3 @c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
4 @c 2001 Free Software Foundation, Inc.
6 @include configdoc.texi
7 @c (configdoc.texi is generated by the Makefile)
14 @c Configure for the generation of man pages
47 * Ld: (ld). The GNU linker.
53 This file documents the @sc{gnu} linker LD version @value{VERSION}.
55 Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
56 2001 Free Software Foundation, Inc.
60 Permission is granted to copy, distribute and/or modify this document
61 under the terms of the GNU Free Documentation License, Version 1.1
62 or any later version published by the Free Software Foundation;
63 with no Invariant Sections, with no Front-Cover Texts, and with no
64 Back-Cover Texts. A copy of the license is included in the
65 section entitled "GNU Free Documentation License".
67 Permission is granted to process this file through Tex and print the
68 results, provided the printed document carries copying permission
69 notice identical to this one except for the removal of this paragraph
70 (this paragraph not being relevant to the printed manual).
76 @setchapternewpage odd
77 @settitle Using LD, the GNU linker
80 @subtitle The GNU linker
82 @subtitle @code{ld} version 2
83 @subtitle Version @value{VERSION}
84 @author Steve Chamberlain
85 @author Ian Lance Taylor
90 \hfill Red Hat Inc\par
91 \hfill nickc\@credhat.com, doc\@redhat.com\par
92 \hfill {\it Using LD, the GNU linker}\par
93 \hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
95 \global\parindent=0pt % Steve likes it this way.
98 @vskip 0pt plus 1filll
99 @c man begin COPYRIGHT
100 Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000 Free Software Foundation, Inc.
102 Permission is granted to copy, distribute and/or modify this document
103 under the terms of the GNU Free Documentation License, Version 1.1
104 or any later version published by the Free Software Foundation;
105 with no Invariant Sections, with no Front-Cover Texts, and with no
106 Back-Cover Texts. A copy of the license is included in the
107 section entitled "GNU Free Documentation License".
112 @c FIXME: Talk about importance of *order* of args, cmds to linker!
117 This file documents the @sc{gnu} linker ld version @value{VERSION}.
119 This document is distributed under the terms of the GNU Free
120 Documentation License. A copy of the license is included in the
121 section entitled "GNU Free Documentation License".
124 * Overview:: Overview
125 * Invocation:: Invocation
126 * Scripts:: Linker Scripts
128 * Machine Dependent:: Machine Dependent Features
132 * H8/300:: ld and the H8/300
135 * Hitachi:: ld and other Hitachi micros
138 * i960:: ld and the Intel 960 family
141 * TI COFF:: ld and the TI COFF
144 @ifclear SingleFormat
147 @c Following blank line required for remaining bug in makeinfo conds/menus
149 * Reporting Bugs:: Reporting Bugs
150 * MRI:: MRI Compatible Script Files
151 * GNU Free Documentation License:: GNU Free Documentation License
159 @cindex @sc{gnu} linker
160 @cindex what is this?
163 @c man begin SYNOPSIS
164 ld [ options ] objfile...
168 ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and
169 the Info entries for @file{binutils} and
174 @c man begin DESCRIPTION
176 @code{ld} combines a number of object and archive files, relocates
177 their data and ties up symbol references. Usually the last step in
178 compiling a program is to run @code{ld}.
180 @code{ld} accepts Linker Command Language files written in
181 a superset of AT&T's Link Editor Command Language syntax,
182 to provide explicit and total control over the linking process.
186 This man page does not describe the command language; see the
187 @code{ld} entry in @code{info}, or the manual
188 ld: the GNU linker, for full details on the command language and
189 on other aspects of the GNU linker.
192 @ifclear SingleFormat
193 This version of @code{ld} uses the general purpose BFD libraries
194 to operate on object files. This allows @code{ld} to read, combine, and
195 write object files in many different formats---for example, COFF or
196 @code{a.out}. Different formats may be linked together to produce any
197 available kind of object file. @xref{BFD}, for more information.
200 Aside from its flexibility, the @sc{gnu} linker is more helpful than other
201 linkers in providing diagnostic information. Many linkers abandon
202 execution immediately upon encountering an error; whenever possible,
203 @code{ld} continues executing, allowing you to identify other errors
204 (or, in some cases, to get an output file in spite of the error).
211 @c man begin DESCRIPTION
213 The @sc{gnu} linker @code{ld} is meant to cover a broad range of situations,
214 and to be as compatible as possible with other linkers. As a result,
215 you have many choices to control its behavior.
221 * Options:: Command Line Options
222 * Environment:: Environment Variables
226 @section Command Line Options
234 The linker supports a plethora of command-line options, but in actual
235 practice few of them are used in any particular context.
236 @cindex standard Unix system
237 For instance, a frequent use of @code{ld} is to link standard Unix
238 object files on a standard, supported Unix system. On such a system, to
239 link a file @code{hello.o}:
242 ld -o @var{output} /lib/crt0.o hello.o -lc
245 This tells @code{ld} to produce a file called @var{output} as the
246 result of linking the file @code{/lib/crt0.o} with @code{hello.o} and
247 the library @code{libc.a}, which will come from the standard search
248 directories. (See the discussion of the @samp{-l} option below.)
250 Some of the command-line options to @code{ld} may be specified at any
251 point in the command line. However, options which refer to files, such
252 as @samp{-l} or @samp{-T}, cause the file to be read at the point at
253 which the option appears in the command line, relative to the object
254 files and other file options. Repeating non-file options with a
255 different argument will either have no further effect, or override prior
256 occurrences (those further to the left on the command line) of that
257 option. Options which may be meaningfully specified more than once are
258 noted in the descriptions below.
261 Non-option arguments are object files or archives which are to be linked
262 together. They may follow, precede, or be mixed in with command-line
263 options, except that an object file argument may not be placed between
264 an option and its argument.
266 Usually the linker is invoked with at least one object file, but you can
267 specify other forms of binary input files using @samp{-l}, @samp{-R},
268 and the script command language. If @emph{no} binary input files at all
269 are specified, the linker does not produce any output, and issues the
270 message @samp{No input files}.
272 If the linker can not recognize the format of an object file, it will
273 assume that it is a linker script. A script specified in this way
274 augments the main linker script used for the link (either the default
275 linker script or the one specified by using @samp{-T}). This feature
276 permits the linker to link against a file which appears to be an object
277 or an archive, but actually merely defines some symbol values, or uses
278 @code{INPUT} or @code{GROUP} to load other objects. Note that
279 specifying a script in this way should only be used to augment the main
280 linker script; if you want to use some command that logically can only
281 appear once, such as the @code{SECTIONS} or @code{MEMORY} command, you
282 must replace the default linker script using the @samp{-T} option.
285 For options whose names are a single letter,
286 option arguments must either follow the option letter without intervening
287 whitespace, or be given as separate arguments immediately following the
288 option that requires them.
290 For options whose names are multiple letters, either one dash or two can
291 precede the option name; for example, @samp{-trace-symbol} and
292 @samp{--trace-symbol} are equivalent. Note - there is one exception to
293 this rule. Multiple letter options that start with a lower case 'o' can
294 only be preceeded by two dashes. This is to reduce confusion with the
295 @samp{-o} option. So for example @samp{-omagic} sets the output file
296 name to @samp{magic} whereas @samp{--omagic} sets the NMAGIC flag on the
299 Arguments to multiple-letter options must either be separated from the
300 option name by an equals sign, or be given as separate arguments
301 immediately following the option that requires them. For example,
302 @samp{--trace-symbol foo} and @samp{--trace-symbol=foo} are equivalent.
303 Unique abbreviations of the names of multiple-letter options are
306 Note - if the linker is being invoked indirectly, via a compiler driver
307 (eg @samp{gcc}) then all the linker command line options should be
308 prefixed by @samp{-Wl,} (or whatever is appropriate for the particular
309 compiler driver) like this:
312 gcc -Wl,--startgroup foo.o bar.o -Wl,--endgroup
315 This is important, because otherwise the compiler driver program may
316 silently drop the linker options, resulting in a bad link.
318 Here is a table of the generic command line switches accepted by the GNU
322 @kindex -a@var{keyword}
323 @item -a@var{keyword}
324 This option is supported for HP/UX compatibility. The @var{keyword}
325 argument must be one of the strings @samp{archive}, @samp{shared}, or
326 @samp{default}. @samp{-aarchive} is functionally equivalent to
327 @samp{-Bstatic}, and the other two keywords are functionally equivalent
328 to @samp{-Bdynamic}. This option may be used any number of times.
331 @cindex architectures
333 @item -A@var{architecture}
334 @kindex --architecture=@var{arch}
335 @itemx --architecture=@var{architecture}
336 In the current release of @code{ld}, this option is useful only for the
337 Intel 960 family of architectures. In that @code{ld} configuration, the
338 @var{architecture} argument identifies the particular architecture in
339 the 960 family, enabling some safeguards and modifying the
340 archive-library search path. @xref{i960,,@code{ld} and the Intel 960
341 family}, for details.
343 Future releases of @code{ld} may support similar functionality for
344 other architecture families.
347 @ifclear SingleFormat
348 @cindex binary input format
349 @kindex -b @var{format}
350 @kindex --format=@var{format}
353 @item -b @var{input-format}
354 @itemx --format=@var{input-format}
355 @code{ld} may be configured to support more than one kind of object
356 file. If your @code{ld} is configured this way, you can use the
357 @samp{-b} option to specify the binary format for input object files
358 that follow this option on the command line. Even when @code{ld} is
359 configured to support alternative object formats, you don't usually need
360 to specify this, as @code{ld} should be configured to expect as a
361 default input format the most usual format on each machine.
362 @var{input-format} is a text string, the name of a particular format
363 supported by the BFD libraries. (You can list the available binary
364 formats with @samp{objdump -i}.)
367 You may want to use this option if you are linking files with an unusual
368 binary format. You can also use @samp{-b} to switch formats explicitly (when
369 linking object files of different formats), by including
370 @samp{-b @var{input-format}} before each group of object files in a
373 The default format is taken from the environment variable
378 You can also define the input format from a script, using the command
381 see @ref{Format Commands}.
385 @kindex -c @var{MRI-cmdfile}
386 @kindex --mri-script=@var{MRI-cmdfile}
387 @cindex compatibility, MRI
388 @item -c @var{MRI-commandfile}
389 @itemx --mri-script=@var{MRI-commandfile}
390 For compatibility with linkers produced by MRI, @code{ld} accepts script
391 files written in an alternate, restricted command language, described in
393 @ref{MRI,,MRI Compatible Script Files}.
396 the MRI Compatible Script Files section of GNU ld documentation.
398 Introduce MRI script files with
399 the option @samp{-c}; use the @samp{-T} option to run linker
400 scripts written in the general-purpose @code{ld} scripting language.
401 If @var{MRI-cmdfile} does not exist, @code{ld} looks for it in the directories
402 specified by any @samp{-L} options.
404 @cindex common allocation
411 These three options are equivalent; multiple forms are supported for
412 compatibility with other linkers. They assign space to common symbols
413 even if a relocatable output file is specified (with @samp{-r}). The
414 script command @code{FORCE_COMMON_ALLOCATION} has the same effect.
415 @xref{Miscellaneous Commands}.
417 @cindex entry point, from command line
418 @kindex -e @var{entry}
419 @kindex --entry=@var{entry}
421 @itemx --entry=@var{entry}
422 Use @var{entry} as the explicit symbol for beginning execution of your
423 program, rather than the default entry point. If there is no symbol
424 named @var{entry}, the linker will try to parse @var{entry} as a number,
425 and use that as the entry address (the number will be interpreted in
426 base 10; you may use a leading @samp{0x} for base 16, or a leading
427 @samp{0} for base 8). @xref{Entry Point}, for a discussion of defaults
428 and other ways of specifying the entry point.
430 @cindex dynamic symbol table
432 @kindex --export-dynamic
434 @itemx --export-dynamic
435 When creating a dynamically linked executable, add all symbols to the
436 dynamic symbol table. The dynamic symbol table is the set of symbols
437 which are visible from dynamic objects at run time.
439 If you do not use this option, the dynamic symbol table will normally
440 contain only those symbols which are referenced by some dynamic object
441 mentioned in the link.
443 If you use @code{dlopen} to load a dynamic object which needs to refer
444 back to the symbols defined by the program, rather than some other
445 dynamic object, then you will probably need to use this option when
446 linking the program itself.
448 You can also use the version script to control what symbols should
449 be added to the dynamic symbol table if the output format supports it.
450 See the description of @samp{--version-script} in @ref{VERSION}.
452 @cindex big-endian objects
456 Link big-endian objects. This affects the default output format.
458 @cindex little-endian objects
461 Link little-endian objects. This affects the default output format.
466 @itemx --auxiliary @var{name}
467 When creating an ELF shared object, set the internal DT_AUXILIARY field
468 to the specified name. This tells the dynamic linker that the symbol
469 table of the shared object should be used as an auxiliary filter on the
470 symbol table of the shared object @var{name}.
472 If you later link a program against this filter object, then, when you
473 run the program, the dynamic linker will see the DT_AUXILIARY field. If
474 the dynamic linker resolves any symbols from the filter object, it will
475 first check whether there is a definition in the shared object
476 @var{name}. If there is one, it will be used instead of the definition
477 in the filter object. The shared object @var{name} need not exist.
478 Thus the shared object @var{name} may be used to provide an alternative
479 implementation of certain functions, perhaps for debugging or for
480 machine specific performance.
482 This option may be specified more than once. The DT_AUXILIARY entries
483 will be created in the order in which they appear on the command line.
488 @itemx --filter @var{name}
489 When creating an ELF shared object, set the internal DT_FILTER field to
490 the specified name. This tells the dynamic linker that the symbol table
491 of the shared object which is being created should be used as a filter
492 on the symbol table of the shared object @var{name}.
494 If you later link a program against this filter object, then, when you
495 run the program, the dynamic linker will see the DT_FILTER field. The
496 dynamic linker will resolve symbols according to the symbol table of the
497 filter object as usual, but it will actually link to the definitions
498 found in the shared object @var{name}. Thus the filter object can be
499 used to select a subset of the symbols provided by the object
502 Some older linkers used the @code{-F} option throughout a compilation
503 toolchain for specifying object-file format for both input and output
504 object files. The @sc{gnu} linker uses other mechanisms for this
505 purpose: the @code{-b}, @code{--format}, @code{--oformat} options, the
506 @code{TARGET} command in linker scripts, and the @code{GNUTARGET}
507 environment variable. The @sc{gnu} linker will ignore the @code{-F}
508 option when not creating an ELF shared object.
510 @cindex finalization function
512 @item -fini @var{name}
513 When creating an ELF executable or shared object, call NAME when the
514 executable or shared object is unloaded, by setting DT_FINI to the
515 address of the function. By default, the linker uses @code{_fini} as
516 the function to call.
520 Ignored. Provided for compatibility with other tools.
526 @itemx --gpsize=@var{value}
527 Set the maximum size of objects to be optimized using the GP register to
528 @var{size}. This is only meaningful for object file formats such as
529 MIPS ECOFF which supports putting large and small objects into different
530 sections. This is ignored for other object file formats.
532 @cindex runtime library name
534 @kindex -soname=@var{name}
536 @itemx -soname=@var{name}
537 When creating an ELF shared object, set the internal DT_SONAME field to
538 the specified name. When an executable is linked with a shared object
539 which has a DT_SONAME field, then when the executable is run the dynamic
540 linker will attempt to load the shared object specified by the DT_SONAME
541 field rather than the using the file name given to the linker.
544 @cindex incremental link
546 Perform an incremental link (same as option @samp{-r}).
548 @cindex initialization function
550 @item -init @var{name}
551 When creating an ELF executable or shared object, call NAME when the
552 executable or shared object is loaded, by setting DT_INIT to the address
553 of the function. By default, the linker uses @code{_init} as the
556 @cindex archive files, from cmd line
557 @kindex -l@var{archive}
558 @kindex --library=@var{archive}
559 @item -l@var{archive}
560 @itemx --library=@var{archive}
561 Add archive file @var{archive} to the list of files to link. This
562 option may be used any number of times. @code{ld} will search its
563 path-list for occurrences of @code{lib@var{archive}.a} for every
564 @var{archive} specified.
566 On systems which support shared libraries, @code{ld} may also search for
567 libraries with extensions other than @code{.a}. Specifically, on ELF
568 and SunOS systems, @code{ld} will search a directory for a library with
569 an extension of @code{.so} before searching for one with an extension of
570 @code{.a}. By convention, a @code{.so} extension indicates a shared
573 The linker will search an archive only once, at the location where it is
574 specified on the command line. If the archive defines a symbol which
575 was undefined in some object which appeared before the archive on the
576 command line, the linker will include the appropriate file(s) from the
577 archive. However, an undefined symbol in an object appearing later on
578 the command line will not cause the linker to search the archive again.
580 See the @code{-(} option for a way to force the linker to search
581 archives multiple times.
583 You may list the same archive multiple times on the command line.
586 This type of archive searching is standard for Unix linkers. However,
587 if you are using @code{ld} on AIX, note that it is different from the
588 behaviour of the AIX linker.
591 @cindex search directory, from cmd line
593 @kindex --library-path=@var{dir}
594 @item -L@var{searchdir}
595 @itemx --library-path=@var{searchdir}
596 Add path @var{searchdir} to the list of paths that @code{ld} will search
597 for archive libraries and @code{ld} control scripts. You may use this
598 option any number of times. The directories are searched in the order
599 in which they are specified on the command line. Directories specified
600 on the command line are searched before the default directories. All
601 @code{-L} options apply to all @code{-l} options, regardless of the
602 order in which the options appear.
605 The default set of paths searched (without being specified with
606 @samp{-L}) depends on which emulation mode @code{ld} is using, and in
607 some cases also on how it was configured. @xref{Environment}.
610 The paths can also be specified in a link script with the
611 @code{SEARCH_DIR} command. Directories specified this way are searched
612 at the point in which the linker script appears in the command line.
615 @kindex -m @var{emulation}
616 @item -m@var{emulation}
617 Emulate the @var{emulation} linker. You can list the available
618 emulations with the @samp{--verbose} or @samp{-V} options.
620 If the @samp{-m} option is not used, the emulation is taken from the
621 @code{LDEMULATION} environment variable, if that is defined.
623 Otherwise, the default emulation depends upon how the linker was
631 Print a link map to the standard output. A link map provides
632 information about the link, including the following:
636 Where object files and symbols are mapped into memory.
638 How common symbols are allocated.
640 All archive members included in the link, with a mention of the symbol
641 which caused the archive member to be brought in.
645 @cindex read-only text
650 Turn off page alignment of sections, and mark the output as
651 @code{NMAGIC} if possible.
655 @cindex read/write from cmd line
659 Set the text and data sections to be readable and writable. Also, do
660 not page-align the data segment. If the output format supports Unix
661 style magic numbers, mark the output as @code{OMAGIC}.
663 @kindex -o @var{output}
664 @kindex --output=@var{output}
665 @cindex naming the output file
666 @item -o @var{output}
667 @itemx --output=@var{output}
668 Use @var{output} as the name for the program produced by @code{ld}; if this
669 option is not specified, the name @file{a.out} is used by default. The
670 script command @code{OUTPUT} can also specify the output file name.
672 @kindex -O @var{level}
673 @cindex generating optimized output
675 If @var{level} is a numeric values greater than zero @code{ld} optimizes
676 the output. This might take significantly longer and therefore probably
677 should only be enabled for the final binary.
680 @kindex --emit-relocs
681 @cindex retain relocations in final executable
684 Leave relocation sections and contents in fully linked exececutables.
685 Post link analysis and optimization tools may need this information in
686 order to perform correct modifications of executables. This results
687 in larger executables.
690 @cindex relocatable output
692 @kindex --relocateable
694 @itemx --relocateable
695 Generate relocatable output---i.e., generate an output file that can in
696 turn serve as input to @code{ld}. This is often called @dfn{partial
697 linking}. As a side effect, in environments that support standard Unix
698 magic numbers, this option also sets the output file's magic number to
701 If this option is not specified, an absolute file is produced. When
702 linking C++ programs, this option @emph{will not} resolve references to
703 constructors; to do that, use @samp{-Ur}.
705 When an input file does not have the same format as the output file,
706 partial linking is only supported if that input file does not contain any
707 relocations. Different output formats can have further restrictions; for
708 example some @code{a.out}-based formats do not support partial linking
709 with input files in other formats at all.
