]> git.ipfire.org Git - thirdparty/glibc.git/blame - manual/maint.texi
manual: Manual update for strlcat, strlcpy, wcslcat, wclscpy
[thirdparty/glibc.git] / manual / maint.texi
CommitLineData
d9dc34cd 1@node Maintenance, Platform, Installation, Top
7a68c94a 2@c %MENU% How to enhance and port the GNU C Library
28f540f4
RM
3@appendix Library Maintenance
4
5@menu
28f540f4 6* Source Layout:: How to add new functions or header files
1f77f049 7 to the GNU C Library.
3d3a2911 8* Source Fortification:: Fortification of function calls.
6e15f3e2 9* Symbol handling:: How to handle symbols in the GNU C Library.
1f77f049 10* Porting:: How to port the GNU C Library to
28f540f4 11 a new machine or operating system.
7da3079b 12@end menu
28f540f4 13
28f540f4
RM
14@node Source Layout
15@appendixsec Adding New Functions
16
17The process of building the library is driven by the makefiles, which
18make heavy use of special features of GNU @code{make}. The makefiles
19are very complex, and you probably don't want to try to understand them.
20But what they do is fairly straightforward, and only requires that you
21define a few variables in the right places.
22
23The library sources are divided into subdirectories, grouped by topic.
41f27456 24
28f540f4 25The @file{string} subdirectory has all the string-manipulation
41f27456 26functions, @file{math} has all the mathematical functions, etc.
28f540f4
RM
27
28Each subdirectory contains a simple makefile, called @file{Makefile},
29which defines a few @code{make} variables and then includes the global
30makefile @file{Rules} with a line like:
31
32@smallexample
33include ../Rules
34@end smallexample
35
36@noindent
37The basic variables that a subdirectory makefile defines are:
38
39@table @code
40@item subdir
41The name of the subdirectory, for example @file{stdio}.
42This variable @strong{must} be defined.
43
44@item headers
45The names of the header files in this section of the library,
46such as @file{stdio.h}.
47
48@item routines
49@itemx aux
50The names of the modules (source files) in this section of the library.
51These should be simple names, such as @samp{strlen} (rather than
52complete file names, such as @file{strlen.c}). Use @code{routines} for
53modules that define functions in the library, and @code{aux} for
54auxiliary modules containing things like data definitions. But the
55values of @code{routines} and @code{aux} are just concatenated, so there
0005e54f 56really is no practical difference.
28f540f4
RM
57
58@item tests
59The names of test programs for this section of the library. These
60should be simple names, such as @samp{tester} (rather than complete file
61names, such as @file{tester.c}). @w{@samp{make tests}} will build and
62run all the test programs. If a test program needs input, put the test
63data in a file called @file{@var{test-program}.input}; it will be given to
64the test program on its standard input. If a test program wants to be
65run with arguments, put the arguments (all on a single line) in a file
41f27456
RM
66called @file{@var{test-program}.args}. Test programs should exit with
67zero status when the test passes, and nonzero status when the test
68indicates a bug in the library or error in building.
28f540f4
RM
69
70@item others
71The names of ``other'' programs associated with this section of the
72library. These are programs which are not tests per se, but are other
73small programs included with the library. They are built by
0005e54f 74@w{@samp{make others}}.
28f540f4
RM
75
76@item install-lib
77@itemx install-data
78@itemx install
79Files to be installed by @w{@samp{make install}}. Files listed in
80@samp{install-lib} are installed in the directory specified by
81@samp{libdir} in @file{configparms} or @file{Makeconfig}
82(@pxref{Installation}). Files listed in @code{install-data} are
83installed in the directory specified by @samp{datadir} in
84@file{configparms} or @file{Makeconfig}. Files listed in @code{install}
85are installed in the directory specified by @samp{bindir} in
0005e54f 86@file{configparms} or @file{Makeconfig}.
28f540f4
RM
87
88@item distribute
89Other files from this subdirectory which should be put into a
90distribution tar file. You need not list here the makefile itself or
91the source and header files listed in the other standard variables.
92Only define @code{distribute} if there are files used in an unusual way
93that should go into the distribution.
94
95@item generated
96Files which are generated by @file{Makefile} in this subdirectory.
97These files will be removed by @w{@samp{make clean}}, and they will
98never go into a distribution.
99
100@item extra-objs
101Extra object files which are built by @file{Makefile} in this
102subdirectory. This should be a list of file names like @file{foo.o};
103the files will actually be found in whatever directory object files are
104being built in. These files will be removed by @w{@samp{make clean}}.
