\input texinfo
@setfilename ld.info
@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-@c 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
+@c 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
@syncodeindex ky cp
@c man begin INCLUDE
@include configdoc.texi
@c (configdoc.texi is generated by the Makefile)
-@include ldver.texi
+@include bfdver.texi
@c man end
@c @smallbook
@c Configure for the generation of man pages
@set UsesEnvVars
@set GENERIC
-@set ARC
@set ARM
-@set D10V
-@set D30V
-@set H8/300
-@set H8/500
+@set H8300
@set HPPA
-@set I370
-@set I80386
-@set I860
@set I960
-@set M32R
@set M68HC11
-@set M680X0
-@set MCORE
-@set MIPS
+@set M68K
@set MMIX
@set MSP430
-@set PDP11
-@set PJ
@set POWERPC
@set POWERPC64
-@set SH
-@set SPARC
-@set TIC54X
-@set V850
-@set VAX
+@set Renesas
+@set SPU
+@set TICOFF
@set WIN32
@set XTENSA
@end ifset
@end format
@end ifinfo
-@ifinfo
-This file documents the @sc{gnu} linker LD version @value{VERSION}.
-
-Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
-2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
+@copying
+This file documents the @sc{gnu} linker LD
+@ifset VERSION_PACKAGE
+@value{VERSION_PACKAGE}
+@end ifset
+version @value{VERSION}.
-@ignore
+Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
+2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
with no Invariant Sections, with no Front-Cover Texts, and with no
Back-Cover Texts. A copy of the license is included in the
section entitled ``GNU Free Documentation License''.
-
-Permission is granted to process this file through Tex and print the
-results, provided the printed document carries copying permission
-notice identical to this one except for the removal of this paragraph
-(this paragraph not being relevant to the printed manual).
-
-@end ignore
-@end ifinfo
+@end copying
@iftex
@finalout
@setchapternewpage odd
@titlepage
@title The GNU linker
@sp 1
-@subtitle @code{ld} version 2
+@subtitle @code{ld}
+@ifset VERSION_PACKAGE
+@subtitle @value{VERSION_PACKAGE}
+@end ifset
@subtitle Version @value{VERSION}
@author Steve Chamberlain
@author Ian Lance Taylor
@vskip 0pt plus 1filll
@c man begin COPYRIGHT
Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001,
-2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
+2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
@end titlepage
@end iftex
+@contents
@c FIXME: Talk about importance of *order* of args, cmds to linker!
@ifnottex
@node Top
@top LD
-This file documents the @sc{gnu} linker ld version @value{VERSION}.
+This file documents the @sc{gnu} linker ld
+@ifset VERSION_PACKAGE
+@value{VERSION_PACKAGE}
+@end ifset
+version @value{VERSION}.
This document is distributed under the terms of the GNU Free
Documentation License. A copy of the license is included in the
@ifset M68HC11
* M68HC11/68HC12:: ld and the Motorola 68HC11 and 68HC12 families
@end ifset
+@ifset M68K
+* M68K:: ld and Motorola 68K family
+@end ifset
@ifset POWERPC
* PowerPC ELF32:: ld and PowerPC 32-bit ELF Support
@end ifset
@ifset POWERPC64
* PowerPC64 ELF64:: ld and PowerPC64 64-bit ELF Support
@end ifset
+@ifset SPU
+* SPU ELF:: ld and SPU ELF Support
+@end ifset
@ifset TICOFF
* TI COFF:: ld and the TI COFF
@end ifset
linker script or the one specified by using @samp{-T}). This feature
permits the linker to link against a file which appears to be an object
or an archive, but actually merely defines some symbol values, or uses
-@code{INPUT} or @code{GROUP} to load other objects. Note that
-specifying a script in this way merely augments the main linker script;
-use the @samp{-T} option to replace the default linker script entirely.
-@xref{Scripts}.
+@code{INPUT} or @code{GROUP} to load other objects. Specifying a
+script in this way merely augments the main linker script, with the
+extra commands placed after the main script; use the @samp{-T} option
+to replace the default linker script entirely, but note the effect of
+the @code{INSERT} command. @xref{Scripts}.
For options whose names are a single letter,
option arguments must either follow the option letter without intervening
function to call.
@cindex archive files, from cmd line
-@kindex -l@var{archive}
-@kindex --library=@var{archive}
-@item -l@var{archive}
-@itemx --library=@var{archive}
-Add archive file @var{archive} to the list of files to link. This
-option may be used any number of times. @command{ld} will search its
-path-list for occurrences of @code{lib@var{archive}.a} for every
-@var{archive} specified.
+@kindex -l@var{namespec}
+@kindex --library=@var{namespec}
+@item -l@var{namespec}
+@itemx --library=@var{namespec}
+Add the archive or object file specified by @var{namespec} to the
+list of files to link. This option may be used any number of times.
+If @var{namespec} is of the form @file{:@var{filename}}, @command{ld}
+will search the library path for a file called @var{filename}, otherise it
+will search the library path for a file called @file{lib@var{namespec}.a}.
On systems which support shared libraries, @command{ld} may also search for
-libraries with extensions other than @code{.a}. Specifically, on ELF
-and SunOS systems, @command{ld} will search a directory for a library with
-an extension of @code{.so} before searching for one with an extension of
-@code{.a}. By convention, a @code{.so} extension indicates a shared
-library.
+files other than @file{lib@var{namespec}.a}. Specifically, on ELF
+and SunOS systems, @command{ld} will search a directory for a library
+called @file{lib@var{namespec}.so} before searching for one called
+@file{lib@var{namespec}.a}. (By convention, a @code{.so} extension
+indicates a shared library.) Note that this behavior does not apply
+to @file{:@var{filename}}, which always specifies a file called
+@var{filename}.