711 This option does the same thing as @samp{-i}.
713 @kindex -R @var{file}
714 @kindex --just-symbols=@var{file}
715 @cindex symbol-only input
716 @item -R @var{filename}
717 @itemx --just-symbols=@var{filename}
718 Read symbol names and their addresses from @var{filename}, but do not
719 relocate it or include it in the output. This allows your output file
720 to refer symbolically to absolute locations of memory defined in other
721 programs. You may use this option more than once.
723 For compatibility with other ELF linkers, if the @code{-R} option is
724 followed by a directory name, rather than a file name, it is treated as
725 the @code{-rpath} option.
729 @cindex strip all symbols
732 Omit all symbol information from the output file.
735 @kindex --strip-debug
736 @cindex strip debugger symbols
739 Omit debugger symbol information (but not all symbols) from the output file.
743 @cindex input files, displaying
746 Print the names of the input files as @code{ld} processes them.
748 @kindex -T @var{script}
749 @kindex --script=@var{script}
751 @item -T @var{scriptfile}
752 @itemx --script=@var{scriptfile}
753 Use @var{scriptfile} as the linker script. This script replaces
754 @code{ld}'s default linker script (rather than adding to it), so
755 @var{commandfile} must specify everything necessary to describe the
756 output file. You must use this option if you want to use a command
757 which can only appear once in a linker script, such as the
758 @code{SECTIONS} or @code{MEMORY} command. @xref{Scripts}. If
759 @var{scriptfile} does not exist in the current directory, @code{ld}
760 looks for it in the directories specified by any preceding @samp{-L}
761 options. Multiple @samp{-T} options accumulate.
763 @kindex -u @var{symbol}
764 @kindex --undefined=@var{symbol}
765 @cindex undefined symbol
766 @item -u @var{symbol}
767 @itemx --undefined=@var{symbol}
768 Force @var{symbol} to be entered in the output file as an undefined
769 symbol. Doing this may, for example, trigger linking of additional
770 modules from standard libraries. @samp{-u} may be repeated with
771 different option arguments to enter additional undefined symbols. This
772 option is equivalent to the @code{EXTERN} linker script command.
777 For anything other than C++ programs, this option is equivalent to
778 @samp{-r}: it generates relocatable output---i.e., an output file that can in
779 turn serve as input to @code{ld}. When linking C++ programs, @samp{-Ur}
780 @emph{does} resolve references to constructors, unlike @samp{-r}.
781 It does not work to use @samp{-Ur} on files that were themselves linked
782 with @samp{-Ur}; once the constructor table has been built, it cannot
783 be added to. Use @samp{-Ur} only for the last partial link, and
784 @samp{-r} for the others.
786 @kindex --unique[=@var{SECTION}]
787 @item --unique[=@var{SECTION}]
788 Creates a separate output section for every input section matching
789 @var{SECTION}, or if the optional wildcard @var{SECTION} argument is
790 missing, for every orphan input section. An orphan section is one not
791 specifically mentioned in a linker script. You may use this option
792 multiple times on the command line; It prevents the normal merging of
793 input sections with the same name, overriding output section assignments
803 Display the version number for @code{ld}. The @code{-V} option also
804 lists the supported emulations.
807 @kindex --discard-all
808 @cindex deleting local symbols
811 Delete all local symbols.
814 @kindex --discard-locals
815 @cindex local symbols, deleting
816 @cindex L, deleting symbols beginning
818 @itemx --discard-locals
819 Delete all temporary local symbols. For most targets, this is all local
820 symbols whose names begin with @samp{L}.
822 @kindex -y @var{symbol}
823 @kindex --trace-symbol=@var{symbol}
824 @cindex symbol tracing
825 @item -y @var{symbol}
826 @itemx --trace-symbol=@var{symbol}
827 Print the name of each linked file in which @var{symbol} appears. This
828 option may be given any number of times. On many systems it is necessary
829 to prepend an underscore.
831 This option is useful when you have an undefined symbol in your link but
832 don't know where the reference is coming from.
834 @kindex -Y @var{path}
836 Add @var{path} to the default library search path. This option exists
837 for Solaris compatibility.
839 @kindex -z @var{keyword}
840 @item -z @var{keyword}
841 The recognized keywords are @code{initfirst}, @code{interpose},
842 @code{loadfltr}, @code{nodefaultlib}, @code{nodelete}, @code{nodlopen},
843 @code{nodump}, @code{now}, @code{origin}, @code{combreloc} and
844 @code{nocombreloc}. The other keywords are
845 ignored for Solaris compatibility. @code{initfirst} marks the object
846 to be initialized first at runtime before any other objects.
847 @code{interpose} marks the object that its symbol table interposes
848 before all symbols but the primary executable. @code{loadfltr} marks
849 the object that its filtees be processed immediately at runtime.
850 @code{nodefaultlib} marks the object that the search for dependencies
851 of this object will ignore any default library search paths.
852 @code{nodelete} marks the object shouldn't be unloaded at runtime.
853 @code{nodlopen} marks the object not available to @code{dlopen}.
854 @code{nodump} marks the object can not be dumped by @code{dldump}.
855 @code{now} marks the object with the non-lazy runtime binding.
856 @code{origin} marks the object may contain $ORIGIN.
857 @code{defs} disallows undefined symbols.
858 @code{combreloc} combines multiple reloc sections and sorts them
859 to make dynamic symbol lookup caching possible.
860 @code{nocombreloc} disables multiple reloc sections combining.
863 @cindex groups of archives
864 @item -( @var{archives} -)
865 @itemx --start-group @var{archives} --end-group
866 The @var{archives} should be a list of archive files. They may be
867 either explicit file names, or @samp{-l} options.
869 The specified archives are searched repeatedly until no new undefined
870 references are created. Normally, an archive is searched only once in
871 the order that it is specified on the command line. If a symbol in that
872 archive is needed to resolve an undefined symbol referred to by an
873 object in an archive that appears later on the command line, the linker
874 would not be able to resolve that reference. By grouping the archives,
875 they all be searched repeatedly until all possible references are
878 Using this option has a significant performance cost. It is best to use
879 it only when there are unavoidable circular references between two or
882 @kindex -assert @var{keyword}
883 @item -assert @var{keyword}
884 This option is ignored for SunOS compatibility.
892 Link against dynamic libraries. This is only meaningful on platforms
893 for which shared libraries are supported. This option is normally the
894 default on such platforms. The different variants of this option are
895 for compatibility with various systems. You may use this option
896 multiple times on the command line: it affects library searching for
897 @code{-l} options which follow it.
901 Set the @code{DF_1_GROUP} flag in the @code{DT_FLAGS_1} entry in the dynamic
902 section. This causes the runtime linker to handle lookups in this
903 object and its dependencies to be performed only inside the group.
904 @code{--no-undefined} is implied. This option is only meaningful on ELF
905 platforms which support shared libraries.
915 Do not link against shared libraries. This is only meaningful on
916 platforms for which shared libraries are supported. The different
917 variants of this option are for compatibility with various systems. You
918 may use this option multiple times on the command line: it affects
919 library searching for @code{-l} options which follow it.
923 When creating a shared library, bind references to global symbols to the
924 definition within the shared library, if any. Normally, it is possible
925 for a program linked against a shared library to override the definition
926 within the shared library. This option is only meaningful on ELF
927 platforms which support shared libraries.
929 @kindex --check-sections
930 @kindex --no-check-sections
931 @item --check-sections
932 @itemx --no-check-sections
933 Asks the linker @emph{not} to check section addresses after they have
934 been assigned to see if there any overlaps. Normally the linker will
935 perform this check, and if it finds any overlaps it will produce
936 suitable error messages. The linker does know about, and does make
937 allowances for sections in overlays. The default behaviour can be
938 restored by using the command line switch @samp{--check-sections}.
940 @cindex cross reference table
943 Output a cross reference table. If a linker map file is being
944 generated, the cross reference table is printed to the map file.
945 Otherwise, it is printed on the standard output.
947 The format of the table is intentionally simple, so that it may be
948 easily processed by a script if necessary. The symbols are printed out,
949 sorted by name. For each symbol, a list of file names is given. If the
950 symbol is defined, the first file listed is the location of the
951 definition. The remaining files contain references to the symbol.
953 @cindex symbols, from command line
954 @kindex --defsym @var{symbol}=@var{exp}
955 @item --defsym @var{symbol}=@var{expression}
956 Create a global symbol in the output file, containing the absolute
957 address given by @var{expression}. You may use this option as many
958 times as necessary to define multiple symbols in the command line. A
959 limited form of arithmetic is supported for the @var{expression} in this
960 context: you may give a hexadecimal constant or the name of an existing
961 symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
962 constants or symbols. If you need more elaborate expressions, consider
963 using the linker command language from a script (@pxref{Assignments,,
964 Assignment: Symbol Definitions}). @emph{Note:} there should be no white
965 space between @var{symbol}, the equals sign (``@key{=}''), and
968 @cindex demangling, from command line
969 @kindex --demangle[=@var{style}]
970 @kindex --no-demangle
971 @item --demangle[=@var{style}]
973 These options control whether to demangle symbol names in error messages
974 and other output. When the linker is told to demangle, it tries to
975 present symbol names in a readable fashion: it strips leading
976 underscores if they are used by the object file format, and converts C++
977 mangled symbol names into user readable names. Different compilers have
978 different mangling styles. The optional demangling style argument can be used
979 to choose an appropriate demangling style for your compiler. The linker will
980 demangle by default unless the environment variable @samp{COLLECT_NO_DEMANGLE}
981 is set. These options may be used to override the default.
983 @cindex dynamic linker, from command line
985 @kindex --dynamic-linker @var{file}
986 @item --dynamic-linker @var{file}
987 Set the name of the dynamic linker. This is only meaningful when
988 generating dynamically linked ELF executables. The default dynamic
989 linker is normally correct; don't use this unless you know what you are
992 @cindex MIPS embedded PIC code
993 @kindex --embedded-relocs
994 @item --embedded-relocs
995 This option is only meaningful when linking MIPS embedded PIC code,
996 generated by the -membedded-pic option to the @sc{gnu} compiler and
997 assembler. It causes the linker to create a table which may be used at
998 runtime to relocate any data which was statically initialized to pointer
999 values. See the code in testsuite/ld-empic for details.
1002 @kindex --fatal-warnings
1003 @item --fatal-warnings
1004 Treat all warnings as errors.
1006 @kindex --force-exe-suffix
1007 @item --force-exe-suffix
1008 Make sure that an output file has a .exe suffix.
1010 If a successfully built fully linked output file does not have a
1011 @code{.exe} or @code{.dll} suffix, this option forces the linker to copy
1012 the output file to one of the same name with a @code{.exe} suffix. This
1013 option is useful when using unmodified Unix makefiles on a Microsoft
1014 Windows host, since some versions of Windows won't run an image unless
1015 it ends in a @code{.exe} suffix.
1017 @kindex --gc-sections
1018 @kindex --no-gc-sections
1019 @cindex garbage collection
1020 @item --no-gc-sections
1021 @itemx --gc-sections
1022 Enable garbage collection of unused input sections. It is ignored on
1023 targets that do not support this option. This option is not compatible
1024 with @samp{-r}, nor should it be used with dynamic linking. The default
1025 behaviour (of not performing this garbage collection) can be restored by
1026 specifying @samp{--no-gc-sections} on the command line.
1032 Print a summary of the command-line options on the standard output and exit.
1034 @kindex --target-help
1036 Print a summary of all target specific options on the standard output and exit.
1039 @item -Map @var{mapfile}
1040 Print a link map to the file @var{mapfile}. See the description of the
1041 @samp{-M} option, above.
1043 @cindex memory usage
1044 @kindex --no-keep-memory
1045 @item --no-keep-memory
1046 @code{ld} normally optimizes for speed over memory usage by caching the
1047 symbol tables of input files in memory. This option tells @code{ld} to
1048 instead optimize for memory usage, by rereading the symbol tables as
1049 necessary. This may be required if @code{ld} runs out of memory space
1050 while linking a large executable.
1052 @kindex --no-undefined
1054 @item --no-undefined
1056 Normally when creating a non-symbolic shared library, undefined symbols
1057 are allowed and left to be resolved by the runtime loader. These options
1058 disallows such undefined symbols.
1060 @kindex --allow-shlib-undefined
1061 @item --allow-shlib-undefined
1062 Allow undefined symbols in shared objects even when --no-undefined is
1063 set. The net result will be that undefined symbols in regular objects
1064 will still trigger an error, but undefined symbols in shared objects
1065 will be ignored. The implementation of no_undefined makes the
1066 assumption that the runtime linker will choke on undefined symbols.
1067 However there is at least one system (BeOS) where undefined symbols in
1068 shared libraries is normal since the kernel patches them at load time to
1069 select which function is most appropriate for the current architecture.
1070 I.E. dynamically select an appropriate memset function. Apparently it
1071 is also normal for HPPA shared libraries to have undefined symbols.
1073 @kindex --no-warn-mismatch
1074 @item --no-warn-mismatch
1075 Normally @code{ld} will give an error if you try to link together input
1076 files that are mismatched for some reason, perhaps because they have
1077 been compiled for different processors or for different endiannesses.
1078 This option tells @code{ld} that it should silently permit such possible
1079 errors. This option should only be used with care, in cases when you
1080 have taken some special action that ensures that the linker errors are
1083 @kindex --no-whole-archive
1084 @item --no-whole-archive
1085 Turn off the effect of the @code{--whole-archive} option for subsequent
1088 @cindex output file after errors
1089 @kindex --noinhibit-exec
1090 @item --noinhibit-exec
1091 Retain the executable output file whenever it is still usable.
1092 Normally, the linker will not produce an output file if it encounters
1093 errors during the link process; it exits without writing an output file
1094 when it issues any error whatsoever.
1096 @ifclear SingleFormat
1098 @item --oformat @var{output-format}
1099 @code{ld} may be configured to support more than one kind of object
1100 file. If your @code{ld} is configured this way, you can use the
1101 @samp{--oformat} option to specify the binary format for the output
1102 object file. Even when @code{ld} is configured to support alternative
1103 object formats, you don't usually need to specify this, as @code{ld}
1104 should be configured to produce as a default output format the most
1105 usual format on each machine. @var{output-format} is a text string, the
1106 name of a particular format supported by the BFD libraries. (You can
1107 list the available binary formats with @samp{objdump -i}.) The script
1108 command @code{OUTPUT_FORMAT} can also specify the output format, but
1109 this option overrides it. @xref{BFD}.
1114 This option is ignored for Linux compatibility.
1118 This option is ignored for SVR4 compatibility.
1121 @cindex synthesizing linker
1122 @cindex relaxing addressing modes
1124 An option with machine dependent effects.
1126 This option is only supported on a few targets.
1129 @xref{H8/300,,@code{ld} and the H8/300}.
1132 @xref{i960,, @code{ld} and the Intel 960 family}.
1136 On some platforms, the @samp{--relax} option performs global
1137 optimizations that become possible when the linker resolves addressing
1138 in the program, such as relaxing address modes and synthesizing new
1139 instructions in the output object file.
1141 On some platforms these link time global optimizations may make symbolic
1142 debugging of the resulting executable impossible.
1145 the case for the Matsushita MN10200 and MN10300 family of processors.
1149 On platforms where this is not supported, @samp{--relax} is accepted,
1153 @cindex retaining specified symbols
1154 @cindex stripping all but some symbols
1155 @cindex symbols, retaining selectively
1156 @item --retain-symbols-file @var{filename}
1157 Retain @emph{only} the symbols listed in the file @var{filename},
1158 discarding all others. @var{filename} is simply a flat file, with one
1159 symbol name per line. This option is especially useful in environments
1163 where a large global symbol table is accumulated gradually, to conserve
1166 @samp{--retain-symbols-file} does @emph{not} discard undefined symbols,
1167 or symbols needed for relocations.
1169 You may only specify @samp{--retain-symbols-file} once in the command
1170 line. It overrides @samp{-s} and @samp{-S}.
1173 @item -rpath @var{dir}
1174 @cindex runtime library search path
1176 Add a directory to the runtime library search path. This is used when
1177 linking an ELF executable with shared objects. All @code{-rpath}
1178 arguments are concatenated and passed to the runtime linker, which uses
1179 them to locate shared objects at runtime. The @code{-rpath} option is
1180 also used when locating shared objects which are needed by shared
1181 objects explicitly included in the link; see the description of the
1182 @code{-rpath-link} option. If @code{-rpath} is not used when linking an
1183 ELF executable, the contents of the environment variable
1184 @code{LD_RUN_PATH} will be used if it is defined.
1186 The @code{-rpath} option may also be used on SunOS. By default, on
1187 SunOS, the linker will form a runtime search patch out of all the
1188 @code{-L} options it is given. If a @code{-rpath} option is used, the
1189 runtime search path will be formed exclusively using the @code{-rpath}
1190 options, ignoring the @code{-L} options. This can be useful when using
1191 gcc, which adds many @code{-L} options which may be on NFS mounted
1194 For compatibility with other ELF linkers, if the @code{-R} option is
1195 followed by a directory name, rather than a file name, it is treated as
1196 the @code{-rpath} option.
1200 @cindex link-time runtime library search path
1202 @item -rpath-link @var{DIR}
1203 When using ELF or SunOS, one shared library may require another. This
1204 happens when an @code{ld -shared} link includes a shared library as one
1207 When the linker encounters such a dependency when doing a non-shared,
1208 non-relocatable link, it will automatically try to locate the required
1209 shared library and include it in the link, if it is not included
1210 explicitly. In such a case, the @code{-rpath-link} option
1211 specifies the first set of directories to search. The
1212 @code{-rpath-link} option may specify a sequence of directory names
1213 either by specifying a list of names separated by colons, or by
1214 appearing multiple times.
1216 This option should be used with caution as it overrides the search path
1217 that may have been hard compiled into a shared library. In such a case it
1218 is possible to use unintentionally a different search path than the
1219 runtime linker would do.
1221 The linker uses the following search paths to locate required shared
1225 Any directories specified by @code{-rpath-link} options.
1227 Any directories specified by @code{-rpath} options. The difference
1228 between @code{-rpath} and @code{-rpath-link} is that directories
1229 specified by @code{-rpath} options are included in the executable and
1230 used at runtime, whereas the @code{-rpath-link} option is only effective
1231 at link time. It is for the native linker only.
1233 On an ELF system, if the @code{-rpath} and @code{rpath-link} options
1234 were not used, search the contents of the environment variable
1235 @code{LD_RUN_PATH}. It is for the native linker only.
1237 On SunOS, if the @code{-rpath} option was not used, search any
1238 directories specified using @code{-L} options.
1240 For a native linker, the contents of the environment variable
1241 @code{LD_LIBRARY_PATH}.
1243 For a native ELF linker, the directories in @code{DT_RUNPATH} or
1244 @code{DT_RPATH} of a shared library are searched for shared
1245 libraries needed by it. The @code{DT_RPATH} entries are ignored if
1246 @code{DT_RUNPATH} entries exist.
1248 The default directories, normally @file{/lib} and @file{/usr/lib}.
1250 For a native linker on an ELF system, if the file @file{/etc/ld.so.conf}
1251 exists, the list of directories found in that file.
1254 If the required shared library is not found, the linker will issue a
1255 warning and continue with the link.
1262 @cindex shared libraries
1263 Create a shared library. This is currently only supported on ELF, XCOFF
1264 and SunOS platforms. On SunOS, the linker will automatically create a
1265 shared library if the @code{-e} option is not used and there are
1266 undefined symbols in the link.
1269 @kindex --sort-common
1270 This option tells @code{ld} to sort the common symbols by size when it
1271 places them in the appropriate output sections. First come all the one
1272 byte symbols, then all the two byte, then all the four byte, and then
1273 everything else. This is to prevent gaps between symbols due to
1274 alignment constraints.
1276 @kindex --split-by-file
1277 @item --split-by-file [@var{size}]
1278 Similar to @code{--split-by-reloc} but creates a new output section for
1279 each input file when @var{size} is reached. @var{size} defaults to a
1280 size of 1 if not given.
1282 @kindex --split-by-reloc
1283 @item --split-by-reloc [@var{count}]
1284 Tries to creates extra sections in the output file so that no single
1285 output section in the file contains more than @var{count} relocations.
1286 This is useful when generating huge relocatable files for downloading into
1287 certain real time kernels with the COFF object file format; since COFF
1288 cannot represent more than 65535 relocations in a single section. Note
1289 that this will fail to work with object file formats which do not
1290 support arbitrary sections. The linker will not split up individual
1291 input sections for redistribution, so if a single input section contains
1292 more than @var{count} relocations one output section will contain that
1293 many relocations. @var{count} defaults to a value of 32768.
1297 Compute and display statistics about the operation of the linker, such
1298 as execution time and memory usage.