105This variable is used for secondary object files needed to build
106@code{others} or @code{tests}.
107@end table
108
d9dc34cd
TMQMF
109@menu
110* Platform: Adding Platform-specific. Adding platform-specific
111 features.
112@end menu
113
114@node Adding Platform-specific
115@appendixsubsec Platform-specific types, macros and functions
116
117It's sometimes necessary to provide nonstandard, platform-specific
118features to developers. The C library is traditionally the
119lowest library layer, so it makes sense for it to provide these
120low-level features. However, including these features in the C
121library may be a disadvantage if another package provides them
122as well as there will be two conflicting versions of them. Also,
123the features won't be available to projects that do not use
124@theglibc{} but use other GNU tools, like GCC.
125
126The current guidelines are:
127@itemize @bullet
128@item
129If the header file provides features that only make sense on a particular
130machine architecture and have nothing to do with an operating system, then
131the features should ultimately be provided as GCC built-in functions. Until
132then, @theglibc{} may provide them in the header file. When the GCC built-in
133functions become available, those provided in the header file should be made
134conditionally available prior to the GCC version in which the built-in
135function was made available.
136
137@item
138If the header file provides features that are specific to an operating system,
139both GCC and @theglibc{} could provide it, but @theglibc{} is preferred
140as it already has a lot of information about the operating system.
141
142@item
143If the header file provides features that are specific to an operating system
144but used by @theglibc{}, then @theglibc{} should provide them.
145@end itemize
146
147The general solution for providing low-level features is to export them as
148follows:
149
150@itemize @bullet
151@item
152A nonstandard, low-level header file that defines macros and inline
153functions should be called @file{sys/platform/@var{name}.h}.
154
155@item
156Each header file's name should include the platform name, to avoid
6d2857d3 157users thinking there is anything in common between the different
d9dc34cd
TMQMF
158header files for different platforms. For example, a
159@file{sys/platform/@var{arch}.h} name such as
160@file{sys/platform/ppc.h} is better than @file{sys/platform.h}.
161
162@item
163A platform-specific header file provided by @theglibc{} should coordinate
164with GCC such that compiler built-in versions of the functions and macros are
165preferred if available. This means that user programs will only ever need to
166include @file{sys/platform/@var{arch}.h}, keeping the same names of types,
167macros, and functions for convenience and portability.
168
169@item
170Each included symbol must have the prefix @code{__@var{arch}_}, such as
171@code{__ppc_get_timebase}.
172@end itemize
173
174
175The easiest way to provide a header file is to add it to the
176@code{sysdep_headers} variable. For example, the combination of
177Linux-specific header files on PowerPC could be provided like this:
178
179@smallexample
180sysdep_headers += sys/platform/ppc.h
181@end smallexample
182
183Then ensure that you have added a @file{sys/platform/ppc.h}
184header file in the machine-specific directory, e.g.,
185@file{sysdeps/powerpc/sys/platform/ppc.h}.
186
187
3d3a2911
SP
188@node Source Fortification
189@appendixsec Fortification of function calls
190
191This section contains implementation details of @theglibc{} and may not
192remain stable across releases.
193
194The @code{_FORTIFY_SOURCE} macro may be defined by users to control
195hardening of calls into some functions in @theglibc{}. The definition
196should be at the top of the source file before any headers are included
197or at the pre-processor commandline using the @code{-D} switch. The
198hardening primarily focuses on accesses to buffers passed to the
199functions but may also include checks for validity of other inputs to
200the functions.
201
202When the @code{_FORTIFY_SOURCE} macro is defined, it enables code that
203validates inputs passed to some functions in @theglibc to determine if
204they are safe. If the compiler is unable to determine that the inputs
205to the function call are safe, the call may be replaced by a call to its
206hardened variant that does additional safety checks at runtime. Some
207hardened variants need the size of the buffer to perform access
208validation and this is provided by the @code{__builtin_object_size} or
209the @code{__builtin_dynamic_object_size} builtin functions.
ac2a1434
SP
210@code{_FORTIFY_SOURCE} also enables additional compile time diagnostics,
211such as unchecked return values from some functions, to encourage
212developers to add error checking for those functions.
3d3a2911
SP
213
214At runtime, if any of those safety checks fail, the program will
215terminate with a @code{SIGABRT} signal. @code{_FORTIFY_SOURCE} may be
216defined to one of the following values:
217
218@itemize @bullet
219@item @math{1}: This enables buffer bounds checking using the value
220returned by the @code{__builtin_object_size} compiler builtin function.