The linker will search an archive only once, at the location where it is
specified on the command line. If the archive defines a symbol which
@item -O @var{level}
If @var{level} is a numeric values greater than zero @command{ld} optimizes
the output. This might take significantly longer and therefore probably
-should only be enabled for the final binary.
+should only be enabled for the final binary. At the moment this
+option only affects ELF shared library generation. Future releases of
+the linker may make more use of this option. Also currently there is
+no difference in the linker's behaviour for different non-zero values
+of this option. Again this may change with future releases.
@kindex -q
@kindex --emit-relocs
@kindex -Bsymbolic-functions
@item -Bsymbolic-functions
When creating a shared library, bind references to global function
-symbols to the definition within the shared library, if any.
+symbols to the definition within the shared library, if any.
This option is only meaningful on ELF platforms which support shared
libraries.
@item --gc-sections
@itemx --no-gc-sections
Enable garbage collection of unused input sections. It is ignored on
-targets that do not support this option. This option is not compatible
-with @samp{-r} or @samp{--emit-relocs}. The default behaviour (of not
+targets that do not support this option. The default behaviour (of not
performing this garbage collection) can be restored by specifying
@samp{--no-gc-sections} on the command line.
+@samp{--gc-sections} decides which input sections are used by
+examining symbols and relocations. The section containing the entry
+symbol and all sections containing symbols undefined on the
+command-line will be kept, as will sections containing symbols
+referenced by dynamic objects. Note that when building shared
+libraries, the linker must assume that any visible symbol is
+referenced. Once this initial set of sections has been determined,
+the linker recursively marks as used any section referenced by their
+relocations. See @samp{--entry} and @samp{--undefined}.
+
+This option can be set when doing a partial link (enabled with option
+@samp{-r}). In this case the root of symbols kept must be explicitely
+specified either by an @samp{--entry} or @samp{--undefined} option or by
+a @code{ENTRY} command in the linker script.
+
@kindex --print-gc-sections
@kindex --no-print-gc-sections
@cindex garbage collection
have taken some special action that ensures that the linker errors are
inappropriate.
+@kindex --no-warn-search-mismatch
+@item --no-warn-search-mismatch
+Normally @command{ld} will give a warning if it finds an incompatible
+library during a library search. This option silences the warning.
+
@kindex --no-whole-archive
@item --no-whole-archive
Turn off the effect of the @option{--whole-archive} option for subsequent
by native linkers and cross linkers which have been configured with
the @option{--with-sysroot} option.
@item
-On an ELF system, if the @option{-rpath} and @code{rpath-link} options
-were not used, search the contents of the environment variable
-@code{LD_RUN_PATH}. It is for the native linker only.
+On an ELF system, for native linkers, if the @option{-rpath} and
+@option{-rpath-link} options were not used, search the contents of the
+environment variable @code{LD_RUN_PATH}.
@item
On SunOS, if the @option{-rpath} option was not used, search any
directories specified using @option{-L} options.
@item
-For a native linker, the contents of the environment variable
-@code{LD_LIBRARY_PATH}.
+For a native linker, the search the contents of the environment
+variable @code{LD_LIBRARY_PATH}.
@item
For a native ELF linker, the directories in @code{DT_RUNPATH} or
@code{DT_RPATH} of a shared library are searched for shared
@item --sort-common
@kindex --sort-common
-This option tells @command{ld} to sort the common symbols by size when it
-places them in the appropriate output sections. First come all the one
-byte symbols, then all the two byte, then all the four byte, and then
-everything else. This is to prevent gaps between symbols due to
-alignment constraints.
+This option tells @command{ld} to sort the common symbols by alignment when
+it places them in the appropriate output sections. First come all the
+sixteen-byte aligned symbols, then all the eight-byte, then all the
+four-byte, then all the two-byte, and then everything else. This is to
+prevent gaps between symbols due to alignment constraints.
@kindex --sort-section name
@item --sort-section name
The @option{--reduce-memory-overheads} switch may be also be used to
enable other tradeoffs in future versions of the linker.
+@kindex --build-id
+@kindex --build-id=@var{style}
+@item --build-id
+@itemx --build-id=@var{style}
+Request creation of @code{.note.gnu.build-id} ELF note section.
+The contents of the note are unique bits identifying this linked
+file. @var{style} can be @code{uuid} to use 128 random bits,
+@code{sha1} to use a 160-bit @sc{SHA1} hash on the normative
+parts of the output contents, @code{md5} to use a 128-bit
+@sc{MD5} hash on the normative parts of the output contents, or
+@code{0x@var{hexstring}} to use a chosen bit string specified as
+an even number of hexadecimal digits (@code{-} and @code{:}
+characters between digit pairs are ignored). If @var{style} is
+omitted, @code{sha1} is used.
+
+The @code{md5} and @code{sha1} styles produces an identifier
+that is always the same in an identical output file, but will be
+unique among all nonidentical output files. It is not intended
+to be compared as a checksum for the file's contents. A linked
+file may be changed later by other tools, but the build ID bit
+string identifying the original linked file does not change.
+
+Passing @code{none} for @var{style} disables the setting from any
+@code{--build-id} options earlier on the command line.
@end table
@c man end
@kindex --heap
@item --heap @var{reserve}
@itemx --heap @var{reserve},@var{commit}
-Specify the amount of memory to reserve (and optionally commit) to be
-used as heap for this program. The default is 1Mb reserved, 4K
+Specify the number of bytes of memory to reserve (and optionally commit)
+to be used as heap for this program. The default is 1Mb reserved, 4K
committed.
[This option is specific to the i386 PE targeted port of the linker]
to be made writable. This does not conform to the PE-COFF format
specification published by Microsoft.