1300 @kindex --traditional-format
1301 @cindex traditional format
1302 @item --traditional-format
1303 For some targets, the output of @code{ld} is different in some ways from
1304 the output of some existing linker. This switch requests @code{ld} to
1305 use the traditional format instead.
1308 For example, on SunOS, @code{ld} combines duplicate entries in the
1309 symbol string table. This can reduce the size of an output file with
1310 full debugging information by over 30 percent. Unfortunately, the SunOS
1311 @code{dbx} program can not read the resulting program (@code{gdb} has no
1312 trouble). The @samp{--traditional-format} switch tells @code{ld} to not
1313 combine duplicate entries.
1315 @kindex --section-start @var{sectionname}=@var{org}
1316 @item --section-start @var{sectionname}=@var{org}
1317 Locate a section in the output file at the absolute
1318 address given by @var{org}. You may use this option as many
1319 times as necessary to locate multiple sections in the command
1321 @var{org} must be a single hexadecimal integer;
1322 for compatibility with other linkers, you may omit the leading
1323 @samp{0x} usually associated with hexadecimal values. @emph{Note:} there
1324 should be no white space between @var{sectionname}, the equals
1325 sign (``@key{=}''), and @var{org}.
1327 @kindex -Tbss @var{org}
1328 @kindex -Tdata @var{org}
1329 @kindex -Ttext @var{org}
1330 @cindex segment origins, cmd line
1331 @item -Tbss @var{org}
1332 @itemx -Tdata @var{org}
1333 @itemx -Ttext @var{org}
1334 Use @var{org} as the starting address for---respectively---the
1335 @code{bss}, @code{data}, or the @code{text} segment of the output file.
1336 @var{org} must be a single hexadecimal integer;
1337 for compatibility with other linkers, you may omit the leading
1338 @samp{0x} usually associated with hexadecimal values.
1344 Display the version number for @code{ld} and list the linker emulations
1345 supported. Display which input files can and cannot be opened. Display
1346 the linker script being used by the linker.
1348 @kindex --version-script=@var{version-scriptfile}
1349 @cindex version script, symbol versions
1350 @itemx --version-script=@var{version-scriptfile}
1351 Specify the name of a version script to the linker. This is typically
1352 used when creating shared libraries to specify additional information
1353 about the version heirarchy for the library being created. This option
1354 is only meaningful on ELF platforms which support shared libraries.
1357 @kindex --warn-common
1358 @cindex warnings, on combining symbols
1359 @cindex combining symbols, warnings on
1361 Warn when a common symbol is combined with another common symbol or with
1362 a symbol definition. Unix linkers allow this somewhat sloppy practice,
1363 but linkers on some other operating systems do not. This option allows
1364 you to find potential problems from combining global symbols.
1365 Unfortunately, some C libraries use this practice, so you may get some
1366 warnings about symbols in the libraries as well as in your programs.
1368 There are three kinds of global symbols, illustrated here by C examples:
1372 A definition, which goes in the initialized data section of the output
1376 An undefined reference, which does not allocate space.
1377 There must be either a definition or a common symbol for the
1381 A common symbol. If there are only (one or more) common symbols for a
1382 variable, it goes in the uninitialized data area of the output file.
1383 The linker merges multiple common symbols for the same variable into a
1384 single symbol. If they are of different sizes, it picks the largest
1385 size. The linker turns a common symbol into a declaration, if there is
1386 a definition of the same variable.
1389 The @samp{--warn-common} option can produce five kinds of warnings.
1390 Each warning consists of a pair of lines: the first describes the symbol
1391 just encountered, and the second describes the previous symbol
1392 encountered with the same name. One or both of the two symbols will be
1397 Turning a common symbol into a reference, because there is already a
1398 definition for the symbol.
1400 @var{file}(@var{section}): warning: common of `@var{symbol}'
1401 overridden by definition
1402 @var{file}(@var{section}): warning: defined here
1406 Turning a common symbol into a reference, because a later definition for
1407 the symbol is encountered. This is the same as the previous case,
1408 except that the symbols are encountered in a different order.
1410 @var{file}(@var{section}): warning: definition of `@var{symbol}'
1412 @var{file}(@var{section}): warning: common is here
1416 Merging a common symbol with a previous same-sized common symbol.
1418 @var{file}(@var{section}): warning: multiple common
1420 @var{file}(@var{section}): warning: previous common is here
1424 Merging a common symbol with a previous larger common symbol.
1426 @var{file}(@var{section}): warning: common of `@var{symbol}'
1427 overridden by larger common
1428 @var{file}(@var{section}): warning: larger common is here
1432 Merging a common symbol with a previous smaller common symbol. This is
1433 the same as the previous case, except that the symbols are
1434 encountered in a different order.
1436 @var{file}(@var{section}): warning: common of `@var{symbol}'
1437 overriding smaller common
1438 @var{file}(@var{section}): warning: smaller common is here
1442 @kindex --warn-constructors
1443 @item --warn-constructors
1444 Warn if any global constructors are used. This is only useful for a few
1445 object file formats. For formats like COFF or ELF, the linker can not
1446 detect the use of global constructors.
1448 @kindex --warn-multiple-gp
1449 @item --warn-multiple-gp
1450 Warn if multiple global pointer values are required in the output file.
1451 This is only meaningful for certain processors, such as the Alpha.
1452 Specifically, some processors put large-valued constants in a special
1453 section. A special register (the global pointer) points into the middle
1454 of this section, so that constants can be loaded efficiently via a
1455 base-register relative addressing mode. Since the offset in
1456 base-register relative mode is fixed and relatively small (e.g., 16
1457 bits), this limits the maximum size of the constant pool. Thus, in
1458 large programs, it is often necessary to use multiple global pointer
1459 values in order to be able to address all possible constants. This
1460 option causes a warning to be issued whenever this case occurs.
1463 @cindex warnings, on undefined symbols
1464 @cindex undefined symbols, warnings on
1466 Only warn once for each undefined symbol, rather than once per module
1469 @kindex --warn-section-align
1470 @cindex warnings, on section alignment
1471 @cindex section alignment, warnings on
1472 @item --warn-section-align
1473 Warn if the address of an output section is changed because of
1474 alignment. Typically, the alignment will be set by an input section.
1475 The address will only be changed if it not explicitly specified; that
1476 is, if the @code{SECTIONS} command does not specify a start address for
1477 the section (@pxref{SECTIONS}).
1479 @kindex --whole-archive
1480 @cindex including an entire archive
1481 @item --whole-archive
1482 For each archive mentioned on the command line after the
1483 @code{--whole-archive} option, include every object file in the archive
1484 in the link, rather than searching the archive for the required object
1485 files. This is normally used to turn an archive file into a shared
1486 library, forcing every object to be included in the resulting shared
1487 library. This option may be used more than once.
1489 Two notes when using this option from gcc: First, gcc doesn't know
1490 about this option, so you have to use @code{-Wl,-whole-archive}.
1491 Second, don't forget to use @code{-Wl,-no-whole-archive} after your
1492 list of archives, because gcc will add its own list of archives to
1493 your link and you may not want this flag to affect those as well.
1496 @item --wrap @var{symbol}
1497 Use a wrapper function for @var{symbol}. Any undefined reference to
1498 @var{symbol} will be resolved to @code{__wrap_@var{symbol}}. Any
1499 undefined reference to @code{__real_@var{symbol}} will be resolved to
1502 This can be used to provide a wrapper for a system function. The
1503 wrapper function should be called @code{__wrap_@var{symbol}}. If it
1504 wishes to call the system function, it should call
1505 @code{__real_@var{symbol}}.
1507 Here is a trivial example:
1511 __wrap_malloc (int c)
1513 printf ("malloc called with %ld\n", c);
1514 return __real_malloc (c);
1518 If you link other code with this file using @code{--wrap malloc}, then
1519 all calls to @code{malloc} will call the function @code{__wrap_malloc}
1520 instead. The call to @code{__real_malloc} in @code{__wrap_malloc} will
1521 call the real @code{malloc} function.
1523 You may wish to provide a @code{__real_malloc} function as well, so that
1524 links without the @code{--wrap} option will succeed. If you do this,
1525 you should not put the definition of @code{__real_malloc} in the same
1526 file as @code{__wrap_malloc}; if you do, the assembler may resolve the
1527 call before the linker has a chance to wrap it to @code{malloc}.
1529 @kindex --enable-new-dtags
1530 @kindex --disable-new-dtags
1531 @item --enable-new-dtags
1532 @itemx --disable-new-dtags
1533 This linker can create the new dynamic tags in ELF. But the older ELF
1534 systems may not understand them. If you specify
1535 @code{--enable-new-dtags}, the dynamic tags will be created as needed.
1536 If you specify @code{--disable-new-dtags}, no new dynamic tags will be
1537 created. By default, the new dynamic tags are not created. Note that
1538 those options are only available for ELF systems.
1544 @subsection Options specific to i386 PE targets
1546 @c man begin OPTIONS
1548 The i386 PE linker supports the @code{-shared} option, which causes
1549 the output to be a dynamically linked library (DLL) instead of a
1550 normal executable. You should name the output @code{*.dll} when you
1551 use this option. In addition, the linker fully supports the standard
1552 @code{*.def} files, which may be specified on the linker command line
1553 like an object file (in fact, it should precede archives it exports
1554 symbols from, to ensure that they get linked in, just like a normal
1557 In addition to the options common to all targets, the i386 PE linker
1558 support additional command line options that are specific to the i386
1559 PE target. Options that take values may be separated from their
1560 values by either a space or an equals sign.
1564 @kindex --add-stdcall-alias
1565 @item --add-stdcall-alias
1566 If given, symbols with a stdcall suffix (@@@var{nn}) will be exported
1567 as-is and also with the suffix stripped.
1570 @item --base-file @var{file}
1571 Use @var{file} as the name of a file in which to save the base
1572 addresses of all the relocations needed for generating DLLs with
1577 Create a DLL instead of a regular executable. You may also use
1578 @code{-shared} or specify a @code{LIBRARY} in a given @code{.def}
1581 @kindex --enable-stdcall-fixup
1582 @kindex --disable-stdcall-fixup
1583 @item --enable-stdcall-fixup
1584 @itemx --disable-stdcall-fixup
1585 If the link finds a symbol that it cannot resolve, it will attempt to
1586 do "fuzzy linking" by looking for another defined symbol that differs
1587 only in the format of the symbol name (cdecl vs stdcall) and will
1588 resolve that symbol by linking to the match. For example, the
1589 undefined symbol @code{_foo} might be linked to the function
1590 @code{_foo@@12}, or the undefined symbol @code{_bar@@16} might be linked
1591 to the function @code{_bar}. When the linker does this, it prints a
1592 warning, since it normally should have failed to link, but sometimes
1593 import libraries generated from third-party dlls may need this feature
1594 to be usable. If you specify @code{--enable-stdcall-fixup}, this
1595 feature is fully enabled and warnings are not printed. If you specify
1596 @code{--disable-stdcall-fixup}, this feature is disabled and such
1597 mismatches are considered to be errors.
1599 @cindex DLLs, creating
1600 @kindex --export-all-symbols
1601 @item --export-all-symbols
1602 If given, all global symbols in the objects used to build a DLL will
1603 be exported by the DLL. Note that this is the default if there
1604 otherwise wouldn't be any exported symbols. When symbols are
1605 explicitly exported via DEF files or implicitly exported via function
1606 attributes, the default is to not export anything else unless this
1607 option is given. Note that the symbols @code{DllMain@@12},
1608 @code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and
1609 @code{impure_ptr} will not be automatically
1610 exported. Also, symbols imported from other DLLs will not be
1611 re-exported, nor will symbols specifying the DLL's internal layout
1612 such as those beginning with @code{_head_} or ending with
1613 @code{_iname}. In addition, no symbols from @code{libgcc},
1614 @code{libstd++}, @code{libmingw32}, or @code{crtX.o} will be exported.
1615 Symbols whose names begin with @code{__rtti_} or @code{__builtin_} will
1616 not be exported, to help with C++ DLLs. Finally, there is an
1617 extensive list of cygwin-private symbols that are not exported
1618 (obviously, this applies on when building DLLs for cygwin targets).
1619 These cygwin-excludes are: @code{_cygwin_dll_entry@@12},
1620 @code{_cygwin_crt0_common@@8}, @code{_cygwin_noncygwin_dll_entry@@12},
1621 @code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll},
1622 @code{cygwin_premain0}, @code{cygwin_premain1}, @code{cygwin_premain2},
1623 @code{cygwin_premain3}, and @code{environ}.
1625 @kindex --exclude-symbols
1626 @item --exclude-symbols @var{symbol},@var{symbol},...
1627 Specifies a list of symbols which should not be automatically
1628 exported. The symbol names may be delimited by commas or colons.
1630 @kindex --file-alignment
1631 @item --file-alignment
1632 Specify the file alignment. Sections in the file will always begin at
1633 file offsets which are multiples of this number. This defaults to
1638 @item --heap @var{reserve}
1639 @itemx --heap @var{reserve},@var{commit}
1640 Specify the amount of memory to reserve (and optionally commit) to be
1641 used as heap for this program. The default is 1Mb reserved, 4K
1645 @kindex --image-base
1646 @item --image-base @var{value}
1647 Use @var{value} as the base address of your program or dll. This is
1648 the lowest memory location that will be used when your program or dll
1649 is loaded. To reduce the need to relocate and improve performance of
1650 your dlls, each should have a unique base address and not overlap any
1651 other dlls. The default is 0x400000 for executables, and 0x10000000
1656 If given, the stdcall suffixes (@@@var{nn}) will be stripped from
1657 symbols before they are exported.
1659 @kindex --major-image-version
1660 @item --major-image-version @var{value}
1661 Sets the major number of the "image version". Defaults to 1.
1663 @kindex --major-os-version
1664 @item --major-os-version @var{value}
1665 Sets the major number of the "os version". Defaults to 4.
1667 @kindex --major-subsystem-version
1668 @item --major-subsystem-version @var{value}
1669 Sets the major number of the "subsystem version". Defaults to 4.
1671 @kindex --minor-image-version
1672 @item --minor-image-version @var{value}
1673 Sets the minor number of the "image version". Defaults to 0.
1675 @kindex --minor-os-version
1676 @item --minor-os-version @var{value}
1677 Sets the minor number of the "os version". Defaults to 0.
1679 @kindex --minor-subsystem-version
1680 @item --minor-subsystem-version @var{value}
1681 Sets the minor number of the "subsystem version". Defaults to 0.
1683 @cindex DEF files, creating
1684 @cindex DLLs, creating
1685 @kindex --output-def
1686 @item --output-def @var{file}
1687 The linker will create the file @var{file} which will contain a DEF
1688 file corresponding to the DLL the linker is generating. This DEF file
1689 (which should be called @code{*.def}) may be used to create an import
1690 library with @code{dlltool} or may be used as a reference to
1691 automatically or implicitly exported symbols.
1693 @cindex DLLs, creating
1694 @kindex --out-implib
1695 @item --out-implib @var{file}
1696 The linker will create the file @var{file} which will contain an
1697 import lib corresponding to the DLL the linker is generating. This
1698 import lib (which should be called @code{*.dll.a} or @code{*.a}
1699 may be used to link clients against the generated DLL; this behavior
1700 makes it possible to skip a separate @code{dlltool} import library
1703 @kindex --enable-auto-image-base
1704 @item --enable-auto-image-base
1705 Automatically choose the image base for DLLs, unless one is specified
1706 using the @code{--image-base} argument. By using a hash generated
1707 from the dllname to create unique image bases for each DLL, in-memory
1708 collisions and relocations which can delay program execution are
1711 @kindex --disable-auto-image-base
1712 @item --disable-auto-image-base
1713 Do not automatically generate a unique image base. If there is no
1714 user-specified image base (@code{--image-base}) then use the platform
1717 @cindex DLLs, linking to
1718 @kindex --dll-search-prefix
1719 @item --dll-search-prefix @var{string}
1720 When linking dynamically to a dll without an import library, i
1721 search for @code{<string><basename>.dll} in preference to
1722 @code{lib<basename>.dll}. This behavior allows easy distinction
1723 between DLLs built for the various "subplatforms": native, cygwin,
1724 uwin, pw, etc. For instance, cygwin DLLs typically use
1725 @code{--dll-search-prefix=cyg}.
1727 @kindex --enable-auto-import
1728 @item --enable-auto-import
1729 Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for
1730 DATA imports from DLLs, and create the necessary thunking symbols when
1731 building the DLLs with those DATA exports. This generally will 'just
1732 work' -- but sometimes you may see this message:
1734 "variable '<var>' can't be auto-imported. Please read the
1735 documentation for ld's @code{--enable-auto-import} for details."
1737 This message occurs when some (sub)expression accesses an address
1738 ultimately given by the sum of two constants (Win32 import tables only
1739 allow one). Instances where this may occur include accesses to member
1740 fields of struct variables imported from a DLL, as well as using a
1741 constant index into an array variable imported from a DLL. Any
1742 multiword variable (arrays, structs, long long, etc) may trigger
1743 this error condition. However, regardless of the exact data type
1744 of the offending exported variable, ld will always detect it, issue
1745 the warning, and exit.
1747 There are several ways to address this difficulty, regardless of the
1748 data type of the exported variable:
1750 One solution is to force one of the 'constants' to be a variable --
1751 that is, unknown and un-optimizable at compile time. For arrays,
1752 there are two possibilities: a) make the indexee (the array's address)
1753 a variable, or b) make the 'constant' index a variable. Thus:
1756 extern type extern_array[];
1758 @{ volatile type *t=extern_array; t[1] @}
1764 extern type extern_array[];
1766 @{ volatile int t=1; extern_array[t] @}
1769 For structs (and most other multiword data types) the only option
1770 is to make the struct itself (or the long long, or the ...) variable:
1773 extern struct s extern_struct;
1774 extern_struct.field -->
1775 @{ volatile struct s *t=&extern_struct; t->field @}
1778 A second method of dealing with this difficulty is to abandon
1779 'auto-import' for the offending symbol and mark it with
1780 @code{__declspec(dllimport)}. However, in practice that
1781 requires using compile-time #defines to indicate whether you are
1782 building a DLL, building client code that will link to the DLL, or
1783 merely building/linking to a static library. In making the choice
1784 between the various methods of resolving the 'direct address with
1785 constant offset' problem, you should consider typical real-world usage:
1793 void main(int argc, char **argv)@{
1794 printf("%d\n",arr[1]);
1804 void main(int argc, char **argv)@{
1805 /* This workaround is for win32 and cygwin; do not "optimize" */
1806 volatile int *parr = arr;
1807 printf("%d\n",parr[1]);
1814 /* Note: auto-export is assumed (no __declspec(dllexport)) */
1815 #if (defined(_WIN32) || defined(__CYGWIN__)) && \
1816 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
1817 #define FOO_IMPORT __declspec(dllimport)
1821 extern FOO_IMPORT int arr[];
1824 void main(int argc, char **argv)@{
1825 printf("%d\n",arr[1]);
1829 A third way to avoid this problem is to re-code your
1830 library to use a functional interface rather than a data interface
1831 for the offending variables (e.g. set_foo() and get_foo() accessor
1834 @kindex --disable-auto-import
1835 @item --disable-auto-import
1836 Do not attempt to do sophisticalted linking of @code{_symbol} to
1837 @code{__imp__symbol} for DATA imports from DLLs.
1839 @kindex --enable-extra-pe-debug
1840 @item --enable-extra-pe-debug
1841 Show additional debug info related to auto-import symbol thunking.
1843 @kindex --section-alignment
1844 @item --section-alignment
1845 Sets the section alignment. Sections in memory will always begin at
1846 addresses which are a multiple of this number. Defaults to 0x1000.
1850 @item --stack @var{reserve}
1851 @itemx --stack @var{reserve},@var{commit}
1852 Specify the amount of memory to reserve (and optionally commit) to be
1853 used as stack for this program. The default is 2Mb reserved, 4K
1857 @item --subsystem @var{which}
1858 @itemx --subsystem @var{which}:@var{major}
1859 @itemx --subsystem @var{which}:@var{major}.@var{minor}
1860 Specifies the subsystem under which your program will execute. The
1861 legal values for @var{which} are @code{native}, @code{windows},
1862 @code{console}, and @code{posix}. You may optionally set the
1863 subsystem version also.
1871 @section Environment Variables
1873 @c man begin ENVIRONMENT
1875 You can change the behavior of @code{ld} with the environment variables
1876 @code{GNUTARGET}, @code{LDEMULATION}, and @code{COLLECT_NO_DEMANGLE}.