221If the function returns @code{(size_t) -1}, the function call is left
222untouched. Additionally, this level also enables validation of flags to
223the @code{open}, @code{open64}, @code{openat} and @code{openat64}
224functions.
225
226@item @math{2}: This behaves like @math{1}, with the addition of some
227checks that may trap code that is conforming but unsafe, e.g. accepting
228@code{%n} only in read-only format strings.
229
230@item @math{3}: This enables buffer bounds checking using the value
231returned by the @code{__builtin_dynamic_object_size} compiler builtin
232function. If the function returns @code{(size_t) -1}, the function call
233is left untouched. Fortification at this level may have a impact on
234program performance if the function call that is fortified is frequently
235encountered and the size expression returned by
236@code{__builtin_dynamic_object_size} is complex.
237@end itemize
238
239In general, the fortified variants of the function calls use the name of
240the function with a @code{__} prefix and a @code{_chk} suffix. There
241are some exceptions, e.g. the @code{printf} family of functions where,
242depending on the architecture, one may also see fortified variants have
243the @code{_chkieee128} suffix or the @code{__nldbl___} prefix to their
244names.
245
246Another exception is the @code{open} family of functions, where their
247fortified replacements have the @code{__} prefix and a @code{_2} suffix.
248The @code{FD_SET}, @code{FD_CLR} and @code{FD_ISSET} macros use the
249@code{__fdelt_chk} function on fortification.
250
251The following functions and macros are fortified in @theglibc{}:
252@c Generated using the following command:
253@c find . -name Versions | xargs grep -e "_chk;" -e "_2;" |
254@c cut -d ':' -f 2 | sed 's/;/\n/g' | sed 's/ *//g' | grep -v "^$" |
255@c sort -u | grep ^__ |
256@c grep -v -e ieee128 -e __nldbl -e align_cpy -e "fdelt_warn" |
257@c sed 's/__fdelt_chk/@item @code{FD_SET}\n\n@item @code{FD_CLR}\n\n@item @code{FD_ISSET}\n/' |
258@c sed 's/__\(.*\)_\(chk\|2\)/@item @code{\1}\n/'
259
260@itemize @bullet
261
262@item @code{asprintf}
263
264@item @code{confstr}
265
266@item @code{dprintf}
267
268@item @code{explicit_bzero}
269
270@item @code{FD_SET}
271
272@item @code{FD_CLR}
273
274@item @code{FD_ISSET}
275
276@item @code{fgets}
277
278@item @code{fgets_unlocked}
279
280@item @code{fgetws}
281
282@item @code{fgetws_unlocked}
283
284@item @code{fprintf}
285
286@item @code{fread}
287
288@item @code{fread_unlocked}
289
290@item @code{fwprintf}
291
292@item @code{getcwd}
293
294@item @code{getdomainname}
295
296@item @code{getgroups}
297
298@item @code{gethostname}
299
300@item @code{getlogin_r}
301
302@item @code{gets}
303
304@item @code{getwd}
305
306@item @code{longjmp}
307
308@item @code{mbsnrtowcs}
309
310@item @code{mbsrtowcs}
311
312@item @code{mbstowcs}
313
314@item @code{memcpy}
315
316@item @code{memmove}
317
318@item @code{mempcpy}
319
320@item @code{memset}
321
322@item @code{mq_open}
323
324@item @code{obstack_printf}
325
326@item @code{obstack_vprintf}
327
328@item @code{open}
329
330@item @code{open64}
331
332@item @code{openat}
333
334@item @code{openat64}
335
336@item @code{poll}
337
338@item @code{ppoll64}
339
340@item @code{ppoll}
341
342@item @code{pread64}
343
344@item @code{pread}
345
346@item @code{printf}
347
348@item @code{ptsname_r}
349
350@item @code{read}
351
352@item @code{readlinkat}
353
354@item @code{readlink}
355
356@item @code{realpath}
357
358@item @code{recv}
359
360@item @code{recvfrom}
361
362@item @code{snprintf}
363
364@item @code{sprintf}
365
366@item @code{stpcpy}
367
368@item @code{stpncpy}
369
370@item @code{strcat}
371
372@item @code{strcpy}
373
d2fda60e
PE
374@item @code{strlcat}
375
376@item @code{strlcpy}
377
3d3a2911
SP
378@item @code{strncat}
379
380@item @code{strncpy}
381
382@item @code{swprintf}
383
384@item @code{syslog}
385
386@item @code{ttyname_r}
387
388@item @code{vasprintf}
