARG
3280 @hook TARGET_USE_PSEUDO_PIC_REG
3282 @hook TARGET_INIT_PIC_REG
3284 @hook TARGET_ARG_PARTIAL_BYTES
3286 @hook TARGET_PASS_BY_REFERENCE
3288 @hook TARGET_CALLEE_COPIES
3290 @defmac CUMULATIVE_ARGS
3291 A C type for declaring a variable that is used as the first argument
3292 of @code{TARGET_FUNCTION_ARG} and other related values. For some
3293 target machines, the type @code{int} suffices and can hold the number
3294 of bytes of argument so far.
3296 There is no need to record in @code{CUMULATIVE_ARGS} anything about the
3297 arguments that have been passed on the stack. The compiler has other
3298 variables to keep track of that. For target machines on which all
3299 arguments are passed on the stack, there is no need to store anything in
3300 @code{CUMULATIVE_ARGS}; however, the data structure must exist and
3301 should not be empty, so use @code{int}.
3304 @defmac OVERRIDE_ABI_FORMAT (@var{fndecl})
3305 If defined, this macro is called before generating any code for a
3306 function, but after the @var{cfun} descriptor for the function has been
3307 created. The back end may use this macro to update @var{cfun} to
3308 reflect an ABI other than that which would normally be used by default.
3309 If the compiler is generating code for a compiler-generated function,
3310 @var{fndecl} may be @code{NULL}.
3313 @defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args})
3314 A C statement (sans semicolon) for initializing the variable
3315 @var{cum} for the state at the beginning of the argument list. The
3316 variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
3317 is the tree node for the data type of the function which will receive
3318 the args, or 0 if the args are to a compiler support library function.
3319 For direct calls that are not libcalls, @var{fndecl} contain the
3320 declaration node of the function. @var{fndecl} is also set when
3321 @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
3322 being compiled. @var{n_named_args} is set to the number of named
3323 arguments, including a structure return address if it is passed as a
3324 parameter, when making a call. When processing incoming arguments,
3325 @var{n_named_args} is set to @minus{}1.
3327 When processing a call to a compiler support library function,
3328 @var{libname} identifies which one. It is a @code{symbol_ref} rtx which
3329 contains the name of the function, as a string. @var{libname} is 0 when
3330 an ordinary C function call is being processed. Thus, each time this
3331 macro is called, either @var{libname} or @var{fntype} is nonzero, but
3332 never both of them at once.
3335 @defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
3336 Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
3337 it gets a @code{MODE} argument instead of @var{fntype}, that would be
3338 @code{NULL}. @var{indirect} would always be zero, too. If this macro
3339 is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
3340 0)} is used instead.
3343 @defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
3344 Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
3345 finding the arguments for the function being compiled. If this macro is
3346 undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
3348 The value passed for @var{libname} is always 0, since library routines
3349 with special calling conventions are never compiled with GCC@. The
3350 argument @var{libname} exists for symmetry with
3351 @code{INIT_CUMULATIVE_ARGS}.
3352 @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
3353 @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
3356 @hook TARGET_FUNCTION_ARG_ADVANCE
3358 @defmac FUNCTION_ARG_OFFSET (@var{mode}, @var{type})
3359 If defined, a C expression that is the number of bytes to add to the
3360 offset of the argument passed in memory. This is needed for the SPU,
3361 which passes @code{char} and @code{short} arguments in the preferred
3362 slot that is in the middle of the quad word instead of starting at the
3366 @hook TARGET_FUNCTION_ARG_PADDING
3368 @defmac PAD_VARARGS_DOWN
3369 If defined, a C expression which determines whether the default
3370 implementation of va_arg will attempt to pad down before reading the
3371 next argument, if that argument is smaller than its aligned space as
3372 controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
3373 arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
3376 @defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
3377 Specify padding for the last element of a block move between registers and
3378 memory. @var{first} is nonzero if this is the only element. Defining this
3379 macro allows better control of register function parameters on big-endian
3380 machines, without using @code{PARALLEL} rtl. In particular,
3381 @code{MUST_PASS_IN_STACK} need not test padding and mode of types in
3382 registers, as there is no longer a "wrong" part of a register; For example,
3383 a three byte aggregate may be passed in the high part of a register if so
3387 @hook TARGET_FUNCTION_ARG_BOUNDARY
3389 @hook TARGET_FUNCTION_ARG_ROUND_BOUNDARY
3391 @defmac FUNCTION_ARG_REGNO_P (@var{regno})
3392 A C expression that is nonzero if @var{regno} is the number of a hard
3393 register in which function arguments are sometimes passed. This does
3394 @emph{not} include implicit arguments such as the static chain and
3395 the structure-value address. On many machines, no registers can be
3396 used for this purpose since all function arguments are pushed on the
3400 @hook TARGET_SPLIT_COMPLEX_ARG
3402 @hook TARGET_BUILD_BUILTIN_VA_LIST
3404 @hook TARGET_ENUM_VA_LIST_P
3406 @hook TARGET_FN_ABI_VA_LIST
3408 @hook TARGET_CANONICAL_VA_LIST_TYPE
3410 @hook TARGET_GIMPLIFY_VA_ARG_EXPR
3412 @hook TARGET_VALID_POINTER_MODE
3414 @hook TARGET_REF_MAY_ALIAS_ERRNO
3416 @hook TARGET_SCALAR_MODE_SUPPORTED_P
3418 @hook TARGET_VECTOR_MODE_SUPPORTED_P
3420 @hook TARGET_ARRAY_MODE_SUPPORTED_P
3422 @hook TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P
3424 @hook TARGET_FLOATN_MODE
3426 @hook TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P
3429 @subsection How Scalar Function Values Are Returned
3430 @cindex return values in registers
3431 @cindex values, returned by functions
3432 @cindex scalars, returned as values
3434 This section discusses the macros that control returning scalars as
3435 values---values that can fit in registers.
3437 @hook TARGET_FUNCTION_VALUE
3439 @defmac FUNCTION_VALUE (@var{valtype}, @var{func})
3440 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for
3441 a new target instead.
3444 @defmac LIBCALL_VALUE (@var{mode})
3445 A C expression to create an RTX representing the place where a library
3446 function returns a value of mode @var{mode}.
3448 Note that ``library function'' in this context means a compiler
3449 support routine, used to perform arithmetic, whose name is known
3450 specially by the compiler and was not mentioned in the C code being
3454 @hook TARGET_LIBCALL_VALUE
3456 @defmac FUNCTION_VALUE_REGNO_P (@var{regno})
3457 A C expression that is nonzero if @var{regno} is the number of a hard
3458 register in which the values of called function may come back.
3460 A register whose use for returning values is limited to serving as the
3461 second of a pair (for a value of type @code{double}, say) need not be
3462 recognized by this macro. So for most machines, this definition
3466 #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
3469 If the machine has register windows, so that the caller and the called
3470 function use different registers for the return value, this macro
3471 should recognize only the caller's register numbers.
3473 This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE_REGNO_P}
3474 for a new target instead.
3477 @hook TARGET_FUNCTION_VALUE_REGNO_P
3479 @defmac APPLY_RESULT_SIZE
3480 Define this macro if @samp{untyped_call} and @samp{untyped_return}
3481 need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
3482 saving and restoring an arbitrary return value.
3485 @hook TARGET_OMIT_STRUCT_RETURN_REG
3487 @hook TARGET_RETURN_IN_MSB
3489 @node Aggregate Return
3490 @subsection How Large Values Are Returned
3491 @cindex aggregates as return values
3492 @cindex large return values
3493 @cindex returning aggregate values
3494 @cindex structure value address
3496 When a function value's mode is @code{BLKmode} (and in some other
3497 cases), the value is not returned according to
3498 @code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the
3499 caller passes the address of a block of memory in which the value
3500 should be stored. This address is called the @dfn{structure value
3503 This section describes how to control returning structure values in
3506 @hook TARGET_RETURN_IN_MEMORY
3508 @defmac DEFAULT_PCC_STRUCT_RETURN
3509 Define this macro to be 1 if all structure and union return values must be
3510 in memory. Since this results in slower code, this should be defined
3511 only if needed for compatibility with other compilers or with an ABI@.
3512 If you define this macro to be 0, then the conventions used for structure
3513 and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
3516 If not defined, this defaults to the value 1.
3519 @hook TARGET_STRUCT_VALUE_RTX
3521 @defmac PCC_STATIC_STRUCT_RETURN
3522 Define this macro if the usual system convention on the target machine
3523 for returning structures and unions is for the called function to return
3524 the address of a static variable containing the value.
3526 Do not define this if the usual system convention is for the caller to
3527 pass an address to the subroutine.
3529 This macro has effect in @option{-fpcc-struct-return} mode, but it does
3530 nothing when you use @option{-freg-struct-return} mode.
3533 @hook TARGET_GET_RAW_RESULT_MODE
3535 @hook TARGET_GET_RAW_ARG_MODE
3538 @subsection Caller-Saves Register Allocation
3540 If you enable it, GCC can save registers around function calls. This
3541 makes it possible to use call-clobbered registers to hold variables that
3542 must live across calls.
3544 @defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
3545 A C expression specifying which mode is required for saving @var{nregs}
3546 of a pseudo-register in call-clobbered hard register @var{regno}. If
3547 @var{regno} is unsuitable for caller save, @code{VOIDmode} should be
3548 returned. For most machines this macro need not be defined since GCC
3549 will select the smallest suitable mode.
3552 @node Function Entry
3553 @subsection Function Entry and Exit
3554 @cindex function entry and exit
3558 This section describes the macros that output function entry
3559 (@dfn{prologue}) and exit (@dfn{epilogue}) code.
3561 @hook TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY
3563 @hook TARGET_ASM_FUNCTION_PROLOGUE
3565 @hook TARGET_ASM_FUNCTION_END_PROLOGUE
3567 @hook TARGET_ASM_FUNCTION_BEGIN_EPILOGUE
3569 @hook TARGET_ASM_FUNCTION_EPILOGUE
3573 @findex pretend_args_size
3574 @findex crtl->args.pretend_args_size
3575 A region of @code{crtl->args.pretend_args_size} bytes of
3576 uninitialized space just underneath the first argument arriving on the
3577 stack. (This may not be at the very start of the allocated stack region
3578 if the calling sequence has pushed anything else since pushing the stack
3579 arguments. But usually, on such machines, nothing else has been pushed
3580 yet, because the function prologue itself does all the pushing.) This
3581 region is used on machines where an argument may be passed partly in
3582 registers and partly in memory, and, in some cases to support the
3583 features in @code{<stdarg.h>}.
3586 An area of memory used to save certain registers used by the function.
3587 The size of this area, which may also include space for such things as
3588 the return address and pointers to previous stack frames, is
3589 machine-specific and usually depends on which registers have been used
3590 in the function. Machines with register windows often do not require
3594 A region of at least @var{size} bytes, possibly rounded up to an allocation
3595 boundary, to contain the local variables of the function. On some machines,
3596 this region and the save area may occur in the opposite order, with the
3597 save area closer to the top of the stack.
3600 @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
3601 Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
3602 @code{crtl->outgoing_args_size} bytes to be used for outgoing
3603 argument lists of the function. @xref{Stack Arguments}.
3606 @defmac EXIT_IGNORE_STACK
3607 Define this macro as a C expression that is nonzero if the return
3608 instruction or the function epilogue ignores the value of the stack
3609 pointer; in other words, if it is safe to delete an instruction to
3610 adjust the stack pointer before a return from the function. The
3613 Note that this macro's value is relevant only for functions for which
3614 frame pointers are maintained. It is never safe to delete a final
3615 stack adjustment in a function that has no frame pointer, and the
3616 compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
3619 @defmac EPILOGUE_USES (@var{regno})
3620 Define this macro as a C expression that is nonzero for registers that are
3621 used by the epilogue or the @samp{return} pattern. The stack and frame
3622 pointer registers are already assumed to be used as needed.
3625 @defmac EH_USES (@var{regno})
3626 Define this macro as a C expression that is nonzero for registers that are
3627 used by the exception handling mechanism, and so should be considered live
3628 on entry to an exception edge.
3631 @hook TARGET_ASM_OUTPUT_MI_THUNK
3633 @hook TARGET_ASM_CAN_OUTPUT_MI_THUNK
3636 @subsection Generating Code for Profiling
3637 @cindex profiling, code generation
3639 These macros will help you generate code for profiling.
3641 @defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
3642 A C statement or compound statement to output to @var{file} some
3643 assembler code to call the profiling subroutine @code{mcount}.
3646 The details of how @code{mcount} expects to be called are determined by
3647 your operating system environment, not by GCC@. To figure them out,
3648 compile a small program for profiling using the system's installed C
3649 compiler and look at the assembler code that results.
3651 Older implementations of @code{mcount} expect the address of a counter
3652 variable to be loaded into some register. The name of this variable is
3653 @samp{LP} followed by the number @var{labelno}, so you would generate
3654 the name using @samp{LP%d} in a @code{fprintf}.
3657 @defmac PROFILE_HOOK
3658 A C statement or compound statement to output to @var{file} some assembly
3659 code to call the profiling subroutine @code{mcount} even the target does
3660 not support profiling.
3663 @defmac NO_PROFILE_COUNTERS
3664 Define this macro to be an expression with a nonzero value if the
3665 @code{mcount} subroutine on your system does not need a counter variable
3666 allocated for each function. This is true for almost all modern
3667 implementations. If you define this macro, you must not use the
3668 @var{labelno} argument to @code{FUNCTION_PROFILER}.
3671 @defmac PROFILE_BEFORE_PROLOGUE
3672 Define this macro if the code for function profiling should come before
3673 the function prologue. Normally, the profiling code comes after.
3676 @hook TARGET_KEEP_LEAF_WHEN_PROFILED
3679 @subsection Permitting tail calls
3682 @hook TARGET_FUNCTION_OK_FOR_SIBCALL
3684 @hook TARGET_EXTRA_LIVE_ON_ENTRY
3686 @hook TARGET_SET_UP_BY_PROLOGUE
3688 @hook TARGET_WARN_FUNC_RETURN
3690 @node Shrink-wrapping separate components
3691 @subsection Shrink-wrapping separate components
3692 @cindex shrink-wrapping separate components
3694 The prologue may perform a variety of target dependent tasks such as
3695 saving callee-saved registers, saving the return address, aligning the
3696 stack, creating a stack frame, initializing the PIC register, setting
3697 up the static chain, etc.
3699 On some targets some of these tasks may be independent of others and
3700 thus may be shrink-wrapped separately. These independent tasks are
3701 referred to as components and are handled generically by the target
3702 independent parts of GCC.
3704 Using the following hooks those prologue or epilogue components can be
3705 shrink-wrapped separately, so that the initialization (and possibly
3706 teardown) those components do is not done as frequently on execution
3707 paths where this would unnecessary.
3709 What exactly those components are is up to the target code; the generic
3710 code treats them abstractly, as a bit in an @code{sbitmap}. These
3711 @code{sbitmap}s are allocated by the @code{shrink_wrap.get_separate_components}
3712 and @code{shrink_wrap.components_for_bb} hooks, and deallocated by the
3715 @hook TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS
3717 @hook TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB
3719 @hook TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS
3721 @hook TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS
3723 @hook TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS
3725 @hook TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS
3727 @node Stack Smashing Protection
3728 @subsection Stack smashing protection
3729 @cindex stack smashing protection
3731 @hook TARGET_STACK_PROTECT_GUARD
3733 @hook TARGET_STACK_PROTECT_FAIL
3735 @hook TARGET_STACK_PROTECT_RUNTIME_ENABLED_P
3737 @hook TARGET_SUPPORTS_SPLIT_STACK
3739 @node Miscellaneous Register Hooks
3740 @subsection Miscellaneous register hooks
3741 @cindex miscellaneous register hooks
3743 @hook TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS
3746 @section Implementing the Varargs Macros
3747 @cindex varargs implementation
3749 GCC comes with an implementation of @code{<varargs.h>} and
3750 @code{<stdarg.h>} that work without change on machines that pass arguments
3751 on the stack. Other machines require their own implementations of
3752 varargs, and the two machine independent header files must have
3753 conditionals to include it.
3755 ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
3756 the calling convention for @code{va_start}. The traditional
3757 implementation takes just one argument, which is the variable in which
3758 to store the argument pointer. The ISO implementation of
3759 @code{va_start} takes an additional second argument. The user is
3760 supposed to write the last named argument of the function here.
3762 However, @code{va_start} should not use this argument. The way to find
3763 the end of the named arguments is with the built-in functions described
3766 @defmac __builtin_saveregs ()
3767 Use this built-in function to save the argument registers in memory so
3768 that the varargs mechanism can access them. Both ISO and traditional
3769 versions of @code{va_start} must use @code{__builtin_saveregs}, unless
3770 you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead.
3772 On some machines, @code{__builtin_saveregs} is open-coded under the
3773 control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On
3774 other machines, it calls a routine written in assembler language,
3775 found in @file{libgcc2.c}.
3777 Code generated for the call to @code{__builtin_saveregs} appears at the
3778 beginning of the function, as opposed to where the call to
3779 @code{__builtin_saveregs} is written, regardless of what the code is.
3780 This is because the registers must be saved before the function starts
3781 to use them for its own purposes.
3782 @c i rewrote the first sentence above to fix an overfull hbox. --mew
3786 @defmac __builtin_next_arg (@var{lastarg})
3787 This builtin returns the address of the first anonymous stack
3788 argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
3789 returns the address of the location above the first anonymous stack
3790 argument. Use it in @code{va_start} to initialize the pointer for
3791 fetching arguments from the stack. Also use it in @code{va_start} to
3792 verify that the second parameter @var{lastarg} is the last named argument
3793 of the current function.
3796 @defmac __builtin_classify_type (@var{object})
3797 Since each machine has its own conventions for which data types are
3798 passed in which kind of register, your implementation of @code{va_arg}
3799 has to embody these conventions. The easiest way to categorize the
3800 specified data type is to use @code{__builtin_classify_type} together
3801 with @code{sizeof} and @code{__alignof__}.
3803 @code{__builtin_classify_type} ignores the value of @var{object},
3804 considering only its data type. It returns an integer describing what
3805 kind of type that is---integer, floating, pointer, structure, and so on.
3807 The file @file{typeclass.h} defines an enumeration that you can use to
3808 interpret the values of @code{__builtin_classify_type}.
3811 These machine description macros help implement varargs:
3813 @hook TARGET_EXPAND_BUILTIN_SAVEREGS
3815 @hook TARGET_SETUP_INCOMING_VARARGS
3817 @hook TARGET_STRICT_ARGUMENT_NAMING
3819 @hook TARGET_CALL_ARGS
3821 @hook TARGET_END_CALL_ARGS
3823 @hook TARGET_PRETEND_OUTGOING_VARARGS_NAMED
3825 @hook TARGET_LOAD_BOUNDS_FOR_ARG
3827 @hook TARGET_STORE_BOUNDS_FOR_ARG
3829 @hook TARGET_LOAD_RETURNED_BOUNDS
3831 @hook TARGET_STORE_RETURNED_BOUNDS
3833 @hook TARGET_CHKP_FUNCTION_VALUE_BOUNDS
3835 @hook TARGET_SETUP_INCOMING_VARARG_BOUNDS
3838 @section Trampolines for Nested Functions
3839 @cindex trampolines for nested functions
3840 @cindex nested functions, trampolines for
3842 A @dfn{trampoline} is a small piece of code that is created at run time
3843 when the address of a nested function is taken. It normally resides on
3844 the stack, in the stack frame of the containing function. These macros
3845 tell GCC how to generate code to allocate and initialize a
3848 The instructions in the trampoline must do two things: load a constant
3849 address into the static chain register, and jump to the real address of
3850 the nested function. On CISC machines such as the m68k, this requires
3851 two instructions, a move immediate and a jump. Then the two addresses
3852 exist in the trampoline as word-long immediate operands. On RISC
3853 machines, it is often necessary to load each address into a register in
3854 two parts. Then pieces of each address form separate immediate
3857 The code generated to initialize the trampoline must store the variable
3858 parts---the static chain value and the function address---into the
3859 immediate operands of the instructions. On a CISC machine, this is
3860 simply a matter of copying each address to a memory reference at the
3861 proper offset from the start of the trampoline. On a RISC machine, it
3862 may be necessary to take out pieces of the address and store them
3865 @hook TARGET_ASM_TRAMPOLINE_TEMPLATE
3867 @defmac TRAMPOLINE_SECTION
3868 Return the section into which the trampoline template is to be placed
3869 (@pxref{Sections}). The default value is @code{readonly_data_section}.
3872 @defmac TRAMPOLINE_SIZE
3873 A C expression for the size in bytes of the trampoline, as an integer.
3876 @defmac TRAMPOLINE_ALIGNMENT
3877 Alignment required for trampolines, in bits.
3879 If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT}
3880 is used for aligning trampolines.
3883 @hook TARGET_TRAMPOLINE_INIT
3885 @hook TARGET_TRAMPOLINE_ADJUST_ADDRESS
3887 @hook TARGET_CUSTOM_FUNCTION_DESCRIPTORS
3889 Implementing trampolines is difficult on many machines because they have
3890 separate instruction and data caches. Writing into a stack location
3891 fails to clear the memory in the instruction cache, so when the program
3892 jumps to that location, it executes the old contents.
3894 Here are two possible solutions. One is to clear the relevant parts of
3895 the instruction cache whenever a trampoline is set up. The other is to
3896 make all trampolines identical, by having them jump to a standard
3897 subroutine. The former technique makes trampoline execution faster; the
3898 latter makes initialization faster.
3900 To clear the instruction cache when a trampoline is initialized, define
3901 the following macro.