1879 @cindex default input format
1880 @code{GNUTARGET} determines the input-file object format if you don't
1881 use @samp{-b} (or its synonym @samp{--format}). Its value should be one
1882 of the BFD names for an input format (@pxref{BFD}). If there is no
1883 @code{GNUTARGET} in the environment, @code{ld} uses the natural format
1884 of the target. If @code{GNUTARGET} is set to @code{default} then BFD
1885 attempts to discover the input format by examining binary input files;
1886 this method often succeeds, but there are potential ambiguities, since
1887 there is no method of ensuring that the magic number used to specify
1888 object-file formats is unique. However, the configuration procedure for
1889 BFD on each system places the conventional format for that system first
1890 in the search-list, so ambiguities are resolved in favor of convention.
1893 @cindex default emulation
1894 @cindex emulation, default
1895 @code{LDEMULATION} determines the default emulation if you don't use the
1896 @samp{-m} option. The emulation can affect various aspects of linker
1897 behaviour, particularly the default linker script. You can list the
1898 available emulations with the @samp{--verbose} or @samp{-V} options. If
1899 the @samp{-m} option is not used, and the @code{LDEMULATION} environment
1900 variable is not defined, the default emulation depends upon how the
1901 linker was configured.
1903 @kindex COLLECT_NO_DEMANGLE
1904 @cindex demangling, default
1905 Normally, the linker will default to demangling symbols. However, if
1906 @code{COLLECT_NO_DEMANGLE} is set in the environment, then it will
1907 default to not demangling symbols. This environment variable is used in
1908 a similar fashion by the @code{gcc} linker wrapper program. The default
1909 may be overridden by the @samp{--demangle} and @samp{--no-demangle}
1916 @chapter Linker Scripts
1919 @cindex linker scripts
1920 @cindex command files
1921 Every link is controlled by a @dfn{linker script}. This script is
1922 written in the linker command language.
1924 The main purpose of the linker script is to describe how the sections in
1925 the input files should be mapped into the output file, and to control
1926 the memory layout of the output file. Most linker scripts do nothing
1927 more than this. However, when necessary, the linker script can also
1928 direct the linker to perform many other operations, using the commands
1931 The linker always uses a linker script. If you do not supply one
1932 yourself, the linker will use a default script that is compiled into the
1933 linker executable. You can use the @samp{--verbose} command line option
1934 to display the default linker script. Certain command line options,
1935 such as @samp{-r} or @samp{-N}, will affect the default linker script.
1937 You may supply your own linker script by using the @samp{-T} command
1938 line option. When you do this, your linker script will replace the
1939 default linker script.
1941 You may also use linker scripts implicitly by naming them as input files
1942 to the linker, as though they were files to be linked. @xref{Implicit
1946 * Basic Script Concepts:: Basic Linker Script Concepts
1947 * Script Format:: Linker Script Format
1948 * Simple Example:: Simple Linker Script Example
1949 * Simple Commands:: Simple Linker Script Commands
1950 * Assignments:: Assigning Values to Symbols
1951 * SECTIONS:: SECTIONS Command
1952 * MEMORY:: MEMORY Command
1953 * PHDRS:: PHDRS Command
1954 * VERSION:: VERSION Command
1955 * Expressions:: Expressions in Linker Scripts
1956 * Implicit Linker Scripts:: Implicit Linker Scripts
1959 @node Basic Script Concepts
1960 @section Basic Linker Script Concepts
1961 @cindex linker script concepts
1962 We need to define some basic concepts and vocabulary in order to
1963 describe the linker script language.
1965 The linker combines input files into a single output file. The output
1966 file and each input file are in a special data format known as an
1967 @dfn{object file format}. Each file is called an @dfn{object file}.
1968 The output file is often called an @dfn{executable}, but for our
1969 purposes we will also call it an object file. Each object file has,
1970 among other things, a list of @dfn{sections}. We sometimes refer to a
1971 section in an input file as an @dfn{input section}; similarly, a section
1972 in the output file is an @dfn{output section}.
1974 Each section in an object file has a name and a size. Most sections
1975 also have an associated block of data, known as the @dfn{section
1976 contents}. A section may be marked as @dfn{loadable}, which mean that
1977 the contents should be loaded into memory when the output file is run.
1978 A section with no contents may be @dfn{allocatable}, which means that an
1979 area in memory should be set aside, but nothing in particular should be
1980 loaded there (in some cases this memory must be zeroed out). A section
1981 which is neither loadable nor allocatable typically contains some sort
1982 of debugging information.
1984 Every loadable or allocatable output section has two addresses. The
1985 first is the @dfn{VMA}, or virtual memory address. This is the address
1986 the section will have when the output file is run. The second is the
1987 @dfn{LMA}, or load memory address. This is the address at which the
1988 section will be loaded. In most cases the two addresses will be the
1989 same. An example of when they might be different is when a data section
1990 is loaded into ROM, and then copied into RAM when the program starts up
1991 (this technique is often used to initialize global variables in a ROM
1992 based system). In this case the ROM address would be the LMA, and the
1993 RAM address would be the VMA.
1995 You can see the sections in an object file by using the @code{objdump}
1996 program with the @samp{-h} option.
1998 Every object file also has a list of @dfn{symbols}, known as the
1999 @dfn{symbol table}. A symbol may be defined or undefined. Each symbol
2000 has a name, and each defined symbol has an address, among other
2001 information. If you compile a C or C++ program into an object file, you
2002 will get a defined symbol for every defined function and global or
2003 static variable. Every undefined function or global variable which is
2004 referenced in the input file will become an undefined symbol.
2006 You can see the symbols in an object file by using the @code{nm}
2007 program, or by using the @code{objdump} program with the @samp{-t}
2011 @section Linker Script Format
2012 @cindex linker script format
2013 Linker scripts are text files.
2015 You write a linker script as a series of commands. Each command is
2016 either a keyword, possibly followed by arguments, or an assignment to a
2017 symbol. You may separate commands using semicolons. Whitespace is
2020 Strings such as file or format names can normally be entered directly.
2021 If the file name contains a character such as a comma which would
2022 otherwise serve to separate file names, you may put the file name in
2023 double quotes. There is no way to use a double quote character in a
2026 You may include comments in linker scripts just as in C, delimited by
2027 @samp{/*} and @samp{*/}. As in C, comments are syntactically equivalent
2030 @node Simple Example
2031 @section Simple Linker Script Example
2032 @cindex linker script example
2033 @cindex example of linker script
2034 Many linker scripts are fairly simple.
2036 The simplest possible linker script has just one command:
2037 @samp{SECTIONS}. You use the @samp{SECTIONS} command to describe the
2038 memory layout of the output file.
2040 The @samp{SECTIONS} command is a powerful command. Here we will
2041 describe a simple use of it. Let's assume your program consists only of
2042 code, initialized data, and uninitialized data. These will be in the
2043 @samp{.text}, @samp{.data}, and @samp{.bss} sections, respectively.
2044 Let's assume further that these are the only sections which appear in
2047 For this example, let's say that the code should be loaded at address
2048 0x10000, and that the data should start at address 0x8000000. Here is a
2049 linker script which will do that:
2054 .text : @{ *(.text) @}
2056 .data : @{ *(.data) @}
2057 .bss : @{ *(.bss) @}
2061 You write the @samp{SECTIONS} command as the keyword @samp{SECTIONS},
2062 followed by a series of symbol assignments and output section
2063 descriptions enclosed in curly braces.
2065 The first line inside the @samp{SECTIONS} command of the above example
2066 sets the value of the special symbol @samp{.}, which is the location
2067 counter. If you do not specify the address of an output section in some
2068 other way (other ways are described later), the address is set from the
2069 current value of the location counter. The location counter is then
2070 incremented by the size of the output section. At the start of the
2071 @samp{SECTIONS} command, the location counter has the value @samp{0}.
2073 The second line defines an output section, @samp{.text}. The colon is
2074 required syntax which may be ignored for now. Within the curly braces
2075 after the output section name, you list the names of the input sections
2076 which should be placed into this output section. The @samp{*} is a
2077 wildcard which matches any file name. The expression @samp{*(.text)}
2078 means all @samp{.text} input sections in all input files.
2080 Since the location counter is @samp{0x10000} when the output section
2081 @samp{.text} is defined, the linker will set the address of the
2082 @samp{.text} section in the output file to be @samp{0x10000}.
2084 The remaining lines define the @samp{.data} and @samp{.bss} sections in
2085 the output file. The linker will place the @samp{.data} output section
2086 at address @samp{0x8000000}. After the linker places the @samp{.data}
2087 output section, the value of the location counter will be
2088 @samp{0x8000000} plus the size of the @samp{.data} output section. The
2089 effect is that the linker will place the @samp{.bss} output section
2090 immediately after the @samp{.data} output section in memory
2092 The linker will ensure that each output section has the required
2093 alignment, by increasing the location counter if necessary. In this
2094 example, the specified addresses for the @samp{.text} and @samp{.data}
2095 sections will probably satisfy any alignment constraints, but the linker
2096 may have to create a small gap between the @samp{.data} and @samp{.bss}
2099 That's it! That's a simple and complete linker script.
2101 @node Simple Commands
2102 @section Simple Linker Script Commands
2103 @cindex linker script simple commands
2104 In this section we describe the simple linker script commands.
2107 * Entry Point:: Setting the entry point
2108 * File Commands:: Commands dealing with files
2109 @ifclear SingleFormat
2110 * Format Commands:: Commands dealing with object file formats
2113 * Miscellaneous Commands:: Other linker script commands
2117 @subsection Setting the entry point
2118 @kindex ENTRY(@var{symbol})
2119 @cindex start of execution
2120 @cindex first instruction
2122 The first instruction to execute in a program is called the @dfn{entry
2123 point}. You can use the @code{ENTRY} linker script command to set the
2124 entry point. The argument is a symbol name:
2129 There are several ways to set the entry point. The linker will set the
2130 entry point by trying each of the following methods in order, and
2131 stopping when one of them succeeds:
2134 the @samp{-e} @var{entry} command-line option;
2136 the @code{ENTRY(@var{symbol})} command in a linker script;
2138 the value of the symbol @code{start}, if defined;
2140 the address of the first byte of the @samp{.text} section, if present;
2142 The address @code{0}.
2146 @subsection Commands dealing with files
2147 @cindex linker script file commands
2148 Several linker script commands deal with files.
2151 @item INCLUDE @var{filename}
2152 @kindex INCLUDE @var{filename}
2153 @cindex including a linker script
2154 Include the linker script @var{filename} at this point. The file will
2155 be searched for in the current directory, and in any directory specified
2156 with the @code{-L} option. You can nest calls to @code{INCLUDE} up to
2159 @item INPUT(@var{file}, @var{file}, @dots{})
2160 @itemx INPUT(@var{file} @var{file} @dots{})
2161 @kindex INPUT(@var{files})
2162 @cindex input files in linker scripts
2163 @cindex input object files in linker scripts
2164 @cindex linker script input object files
2165 The @code{INPUT} command directs the linker to include the named files
2166 in the link, as though they were named on the command line.
2168 For example, if you always want to include @file{subr.o} any time you do
2169 a link, but you can't be bothered to put it on every link command line,
2170 then you can put @samp{INPUT (subr.o)} in your linker script.
2172 In fact, if you like, you can list all of your input files in the linker
2173 script, and then invoke the linker with nothing but a @samp{-T} option.
2175 The linker will first try to open the file in the current directory. If
2176 it is not found, the linker will search through the archive library
2177 search path. See the description of @samp{-L} in @ref{Options,,Command
2180 If you use @samp{INPUT (-l@var{file})}, @code{ld} will transform the
2181 name to @code{lib@var{file}.a}, as with the command line argument
2184 When you use the @code{INPUT} command in an implicit linker script, the
2185 files will be included in the link at the point at which the linker
2186 script file is included. This can affect archive searching.
2188 @item GROUP(@var{file}, @var{file}, @dots{})
2189 @itemx GROUP(@var{file} @var{file} @dots{})
2190 @kindex GROUP(@var{files})
2191 @cindex grouping input files
2192 The @code{GROUP} command is like @code{INPUT}, except that the named
2193 files should all be archives, and they are searched repeatedly until no
2194 new undefined references are created. See the description of @samp{-(}
2195 in @ref{Options,,Command Line Options}.
2197 @item OUTPUT(@var{filename})
2198 @kindex OUTPUT(@var{filename})
2199 @cindex output file name in linker scripot
2200 The @code{OUTPUT} command names the output file. Using
2201 @code{OUTPUT(@var{filename})} in the linker script is exactly like using
2202 @samp{-o @var{filename}} on the command line (@pxref{Options,,Command
2203 Line Options}). If both are used, the command line option takes
2206 You can use the @code{OUTPUT} command to define a default name for the
2207 output file other than the usual default of @file{a.out}.
2209 @item SEARCH_DIR(@var{path})
2210 @kindex SEARCH_DIR(@var{path})
2211 @cindex library search path in linker script
2212 @cindex archive search path in linker script
2213 @cindex search path in linker script
2214 The @code{SEARCH_DIR} command adds @var{path} to the list of paths where
2215 @code{ld} looks for archive libraries. Using
2216 @code{SEARCH_DIR(@var{path})} is exactly like using @samp{-L @var{path}}
2217 on the command line (@pxref{Options,,Command Line Options}). If both
2218 are used, then the linker will search both paths. Paths specified using
2219 the command line option are searched first.
2221 @item STARTUP(@var{filename})
2222 @kindex STARTUP(@var{filename})
2223 @cindex first input file
2224 The @code{STARTUP} command is just like the @code{INPUT} command, except
2225 that @var{filename} will become the first input file to be linked, as
2226 though it were specified first on the command line. This may be useful
2227 when using a system in which the entry point is always the start of the
2231 @ifclear SingleFormat
2232 @node Format Commands
2233 @subsection Commands dealing with object file formats
2234 A couple of linker script commands deal with object file formats.
2237 @item OUTPUT_FORMAT(@var{bfdname})
2238 @itemx OUTPUT_FORMAT(@var{default}, @var{big}, @var{little})
2239 @kindex OUTPUT_FORMAT(@var{bfdname})
2240 @cindex output file format in linker script
2241 The @code{OUTPUT_FORMAT} command names the BFD format to use for the
2242 output file (@pxref{BFD}). Using @code{OUTPUT_FORMAT(@var{bfdname})} is
2243 exactly like using @samp{-oformat @var{bfdname}} on the command line
2244 (@pxref{Options,,Command Line Options}). If both are used, the command
2245 line option takes precedence.
2247 You can use @code{OUTPUT_FORMAT} with three arguments to use different
2248 formats based on the @samp{-EB} and @samp{-EL} command line options.
2249 This permits the linker script to set the output format based on the
2252 If neither @samp{-EB} nor @samp{-EL} are used, then the output format
2253 will be the first argument, @var{default}. If @samp{-EB} is used, the
2254 output format will be the second argument, @var{big}. If @samp{-EL} is
2255 used, the output format will be the third argument, @var{little}.
2257 For example, the default linker script for the MIPS ELF target uses this
2260 OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips)
2262 This says that the default format for the output file is
2263 @samp{elf32-bigmips}, but if the user uses the @samp{-EL} command line
2264 option, the output file will be created in the @samp{elf32-littlemips}
2267 @item TARGET(@var{bfdname})
2268 @kindex TARGET(@var{bfdname})
2269 @cindex input file format in linker script
2270 The @code{TARGET} command names the BFD format to use when reading input
2271 files. It affects subsequent @code{INPUT} and @code{GROUP} commands.
2272 This command is like using @samp{-b @var{bfdname}} on the command line
2273 (@pxref{Options,,Command Line Options}). If the @code{TARGET} command
2274 is used but @code{OUTPUT_FORMAT} is not, then the last @code{TARGET}
2275 command is also used to set the format for the output file. @xref{BFD}.
2279 @node Miscellaneous Commands
2280 @subsection Other linker script commands
2281 There are a few other linker scripts commands.
2284 @item ASSERT(@var{exp}, @var{message})
2286 @cindex assertion in linker script
2287 Ensure that @var{exp} is non-zero. If it is zero, then exit the linker
2288 with an error code, and print @var{message}.
2290 @item EXTERN(@var{symbol} @var{symbol} @dots{})
2292 @cindex undefined symbol in linker script
2293 Force @var{symbol} to be entered in the output file as an undefined
2294 symbol. Doing this may, for example, trigger linking of additional
2295 modules from standard libraries. You may list several @var{symbol}s for
2296 each @code{EXTERN}, and you may use @code{EXTERN} multiple times. This
2297 command has the same effect as the @samp{-u} command-line option.
2299 @item FORCE_COMMON_ALLOCATION
2300 @kindex FORCE_COMMON_ALLOCATION
2301 @cindex common allocation in linker script
2302 This command has the same effect as the @samp{-d} command-line option:
2303 to make @code{ld} assign space to common symbols even if a relocatable
2304 output file is specified (@samp{-r}).
2306 @item NOCROSSREFS(@var{section} @var{section} @dots{})
2307 @kindex NOCROSSREFS(@var{sections})
2308 @cindex cross references
2309 This command may be used to tell @code{ld} to issue an error about any
2310 references among certain output sections.
2312 In certain types of programs, particularly on embedded systems when
2313 using overlays, when one section is loaded into memory, another section
2314 will not be. Any direct references between the two sections would be
2315 errors. For example, it would be an error if code in one section called
2316 a function defined in the other section.
2318 The @code{NOCROSSREFS} command takes a list of output section names. If
2319 @code{ld} detects any cross references between the sections, it reports
2320 an error and returns a non-zero exit status. Note that the
2321 @code{NOCROSSREFS} command uses output section names, not input section
2324 @ifclear SingleFormat
2325 @item OUTPUT_ARCH(@var{bfdarch})
2326 @kindex OUTPUT_ARCH(@var{bfdarch})
2327 @cindex machine architecture
2328 @cindex architecture
2329 Specify a particular output machine architecture. The argument is one
2330 of the names used by the BFD library (@pxref{BFD}). You can see the
2331 architecture of an object file by using the @code{objdump} program with
2332 the @samp{-f} option.
2337 @section Assigning Values to Symbols
2338 @cindex assignment in scripts
2339 @cindex symbol definition, scripts
2340 @cindex variables, defining
2341 You may assign a value to a symbol in a linker script. This will define
2342 the symbol as a global symbol.
2345 * Simple Assignments:: Simple Assignments
2349 @node Simple Assignments
2350 @subsection Simple Assignments
2352 You may assign to a symbol using any of the C assignment operators:
2355 @item @var{symbol} = @var{expression} ;
2356 @itemx @var{symbol} += @var{expression} ;
2357 @itemx @var{symbol} -= @var{expression} ;
2358 @itemx @var{symbol} *= @var{expression} ;
2359 @itemx @var{symbol} /= @var{expression} ;
2360 @itemx @var{symbol} <<= @var{expression} ;
2361 @itemx @var{symbol} >>= @var{expression} ;
2362 @itemx @var{symbol} &= @var{expression} ;
2363 @itemx @var{symbol} |= @var{expression} ;
2366 The first case will define @var{symbol} to the value of
2367 @var{expression}. In the other cases, @var{symbol} must already be
2368 defined, and the value will be adjusted accordingly.
2370 The special symbol name @samp{.} indicates the location counter. You
2371 may only use this within a @code{SECTIONS} command.
2373 The semicolon after @var{expression} is required.
2375 Expressions are defined below; see @ref{Expressions}.
2377 You may write symbol assignments as commands in their own right, or as
2378 statements within a @code{SECTIONS} command, or as part of an output
2379 section description in a @code{SECTIONS} command.
2381 The section of the symbol will be set from the section of the
2382 expression; for more information, see @ref{Expression Section}.
2384 Here is an example showing the three different places that symbol
2385 assignments may be used:
2396 _bdata = (. + 3) & ~ 3;
2397 .data : @{ *(.data) @}
2401 In this example, the symbol @samp{floating_point} will be defined as
2402 zero. The symbol @samp{_etext} will be defined as the address following
2403 the last @samp{.text} input section. The symbol @samp{_bdata} will be
2404 defined as the address following the @samp{.text} output section aligned
2405 upward to a 4 byte boundary.
2410 In some cases, it is desirable for a linker script to define a symbol
2411 only if it is referenced and is not defined by any object included in
2412 the link. For example, traditional linkers defined the symbol
2413 @samp{etext}. However, ANSI C requires that the user be able to use
2414 @samp{etext} as a function name without encountering an error. The
2415 @code{PROVIDE} keyword may be used to define a symbol, such as
2416 @samp{etext}, only if it is referenced but not defined. The syntax is
2417 @code{PROVIDE(@var{symbol} = @var{expression})}.