389
390@item @code{vdprintf}
391
392@item @code{vfprintf}
393
394@item @code{vfwprintf}
395
396@item @code{vprintf}
397
398@item @code{vsnprintf}
399
400@item @code{vsprintf}
401
402@item @code{vswprintf}
403
404@item @code{vsyslog}
405
406@item @code{vwprintf}
407
408@item @code{wcpcpy}
409
410@item @code{wcpncpy}
411
412@item @code{wcrtomb}
413
414@item @code{wcscat}
415
416@item @code{wcscpy}
417
d2fda60e
PE
418@item @code{wcslcat}
419
420@item @code{wcslcpy}
421
3d3a2911
SP
422@item @code{wcsncat}
423
424@item @code{wcsncpy}
425
426@item @code{wcsnrtombs}
427
428@item @code{wcsrtombs}
429
430@item @code{wcstombs}
431
432@item @code{wctomb}
433
434@item @code{wmemcpy}
435
436@item @code{wmemmove}
437
438@item @code{wmempcpy}
439
440@item @code{wmemset}
441
442@item @code{wprintf}
443
444@end itemize
445
446
6e15f3e2
AA
447@node Symbol handling
448@appendixsec Symbol handling in the GNU C Library
449
450@menu
451* 64-bit time symbol handling :: How to handle 64-bit time related
452 symbols in the GNU C Library.
453@end menu
454
455@node 64-bit time symbol handling
456@appendixsubsec 64-bit time symbol handling in the GNU C Library
457
bfb79db4 458With respect to time handling, @glibcadj{} configurations fall in two
6e15f3e2
AA
459classes depending on the value of @code{__TIMESIZE}:
460
461@table @code
462
463@item @code{__TIMESIZE == 32}
464
465These @dfn{dual-time} configurations have both 32-bit and 64-bit time
466support. 32-bit time support provides type @code{time_t} and cannot
467handle dates beyond @dfn{Y2038}. 64-bit time support provides type
468@code{__time64_t} and can handle dates beyond @dfn{Y2038}.
469
470In these configurations, time-related types have two declarations,
471a 64-bit one, and a 32-bit one; and time-related functions generally
472have two definitions: a 64-bit one, and a 32-bit one which is a wrapper
473around the former. Therefore, for every @code{time_t}-related symbol,
474there is a corresponding @code{__time64_t}-related symbol, the name of
475which is usually the 32-bit symbol's name with @code{__} (a double
476underscore) prepended and @code{64} appended. For instance, the
47764-bit-time counterpart of @code{clock_gettime} is
478@code{__clock_gettime64}.
479
480@item @code{__TIMESIZE == 64}
481
482These @dfn{single-time} configurations only have a 64-bit @code{time_t}
483and related functions, which can handle dates beyond 2038-01-19
48403:14:07 (aka @dfn{Y2038}).
485
486In these configurations, time-related types only have a 64-bit
487declaration; and time-related functions only have one 64-bit definition.
488However, for every @code{time_t}-related symbol, there is a
489corresponding @code{__time64_t}-related macro, the name of which is
490derived as in the dual-time configuration case, and which expands to
491the symbol's name. For instance, the macro @code{__clock_gettime64}
492expands to @code{clock_gettime}.
493
494These macros are purely internal to @theglibc{} and exist only so that
495a single definition of the 64-bit time functions can be used on both
496single-time and dual-time configurations, and so that glibc code can
497freely call the 64-bit functions internally in all configurations.
498
499@end table
500
501@c The following paragraph should be removed once external interfaces
502@c get support for both time sizes.
503
504Note: at this point, 64-bit time support in dual-time configurations is
505work-in-progress, so for these configurations, the public API only makes
506the 32-bit time support available. In a later change, the public API
507will allow user code to choose the time size for a given compilation
508unit.
509
51064-bit variants of time-related types or functions are defined for all
511configurations and use 64-bit-time symbol names (for dual-time
512configurations) or macros (for single-time configurations).
513
51432-bit variants of time-related types or functions are defined only for
515dual-time configurations.