+Note - use of the 'auto-import' extension will also cause read only
+data which would normally be placed into the .rdata section to be
+placed into the .data section instead. This is in order to work
+around a problem with consts that is described here:
+http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
+
Using 'auto-import' generally will 'just work' -- but sometimes you may
see this message:
This message occurs when some (sub)expression accesses an address
ultimately given by the sum of two constants (Win32 import tables only
-allow one). Instances where this may occur include accesses to member
-fields of struct variables imported from a DLL, as well as using a
-constant index into an array variable imported from a DLL. Any
+allow one). Instances where this may occur include accesses to member
+fields of struct variables imported from a DLL, as well as using a
+constant index into an array variable imported from a DLL. Any
multiword variable (arrays, structs, long long, etc) may trigger
this error condition. However, regardless of the exact data type
of the offending exported variable, ld will always detect it, issue
of adjusting references in your client code for runtime environment, so
this method works only when runtime environment supports this feature.
-A second solution is to force one of the 'constants' to be a variable --
-that is, unknown and un-optimizable at compile time. For arrays,
-there are two possibilities: a) make the indexee (the array's address)
+A second solution is to force one of the 'constants' to be a variable --
+that is, unknown and un-optimizable at compile time. For arrays,
+there are two possibilities: a) make the indexee (the array's address)
a variable, or b) make the 'constant' index a variable. Thus:
@example
extern type extern_array[];
-extern_array[1] -->
+extern_array[1] -->
@{ volatile type *t=extern_array; t[1] @}
@end example
@example
extern type extern_array[];
-extern_array[1] -->
+extern_array[1] -->
@{ volatile int t=1; extern_array[t] @}
@end example
-For structs (and most other multiword data types) the only option
+For structs (and most other multiword data types) the only option
is to make the struct itself (or the long long, or the ...) variable:
@example
extern struct s extern_struct;
-extern_struct.field -->
+extern_struct.field -->
@{ volatile struct s *t=&extern_struct; t->field @}
@end example
@end example
A third method of dealing with this difficulty is to abandon
-'auto-import' for the offending symbol and mark it with
+'auto-import' for the offending symbol and mark it with
@code{__declspec(dllimport)}. However, in practise that
requires using compile-time #defines to indicate whether you are
-building a DLL, building client code that will link to the DLL, or
-merely building/linking to a static library. In making the choice
-between the various methods of resolving the 'direct address with
+building a DLL, building client code that will link to the DLL, or
+merely building/linking to a static library. In making the choice
+between the various methods of resolving the 'direct address with
constant offset' problem, you should consider typical real-world usage:
Original:
@}
@end example
-A fourth way to avoid this problem is to re-code your
+A fourth way to avoid this problem is to re-code your
library to use a functional interface rather than a data interface
for the offending variables (e.g. set_foo() and get_foo() accessor
functions).
@kindex --disable-auto-import
@item --disable-auto-import
-Do not attempt to do sophisticated linking of @code{_symbol} to
+Do not attempt to do sophisticated linking of @code{_symbol} to
@code{__imp__symbol} for DATA imports from DLLs.
[This option is specific to the i386 PE targeted port of the linker]
If your code contains expressions described in --enable-auto-import section,
that is, DATA imports from DLL with non-zero offset, this switch will create
a vector of 'runtime pseudo relocations' which can be used by runtime
-environment to adjust references to such data in your client code.
+environment to adjust references to such data in your client code.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --disable-runtime-pseudo-reloc
@kindex --stack
@item --stack @var{reserve}
@itemx --stack @var{reserve},@var{commit}
-Specify the amount of memory to reserve (and optionally commit) to be
-used as stack for this program. The default is 2Mb reserved, 4K
+Specify the number of bytes of memory to reserve (and optionally commit)
+to be used as stack for this program. The default is 2Mb reserved, 4K
committed.
[This option is specific to the i386 PE targeted port of the linker]
@c man end
@end ifset
+@ifset M68K
+@subsection Options specific to Motorola 68K target
+
+@c man begin OPTIONS
+
+The following options are supported to control handling of GOT generation
+when linking for 68K targets.
+
+@table @gcctabopt
+
+@kindex --got
+@item --got=@var{type}
+This option tells the linker which GOT generation scheme to use.
+@var{type} should be one of @samp{single}, @samp{negative},
+@samp{multigot} or @samp{target}. For more information refer to the
+Info entry for @file{ld}.
+
+@end table
+
+@c man end
+@end ifset
+
@ifset UsesEnvVars
@node Environment
@section Environment Variables
command-line option: to make @code{ld} omit the assignment of addresses
to common symbols even for a non-relocatable output file.
+@item INSERT [ AFTER | BEFORE ] @var{output_section}
+@kindex INSERT
+@cindex insert user script into default script
+This command is typically used in a script specified by @samp{-T} to
+augment the default @code{SECTIONS} with, for example, overlays. It
+inserts all prior linker script statements after (or before)
+@var{output_section}, and also causes @samp{-T} to not override the
+default linker script. The exact insertion point is as for orphan
+sections. @xref{Location Counter}. The insertion happens after the
+linker has mapped input sections to output sections. Prior to the
+insertion, since @samp{-T} scripts are parsed before the default
+linker script, statements in the @samp{-T} script occur before the
+default linker script statements in the internal linker representation
+of the script. In particular, input section assignments will be made
+to @samp{-T} output sections before those in the default script. Here
+is an example of how a @samp{-T} script using @code{INSERT} might look:
+
+@smallexample
+SECTIONS
+@{
+ OVERLAY :
+ @{
+ .ov1 @{ ov1*(.text) @}
+ .ov2 @{ ov2*(.text) @}
+ @}
+@}
+INSERT AFTER .text;
+@end smallexample
+
@item NOCROSSREFS(@var{section} @var{section} @dots{})
@kindex NOCROSSREFS(@var{sections})
@cindex cross references
@smallexample
@group
extern char start_of_ROM, end_of_ROM, start_of_FLASH;
-
+
memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);
@end group
@end smallexample
match all files except the ones specified in the EXCLUDE_FILE list. For
example:
@smallexample
-(*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors))
+*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
@end smallexample
will cause all .ctors sections from all files except @file{crtend.o} and
@file{otherfile.o} to be included.