2419 Here is an example of using @code{PROVIDE} to define @samp{etext}:
2432 In this example, if the program defines @samp{_etext} (with a leading
2433 underscore), the linker will give a multiple definition error. If, on
2434 the other hand, the program defines @samp{etext} (with no leading
2435 underscore), the linker will silently use the definition in the program.
2436 If the program references @samp{etext} but does not define it, the
2437 linker will use the definition in the linker script.
2440 @section SECTIONS command
2442 The @code{SECTIONS} command tells the linker how to map input sections
2443 into output sections, and how to place the output sections in memory.
2445 The format of the @code{SECTIONS} command is:
2449 @var{sections-command}
2450 @var{sections-command}
2455 Each @var{sections-command} may of be one of the following:
2459 an @code{ENTRY} command (@pxref{Entry Point,,Entry command})
2461 a symbol assignment (@pxref{Assignments})
2463 an output section description
2465 an overlay description
2468 The @code{ENTRY} command and symbol assignments are permitted inside the
2469 @code{SECTIONS} command for convenience in using the location counter in
2470 those commands. This can also make the linker script easier to
2471 understand because you can use those commands at meaningful points in
2472 the layout of the output file.
2474 Output section descriptions and overlay descriptions are described
2477 If you do not use a @code{SECTIONS} command in your linker script, the
2478 linker will place each input section into an identically named output
2479 section in the order that the sections are first encountered in the
2480 input files. If all input sections are present in the first file, for
2481 example, the order of sections in the output file will match the order
2482 in the first input file. The first section will be at address zero.
2485 * Output Section Description:: Output section description
2486 * Output Section Name:: Output section name
2487 * Output Section Address:: Output section address
2488 * Input Section:: Input section description
2489 * Output Section Data:: Output section data
2490 * Output Section Keywords:: Output section keywords
2491 * Output Section Discarding:: Output section discarding
2492 * Output Section Attributes:: Output section attributes
2493 * Overlay Description:: Overlay description
2496 @node Output Section Description
2497 @subsection Output section description
2498 The full description of an output section looks like this:
2501 @var{section} [@var{address}] [(@var{type})] : [AT(@var{lma})]
2503 @var{output-section-command}
2504 @var{output-section-command}
2506 @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}]
2510 Most output sections do not use most of the optional section attributes.
2512 The whitespace around @var{section} is required, so that the section
2513 name is unambiguous. The colon and the curly braces are also required.
2514 The line breaks and other white space are optional.
2516 Each @var{output-section-command} may be one of the following:
2520 a symbol assignment (@pxref{Assignments})
2522 an input section description (@pxref{Input Section})
2524 data values to include directly (@pxref{Output Section Data})
2526 a special output section keyword (@pxref{Output Section Keywords})
2529 @node Output Section Name
2530 @subsection Output section name
2531 @cindex name, section
2532 @cindex section name
2533 The name of the output section is @var{section}. @var{section} must
2534 meet the constraints of your output format. In formats which only
2535 support a limited number of sections, such as @code{a.out}, the name
2536 must be one of the names supported by the format (@code{a.out}, for
2537 example, allows only @samp{.text}, @samp{.data} or @samp{.bss}). If the
2538 output format supports any number of sections, but with numbers and not
2539 names (as is the case for Oasys), the name should be supplied as a
2540 quoted numeric string. A section name may consist of any sequence of
2541 characters, but a name which contains any unusual characters such as
2542 commas must be quoted.
2544 The output section name @samp{/DISCARD/} is special; @ref{Output Section
2547 @node Output Section Address
2548 @subsection Output section address
2549 @cindex address, section
2550 @cindex section address
2551 The @var{address} is an expression for the VMA (the virtual memory
2552 address) of the output section. If you do not provide @var{address},
2553 the linker will set it based on @var{region} if present, or otherwise
2554 based on the current value of the location counter.
2556 If you provide @var{address}, the address of the output section will be
2557 set to precisely that. If you provide neither @var{address} nor
2558 @var{region}, then the address of the output section will be set to the
2559 current value of the location counter aligned to the alignment
2560 requirements of the output section. The alignment requirement of the
2561 output section is the strictest alignment of any input section contained
2562 within the output section.
2566 .text . : @{ *(.text) @}
2571 .text : @{ *(.text) @}
2574 are subtly different. The first will set the address of the
2575 @samp{.text} output section to the current value of the location
2576 counter. The second will set it to the current value of the location
2577 counter aligned to the strictest alignment of a @samp{.text} input
2580 The @var{address} may be an arbitrary expression; @ref{Expressions}.
2581 For example, if you want to align the section on a 0x10 byte boundary,
2582 so that the lowest four bits of the section address are zero, you could
2583 do something like this:
2585 .text ALIGN(0x10) : @{ *(.text) @}
2588 This works because @code{ALIGN} returns the current location counter
2589 aligned upward to the specified value.
2591 Specifying @var{address} for a section will change the value of the
2595 @subsection Input section description
2596 @cindex input sections
2597 @cindex mapping input sections to output sections
2598 The most common output section command is an input section description.
2600 The input section description is the most basic linker script operation.
2601 You use output sections to tell the linker how to lay out your program
2602 in memory. You use input section descriptions to tell the linker how to
2603 map the input files into your memory layout.
2606 * Input Section Basics:: Input section basics
2607 * Input Section Wildcards:: Input section wildcard patterns
2608 * Input Section Common:: Input section for common symbols
2609 * Input Section Keep:: Input section and garbage collection
2610 * Input Section Example:: Input section example
2613 @node Input Section Basics
2614 @subsubsection Input section basics
2615 @cindex input section basics
2616 An input section description consists of a file name optionally followed
2617 by a list of section names in parentheses.
2619 The file name and the section name may be wildcard patterns, which we
2620 describe further below (@pxref{Input Section Wildcards}).
2622 The most common input section description is to include all input
2623 sections with a particular name in the output section. For example, to
2624 include all input @samp{.text} sections, you would write:
2629 Here the @samp{*} is a wildcard which matches any file name. To exclude a list
2630 of files from matching the file name wildcard, EXCLUDE_FILE may be used to
2631 match all files except the ones specified in the EXCLUDE_FILE list. For
2634 (*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors))
2636 will cause all .ctors sections from all files except @file{crtend.o} and
2637 @file{otherfile.o} to be included.
2639 There are two ways to include more than one section:
2645 The difference between these is the order in which the @samp{.text} and
2646 @samp{.rdata} input sections will appear in the output section. In the
2647 first example, they will be intermingled, appearing in the same order as
2648 they are found in the linker input. In the second example, all
2649 @samp{.text} input sections will appear first, followed by all
2650 @samp{.rdata} input sections.
2652 You can specify a file name to include sections from a particular file.
2653 You would do this if one or more of your files contain special data that
2654 needs to be at a particular location in memory. For example:
2659 If you use a file name without a list of sections, then all sections in
2660 the input file will be included in the output section. This is not
2661 commonly done, but it may by useful on occasion. For example:
2666 When you use a file name which does not contain any wild card
2667 characters, the linker will first see if you also specified the file
2668 name on the linker command line or in an @code{INPUT} command. If you
2669 did not, the linker will attempt to open the file as an input file, as
2670 though it appeared on the command line. Note that this differs from an
2671 @code{INPUT} command, because the linker will not search for the file in
2672 the archive search path.
2674 @node Input Section Wildcards
2675 @subsubsection Input section wildcard patterns
2676 @cindex input section wildcards
2677 @cindex wildcard file name patterns
2678 @cindex file name wildcard patterns
2679 @cindex section name wildcard patterns
2680 In an input section description, either the file name or the section
2681 name or both may be wildcard patterns.
2683 The file name of @samp{*} seen in many examples is a simple wildcard
2684 pattern for the file name.
2686 The wildcard patterns are like those used by the Unix shell.
2690 matches any number of characters
2692 matches any single character
2694 matches a single instance of any of the @var{chars}; the @samp{-}
2695 character may be used to specify a range of characters, as in
2696 @samp{[a-z]} to match any lower case letter
2698 quotes the following character
2701 When a file name is matched with a wildcard, the wildcard characters
2702 will not match a @samp{/} character (used to separate directory names on
2703 Unix). A pattern consisting of a single @samp{*} character is an
2704 exception; it will always match any file name, whether it contains a
2705 @samp{/} or not. In a section name, the wildcard characters will match
2706 a @samp{/} character.
2708 File name wildcard patterns only match files which are explicitly
2709 specified on the command line or in an @code{INPUT} command. The linker
2710 does not search directories to expand wildcards.
2712 If a file name matches more than one wildcard pattern, or if a file name
2713 appears explicitly and is also matched by a wildcard pattern, the linker
2714 will use the first match in the linker script. For example, this
2715 sequence of input section descriptions is probably in error, because the
2716 @file{data.o} rule will not be used:
2718 .data : @{ *(.data) @}
2719 .data1 : @{ data.o(.data) @}
2723 Normally, the linker will place files and sections matched by wildcards
2724 in the order in which they are seen during the link. You can change
2725 this by using the @code{SORT} keyword, which appears before a wildcard
2726 pattern in parentheses (e.g., @code{SORT(.text*)}). When the
2727 @code{SORT} keyword is used, the linker will sort the files or sections
2728 into ascending order by name before placing them in the output file.
2730 If you ever get confused about where input sections are going, use the
2731 @samp{-M} linker option to generate a map file. The map file shows
2732 precisely how input sections are mapped to output sections.
2734 This example shows how wildcard patterns might be used to partition
2735 files. This linker script directs the linker to place all @samp{.text}
2736 sections in @samp{.text} and all @samp{.bss} sections in @samp{.bss}.
2737 The linker will place the @samp{.data} section from all files beginning
2738 with an upper case character in @samp{.DATA}; for all other files, the
2739 linker will place the @samp{.data} section in @samp{.data}.
2743 .text : @{ *(.text) @}
2744 .DATA : @{ [A-Z]*(.data) @}
2745 .data : @{ *(.data) @}
2746 .bss : @{ *(.bss) @}
2751 @node Input Section Common
2752 @subsubsection Input section for common symbols
2753 @cindex common symbol placement
2754 @cindex uninitialized data placement
2755 A special notation is needed for common symbols, because in many object
2756 file formats common symbols do not have a particular input section. The
2757 linker treats common symbols as though they are in an input section
2758 named @samp{COMMON}.
2760 You may use file names with the @samp{COMMON} section just as with any
2761 other input sections. You can use this to place common symbols from a
2762 particular input file in one section while common symbols from other
2763 input files are placed in another section.
2765 In most cases, common symbols in input files will be placed in the
2766 @samp{.bss} section in the output file. For example:
2768 .bss @{ *(.bss) *(COMMON) @}
2771 @cindex scommon section
2772 @cindex small common symbols
2773 Some object file formats have more than one type of common symbol. For
2774 example, the MIPS ELF object file format distinguishes standard common
2775 symbols and small common symbols. In this case, the linker will use a
2776 different special section name for other types of common symbols. In
2777 the case of MIPS ELF, the linker uses @samp{COMMON} for standard common
2778 symbols and @samp{.scommon} for small common symbols. This permits you
2779 to map the different types of common symbols into memory at different
2783 You will sometimes see @samp{[COMMON]} in old linker scripts. This
2784 notation is now considered obsolete. It is equivalent to
2787 @node Input Section Keep
2788 @subsubsection Input section and garbage collection
2790 @cindex garbage collection
2791 When link-time garbage collection is in use (@samp{--gc-sections}),
2792 it is often useful to mark sections that should not be eliminated.
2793 This is accomplished by surrounding an input section's wildcard entry
2794 with @code{KEEP()}, as in @code{KEEP(*(.init))} or
2795 @code{KEEP(SORT(*)(.ctors))}.
2797 @node Input Section Example
2798 @subsubsection Input section example
2799 The following example is a complete linker script. It tells the linker
2800 to read all of the sections from file @file{all.o} and place them at the
2801 start of output section @samp{outputa} which starts at location
2802 @samp{0x10000}. All of section @samp{.input1} from file @file{foo.o}
2803 follows immediately, in the same output section. All of section
2804 @samp{.input2} from @file{foo.o} goes into output section
2805 @samp{outputb}, followed by section @samp{.input1} from @file{foo1.o}.
2806 All of the remaining @samp{.input1} and @samp{.input2} sections from any
2807 files are written to output section @samp{outputc}.
2831 @node Output Section Data
2832 @subsection Output section data
2834 @cindex section data
2835 @cindex output section data
2836 @kindex BYTE(@var{expression})
2837 @kindex SHORT(@var{expression})
2838 @kindex LONG(@var{expression})
2839 @kindex QUAD(@var{expression})
2840 @kindex SQUAD(@var{expression})
2841 You can include explicit bytes of data in an output section by using
2842 @code{BYTE}, @code{SHORT}, @code{LONG}, @code{QUAD}, or @code{SQUAD} as
2843 an output section command. Each keyword is followed by an expression in
2844 parentheses providing the value to store (@pxref{Expressions}). The
2845 value of the expression is stored at the current value of the location
2848 The @code{BYTE}, @code{SHORT}, @code{LONG}, and @code{QUAD} commands
2849 store one, two, four, and eight bytes (respectively). After storing the
2850 bytes, the location counter is incremented by the number of bytes
2853 For example, this will store the byte 1 followed by the four byte value
2854 of the symbol @samp{addr}:
2860 When using a 64 bit host or target, @code{QUAD} and @code{SQUAD} are the
2861 same; they both store an 8 byte, or 64 bit, value. When both host and
2862 target are 32 bits, an expression is computed as 32 bits. In this case
2863 @code{QUAD} stores a 32 bit value zero extended to 64 bits, and
2864 @code{SQUAD} stores a 32 bit value sign extended to 64 bits.
2866 If the object file format of the output file has an explicit endianness,
2867 which is the normal case, the value will be stored in that endianness.
2868 When the object file format does not have an explicit endianness, as is
2869 true of, for example, S-records, the value will be stored in the
2870 endianness of the first input object file.
2872 Note - these commands only work inside a section description and not
2873 between them, so the following will produce an error from the linker:
2875 SECTIONS @{@ .text : @{@ *(.text) @}@ LONG(1) .data : @{@ *(.data) @}@ @}@
2877 whereas this will work:
2879 SECTIONS @{@ .text : @{@ *(.text) ; LONG(1) @}@ .data : @{@ *(.data) @}@ @}@
2882 @kindex FILL(@var{expression})
2883 @cindex holes, filling
2884 @cindex unspecified memory
2885 You may use the @code{FILL} command to set the fill pattern for the
2886 current section. It is followed by an expression in parentheses. Any
2887 otherwise unspecified regions of memory within the section (for example,
2888 gaps left due to the required alignment of input sections) are filled
2889 with the four least significant bytes of the expression, repeated as
2890 necessary. A @code{FILL} statement covers memory locations after the
2891 point at which it occurs in the section definition; by including more
2892 than one @code{FILL} statement, you can have different fill patterns in
2893 different parts of an output section.
2895 This example shows how to fill unspecified regions of memory with the
2901 The @code{FILL} command is similar to the @samp{=@var{fillexp}} output
2902 section attribute (@pxref{Output Section Fill}), but it only affects the
2903 part of the section following the @code{FILL} command, rather than the
2904 entire section. If both are used, the @code{FILL} command takes
2907 @node Output Section Keywords
2908 @subsection Output section keywords
2909 There are a couple of keywords which can appear as output section
2913 @kindex CREATE_OBJECT_SYMBOLS
2914 @cindex input filename symbols
2915 @cindex filename symbols
2916 @item CREATE_OBJECT_SYMBOLS
2917 The command tells the linker to create a symbol for each input file.
2918 The name of each symbol will be the name of the corresponding input
2919 file. The section of each symbol will be the output section in which
2920 the @code{CREATE_OBJECT_SYMBOLS} command appears.
2922 This is conventional for the a.out object file format. It is not
2923 normally used for any other object file format.
2925 @kindex CONSTRUCTORS
2926 @cindex C++ constructors, arranging in link
2927 @cindex constructors, arranging in link
2929 When linking using the a.out object file format, the linker uses an
2930 unusual set construct to support C++ global constructors and
2931 destructors. When linking object file formats which do not support
2932 arbitrary sections, such as ECOFF and XCOFF, the linker will
2933 automatically recognize C++ global constructors and destructors by name.
2934 For these object file formats, the @code{CONSTRUCTORS} command tells the
2935 linker to place constructor information in the output section where the
2936 @code{CONSTRUCTORS} command appears. The @code{CONSTRUCTORS} command is
2937 ignored for other object file formats.
2939 The symbol @w{@code{__CTOR_LIST__}} marks the start of the global
2940 constructors, and the symbol @w{@code{__DTOR_LIST}} marks the end. The
2941 first word in the list is the number of entries, followed by the address
2942 of each constructor or destructor, followed by a zero word. The
2943 compiler must arrange to actually run the code. For these object file
2944 formats @sc{gnu} C++ normally calls constructors from a subroutine
2945 @code{__main}; a call to @code{__main} is automatically inserted into
2946 the startup code for @code{main}. @sc{gnu} C++ normally runs
2947 destructors either by using @code{atexit}, or directly from the function
2950 For object file formats such as @code{COFF} or @code{ELF} which support
2951 arbitrary section names, @sc{gnu} C++ will normally arrange to put the
2952 addresses of global constructors and destructors into the @code{.ctors}
2953 and @code{.dtors} sections. Placing the following sequence into your
2954 linker script will build the sort of table which the @sc{gnu} C++
2955 runtime code expects to see.
2959 LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
2964 LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
2970 If you are using the @sc{gnu} C++ support for initialization priority,
2971 which provides some control over the order in which global constructors
2972 are run, you must sort the constructors at link time to ensure that they
2973 are executed in the correct order. When using the @code{CONSTRUCTORS}
2974 command, use @samp{SORT(CONSTRUCTORS)} instead. When using the
2975 @code{.ctors} and @code{.dtors} sections, use @samp{*(SORT(.ctors))} and
2976 @samp{*(SORT(.dtors))} instead of just @samp{*(.ctors)} and
2979 Normally the compiler and linker will handle these issues automatically,
2980 and you will not need to concern yourself with them. However, you may
2981 need to consider this if you are using C++ and writing your own linker
2986 @node Output Section Discarding
2987 @subsection Output section discarding
2988 @cindex discarding sections
2989 @cindex sections, discarding
2990 @cindex removing sections
2991 The linker will not create output section which do not have any
2992 contents. This is for convenience when referring to input sections that
2993 may or may not be present in any of the input files. For example:
2998 will only create a @samp{.foo} section in the output file if there is a
2999 @samp{.foo} section in at least one input file.
3001 If you use anything other than an input section description as an output
3002 section command, such as a symbol assignment, then the output section
3003 will always be created, even if there are no matching input sections.
3006 The special output section name @samp{/DISCARD/} may be used to discard
3007 input sections. Any input sections which are assigned to an output
3008 section named @samp{/DISCARD/} are not included in the output file.
3010 @node Output Section Attributes
3011 @subsection Output section attributes
3012 @cindex output section attributes
3013 We showed above that the full description of an output section looked
3017 @var{section} [@var{address}] [(@var{type})] : [AT(@var{lma})]
3019 @var{output-section-command}
3020 @var{output-section-command}
3022 @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}]
3025 We've already described @var{section}, @var{address}, and
3026 @var{output-section-command}. In this section we will describe the
3027 remaining section attributes.
3030 * Output Section Type:: Output section type
3031 * Output Section LMA:: Output section LMA
3032 * Output Section Region:: Output section region
3033 * Output Section Phdr:: Output section phdr
3034 * Output Section Fill:: Output section fill
3037 @node Output Section Type
3038 @subsubsection Output section type
3039 Each output section may have a type. The type is a keyword in
3040 parentheses. The following types are defined:
3044 The section should be marked as not loadable, so that it will not be
3045 loaded into memory when the program is run.
3050 These type names are supported for backward compatibility, and are
3051 rarely used. They all have the same effect: the section should be
3052 marked as not allocatable, so that no memory is allocated for the
3053 section when the program is run.
3057 @cindex prevent unnecessary loading
3058 @cindex loading, preventing
3059 The linker normally sets the attributes of an output section based on
3060 the input sections which map into it. You can override this by using
3061 the section type. For example, in the script sample below, the
3062 @samp{ROM} section is addressed at memory location @samp{0} and does not
3063 need to be loaded when the program is run. The contents of the
3064 @samp{ROM} section will appear in the linker output file as usual.