3903 @defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
3904 If defined, expands to a C expression clearing the @emph{instruction
3905 cache} in the specified interval. The definition of this macro would
3906 typically be a series of @code{asm} statements. Both @var{beg} and
3907 @var{end} are both pointer expressions.
3910 To use a standard subroutine, define the following macro. In addition,
3911 you must make sure that the instructions in a trampoline fill an entire
3912 cache line with identical instructions, or else ensure that the
3913 beginning of the trampoline code is always aligned at the same point in
3914 its cache line. Look in @file{m68k.h} as a guide.
3916 @defmac TRANSFER_FROM_TRAMPOLINE
3917 Define this macro if trampolines need a special subroutine to do their
3918 work. The macro should expand to a series of @code{asm} statements
3919 which will be compiled with GCC@. They go in a library function named
3920 @code{__transfer_from_trampoline}.
3922 If you need to avoid executing the ordinary prologue code of a compiled
3923 C function when you jump to the subroutine, you can do so by placing a
3924 special label of your own in the assembler code. Use one @code{asm}
3925 statement to generate an assembler label, and another to make the label
3926 global. Then trampolines can use that label to jump directly to your
3927 special assembler code.
3931 @section Implicit Calls to Library Routines
3932 @cindex library subroutine names
3933 @cindex @file{libgcc.a}
3935 @c prevent bad page break with this line
3936 Here is an explanation of implicit calls to library routines.
3938 @defmac DECLARE_LIBRARY_RENAMES
3939 This macro, if defined, should expand to a piece of C code that will get
3940 expanded when compiling functions for libgcc.a. It can be used to
3941 provide alternate names for GCC's internal library functions if there
3942 are ABI-mandated names that the compiler should provide.
3945 @findex set_optab_libfunc
3946 @findex init_one_libfunc
3947 @hook TARGET_INIT_LIBFUNCS
3949 @hook TARGET_LIBFUNC_GNU_PREFIX
3951 @defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
3952 This macro should return @code{true} if the library routine that
3953 implements the floating point comparison operator @var{comparison} in
3954 mode @var{mode} will return a boolean, and @var{false} if it will
3957 GCC's own floating point libraries return tristates from the
3958 comparison operators, so the default returns false always. Most ports
3959 don't need to define this macro.
3962 @defmac TARGET_LIB_INT_CMP_BIASED
3963 This macro should evaluate to @code{true} if the integer comparison
3964 functions (like @code{__cmpdi2}) return 0 to indicate that the first
3965 operand is smaller than the second, 1 to indicate that they are equal,
3966 and 2 to indicate that the first operand is greater than the second.
3967 If this macro evaluates to @code{false} the comparison functions return
3968 @minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines
3969 in @file{libgcc.a}, you do not need to define this macro.
3972 @defmac TARGET_HAS_NO_HW_DIVIDE
3973 This macro should be defined if the target has no hardware divide
3974 instructions. If this macro is defined, GCC will use an algorithm which
3975 make use of simple logical and arithmetic operations for 64-bit
3976 division. If the macro is not defined, GCC will use an algorithm which
3977 make use of a 64-bit by 32-bit divide primitive.
3980 @cindex @code{EDOM}, implicit usage
3983 The value of @code{EDOM} on the target machine, as a C integer constant
3984 expression. If you don't define this macro, GCC does not attempt to
3985 deposit the value of @code{EDOM} into @code{errno} directly. Look in
3986 @file{/usr/include/errno.h} to find the value of @code{EDOM} on your
3989 If you do not define @code{TARGET_EDOM}, then compiled code reports
3990 domain errors by calling the library function and letting it report the
3991 error. If mathematical functions on your system use @code{matherr} when
3992 there is an error, then you should leave @code{TARGET_EDOM} undefined so
3993 that @code{matherr} is used normally.
3996 @cindex @code{errno}, implicit usage
3997 @defmac GEN_ERRNO_RTX
3998 Define this macro as a C expression to create an rtl expression that
3999 refers to the global ``variable'' @code{errno}. (On certain systems,
4000 @code{errno} may not actually be a variable.) If you don't define this
4001 macro, a reasonable default is used.
4004 @hook TARGET_LIBC_HAS_FUNCTION
4006 @defmac NEXT_OBJC_RUNTIME
4007 Set this macro to 1 to use the "NeXT" Objective-C message sending conventions
4008 by default. This calling convention involves passing the object, the selector
4009 and the method arguments all at once to the method-lookup library function.
4010 This is the usual setting when targeting Darwin/Mac OS X systems, which have
4011 the NeXT runtime installed.
4013 If the macro is set to 0, the "GNU" Objective-C message sending convention
4014 will be used by default. This convention passes just the object and the
4015 selector to the method-lookup function, which returns a pointer to the method.
4017 In either case, it remains possible to select code-generation for the alternate
4018 scheme, by means of compiler command line switches.
4021 @node Addressing Modes
4022 @section Addressing Modes
4023 @cindex addressing modes
4025 @c prevent bad page break with this line
4026 This is about addressing modes.
4028 @defmac HAVE_PRE_INCREMENT
4029 @defmacx HAVE_PRE_DECREMENT
4030 @defmacx HAVE_POST_INCREMENT
4031 @defmacx HAVE_POST_DECREMENT
4032 A C expression that is nonzero if the machine supports pre-increment,
4033 pre-decrement, post-increment, or post-decrement addressing respectively.
4036 @defmac HAVE_PRE_MODIFY_DISP
4037 @defmacx HAVE_POST_MODIFY_DISP
4038 A C expression that is nonzero if the machine supports pre- or
4039 post-address side-effect generation involving constants other than
4040 the size of the memory operand.
4043 @defmac HAVE_PRE_MODIFY_REG
4044 @defmacx HAVE_POST_MODIFY_REG
4045 A C expression that is nonzero if the machine supports pre- or
4046 post-address side-effect generation involving a register displacement.
4049 @defmac CONSTANT_ADDRESS_P (@var{x})
4050 A C expression that is 1 if the RTX @var{x} is a constant which
4051 is a valid address. On most machines the default definition of
4052 @code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)}
4053 is acceptable, but a few machines are more restrictive as to which
4054 constant addresses are supported.
4057 @defmac CONSTANT_P (@var{x})
4058 @code{CONSTANT_P}, which is defined by target-independent code,
4059 accepts integer-values expressions whose values are not explicitly
4060 known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
4061 expressions and @code{const} arithmetic expressions, in addition to
4062 @code{const_int} and @code{const_double} expressions.
4065 @defmac MAX_REGS_PER_ADDRESS
4066 A number, the maximum number of registers that can appear in a valid
4067 memory address. Note that it is up to you to specify a value equal to
4068 the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever
4072 @hook TARGET_LEGITIMATE_ADDRESS_P
4074 @defmac TARGET_MEM_CONSTRAINT
4075 A single character to be used instead of the default @code{'m'}
4076 character for general memory addresses. This defines the constraint
4077 letter which matches the memory addresses accepted by
4078 @code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to
4079 support new address formats in your back end without changing the
4080 semantics of the @code{'m'} constraint. This is necessary in order to
4081 preserve functionality of inline assembly constructs using the
4082 @code{'m'} constraint.
4085 @defmac FIND_BASE_TERM (@var{x})
4086 A C expression to determine the base term of address @var{x},
4087 or to provide a simplified version of @var{x} from which @file{alias.c}
4088 can easily find the base term. This macro is used in only two places:
4089 @code{find_base_value} and @code{find_base_term} in @file{alias.c}.
4091 It is always safe for this macro to not be defined. It exists so
4092 that alias analysis can understand machine-dependent addresses.
4094 The typical use of this macro is to handle addresses containing
4095 a label_ref or symbol_ref within an UNSPEC@.
4098 @hook TARGET_LEGITIMIZE_ADDRESS
4100 @defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
4101 A C compound statement that attempts to replace @var{x}, which is an address
4102 that needs reloading, with a valid memory address for an operand of mode
4103 @var{mode}. @var{win} will be a C statement label elsewhere in the code.
4104 It is not necessary to define this macro, but it might be useful for
4105 performance reasons.
4107 For example, on the i386, it is sometimes possible to use a single
4108 reload register instead of two by reloading a sum of two pseudo
4109 registers into a register. On the other hand, for number of RISC
4110 processors offsets are limited so that often an intermediate address
4111 needs to be generated in order to address a stack slot. By defining
4112 @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
4113 generated for adjacent some stack slots can be made identical, and thus
4116 @emph{Note}: This macro should be used with caution. It is necessary
4117 to know something of how reload works in order to effectively use this,
4118 and it is quite easy to produce macros that build in too much knowledge
4119 of reload internals.
4121 @emph{Note}: This macro must be able to reload an address created by a
4122 previous invocation of this macro. If it fails to handle such addresses
4123 then the compiler may generate incorrect code or abort.
4126 The macro definition should use @code{push_reload} to indicate parts that
4127 need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
4128 suitable to be passed unaltered to @code{push_reload}.
4130 The code generated by this macro must not alter the substructure of
4131 @var{x}. If it transforms @var{x} into a more legitimate form, it
4132 should assign @var{x} (which will always be a C variable) a new value.
4133 This also applies to parts that you change indirectly by calling
4136 @findex strict_memory_address_p
4137 The macro definition may use @code{strict_memory_address_p} to test if
4138 the address has become legitimate.
4141 If you want to change only a part of @var{x}, one standard way of doing
4142 this is to use @code{copy_rtx}. Note, however, that it unshares only a
4143 single level of rtl. Thus, if the part to be changed is not at the
4144 top level, you'll need to replace first the top level.
4145 It is not necessary for this macro to come up with a legitimate
4146 address; but often a machine-dependent strategy can generate better code.
4149 @hook TARGET_MODE_DEPENDENT_ADDRESS_P
4151 @hook TARGET_LEGITIMATE_CONSTANT_P
4153 @hook TARGET_DELEGITIMIZE_ADDRESS
4155 @hook TARGET_CONST_NOT_OK_FOR_DEBUG_P
4157 @hook TARGET_CANNOT_FORCE_CONST_MEM
4159 @hook TARGET_USE_BLOCKS_FOR_CONSTANT_P
4161 @hook TARGET_USE_BLOCKS_FOR_DECL_P
4163 @hook TARGET_BUILTIN_RECIPROCAL
4165 @hook TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD
4167 @hook TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST
4169 @hook TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE
4171 @hook TARGET_VECTORIZE_VEC_PERM_CONST_OK
4173 @hook TARGET_VECTORIZE_BUILTIN_CONVERSION
4175 @hook TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION
4177 @hook TARGET_VECTORIZE_BUILTIN_MD_VECTORIZED_FUNCTION
4179 @hook TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT
4181 @hook TARGET_VECTORIZE_PREFERRED_SIMD_MODE
4183 @hook TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_SIZES
4185 @hook TARGET_VECTORIZE_GET_MASK_MODE
4187 @hook TARGET_VECTORIZE_INIT_COST
4189 @hook TARGET_VECTORIZE_ADD_STMT_COST
4191 @hook TARGET_VECTORIZE_FINISH_COST
4193 @hook TARGET_VECTORIZE_DESTROY_COST_DATA
4195 @hook TARGET_VECTORIZE_BUILTIN_GATHER
4197 @hook TARGET_VECTORIZE_BUILTIN_SCATTER
4199 @hook TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN
4201 @hook TARGET_SIMD_CLONE_ADJUST
4203 @hook TARGET_SIMD_CLONE_USABLE
4205 @hook TARGET_SIMT_VF
4207 @hook TARGET_GOACC_VALIDATE_DIMS
4209 @hook TARGET_GOACC_DIM_LIMIT
4211 @hook TARGET_GOACC_FORK_JOIN
4213 @hook TARGET_GOACC_REDUCTION
4215 @node Anchored Addresses
4216 @section Anchored Addresses
4217 @cindex anchored addresses
4218 @cindex @option{-fsection-anchors}
4220 GCC usually addresses every static object as a separate entity.
4221 For example, if we have:
4225 int foo (void) @{ return a + b + c; @}
4228 the code for @code{foo} will usually calculate three separate symbolic
4229 addresses: those of @code{a}, @code{b} and @code{c}. On some targets,
4230 it would be better to calculate just one symbolic address and access
4231 the three variables relative to it. The equivalent pseudocode would
4237 register int *xr = &x;
4238 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
4242 (which isn't valid C). We refer to shared addresses like @code{x} as
4243 ``section anchors''. Their use is controlled by @option{-fsection-anchors}.
4245 The hooks below describe the target properties that GCC needs to know
4246 in order to make effective use of section anchors. It won't use
4247 section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET}
4248 or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value.
4250 @hook TARGET_MIN_ANCHOR_OFFSET
4252 @hook TARGET_MAX_ANCHOR_OFFSET
4254 @hook TARGET_ASM_OUTPUT_ANCHOR
4256 @hook TARGET_USE_ANCHORS_FOR_SYMBOL_P
4258 @node Condition Code
4259 @section Condition Code Status
4260 @cindex condition code status
4262 The macros in this section can be split in two families, according to the
4263 two ways of representing condition codes in GCC.
4265 The first representation is the so called @code{(cc0)} representation
4266 (@pxref{Jump Patterns}), where all instructions can have an implicit
4267 clobber of the condition codes. The second is the condition code
4268 register representation, which provides better schedulability for
4269 architectures that do have a condition code register, but on which
4270 most instructions do not affect it. The latter category includes
4273 The implicit clobbering poses a strong restriction on the placement of
4274 the definition and use of the condition code. In the past the definition
4275 and use were always adjacent. However, recent changes to support trapping
4276 arithmatic may result in the definition and user being in different blocks.
4277 Thus, there may be a @code{NOTE_INSN_BASIC_BLOCK} between them. Additionally,
4278 the definition may be the source of exception handling edges.
4280 These restrictions can prevent important
4281 optimizations on some machines. For example, on the IBM RS/6000, there
4282 is a delay for taken branches unless the condition code register is set
4283 three instructions earlier than the conditional branch. The instruction
4284 scheduler cannot perform this optimization if it is not permitted to
4285 separate the definition and use of the condition code register.
4287 For this reason, it is possible and suggested to use a register to
4288 represent the condition code for new ports. If there is a specific
4289 condition code register in the machine, use a hard register. If the
4290 condition code or comparison result can be placed in any general register,
4291 or if there are multiple condition registers, use a pseudo register.
4292 Registers used to store the condition code value will usually have a mode
4293 that is in class @code{MODE_CC}.
4295 Alternatively, you can use @code{BImode} if the comparison operator is
4296 specified already in the compare instruction. In this case, you are not
4297 interested in most macros in this section.
4300 * CC0 Condition Codes:: Old style representation of condition codes.
4301 * MODE_CC Condition Codes:: Modern representation of condition codes.
4304 @node CC0 Condition Codes
4305 @subsection Representation of condition codes using @code{(cc0)}
4309 The file @file{conditions.h} defines a variable @code{cc_status} to
4310 describe how the condition code was computed (in case the interpretation of
4311 the condition code depends on the instruction that it was set by). This
4312 variable contains the RTL expressions on which the condition code is
4313 currently based, and several standard flags.
4315 Sometimes additional machine-specific flags must be defined in the machine
4316 description header file. It can also add additional machine-specific
4317 information by defining @code{CC_STATUS_MDEP}.
4319 @defmac CC_STATUS_MDEP
4320 C code for a data type which is used for declaring the @code{mdep}
4321 component of @code{cc_status}. It defaults to @code{int}.
4323 This macro is not used on machines that do not use @code{cc0}.
4326 @defmac CC_STATUS_MDEP_INIT
4327 A C expression to initialize the @code{mdep} field to ``empty''.
4328 The default definition does nothing, since most machines don't use
4329 the field anyway. If you want to use the field, you should probably
4330 define this macro to initialize it.
4332 This macro is not used on machines that do not use @code{cc0}.
4335 @defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
4336 A C compound statement to set the components of @code{cc_status}
4337 appropriately for an insn @var{insn} whose body is @var{exp}. It is
4338 this macro's responsibility to recognize insns that set the condition
4339 code as a byproduct of other activity as well as those that explicitly
4342 This macro is not used on machines that do not use @code{cc0}.
4344 If there are insns that do not set the condition code but do alter
4345 other machine registers, this macro must check to see whether they
4346 invalidate the expressions that the condition code is recorded as
4347 reflecting. For example, on the 68000, insns that store in address
4348 registers do not set the condition code, which means that usually
4349 @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
4350 insns. But suppose that the previous insn set the condition code
4351 based on location @samp{a4@@(102)} and the current insn stores a new
4352 value in @samp{a4}. Although the condition code is not changed by
4353 this, it will no longer be true that it reflects the contents of
4354 @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter
4355 @code{cc_status} in this case to say that nothing is known about the
4356 condition code value.
4358 The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
4359 with the results of peephole optimization: insns whose patterns are
4360 @code{parallel} RTXs containing various @code{reg}, @code{mem} or
4361 constants which are just the operands. The RTL structure of these
4362 insns is not sufficient to indicate what the insns actually do. What
4363 @code{NOTICE_UPDATE_CC} should do when it sees one is just to run
4364 @code{CC_STATUS_INIT}.
4366 A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
4367 that looks at an attribute (@pxref{Insn Attributes}) named, for example,
4368 @samp{cc}. This avoids having detailed information about patterns in
4369 two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
4372 @node MODE_CC Condition Codes
4373 @subsection Representation of condition codes using registers
4377 @defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
4378 On many machines, the condition code may be produced by other instructions
4379 than compares, for example the branch can use directly the condition
4380 code set by a subtract instruction. However, on some machines
4381 when the condition code is set this way some bits (such as the overflow
4382 bit) are not set in the same way as a test instruction, so that a different
4383 branch instruction must be used for some conditional branches. When
4384 this happens, use the machine mode of the condition code register to
4385 record different formats of the condition code register. Modes can
4386 also be used to record which compare instruction (e.g. a signed or an
4387 unsigned comparison) produced the condition codes.
4389 If other modes than @code{CCmode} are required, add them to
4390 @file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose
4391 a mode given an operand of a compare. This is needed because the modes
4392 have to be chosen not only during RTL generation but also, for example,
4393 by instruction combination. The result of @code{SELECT_CC_MODE} should
4394 be consistent with the mode used in the patterns; for example to support
4395 the case of the add on the SPARC discussed above, we have the pattern
4401 (plus:SI (match_operand:SI 0 "register_operand" "%r")
4402 (match_operand:SI 1 "arith_operand" "rI"))
4409 together with a @code{SELECT_CC_MODE} that returns @code{CCNZmode}
4410 for comparisons whose argument is a @code{plus}:
4413 #define SELECT_CC_MODE(OP,X,Y) \
4414 (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
4415 ? ((OP == LT || OP == LE || OP == GT || OP == GE) \
4416 ? CCFPEmode : CCFPmode) \
4417 : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
4418 || GET_CODE (X) == NEG || GET_CODE (x) == ASHIFT) \
4419 ? CCNZmode : CCmode))
4422 Another reason to use modes is to retain information on which operands
4423 were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in
4426 You should define this macro if and only if you define extra CC modes
4427 in @file{@var{machine}-modes.def}.
4430 @hook TARGET_CANONICALIZE_COMPARISON
4432 @defmac REVERSIBLE_CC_MODE (@var{mode})
4433 A C expression whose value is one if it is always safe to reverse a
4434 comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
4435 can ever return @var{mode} for a floating-point inequality comparison,
4436 then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
4438 You need not define this macro if it would always returns zero or if the
4439 floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
4440 For example, here is the definition used on the SPARC, where floating-point
4441 inequality comparisons are given either @code{CCFPEmode} or @code{CCFPmode}:
4444 #define REVERSIBLE_CC_MODE(MODE) \
4445 ((MODE) != CCFPEmode && (MODE) != CCFPmode)
4449 @defmac REVERSE_CONDITION (@var{code}, @var{mode})
4450 A C expression whose value is reversed condition code of the @var{code} for
4451 comparison done in CC_MODE @var{mode}. The macro is used only in case
4452 @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
4453 machine has some non-standard way how to reverse certain conditionals. For
4454 instance in case all floating point conditions are non-trapping, compiler may
4455 freely convert unordered compares to ordered ones. Then definition may look
4459 #define REVERSE_CONDITION(CODE, MODE) \
4460 ((MODE) != CCFPmode ? reverse_condition (CODE) \
4461 : reverse_condition_maybe_unordered (CODE))
4465 @hook TARGET_FIXED_CONDITION_CODE_REGS
4467 @hook TARGET_CC_MODES_COMPATIBLE
4469 @hook TARGET_FLAGS_REGNUM
4472 @section Describing Relative Costs of Operations
4473 @cindex costs of instructions
4474 @cindex relative costs
4475 @cindex speed of instructions
4477 These macros let you describe the relative speed of various operations
4478 on the target machine.
4480 @defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
4481 A C expression for the cost of moving data of mode @var{mode} from a
4482 register in class @var{from} to one in class @var{to}. The classes are
4483 expressed using the enumeration values such as @code{GENERAL_REGS}. A
4484 value of 2 is the default; other values are interpreted relative to
4487 It is not required that the cost always equal 2 when @var{from} is the
4488 same as @var{to}; on some machines it is expensive to move between
4489 registers if they are not general registers.
4491 If reload sees an insn consisting of a single @code{set} between two
4492 hard registers, and if @code{REGISTER_MOVE_COST} applied to their
4493 classes returns a value of 2, reload does not check to ensure that the
4494 constraints of the insn are met. Setting a cost of other than 2 will
4495 allow reload to verify that the constraints are met. You should do this
4496 if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
4498 These macros are obsolete, new ports should use the target hook
4499 @code{TARGET_REGISTER_MOVE_COST} instead.