It will sort the input sections by alignment first, then by name if 2
sections have the same alignment.
@item
-@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
+@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
treated the same as @code{SORT_BY_NAME} (wildcard section pattern).
@item
@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern))
NOCROSSREFS}.
For each section within the @code{OVERLAY}, the linker automatically
-defines two symbols. The symbol @code{__load_start_@var{secname}} is
+provides two symbols. The symbol @code{__load_start_@var{secname}} is
defined as the starting load address of the section. The symbol
@code{__load_stop_@var{secname}} is defined as the final load address of
the section. Any characters within @var{secname} which are not legal
This will define both @samp{.text0} and @samp{.text1} to start at
address 0x1000. @samp{.text0} will be loaded at address 0x4000, and
@samp{.text1} will be loaded immediately after @samp{.text0}. The
-following symbols will be defined: @code{__load_start_text0},
+following symbols will be defined if referenced: @code{__load_start_text0},
@code{__load_stop_text0}, @code{__load_start_text1},
@code{__load_stop_text1}.
@smallexample
@group
.text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
- __load_start_text0 = LOADADDR (.text0);
- __load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0);
+ PROVIDE (__load_start_text0 = LOADADDR (.text0));
+ PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0));
.text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
- __load_start_text1 = LOADADDR (.text1);
- __load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1);
+ PROVIDE (__load_start_text1 = LOADADDR (.text1));
+ PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1));
. = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
@end group
@end smallexample
region, the linker will issue an error message.
It is possible to access the origin and length of a memory in an
-expression via the @code{ORIGIN(@var{memory})} and
+expression via the @code{ORIGIN(@var{memory})} and
@code{LENGTH(@var{memory})} functions:
@smallexample
@group
- _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
+ _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
@end group
@end smallexample
VERS_2.0 @{
bar1; bar2;
- extern "C++" @{
+ extern "C++" @{
ns::*;
"int f(int, double)";
- @}
+ @}
@} VERS_1.2;
@end smallexample
VERSION extern "lang" @{ version-script-commands @}
@end smallexample
-The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
+The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
The linker will iterate over the list of symbols at the link time and
demangle them according to @samp{lang} before matching them to the
patterns specified in @samp{version-script-commands}.
For ELF targets, the attribute of the section includes section type as
well as section flag.
+If an orphaned section's name is representable as a C identifier then
+the linker will automatically @xref{PROVIDE} two symbols:
+__start_SECNAME and __end_SECNAME, where SECNAME is the name of the
+section. These indicate the start address and end address of the
+orphaned section respectively. Note: most section names are not
+representable as C identifiers because they contain a @samp{.}
+character.
+
@node Location Counter
@subsection The Location Counter
@kindex .
The builtin function @code{NEXT} is closely related to @code{ALIGN}.
+@item ALIGNOF(@var{section})
+@kindex ALIGNOF(@var{section})
+@cindex section alignment
+Return the alignment in bytes of the named @var{section}, if that section has
+been allocated. If the section has not been allocated when this is
+evaluated, the linker will report an error. In the following example,
+the alignment of the @code{.output} section is stored as the first
+value in that section.
+@smallexample
+@group
+SECTIONS@{ @dots{}
+ .output @{
+ LONG (ALIGNOF (.output))
+ @dots{}
+ @}
+@dots{} @}
+@end group
+@end smallexample
+
@item BLOCK(@var{exp})
@kindex BLOCK(@var{exp})
This is a synonym for @code{ALIGN}, for compatibility with older linker
@ifset HPPA
* HPPA ELF32:: @command{ld} and HPPA 32-bit ELF
@end ifset
+@ifset M68K
+* M68K:: @command{ld} and the Motorola 68K family
+@end ifset
@ifset MMIX
* MMIX:: @command{ld} and MMIX
@end ifset
@ifset POWERPC64
* PowerPC64 ELF64:: @command{ld} and PowerPC64 64-bit ELF Support
@end ifset
+@ifset SPU
+* SPU ELF:: @command{ld} and SPU ELF Support
+@end ifset
@ifset TICOFF
* TI COFF:: @command{ld} and TI COFF
@end ifset
top page of memory).
@item bit manipulation instructions
-@command{ld} finds all bit manipulation instructions like @code{band, bclr,
+@command{ld} finds all bit manipulation instructions like @code{band, bclr,
biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor}
-which use 32 bit and 16 bit absolute address form, but refer to the top
+which use 32 bit and 16 bit absolute address form, but refer to the top
page of memory, and changes them to use the 8 bit address form.
(That is: the linker turns @samp{bset #xx:3,@code{@@}@var{aa}:32} into
-@samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
+@samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
the top page of memory).
@item system control instructions
-@command{ld} finds all @code{ldc.w, stc.w} instructions which use the
-32 bit absolute address form, but refer to the top page of memory, and
+@command{ld} finds all @code{ldc.w, stc.w} instructions which use the
+32 bit absolute address form, but refer to the top page of memory, and
changes them to use 16 bit address form.
(That is: the linker turns @samp{ldc.w @code{@@}@var{aa}:32,ccr} into
-@samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
+@samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
the top page of memory).
@end table
@cindex trampoline generation on M68HC12
For 68HC11 and 68HC12, @command{ld} can generate trampoline code to
call a far function using a normal @code{jsr} instruction. The linker
-will also change the relocation to some far function to use the
+will also change the relocation to some far function to use the
trampoline address instead of the function address. This is typically the
case when a pointer to a function is taken. The pointer will in fact
point to the function trampoline.