3068 ROM 0 (NOLOAD) : @{ @dots{} @}
3074 @node Output Section LMA
3075 @subsubsection Output section LMA
3076 @kindex AT>@var{lma_region}
3077 @kindex AT(@var{lma})
3078 @cindex load address
3079 @cindex section load address
3080 Every section has a virtual address (VMA) and a load address (LMA); see
3081 @ref{Basic Script Concepts}. The address expression which may appear in
3082 an output section description sets the VMA (@pxref{Output Section
3085 The linker will normally set the LMA equal to the VMA. You can change
3086 that by using the @code{AT} keyword. The expression @var{lma} that
3087 follows the @code{AT} keyword specifies the load address of the
3088 section. Alternatively, with @samp{AT>@var{lma_region}} expression,
3089 you may specify a memory region for the section's load address. @xref{MEMORY}.
3091 @cindex ROM initialized data
3092 @cindex initialized data in ROM
3093 This feature is designed to make it easy to build a ROM image. For
3094 example, the following linker script creates three output sections: one
3095 called @samp{.text}, which starts at @code{0x1000}, one called
3096 @samp{.mdata}, which is loaded at the end of the @samp{.text} section
3097 even though its VMA is @code{0x2000}, and one called @samp{.bss} to hold
3098 uninitialized data at address @code{0x3000}. The symbol @code{_data} is
3099 defined with the value @code{0x2000}, which shows that the location
3100 counter holds the VMA value, not the LMA value.
3106 .text 0x1000 : @{ *(.text) _etext = . ; @}
3108 AT ( ADDR (.text) + SIZEOF (.text) )
3109 @{ _data = . ; *(.data); _edata = . ; @}
3111 @{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;@}
3116 The run-time initialization code for use with a program generated with
3117 this linker script would include something like the following, to copy
3118 the initialized data from the ROM image to its runtime address. Notice
3119 how this code takes advantage of the symbols defined by the linker
3124 extern char _etext, _data, _edata, _bstart, _bend;
3125 char *src = &_etext;
3128 /* ROM has data at end of text; copy it. */
3129 while (dst < &_edata) @{
3134 for (dst = &_bstart; dst< &_bend; dst++)
3139 @node Output Section Region
3140 @subsubsection Output section region
3141 @kindex >@var{region}
3142 @cindex section, assigning to memory region
3143 @cindex memory regions and sections
3144 You can assign a section to a previously defined region of memory by
3145 using @samp{>@var{region}}. @xref{MEMORY}.
3147 Here is a simple example:
3150 MEMORY @{ rom : ORIGIN = 0x1000, LENGTH = 0x1000 @}
3151 SECTIONS @{ ROM : @{ *(.text) @} >rom @}
3155 @node Output Section Phdr
3156 @subsubsection Output section phdr
3158 @cindex section, assigning to program header
3159 @cindex program headers and sections
3160 You can assign a section to a previously defined program segment by
3161 using @samp{:@var{phdr}}. @xref{PHDRS}. If a section is assigned to
3162 one or more segments, then all subsequent allocated sections will be
3163 assigned to those segments as well, unless they use an explicitly
3164 @code{:@var{phdr}} modifier. You can use @code{:NONE} to tell the
3165 linker to not put the section in any segment at all.
3167 Here is a simple example:
3170 PHDRS @{ text PT_LOAD ; @}
3171 SECTIONS @{ .text : @{ *(.text) @} :text @}
3175 @node Output Section Fill
3176 @subsubsection Output section fill
3177 @kindex =@var{fillexp}
3178 @cindex section fill pattern
3179 @cindex fill pattern, entire section
3180 You can set the fill pattern for an entire section by using
3181 @samp{=@var{fillexp}}. @var{fillexp} is an expression
3182 (@pxref{Expressions}). Any otherwise unspecified regions of memory
3183 within the output section (for example, gaps left due to the required
3184 alignment of input sections) will be filled with the four least
3185 significant bytes of the value, repeated as necessary.
3187 You can also change the fill value with a @code{FILL} command in the
3188 output section commands; see @ref{Output Section Data}.
3190 Here is a simple example:
3193 SECTIONS @{ .text : @{ *(.text) @} =0x90909090 @}
3197 @node Overlay Description
3198 @subsection Overlay description
3201 An overlay description provides an easy way to describe sections which
3202 are to be loaded as part of a single memory image but are to be run at
3203 the same memory address. At run time, some sort of overlay manager will
3204 copy the overlaid sections in and out of the runtime memory address as
3205 required, perhaps by simply manipulating addressing bits. This approach
3206 can be useful, for example, when a certain region of memory is faster
3209 Overlays are described using the @code{OVERLAY} command. The
3210 @code{OVERLAY} command is used within a @code{SECTIONS} command, like an
3211 output section description. The full syntax of the @code{OVERLAY}
3212 command is as follows:
3215 OVERLAY [@var{start}] : [NOCROSSREFS] [AT ( @var{ldaddr} )]
3219 @var{output-section-command}
3220 @var{output-section-command}
3222 @} [:@var{phdr}@dots{}] [=@var{fill}]
3225 @var{output-section-command}
3226 @var{output-section-command}
3228 @} [:@var{phdr}@dots{}] [=@var{fill}]
3230 @} [>@var{region}] [:@var{phdr}@dots{}] [=@var{fill}]
3234 Everything is optional except @code{OVERLAY} (a keyword), and each
3235 section must have a name (@var{secname1} and @var{secname2} above). The
3236 section definitions within the @code{OVERLAY} construct are identical to
3237 those within the general @code{SECTIONS} contruct (@pxref{SECTIONS}),
3238 except that no addresses and no memory regions may be defined for
3239 sections within an @code{OVERLAY}.
3241 The sections are all defined with the same starting address. The load
3242 addresses of the sections are arranged such that they are consecutive in
3243 memory starting at the load address used for the @code{OVERLAY} as a
3244 whole (as with normal section definitions, the load address is optional,
3245 and defaults to the start address; the start address is also optional,
3246 and defaults to the current value of the location counter).
3248 If the @code{NOCROSSREFS} keyword is used, and there any references
3249 among the sections, the linker will report an error. Since the sections
3250 all run at the same address, it normally does not make sense for one
3251 section to refer directly to another. @xref{Miscellaneous Commands,
3254 For each section within the @code{OVERLAY}, the linker automatically
3255 defines two symbols. The symbol @code{__load_start_@var{secname}} is
3256 defined as the starting load address of the section. The symbol
3257 @code{__load_stop_@var{secname}} is defined as the final load address of
3258 the section. Any characters within @var{secname} which are not legal
3259 within C identifiers are removed. C (or assembler) code may use these
3260 symbols to move the overlaid sections around as necessary.
3262 At the end of the overlay, the value of the location counter is set to
3263 the start address of the overlay plus the size of the largest section.
3265 Here is an example. Remember that this would appear inside a
3266 @code{SECTIONS} construct.
3269 OVERLAY 0x1000 : AT (0x4000)
3271 .text0 @{ o1/*.o(.text) @}
3272 .text1 @{ o2/*.o(.text) @}
3277 This will define both @samp{.text0} and @samp{.text1} to start at
3278 address 0x1000. @samp{.text0} will be loaded at address 0x4000, and
3279 @samp{.text1} will be loaded immediately after @samp{.text0}. The
3280 following symbols will be defined: @code{__load_start_text0},
3281 @code{__load_stop_text0}, @code{__load_start_text1},
3282 @code{__load_stop_text1}.
3284 C code to copy overlay @code{.text1} into the overlay area might look
3289 extern char __load_start_text1, __load_stop_text1;
3290 memcpy ((char *) 0x1000, &__load_start_text1,
3291 &__load_stop_text1 - &__load_start_text1);
3295 Note that the @code{OVERLAY} command is just syntactic sugar, since
3296 everything it does can be done using the more basic commands. The above
3297 example could have been written identically as follows.
3301 .text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
3302 __load_start_text0 = LOADADDR (.text0);
3303 __load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0);
3304 .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
3305 __load_start_text1 = LOADADDR (.text1);
3306 __load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1);
3307 . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
3312 @section MEMORY command
3314 @cindex memory regions
3315 @cindex regions of memory
3316 @cindex allocating memory
3317 @cindex discontinuous memory
3318 The linker's default configuration permits allocation of all available
3319 memory. You can override this by using the @code{MEMORY} command.
3321 The @code{MEMORY} command describes the location and size of blocks of
3322 memory in the target. You can use it to describe which memory regions
3323 may be used by the linker, and which memory regions it must avoid. You
3324 can then assign sections to particular memory regions. The linker will
3325 set section addresses based on the memory regions, and will warn about
3326 regions that become too full. The linker will not shuffle sections
3327 around to fit into the available regions.
3329 A linker script may contain at most one use of the @code{MEMORY}
3330 command. However, you can define as many blocks of memory within it as
3331 you wish. The syntax is:
3336 @var{name} [(@var{attr})] : ORIGIN = @var{origin}, LENGTH = @var{len}
3342 The @var{name} is a name used in the linker script to refer to the
3343 region. The region name has no meaning outside of the linker script.
3344 Region names are stored in a separate name space, and will not conflict
3345 with symbol names, file names, or section names. Each memory region
3346 must have a distinct name.
3348 @cindex memory region attributes
3349 The @var{attr} string is an optional list of attributes that specify
3350 whether to use a particular memory region for an input section which is
3351 not explicitly mapped in the linker script. As described in
3352 @ref{SECTIONS}, if you do not specify an output section for some input
3353 section, the linker will create an output section with the same name as
3354 the input section. If you define region attributes, the linker will use
3355 them to select the memory region for the output section that it creates.
3357 The @var{attr} string must consist only of the following characters:
3372 Invert the sense of any of the preceding attributes
3375 If a unmapped section matches any of the listed attributes other than
3376 @samp{!}, it will be placed in the memory region. The @samp{!}
3377 attribute reverses this test, so that an unmapped section will be placed
3378 in the memory region only if it does not match any of the listed
3384 The @var{origin} is an expression for the start address of the memory
3385 region. The expression must evaluate to a constant before memory
3386 allocation is performed, which means that you may not use any section
3387 relative symbols. The keyword @code{ORIGIN} may be abbreviated to
3388 @code{org} or @code{o} (but not, for example, @code{ORG}).
3393 The @var{len} is an expression for the size in bytes of the memory
3394 region. As with the @var{origin} expression, the expression must
3395 evaluate to a constant before memory allocation is performed. The
3396 keyword @code{LENGTH} may be abbreviated to @code{len} or @code{l}.
3398 In the following example, we specify that there are two memory regions
3399 available for allocation: one starting at @samp{0} for 256 kilobytes,
3400 and the other starting at @samp{0x40000000} for four megabytes. The
3401 linker will place into the @samp{rom} memory region every section which
3402 is not explicitly mapped into a memory region, and is either read-only
3403 or executable. The linker will place other sections which are not
3404 explicitly mapped into a memory region into the @samp{ram} memory
3411 rom (rx) : ORIGIN = 0, LENGTH = 256K
3412 ram (!rx) : org = 0x40000000, l = 4M
3417 Once you define a memory region, you can direct the linker to place
3418 specific output sections into that memory region by using the
3419 @samp{>@var{region}} output section attribute. For example, if you have
3420 a memory region named @samp{mem}, you would use @samp{>mem} in the
3421 output section definition. @xref{Output Section Region}. If no address
3422 was specified for the output section, the linker will set the address to
3423 the next available address within the memory region. If the combined
3424 output sections directed to a memory region are too large for the
3425 region, the linker will issue an error message.
3428 @section PHDRS Command
3430 @cindex program headers
3431 @cindex ELF program headers
3432 @cindex program segments
3433 @cindex segments, ELF
3434 The ELF object file format uses @dfn{program headers}, also knows as
3435 @dfn{segments}. The program headers describe how the program should be
3436 loaded into memory. You can print them out by using the @code{objdump}
3437 program with the @samp{-p} option.
3439 When you run an ELF program on a native ELF system, the system loader
3440 reads the program headers in order to figure out how to load the
3441 program. This will only work if the program headers are set correctly.
3442 This manual does not describe the details of how the system loader
3443 interprets program headers; for more information, see the ELF ABI.
3445 The linker will create reasonable program headers by default. However,
3446 in some cases, you may need to specify the program headers more
3447 precisely. You may use the @code{PHDRS} command for this purpose. When
3448 the linker sees the @code{PHDRS} command in the linker script, it will
3449 not create any program headers other than the ones specified.
3451 The linker only pays attention to the @code{PHDRS} command when
3452 generating an ELF output file. In other cases, the linker will simply
3453 ignore @code{PHDRS}.
3455 This is the syntax of the @code{PHDRS} command. The words @code{PHDRS},
3456 @code{FILEHDR}, @code{AT}, and @code{FLAGS} are keywords.
3462 @var{name} @var{type} [ FILEHDR ] [ PHDRS ] [ AT ( @var{address} ) ]
3463 [ FLAGS ( @var{flags} ) ] ;
3468 The @var{name} is used only for reference in the @code{SECTIONS} command
3469 of the linker script. It is not put into the output file. Program
3470 header names are stored in a separate name space, and will not conflict
3471 with symbol names, file names, or section names. Each program header
3472 must have a distinct name.
3474 Certain program header types describe segments of memory which the
3475 system loader will load from the file. In the linker script, you
3476 specify the contents of these segments by placing allocatable output
3477 sections in the segments. You use the @samp{:@var{phdr}} output section
3478 attribute to place a section in a particular segment. @xref{Output
3481 It is normal to put certain sections in more than one segment. This
3482 merely implies that one segment of memory contains another. You may
3483 repeat @samp{:@var{phdr}}, using it once for each segment which should
3484 contain the section.
3486 If you place a section in one or more segments using @samp{:@var{phdr}},
3487 then the linker will place all subsequent allocatable sections which do
3488 not specify @samp{:@var{phdr}} in the same segments. This is for
3489 convenience, since generally a whole set of contiguous sections will be
3490 placed in a single segment. You can use @code{:NONE} to override the
3491 default segment and tell the linker to not put the section in any
3496 You may use the @code{FILEHDR} and @code{PHDRS} keywords appear after
3497 the program header type to further describe the contents of the segment.
3498 The @code{FILEHDR} keyword means that the segment should include the ELF
3499 file header. The @code{PHDRS} keyword means that the segment should
3500 include the ELF program headers themselves.
3502 The @var{type} may be one of the following. The numbers indicate the
3503 value of the keyword.
3506 @item @code{PT_NULL} (0)
3507 Indicates an unused program header.
3509 @item @code{PT_LOAD} (1)
3510 Indicates that this program header describes a segment to be loaded from
3513 @item @code{PT_DYNAMIC} (2)
3514 Indicates a segment where dynamic linking information can be found.
3516 @item @code{PT_INTERP} (3)
3517 Indicates a segment where the name of the program interpreter may be
3520 @item @code{PT_NOTE} (4)
3521 Indicates a segment holding note information.
3523 @item @code{PT_SHLIB} (5)
3524 A reserved program header type, defined but not specified by the ELF
3527 @item @code{PT_PHDR} (6)
3528 Indicates a segment where the program headers may be found.
3530 @item @var{expression}
3531 An expression giving the numeric type of the program header. This may
3532 be used for types not defined above.
3535 You can specify that a segment should be loaded at a particular address
3536 in memory by using an @code{AT} expression. This is identical to the
3537 @code{AT} command used as an output section attribute (@pxref{Output
3538 Section LMA}). The @code{AT} command for a program header overrides the
3539 output section attribute.
3541 The linker will normally set the segment flags based on the sections
3542 which comprise the segment. You may use the @code{FLAGS} keyword to
3543 explicitly specify the segment flags. The value of @var{flags} must be
3544 an integer. It is used to set the @code{p_flags} field of the program
3547 Here is an example of @code{PHDRS}. This shows a typical set of program
3548 headers used on a native ELF system.
3554 headers PT_PHDR PHDRS ;
3556 text PT_LOAD FILEHDR PHDRS ;
3558 dynamic PT_DYNAMIC ;
3564 .interp : @{ *(.interp) @} :text :interp
3565 .text : @{ *(.text) @} :text
3566 .rodata : @{ *(.rodata) @} /* defaults to :text */
3568 . = . + 0x1000; /* move to a new page in memory */
3569 .data : @{ *(.data) @} :data
3570 .dynamic : @{ *(.dynamic) @} :data :dynamic
3577 @section VERSION Command
3578 @kindex VERSION @{script text@}
3579 @cindex symbol versions
3580 @cindex version script
3581 @cindex versions of symbols
3582 The linker supports symbol versions when using ELF. Symbol versions are
3583 only useful when using shared libraries. The dynamic linker can use
3584 symbol versions to select a specific version of a function when it runs
3585 a program that may have been linked against an earlier version of the
3588 You can include a version script directly in the main linker script, or
3589 you can supply the version script as an implicit linker script. You can
3590 also use the @samp{--version-script} linker option.
3592 The syntax of the @code{VERSION} command is simply
3594 VERSION @{ version-script-commands @}
3597 The format of the version script commands is identical to that used by
3598 Sun's linker in Solaris 2.5. The version script defines a tree of
3599 version nodes. You specify the node names and interdependencies in the
3600 version script. You can specify which symbols are bound to which
3601 version nodes, and you can reduce a specified set of symbols to local
3602 scope so that they are not globally visible outside of the shared
3605 The easiest way to demonstrate the version script language is with a few
3627 This example version script defines three version nodes. The first
3628 version node defined is @samp{VERS_1.1}; it has no other dependencies.
3629 The script binds the symbol @samp{foo1} to @samp{VERS_1.1}. It reduces
3630 a number of symbols to local scope so that they are not visible outside
3631 of the shared library.
3633 Next, the version script defines node @samp{VERS_1.2}. This node
3634 depends upon @samp{VERS_1.1}. The script binds the symbol @samp{foo2}
3635 to the version node @samp{VERS_1.2}.
3637 Finally, the version script defines node @samp{VERS_2.0}. This node
3638 depends upon @samp{VERS_1.2}. The scripts binds the symbols @samp{bar1}
3639 and @samp{bar2} are bound to the version node @samp{VERS_2.0}.
3641 When the linker finds a symbol defined in a library which is not
3642 specifically bound to a version node, it will effectively bind it to an
3643 unspecified base version of the library. You can bind all otherwise
3644 unspecified symbols to a given version node by using @samp{global: *}
3645 somewhere in the version script.
3647 The names of the version nodes have no specific meaning other than what
3648 they might suggest to the person reading them. The @samp{2.0} version
3649 could just as well have appeared in between @samp{1.1} and @samp{1.2}.
3650 However, this would be a confusing way to write a version script.
3652 When you link an application against a shared library that has versioned
3653 symbols, the application itself knows which version of each symbol it
3654 requires, and it also knows which version nodes it needs from each
3655 shared library it is linked against. Thus at runtime, the dynamic
3656 loader can make a quick check to make sure that the libraries you have
3657 linked against do in fact supply all of the version nodes that the
3658 application will need to resolve all of the dynamic symbols. In this
3659 way it is possible for the dynamic linker to know with certainty that
3660 all external symbols that it needs will be resolvable without having to
3661 search for each symbol reference.
3663 The symbol versioning is in effect a much more sophisticated way of
3664 doing minor version checking that SunOS does. The fundamental problem
3665 that is being addressed here is that typically references to external
3666 functions are bound on an as-needed basis, and are not all bound when
3667 the application starts up. If a shared library is out of date, a
3668 required interface may be missing; when the application tries to use
3669 that interface, it may suddenly and unexpectedly fail. With symbol
3670 versioning, the user will get a warning when they start their program if
3671 the libraries being used with the application are too old.
3673 There are several GNU extensions to Sun's versioning approach. The
3674 first of these is the ability to bind a symbol to a version node in the
3675 source file where the symbol is defined instead of in the versioning
3676 script. This was done mainly to reduce the burden on the library
3677 maintainer. You can do this by putting something like:
3679 __asm__(".symver original_foo,foo@@VERS_1.1");
3682 in the C source file. This renames the function @samp{original_foo} to
3683 be an alias for @samp{foo} bound to the version node @samp{VERS_1.1}.
3684 The @samp{local:} directive can be used to prevent the symbol
3685 @samp{original_foo} from being exported.
3687 The second GNU extension is to allow multiple versions of the same
3688 function to appear in a given shared library. In this way you can make
3689 an incompatible change to an interface without increasing the major
3690 version number of the shared library, while still allowing applications
3691 linked against the old interface to continue to function.