4502 @hook TARGET_REGISTER_MOVE_COST
4504 @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
4505 A C expression for the cost of moving data of mode @var{mode} between a
4506 register of class @var{class} and memory; @var{in} is zero if the value
4507 is to be written to memory, nonzero if it is to be read in. This cost
4508 is relative to those in @code{REGISTER_MOVE_COST}. If moving between
4509 registers and memory is more expensive than between two registers, you
4510 should define this macro to express the relative cost.
4512 If you do not define this macro, GCC uses a default cost of 4 plus
4513 the cost of copying via a secondary reload register, if one is
4514 needed. If your machine requires a secondary reload register to copy
4515 between memory and a register of @var{class} but the reload mechanism is
4516 more complex than copying via an intermediate, define this macro to
4517 reflect the actual cost of the move.
4519 GCC defines the function @code{memory_move_secondary_cost} if
4520 secondary reloads are needed. It computes the costs due to copying via
4521 a secondary register. If your machine copies from memory using a
4522 secondary register in the conventional way but the default base value of
4523 4 is not correct for your machine, define this macro to add some other
4524 value to the result of that function. The arguments to that function
4525 are the same as to this macro.
4527 These macros are obsolete, new ports should use the target hook
4528 @code{TARGET_MEMORY_MOVE_COST} instead.
4531 @hook TARGET_MEMORY_MOVE_COST
4533 @defmac BRANCH_COST (@var{speed_p}, @var{predictable_p})
4534 A C expression for the cost of a branch instruction. A value of 1 is
4535 the default; other values are interpreted relative to that. Parameter
4536 @var{speed_p} is true when the branch in question should be optimized
4537 for speed. When it is false, @code{BRANCH_COST} should return a value
4538 optimal for code size rather than performance. @var{predictable_p} is
4539 true for well-predicted branches. On many architectures the
4540 @code{BRANCH_COST} can be reduced then.
4543 Here are additional macros which do not specify precise relative costs,
4544 but only that certain actions are more expensive than GCC would
4547 @defmac SLOW_BYTE_ACCESS
4548 Define this macro as a C expression which is nonzero if accessing less
4549 than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
4550 faster than accessing a word of memory, i.e., if such access
4551 require more than one instruction or if there is no difference in cost
4552 between byte and (aligned) word loads.
4554 When this macro is not defined, the compiler will access a field by
4555 finding the smallest containing object; when it is defined, a fullword
4556 load will be used if alignment permits. Unless bytes accesses are
4557 faster than word accesses, using word accesses is preferable since it
4558 may eliminate subsequent memory access if subsequent accesses occur to
4559 other fields in the same word of the structure, but to different bytes.
4562 @hook TARGET_SLOW_UNALIGNED_ACCESS
4564 @defmac MOVE_RATIO (@var{speed})
4565 The threshold of number of scalar memory-to-memory move insns, @emph{below}
4566 which a sequence of insns should be generated instead of a
4567 string move insn or a library call. Increasing the value will always
4568 make code faster, but eventually incurs high cost in increased code size.
4570 Note that on machines where the corresponding move insn is a
4571 @code{define_expand} that emits a sequence of insns, this macro counts
4572 the number of such sequences.
4574 The parameter @var{speed} is true if the code is currently being
4575 optimized for speed rather than size.
4577 If you don't define this, a reasonable default is used.
4580 @hook TARGET_USE_BY_PIECES_INFRASTRUCTURE_P
4582 @hook TARGET_COMPARE_BY_PIECES_BRANCH_RATIO
4584 @defmac MOVE_MAX_PIECES
4585 A C expression used by @code{move_by_pieces} to determine the largest unit
4586 a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
4589 @defmac STORE_MAX_PIECES
4590 A C expression used by @code{store_by_pieces} to determine the largest unit
4591 a store used to memory is. Defaults to @code{MOVE_MAX_PIECES}, or two times
4592 the size of @code{HOST_WIDE_INT}, whichever is smaller.
4595 @defmac COMPARE_MAX_PIECES
4596 A C expression used by @code{compare_by_pieces} to determine the largest unit
4597 a load or store used to compare memory is. Defaults to
4598 @code{MOVE_MAX_PIECES}.
4601 @defmac CLEAR_RATIO (@var{speed})
4602 The threshold of number of scalar move insns, @emph{below} which a sequence
4603 of insns should be generated to clear memory instead of a string clear insn
4604 or a library call. Increasing the value will always make code faster, but
4605 eventually incurs high cost in increased code size.
4607 The parameter @var{speed} is true if the code is currently being
4608 optimized for speed rather than size.
4610 If you don't define this, a reasonable default is used.
4613 @defmac SET_RATIO (@var{speed})
4614 The threshold of number of scalar move insns, @emph{below} which a sequence
4615 of insns should be generated to set memory to a constant value, instead of
4616 a block set insn or a library call.
4617 Increasing the value will always make code faster, but
4618 eventually incurs high cost in increased code size.
4620 The parameter @var{speed} is true if the code is currently being
4621 optimized for speed rather than size.
4623 If you don't define this, it defaults to the value of @code{MOVE_RATIO}.
4626 @defmac USE_LOAD_POST_INCREMENT (@var{mode})
4627 A C expression used to determine whether a load postincrement is a good
4628 thing to use for a given mode. Defaults to the value of
4629 @code{HAVE_POST_INCREMENT}.
4632 @defmac USE_LOAD_POST_DECREMENT (@var{mode})
4633 A C expression used to determine whether a load postdecrement is a good
4634 thing to use for a given mode. Defaults to the value of
4635 @code{HAVE_POST_DECREMENT}.
4638 @defmac USE_LOAD_PRE_INCREMENT (@var{mode})
4639 A C expression used to determine whether a load preincrement is a good
4640 thing to use for a given mode. Defaults to the value of
4641 @code{HAVE_PRE_INCREMENT}.
4644 @defmac USE_LOAD_PRE_DECREMENT (@var{mode})
4645 A C expression used to determine whether a load predecrement is a good
4646 thing to use for a given mode. Defaults to the value of
4647 @code{HAVE_PRE_DECREMENT}.
4650 @defmac USE_STORE_POST_INCREMENT (@var{mode})
4651 A C expression used to determine whether a store postincrement is a good
4652 thing to use for a given mode. Defaults to the value of
4653 @code{HAVE_POST_INCREMENT}.
4656 @defmac USE_STORE_POST_DECREMENT (@var{mode})
4657 A C expression used to determine whether a store postdecrement is a good
4658 thing to use for a given mode. Defaults to the value of
4659 @code{HAVE_POST_DECREMENT}.
4662 @defmac USE_STORE_PRE_INCREMENT (@var{mode})
4663 This macro is used to determine whether a store preincrement is a good
4664 thing to use for a given mode. Defaults to the value of
4665 @code{HAVE_PRE_INCREMENT}.
4668 @defmac USE_STORE_PRE_DECREMENT (@var{mode})
4669 This macro is used to determine whether a store predecrement is a good
4670 thing to use for a given mode. Defaults to the value of
4671 @code{HAVE_PRE_DECREMENT}.
4674 @defmac NO_FUNCTION_CSE
4675 Define this macro to be true if it is as good or better to call a constant
4676 function address than to call an address kept in a register.
4679 @defmac LOGICAL_OP_NON_SHORT_CIRCUIT
4680 Define this macro if a non-short-circuit operation produced by
4681 @samp{fold_range_test ()} is optimal. This macro defaults to true if
4682 @code{BRANCH_COST} is greater than or equal to the value 2.
4685 @hook TARGET_OPTAB_SUPPORTED_P
4687 @hook TARGET_RTX_COSTS
4689 @hook TARGET_ADDRESS_COST
4691 @hook TARGET_MAX_NOCE_IFCVT_SEQ_COST
4693 @hook TARGET_NOCE_CONVERSION_PROFITABLE_P
4695 @hook TARGET_NO_SPECULATION_IN_DELAY_SLOTS_P
4698 @section Adjusting the Instruction Scheduler
4700 The instruction scheduler may need a fair amount of machine-specific
4701 adjustment in order to produce good code. GCC provides several target
4702 hooks for this purpose. It is usually enough to define just a few of
4703 them: try the first ones in this list first.
4705 @hook TARGET_SCHED_ISSUE_RATE
4707 @hook TARGET_SCHED_VARIABLE_ISSUE
4709 @hook TARGET_SCHED_ADJUST_COST
4711 @hook TARGET_SCHED_ADJUST_PRIORITY
4713 @hook TARGET_SCHED_REORDER
4715 @hook TARGET_SCHED_REORDER2
4717 @hook TARGET_SCHED_MACRO_FUSION_P
4719 @hook TARGET_SCHED_MACRO_FUSION_PAIR_P
4721 @hook TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK
4723 @hook TARGET_SCHED_INIT
4725 @hook TARGET_SCHED_FINISH
4727 @hook TARGET_SCHED_INIT_GLOBAL
4729 @hook TARGET_SCHED_FINISH_GLOBAL
4731 @hook TARGET_SCHED_DFA_PRE_CYCLE_INSN
4733 @hook TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN
4735 @hook TARGET_SCHED_DFA_POST_CYCLE_INSN
4737 @hook TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN
4739 @hook TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE
4741 @hook TARGET_SCHED_DFA_POST_ADVANCE_CYCLE
4743 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD
4745 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD
4747 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN
4749 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE
4751 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK
4753 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END
4755 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT
4757 @hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI
4759 @hook TARGET_SCHED_DFA_NEW_CYCLE
4761 @hook TARGET_SCHED_IS_COSTLY_DEPENDENCE
4763 @hook TARGET_SCHED_H_I_D_EXTENDED
4765 @hook TARGET_SCHED_ALLOC_SCHED_CONTEXT
4767 @hook TARGET_SCHED_INIT_SCHED_CONTEXT
4769 @hook TARGET_SCHED_SET_SCHED_CONTEXT
4771 @hook TARGET_SCHED_CLEAR_SCHED_CONTEXT
4773 @hook TARGET_SCHED_FREE_SCHED_CONTEXT
4775 @hook TARGET_SCHED_SPECULATE_INSN
4777 @hook TARGET_SCHED_NEEDS_BLOCK_P
4779 @hook TARGET_SCHED_GEN_SPEC_CHECK
4781 @hook TARGET_SCHED_SET_SCHED_FLAGS
4783 @hook TARGET_SCHED_CAN_SPECULATE_INSN
4785 @hook TARGET_SCHED_SMS_RES_MII
4787 @hook TARGET_SCHED_DISPATCH
4789 @hook TARGET_SCHED_DISPATCH_DO
4791 @hook TARGET_SCHED_EXPOSED_PIPELINE
4793 @hook TARGET_SCHED_REASSOCIATION_WIDTH
4795 @hook TARGET_SCHED_FUSION_PRIORITY
4797 @hook TARGET_EXPAND_DIVMOD_LIBFUNC
4800 @section Dividing the Output into Sections (Texts, Data, @dots{})
4801 @c the above section title is WAY too long. maybe cut the part between
4802 @c the (...)? --mew 10feb93
4804 An object file is divided into sections containing different types of
4805 data. In the most common case, there are three sections: the @dfn{text
4806 section}, which holds instructions and read-only data; the @dfn{data
4807 section}, which holds initialized writable data; and the @dfn{bss
4808 section}, which holds uninitialized data. Some systems have other kinds
4811 @file{varasm.c} provides several well-known sections, such as
4812 @code{text_section}, @code{data_section} and @code{bss_section}.
4813 The normal way of controlling a @code{@var{foo}_section} variable
4814 is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro,
4815 as described below. The macros are only read once, when @file{varasm.c}
4816 initializes itself, so their values must be run-time constants.
4817 They may however depend on command-line flags.
4819 @emph{Note:} Some run-time files, such @file{crtstuff.c}, also make
4820 use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them
4821 to be string literals.
4823 Some assemblers require a different string to be written every time a
4824 section is selected. If your assembler falls into this category, you
4825 should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use
4826 @code{get_unnamed_section} to set up the sections.
4828 You must always create a @code{text_section}, either by defining
4829 @code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section}
4830 in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of
4831 @code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not
4832 create a distinct @code{readonly_data_section}, the default is to
4833 reuse @code{text_section}.
4835 All the other @file{varasm.c} sections are optional, and are null
4836 if the target does not provide them.
4838 @defmac TEXT_SECTION_ASM_OP
4839 A C expression whose value is a string, including spacing, containing the
4840 assembler operation that should precede instructions and read-only data.
4841 Normally @code{"\t.text"} is right.
4844 @defmac HOT_TEXT_SECTION_NAME
4845 If defined, a C string constant for the name of the section containing most
4846 frequently executed functions of the program. If not defined, GCC will provide
4847 a default definition if the target supports named sections.
4850 @defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
4851 If defined, a C string constant for the name of the section containing unlikely
4852 executed functions in the program.
4855 @defmac DATA_SECTION_ASM_OP
4856 A C expression whose value is a string, including spacing, containing the
4857 assembler operation to identify the following data as writable initialized
4858 data. Normally @code{"\t.data"} is right.
4861 @defmac SDATA_SECTION_ASM_OP
4862 If defined, a C expression whose value is a string, including spacing,
4863 containing the assembler operation to identify the following data as
4864 initialized, writable small data.
4867 @defmac READONLY_DATA_SECTION_ASM_OP
4868 A C expression whose value is a string, including spacing, containing the
4869 assembler operation to identify the following data as read-only initialized
4873 @defmac BSS_SECTION_ASM_OP
4874 If defined, a C expression whose value is a string, including spacing,
4875 containing the assembler operation to identify the following data as
4876 uninitialized global data. If not defined, and
4877 @code{ASM_OUTPUT_ALIGNED_BSS} not defined,
4878 uninitialized global data will be output in the data section if
4879 @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
4883 @defmac SBSS_SECTION_ASM_OP
4884 If defined, a C expression whose value is a string, including spacing,
4885 containing the assembler operation to identify the following data as
4886 uninitialized, writable small data.
4889 @defmac TLS_COMMON_ASM_OP
4890 If defined, a C expression whose value is a string containing the
4891 assembler operation to identify the following data as thread-local
4892 common data. The default is @code{".tls_common"}.
4895 @defmac TLS_SECTION_ASM_FLAG
4896 If defined, a C expression whose value is a character constant
4897 containing the flag used to mark a section as a TLS section. The
4898 default is @code{'T'}.
4901 @defmac INIT_SECTION_ASM_OP
4902 If defined, a C expression whose value is a string, including spacing,
4903 containing the assembler operation to identify the following data as
4904 initialization code. If not defined, GCC will assume such a section does
4905 not exist. This section has no corresponding @code{init_section}
4906 variable; it is used entirely in runtime code.
4909 @defmac FINI_SECTION_ASM_OP
4910 If defined, a C expression whose value is a string, including spacing,
4911 containing the assembler operation to identify the following data as
4912 finalization code. If not defined, GCC will assume such a section does
4913 not exist. This section has no corresponding @code{fini_section}
4914 variable; it is used entirely in runtime code.
4917 @defmac INIT_ARRAY_SECTION_ASM_OP
4918 If defined, a C expression whose value is a string, including spacing,
4919 containing the assembler operation to identify the following data as
4920 part of the @code{.init_array} (or equivalent) section. If not
4921 defined, GCC will assume such a section does not exist. Do not define
4922 both this macro and @code{INIT_SECTION_ASM_OP}.
4925 @defmac FINI_ARRAY_SECTION_ASM_OP
4926 If defined, a C expression whose value is a string, including spacing,
4927 containing the assembler operation to identify the following data as
4928 part of the @code{.fini_array} (or equivalent) section. If not
4929 defined, GCC will assume such a section does not exist. Do not define
4930 both this macro and @code{FINI_SECTION_ASM_OP}.
4933 @defmac MACH_DEP_SECTION_ASM_FLAG
4934 If defined, a C expression whose value is a character constant
4935 containing the flag used to mark a machine-dependent section. This
4936 corresponds to the @code{SECTION_MACH_DEP} section flag.
4939 @defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
4940 If defined, an ASM statement that switches to a different section
4941 via @var{section_op}, calls @var{function}, and switches back to
4942 the text section. This is used in @file{crtstuff.c} if
4943 @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
4944 to initialization and finalization functions from the init and fini
4945 sections. By default, this macro uses a simple function call. Some
4946 ports need hand-crafted assembly code to avoid dependencies on
4947 registers initialized in the function prologue or to ensure that
4948 constant pools don't end up too far way in the text section.
4951 @defmac TARGET_LIBGCC_SDATA_SECTION
4952 If defined, a string which names the section into which small
4953 variables defined in crtstuff and libgcc should go. This is useful
4954 when the target has options for optimizing access to small data, and
4955 you want the crtstuff and libgcc routines to be conservative in what
4956 they expect of your application yet liberal in what your application
4957 expects. For example, for targets with a @code{.sdata} section (like
4958 MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't
4959 require small data support from your application, but use this macro
4960 to put small data into @code{.sdata} so that your application can
4961 access these variables whether it uses small data or not.
4964 @defmac FORCE_CODE_SECTION_ALIGN
4965 If defined, an ASM statement that aligns a code section to some
4966 arbitrary boundary. This is used to force all fragments of the
4967 @code{.init} and @code{.fini} sections to have to same alignment
4968 and thus prevent the linker from having to add any padding.
4971 @defmac JUMP_TABLES_IN_TEXT_SECTION
4972 Define this macro to be an expression with a nonzero value if jump
4973 tables (for @code{tablejump} insns) should be output in the text
4974 section, along with the assembler instructions. Otherwise, the
4975 readonly data section is used.
4977 This macro is irrelevant if there is no separate readonly data section.
4980 @hook TARGET_ASM_INIT_SECTIONS
4982 @hook TARGET_ASM_RELOC_RW_MASK
4984 @hook TARGET_ASM_SELECT_SECTION
4986 @defmac USE_SELECT_SECTION_FOR_FUNCTIONS
4987 Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called
4988 for @code{FUNCTION_DECL}s as well as for variables and constants.
4990 In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the
4991 function has been determined to be likely to be called, and nonzero if
4992 it is unlikely to be called.
4995 @hook TARGET_ASM_UNIQUE_SECTION
4997 @hook TARGET_ASM_FUNCTION_RODATA_SECTION
4999 @hook TARGET_ASM_MERGEABLE_RODATA_PREFIX
5001 @hook TARGET_ASM_TM_CLONE_TABLE_SECTION
5003 @hook TARGET_ASM_SELECT_RTX_SECTION
5005 @hook TARGET_MANGLE_DECL_ASSEMBLER_NAME
5007 @hook TARGET_ENCODE_SECTION_INFO
5009 @hook TARGET_STRIP_NAME_ENCODING
5011 @hook TARGET_IN_SMALL_DATA_P
5013 @hook TARGET_HAVE_SRODATA_SECTION
5015 @hook TARGET_PROFILE_BEFORE_PROLOGUE
5017 @hook TARGET_BINDS_LOCAL_P
5019 @hook TARGET_HAVE_TLS
5023 @section Position Independent Code
5024 @cindex position independent code
5027 This section describes macros that help implement generation of position
5028 independent code. Simply defining these macros is not enough to
5029 generate valid PIC; you must also add support to the hook
5030 @code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro
5031 @code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You
5032 must modify the definition of @samp{movsi} to do something appropriate
5033 when the source operand contains a symbolic address. You may also
5034 need to alter the handling of switch statements so that they use
5036 @c i rearranged the order of the macros above to try to force one of
5037 @c them to the next line, to eliminate an overfull hbox. --mew 10feb93
5039 @defmac PIC_OFFSET_TABLE_REGNUM
5040 The register number of the register used to address a table of static
5041 data addresses in memory. In some cases this register is defined by a
5042 processor's ``application binary interface'' (ABI)@. When this macro
5043 is defined, RTL is generated for this register once, as with the stack
5044 pointer and frame pointer registers. If this macro is not defined, it
5045 is up to the machine-dependent files to allocate such a register (if
5046 necessary). Note that this register must be fixed when in use (e.g.@:
5047 when @code{flag_pic} is true).
5050 @defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
5051 A C expression that is nonzero if the register defined by
5052 @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. If not defined,
5053 the default is zero. Do not define
5054 this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
5057 @defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
5058 A C expression that is nonzero if @var{x} is a legitimate immediate
5059 operand on the target machine when generating position independent code.
5060 You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
5061 check this. You can also assume @var{flag_pic} is true, so you need not
5062 check it either. You need not define this macro if all constants
5063 (including @code{SYMBOL_REF}) can be immediate operands when generating
5064 position independent code.
5067 @node Assembler Format
5068 @section Defining the Output Assembler Language
5070 This section describes macros whose principal purpose is to describe how
5071 to write instructions in assembler language---rather than what the
5075 * File Framework:: Structural information for the assembler file.
5076 * Data Output:: Output of constants (numbers, strings, addresses).
5077 * Uninitialized Data:: Output of uninitialized variables.
5078 * Label Output:: Output and generation of labels.
5079 * Initialization:: General principles of initialization
5080 and termination routines.
5081 * Macros for Initialization::
5082 Specific macros that control the handling of
5083 initialization and termination routines.
5084 * Instruction Output:: Output of actual instructions.
5085 * Dispatch Tables:: Output of jump tables.
5086 * Exception Region Output:: Output of exception region code.
5087 * Alignment Output:: Pseudo ops for alignment and skipping data.