In the former case, the switch should not be used, and @samp{R_ARM_V4BX}
relocations are ignored.
+@cindex FIX_V4BX_INTERWORKING
+@kindex --fix-v4bx-interworking
+Replace @code{BX rM} instructions identified by @samp{R_ARM_V4BX}
+relocations with a branch to the following veneer:
+
+@smallexample
+TST rM, #1
+MOVEQ PC, rM
+BX Rn
+@end smallexample
+
+This allows generation of libraries/applications that work on ARMv4 cores
+and are still interworking safe. Note that the above veneer clobbers the
+condition flags, so may cause incorrect progrm behavior in rare cases.
+
@cindex USE_BLX
@kindex --use-blx
The @samp{--use-blx} switch enables the linker to use ARM/Thumb
This option is enabled implicitly for SymbianOS, so there is no need to
specify it if you are using that target.
+@cindex VFP11_DENORM_FIX
+@kindex --vfp11-denorm-fix
+The @samp{--vfp11-denorm-fix} switch enables a link-time workaround for a
+bug in certain VFP11 coprocessor hardware, which sometimes allows
+instructions with denorm operands (which must be handled by support code)
+to have those operands overwritten by subsequent instructions before
+the support code can read the intended values.
+
+The bug may be avoided in scalar mode if you allow at least one
+intervening instruction between a VFP11 instruction which uses a register
+and another instruction which writes to the same register, or at least two
+intervening instructions if vector mode is in use. The bug only affects
+full-compliance floating-point mode: you do not need this workaround if
+you are using "runfast" mode. Please contact ARM for further details.
+
+If you know you are using buggy VFP11 hardware, you can
+enable this workaround by specifying the linker option
+@samp{--vfp-denorm-fix=scalar} if you are using the VFP11 scalar
+mode only, or @samp{--vfp-denorm-fix=vector} if you are using
+vector mode (the latter also works for scalar code). The default is
+@samp{--vfp-denorm-fix=none}.
+
+If the workaround is enabled, instructions are scanned for
+potentially-troublesome sequences, and a veneer is created for each
+such sequence which may trigger the erratum. The veneer consists of the
+first instruction of the sequence and a branch back to the subsequent
+instruction. The original instruction is then replaced with a branch to
+the veneer. The extra cycles required to call and return from the veneer
+are sufficient to avoid the erratum in both the scalar and vector cases.
+
+@cindex NO_ENUM_SIZE_WARNING
+@kindex --no-enum-size-warning
+The @option{--no-enum-size-warning} switch prevents the linker from
+warning when linking object files that specify incompatible EABI
+enumeration size attributes. For example, with this switch enabled,
+linking of an object file using 32-bit enumeration values with another
+using enumeration values fitted into the smallest possible space will
+not be diagnosed.
+
+@cindex PIC_VENEER
+@kindex --pic-veneer
+The @samp{--pic-veneer} switch makes the linker use PIC sequences for
+ARM/Thumb interworking veneers, even if the rest of the binary
+is not PIC. This avoids problems on uClinux targets where
+@samp{--emit-relocs} is used to generate relocatable binaries.
+
+@cindex STUB_GROUP_SIZE
+@kindex --stub-group-size=@var{N}
+The linker will automatically generate and insert small sequences of
+code into a linked ARM ELF executable whenever an attempt is made to
+perform a function call to a symbol that is too far away. The
+placement of these sequences of instructions - called stubs - is
+controlled by the command line option @option{--stub-group-size=N}.
+The placement is important because a poor choice can create a need for
+duplicate stubs, increasing the code sizw. The linker will try to
+group stubs together in order to reduce interruptions to the flow of
+code, but it needs guidance as to how big these groups should be and
+where they should be placed.
+
+The value of @samp{N}, the parameter to the
+@option{--stub-group-size=} option controls where the stub groups are
+placed. If it is negative then all stubs are placed before the first
+branch that needs them. If it is positive then the stubs can be
+placed either before or after the branches that need them. If the
+value of @samp{N} is 1 (either +1 or -1) then the linker will choose
+exactly where to place groups of stubs, using its built in heuristics.
+A value of @samp{N} greater than 1 (or smaller than -1) tells the
+linker that a single group of stubs can service at most @samp{N} bytes
+from the input sections.
+
+The default, if @option{--stub-group-size=} is not specified, is
+@samp{N = +1}.
+
@ifclear GENERIC
@lowersections
@end ifclear
@end ifclear
@end ifset
+@ifset M68K
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node M68K
+@section @command{ld} and the Motorola 68K family
+
+@cindex Motorola 68K GOT generation
+@kindex --got=@var{type}
+The @samp{--got=@var{type}} option lets you choose the GOT generation scheme.
+The choices are @samp{single}, @samp{negative}, @samp{multigot} and
+@samp{target}. When @samp{target} is selected the linker chooses
+the default GOT generation scheme for the current target.
+@samp{single} tells the linker to generate a single GOT with
+entries only at non-negative offsets.
+@samp{negative} instructs the linker to generate a single GOT with
+entries at both negative and positive offsets. Not all environments
+support such GOTs.
+@samp{multigot} allows the linker to generate several GOTs in the
+output file. All GOT references from a single input object
+file access the same GOT, but references from different input object
+files might access different GOTs. Not all environments support such GOTs.
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
@ifset MMIX
@ifclear GENERIC
@raisesections
Defines an information memory section (if applicable). Any code in
this section will be uploaded to the MPU.
-@item @samp{.infomemnobits}
+@item @samp{.infomemnobits}
This is the same as the @samp{.infomem} section except that any code
in this section will not be uploaded to the MPU.
@item @samp{.noinit}
Denotes a portion of RAM located above @samp{.bss} section.
-The last two sections are used by gcc.
+The last two sections are used by gcc.