516
517Here is an example with @code{localtime}:
518
519Function @code{localtime} is declared in @file{time/time.h} as
520@smallexample
521extern struct tm *localtime (const time_t *__timer) __THROW;
522libc_hidden_proto (localtime)
523@end smallexample
524
525For single-time configurations, @code{__localtime64} is a macro which
526evaluates to @code{localtime}; for dual-time configurations,
527@code{__localtime64} is a function similar to @code{localtime} except
528it uses Y2038-proof types:
529@smallexample
530#if __TIMESIZE == 64
531# define __localtime64 localtime
532#else
533extern struct tm *__localtime64 (const __time64_t *__timer) __THROW;
534libc_hidden_proto (__localtime64)
535#endif
536@end smallexample
537
538(note: type @code{time_t} is replaced with @code{__time64_t} because
539@code{time_t} is not Y2038-proof, but @code{struct tm} is not
540replaced because it is already Y2038-proof.)
541
542The 64-bit-time implementation of @code{localtime} is written as follows
543and is compiled for both dual-time and single-time configuration classes.
544
545@smallexample
546struct tm *
547__localtime64 (const __time64_t *t)
8b18d418 548@{
6e15f3e2 549 return __tz_convert (*t, 1, &_tmbuf);
8b18d418 550@}
6e15f3e2
AA
551libc_hidden_def (__localtime64)
552@end smallexample
553
554The 32-bit-time implementation is a wrapper and is only compiled for
555dual-time configurations:
556
557@smallexample
558#if __TIMESIZE != 64
559
560struct tm *
561localtime (const time_t *t)
8b18d418 562@{
6e15f3e2
AA
563 __time64_t t64 = *t;
564 return __localtime64 (&t64);
8b18d418 565@}
6e15f3e2
AA
566libc_hidden_def (localtime)
567
568#endif
569@end smallexample
570
28f540f4 571@node Porting
1f77f049 572@appendixsec Porting @theglibc{}
28f540f4 573
1f77f049 574@Theglibc{} is written to be easily portable to a variety of
28f540f4
RM
575machines and operating systems. Machine- and operating system-dependent
576functions are well separated to make it easy to add implementations for
577new machines or operating systems. This section describes the layout of
578the library source tree and explains the mechanisms used to select
579machine-dependent code to use.
580
581All the machine-dependent and operating system-dependent files in the
582library are in the subdirectory @file{sysdeps} under the top-level
583library source directory. This directory contains a hierarchy of
584subdirectories (@pxref{Hierarchy Conventions}).
585
586Each subdirectory of @file{sysdeps} contains source files for a
587particular machine or operating system, or for a class of machine or
588operating system (for example, systems by a particular vendor, or all
589machines that use IEEE 754 floating-point format). A configuration
590specifies an ordered list of these subdirectories. Each subdirectory
591implicitly appends its parent directory to the list. For example,
592specifying the list @file{unix/bsd/vax} is equivalent to specifying the
593list @file{unix/bsd/vax unix/bsd unix}. A subdirectory can also specify
594that it implies other subdirectories which are not directly above it in
595the directory hierarchy. If the file @file{Implies} exists in a
596subdirectory, it lists other subdirectories of @file{sysdeps} which are
597appended to the list, appearing after the subdirectory containing the
598@file{Implies} file. Lines in an @file{Implies} file that begin with a
599@samp{#} character are ignored as comments. For example,
0005e54f 600@file{unix/bsd/Implies} contains:
28f540f4
RM
601@smallexample
602# BSD has Internet-related things.
603unix/inet
604@end smallexample
605@noindent
606and @file{unix/Implies} contains:
607@need 300
608@smallexample
609posix
610@end smallexample
611
612@noindent
613So the final list is @file{unix/bsd/vax unix/bsd unix/inet unix posix}.
614
f2ea0f5b
UD
615@file{sysdeps} has a ``special'' subdirectory called @file{generic}. It
616is always implicitly appended to the list of subdirectories, so you
617needn't put it in an @file{Implies} file, and you should not create any
618subdirectories under it intended to be new specific categories.
619@file{generic} serves two purposes. First, the makefiles do not bother
620to look for a system-dependent version of a file that's not in
621@file{generic}. This means that any system-dependent source file must
622have an analogue in @file{generic}, even if the routines defined by that
11bf311e 623file are not implemented on other platforms. Second, the @file{generic}
f2ea0f5b
UD
624version of a system-dependent file is used if the makefiles do not find
625a version specific to the system you're compiling for.
626
627If it is possible to implement the routines in a @file{generic} file in
628machine-independent C, using only other machine-independent functions in
629the C library, then you should do so. Otherwise, make them stubs. A
630@dfn{stub} function is a function which cannot be implemented on a
631particular machine or operating system. Stub functions always return an
632error, and set @code{errno} to @code{ENOSYS} (Function not implemented).