5090 @node File Framework
5091 @subsection The Overall Framework of an Assembler File
5092 @cindex assembler format
5093 @cindex output of assembler code
5095 @c prevent bad page break with this line
5096 This describes the overall framework of an assembly file.
5098 @findex default_file_start
5099 @hook TARGET_ASM_FILE_START
5101 @hook TARGET_ASM_FILE_START_APP_OFF
5103 @hook TARGET_ASM_FILE_START_FILE_DIRECTIVE
5105 @hook TARGET_ASM_FILE_END
5107 @deftypefun void file_end_indicate_exec_stack ()
5108 Some systems use a common convention, the @samp{.note.GNU-stack}
5109 special section, to indicate whether or not an object file relies on
5110 the stack being executable. If your system uses this convention, you
5111 should define @code{TARGET_ASM_FILE_END} to this function. If you
5112 need to do other things in that hook, have your hook function call
5116 @hook TARGET_ASM_LTO_START
5118 @hook TARGET_ASM_LTO_END
5120 @hook TARGET_ASM_CODE_END
5122 @defmac ASM_COMMENT_START
5123 A C string constant describing how to begin a comment in the target
5124 assembler language. The compiler assumes that the comment will end at
5125 the end of the line.
5129 A C string constant for text to be output before each @code{asm}
5130 statement or group of consecutive ones. Normally this is
5131 @code{"#APP"}, which is a comment that has no effect on most
5132 assemblers but tells the GNU assembler that it must check the lines
5133 that follow for all valid assembler constructs.
5137 A C string constant for text to be output after each @code{asm}
5138 statement or group of consecutive ones. Normally this is
5139 @code{"#NO_APP"}, which tells the GNU assembler to resume making the
5140 time-saving assumptions that are valid for ordinary compiler output.
5143 @defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
5144 A C statement to output COFF information or DWARF debugging information
5145 which indicates that filename @var{name} is the current source file to
5146 the stdio stream @var{stream}.
5148 This macro need not be defined if the standard form of output
5149 for the file format in use is appropriate.
5152 @hook TARGET_ASM_OUTPUT_SOURCE_FILENAME
5154 @hook TARGET_ASM_OUTPUT_IDENT
5156 @defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
5157 A C statement to output the string @var{string} to the stdio stream
5158 @var{stream}. If you do not call the function @code{output_quoted_string}
5159 in your config files, GCC will only call it to output filenames to
5160 the assembler source. So you can use it to canonicalize the format
5161 of the filename using this macro.
5164 @hook TARGET_ASM_NAMED_SECTION
5166 @hook TARGET_ASM_ELF_FLAGS_NUMERIC
5168 @hook TARGET_ASM_FUNCTION_SECTION
5170 @hook TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS
5172 @hook TARGET_HAVE_NAMED_SECTIONS
5173 This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
5174 It must not be modified by command-line option processing.
5177 @anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}
5178 @hook TARGET_HAVE_SWITCHABLE_BSS_SECTIONS
5180 @hook TARGET_SECTION_TYPE_FLAGS
5182 @hook TARGET_ASM_RECORD_GCC_SWITCHES
5184 @hook TARGET_ASM_RECORD_GCC_SWITCHES_SECTION
5188 @subsection Output of Data
5191 @hook TARGET_ASM_BYTE_OP
5193 @hook TARGET_ASM_INTEGER
5195 @hook TARGET_ASM_DECL_END
5197 @hook TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA
5199 @defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
5200 A C statement to output to the stdio stream @var{stream} an assembler
5201 instruction to assemble a string constant containing the @var{len}
5202 bytes at @var{ptr}. @var{ptr} will be a C expression of type
5203 @code{char *} and @var{len} a C expression of type @code{int}.
5205 If the assembler has a @code{.ascii} pseudo-op as found in the
5206 Berkeley Unix assembler, do not define the macro
5207 @code{ASM_OUTPUT_ASCII}.
5210 @defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
5211 A C statement to output word @var{n} of a function descriptor for
5212 @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
5213 is defined, and is otherwise unused.
5216 @defmac CONSTANT_POOL_BEFORE_FUNCTION
5217 You may define this macro as a C expression. You should define the
5218 expression to have a nonzero value if GCC should output the constant
5219 pool for a function before the code for the function, or a zero value if
5220 GCC should output the constant pool after the function. If you do
5221 not define this macro, the usual case, GCC will output the constant
5222 pool before the function.
5225 @defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
5226 A C statement to output assembler commands to define the start of the
5227 constant pool for a function. @var{funname} is a string giving
5228 the name of the function. Should the return type of the function
5229 be required, it can be obtained via @var{fundecl}. @var{size}
5230 is the size, in bytes, of the constant pool that will be written
5231 immediately after this call.
5233 If no constant-pool prefix is required, the usual case, this macro need
5237 @defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
5238 A C statement (with or without semicolon) to output a constant in the
5239 constant pool, if it needs special treatment. (This macro need not do
5240 anything for RTL expressions that can be output normally.)
5242 The argument @var{file} is the standard I/O stream to output the
5243 assembler code on. @var{x} is the RTL expression for the constant to
5244 output, and @var{mode} is the machine mode (in case @var{x} is a
5245 @samp{const_int}). @var{align} is the required alignment for the value
5246 @var{x}; you should output an assembler directive to force this much
5249 The argument @var{labelno} is a number to use in an internal label for
5250 the address of this pool entry. The definition of this macro is
5251 responsible for outputting the label definition at the proper place.
5252 Here is how to do this:
5255 @code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
5258 When you output a pool entry specially, you should end with a
5259 @code{goto} to the label @var{jumpto}. This will prevent the same pool
5260 entry from being output a second time in the usual manner.
5262 You need not define this macro if it would do nothing.
5265 @defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
5266 A C statement to output assembler commands to at the end of the constant
5267 pool for a function. @var{funname} is a string giving the name of the
5268 function. Should the return type of the function be required, you can
5269 obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
5270 constant pool that GCC wrote immediately before this call.
5272 If no constant-pool epilogue is required, the usual case, you need not
5276 @defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR})
5277 Define this macro as a C expression which is nonzero if @var{C} is
5278 used as a logical line separator by the assembler. @var{STR} points
5279 to the position in the string where @var{C} was found; this can be used if
5280 a line separator uses multiple characters.
5282 If you do not define this macro, the default is that only
5283 the character @samp{;} is treated as a logical line separator.
5286 @hook TARGET_ASM_OPEN_PAREN
5288 These macros are provided by @file{real.h} for writing the definitions
5289 of @code{ASM_OUTPUT_DOUBLE} and the like:
5291 @defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
5292 @defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
5293 @defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
5294 @defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l})
5295 @defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l})
5296 @defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l})
5297 These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the
5298 target's floating point representation, and store its bit pattern in
5299 the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and
5300 @code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a
5301 simple @code{long int}. For the others, it should be an array of
5302 @code{long int}. The number of elements in this array is determined
5303 by the size of the desired target floating point data type: 32 bits of
5304 it go in each @code{long int} array element. Each array element holds
5305 32 bits of the result, even if @code{long int} is wider than 32 bits
5306 on the host machine.
5308 The array element values are designed so that you can print them out
5309 using @code{fprintf} in the order they should appear in the target
5313 @node Uninitialized Data
5314 @subsection Output of Uninitialized Variables
5316 Each of the macros in this section is used to do the whole job of
5317 outputting a single uninitialized variable.
5319 @defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
5320 A C statement (sans semicolon) to output to the stdio stream
5321 @var{stream} the assembler definition of a common-label named
5322 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
5323 is the size rounded up to whatever alignment the caller wants. It is
5324 possible that @var{size} may be zero, for instance if a struct with no
5325 other member than a zero-length array is defined. In this case, the
5326 backend must output a symbol definition that allocates at least one
5327 byte, both so that the address of the resulting object does not compare
5328 equal to any other, and because some object formats cannot even express
5329 the concept of a zero-sized common symbol, as that is how they represent
5330 an ordinary undefined external.
5332 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
5333 output the name itself; before and after that, output the additional
5334 assembler syntax for defining the name, and a newline.
5336 This macro controls how the assembler definitions of uninitialized
5337 common global variables are output.
5340 @defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
5341 Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
5342 separate, explicit argument. If you define this macro, it is used in
5343 place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
5344 handling the required alignment of the variable. The alignment is specified
5345 as the number of bits.
5348 @defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
5349 Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
5350 variable to be output, if there is one, or @code{NULL_TREE} if there
5351 is no corresponding variable. If you define this macro, GCC will use it
5352 in place of both @code{ASM_OUTPUT_COMMON} and
5353 @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
5354 the variable's decl in order to chose what to output.
5357 @defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
5358 A C statement (sans semicolon) to output to the stdio stream
5359 @var{stream} the assembler definition of uninitialized global @var{decl} named
5360 @var{name} whose size is @var{size} bytes. The variable @var{alignment}
5361 is the alignment specified as the number of bits.
5363 Try to use function @code{asm_output_aligned_bss} defined in file
5364 @file{varasm.c} when defining this macro. If unable, use the expression
5365 @code{assemble_name (@var{stream}, @var{name})} to output the name itself;
5366 before and after that, output the additional assembler syntax for defining
5367 the name, and a newline.
5369 There are two ways of handling global BSS@. One is to define this macro.
5370 The other is to have @code{TARGET_ASM_SELECT_SECTION} return a
5371 switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}).
5372 You do not need to do both.
5374 Some languages do not have @code{common} data, and require a
5375 non-common form of global BSS in order to handle uninitialized globals
5376 efficiently. C++ is one example of this. However, if the target does
5377 not support global BSS, the front end may choose to make globals
5378 common in order to save space in the object file.
5381 @defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
5382 A C statement (sans semicolon) to output to the stdio stream
5383 @var{stream} the assembler definition of a local-common-label named
5384 @var{name} whose size is @var{size} bytes. The variable @var{rounded}
5385 is the size rounded up to whatever alignment the caller wants.
5387 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
5388 output the name itself; before and after that, output the additional
5389 assembler syntax for defining the name, and a newline.
5391 This macro controls how the assembler definitions of uninitialized
5392 static variables are output.
5395 @defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
5396 Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
5397 separate, explicit argument. If you define this macro, it is used in
5398 place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
5399 handling the required alignment of the variable. The alignment is specified
5400 as the number of bits.
5403 @defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
5404 Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
5405 variable to be output, if there is one, or @code{NULL_TREE} if there
5406 is no corresponding variable. If you define this macro, GCC will use it
5407 in place of both @code{ASM_OUTPUT_DECL} and
5408 @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see
5409 the variable's decl in order to chose what to output.
5413 @subsection Output and Generation of Labels
5415 @c prevent bad page break with this line
5416 This is about outputting labels.
5418 @findex assemble_name
5419 @defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
5420 A C statement (sans semicolon) to output to the stdio stream
5421 @var{stream} the assembler definition of a label named @var{name}.
5422 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
5423 output the name itself; before and after that, output the additional
5424 assembler syntax for defining the name, and a newline. A default
5425 definition of this macro is provided which is correct for most systems.
5428 @defmac ASM_OUTPUT_FUNCTION_LABEL (@var{stream}, @var{name}, @var{decl})
5429 A C statement (sans semicolon) to output to the stdio stream
5430 @var{stream} the assembler definition of a label named @var{name} of
5432 Use the expression @code{assemble_name (@var{stream}, @var{name})} to
5433 output the name itself; before and after that, output the additional
5434 assembler syntax for defining the name, and a newline. A default
5435 definition of this macro is provided which is correct for most systems.
5437 If this macro is not defined, then the function name is defined in the
5438 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
5441 @findex assemble_name_raw
5442 @defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name})
5443 Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known
5444 to refer to a compiler-generated label. The default definition uses
5445 @code{assemble_name_raw}, which is like @code{assemble_name} except
5446 that it is more efficient.
5450 A C string containing the appropriate assembler directive to specify the
5451 size of a symbol, without any arguments. On systems that use ELF, the
5452 default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
5453 systems, the default is not to define this macro.
5455 Define this macro only if it is correct to use the default definitions
5456 of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
5457 for your system. If you need your own custom definitions of those
5458 macros, or if you do not need explicit symbol sizes at all, do not
5462 @defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
5463 A C statement (sans semicolon) to output to the stdio stream
5464 @var{stream} a directive telling the assembler that the size of the
5465 symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
5466 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
5470 @defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
5471 A C statement (sans semicolon) to output to the stdio stream
5472 @var{stream} a directive telling the assembler to calculate the size of
5473 the symbol @var{name} by subtracting its address from the current
5476 If you define @code{SIZE_ASM_OP}, a default definition of this macro is
5477 provided. The default assumes that the assembler recognizes a special
5478 @samp{.} symbol as referring to the current address, and can calculate
5479 the difference between this and another symbol. If your assembler does
5480 not recognize @samp{.} or cannot do calculations with it, you will need
5481 to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
5484 @defmac NO_DOLLAR_IN_LABEL
5485 Define this macro if the assembler does not accept the character
5486 @samp{$} in label names. By default constructors and destructors in
5487 G++ have @samp{$} in the identifiers. If this macro is defined,
5488 @samp{.} is used instead.
5491 @defmac NO_DOT_IN_LABEL
5492 Define this macro if the assembler does not accept the character
5493 @samp{.} in label names. By default constructors and destructors in G++
5494 have names that use @samp{.}. If this macro is defined, these names
5495 are rewritten to avoid @samp{.}.
5499 A C string containing the appropriate assembler directive to specify the
5500 type of a symbol, without any arguments. On systems that use ELF, the
5501 default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
5502 systems, the default is not to define this macro.
5504 Define this macro only if it is correct to use the default definition of
5505 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
5506 custom definition of this macro, or if you do not need explicit symbol
5507 types at all, do not define this macro.
5510 @defmac TYPE_OPERAND_FMT
5511 A C string which specifies (using @code{printf} syntax) the format of
5512 the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
5513 default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
5514 the default is not to define this macro.
5516 Define this macro only if it is correct to use the default definition of
5517 @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
5518 custom definition of this macro, or if you do not need explicit symbol
5519 types at all, do not define this macro.
5522 @defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
5523 A C statement (sans semicolon) to output to the stdio stream
5524 @var{stream} a directive telling the assembler that the type of the
5525 symbol @var{name} is @var{type}. @var{type} is a C string; currently,
5526 that string is always either @samp{"function"} or @samp{"object"}, but
5527 you should not count on this.
5529 If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
5530 definition of this macro is provided.
5533 @defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
5534 A C statement (sans semicolon) to output to the stdio stream
5535 @var{stream} any text necessary for declaring the name @var{name} of a
5536 function which is being defined. This macro is responsible for
5537 outputting the label definition (perhaps using
5538 @code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the
5539 @code{FUNCTION_DECL} tree node representing the function.
5541 If this macro is not defined, then the function name is defined in the
5542 usual manner as a label (by means of @code{ASM_OUTPUT_FUNCTION_LABEL}).
5544 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
5548 @defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
5549 A C statement (sans semicolon) to output to the stdio stream
5550 @var{stream} any text necessary for declaring the size of a function
5551 which is being defined. The argument @var{name} is the name of the
5552 function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
5553 representing the function.
5555 If this macro is not defined, then the function size is not defined.
5557 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
5561 @defmac ASM_DECLARE_COLD_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
5562 A C statement (sans semicolon) to output to the stdio stream
5563 @var{stream} any text necessary for declaring the name @var{name} of a
5564 cold function partition which is being defined. This macro is responsible
5565 for outputting the label definition (perhaps using
5566 @code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the
5567 @code{FUNCTION_DECL} tree node representing the function.
5569 If this macro is not defined, then the cold partition name is defined in the
5570 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
5572 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
5576 @defmac ASM_DECLARE_COLD_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
5577 A C statement (sans semicolon) to output to the stdio stream
5578 @var{stream} any text necessary for declaring the size of a cold function
5579 partition which is being defined. The argument @var{name} is the name of the
5580 cold partition of the function. The argument @var{decl} is the
5581 @code{FUNCTION_DECL} tree node representing the function.
5583 If this macro is not defined, then the partition size is not defined.
5585 You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
5589 @defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
5590 A C statement (sans semicolon) to output to the stdio stream
5591 @var{stream} any text necessary for declaring the name @var{name} of an
5592 initialized variable which is being defined. This macro must output the
5593 label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
5594 @var{decl} is the @code{VAR_DECL} tree node representing the variable.
5596 If this macro is not defined, then the variable name is defined in the
5597 usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
5599 You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
5600 @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
5603 @hook TARGET_ASM_DECLARE_CONSTANT_NAME
5605 @defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
5606 A C statement (sans semicolon) to output to the stdio stream
5607 @var{stream} any text necessary for claiming a register @var{regno}
5608 for a global variable @var{decl} with name @var{name}.
5610 If you don't define this macro, that is equivalent to defining it to do
5614 @defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
5615 A C statement (sans semicolon) to finish up declaring a variable name
5616 once the compiler has processed its initializer fully and thus has had a
5617 chance to determine the size of an array when controlled by an
5618 initializer. This is used on systems where it's necessary to declare
5619 something about the size of the object.
5621 If you don't define this macro, that is equivalent to defining it to do
5624 You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
5625 @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
5628 @hook TARGET_ASM_GLOBALIZE_LABEL
5630 @hook TARGET_ASM_GLOBALIZE_DECL_NAME
5632 @hook TARGET_ASM_ASSEMBLE_UNDEFINED_DECL
5634 @defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
5635 A C statement (sans semicolon) to output to the stdio stream
5636 @var{stream} some commands that will make the label @var{name} weak;
5637 that is, available for reference from other files but only used if
5638 no other definition is available. Use the expression
5639 @code{assemble_name (@var{stream}, @var{name})} to output the name
5640 itself; before and after that, output the additional assembler syntax
5641 for making that name weak, and a newline.
5643 If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
5644 support weak symbols and you should not define the @code{SUPPORTS_WEAK}
5648 @defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
5649 Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
5650 @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
5651 or variable decl. If @var{value} is not @code{NULL}, this C statement
5652 should output to the stdio stream @var{stream} assembler code which
5653 defines (equates) the weak symbol @var{name} to have the value
5654 @var{value}. If @var{value} is @code{NULL}, it should output commands
5655 to make @var{name} weak.
5658 @defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value})
5659 Outputs a directive that enables @var{name} to be used to refer to
5660 symbol @var{value} with weak-symbol semantics. @code{decl} is the
5661 declaration of @code{name}.
5664 @defmac SUPPORTS_WEAK
5665 A preprocessor constant expression which evaluates to true if the target
5666 supports weak symbols.
5668 If you don't define this macro, @file{defaults.h} provides a default
5669 definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
5670 is defined, the default definition is @samp{1}; otherwise, it is @samp{0}.
5673 @defmac TARGET_SUPPORTS_WEAK
5674 A C expression which evaluates to true if the target supports weak symbols.
5676 If you don't define this macro, @file{defaults.h} provides a default
5677 definition. The default definition is @samp{(SUPPORTS_WEAK)}. Define
5678 this macro if you want to control weak symbol support with a compiler
5679 flag such as @option{-melf}.
5682 @defmac MAKE_DECL_ONE_ONLY (@var{decl})
5683 A C statement (sans semicolon) to mark @var{decl} to be emitted as a
5684 public symbol such that extra copies in multiple translation units will
5685 be discarded by the linker. Define this macro if your object file
5686 format provides support for this concept, such as the @samp{COMDAT}
5687 section flags in the Microsoft Windows PE/COFF format, and this support
5688 requires changes to @var{decl}, such as putting it in a separate section.
5691 @defmac SUPPORTS_ONE_ONLY
5692 A C expression which evaluates to true if the target supports one-only
5695 If you don't define this macro, @file{varasm.c} provides a default
5696 definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
5697 definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
5698 you want to control one-only symbol support with a compiler flag, or if
5699 setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
5700 be emitted as one-only.
5703 @hook TARGET_ASM_ASSEMBLE_VISIBILITY
5705 @defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC
5706 A C expression that evaluates to true if the target's linker expects
5707 that weak symbols do not appear in a static archive's table of contents.
5708 The default is @code{0}.
5710 Leaving weak symbols out of an archive's table of contents means that,
5711 if a symbol will only have a definition in one translation unit and
5712 will have undefined references from other translation units, that
5713 symbol should not be weak. Defining this macro to be nonzero will
5714 thus have the effect that certain symbols that would normally be weak
5715 (explicit template instantiations, and vtables for polymorphic classes
5716 with noninline key methods) will instead be nonweak.
5718 The C++ ABI requires this macro to be zero. Define this macro for
5719 targets where full C++ ABI compliance is impossible and where linker
5720 restrictions require weak symbols to be left out of a static archive's
5724 @defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
5725 A C statement (sans semicolon) to output to the stdio stream
5726 @var{stream} any text necessary for declaring the name of an external
5727 symbol named @var{name} which is referenced in this compilation but
5728 not defined. The value of @var{decl} is the tree node for the
5731 This macro need not be defined if it does not need to output anything.
5732 The GNU assembler and most Unix assemblers don't require anything.
5735 @hook TARGET_ASM_EXTERNAL_LIBCALL
5737 @hook TARGET_ASM_MARK_DECL_PRESERVED
5739 @defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
5740 A C statement (sans semicolon) to output to the stdio stream
5741 @var{stream} a reference in assembler syntax to a label named
5742 @var{name}. This should add @samp{_} to the front of the name, if that
5743 is customary on your operating system, as it is in most Berkeley Unix
5744 systems. This macro is used in @code{assemble_name}.
5747 @hook TARGET_MANGLE_ASSEMBLER_NAME
5749 @defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
5750 A C statement (sans semicolon) to output a reference to
5751 @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
5752 will be used to output the name of the symbol. This macro may be used
5753 to modify the way a symbol is referenced depending on information
5754 encoded by @code{TARGET_ENCODE_SECTION_INFO}.
5757 @defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
5758 A C statement (sans semicolon) to output a reference to @var{buf}, the
5759 result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
5760 @code{assemble_name} will be used to output the name of the symbol.