@end table
@ifclear GENERIC
compiled with @samp{-msecure-plt}. @samp{--bss-plt} forces the old
BSS PLT (and GOT layout) which can give slightly better performance.
+@kindex --secure-plt
+@item --secure-plt
+@command{ld} will use the new PLT and GOT layout if it is linking new
+@samp{-fpic} or @samp{-fPIC} code, but does not do so automatically
+when linking non-PIC code. This option requests the new PLT and GOT
+layout. A warning will be given if some object file requires the old
+style BSS PLT.
+
@cindex PowerPC GOT
@kindex --sdata-got
@item --sdata-got
@item --no-opd-optimize
PowerPC64 @command{ld} normally removes @code{.opd} section entries
corresponding to deleted link-once functions, or functions removed by
-the action of @samp{--gc-sections} or linker scrip @code{/DISCARD/}.
+the action of @samp{--gc-sections} or linker script @code{/DISCARD/}.
Use this option to disable @code{.opd} optimization.
@cindex PowerPC64 OPD spacing
@end ifclear
@end ifset
+@ifset SPU
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node SPU ELF
+@section @command{ld} and SPU ELF Support
+
+@cindex SPU ELF options
+@table @option
+
+@cindex SPU plugins
+@kindex --plugin
+@item --plugin
+This option marks an executable as a PIC plugin module.
+
+@cindex SPU overlays
+@kindex --no-overlays
+@item --no-overlays
+Normally, @command{ld} recognizes calls to functions within overlay
+regions, and redirects such calls to an overlay manager via a stub.
+@command{ld} also provides a built-in overlay manager. This option
+turns off all this special overlay handling.
+
+@cindex SPU overlay stub symbols
+@kindex --emit-stub-syms
+@item --emit-stub-syms
+This option causes @command{ld} to label overlay stubs with a local
+symbol that encodes the stub type and destination.
+
+@cindex SPU extra overlay stubs
+@kindex --extra-overlay-stubs
+@item --extra-overlay-stubs
+This option causes @command{ld} to add overlay call stubs on all
+function calls out of overlay regions. Normally stubs are not added
+on calls to non-overlay regions.
+
+@cindex SPU local store size
+@kindex --local-store=lo:hi
+@item --local-store=lo:hi
+@command{ld} usually checks that a final executable for SPU fits in
+the address range 0 to 256k. This option may be used to change the
+range. Disable the check entirely with @option{--local-store=0:0}.
+
+@cindex SPU
+@kindex --stack-analysis
+@item --stack-analysis
+SPU local store space is limited. Over-allocation of stack space
+unnecessarily limits space available for code and data, while
+under-allocation results in runtime failures. If given this option,
+@command{ld} will provide an estimate of maximum stack usage.
+@command{ld} does this by examining symbols in code sections to
+determine the extents of functions, and looking at function prologues
+for stack adjusting instructions. A call-graph is created by looking
+for relocations on branch instructions. The graph is then searched
+for the maximum stack usage path. Note that this analysis does not
+find calls made via function pointers, and does not handle recursion
+and other cycles in the call graph. Stack usage may be
+under-estimated if your code makes such calls. Also, stack usage for
+dynamic allocation, e.g. alloca, will not be detected. If a link map
+is requested, detailed information about each function's stack usage
+and calls will be given.
+
+@cindex SPU
+@kindex --emit-stack-syms
+@item --emit-stack-syms
+This option, if given along with @option{--stack-analysis} will result
+in @command{ld} emitting stack sizing symbols for each function.
+These take the form @code{__stack_<function_name>} for global
+functions, and @code{__stack_<number>_<function_name>} for static
+functions. @code{<number>} is the section id in hex. The value of
+such symbols is the stack requirement for the corresponding function.
+The symbol size will be zero, type @code{STT_NOTYPE}, binding
+@code{STB_LOCAL}, and section @code{SHN_ABS}.
+@end table
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
@ifset TICOFF
@ifclear GENERIC
@raisesections
@node WIN32
@section @command{ld} and WIN32 (cygwin/mingw)
-This section describes some of the win32 specific @command{ld} issues.
+This section describes some of the win32 specific @command{ld} issues.
See @ref{Options,,Command Line Options} for detailed description of the
command line options mentioned here.
@table @emph
-@cindex import libraries
-@item import libraries
+@cindex import libraries
+@item import libraries
The standard Windows linker creates and uses so-called import
libraries, which contains information for linking to dll's. They are
regular static archives and are handled as any other static
support for creating such libraries provided with the
@samp{--out-implib} command line option.
-@item exporting DLL symbols
-@cindex exporting DLL symbols
+@item exporting DLL symbols
+@cindex exporting DLL symbols
The cygwin/mingw @command{ld} has several ways to export symbols for dll's.
@table @emph
@item --exclude-libs
@end itemize
-If, however, @samp{--export-all-symbols} is not given explicitly on the
+If, however, @samp{--export-all-symbols} is not given explicitly on the
command line, then the default auto-export behavior will be @emph{disabled}
if either of the following are true:
@item Any symbol in any object file was marked with the __declspec(dllexport) attribute.
@end itemize
-@item using a DEF file
-@cindex using a DEF file
+@item using a DEF file
+@cindex using a DEF file
Another way of exporting symbols is using a DEF file. A DEF file is
an ASCII file containing definitions of symbols which should be
exported when a dll is created. Usually it is named @samp{<dll
_bar = bar
another_foo = abc.dll.afoo
var1 DATA
-@end example
+@end example
This example defines a DLL with a non-default base address and five
symbols in the export table. The third exported symbol @code{_bar} is an
When the .DEF file is used to build an application, rather than a
library, the @code{NAME <name>} command should be used instead of
@code{LIBRARY}. If @samp{<name>} does not include a suffix, the default
-executable suffix, @samp{.EXE} is appended.