633@xref{Error Reporting}. If you define a stub function, you must place
634the statement @code{stub_warning(@var{function})}, where @var{function}
b830319d 635is the name of your function, after its definition. This causes the
f2ea0f5b
UD
636function to be listed in the installed @code{<gnu/stubs.h>}, and
637makes GNU ld warn when the function is used.
638
cc3fa755
UD
639Some rare functions are only useful on specific systems and aren't
640defined at all on others; these do not appear anywhere in the
641system-independent source code or makefiles (including the
642@file{generic} directory), only in the system-dependent @file{Makefile}
643in the specific system's subdirectory.
28f540f4
RM
644
645If you come across a file that is in one of the main source directories
646(@file{string}, @file{stdio}, etc.), and you want to write a machine- or
647operating system-dependent version of it, move the file into
648@file{sysdeps/generic} and write your new implementation in the
649appropriate system-specific subdirectory. Note that if a file is to be
650system-dependent, it @strong{must not} appear in one of the main source
0005e54f 651directories.
28f540f4
RM
652
653There are a few special files that may exist in each subdirectory of
654@file{sysdeps}:
655
656@comment Blank lines after items make the table look better.
657@table @file
658@item Makefile
659
660A makefile for this machine or operating system, or class of machine or
661operating system. This file is included by the library makefile
662@file{Makerules}, which is used by the top-level makefile and the
663subdirectory makefiles. It can change the variables set in the
664including makefile or add new rules. It can use GNU @code{make}
665conditional directives based on the variable @samp{subdir} (see above) to
666select different sets of variables and rules for different sections of
667the library. It can also set the @code{make} variable
668@samp{sysdep-routines}, to specify extra modules to be included in the
669library. You should use @samp{sysdep-routines} rather than adding
670modules to @samp{routines} because the latter is used in determining
0005e54f 671what to distribute for each subdirectory of the main source tree.
28f540f4
RM
672
673Each makefile in a subdirectory in the ordered list of subdirectories to
674be searched is included in order. Since several system-dependent
675makefiles may be included, each should append to @samp{sysdep-routines}
676rather than simply setting it:
677
678@smallexample
679sysdep-routines := $(sysdep-routines) foo bar
680@end smallexample
681
682@need 1000
683@item Subdirs
684
685This file contains the names of new whole subdirectories under the
686top-level library source tree that should be included for this system.
687These subdirectories are treated just like the system-independent
688subdirectories in the library source tree, such as @file{stdio} and
689@file{math}.
690
691Use this when there are completely new sets of functions and header
692files that should go into the library for the system this subdirectory
693of @file{sysdeps} implements. For example,
694@file{sysdeps/unix/inet/Subdirs} contains @file{inet}; the @file{inet}
695directory contains various network-oriented operations which only make
0005e54f 696sense to put in the library on systems that support the Internet.
28f540f4 697
28f540f4
RM
698@item configure
699
700This file is a shell script fragment to be run at configuration time.
701The top-level @file{configure} script uses the shell @code{.} command to
702read the @file{configure} file in each system-dependent directory
703chosen, in order. The @file{configure} files are often generated from
cb8a6dbd 704@file{configure.ac} files using Autoconf.
28f540f4
RM
705
706A system-dependent @file{configure} script will usually add things to
707the shell variables @samp{DEFS} and @samp{config_vars}; see the
708top-level @file{configure} script for details. The script can check for
709@w{@samp{--with-@var{package}}} options that were passed to the
710top-level @file{configure}. For an option
711@w{@samp{--with-@var{package}=@var{value}}} @file{configure} sets the
712shell variable @w{@samp{with_@var{package}}} (with any dashes in
713@var{package} converted to underscores) to @var{value}; if the option is
714just @w{@samp{--with-@var{package}}} (no argument), then it sets
715@w{@samp{with_@var{package}}} to @samp{yes}.
716
cb8a6dbd 717@item configure.ac
28f540f4
RM
718
719This file is an Autoconf input fragment to be processed into the file
720@file{configure} in this subdirectory. @xref{Introduction,,,
721autoconf.info, Autoconf: Generating Automatic Configuration Scripts},
722for a description of Autoconf. You should write either @file{configure}
cb8a6dbd
MF
723or @file{configure.ac}, but not both. The first line of
724@file{configure.ac} should invoke the @code{m4} macro
28f540f4
RM
725@samp{GLIBC_PROVIDES}. This macro does several @code{AC_PROVIDE} calls
726for Autoconf macros which are used by the top-level @file{configure}
727script; without this, those macros might be invoked again unnecessarily
728by Autoconf.