5761 This macro is not used by @code{output_asm_label}, or the @code{%l}
5762 specifier that calls it; the intention is that this macro should be set
5763 when it is necessary to output a label differently when its address is
5767 @hook TARGET_ASM_INTERNAL_LABEL
5769 @defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
5770 A C statement to output to the stdio stream @var{stream} a debug info
5771 label whose name is made from the string @var{prefix} and the number
5772 @var{num}. This is useful for VLIW targets, where debug info labels
5773 may need to be treated differently than branch target labels. On some
5774 systems, branch target labels must be at the beginning of instruction
5775 bundles, but debug info labels can occur in the middle of instruction
5778 If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
5782 @defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
5783 A C statement to store into the string @var{string} a label whose name
5784 is made from the string @var{prefix} and the number @var{num}.
5786 This string, when output subsequently by @code{assemble_name}, should
5787 produce the output that @code{(*targetm.asm_out.internal_label)} would produce
5788 with the same @var{prefix} and @var{num}.
5790 If the string begins with @samp{*}, then @code{assemble_name} will
5791 output the rest of the string unchanged. It is often convenient for
5792 @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
5793 string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
5794 to output the string, and may change it. (Of course,
5795 @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
5796 you should know what it does on your machine.)
5799 @defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
5800 A C expression to assign to @var{outvar} (which is a variable of type
5801 @code{char *}) a newly allocated string made from the string
5802 @var{name} and the number @var{number}, with some suitable punctuation
5803 added. Use @code{alloca} to get space for the string.
5805 The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
5806 produce an assembler label for an internal static variable whose name is
5807 @var{name}. Therefore, the string must be such as to result in valid
5808 assembler code. The argument @var{number} is different each time this
5809 macro is executed; it prevents conflicts between similarly-named
5810 internal static variables in different scopes.
5812 Ideally this string should not be a valid C identifier, to prevent any
5813 conflict with the user's own symbols. Most assemblers allow periods
5814 or percent signs in assembler symbols; putting at least one of these
5815 between the name and the number will suffice.
5817 If this macro is not defined, a default definition will be provided
5818 which is correct for most systems.
5821 @defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
5822 A C statement to output to the stdio stream @var{stream} assembler code
5823 which defines (equates) the symbol @var{name} to have the value @var{value}.
5826 If @code{SET_ASM_OP} is defined, a default definition is provided which is
5827 correct for most systems.
5830 @defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
5831 A C statement to output to the stdio stream @var{stream} assembler code
5832 which defines (equates) the symbol whose tree node is @var{decl_of_name}
5833 to have the value of the tree node @var{decl_of_value}. This macro will
5834 be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
5835 the tree nodes are available.
5838 If @code{SET_ASM_OP} is defined, a default definition is provided which is
5839 correct for most systems.
5842 @defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value})
5843 A C statement that evaluates to true if the assembler code which defines
5844 (equates) the symbol whose tree node is @var{decl_of_name} to have the value
5845 of the tree node @var{decl_of_value} should be emitted near the end of the
5846 current compilation unit. The default is to not defer output of defines.
5847 This macro affects defines output by @samp{ASM_OUTPUT_DEF} and
5848 @samp{ASM_OUTPUT_DEF_FROM_DECLS}.
5851 @defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
5852 A C statement to output to the stdio stream @var{stream} assembler code
5853 which defines (equates) the weak symbol @var{name} to have the value
5854 @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
5855 an undefined weak symbol.
5857 Define this macro if the target only supports weak aliases; define
5858 @code{ASM_OUTPUT_DEF} instead if possible.
5861 @defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
5862 Define this macro to override the default assembler names used for
5863 Objective-C methods.
5865 The default name is a unique method number followed by the name of the
5866 class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
5867 the category is also included in the assembler name (e.g.@:
5870 These names are safe on most systems, but make debugging difficult since
5871 the method's selector is not present in the name. Therefore, particular
5872 systems define other ways of computing names.
5874 @var{buf} is an expression of type @code{char *} which gives you a
5875 buffer in which to store the name; its length is as long as
5876 @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
5877 50 characters extra.
5879 The argument @var{is_inst} specifies whether the method is an instance
5880 method or a class method; @var{class_name} is the name of the class;
5881 @var{cat_name} is the name of the category (or @code{NULL} if the method is not
5882 in a category); and @var{sel_name} is the name of the selector.
5884 On systems where the assembler can handle quoted names, you can use this
5885 macro to provide more human-readable names.
5888 @node Initialization
5889 @subsection How Initialization Functions Are Handled
5890 @cindex initialization routines
5891 @cindex termination routines
5892 @cindex constructors, output of
5893 @cindex destructors, output of
5895 The compiled code for certain languages includes @dfn{constructors}
5896 (also called @dfn{initialization routines})---functions to initialize
5897 data in the program when the program is started. These functions need
5898 to be called before the program is ``started''---that is to say, before
5899 @code{main} is called.
5901 Compiling some languages generates @dfn{destructors} (also called
5902 @dfn{termination routines}) that should be called when the program
5905 To make the initialization and termination functions work, the compiler
5906 must output something in the assembler code to cause those functions to
5907 be called at the appropriate time. When you port the compiler to a new
5908 system, you need to specify how to do this.
5910 There are two major ways that GCC currently supports the execution of
5911 initialization and termination functions. Each way has two variants.
5912 Much of the structure is common to all four variations.
5914 @findex __CTOR_LIST__
5915 @findex __DTOR_LIST__
5916 The linker must build two lists of these functions---a list of
5917 initialization functions, called @code{__CTOR_LIST__}, and a list of
5918 termination functions, called @code{__DTOR_LIST__}.
5920 Each list always begins with an ignored function pointer (which may hold
5921 0, @minus{}1, or a count of the function pointers after it, depending on
5922 the environment). This is followed by a series of zero or more function
5923 pointers to constructors (or destructors), followed by a function
5924 pointer containing zero.
5926 Depending on the operating system and its executable file format, either
5927 @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
5928 time and exit time. Constructors are called in reverse order of the
5929 list; destructors in forward order.
5931 The best way to handle static constructors works only for object file
5932 formats which provide arbitrarily-named sections. A section is set
5933 aside for a list of constructors, and another for a list of destructors.
5934 Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
5935 object file that defines an initialization function also puts a word in
5936 the constructor section to point to that function. The linker
5937 accumulates all these words into one contiguous @samp{.ctors} section.
5938 Termination functions are handled similarly.
5940 This method will be chosen as the default by @file{target-def.h} if
5941 @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
5942 support arbitrary sections, but does support special designated
5943 constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
5944 and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
5946 When arbitrary sections are available, there are two variants, depending
5947 upon how the code in @file{crtstuff.c} is called. On systems that
5948 support a @dfn{.init} section which is executed at program startup,
5949 parts of @file{crtstuff.c} are compiled into that section. The
5950 program is linked by the @command{gcc} driver like this:
5953 ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
5956 The prologue of a function (@code{__init}) appears in the @code{.init}
5957 section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
5958 for the function @code{__fini} in the @dfn{.fini} section. Normally these
5959 files are provided by the operating system or by the GNU C library, but
5960 are provided by GCC for a few targets.
5962 The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
5963 compiled from @file{crtstuff.c}. They contain, among other things, code
5964 fragments within the @code{.init} and @code{.fini} sections that branch
5965 to routines in the @code{.text} section. The linker will pull all parts
5966 of a section together, which results in a complete @code{__init} function
5967 that invokes the routines we need at startup.
5969 To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
5972 If no init section is available, when GCC compiles any function called
5973 @code{main} (or more accurately, any function designated as a program
5974 entry point by the language front end calling @code{expand_main_function}),
5975 it inserts a procedure call to @code{__main} as the first executable code
5976 after the function prologue. The @code{__main} function is defined
5977 in @file{libgcc2.c} and runs the global constructors.
5979 In file formats that don't support arbitrary sections, there are again
5980 two variants. In the simplest variant, the GNU linker (GNU @code{ld})
5981 and an `a.out' format must be used. In this case,
5982 @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
5983 entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
5984 and with the address of the void function containing the initialization
5985 code as its value. The GNU linker recognizes this as a request to add
5986 the value to a @dfn{set}; the values are accumulated, and are eventually
5987 placed in the executable as a vector in the format described above, with
5988 a leading (ignored) count and a trailing zero element.
5989 @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
5990 section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
5991 the compilation of @code{main} to call @code{__main} as above, starting
5992 the initialization process.
5994 The last variant uses neither arbitrary sections nor the GNU linker.
5995 This is preferable when you want to do dynamic linking and when using
5996 file formats which the GNU linker does not support, such as `ECOFF'@. In
5997 this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
5998 termination functions are recognized simply by their names. This requires
5999 an extra program in the linkage step, called @command{collect2}. This program
6000 pretends to be the linker, for use with GCC; it does its job by running
6001 the ordinary linker, but also arranges to include the vectors of
6002 initialization and termination functions. These functions are called
6003 via @code{__main} as described above. In order to use this method,
6004 @code{use_collect2} must be defined in the target in @file{config.gcc}.
6007 The following section describes the specific macros that control and
6008 customize the handling of initialization and termination functions.
6011 @node Macros for Initialization
6012 @subsection Macros Controlling Initialization Routines
6014 Here are the macros that control how the compiler handles initialization
6015 and termination functions:
6017 @defmac INIT_SECTION_ASM_OP
6018 If defined, a C string constant, including spacing, for the assembler
6019 operation to identify the following data as initialization code. If not
6020 defined, GCC will assume such a section does not exist. When you are
6021 using special sections for initialization and termination functions, this
6022 macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
6023 run the initialization functions.
6026 @defmac HAS_INIT_SECTION
6027 If defined, @code{main} will not call @code{__main} as described above.
6028 This macro should be defined for systems that control start-up code
6029 on a symbol-by-symbol basis, such as OSF/1, and should not
6030 be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
6033 @defmac LD_INIT_SWITCH
6034 If defined, a C string constant for a switch that tells the linker that
6035 the following symbol is an initialization routine.
6038 @defmac LD_FINI_SWITCH
6039 If defined, a C string constant for a switch that tells the linker that
6040 the following symbol is a finalization routine.
6043 @defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
6044 If defined, a C statement that will write a function that can be
6045 automatically called when a shared library is loaded. The function
6046 should call @var{func}, which takes no arguments. If not defined, and
6047 the object format requires an explicit initialization function, then a
6048 function called @code{_GLOBAL__DI} will be generated.
6050 This function and the following one are used by collect2 when linking a
6051 shared library that needs constructors or destructors, or has DWARF2
6052 exception tables embedded in the code.
6055 @defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
6056 If defined, a C statement that will write a function that can be
6057 automatically called when a shared library is unloaded. The function
6058 should call @var{func}, which takes no arguments. If not defined, and
6059 the object format requires an explicit finalization function, then a
6060 function called @code{_GLOBAL__DD} will be generated.
6063 @defmac INVOKE__main
6064 If defined, @code{main} will call @code{__main} despite the presence of
6065 @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
6066 where the init section is not actually run automatically, but is still
6067 useful for collecting the lists of constructors and destructors.
6070 @defmac SUPPORTS_INIT_PRIORITY
6071 If nonzero, the C++ @code{init_priority} attribute is supported and the
6072 compiler should emit instructions to control the order of initialization
6073 of objects. If zero, the compiler will issue an error message upon
6074 encountering an @code{init_priority} attribute.
6077 @hook TARGET_HAVE_CTORS_DTORS
6079 @hook TARGET_ASM_CONSTRUCTOR
6081 @hook TARGET_ASM_DESTRUCTOR
6083 If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
6084 generated for the generated object file will have static linkage.
6086 If your system uses @command{collect2} as the means of processing
6087 constructors, then that program normally uses @command{nm} to scan
6088 an object file for constructor functions to be called.
6090 On certain kinds of systems, you can define this macro to make
6091 @command{collect2} work faster (and, in some cases, make it work at all):
6093 @defmac OBJECT_FORMAT_COFF
6094 Define this macro if the system uses COFF (Common Object File Format)
6095 object files, so that @command{collect2} can assume this format and scan
6096 object files directly for dynamic constructor/destructor functions.
6098 This macro is effective only in a native compiler; @command{collect2} as
6099 part of a cross compiler always uses @command{nm} for the target machine.
6102 @defmac REAL_NM_FILE_NAME
6103 Define this macro as a C string constant containing the file name to use
6104 to execute @command{nm}. The default is to search the path normally for
6109 @command{collect2} calls @command{nm} to scan object files for static
6110 constructors and destructors and LTO info. By default, @option{-n} is
6111 passed. Define @code{NM_FLAGS} to a C string constant if other options
6112 are needed to get the same output format as GNU @command{nm -n}
6116 If your system supports shared libraries and has a program to list the
6117 dynamic dependencies of a given library or executable, you can define
6118 these macros to enable support for running initialization and
6119 termination functions in shared libraries:
6122 Define this macro to a C string constant containing the name of the program
6123 which lists dynamic dependencies, like @command{ldd} under SunOS 4.
6126 @defmac PARSE_LDD_OUTPUT (@var{ptr})
6127 Define this macro to be C code that extracts filenames from the output
6128 of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
6129 of type @code{char *} that points to the beginning of a line of output
6130 from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
6131 code must advance @var{ptr} to the beginning of the filename on that
6132 line. Otherwise, it must set @var{ptr} to @code{NULL}.
6135 @defmac SHLIB_SUFFIX
6136 Define this macro to a C string constant containing the default shared
6137 library extension of the target (e.g., @samp{".so"}). @command{collect2}
6138 strips version information after this suffix when generating global
6139 constructor and destructor names. This define is only needed on targets
6140 that use @command{collect2} to process constructors and destructors.
6143 @node Instruction Output
6144 @subsection Output of Assembler Instructions
6146 @c prevent bad page break with this line
6147 This describes assembler instruction output.
6149 @defmac REGISTER_NAMES
6150 A C initializer containing the assembler's names for the machine
6151 registers, each one as a C string constant. This is what translates
6152 register numbers in the compiler into assembler language.
6155 @defmac ADDITIONAL_REGISTER_NAMES
6156 If defined, a C initializer for an array of structures containing a name
6157 and a register number. This macro defines additional names for hard
6158 registers, thus allowing the @code{asm} option in declarations to refer
6159 to registers using alternate names.
6162 @defmac OVERLAPPING_REGISTER_NAMES
6163 If defined, a C initializer for an array of structures containing a
6164 name, a register number and a count of the number of consecutive
6165 machine registers the name overlaps. This macro defines additional
6166 names for hard registers, thus allowing the @code{asm} option in
6167 declarations to refer to registers using alternate names. Unlike
6168 @code{ADDITIONAL_REGISTER_NAMES}, this macro should be used when the
6169 register name implies multiple underlying registers.
6171 This macro should be used when it is important that a clobber in an
6172 @code{asm} statement clobbers all the underlying values implied by the
6173 register name. For example, on ARM, clobbering the double-precision
6174 VFP register ``d0'' implies clobbering both single-precision registers
6178 @defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
6179 Define this macro if you are using an unusual assembler that
6180 requires different names for the machine instructions.
6182 The definition is a C statement or statements which output an
6183 assembler instruction opcode to the stdio stream @var{stream}. The
6184 macro-operand @var{ptr} is a variable of type @code{char *} which
6185 points to the opcode name in its ``internal'' form---the form that is
6186 written in the machine description. The definition should output the
6187 opcode name to @var{stream}, performing any translation you desire, and
6188 increment the variable @var{ptr} to point at the end of the opcode
6189 so that it will not be output twice.
6191 In fact, your macro definition may process less than the entire opcode
6192 name, or more than the opcode name; but if you want to process text
6193 that includes @samp{%}-sequences to substitute operands, you must take
6194 care of the substitution yourself. Just be sure to increment
6195 @var{ptr} over whatever text should not be output normally.
6197 @findex recog_data.operand
6198 If you need to look at the operand values, they can be found as the
6199 elements of @code{recog_data.operand}.
6201 If the macro definition does nothing, the instruction is output
6205 @defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
6206 If defined, a C statement to be executed just prior to the output of
6207 assembler code for @var{insn}, to modify the extracted operands so
6208 they will be output differently.
6210 Here the argument @var{opvec} is the vector containing the operands
6211 extracted from @var{insn}, and @var{noperands} is the number of
6212 elements of the vector which contain meaningful data for this insn.
6213 The contents of this vector are what will be used to convert the insn
6214 template into assembler code, so you can change the assembler output
6215 by changing the contents of the vector.
6217 This macro is useful when various assembler syntaxes share a single
6218 file of instruction patterns; by defining this macro differently, you
6219 can cause a large class of instructions to be output differently (such
6220 as with rearranged operands). Naturally, variations in assembler
6221 syntax affecting individual insn patterns ought to be handled by
6222 writing conditional output routines in those patterns.
6224 If this macro is not defined, it is equivalent to a null statement.
6227 @hook TARGET_ASM_FINAL_POSTSCAN_INSN
6229 @defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
6230 A C compound statement to output to stdio stream @var{stream} the
6231 assembler syntax for an instruction operand @var{x}. @var{x} is an
6234 @var{code} is a value that can be used to specify one of several ways
6235 of printing the operand. It is used when identical operands must be
6236 printed differently depending on the context. @var{code} comes from
6237 the @samp{%} specification that was used to request printing of the
6238 operand. If the specification was just @samp{%@var{digit}} then
6239 @var{code} is 0; if the specification was @samp{%@var{ltr}
6240 @var{digit}} then @var{code} is the ASCII code for @var{ltr}.
6243 If @var{x} is a register, this macro should print the register's name.
6244 The names can be found in an array @code{reg_names} whose type is
6245 @code{char *[]}. @code{reg_names} is initialized from
6246 @code{REGISTER_NAMES}.
6248 When the machine description has a specification @samp{%@var{punct}}
6249 (a @samp{%} followed by a punctuation character), this macro is called
6250 with a null pointer for @var{x} and the punctuation character for
6254 @defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
6255 A C expression which evaluates to true if @var{code} is a valid
6256 punctuation character for use in the @code{PRINT_OPERAND} macro. If
6257 @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
6258 punctuation characters (except for the standard one, @samp{%}) are used
6262 @defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
6263 A C compound statement to output to stdio stream @var{stream} the
6264 assembler syntax for an instruction operand that is a memory reference
6265 whose address is @var{x}. @var{x} is an RTL expression.
6267 @cindex @code{TARGET_ENCODE_SECTION_INFO} usage
6268 On some machines, the syntax for a symbolic address depends on the
6269 section that the address refers to. On these machines, define the hook
6270 @code{TARGET_ENCODE_SECTION_INFO} to store the information into the
6271 @code{symbol_ref}, and then check for it here. @xref{Assembler
6275 @findex dbr_sequence_length
6276 @defmac DBR_OUTPUT_SEQEND (@var{file})
6277 A C statement, to be executed after all slot-filler instructions have
6278 been output. If necessary, call @code{dbr_sequence_length} to
6279 determine the number of slots filled in a sequence (zero if not
6280 currently outputting a sequence), to decide how many no-ops to output,
6283 Don't define this macro if it has nothing to do, but it is helpful in
6284 reading assembly output if the extent of the delay sequence is made
6285 explicit (e.g.@: with white space).
6288 @findex final_sequence
6289 Note that output routines for instructions with delay slots must be
6290 prepared to deal with not being output as part of a sequence
6291 (i.e.@: when the scheduling pass is not run, or when no slot fillers could be
6292 found.) The variable @code{final_sequence} is null when not
6293 processing a sequence, otherwise it contains the @code{sequence} rtx
6297 @defmac REGISTER_PREFIX
6298 @defmacx LOCAL_LABEL_PREFIX
6299 @defmacx USER_LABEL_PREFIX
6300 @defmacx IMMEDIATE_PREFIX
6301 If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
6302 @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
6303 @file{final.c}). These are useful when a single @file{md} file must
6304 support multiple assembler formats. In that case, the various @file{tm.h}
6305 files can define these macros differently.
6308 @defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
6309 If defined this macro should expand to a series of @code{case}
6310 statements which will be parsed inside the @code{switch} statement of
6311 the @code{asm_fprintf} function. This allows targets to define extra
6312 printf formats which may useful when generating their assembler
6313 statements. Note that uppercase letters are reserved for future
6314 generic extensions to asm_fprintf, and so are not available to target
6315 specific code. The output file is given by the parameter @var{file}.
6316 The varargs input pointer is @var{argptr} and the rest of the format
6317 string, starting the character after the one that is being switched
6318 upon, is pointed to by @var{format}.
6321 @defmac ASSEMBLER_DIALECT
6322 If your target supports multiple dialects of assembler language (such as
6323 different opcodes), define this macro as a C expression that gives the
6324 numeric index of the assembler language dialect to use, with zero as the
6327 If this macro is defined, you may use constructs of the form
6329 @samp{@{option0|option1|option2@dots{}@}}
6332 in the output templates of patterns (@pxref{Output Template}) or in the
6333 first argument of @code{asm_fprintf}. This construct outputs
6334 @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
6335 @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
6336 within these strings retain their usual meaning. If there are fewer
6337 alternatives within the braces than the value of
6338 @code{ASSEMBLER_DIALECT}, the construct outputs nothing. If it's needed
6339 to print curly braces or @samp{|} character in assembler output directly,
6340 @samp{%@{}, @samp{%@}} and @samp{%|} can be used.
6342 If you do not define this macro, the characters @samp{@{}, @samp{|} and
6343 @samp{@}} do not have any special meaning when used in templates or
6344 operands to @code{asm_fprintf}.
6346 Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
6347 @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
6348 the variations in assembler language syntax with that mechanism. Define
6349 @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
6350 if the syntax variant are larger and involve such things as different
6351 opcodes or operand order.
6354 @defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
6355 A C expression to output to @var{stream} some assembler code
6356 which will push hard register number @var{regno} onto the stack.
6357 The code need not be optimal, since this macro is used only when
6361 @defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
6362 A C expression to output to @var{stream} some assembler code
6363 which will pop hard register number @var{regno} off of the stack.