+executable suffix, @samp{.EXE} is appended.
With either @code{LIBRARY <name>} or @code{NAME <name>} the optional
specification @code{BASE = <number>} may be used to specify a
-non-default base address for the image.
+non-default base address for the image.
If neither @code{LIBRARY <name>} nor @code{NAME <name>} is specified,
or they specify an empty string, the internal name is the same as the
( ( ( <name1> [ = <name2> ] )
| ( <name1> = <module-name> . <external-name>))
[ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] ) *
-@end example
+@end example
Declares @samp{<name1>} as an exported symbol from the DLL, or declares
@samp{<name1>} as an exported alias for @samp{<name2>}; or declares
symbol can still be imported using the @code{LoadLibrary/GetProcAddress}
API at runtime or by by using the GNU ld extension of linking directly to
the DLL without an import library.
-
+
See ld/deffilep.y in the binutils sources for the full specification of
other DEF file statements
the @samp{--export-all-symbols} option is also used.
Note that object files that wish to access these symbols must @emph{not}
-decorate them with dllexport. Instead, they should use dllimport,
+decorate them with dllexport. Instead, they should use dllimport,
instead:
@example
__declspec(dllimport) void a_function(int with_args)
@end example
-This complicates the structure of library header files, because
-when included by the library itself the header must declare the
+This complicates the structure of library header files, because
+when included by the library itself the header must declare the
variables and functions as dllexport, but when included by client
code the header must declare them as dllimport. There are a number
-of idioms that are typically used to do this; often client code can
+of idioms that are typically used to do this; often client code can
omit the __declspec() declaration completely. See
@samp{--enable-auto-import} and @samp{automatic data imports} for more
information.
-@end table
+@end table
@cindex automatic data imports
@item automatic data imports
The standard Windows dll format supports data imports from dlls only
by adding special decorations (dllimport/dllexport), which let the
compiler produce specific assembler instructions to deal with this
-issue. This increases the effort necessary to port existing Un*x
+issue. This increases the effort necessary to port existing Un*x
code to these platforms, especially for large
c++ libraries and applications. The auto-import feature, which was
-initially provided by Paul Sokolovsky, allows one to omit the
+initially provided by Paul Sokolovsky, allows one to omit the
decorations to achieve a behavior that conforms to that on POSIX/Un*x
-platforms. This feature is enabled with the @samp{--enable-auto-import}
+platforms. This feature is enabled with the @samp{--enable-auto-import}
command-line option, although it is enabled by default on cygwin/mingw.
The @samp{--enable-auto-import} option itself now serves mainly to
suppress any warnings that are ordinarily emitted when linked objects
trigger the feature's use.
-auto-import of variables does not always work flawlessly without
+auto-import of variables does not always work flawlessly without
additional assistance. Sometimes, you will see this message
-"variable '<var>' can't be auto-imported. Please read the
+"variable '<var>' can't be auto-imported. Please read the
documentation for ld's @code{--enable-auto-import} for details."
-The @samp{--enable-auto-import} documentation explains why this error
-occurs, and several methods that can be used to overcome this difficulty.
-One of these methods is the @emph{runtime pseudo-relocs} feature, described
+The @samp{--enable-auto-import} documentation explains why this error
+occurs, and several methods that can be used to overcome this difficulty.
+One of these methods is the @emph{runtime pseudo-relocs} feature, described
below.
@cindex runtime pseudo-relocation
-For complex variables imported from DLLs (such as structs or classes),
-object files typically contain a base address for the variable and an
-offset (@emph{addend}) within the variable--to specify a particular
-field or public member, for instance. Unfortunately, the runtime loader used
-in win32 environments is incapable of fixing these references at runtime
+For complex variables imported from DLLs (such as structs or classes),
+object files typically contain a base address for the variable and an
+offset (@emph{addend}) within the variable--to specify a particular
+field or public member, for instance. Unfortunately, the runtime loader used
+in win32 environments is incapable of fixing these references at runtime
without the additional information supplied by dllimport/dllexport decorations.
-The standard auto-import feature described above is unable to resolve these
+The standard auto-import feature described above is unable to resolve these
references.
-The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
-be resolved without error, while leaving the task of adjusting the references
-themselves (with their non-zero addends) to specialized code provided by the
-runtime environment. Recent versions of the cygwin and mingw environments and
-compilers provide this runtime support; older versions do not. However, the
-support is only necessary on the developer's platform; the compiled result will
+The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
+be resolved without error, while leaving the task of adjusting the references
+themselves (with their non-zero addends) to specialized code provided by the
+runtime environment. Recent versions of the cygwin and mingw environments and
+compilers provide this runtime support; older versions do not. However, the
+support is only necessary on the developer's platform; the compiled result will
run without error on an older system.
-@samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
-enabled as needed.
+@samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
+enabled as needed.
@cindex direct linking to a dll
@item direct linking to a dll
including data symbols, to a dll without the usage of any import
libraries. This is much faster and uses much less memory than does the
traditional import library method, especially when linking large
-libraries or applications. When @command{ld} creates an import lib, each
-function or variable exported from the dll is stored in its own bfd, even
-though a single bfd could contain many exports. The overhead involved in
+libraries or applications. When @command{ld} creates an import lib, each
+function or variable exported from the dll is stored in its own bfd, even
+though a single bfd could contain many exports. The overhead involved in
storing, loading, and processing so many bfd's is quite large, and explains the
-tremendous time, memory, and storage needed to link against particularly
+tremendous time, memory, and storage needed to link against particularly
large or complex libraries when using import libs.
-Linking directly to a dll uses no extra command-line switches other than
+Linking directly to a dll uses no extra command-line switches other than
@samp{-L} and @samp{-l}, because @command{ld} already searches for a number
-of names to match each library. All that is needed from the developer's
+of names to match each library. All that is needed from the developer's
perspective is an understanding of this search, in order to force ld to
select the dll instead of an import library.
before moving on to the next directory in the search path.