729@end table
730
731That is the general system for how system-dependencies are isolated.
732@iftex
733The next section explains how to decide what directories in
734@file{sysdeps} to use. @ref{Porting to Unix}, has some tips on porting
735the library to Unix variants.
736@end iftex
737
738@menu
739* Hierarchy Conventions:: The layout of the @file{sysdeps} hierarchy.
740* Porting to Unix:: Porting the library to an average
741 Unix-like system.
742@end menu
743
744@node Hierarchy Conventions
745@appendixsubsec Layout of the @file{sysdeps} Directory Hierarchy
746
747A GNU configuration name has three parts: the CPU type, the
748manufacturer's name, and the operating system. @file{configure} uses
749these to pick the list of system-dependent directories to look for. If
750the @samp{--nfp} option is @emph{not} passed to @file{configure}, the
751directory @file{@var{machine}/fpu} is also used. The operating system
752often has a @dfn{base operating system}; for example, if the operating
68b50604 753system is @samp{Linux}, the base operating system is @samp{unix/sysv}.
28f540f4
RM
754The algorithm used to pick the list of directories is simple:
755@file{configure} makes a list of the base operating system,
756manufacturer, CPU type, and operating system, in that order. It then
757concatenates all these together with slashes in between, to produce a
68b50604
UD
758directory name; for example, the configuration @w{@samp{i686-linux-gnu}}
759results in @file{unix/sysv/linux/i386/i686}. @file{configure} then
28f540f4 760tries removing each element of the list in turn, so
68b50604 761@file{unix/sysv/linux} and @file{unix/sysv} are also tried, among others.
28f540f4
RM
762Since the precise version number of the operating system is often not
763important, and it would be very inconvenient, for example, to have
68b50604 764identical @file{irix6.2} and @file{irix6.3} directories,
28f540f4
RM
765@file{configure} tries successively less specific operating system names
766by removing trailing suffixes starting with a period.
767
768As an example, here is the complete list of directories that would be
644d3857 769tried for the configuration @w{@samp{i686-linux-gnu}}:
28f540f4
RM
770
771@smallexample
68b50604 772sysdeps/i386/elf
68b50604
UD
773sysdeps/unix/sysv/linux/i386
774sysdeps/unix/sysv/linux
775sysdeps/gnu
776sysdeps/unix/common
777sysdeps/unix/mman
778sysdeps/unix/inet
779sysdeps/unix/sysv/i386/i686
780sysdeps/unix/sysv/i386
781sysdeps/unix/sysv
782sysdeps/unix/i386
783sysdeps/unix
784sysdeps/posix
785sysdeps/i386/i686
786sysdeps/i386/i486
787sysdeps/libm-i387/i686
788sysdeps/i386/fpu
789sysdeps/libm-i387
790sysdeps/i386
791sysdeps/wordsize-32
792sysdeps/ieee754
793sysdeps/libm-ieee754
794sysdeps/generic
28f540f4
RM
795@end smallexample
796
797Different machine architectures are conventionally subdirectories at the
798top level of the @file{sysdeps} directory tree. For example,
799@w{@file{sysdeps/sparc}} and @w{@file{sysdeps/m68k}}. These contain
800files specific to those machine architectures, but not specific to any
801particular operating system. There might be subdirectories for
802specializations of those architectures, such as
cf822e3c 803@w{@file{sysdeps/m68k/68020}}. Code which is specific to the
28f540f4
RM
804floating-point coprocessor used with a particular machine should go in
805@w{@file{sysdeps/@var{machine}/fpu}}.
806
807There are a few directories at the top level of the @file{sysdeps}
808hierarchy that are not for particular machine architectures.
809
810@table @file
811@item generic
f2ea0f5b 812As described above (@pxref{Porting}), this is the subdirectory
28f540f4
RM
813that every configuration implicitly uses after all others.
814
815@item ieee754
816This directory is for code using the IEEE 754 floating-point format,
817where the C type @code{float} is IEEE 754 single-precision format, and
818@code{double} is IEEE 754 double-precision format. Usually this
819directory is referred to in the @file{Implies} file in a machine
820architecture-specific directory, such as @file{m68k/Implies}.