6364 The code need not be optimal, since this macro is used only when
6368 @node Dispatch Tables
6369 @subsection Output of Dispatch Tables
6371 @c prevent bad page break with this line
6372 This concerns dispatch tables.
6374 @cindex dispatch table
6375 @defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
6376 A C statement to output to the stdio stream @var{stream} an assembler
6377 pseudo-instruction to generate a difference between two labels.
6378 @var{value} and @var{rel} are the numbers of two internal labels. The
6379 definitions of these labels are output using
6380 @code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
6381 way here. For example,
6384 fprintf (@var{stream}, "\t.word L%d-L%d\n",
6385 @var{value}, @var{rel})
6388 You must provide this macro on machines where the addresses in a
6389 dispatch table are relative to the table's own address. If defined, GCC
6390 will also use this macro on all machines when producing PIC@.
6391 @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
6392 mode and flags can be read.
6395 @defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
6396 This macro should be provided on machines where the addresses
6397 in a dispatch table are absolute.
6399 The definition should be a C statement to output to the stdio stream
6400 @var{stream} an assembler pseudo-instruction to generate a reference to
6401 a label. @var{value} is the number of an internal label whose
6402 definition is output using @code{(*targetm.asm_out.internal_label)}.
6406 fprintf (@var{stream}, "\t.word L%d\n", @var{value})
6410 @defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
6411 Define this if the label before a jump-table needs to be output
6412 specially. The first three arguments are the same as for
6413 @code{(*targetm.asm_out.internal_label)}; the fourth argument is the
6414 jump-table which follows (a @code{jump_table_data} containing an
6415 @code{addr_vec} or @code{addr_diff_vec}).
6417 This feature is used on system V to output a @code{swbeg} statement
6420 If this macro is not defined, these labels are output with
6421 @code{(*targetm.asm_out.internal_label)}.
6424 @defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
6425 Define this if something special must be output at the end of a
6426 jump-table. The definition should be a C statement to be executed
6427 after the assembler code for the table is written. It should write
6428 the appropriate code to stdio stream @var{stream}. The argument
6429 @var{table} is the jump-table insn, and @var{num} is the label-number
6430 of the preceding label.
6432 If this macro is not defined, nothing special is output at the end of
6436 @hook TARGET_ASM_EMIT_UNWIND_LABEL
6438 @hook TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL
6440 @hook TARGET_ASM_EMIT_EXCEPT_PERSONALITY
6442 @hook TARGET_ASM_UNWIND_EMIT
6444 @hook TARGET_ASM_UNWIND_EMIT_BEFORE_INSN
6446 @node Exception Region Output
6447 @subsection Assembler Commands for Exception Regions
6449 @c prevent bad page break with this line
6451 This describes commands marking the start and the end of an exception
6454 @defmac EH_FRAME_SECTION_NAME
6455 If defined, a C string constant for the name of the section containing
6456 exception handling frame unwind information. If not defined, GCC will
6457 provide a default definition if the target supports named sections.
6458 @file{crtstuff.c} uses this macro to switch to the appropriate section.
6460 You should define this symbol if your target supports DWARF 2 frame
6461 unwind information and the default definition does not work.
6464 @defmac EH_FRAME_THROUGH_COLLECT2
6465 If defined, DWARF 2 frame unwind information will identified by
6466 specially named labels. The collect2 process will locate these
6467 labels and generate code to register the frames.
6469 This might be necessary, for instance, if the system linker will not
6470 place the eh_frames in-between the sentinals from @file{crtstuff.c},
6471 or if the system linker does garbage collection and sections cannot
6472 be marked as not to be collected.
6475 @defmac EH_TABLES_CAN_BE_READ_ONLY
6476 Define this macro to 1 if your target is such that no frame unwind
6477 information encoding used with non-PIC code will ever require a
6478 runtime relocation, but the linker may not support merging read-only
6479 and read-write sections into a single read-write section.
6482 @defmac MASK_RETURN_ADDR
6483 An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
6484 that it does not contain any extraneous set bits in it.
6487 @defmac DWARF2_UNWIND_INFO
6488 Define this macro to 0 if your target supports DWARF 2 frame unwind
6489 information, but it does not yet work with exception handling.
6490 Otherwise, if your target supports this information (if it defines
6491 @code{INCOMING_RETURN_ADDR_RTX} and @code{OBJECT_FORMAT_ELF}),
6492 GCC will provide a default definition of 1.
6495 @hook TARGET_EXCEPT_UNWIND_INFO
6496 This hook defines the mechanism that will be used for exception handling
6497 by the target. If the target has ABI specified unwind tables, the hook
6498 should return @code{UI_TARGET}. If the target is to use the
6499 @code{setjmp}/@code{longjmp}-based exception handling scheme, the hook
6500 should return @code{UI_SJLJ}. If the target supports DWARF 2 frame unwind
6501 information, the hook should return @code{UI_DWARF2}.
6503 A target may, if exceptions are disabled, choose to return @code{UI_NONE}.
6504 This may end up simplifying other parts of target-specific code. The
6505 default implementation of this hook never returns @code{UI_NONE}.
6507 Note that the value returned by this hook should be constant. It should
6508 not depend on anything except the command-line switches described by
6509 @var{opts}. In particular, the
6510 setting @code{UI_SJLJ} must be fixed at compiler start-up as C pre-processor
6511 macros and builtin functions related to exception handling are set up
6512 depending on this setting.
6514 The default implementation of the hook first honors the
6515 @option{--enable-sjlj-exceptions} configure option, then
6516 @code{DWARF2_UNWIND_INFO}, and finally defaults to @code{UI_SJLJ}. If
6517 @code{DWARF2_UNWIND_INFO} depends on command-line options, the target
6518 must define this hook so that @var{opts} is used correctly.
6521 @hook TARGET_UNWIND_TABLES_DEFAULT
6522 This variable should be set to @code{true} if the target ABI requires unwinding
6523 tables even when exceptions are not used. It must not be modified by
6524 command-line option processing.
6527 @defmac DONT_USE_BUILTIN_SETJMP
6528 Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme
6529 should use the @code{setjmp}/@code{longjmp} functions from the C library
6530 instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery.
6533 @defmac JMP_BUF_SIZE
6534 This macro has no effect unless @code{DONT_USE_BUILTIN_SETJMP} is also
6535 defined. Define this macro if the default size of @code{jmp_buf} buffer
6536 for the @code{setjmp}/@code{longjmp}-based exception handling mechanism
6537 is not large enough, or if it is much too large.
6538 The default size is @code{FIRST_PSEUDO_REGISTER * sizeof(void *)}.
6541 @defmac DWARF_CIE_DATA_ALIGNMENT
6542 This macro need only be defined if the target might save registers in the
6543 function prologue at an offset to the stack pointer that is not aligned to
6544 @code{UNITS_PER_WORD}. The definition should be the negative minimum
6545 alignment if @code{STACK_GROWS_DOWNWARD} is true, and the positive
6546 minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if
6547 the target supports DWARF 2 frame unwind information.
6550 @hook TARGET_TERMINATE_DW2_EH_FRAME_INFO
6552 @hook TARGET_DWARF_REGISTER_SPAN
6554 @hook TARGET_DWARF_FRAME_REG_MODE
6556 @hook TARGET_INIT_DWARF_REG_SIZES_EXTRA
6558 @hook TARGET_ASM_TTYPE
6560 @hook TARGET_ARM_EABI_UNWINDER
6562 @node Alignment Output
6563 @subsection Assembler Commands for Alignment
6565 @c prevent bad page break with this line
6566 This describes commands for alignment.
6568 @defmac JUMP_ALIGN (@var{label})
6569 The alignment (log base 2) to put in front of @var{label}, which is
6570 a common destination of jumps and has no fallthru incoming edge.
6572 This macro need not be defined if you don't want any special alignment
6573 to be done at such a time. Most machine descriptions do not currently
6576 Unless it's necessary to inspect the @var{label} parameter, it is better
6577 to set the variable @var{align_jumps} in the target's
6578 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
6579 selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
6582 @hook TARGET_ASM_JUMP_ALIGN_MAX_SKIP
6584 @defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
6585 The alignment (log base 2) to put in front of @var{label}, which follows
6588 This macro need not be defined if you don't want any special alignment
6589 to be done at such a time. Most machine descriptions do not currently
6593 @hook TARGET_ASM_LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
6595 @defmac LOOP_ALIGN (@var{label})
6596 The alignment (log base 2) to put in front of @var{label} that heads
6597 a frequently executed basic block (usually the header of a loop).
6599 This macro need not be defined if you don't want any special alignment
6600 to be done at such a time. Most machine descriptions do not currently
6603 Unless it's necessary to inspect the @var{label} parameter, it is better
6604 to set the variable @code{align_loops} in the target's
6605 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
6606 selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
6609 @hook TARGET_ASM_LOOP_ALIGN_MAX_SKIP
6611 @defmac LABEL_ALIGN (@var{label})
6612 The alignment (log base 2) to put in front of @var{label}.
6613 If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
6614 the maximum of the specified values is used.
6616 Unless it's necessary to inspect the @var{label} parameter, it is better
6617 to set the variable @code{align_labels} in the target's
6618 @code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
6619 selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
6622 @hook TARGET_ASM_LABEL_ALIGN_MAX_SKIP
6624 @defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
6625 A C statement to output to the stdio stream @var{stream} an assembler
6626 instruction to advance the location counter by @var{nbytes} bytes.
6627 Those bytes should be zero when loaded. @var{nbytes} will be a C
6628 expression of type @code{unsigned HOST_WIDE_INT}.
6631 @defmac ASM_NO_SKIP_IN_TEXT
6632 Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
6633 text section because it fails to put zeros in the bytes that are skipped.
6634 This is true on many Unix systems, where the pseudo--op to skip bytes
6635 produces no-op instructions rather than zeros when used in the text
6639 @defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
6640 A C statement to output to the stdio stream @var{stream} an assembler
6641 command to advance the location counter to a multiple of 2 to the
6642 @var{power} bytes. @var{power} will be a C expression of type @code{int}.
6645 @defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
6646 Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
6647 for padding, if necessary.
6650 @defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
6651 A C statement to output to the stdio stream @var{stream} an assembler
6652 command to advance the location counter to a multiple of 2 to the
6653 @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
6654 satisfy the alignment request. @var{power} and @var{max_skip} will be
6655 a C expression of type @code{int}.
6659 @node Debugging Info
6660 @section Controlling Debugging Information Format
6662 @c prevent bad page break with this line
6663 This describes how to specify debugging information.
6666 * All Debuggers:: Macros that affect all debugging formats uniformly.
6667 * DBX Options:: Macros enabling specific options in DBX format.
6668 * DBX Hooks:: Hook macros for varying DBX format.
6669 * File Names and DBX:: Macros controlling output of file names in DBX format.
6670 * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats.
6671 * VMS Debug:: Macros for VMS debug format.
6675 @subsection Macros Affecting All Debugging Formats
6677 @c prevent bad page break with this line
6678 These macros affect all debugging formats.
6680 @defmac DBX_REGISTER_NUMBER (@var{regno})
6681 A C expression that returns the DBX register number for the compiler
6682 register number @var{regno}. In the default macro provided, the value
6683 of this expression will be @var{regno} itself. But sometimes there are
6684 some registers that the compiler knows about and DBX does not, or vice
6685 versa. In such cases, some register may need to have one number in the
6686 compiler and another for DBX@.
6688 If two registers have consecutive numbers inside GCC, and they can be
6689 used as a pair to hold a multiword value, then they @emph{must} have
6690 consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
6691 Otherwise, debuggers will be unable to access such a pair, because they
6692 expect register pairs to be consecutive in their own numbering scheme.
6694 If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
6695 does not preserve register pairs, then what you must do instead is
6696 redefine the actual register numbering scheme.
6699 @defmac DEBUGGER_AUTO_OFFSET (@var{x})
6700 A C expression that returns the integer offset value for an automatic
6701 variable having address @var{x} (an RTL expression). The default
6702 computation assumes that @var{x} is based on the frame-pointer and
6703 gives the offset from the frame-pointer. This is required for targets
6704 that produce debugging output for DBX or COFF-style debugging output
6705 for SDB and allow the frame-pointer to be eliminated when the
6706 @option{-g} options is used.
6709 @defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
6710 A C expression that returns the integer offset value for an argument
6711 having address @var{x} (an RTL expression). The nominal offset is
6715 @defmac PREFERRED_DEBUGGING_TYPE
6716 A C expression that returns the type of debugging output GCC should
6717 produce when the user specifies just @option{-g}. Define
6718 this if you have arranged for GCC to support more than one format of
6719 debugging output. Currently, the allowable values are @code{DBX_DEBUG},
6720 @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
6721 @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
6723 When the user specifies @option{-ggdb}, GCC normally also uses the
6724 value of this macro to select the debugging output format, but with two
6725 exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the
6726 value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
6727 defined, GCC uses @code{DBX_DEBUG}.
6729 The value of this macro only affects the default debugging output; the
6730 user can always get a specific type of output by using @option{-gstabs},
6731 @option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}.
6735 @subsection Specific Options for DBX Output
6737 @c prevent bad page break with this line
6738 These are specific options for DBX output.
6740 @defmac DBX_DEBUGGING_INFO
6741 Define this macro if GCC should produce debugging output for DBX
6742 in response to the @option{-g} option.
6745 @defmac XCOFF_DEBUGGING_INFO
6746 Define this macro if GCC should produce XCOFF format debugging output
6747 in response to the @option{-g} option. This is a variant of DBX format.
6750 @defmac DEFAULT_GDB_EXTENSIONS
6751 Define this macro to control whether GCC should by default generate
6752 GDB's extended version of DBX debugging information (assuming DBX-format
6753 debugging information is enabled at all). If you don't define the
6754 macro, the default is 1: always generate the extended information
6755 if there is any occasion to.
6758 @defmac DEBUG_SYMS_TEXT
6759 Define this macro if all @code{.stabs} commands should be output while
6760 in the text section.
6763 @defmac ASM_STABS_OP
6764 A C string constant, including spacing, naming the assembler pseudo op to
6765 use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
6766 If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
6767 applies only to DBX debugging information format.
6770 @defmac ASM_STABD_OP
6771 A C string constant, including spacing, naming the assembler pseudo op to
6772 use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
6773 value is the current location. If you don't define this macro,
6774 @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
6778 @defmac ASM_STABN_OP
6779 A C string constant, including spacing, naming the assembler pseudo op to
6780 use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
6781 name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
6782 macro applies only to DBX debugging information format.
6785 @defmac DBX_NO_XREFS
6786 Define this macro if DBX on your system does not support the construct
6787 @samp{xs@var{tagname}}. On some systems, this construct is used to
6788 describe a forward reference to a structure named @var{tagname}.
6789 On other systems, this construct is not supported at all.
6792 @defmac DBX_CONTIN_LENGTH
6793 A symbol name in DBX-format debugging information is normally
6794 continued (split into two separate @code{.stabs} directives) when it
6795 exceeds a certain length (by default, 80 characters). On some
6796 operating systems, DBX requires this splitting; on others, splitting
6797 must not be done. You can inhibit splitting by defining this macro
6798 with the value zero. You can override the default splitting-length by
6799 defining this macro as an expression for the length you desire.
6802 @defmac DBX_CONTIN_CHAR
6803 Normally continuation is indicated by adding a @samp{\} character to
6804 the end of a @code{.stabs} string when a continuation follows. To use
6805 a different character instead, define this macro as a character
6806 constant for the character you want to use. Do not define this macro
6807 if backslash is correct for your system.
6810 @defmac DBX_STATIC_STAB_DATA_SECTION
6811 Define this macro if it is necessary to go to the data section before
6812 outputting the @samp{.stabs} pseudo-op for a non-global static
6816 @defmac DBX_TYPE_DECL_STABS_CODE
6817 The value to use in the ``code'' field of the @code{.stabs} directive
6818 for a typedef. The default is @code{N_LSYM}.
6821 @defmac DBX_STATIC_CONST_VAR_CODE
6822 The value to use in the ``code'' field of the @code{.stabs} directive
6823 for a static variable located in the text section. DBX format does not
6824 provide any ``right'' way to do this. The default is @code{N_FUN}.
6827 @defmac DBX_REGPARM_STABS_CODE
6828 The value to use in the ``code'' field of the @code{.stabs} directive
6829 for a parameter passed in registers. DBX format does not provide any
6830 ``right'' way to do this. The default is @code{N_RSYM}.
6833 @defmac DBX_REGPARM_STABS_LETTER
6834 The letter to use in DBX symbol data to identify a symbol as a parameter
6835 passed in registers. DBX format does not customarily provide any way to
6836 do this. The default is @code{'P'}.
6839 @defmac DBX_FUNCTION_FIRST
6840 Define this macro if the DBX information for a function and its
6841 arguments should precede the assembler code for the function. Normally,
6842 in DBX format, the debugging information entirely follows the assembler
6846 @defmac DBX_BLOCKS_FUNCTION_RELATIVE
6847 Define this macro, with value 1, if the value of a symbol describing
6848 the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be
6849 relative to the start of the enclosing function. Normally, GCC uses
6850 an absolute address.
6853 @defmac DBX_LINES_FUNCTION_RELATIVE
6854 Define this macro, with value 1, if the value of a symbol indicating
6855 the current line number (@code{N_SLINE}) should be relative to the
6856 start of the enclosing function. Normally, GCC uses an absolute address.
6859 @defmac DBX_USE_BINCL
6860 Define this macro if GCC should generate @code{N_BINCL} and
6861 @code{N_EINCL} stabs for included header files, as on Sun systems. This
6862 macro also directs GCC to output a type number as a pair of a file
6863 number and a type number within the file. Normally, GCC does not
6864 generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
6865 number for a type number.
6869 @subsection Open-Ended Hooks for DBX Format
6871 @c prevent bad page break with this line
6872 These are hooks for DBX format.
6874 @defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
6875 A C statement to output DBX debugging information before code for line
6876 number @var{line} of the current source file to the stdio stream
6877 @var{stream}. @var{counter} is the number of time the macro was
6878 invoked, including the current invocation; it is intended to generate
6879 unique labels in the assembly output.
6881 This macro should not be defined if the default output is correct, or
6882 if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}.
6885 @defmac NO_DBX_FUNCTION_END
6886 Some stabs encapsulation formats (in particular ECOFF), cannot handle the
6887 @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
6888 On those machines, define this macro to turn this feature off without
6889 disturbing the rest of the gdb extensions.
6892 @defmac NO_DBX_BNSYM_ENSYM
6893 Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx
6894 extension construct. On those machines, define this macro to turn this
6895 feature off without disturbing the rest of the gdb extensions.
6898 @node File Names and DBX
6899 @subsection File Names in DBX Format
6901 @c prevent bad page break with this line
6902 This describes file names in DBX format.
6904 @defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
6905 A C statement to output DBX debugging information to the stdio stream
6906 @var{stream}, which indicates that file @var{name} is the main source
6907 file---the file specified as the input file for compilation.
6908 This macro is called only once, at the beginning of compilation.
6910 This macro need not be defined if the standard form of output
6911 for DBX debugging information is appropriate.
6913 It may be necessary to refer to a label equal to the beginning of the
6914 text section. You can use @samp{assemble_name (stream, ltext_label_name)}
6915 to do so. If you do this, you must also set the variable
6916 @var{used_ltext_label_name} to @code{true}.
6919 @defmac NO_DBX_MAIN_SOURCE_DIRECTORY
6920 Define this macro, with value 1, if GCC should not emit an indication
6921 of the current directory for compilation and current source language at
6922 the beginning of the file.
6925 @defmac NO_DBX_GCC_MARKER
6926 Define this macro, with value 1, if GCC should not emit an indication
6927 that this object file was compiled by GCC@. The default is to emit
6928 an @code{N_OPT} stab at the beginning of every source file, with
6929 @samp{gcc2_compiled.} for the string and value 0.
6932 @defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
6933 A C statement to output DBX debugging information at the end of
6934 compilation of the main source file @var{name}. Output should be
6935 written to the stdio stream @var{stream}.
6937 If you don't define this macro, nothing special is output at the end
6938 of compilation, which is correct for most machines.
6941 @defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
6942 Define this macro @emph{instead of} defining
6943 @code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at
6944 the end of compilation is an @code{N_SO} stab with an empty string,
6945 whose value is the highest absolute text address in the file.
6950 @subsection Macros for SDB and DWARF Output
6952 @c prevent bad page break with this line
6953 Here are macros for SDB and DWARF output.
6955 @defmac SDB_DEBUGGING_INFO
6956 Define this macro to 1 if GCC should produce COFF-style debugging output
6957 for SDB in response to the @option{-g} option.
6960 @defmac DWARF2_DEBUGGING_INFO
6961 Define this macro if GCC should produce dwarf version 2 format
6962 debugging output in response to the @option{-g} option.
6964 @hook TARGET_DWARF_CALLING_CONVENTION
6966 To support optional call frame debugging information, you must also
6967 define @code{INCOMING_RETURN_ADDR_RTX} and either set
6968 @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
6969 prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
6970 as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
6973 @defmac DWARF2_FRAME_INFO
6974 Define this macro to a nonzero value if GCC should always output
6975 Dwarf 2 frame information. If @code{TARGET_EXCEPT_UNWIND_INFO}
6976 (@pxref{Exception Region Output}) returns @code{UI_DWARF2}, and
6977 exceptions are enabled, GCC will output this information not matter
6978 how you define @code{DWARF2_FRAME_INFO}.
6981 @hook TARGET_DEBUG_UNWIND_INFO
6983 @defmac DWARF2_ASM_LINE_DEBUG_INFO
6984 Define this macro to be a nonzero value if the assembler can generate Dwarf 2
6985 line debug info sections. This will result in much more compact line number
6986 tables, and hence is desirable if it works.