-(*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
-where @samp{<prefix>} is set by the @command{ld} option
-@samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
-file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
+(*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
+where @samp{<prefix>} is set by the @command{ld} option
+@samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
+file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
@samp{cygxxx.dll}.
-Other win32-based unix environments, such as mingw or pw32, may use other
-@samp{<prefix>}es, although at present only cygwin makes use of this feature. It
+Other win32-based unix environments, such as mingw or pw32, may use other
+@samp{<prefix>}es, although at present only cygwin makes use of this feature. It
was originally intended to help avoid name conflicts among dll's built for the
various win32/un*x environments, so that (for example) two versions of a zlib dll
could coexist on the same machine.
cygxxx.dll
lib/
libxxx.dll.a (in case of dll's)
- libxxx.a (in case of static archive)
+ libxxx.a (in case of static archive)
@end example
-Linking directly to a dll without using the import library can be
-done two ways:
+Linking directly to a dll without using the import library can be
+done two ways:
1. Use the dll directly by adding the @samp{bin} path to the link line
@example
gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx
-@end example
+@end example
However, as the dll's often have version numbers appended to their names
(@samp{cygncurses-5.dll}) this will often fail, unless one specifies
@example
ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a]
-@end example
+@end example
Then you can link without any make environment changes.
@example
gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx
-@end example
+@end example
This technique also avoids the version number problems, because the following is
perfectly legal
bin/
cygxxx-5.dll
lib/
- libxxx.dll.a -> ../bin/cygxxx-5.dll
+ libxxx.dll.a -> ../bin/cygxxx-5.dll
@end example
Linking directly to a dll without using an import lib will work
stdcall-decorated assembly names.
So, import libs are not going away. But the ability to replace
-true import libs with a simple symbolic link to (or a copy of)
-a dll, in many cases, is a useful addition to the suite of tools
-binutils makes available to the win32 developer. Given the
+true import libs with a simple symbolic link to (or a copy of)
+a dll, in many cases, is a useful addition to the suite of tools
+binutils makes available to the win32 developer. Given the
massive improvements in memory requirements during linking, storage
requirements, and linking speed, we expect that many developers
will soon begin to use this feature whenever possible.
-@item symbol aliasing
+@item symbol aliasing
@table @emph
-@item adding additional names
-Sometimes, it is useful to export symbols with additional names.
+@item adding additional names
+Sometimes, it is useful to export symbols with additional names.
A symbol @samp{foo} will be exported as @samp{foo}, but it can also be
exported as @samp{_foo} by using special directives in the DEF file
when creating the dll. This will affect also the optional created
-import library. Consider the following DEF file:
+import library. Consider the following DEF file:
-@example
+@example
LIBRARY "xyz.dll" BASE=0x61000000
EXPORTS
-foo
+foo
_foo = foo
-@end example
+@end example
The line @samp{_foo = foo} maps the symbol @samp{foo} to @samp{_foo}.
Another method for creating a symbol alias is to create it in the
source code using the "weak" attribute:
-@example
-void foo () @{ /* Do something. */; @}
+@example
+void foo () @{ /* Do something. */; @}
void _foo () __attribute__ ((weak, alias ("foo")));
-@end example
+@end example
See the gcc manual for more information about attributes and weak
symbols.
@item renaming symbols
Sometimes it is useful to rename exports. For instance, the cygwin
-kernel does this regularly. A symbol @samp{_foo} can be exported as
+kernel does this regularly. A symbol @samp{_foo} can be exported as
@samp{foo} but not as @samp{_foo} by using special directives in the
DEF file. (This will also affect the import library, if it is
-created). In the following example:
+created). In the following example:
-@example
+@example
LIBRARY "xyz.dll" BASE=0x61000000
EXPORTS
_foo = foo
-@end example
+@end example
The line @samp{_foo = foo} maps the exported symbol @samp{foo} to
@samp{_foo}.
-@end table
+@end table
Note: using a DEF file disables the default auto-export behavior,
-unless the @samp{--export-all-symbols} command line option is used.
+unless the @samp{--export-all-symbols} command line option is used.
If, however, you are trying to rename symbols, then you should list
-@emph{all} desired exports in the DEF file, including the symbols
-that are not being renamed, and do @emph{not} use the
-@samp{--export-all-symbols} option. If you list only the
-renamed symbols in the DEF file, and use @samp{--export-all-symbols}
-to handle the other symbols, then the both the new names @emph{and}
-the original names for the renamed symbols will be exported.
-In effect, you'd be aliasing those symbols, not renaming them,
+@emph{all} desired exports in the DEF file, including the symbols
+that are not being renamed, and do @emph{not} use the
+@samp{--export-all-symbols} option. If you list only the
+renamed symbols in the DEF file, and use @samp{--export-all-symbols}
+to handle the other symbols, then the both the new names @emph{and}
+the original names for the renamed symbols will be exported.
+In effect, you'd be aliasing those symbols, not renaming them,
which is probably not what you wanted.
@cindex weak externals
individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
distribution.
+@ifset BUGURL
Otherwise, send bug reports for @command{ld} to
-@samp{bug-binutils@@gnu.org}.
+@value{BUGURL}.
+@end ifset
The fundamental principle of reporting bugs usefully is this:
@strong{report all the facts}. If you are not sure whether to state a
were different, the contents of that location would fool the linker
into doing the right thing despite the bug. Play it safe and give a
specific, complete example. That is the easiest thing for you to do,
-and the most helpful.
+and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix
the bug if it is new to us. Therefore, always write your bug reports
% Blame: doc@cygnus.com, 28mar91.
@end tex
-
-@contents
@bye