821
68b50604
UD
822@item libm-ieee754
823This directory contains an implementation of a mathematical library
824usable on platforms which use @w{IEEE 754} conformant floating-point
825arithmetic.
826
827@item libm-i387
828This is a special case. Ideally the code should be in
829@file{sysdeps/i386/fpu} but for various reasons it is kept aside.
830
28f540f4
RM
831@item posix
832This directory contains implementations of things in the library in
833terms of @sc{POSIX.1} functions. This includes some of the @sc{POSIX.1}
834functions themselves. Of course, @sc{POSIX.1} cannot be completely
835implemented in terms of itself, so a configuration using just
836@file{posix} cannot be complete.
837
838@item unix
839This is the directory for Unix-like things. @xref{Porting to Unix}.
840@file{unix} implies @file{posix}. There are some special-purpose
841subdirectories of @file{unix}:
842
843@table @file
844@item unix/common
845This directory is for things common to both BSD and System V release 4.
846Both @file{unix/bsd} and @file{unix/sysv/sysv4} imply @file{unix/common}.
847
848@item unix/inet
849This directory is for @code{socket} and related functions on Unix systems.
3c20b9b6 850@file{unix/inet/Subdirs} enables the @file{inet} top-level subdirectory.
28f540f4
RM
851@file{unix/common} implies @file{unix/inet}.
852@end table
853
854@item mach
855This is the directory for things based on the Mach microkernel from CMU
a7a93d50 856(including @gnuhurdsystems{}). Other basic operating systems
28f540f4
RM
857(VMS, for example) would have their own directories at the top level of
858the @file{sysdeps} hierarchy, parallel to @file{unix} and @file{mach}.
859@end table
860
861@node Porting to Unix
1f77f049 862@appendixsubsec Porting @theglibc{} to Unix Systems
28f540f4
RM
863
864Most Unix systems are fundamentally very similar. There are variations
865between different machines, and variations in what facilities are
866provided by the kernel. But the interface to the operating system
867facilities is, for the most part, pretty uniform and simple.
868
869The code for Unix systems is in the directory @file{unix}, at the top
870level of the @file{sysdeps} hierarchy. This directory contains
871subdirectories (and subdirectory trees) for various Unix variants.
872
873The functions which are system calls in most Unix systems are
26b4d766 874implemented in assembly code, which is generated automatically from
3c20b9b6
UD
875specifications in files named @file{syscalls.list}. There are several
876such files, one in @file{sysdeps/unix} and others in its subdirectories.
877Some special system calls are implemented in files that are named with a
26b4d766
UD
878suffix of @samp{.S}; for example, @file{_exit.S}. Files ending in
879@samp{.S} are run through the C preprocessor before being fed to the
880assembler.
28f540f4
RM
881
882These files all use a set of macros that should be defined in
883@file{sysdep.h}. The @file{sysdep.h} file in @file{sysdeps/unix}
884partially defines them; a @file{sysdep.h} file in another directory must
885finish defining them for the particular machine and operating system
886variant. See @file{sysdeps/unix/sysdep.h} and the machine-specific
887@file{sysdep.h} implementations to see what these macros are and what
0005e54f 888they should do.
28f540f4 889
3c20b9b6
UD
890The system-specific makefile for the @file{unix} directory
891(@file{sysdeps/unix/Makefile}) gives rules to generate several files
28f540f4
RM
892from the Unix system you are building the library on (which is assumed
893to be the target system you are building the library @emph{for}). All
894the generated files are put in the directory where the object files are
895kept; they should not affect the source tree itself. The files
896generated are @file{ioctls.h}, @file{errnos.h}, @file{sys/param.h}, and
897@file{errlist.c} (for the @file{stdio} section of the library).
898
899@ignore
900@c This section might be a good idea if it is finished,
901@c but there's no point including it as it stands. --rms
902@c @appendixsec Compatibility with Traditional C
903
904@c ??? This section is really short now. Want to keep it? --roland
905
68b50604
UD
906@c It's not anymore true. glibc 2.1 cannot be used with K&R compilers.
907@c --drepper
908
1f77f049
JM
909Although @theglibc{} implements the @w{ISO C} library facilities, you
910@emph{can} use @theglibc{} with traditional, ``pre-ISO'' C
28f540f4 911compilers. However, you need to be careful because the content and
1f77f049 912organization of the @glibcadj{} header files differs from that of
28f540f4
RM
913traditional C implementations. This means you may need to make changes
914to your program in order to get it to compile.
915@end ignore