6989 @hook TARGET_WANT_DEBUG_PUB_SECTIONS
6991 @hook TARGET_DELAY_SCHED2
6993 @hook TARGET_DELAY_VARTRACK
6995 @hook TARGET_NO_REGISTER_ALLOCATION
6997 @defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
6998 A C statement to issue assembly directives that create a difference
6999 @var{lab1} minus @var{lab2}, using an integer of the given @var{size}.
7002 @defmac ASM_OUTPUT_DWARF_VMS_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
7003 A C statement to issue assembly directives that create a difference
7004 between the two given labels in system defined units, e.g. instruction
7005 slots on IA64 VMS, using an integer of the given size.
7008 @defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{offset}, @var{section})
7009 A C statement to issue assembly directives that create a
7010 section-relative reference to the given @var{label} plus @var{offset}, using
7011 an integer of the given @var{size}. The label is known to be defined in the
7012 given @var{section}.
7015 @defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
7016 A C statement to issue assembly directives that create a self-relative
7017 reference to the given @var{label}, using an integer of the given @var{size}.
7020 @defmac ASM_OUTPUT_DWARF_DATAREL (@var{stream}, @var{size}, @var{label})
7021 A C statement to issue assembly directives that create a reference to the
7022 given @var{label} relative to the dbase, using an integer of the given @var{size}.
7025 @defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label})
7026 A C statement to issue assembly directives that create a reference to
7027 the DWARF table identifier @var{label} from the current section. This
7028 is used on some systems to avoid garbage collecting a DWARF table which
7029 is referenced by a function.
7032 @hook TARGET_ASM_OUTPUT_DWARF_DTPREL
7034 @defmac PUT_SDB_@dots{}
7035 Define these macros to override the assembler syntax for the special
7036 SDB assembler directives. See @file{sdbout.c} for a list of these
7037 macros and their arguments. If the standard syntax is used, you need
7038 not define them yourself.
7042 Some assemblers do not support a semicolon as a delimiter, even between
7043 SDB assembler directives. In that case, define this macro to be the
7044 delimiter to use (usually @samp{\n}). It is not necessary to define
7045 a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
7049 @defmac SDB_ALLOW_UNKNOWN_REFERENCES
7050 Define this macro to allow references to unknown structure,
7051 union, or enumeration tags to be emitted. Standard COFF does not
7052 allow handling of unknown references, MIPS ECOFF has support for
7056 @defmac SDB_ALLOW_FORWARD_REFERENCES
7057 Define this macro to allow references to structure, union, or
7058 enumeration tags that have not yet been seen to be handled. Some
7059 assemblers choke if forward tags are used, while some require it.
7062 @defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line})
7063 A C statement to output SDB debugging information before code for line
7064 number @var{line} of the current source file to the stdio stream
7065 @var{stream}. The default is to emit an @code{.ln} directive.
7070 @subsection Macros for VMS Debug Format
7072 @c prevent bad page break with this line
7073 Here are macros for VMS debug format.
7075 @defmac VMS_DEBUGGING_INFO
7076 Define this macro if GCC should produce debugging output for VMS
7077 in response to the @option{-g} option. The default behavior for VMS
7078 is to generate minimal debug info for a traceback in the absence of
7079 @option{-g} unless explicitly overridden with @option{-g0}. This
7080 behavior is controlled by @code{TARGET_OPTION_OPTIMIZATION} and
7081 @code{TARGET_OPTION_OVERRIDE}.
7084 @node Floating Point
7085 @section Cross Compilation and Floating Point
7086 @cindex cross compilation and floating point
7087 @cindex floating point and cross compilation
7089 While all modern machines use twos-complement representation for integers,
7090 there are a variety of representations for floating point numbers. This
7091 means that in a cross-compiler the representation of floating point numbers
7092 in the compiled program may be different from that used in the machine
7093 doing the compilation.
7095 Because different representation systems may offer different amounts of
7096 range and precision, all floating point constants must be represented in
7097 the target machine's format. Therefore, the cross compiler cannot
7098 safely use the host machine's floating point arithmetic; it must emulate
7099 the target's arithmetic. To ensure consistency, GCC always uses
7100 emulation to work with floating point values, even when the host and
7101 target floating point formats are identical.
7103 The following macros are provided by @file{real.h} for the compiler to
7104 use. All parts of the compiler which generate or optimize
7105 floating-point calculations must use these macros. They may evaluate
7106 their operands more than once, so operands must not have side effects.
7108 @defmac REAL_VALUE_TYPE
7109 The C data type to be used to hold a floating point value in the target
7110 machine's format. Typically this is a @code{struct} containing an
7111 array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
7115 @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
7116 Truncates @var{x} to a signed integer, rounding toward zero.
7119 @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
7120 Truncates @var{x} to an unsigned integer, rounding toward zero. If
7121 @var{x} is negative, returns zero.
7124 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, machine_mode @var{mode})
7125 Converts @var{string} into a floating point number in the target machine's
7126 representation for mode @var{mode}. This routine can handle both
7127 decimal and hexadecimal floating point constants, using the syntax
7128 defined by the C language for both.
7131 @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
7132 Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
7135 @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
7136 Determines whether @var{x} represents infinity (positive or negative).
7139 @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
7140 Determines whether @var{x} represents a ``NaN'' (not-a-number).
7143 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
7144 Returns the negative of the floating point value @var{x}.
7147 @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
7148 Returns the absolute value of @var{x}.
7151 @node Mode Switching
7152 @section Mode Switching Instructions
7153 @cindex mode switching
7154 The following macros control mode switching optimizations:
7156 @defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
7157 Define this macro if the port needs extra instructions inserted for mode
7158 switching in an optimizing compilation.
7160 For an example, the SH4 can perform both single and double precision
7161 floating point operations, but to perform a single precision operation,
7162 the FPSCR PR bit has to be cleared, while for a double precision
7163 operation, this bit has to be set. Changing the PR bit requires a general
7164 purpose register as a scratch register, hence these FPSCR sets have to
7165 be inserted before reload, i.e.@: you cannot put this into instruction emitting
7166 or @code{TARGET_MACHINE_DEPENDENT_REORG}.
7168 You can have multiple entities that are mode-switched, and select at run time
7169 which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
7170 return nonzero for any @var{entity} that needs mode-switching.
7171 If you define this macro, you also have to define
7172 @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{TARGET_MODE_NEEDED},
7173 @code{TARGET_MODE_PRIORITY} and @code{TARGET_MODE_EMIT}.
7174 @code{TARGET_MODE_AFTER}, @code{TARGET_MODE_ENTRY}, and @code{TARGET_MODE_EXIT}
7178 @defmac NUM_MODES_FOR_MODE_SWITCHING
7179 If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
7180 initializer for an array of integers. Each initializer element
7181 N refers to an entity that needs mode switching, and specifies the number
7182 of different modes that might need to be set for this entity.
7183 The position of the initializer in the initializer---starting counting at
7184 zero---determines the integer that is used to refer to the mode-switched
7186 In macros that take mode arguments / yield a mode result, modes are
7187 represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
7188 switch is needed / supplied.
7191 @hook TARGET_MODE_EMIT
7193 @hook TARGET_MODE_NEEDED
7195 @hook TARGET_MODE_AFTER
7197 @hook TARGET_MODE_ENTRY
7199 @hook TARGET_MODE_EXIT
7201 @hook TARGET_MODE_PRIORITY
7203 @node Target Attributes
7204 @section Defining target-specific uses of @code{__attribute__}
7205 @cindex target attributes
7206 @cindex machine attributes
7207 @cindex attributes, target-specific
7209 Target-specific attributes may be defined for functions, data and types.
7210 These are described using the following target hooks; they also need to
7211 be documented in @file{extend.texi}.
7213 @hook TARGET_ATTRIBUTE_TABLE
7215 @hook TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P
7217 @hook TARGET_COMP_TYPE_ATTRIBUTES
7219 @hook TARGET_SET_DEFAULT_TYPE_ATTRIBUTES
7221 @hook TARGET_MERGE_TYPE_ATTRIBUTES
7223 @hook TARGET_MERGE_DECL_ATTRIBUTES
7225 @hook TARGET_VALID_DLLIMPORT_ATTRIBUTE_P
7227 @defmac TARGET_DECLSPEC
7228 Define this macro to a nonzero value if you want to treat
7229 @code{__declspec(X)} as equivalent to @code{__attribute((X))}. By
7230 default, this behavior is enabled only for targets that define
7231 @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation
7232 of @code{__declspec} is via a built-in macro, but you should not rely
7233 on this implementation detail.
7236 @hook TARGET_INSERT_ATTRIBUTES
7238 @hook TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P
7240 @hook TARGET_OPTION_VALID_ATTRIBUTE_P
7242 @hook TARGET_OPTION_SAVE
7244 @hook TARGET_OPTION_RESTORE
7246 @hook TARGET_OPTION_POST_STREAM_IN
7248 @hook TARGET_OPTION_PRINT
7250 @hook TARGET_OPTION_PRAGMA_PARSE
7252 @hook TARGET_OPTION_OVERRIDE
7254 @hook TARGET_OPTION_FUNCTION_VERSIONS
7256 @hook TARGET_CAN_INLINE_P
7258 @hook TARGET_RELAYOUT_FUNCTION
7261 @section Emulating TLS
7262 @cindex Emulated TLS
7264 For targets whose psABI does not provide Thread Local Storage via
7265 specific relocations and instruction sequences, an emulation layer is
7266 used. A set of target hooks allows this emulation layer to be
7267 configured for the requirements of a particular target. For instance
7268 the psABI may in fact specify TLS support in terms of an emulation
7271 The emulation layer works by creating a control object for every TLS
7272 object. To access the TLS object, a lookup function is provided
7273 which, when given the address of the control object, will return the
7274 address of the current thread's instance of the TLS object.
7276 @hook TARGET_EMUTLS_GET_ADDRESS
7278 @hook TARGET_EMUTLS_REGISTER_COMMON
7280 @hook TARGET_EMUTLS_VAR_SECTION
7282 @hook TARGET_EMUTLS_TMPL_SECTION
7284 @hook TARGET_EMUTLS_VAR_PREFIX
7286 @hook TARGET_EMUTLS_TMPL_PREFIX
7288 @hook TARGET_EMUTLS_VAR_FIELDS
7290 @hook TARGET_EMUTLS_VAR_INIT
7292 @hook TARGET_EMUTLS_VAR_ALIGN_FIXED
7294 @hook TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS
7296 @node MIPS Coprocessors
7297 @section Defining coprocessor specifics for MIPS targets.
7298 @cindex MIPS coprocessor-definition macros
7300 The MIPS specification allows MIPS implementations to have as many as 4
7301 coprocessors, each with as many as 32 private registers. GCC supports
7302 accessing these registers and transferring values between the registers
7303 and memory using asm-ized variables. For example:
7306 register unsigned int cp0count asm ("c0r1");
7312 (``c0r1'' is the default name of register 1 in coprocessor 0; alternate
7313 names may be added as described below, or the default names may be
7314 overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
7316 Coprocessor registers are assumed to be epilogue-used; sets to them will
7317 be preserved even if it does not appear that the register is used again
7318 later in the function.
7320 Another note: according to the MIPS spec, coprocessor 1 (if present) is
7321 the FPU@. One accesses COP1 registers through standard mips
7322 floating-point support; they are not included in this mechanism.
7325 @section Parameters for Precompiled Header Validity Checking
7326 @cindex parameters, precompiled headers
7328 @hook TARGET_GET_PCH_VALIDITY
7330 @hook TARGET_PCH_VALID_P
7332 @hook TARGET_CHECK_PCH_TARGET_FLAGS
7334 @hook TARGET_PREPARE_PCH_SAVE
7337 @section C++ ABI parameters
7338 @cindex parameters, c++ abi
7340 @hook TARGET_CXX_GUARD_TYPE
7342 @hook TARGET_CXX_GUARD_MASK_BIT
7344 @hook TARGET_CXX_GET_COOKIE_SIZE
7346 @hook TARGET_CXX_COOKIE_HAS_SIZE
7348 @hook TARGET_CXX_IMPORT_EXPORT_CLASS
7350 @hook TARGET_CXX_CDTOR_RETURNS_THIS
7352 @hook TARGET_CXX_KEY_METHOD_MAY_BE_INLINE
7354 @hook TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY
7356 @hook TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT
7358 @hook TARGET_CXX_LIBRARY_RTTI_COMDAT
7360 @hook TARGET_CXX_USE_AEABI_ATEXIT
7362 @hook TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT
7364 @hook TARGET_CXX_ADJUST_CLASS_AT_DEFINITION
7366 @hook TARGET_CXX_DECL_MANGLING_CONTEXT
7368 @node Named Address Spaces
7369 @section Adding support for named address spaces
7370 @cindex named address spaces
7372 The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275
7373 standards committee, @cite{Programming Languages - C - Extensions to
7374 support embedded processors}, specifies a syntax for embedded
7375 processors to specify alternate address spaces. You can configure a
7376 GCC port to support section 5.1 of the draft report to add support for
7377 address spaces other than the default address space. These address
7378 spaces are new keywords that are similar to the @code{volatile} and
7379 @code{const} type attributes.
7381 Pointers to named address spaces can have a different size than
7382 pointers to the generic address space.
7384 For example, the SPU port uses the @code{__ea} address space to refer
7385 to memory in the host processor, rather than memory local to the SPU
7386 processor. Access to memory in the @code{__ea} address space involves
7387 issuing DMA operations to move data between the host processor and the
7388 local processor memory address space. Pointers in the @code{__ea}
7389 address space are either 32 bits or 64 bits based on the
7390 @option{-mea32} or @option{-mea64} switches (native SPU pointers are
7393 Internally, address spaces are represented as a small integer in the
7394 range 0 to 15 with address space 0 being reserved for the generic
7397 To register a named address space qualifier keyword with the C front end,
7398 the target may call the @code{c_register_addr_space} routine. For example,
7399 the SPU port uses the following to declare @code{__ea} as the keyword for
7400 named address space #1:
7402 #define ADDR_SPACE_EA 1
7403 c_register_addr_space ("__ea", ADDR_SPACE_EA);
7406 @hook TARGET_ADDR_SPACE_POINTER_MODE
7408 @hook TARGET_ADDR_SPACE_ADDRESS_MODE
7410 @hook TARGET_ADDR_SPACE_VALID_POINTER_MODE
7412 @hook TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P
7414 @hook TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS
7416 @hook TARGET_ADDR_SPACE_SUBSET_P
7418 @hook TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID
7420 @hook TARGET_ADDR_SPACE_CONVERT
7422 @hook TARGET_ADDR_SPACE_DEBUG
7424 @hook TARGET_ADDR_SPACE_DIAGNOSE_USAGE
7427 @section Miscellaneous Parameters
7428 @cindex parameters, miscellaneous
7430 @c prevent bad page break with this line
7431 Here are several miscellaneous parameters.
7433 @defmac HAS_LONG_COND_BRANCH
7434 Define this boolean macro to indicate whether or not your architecture
7435 has conditional branches that can span all of memory. It is used in
7436 conjunction with an optimization that partitions hot and cold basic
7437 blocks into separate sections of the executable. If this macro is
7438 set to false, gcc will convert any conditional branches that attempt
7439 to cross between sections into unconditional branches or indirect jumps.
7442 @defmac HAS_LONG_UNCOND_BRANCH
7443 Define this boolean macro to indicate whether or not your architecture
7444 has unconditional branches that can span all of memory. It is used in
7445 conjunction with an optimization that partitions hot and cold basic
7446 blocks into separate sections of the executable. If this macro is
7447 set to false, gcc will convert any unconditional branches that attempt
7448 to cross between sections into indirect jumps.
7451 @defmac CASE_VECTOR_MODE
7452 An alias for a machine mode name. This is the machine mode that
7453 elements of a jump-table should have.
7456 @defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
7457 Optional: return the preferred mode for an @code{addr_diff_vec}
7458 when the minimum and maximum offset are known. If you define this,
7459 it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
7460 To make this work, you also have to define @code{INSN_ALIGN} and
7461 make the alignment for @code{addr_diff_vec} explicit.
7462 The @var{body} argument is provided so that the offset_unsigned and scale
7463 flags can be updated.
7466 @defmac CASE_VECTOR_PC_RELATIVE
7467 Define this macro to be a C expression to indicate when jump-tables
7468 should contain relative addresses. You need not define this macro if
7469 jump-tables never contain relative addresses, or jump-tables should
7470 contain relative addresses only when @option{-fPIC} or @option{-fPIC}
7474 @hook TARGET_CASE_VALUES_THRESHOLD
7476 @defmac WORD_REGISTER_OPERATIONS
7477 Define this macro to 1 if operations between registers with integral mode
7478 smaller than a word are always performed on the entire register.
7479 Most RISC machines have this property and most CISC machines do not.
7482 @hook TARGET_MIN_ARITHMETIC_PRECISION
7484 @defmac LOAD_EXTEND_OP (@var{mem_mode})
7485 Define this macro to be a C expression indicating when insns that read
7486 memory in @var{mem_mode}, an integral mode narrower than a word, set the
7487 bits outside of @var{mem_mode} to be either the sign-extension or the
7488 zero-extension of the data read. Return @code{SIGN_EXTEND} for values
7489 of @var{mem_mode} for which the
7490 insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
7491 @code{UNKNOWN} for other modes.
7493 This macro is not called with @var{mem_mode} non-integral or with a width
7494 greater than or equal to @code{BITS_PER_WORD}, so you may return any
7495 value in this case. Do not define this macro if it would always return
7496 @code{UNKNOWN}. On machines where this macro is defined, you will normally
7497 define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
7499 You may return a non-@code{UNKNOWN} value even if for some hard registers
7500 the sign extension is not performed, if for the @code{REGNO_REG_CLASS}
7501 of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero
7502 when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any
7503 integral mode larger than this but not larger than @code{word_mode}.
7505 You must return @code{UNKNOWN} if for some hard registers that allow this
7506 mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to
7507 @code{word_mode}, but that they can change to another integral mode that
7508 is larger then @var{mem_mode} but still smaller than @code{word_mode}.
7511 @defmac SHORT_IMMEDIATES_SIGN_EXTEND
7512 Define this macro to 1 if loading short immediate values into registers sign
7516 @hook TARGET_MIN_DIVISIONS_FOR_RECIP_MUL
7519 The maximum number of bytes that a single instruction can move quickly
7520 between memory and registers or between two memory locations.
7523 @defmac MAX_MOVE_MAX
7524 The maximum number of bytes that a single instruction can move quickly
7525 between memory and registers or between two memory locations. If this
7526 is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
7527 constant value that is the largest value that @code{MOVE_MAX} can have
7531 @defmac SHIFT_COUNT_TRUNCATED
7532 A C expression that is nonzero if on this machine the number of bits
7533 actually used for the count of a shift operation is equal to the number
7534 of bits needed to represent the size of the object being shifted. When
7535 this macro is nonzero, the compiler will assume that it is safe to omit
7536 a sign-extend, zero-extend, and certain bitwise `and' instructions that
7537 truncates the count of a shift operation. On machines that have
7538 instructions that act on bit-fields at variable positions, which may
7539 include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
7540 also enables deletion of truncations of the values that serve as
7541 arguments to bit-field instructions.
7543 If both types of instructions truncate the count (for shifts) and
7544 position (for bit-field operations), or if no variable-position bit-field
7545 instructions exist, you should define this macro.
7547 However, on some machines, such as the 80386 and the 680x0, truncation
7548 only applies to shift operations and not the (real or pretended)
7549 bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
7550 such machines. Instead, add patterns to the @file{md} file that include
7551 the implied truncation of the shift instructions.
7553 You need not define this macro if it would always have the value of zero.
7556 @anchor{TARGET_SHIFT_TRUNCATION_MASK}
7557 @hook TARGET_SHIFT_TRUNCATION_MASK
7559 @defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
7560 A C expression which is nonzero if on this machine it is safe to
7561 ``convert'' an integer of @var{inprec} bits to one of @var{outprec}
7562 bits (where @var{outprec} is smaller than @var{inprec}) by merely
7563 operating on it as if it had only @var{outprec} bits.
7565 On many machines, this expression can be 1.
7567 @c rearranged this, removed the phrase "it is reported that". this was
7568 @c to fix an overfull hbox. --mew 10feb93
7569 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for modes
7570 for which @code{TARGET_MODES_TIEABLE_P} is false, suboptimal code can result.
7571 If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
7572 such cases may improve things.
7575 @hook TARGET_MODE_REP_EXTENDED
7577 @defmac STORE_FLAG_VALUE
7578 A C expression describing the value returned by a comparison operator
7579 with an integral mode and stored by a store-flag instruction
7580 (@samp{cstore@var{mode}4}) when the condition is true. This description must
7581 apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the
7582 comparison operators whose results have a @code{MODE_INT} mode.
7584 A value of 1 or @minus{}1 means that the instruction implementing the
7585 comparison operator returns exactly 1 or @minus{}1 when the comparison is true
7586 and 0 when the comparison is false. Otherwise, the value indicates
7587 which bits of the result are guaranteed to be 1 when the comparison is
7588 true. This value is interpreted in the mode of the comparison
7589 operation, which is given by the mode of the first operand in the
7590 @samp{cstore@var{mode}4} pattern. Either the low bit or the sign bit of
7591 @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
7594 If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
7595 generate code that depends only on the specified bits. It can also
7596 replace comparison operators with equivalent operations if they cause
7597 the required bits to be set, even if the remaining bits are undefined.
7598 For example, on a machine whose comparison operators return an
7599 @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
7600 @samp{0x80000000}, saying that just the sign bit is relevant, the
7604 (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
7611 (ashift:SI @var{x} (const_int @var{n}))
7615 where @var{n} is the appropriate shift count to move the bit being
7616 tested into the sign bit.