3693 To do this, you must use multiple @samp{.symver} directives in the
3694 source file. Here is an example:
3697 __asm__(".symver original_foo,foo@@");
3698 __asm__(".symver old_foo,foo@@VERS_1.1");
3699 __asm__(".symver old_foo1,foo@@VERS_1.2");
3700 __asm__(".symver new_foo,foo@@@@VERS_2.0");
3703 In this example, @samp{foo@@} represents the symbol @samp{foo} bound to the
3704 unspecified base version of the symbol. The source file that contains this
3705 example would define 4 C functions: @samp{original_foo}, @samp{old_foo},
3706 @samp{old_foo1}, and @samp{new_foo}.
3708 When you have multiple definitions of a given symbol, there needs to be
3709 some way to specify a default version to which external references to
3710 this symbol will be bound. You can do this with the
3711 @samp{foo@@@@VERS_2.0} type of @samp{.symver} directive. You can only
3712 declare one version of a symbol as the default in this manner; otherwise
3713 you would effectively have multiple definitions of the same symbol.
3715 If you wish to bind a reference to a specific version of the symbol
3716 within the shared library, you can use the aliases of convenience
3717 (i.e. @samp{old_foo}), or you can use the @samp{.symver} directive to
3718 specifically bind to an external version of the function in question.
3720 You can also specify the language in the version script:
3723 VERSION extern "lang" @{ version-script-commands @}
3726 The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
3727 The linker will iterate over the list of symbols at the link time and
3728 demangle them according to @samp{lang} before matching them to the
3729 patterns specified in @samp{version-script-commands}.
3732 @section Expressions in Linker Scripts
3735 The syntax for expressions in the linker script language is identical to
3736 that of C expressions. All expressions are evaluated as integers. All
3737 expressions are evaluated in the same size, which is 32 bits if both the
3738 host and target are 32 bits, and is otherwise 64 bits.
3740 You can use and set symbol values in expressions.
3742 The linker defines several special purpose builtin functions for use in
3746 * Constants:: Constants
3747 * Symbols:: Symbol Names
3748 * Location Counter:: The Location Counter
3749 * Operators:: Operators
3750 * Evaluation:: Evaluation
3751 * Expression Section:: The Section of an Expression
3752 * Builtin Functions:: Builtin Functions
3756 @subsection Constants
3757 @cindex integer notation
3758 @cindex constants in linker scripts
3759 All constants are integers.
3761 As in C, the linker considers an integer beginning with @samp{0} to be
3762 octal, and an integer beginning with @samp{0x} or @samp{0X} to be
3763 hexadecimal. The linker considers other integers to be decimal.
3765 @cindex scaled integers
3766 @cindex K and M integer suffixes
3767 @cindex M and K integer suffixes
3768 @cindex suffixes for integers
3769 @cindex integer suffixes
3770 In addition, you can use the suffixes @code{K} and @code{M} to scale a
3774 @c END TEXI2ROFF-KILL
3775 @code{1024} or @code{1024*1024}
3779 ${\rm 1024}$ or ${\rm 1024}^2$
3781 @c END TEXI2ROFF-KILL
3782 respectively. For example, the following all refer to the same quantity:
3790 @subsection Symbol Names
3791 @cindex symbol names
3793 @cindex quoted symbol names
3795 Unless quoted, symbol names start with a letter, underscore, or period
3796 and may include letters, digits, underscores, periods, and hyphens.
3797 Unquoted symbol names must not conflict with any keywords. You can
3798 specify a symbol which contains odd characters or has the same name as a
3799 keyword by surrounding the symbol name in double quotes:
3802 "with a space" = "also with a space" + 10;
3805 Since symbols can contain many non-alphabetic characters, it is safest
3806 to delimit symbols with spaces. For example, @samp{A-B} is one symbol,
3807 whereas @samp{A - B} is an expression involving subtraction.
3809 @node Location Counter
3810 @subsection The Location Counter
3813 @cindex location counter
3814 @cindex current output location
3815 The special linker variable @dfn{dot} @samp{.} always contains the
3816 current output location counter. Since the @code{.} always refers to a
3817 location in an output section, it may only appear in an expression
3818 within a @code{SECTIONS} command. The @code{.} symbol may appear
3819 anywhere that an ordinary symbol is allowed in an expression.
3822 Assigning a value to @code{.} will cause the location counter to be
3823 moved. This may be used to create holes in the output section. The
3824 location counter may never be moved backwards.
3840 In the previous example, the @samp{.text} section from @file{file1} is
3841 located at the beginning of the output section @samp{output}. It is
3842 followed by a 1000 byte gap. Then the @samp{.text} section from
3843 @file{file2} appears, also with a 1000 byte gap following before the
3844 @samp{.text} section from @file{file3}. The notation @samp{= 0x12345678}
3845 specifies what data to write in the gaps (@pxref{Output Section Fill}).
3847 @cindex dot inside sections
3848 Note: @code{.} actually refers to the byte offset from the start of the
3849 current containing object. Normally this is the @code{SECTIONS}
3850 statement, whoes start address is 0, hence @code{.} can be used as an
3851 absolute address. If @code{.} is used inside a section description
3852 however, it refers to the byte offset from the start of that section,
3853 not an absolute address. Thus in a script like this:
3871 The @samp{.text} section will be assigned a starting address of 0x100
3872 and a size of exactly 0x200 bytes, even if there is not enough data in
3873 the @samp{.text} input sections to fill this area. (If there is too
3874 much data, an error will be produced because this would be an attempt to
3875 move @code{.} backwards). The @samp{.data} section will start at 0x500
3876 and it will have an extra 0x600 bytes worth of space after the end of
3877 the values from the @samp{.data} input sections and before the end of
3878 the @samp{.data} output section itself.
3882 @subsection Operators
3883 @cindex operators for arithmetic
3884 @cindex arithmetic operators
3885 @cindex precedence in expressions
3886 The linker recognizes the standard C set of arithmetic operators, with
3887 the standard bindings and precedence levels:
3890 @c END TEXI2ROFF-KILL
3892 precedence associativity Operators Notes
3898 5 left == != > < <= >=
3904 11 right &= += -= *= /= (2)
3908 (1) Prefix operators
3909 (2) @xref{Assignments}.
3913 \vskip \baselineskip
3914 %"lispnarrowing" is the extra indent used generally for smallexample
3915 \hskip\lispnarrowing\vbox{\offinterlineskip
3918 {\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ {\tt #}\ \hfil&\vrule#\cr
3919 height2pt&\omit&&\omit&&\omit&\cr
3920 &Precedence&& Associativity &&{\rm Operators}&\cr
3921 height2pt&\omit&&\omit&&\omit&\cr
3923 height2pt&\omit&&\omit&&\omit&\cr
3925 % '176 is tilde, '~' in tt font
3926 &1&&left&&\qquad- \char'176\ !\qquad\dag&\cr
3927 &2&&left&&* / \%&\cr
3930 &5&&left&&== != > < <= >=&\cr
3933 &8&&left&&{\&\&}&\cr
3936 &11&&right&&\qquad\&= += -= *= /=\qquad\ddag&\cr
3938 height2pt&\omit&&\omit&&\omit&\cr}
3943 @obeylines@parskip=0pt@parindent=0pt
3944 @dag@quad Prefix operators.
3945 @ddag@quad @xref{Assignments}.
3948 @c END TEXI2ROFF-KILL
3951 @subsection Evaluation
3952 @cindex lazy evaluation
3953 @cindex expression evaluation order
3954 The linker evaluates expressions lazily. It only computes the value of
3955 an expression when absolutely necessary.
3957 The linker needs some information, such as the value of the start
3958 address of the first section, and the origins and lengths of memory
3959 regions, in order to do any linking at all. These values are computed
3960 as soon as possible when the linker reads in the linker script.
3962 However, other values (such as symbol values) are not known or needed
3963 until after storage allocation. Such values are evaluated later, when
3964 other information (such as the sizes of output sections) is available
3965 for use in the symbol assignment expression.
3967 The sizes of sections cannot be known until after allocation, so
3968 assignments dependent upon these are not performed until after
3971 Some expressions, such as those depending upon the location counter
3972 @samp{.}, must be evaluated during section allocation.
3974 If the result of an expression is required, but the value is not
3975 available, then an error results. For example, a script like the
3981 .text 9+this_isnt_constant :
3987 will cause the error message @samp{non constant expression for initial
3990 @node Expression Section
3991 @subsection The Section of an Expression
3992 @cindex expression sections
3993 @cindex absolute expressions
3994 @cindex relative expressions
3995 @cindex absolute and relocatable symbols
3996 @cindex relocatable and absolute symbols
3997 @cindex symbols, relocatable and absolute
3998 When the linker evaluates an expression, the result is either absolute
3999 or relative to some section. A relative expression is expressed as a
4000 fixed offset from the base of a section.
4002 The position of the expression within the linker script determines
4003 whether it is absolute or relative. An expression which appears within
4004 an output section definition is relative to the base of the output
4005 section. An expression which appears elsewhere will be absolute.
4007 A symbol set to a relative expression will be relocatable if you request
4008 relocatable output using the @samp{-r} option. That means that a
4009 further link operation may change the value of the symbol. The symbol's
4010 section will be the section of the relative expression.
4012 A symbol set to an absolute expression will retain the same value
4013 through any further link operation. The symbol will be absolute, and
4014 will not have any particular associated section.
4016 You can use the builtin function @code{ABSOLUTE} to force an expression
4017 to be absolute when it would otherwise be relative. For example, to
4018 create an absolute symbol set to the address of the end of the output
4019 section @samp{.data}:
4023 .data : @{ *(.data) _edata = ABSOLUTE(.); @}
4027 If @samp{ABSOLUTE} were not used, @samp{_edata} would be relative to the
4028 @samp{.data} section.
4030 @node Builtin Functions
4031 @subsection Builtin Functions
4032 @cindex functions in expressions
4033 The linker script language includes a number of builtin functions for
4034 use in linker script expressions.
4037 @item ABSOLUTE(@var{exp})
4038 @kindex ABSOLUTE(@var{exp})
4039 @cindex expression, absolute
4040 Return the absolute (non-relocatable, as opposed to non-negative) value
4041 of the expression @var{exp}. Primarily useful to assign an absolute
4042 value to a symbol within a section definition, where symbol values are
4043 normally section relative. @xref{Expression Section}.
4045 @item ADDR(@var{section})
4046 @kindex ADDR(@var{section})
4047 @cindex section address in expression
4048 Return the absolute address (the VMA) of the named @var{section}. Your
4049 script must previously have defined the location of that section. In
4050 the following example, @code{symbol_1} and @code{symbol_2} are assigned
4057 start_of_output_1 = ABSOLUTE(.);
4062 symbol_1 = ADDR(.output1);
4063 symbol_2 = start_of_output_1;
4069 @item ALIGN(@var{exp})
4070 @kindex ALIGN(@var{exp})
4071 @cindex round up location counter
4072 @cindex align location counter
4073 Return the location counter (@code{.}) aligned to the next @var{exp}
4074 boundary. @var{exp} must be an expression whose value is a power of
4075 two. This is equivalent to
4077 (. + @var{exp} - 1) & ~(@var{exp} - 1)
4080 @code{ALIGN} doesn't change the value of the location counter---it just
4081 does arithmetic on it. Here is an example which aligns the output
4082 @code{.data} section to the next @code{0x2000} byte boundary after the
4083 preceding section and sets a variable within the section to the next
4084 @code{0x8000} boundary after the input sections:
4088 .data ALIGN(0x2000): @{
4090 variable = ALIGN(0x8000);
4096 The first use of @code{ALIGN} in this example specifies the location of
4097 a section because it is used as the optional @var{address} attribute of
4098 a section definition (@pxref{Output Section Address}). The second use
4099 of @code{ALIGN} is used to defines the value of a symbol.
4101 The builtin function @code{NEXT} is closely related to @code{ALIGN}.
4103 @item BLOCK(@var{exp})
4104 @kindex BLOCK(@var{exp})
4105 This is a synonym for @code{ALIGN}, for compatibility with older linker
4106 scripts. It is most often seen when setting the address of an output
4109 @item DEFINED(@var{symbol})
4110 @kindex DEFINED(@var{symbol})
4111 @cindex symbol defaults
4112 Return 1 if @var{symbol} is in the linker global symbol table and is
4113 defined, otherwise return 0. You can use this function to provide
4114 default values for symbols. For example, the following script fragment
4115 shows how to set a global symbol @samp{begin} to the first location in
4116 the @samp{.text} section---but if a symbol called @samp{begin} already
4117 existed, its value is preserved:
4123 begin = DEFINED(begin) ? begin : . ;
4131 @item LOADADDR(@var{section})
4132 @kindex LOADADDR(@var{section})
4133 @cindex section load address in expression
4134 Return the absolute LMA of the named @var{section}. This is normally
4135 the same as @code{ADDR}, but it may be different if the @code{AT}
4136 attribute is used in the output section definition (@pxref{Output
4140 @item MAX(@var{exp1}, @var{exp2})
4141 Returns the maximum of @var{exp1} and @var{exp2}.
4144 @item MIN(@var{exp1}, @var{exp2})
4145 Returns the minimum of @var{exp1} and @var{exp2}.
4147 @item NEXT(@var{exp})
4148 @kindex NEXT(@var{exp})
4149 @cindex unallocated address, next
4150 Return the next unallocated address that is a multiple of @var{exp}.
4151 This function is closely related to @code{ALIGN(@var{exp})}; unless you
4152 use the @code{MEMORY} command to define discontinuous memory for the
4153 output file, the two functions are equivalent.
4155 @item SIZEOF(@var{section})
4156 @kindex SIZEOF(@var{section})
4157 @cindex section size
4158 Return the size in bytes of the named @var{section}, if that section has
4159 been allocated. If the section has not been allocated when this is
4160 evaluated, the linker will report an error. In the following example,
4161 @code{symbol_1} and @code{symbol_2} are assigned identical values:
4170 symbol_1 = .end - .start ;
4171 symbol_2 = SIZEOF(.output);
4176 @item SIZEOF_HEADERS
4177 @itemx sizeof_headers
4178 @kindex SIZEOF_HEADERS
4180 Return the size in bytes of the output file's headers. This is
4181 information which appears at the start of the output file. You can use
4182 this number when setting the start address of the first section, if you
4183 choose, to facilitate paging.
4185 @cindex not enough room for program headers
4186 @cindex program headers, not enough room
4187 When producing an ELF output file, if the linker script uses the
4188 @code{SIZEOF_HEADERS} builtin function, the linker must compute the
4189 number of program headers before it has determined all the section
4190 addresses and sizes. If the linker later discovers that it needs
4191 additional program headers, it will report an error @samp{not enough
4192 room for program headers}. To avoid this error, you must avoid using
4193 the @code{SIZEOF_HEADERS} function, or you must rework your linker
4194 script to avoid forcing the linker to use additional program headers, or
4195 you must define the program headers yourself using the @code{PHDRS}
4196 command (@pxref{PHDRS}).
4199 @node Implicit Linker Scripts
4200 @section Implicit Linker Scripts
4201 @cindex implicit linker scripts
4202 If you specify a linker input file which the linker can not recognize as
4203 an object file or an archive file, it will try to read the file as a
4204 linker script. If the file can not be parsed as a linker script, the
4205 linker will report an error.
4207 An implicit linker script will not replace the default linker script.
4209 Typically an implicit linker script would contain only symbol
4210 assignments, or the @code{INPUT}, @code{GROUP}, or @code{VERSION}
4213 Any input files read because of an implicit linker script will be read
4214 at the position in the command line where the implicit linker script was
4215 read. This can affect archive searching.
4218 @node Machine Dependent
4219 @chapter Machine Dependent Features
4221 @cindex machine dependencies
4222 @code{ld} has additional features on some platforms; the following
4223 sections describe them. Machines where @code{ld} has no additional
4224 functionality are not listed.
4227 * H8/300:: @code{ld} and the H8/300
4228 * i960:: @code{ld} and the Intel 960 family
4229 * ARM:: @code{ld} and the ARM family
4230 * HPPA ELF32:: @code{ld} and HPPA 32-bit ELF
4232 * TI COFF:: @code{ld} and TI COFF
4237 @c FIXME! This could use @raisesections/@lowersections, but there seems to be a conflict
4238 @c between those and node-defaulting.
4245 @section @code{ld} and the H8/300
4247 @cindex H8/300 support
4248 For the H8/300, @code{ld} can perform these global optimizations when
4249 you specify the @samp{--relax} command-line option.
4252 @cindex relaxing on H8/300
4253 @item relaxing address modes
4254 @code{ld} finds all @code{jsr} and @code{jmp} instructions whose
4255 targets are within eight bits, and turns them into eight-bit
4256 program-counter relative @code{bsr} and @code{bra} instructions,
4259 @cindex synthesizing on H8/300
4260 @item synthesizing instructions
4261 @c FIXME: specifically mov.b, or any mov instructions really?
4262 @code{ld} finds all @code{mov.b} instructions which use the
4263 sixteen-bit absolute address form, but refer to the top
4264 page of memory, and changes them to use the eight-bit address form.
4265 (That is: the linker turns @samp{mov.b @code{@@}@var{aa}:16} into
4266 @samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the
4267 top page of memory).
4277 @c This stuff is pointless to say unless you're especially concerned
4278 @c with Hitachi chips; don't enable it for generic case, please.
4280 @chapter @code{ld} and other Hitachi chips
4282 @code{ld} also supports the H8/300H, the H8/500, and the Hitachi SH. No
4283 special features, commands, or command-line options are required for
4294 @section @code{ld} and the Intel 960 family
4296 @cindex i960 support
4298 You can use the @samp{-A@var{architecture}} command line option to
4299 specify one of the two-letter names identifying members of the 960
4300 family; the option specifies the desired output target, and warns of any
4301 incompatible instructions in the input files. It also modifies the
4302 linker's search strategy for archive libraries, to support the use of
4303 libraries specific to each particular architecture, by including in the
4304 search loop names suffixed with the string identifying the architecture.
4306 For example, if your @code{ld} command line included @w{@samp{-ACA}} as
4307 well as @w{@samp{-ltry}}, the linker would look (in its built-in search
4308 paths, and in any paths you specify with @samp{-L}) for a library with
4321 The first two possibilities would be considered in any event; the last
4322 two are due to the use of @w{@samp{-ACA}}.
4324 You can meaningfully use @samp{-A} more than once on a command line, since
4325 the 960 architecture family allows combination of target architectures; each
4326 use will add another pair of name variants to search for when @w{@samp{-l}}
4327 specifies a library.
4329 @cindex @code{--relax} on i960
4330 @cindex relaxing on i960
4331 @code{ld} supports the @samp{--relax} option for the i960 family. If
4332 you specify @samp{--relax}, @code{ld} finds all @code{balx} and
4333 @code{calx} instructions whose targets are within 24 bits, and turns
4334 them into 24-bit program-counter relative @code{bal} and @code{cal}
4335 instructions, respectively. @code{ld} also turns @code{cal}
4336 instructions into @code{bal} instructions when it determines that the
4337 target subroutine is a leaf routine (that is, the target subroutine does
4338 not itself call any subroutines).
4350 @section @code{ld}'s support for interworking between ARM and Thumb code
4352 @cindex ARM interworking support
4353 @kindex --support-old-code
4354 For the ARM, @code{ld} will generate code stubs to allow functions calls
4355 betweem ARM and Thumb code. These stubs only work with code that has
4356 been compiled and assembled with the @samp{-mthumb-interwork} command
4357 line option. If it is necessary to link with old ARM object files or
4358 libraries, which have not been compiled with the -mthumb-interwork
4359 option then the @samp{--support-old-code} command line switch should be
4360 given to the linker. This will make it generate larger stub functions
4361 which will work with non-interworking aware ARM code. Note, however,
4362 the linker does not support generating stubs for function calls to
4363 non-interworking aware Thumb code.
4365 @cindex thumb entry point
4366 @cindex entry point, thumb
4367 @kindex --thumb-entry=@var{entry}
4368 The @samp{--thumb-entry} switch is a duplicate of the generic
4369 @samp{--entry} switch, in that it sets the program's starting address.
4370 But it also sets the bottom bit of the address, so that it can be
4371 branched to using a BX instruction, and the program will start
4372 executing in Thumb mode straight away.
4375 @section @code{ld} and HPPA 32-bit ELF support
4376 @cindex HPPA multiple sub-space stubs
4377 @kindex --multi-subspace
4378 When generating a shared library, @code{ld} will by default generate
4379 import stubs suitable for use with a single sub-space application.
4380 The @samp{--multi-subspace} switch causes @code{ld} to generate export
4381 stubs, and different (larger) import stubs suitable for use with
4382 multiple sub-spaces.