7618 There is no way to describe a machine that always sets the low-order bit
7619 for a true value, but does not guarantee the value of any other bits,
7620 but we do not know of any machine that has such an instruction. If you
7621 are trying to port GCC to such a machine, include an instruction to
7622 perform a logical-and of the result with 1 in the pattern for the
7623 comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
7625 Often, a machine will have multiple instructions that obtain a value
7626 from a comparison (or the condition codes). Here are rules to guide the
7627 choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
7632 Use the shortest sequence that yields a valid definition for
7633 @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
7634 ``normalize'' the value (convert it to, e.g., 1 or 0) than for the
7635 comparison operators to do so because there may be opportunities to
7636 combine the normalization with other operations.
7639 For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
7640 slightly preferred on machines with expensive jumps and 1 preferred on
7644 As a second choice, choose a value of @samp{0x80000001} if instructions
7645 exist that set both the sign and low-order bits but do not define the
7649 Otherwise, use a value of @samp{0x80000000}.
7652 Many machines can produce both the value chosen for
7653 @code{STORE_FLAG_VALUE} and its negation in the same number of
7654 instructions. On those machines, you should also define a pattern for
7655 those cases, e.g., one matching
7658 (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
7661 Some machines can also perform @code{and} or @code{plus} operations on
7662 condition code values with less instructions than the corresponding
7663 @samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}. On those
7664 machines, define the appropriate patterns. Use the names @code{incscc}
7665 and @code{decscc}, respectively, for the patterns which perform
7666 @code{plus} or @code{minus} operations on condition code values. See
7667 @file{rs6000.md} for some examples. The GNU Superoptimizer can be used to
7668 find such instruction sequences on other machines.
7670 If this macro is not defined, the default value, 1, is used. You need
7671 not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
7672 instructions, or if the value generated by these instructions is 1.
7675 @defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
7676 A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
7677 returned when comparison operators with floating-point results are true.
7678 Define this macro on machines that have comparison operations that return
7679 floating-point values. If there are no such operations, do not define
7683 @defmac VECTOR_STORE_FLAG_VALUE (@var{mode})
7684 A C expression that gives a rtx representing the nonzero true element
7685 for vector comparisons. The returned rtx should be valid for the inner
7686 mode of @var{mode} which is guaranteed to be a vector mode. Define
7687 this macro on machines that have vector comparison operations that
7688 return a vector result. If there are no such operations, do not define
7689 this macro. Typically, this macro is defined as @code{const1_rtx} or
7690 @code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent
7691 the compiler optimizing such vector comparison operations for the
7695 @defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
7696 @defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
7697 A C expression that indicates whether the architecture defines a value
7698 for @code{clz} or @code{ctz} with a zero operand.
7699 A result of @code{0} indicates the value is undefined.
7700 If the value is defined for only the RTL expression, the macro should
7701 evaluate to @code{1}; if the value applies also to the corresponding optab
7702 entry (which is normally the case if it expands directly into
7703 the corresponding RTL), then the macro should evaluate to @code{2}.
7704 In the cases where the value is defined, @var{value} should be set to
7707 If this macro is not defined, the value of @code{clz} or
7708 @code{ctz} at zero is assumed to be undefined.
7710 This macro must be defined if the target's expansion for @code{ffs}
7711 relies on a particular value to get correct results. Otherwise it
7712 is not necessary, though it may be used to optimize some corner cases, and
7713 to provide a default expansion for the @code{ffs} optab.
7715 Note that regardless of this macro the ``definedness'' of @code{clz}
7716 and @code{ctz} at zero do @emph{not} extend to the builtin functions
7717 visible to the user. Thus one may be free to adjust the value at will
7718 to match the target expansion of these operations without fear of
7723 An alias for the machine mode for pointers. On most machines, define
7724 this to be the integer mode corresponding to the width of a hardware
7725 pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
7726 On some machines you must define this to be one of the partial integer
7727 modes, such as @code{PSImode}.
7729 The width of @code{Pmode} must be at least as large as the value of
7730 @code{POINTER_SIZE}. If it is not equal, you must define the macro
7731 @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
7735 @defmac FUNCTION_MODE
7736 An alias for the machine mode used for memory references to functions
7737 being called, in @code{call} RTL expressions. On most CISC machines,
7738 where an instruction can begin at any byte address, this should be
7739 @code{QImode}. On most RISC machines, where all instructions have fixed
7740 size and alignment, this should be a mode with the same size and alignment
7741 as the machine instruction words - typically @code{SImode} or @code{HImode}.
7744 @defmac STDC_0_IN_SYSTEM_HEADERS
7745 In normal operation, the preprocessor expands @code{__STDC__} to the
7746 constant 1, to signify that GCC conforms to ISO Standard C@. On some
7747 hosts, like Solaris, the system compiler uses a different convention,
7748 where @code{__STDC__} is normally 0, but is 1 if the user specifies
7749 strict conformance to the C Standard.
7751 Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
7752 convention when processing system header files, but when processing user
7753 files @code{__STDC__} will always expand to 1.
7756 @hook TARGET_C_PREINCLUDE
7758 @hook TARGET_CXX_IMPLICIT_EXTERN_C
7760 @defmac NO_IMPLICIT_EXTERN_C
7761 Define this macro if the system header files support C++ as well as C@.
7762 This macro inhibits the usual method of using system header files in
7763 C++, which is to pretend that the file's contents are enclosed in
7764 @samp{extern "C" @{@dots{}@}}.
7769 @defmac REGISTER_TARGET_PRAGMAS ()
7770 Define this macro if you want to implement any target-specific pragmas.
7771 If defined, it is a C expression which makes a series of calls to
7772 @code{c_register_pragma} or @code{c_register_pragma_with_expansion}
7773 for each pragma. The macro may also do any
7774 setup required for the pragmas.
7776 The primary reason to define this macro is to provide compatibility with
7777 other compilers for the same target. In general, we discourage
7778 definition of target-specific pragmas for GCC@.
7780 If the pragma can be implemented by attributes then you should consider
7781 defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
7783 Preprocessor macros that appear on pragma lines are not expanded. All
7784 @samp{#pragma} directives that do not match any registered pragma are
7785 silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
7788 @deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
7789 @deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
7791 Each call to @code{c_register_pragma} or
7792 @code{c_register_pragma_with_expansion} establishes one pragma. The
7793 @var{callback} routine will be called when the preprocessor encounters a
7797 #pragma [@var{space}] @var{name} @dots{}
7800 @var{space} is the case-sensitive namespace of the pragma, or
7801 @code{NULL} to put the pragma in the global namespace. The callback
7802 routine receives @var{pfile} as its first argument, which can be passed
7803 on to cpplib's functions if necessary. You can lex tokens after the
7804 @var{name} by calling @code{pragma_lex}. Tokens that are not read by the
7805 callback will be silently ignored. The end of the line is indicated by
7806 a token of type @code{CPP_EOF}. Macro expansion occurs on the
7807 arguments of pragmas registered with
7808 @code{c_register_pragma_with_expansion} but not on the arguments of
7809 pragmas registered with @code{c_register_pragma}.
7811 Note that the use of @code{pragma_lex} is specific to the C and C++
7812 compilers. It will not work in the Java or Fortran compilers, or any
7813 other language compilers for that matter. Thus if @code{pragma_lex} is going
7814 to be called from target-specific code, it must only be done so when
7815 building the C and C++ compilers. This can be done by defining the
7816 variables @code{c_target_objs} and @code{cxx_target_objs} in the
7817 target entry in the @file{config.gcc} file. These variables should name
7818 the target-specific, language-specific object file which contains the
7819 code that uses @code{pragma_lex}. Note it will also be necessary to add a
7820 rule to the makefile fragment pointed to by @code{tmake_file} that shows
7821 how to build this object file.
7824 @defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION
7825 Define this macro if macros should be expanded in the
7826 arguments of @samp{#pragma pack}.
7829 @defmac TARGET_DEFAULT_PACK_STRUCT
7830 If your target requires a structure packing default other than 0 (meaning
7831 the machine default), define this macro to the necessary value (in bytes).
7832 This must be a value that would also be valid to use with
7833 @samp{#pragma pack()} (that is, a small power of two).
7836 @defmac DOLLARS_IN_IDENTIFIERS
7837 Define this macro to control use of the character @samp{$} in
7838 identifier names for the C family of languages. 0 means @samp{$} is
7839 not allowed by default; 1 means it is allowed. 1 is the default;
7840 there is no need to define this macro in that case.
7843 @defmac INSN_SETS_ARE_DELAYED (@var{insn})
7844 Define this macro as a C expression that is nonzero if it is safe for the
7845 delay slot scheduler to place instructions in the delay slot of @var{insn},
7846 even if they appear to use a resource set or clobbered in @var{insn}.
7847 @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
7848 every @code{call_insn} has this behavior. On machines where some @code{insn}
7849 or @code{jump_insn} is really a function call and hence has this behavior,
7850 you should define this macro.
7852 You need not define this macro if it would always return zero.
7855 @defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
7856 Define this macro as a C expression that is nonzero if it is safe for the
7857 delay slot scheduler to place instructions in the delay slot of @var{insn},
7858 even if they appear to set or clobber a resource referenced in @var{insn}.
7859 @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
7860 some @code{insn} or @code{jump_insn} is really a function call and its operands
7861 are registers whose use is actually in the subroutine it calls, you should
7862 define this macro. Doing so allows the delay slot scheduler to move
7863 instructions which copy arguments into the argument registers into the delay
7866 You need not define this macro if it would always return zero.
7869 @defmac MULTIPLE_SYMBOL_SPACES
7870 Define this macro as a C expression that is nonzero if, in some cases,
7871 global symbols from one translation unit may not be bound to undefined
7872 symbols in another translation unit without user intervention. For
7873 instance, under Microsoft Windows symbols must be explicitly imported
7874 from shared libraries (DLLs).
7876 You need not define this macro if it would always evaluate to zero.
7879 @hook TARGET_MD_ASM_ADJUST
7881 @defmac MATH_LIBRARY
7882 Define this macro as a C string constant for the linker argument to link
7883 in the system math library, minus the initial @samp{"-l"}, or
7884 @samp{""} if the target does not have a
7885 separate math library.
7887 You need only define this macro if the default of @samp{"m"} is wrong.
7890 @defmac LIBRARY_PATH_ENV
7891 Define this macro as a C string constant for the environment variable that
7892 specifies where the linker should look for libraries.
7894 You need only define this macro if the default of @samp{"LIBRARY_PATH"}
7898 @defmac TARGET_POSIX_IO
7899 Define this macro if the target supports the following POSIX@ file
7900 functions, access, mkdir and file locking with fcntl / F_SETLKW@.
7901 Defining @code{TARGET_POSIX_IO} will enable the test coverage code
7902 to use file locking when exiting a program, which avoids race conditions
7903 if the program has forked. It will also create directories at run-time
7904 for cross-profiling.
7907 @defmac MAX_CONDITIONAL_EXECUTE
7909 A C expression for the maximum number of instructions to execute via
7910 conditional execution instructions instead of a branch. A value of
7911 @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
7912 1 if it does use cc0.
7915 @defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
7916 Used if the target needs to perform machine-dependent modifications on the
7917 conditionals used for turning basic blocks into conditionally executed code.
7918 @var{ce_info} points to a data structure, @code{struct ce_if_block}, which
7919 contains information about the currently processed blocks. @var{true_expr}
7920 and @var{false_expr} are the tests that are used for converting the
7921 then-block and the else-block, respectively. Set either @var{true_expr} or
7922 @var{false_expr} to a null pointer if the tests cannot be converted.
7925 @defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
7926 Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
7927 if-statements into conditions combined by @code{and} and @code{or} operations.
7928 @var{bb} contains the basic block that contains the test that is currently
7929 being processed and about to be turned into a condition.
7932 @defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
7933 A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
7934 be converted to conditional execution format. @var{ce_info} points to
7935 a data structure, @code{struct ce_if_block}, which contains information
7936 about the currently processed blocks.
7939 @defmac IFCVT_MODIFY_FINAL (@var{ce_info})
7940 A C expression to perform any final machine dependent modifications in
7941 converting code to conditional execution. The involved basic blocks
7942 can be found in the @code{struct ce_if_block} structure that is pointed
7943 to by @var{ce_info}.
7946 @defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
7947 A C expression to cancel any machine dependent modifications in
7948 converting code to conditional execution. The involved basic blocks
7949 can be found in the @code{struct ce_if_block} structure that is pointed
7950 to by @var{ce_info}.
7953 @defmac IFCVT_MACHDEP_INIT (@var{ce_info})
7954 A C expression to initialize any machine specific data for if-conversion
7955 of the if-block in the @code{struct ce_if_block} structure that is pointed
7956 to by @var{ce_info}.
7959 @hook TARGET_MACHINE_DEPENDENT_REORG
7961 @hook TARGET_INIT_BUILTINS
7963 @hook TARGET_BUILTIN_DECL
7965 @hook TARGET_EXPAND_BUILTIN
7967 @hook TARGET_BUILTIN_CHKP_FUNCTION
7968 @hook TARGET_CHKP_BOUND_TYPE
7969 @hook TARGET_CHKP_BOUND_MODE
7970 @hook TARGET_CHKP_MAKE_BOUNDS_CONSTANT
7971 @hook TARGET_CHKP_INITIALIZE_BOUNDS
7973 @hook TARGET_RESOLVE_OVERLOADED_BUILTIN
7975 @hook TARGET_FOLD_BUILTIN
7977 @hook TARGET_GIMPLE_FOLD_BUILTIN
7979 @hook TARGET_COMPARE_VERSION_PRIORITY
7981 @hook TARGET_GET_FUNCTION_VERSIONS_DISPATCHER
7983 @hook TARGET_GENERATE_VERSION_DISPATCHER_BODY
7985 @hook TARGET_CAN_USE_DOLOOP_P
7987 @hook TARGET_INVALID_WITHIN_DOLOOP
7989 @hook TARGET_LEGITIMATE_COMBINED_INSN
7991 @hook TARGET_CAN_FOLLOW_JUMP
7993 @hook TARGET_COMMUTATIVE_P
7995 @hook TARGET_ALLOCATE_INITIAL_VALUE
7997 @hook TARGET_UNSPEC_MAY_TRAP_P
7999 @hook TARGET_SET_CURRENT_FUNCTION
8001 @defmac TARGET_OBJECT_SUFFIX
8002 Define this macro to be a C string representing the suffix for object
8003 files on your target machine. If you do not define this macro, GCC will
8004 use @samp{.o} as the suffix for object files.
8007 @defmac TARGET_EXECUTABLE_SUFFIX
8008 Define this macro to be a C string representing the suffix to be
8009 automatically added to executable files on your target machine. If you
8010 do not define this macro, GCC will use the null string as the suffix for
8014 @defmac COLLECT_EXPORT_LIST
8015 If defined, @code{collect2} will scan the individual object files
8016 specified on its command line and create an export list for the linker.
8017 Define this macro for systems like AIX, where the linker discards
8018 object files that are not referenced from @code{main} and uses export
8022 @defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
8023 Define this macro to a C expression representing a variant of the
8024 method call @var{mdecl}, if Java Native Interface (JNI) methods
8025 must be invoked differently from other methods on your target.
8026 For example, on 32-bit Microsoft Windows, JNI methods must be invoked using
8027 the @code{stdcall} calling convention and this macro is then
8028 defined as this expression:
8031 build_type_attribute_variant (@var{mdecl},
8033 (get_identifier ("stdcall"),
8038 @hook TARGET_CANNOT_MODIFY_JUMPS_P
8040 @hook TARGET_BRANCH_TARGET_REGISTER_CLASS
8042 @hook TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED
8044 @hook TARGET_HAVE_CONDITIONAL_EXECUTION
8046 @hook TARGET_GEN_CCMP_FIRST
8048 @hook TARGET_GEN_CCMP_NEXT
8050 @hook TARGET_LOOP_UNROLL_ADJUST
8052 @defmac POWI_MAX_MULTS
8053 If defined, this macro is interpreted as a signed integer C expression
8054 that specifies the maximum number of floating point multiplications
8055 that should be emitted when expanding exponentiation by an integer
8056 constant inline. When this value is defined, exponentiation requiring
8057 more than this number of multiplications is implemented by calling the
8058 system library's @code{pow}, @code{powf} or @code{powl} routines.
8059 The default value places no upper bound on the multiplication count.
8062 @deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
8063 This target hook should register any extra include files for the
8064 target. The parameter @var{stdinc} indicates if normal include files
8065 are present. The parameter @var{sysroot} is the system root directory.
8066 The parameter @var{iprefix} is the prefix for the gcc directory.
8069 @deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
8070 This target hook should register any extra include files for the
8071 target before any standard headers. The parameter @var{stdinc}
8072 indicates if normal include files are present. The parameter
8073 @var{sysroot} is the system root directory. The parameter
8074 @var{iprefix} is the prefix for the gcc directory.
8077 @deftypefn Macro void TARGET_OPTF (char *@var{path})
8078 This target hook should register special include paths for the target.
8079 The parameter @var{path} is the include to register. On Darwin
8080 systems, this is used for Framework includes, which have semantics
8081 that are different from @option{-I}.
8084 @defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl})
8085 This target macro returns @code{true} if it is safe to use a local alias
8086 for a virtual function @var{fndecl} when constructing thunks,
8087 @code{false} otherwise. By default, the macro returns @code{true} for all
8088 functions, if a target supports aliases (i.e.@: defines
8089 @code{ASM_OUTPUT_DEF}), @code{false} otherwise,
8092 @defmac TARGET_FORMAT_TYPES
8093 If defined, this macro is the name of a global variable containing
8094 target-specific format checking information for the @option{-Wformat}
8095 option. The default is to have no target-specific format checks.
8098 @defmac TARGET_N_FORMAT_TYPES
8099 If defined, this macro is the number of entries in
8100 @code{TARGET_FORMAT_TYPES}.
8103 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES
8104 If defined, this macro is the name of a global variable containing
8105 target-specific format overrides for the @option{-Wformat} option. The
8106 default is to have no target-specific format overrides. If defined,
8107 @code{TARGET_FORMAT_TYPES} must be defined, too.
8110 @defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT
8111 If defined, this macro specifies the number of entries in
8112 @code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}.
8115 @defmac TARGET_OVERRIDES_FORMAT_INIT
8116 If defined, this macro specifies the optional initialization
8117 routine for target specific customizations of the system printf
8118 and scanf formatter settings.
8121 @hook TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN
8123 @hook TARGET_INVALID_CONVERSION
8125 @hook TARGET_INVALID_UNARY_OP
8127 @hook TARGET_INVALID_BINARY_OP
8129 @hook TARGET_PROMOTED_TYPE
8131 @hook TARGET_CONVERT_TO_TYPE
8134 This macro determines the size of the objective C jump buffer for the
8135 NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value.
8138 @defmac LIBGCC2_UNWIND_ATTRIBUTE
8139 Define this macro if any target-specific attributes need to be attached
8140 to the functions in @file{libgcc} that provide low-level support for
8141 call stack unwinding. It is used in declarations in @file{unwind-generic.h}
8142 and the associated definitions of those functions.
8145 @hook TARGET_UPDATE_STACK_BOUNDARY
8147 @hook TARGET_GET_DRAP_RTX
8149 @hook TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS
8151 @hook TARGET_CONST_ANCHOR
8153 @hook TARGET_ASAN_SHADOW_OFFSET
8155 @hook TARGET_MEMMODEL_CHECK
8157 @hook TARGET_ATOMIC_TEST_AND_SET_TRUEVAL
8159 @hook TARGET_HAS_IFUNC_P
8161 @hook TARGET_ATOMIC_ALIGN_FOR_MODE
8163 @hook TARGET_ATOMIC_ASSIGN_EXPAND_FENV
8165 @hook TARGET_RECORD_OFFLOAD_SYMBOL
8167 @hook TARGET_OFFLOAD_OPTIONS
8169 @defmac TARGET_SUPPORTS_WIDE_INT
8171 On older ports, large integers are stored in @code{CONST_DOUBLE} rtl
8172 objects. Newer ports define @code{TARGET_SUPPORTS_WIDE_INT} to be nonzero
8173 to indicate that large integers are stored in
8174 @code{CONST_WIDE_INT} rtl objects. The @code{CONST_WIDE_INT} allows
8175 very large integer constants to be represented. @code{CONST_DOUBLE}
8176 is limited to twice the size of the host's @code{HOST_WIDE_INT}
8179 Converting a port mostly requires looking for the places where
8180 @code{CONST_DOUBLE}s are used with @code{VOIDmode} and replacing that
8181 code with code that accesses @code{CONST_WIDE_INT}s. @samp{"grep -i
8182 const_double"} at the port level gets you to 95% of the changes that
8183 need to be made. There are a few places that require a deeper look.
8187 There is no equivalent to @code{hval} and @code{lval} for
8188 @code{CONST_WIDE_INT}s. This would be difficult to express in the md
8189 language since there are a variable number of elements.
8191 Most ports only check that @code{hval} is either 0 or -1 to see if the
8192 value is small. As mentioned above, this will no longer be necessary
8193 since small constants are always @code{CONST_INT}. Of course there
8194 are still a few exceptions, the alpha's constraint used by the zap
8195 instruction certainly requires careful examination by C code.
8196 However, all the current code does is pass the hval and lval to C
8197 code, so evolving the c code to look at the @code{CONST_WIDE_INT} is
8198 not really a large change.
8201 Because there is no standard template that ports use to materialize
8202 constants, there is likely to be some futzing that is unique to each
8206 The rtx costs may have to be adjusted to properly account for larger
8207 constants that are represented as @code{CONST_WIDE_INT}.
8210 All and all it does not take long to convert ports that the
8211 maintainer is familiar with.
8215 @hook TARGET_RUN_TARGET_SELFTESTS