4384 @cindex HPPA stub grouping
4385 @kindex --stub-group-size=@var{N}
4386 Long branch stubs and import/export stubs are placed by @code{ld} in
4387 stub sections located between groups of input sections.
4388 @samp{--stub-group-size} specifies the maximum size of a group of input
4389 sections handled by one stub section. Since branch offsets are signed,
4390 a stub section may serve two groups of input sections, one group before
4391 the stub section, and one group after it. However, when using
4392 conditional branches that require stubs, it may be better (for branch
4393 prediction) that stub sections only serve one group of input sections.
4394 A negative value for @samp{N} chooses this scheme, ensuring that
4395 branches to stubs always use a negative offset. Two special values of
4396 @samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct
4397 @code{ld} to automatically size input section groups for the branch types
4398 detected, with the same behaviour regarding stub placement as other
4399 positive or negative values of @samp{N} respectively.
4401 Note that @samp{--stub-group-size} does not split input sections. A
4402 single input section larger than the group size specified will of course
4403 create a larger group (of one section). If input sections are too
4404 large, it may not be possible for a branch to reach its stub.
4408 @section @code{ld}'s support for various TI COFF versions
4409 @cindex TI COFF versions
4410 @kindex --format=@var{version}
4411 The @samp{--format} switch allows selection of one of the various
4412 TI COFF versions. The latest of this writing is 2; versions 0 and 1 are
4413 also supported. The TI COFF versions also vary in header byte-order
4414 format; @code{ld} will read any version or byte order, but the output
4415 header format depends on the default specified by the specific target.
4422 @ifclear SingleFormat
4427 @cindex object file management
4428 @cindex object formats available
4430 The linker accesses object and archive files using the BFD libraries.
4431 These libraries allow the linker to use the same routines to operate on
4432 object files whatever the object file format. A different object file
4433 format can be supported simply by creating a new BFD back end and adding
4434 it to the library. To conserve runtime memory, however, the linker and
4435 associated tools are usually configured to support only a subset of the
4436 object file formats available. You can use @code{objdump -i}
4437 (@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}) to
4438 list all the formats available for your configuration.
4440 @cindex BFD requirements
4441 @cindex requirements for BFD
4442 As with most implementations, BFD is a compromise between
4443 several conflicting requirements. The major factor influencing
4444 BFD design was efficiency: any time used converting between
4445 formats is time which would not have been spent had BFD not
4446 been involved. This is partly offset by abstraction payback; since
4447 BFD simplifies applications and back ends, more time and care
4448 may be spent optimizing algorithms for a greater speed.
4450 One minor artifact of the BFD solution which you should bear in
4451 mind is the potential for information loss. There are two places where
4452 useful information can be lost using the BFD mechanism: during
4453 conversion and during output. @xref{BFD information loss}.
4456 * BFD outline:: How it works: an outline of BFD
4460 @section How it works: an outline of BFD
4461 @cindex opening object files
4462 @include bfdsumm.texi
4465 @node Reporting Bugs
4466 @chapter Reporting Bugs
4467 @cindex bugs in @code{ld}
4468 @cindex reporting bugs in @code{ld}
4470 Your bug reports play an essential role in making @code{ld} reliable.
4472 Reporting a bug may help you by bringing a solution to your problem, or
4473 it may not. But in any case the principal function of a bug report is
4474 to help the entire community by making the next version of @code{ld}
4475 work better. Bug reports are your contribution to the maintenance of
4478 In order for a bug report to serve its purpose, you must include the
4479 information that enables us to fix the bug.
4482 * Bug Criteria:: Have you found a bug?
4483 * Bug Reporting:: How to report bugs
4487 @section Have you found a bug?
4488 @cindex bug criteria
4490 If you are not sure whether you have found a bug, here are some guidelines:
4493 @cindex fatal signal
4494 @cindex linker crash
4495 @cindex crash of linker
4497 If the linker gets a fatal signal, for any input whatever, that is a
4498 @code{ld} bug. Reliable linkers never crash.
4500 @cindex error on valid input
4502 If @code{ld} produces an error message for valid input, that is a bug.
4504 @cindex invalid input
4506 If @code{ld} does not produce an error message for invalid input, that
4507 may be a bug. In the general case, the linker can not verify that
4508 object files are correct.
4511 If you are an experienced user of linkers, your suggestions for
4512 improvement of @code{ld} are welcome in any case.
4516 @section How to report bugs
4518 @cindex @code{ld} bugs, reporting
4520 A number of companies and individuals offer support for @sc{gnu}
4521 products. If you obtained @code{ld} from a support organization, we
4522 recommend you contact that organization first.
4524 You can find contact information for many support companies and
4525 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
4528 Otherwise, send bug reports for @code{ld} to
4529 @samp{bug-binutils@@gnu.org}.
4531 The fundamental principle of reporting bugs usefully is this:
4532 @strong{report all the facts}. If you are not sure whether to state a
4533 fact or leave it out, state it!
4535 Often people omit facts because they think they know what causes the
4536 problem and assume that some details do not matter. Thus, you might
4537 assume that the name of a symbol you use in an example does not matter.
4538 Well, probably it does not, but one cannot be sure. Perhaps the bug is
4539 a stray memory reference which happens to fetch from the location where
4540 that name is stored in memory; perhaps, if the name were different, the
4541 contents of that location would fool the linker into doing the right
4542 thing despite the bug. Play it safe and give a specific, complete
4543 example. That is the easiest thing for you to do, and the most helpful.
4545 Keep in mind that the purpose of a bug report is to enable us to fix the bug if
4546 it is new to us. Therefore, always write your bug reports on the assumption
4547 that the bug has not been reported previously.
4549 Sometimes people give a few sketchy facts and ask, ``Does this ring a
4550 bell?'' Those bug reports are useless, and we urge everyone to
4551 @emph{refuse to respond to them} except to chide the sender to report
4554 To enable us to fix the bug, you should include all these things:
4558 The version of @code{ld}. @code{ld} announces it if you start it with
4559 the @samp{--version} argument.
4561 Without this, we will not know whether there is any point in looking for
4562 the bug in the current version of @code{ld}.
4565 Any patches you may have applied to the @code{ld} source, including any
4566 patches made to the @code{BFD} library.
4569 The type of machine you are using, and the operating system name and
4573 What compiler (and its version) was used to compile @code{ld}---e.g.
4577 The command arguments you gave the linker to link your example and
4578 observe the bug. To guarantee you will not omit something important,
4579 list them all. A copy of the Makefile (or the output from make) is
4582 If we were to try to guess the arguments, we would probably guess wrong
4583 and then we might not encounter the bug.
4586 A complete input file, or set of input files, that will reproduce the
4587 bug. It is generally most helpful to send the actual object files,
4588 uuencoded if necessary to get them through the mail system. Making them
4589 available for anonymous FTP is not as good, but may be the only
4590 reasonable choice for large object files.
4592 If the source files were assembled using @code{gas} or compiled using
4593 @code{gcc}, then it may be OK to send the source files rather than the
4594 object files. In this case, be sure to say exactly what version of
4595 @code{gas} or @code{gcc} was used to produce the object files. Also say
4596 how @code{gas} or @code{gcc} were configured.
4599 A description of what behavior you observe that you believe is
4600 incorrect. For example, ``It gets a fatal signal.''
4602 Of course, if the bug is that @code{ld} gets a fatal signal, then we
4603 will certainly notice it. But if the bug is incorrect output, we might
4604 not notice unless it is glaringly wrong. You might as well not give us
4605 a chance to make a mistake.
4607 Even if the problem you experience is a fatal signal, you should still
4608 say so explicitly. Suppose something strange is going on, such as, your
4609 copy of @code{ld} is out of synch, or you have encountered a bug in the
4610 C library on your system. (This has happened!) Your copy might crash
4611 and ours would not. If you told us to expect a crash, then when ours
4612 fails to crash, we would know that the bug was not happening for us. If
4613 you had not told us to expect a crash, then we would not be able to draw
4614 any conclusion from our observations.
4617 If you wish to suggest changes to the @code{ld} source, send us context
4618 diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or
4619 @samp{-p} option. Always send diffs from the old file to the new file.
4620 If you even discuss something in the @code{ld} source, refer to it by
4621 context, not by line number.
4623 The line numbers in our development sources will not match those in your
4624 sources. Your line numbers would convey no useful information to us.
4627 Here are some things that are not necessary:
4631 A description of the envelope of the bug.
4633 Often people who encounter a bug spend a lot of time investigating
4634 which changes to the input file will make the bug go away and which
4635 changes will not affect it.
4637 This is often time consuming and not very useful, because the way we
4638 will find the bug is by running a single example under the debugger
4639 with breakpoints, not by pure deduction from a series of examples.
4640 We recommend that you save your time for something else.
4642 Of course, if you can find a simpler example to report @emph{instead}
4643 of the original one, that is a convenience for us. Errors in the
4644 output will be easier to spot, running under the debugger will take
4645 less time, and so on.
4647 However, simplification is not vital; if you do not want to do this,
4648 report the bug anyway and send us the entire test case you used.
4651 A patch for the bug.
4653 A patch for the bug does help us if it is a good one. But do not omit
4654 the necessary information, such as the test case, on the assumption that
4655 a patch is all we need. We might see problems with your patch and decide
4656 to fix the problem another way, or we might not understand it at all.
4658 Sometimes with a program as complicated as @code{ld} it is very hard to
4659 construct an example that will make the program follow a certain path
4660 through the code. If you do not send us the example, we will not be
4661 able to construct one, so we will not be able to verify that the bug is
4664 And if we cannot understand what bug you are trying to fix, or why your
4665 patch should be an improvement, we will not install it. A test case will
4666 help us to understand.
4669 A guess about what the bug is or what it depends on.
4671 Such guesses are usually wrong. Even we cannot guess right about such
4672 things without first using the debugger to find the facts.
4676 @appendix MRI Compatible Script Files
4677 @cindex MRI compatibility
4678 To aid users making the transition to @sc{gnu} @code{ld} from the MRI
4679 linker, @code{ld} can use MRI compatible linker scripts as an
4680 alternative to the more general-purpose linker scripting language
4681 described in @ref{Scripts}. MRI compatible linker scripts have a much
4682 simpler command set than the scripting language otherwise used with
4683 @code{ld}. @sc{gnu} @code{ld} supports the most commonly used MRI
4684 linker commands; these commands are described here.
4686 In general, MRI scripts aren't of much use with the @code{a.out} object
4687 file format, since it only has three sections and MRI scripts lack some
4688 features to make use of them.
4690 You can specify a file containing an MRI-compatible script using the
4691 @samp{-c} command-line option.
4693 Each command in an MRI-compatible script occupies its own line; each
4694 command line starts with the keyword that identifies the command (though
4695 blank lines are also allowed for punctuation). If a line of an
4696 MRI-compatible script begins with an unrecognized keyword, @code{ld}
4697 issues a warning message, but continues processing the script.
4699 Lines beginning with @samp{*} are comments.
4701 You can write these commands using all upper-case letters, or all
4702 lower case; for example, @samp{chip} is the same as @samp{CHIP}.
4703 The following list shows only the upper-case form of each command.
4706 @cindex @code{ABSOLUTE} (MRI)
4707 @item ABSOLUTE @var{secname}
4708 @itemx ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
4709 Normally, @code{ld} includes in the output file all sections from all
4710 the input files. However, in an MRI-compatible script, you can use the
4711 @code{ABSOLUTE} command to restrict the sections that will be present in
4712 your output program. If the @code{ABSOLUTE} command is used at all in a
4713 script, then only the sections named explicitly in @code{ABSOLUTE}
4714 commands will appear in the linker output. You can still use other
4715 input sections (whatever you select on the command line, or using
4716 @code{LOAD}) to resolve addresses in the output file.
4718 @cindex @code{ALIAS} (MRI)
4719 @item ALIAS @var{out-secname}, @var{in-secname}
4720 Use this command to place the data from input section @var{in-secname}
4721 in a section called @var{out-secname} in the linker output file.
4723 @var{in-secname} may be an integer.
4725 @cindex @code{ALIGN} (MRI)
4726 @item ALIGN @var{secname} = @var{expression}
4727 Align the section called @var{secname} to @var{expression}. The
4728 @var{expression} should be a power of two.
4730 @cindex @code{BASE} (MRI)
4731 @item BASE @var{expression}
4732 Use the value of @var{expression} as the lowest address (other than
4733 absolute addresses) in the output file.
4735 @cindex @code{CHIP} (MRI)
4736 @item CHIP @var{expression}
4737 @itemx CHIP @var{expression}, @var{expression}
4738 This command does nothing; it is accepted only for compatibility.
4740 @cindex @code{END} (MRI)
4742 This command does nothing whatever; it's only accepted for compatibility.
4744 @cindex @code{FORMAT} (MRI)
4745 @item FORMAT @var{output-format}
4746 Similar to the @code{OUTPUT_FORMAT} command in the more general linker
4747 language, but restricted to one of these output formats:
4751 S-records, if @var{output-format} is @samp{S}
4754 IEEE, if @var{output-format} is @samp{IEEE}
4757 COFF (the @samp{coff-m68k} variant in BFD), if @var{output-format} is
4761 @cindex @code{LIST} (MRI)
4762 @item LIST @var{anything}@dots{}
4763 Print (to the standard output file) a link map, as produced by the
4764 @code{ld} command-line option @samp{-M}.
4766 The keyword @code{LIST} may be followed by anything on the
4767 same line, with no change in its effect.
4769 @cindex @code{LOAD} (MRI)
4770 @item LOAD @var{filename}
4771 @itemx LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
4772 Include one or more object file @var{filename} in the link; this has the
4773 same effect as specifying @var{filename} directly on the @code{ld}
4776 @cindex @code{NAME} (MRI)
4777 @item NAME @var{output-name}
4778 @var{output-name} is the name for the program produced by @code{ld}; the
4779 MRI-compatible command @code{NAME} is equivalent to the command-line
4780 option @samp{-o} or the general script language command @code{OUTPUT}.
4782 @cindex @code{ORDER} (MRI)
4783 @item ORDER @var{secname}, @var{secname}, @dots{} @var{secname}
4784 @itemx ORDER @var{secname} @var{secname} @var{secname}
4785 Normally, @code{ld} orders the sections in its output file in the
4786 order in which they first appear in the input files. In an MRI-compatible
4787 script, you can override this ordering with the @code{ORDER} command. The
4788 sections you list with @code{ORDER} will appear first in your output
4789 file, in the order specified.
4791 @cindex @code{PUBLIC} (MRI)
4792 @item PUBLIC @var{name}=@var{expression}
4793 @itemx PUBLIC @var{name},@var{expression}
4794 @itemx PUBLIC @var{name} @var{expression}
4795 Supply a value (@var{expression}) for external symbol
4796 @var{name} used in the linker input files.
4798 @cindex @code{SECT} (MRI)
4799 @item SECT @var{secname}, @var{expression}
4800 @itemx SECT @var{secname}=@var{expression}
4801 @itemx SECT @var{secname} @var{expression}
4802 You can use any of these three forms of the @code{SECT} command to
4803 specify the start address (@var{expression}) for section @var{secname}.
4804 If you have more than one @code{SECT} statement for the same
4805 @var{secname}, only the @emph{first} sets the start address.
4808 @node GNU Free Documentation License
4809 @appendix GNU Free Documentation License
4810 @cindex GNU Free Documentation License
4812 GNU Free Documentation License
4814 Version 1.1, March 2000
4816 Copyright (C) 2000 Free Software Foundation, Inc.
4817 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
4819 Everyone is permitted to copy and distribute verbatim copies
4820 of this license document, but changing it is not allowed.
4825 The purpose of this License is to make a manual, textbook, or other
4826 written document "free" in the sense of freedom: to assure everyone
4827 the effective freedom to copy and redistribute it, with or without
4828 modifying it, either commercially or noncommercially. Secondarily,
4829 this License preserves for the author and publisher a way to get
4830 credit for their work, while not being considered responsible for
4831 modifications made by others.
4833 This License is a kind of "copyleft", which means that derivative
4834 works of the document must themselves be free in the same sense. It
4835 complements the GNU General Public License, which is a copyleft
4836 license designed for free software.
4838 We have designed this License in order to use it for manuals for free
4839 software, because free software needs free documentation: a free
4840 program should come with manuals providing the same freedoms that the
4841 software does. But this License is not limited to software manuals;
4842 it can be used for any textual work, regardless of subject matter or
4843 whether it is published as a printed book. We recommend this License
4844 principally for works whose purpose is instruction or reference.
4847 1. APPLICABILITY AND DEFINITIONS
4849 This License applies to any manual or other work that contains a
4850 notice placed by the copyright holder saying it can be distributed
4851 under the terms of this License. The "Document", below, refers to any
4852 such manual or work. Any member of the public is a licensee, and is
4855 A "Modified Version" of the Document means any work containing the
4856 Document or a portion of it, either copied verbatim, or with
4857 modifications and/or translated into another language.
4859 A "Secondary Section" is a named appendix or a front-matter section of
4860 the Document that deals exclusively with the relationship of the
4861 publishers or authors of the Document to the Document's overall subject
4862 (or to related matters) and contains nothing that could fall directly
4863 within that overall subject. (For example, if the Document is in part a
4864 textbook of mathematics, a Secondary Section may not explain any
4865 mathematics.) The relationship could be a matter of historical
4866 connection with the subject or with related matters, or of legal,
4867 commercial, philosophical, ethical or political position regarding
4870 The "Invariant Sections" are certain Secondary Sections whose titles
4871 are designated, as being those of Invariant Sections, in the notice
4872 that says that the Document is released under this License.
4874 The "Cover Texts" are certain short passages of text that are listed,
4875 as Front-Cover Texts or Back-Cover Texts, in the notice that says that
4876 the Document is released under this License.
4878 A "Transparent" copy of the Document means a machine-readable copy,
4879 represented in a format whose specification is available to the
4880 general public, whose contents can be viewed and edited directly and
4881 straightforwardly with generic text editors or (for images composed of
4882 pixels) generic paint programs or (for drawings) some widely available
4883 drawing editor, and that is suitable for input to text formatters or
4884 for automatic translation to a variety of formats suitable for input
4885 to text formatters. A copy made in an otherwise Transparent file
4886 format whose markup has been designed to thwart or discourage
4887 subsequent modification by readers is not Transparent. A copy that is
4888 not "Transparent" is called "Opaque".
4890 Examples of suitable formats for Transparent copies include plain
4891 ASCII without markup, Texinfo input format, LaTeX input format, SGML
4892 or XML using a publicly available DTD, and standard-conforming simple
4893 HTML designed for human modification. Opaque formats include
4894 PostScript, PDF, proprietary formats that can be read and edited only
4895 by proprietary word processors, SGML or XML for which the DTD and/or
4896 processing tools are not generally available, and the
4897 machine-generated HTML produced by some word processors for output
4900 The "Title Page" means, for a printed book, the title page itself,
4901 plus such following pages as are needed to hold, legibly, the material
4902 this License requires to appear in the title page. For works in
4903 formats which do not have any title page as such, "Title Page" means
4904 the text near the most prominent appearance of the work's title,
4905 preceding the beginning of the body of the text.
4910 You may copy and distribute the Document in any medium, either
4911 commercially or noncommercially, provided that this License, the
4912 copyright notices, and the license notice saying this License applies
4913 to the Document are reproduced in all copies, and that you add no other
4914 conditions whatsoever to those of this License. You may not use
4915 technical measures to obstruct or control the reading or further
4916 copying of the copies you make or distribute. However, you may accept
4917 compensation in exchange for copies. If you distribute a large enough
4918 number of copies you must also follow the conditions in section 3.
4920 You may also lend copies, under the same conditions stated above, and
4921 you may publicly display copies.
4924 3. COPYING IN QUANTITY
4926 If you publish printed copies of the Document numbering more than 100,
4927 and the Document's license notice requires Cover Texts, you must enclose
4928 the copies in covers that carry, clearly and legibly, all these Cover
4929 Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
4930 the back cover. Both covers must also clearly and legibly identify
4931 you as the publisher of these copies. The front cover must present
4932 the full title with all words of the title equally prominent and
4933 visible. You may add other material on the covers in addition.
4934 Copying with changes limited to the covers, as long as they preserve
4935 the title of the Document and satisfy these conditions, can be treated
4936 as verbatim copying in other respects.
4938 If the required texts for either cover are too voluminous to fit
4939 legibly, you should put the first ones listed (as many as fit
4940 reasonably) on the actual cover, and continue the rest onto adjacent
4943 If you publish or distribute Opaque copies of the Document numbering
4944 more than 100, you must either include a machine-readable Transparent
4945 copy along with each Opaque copy, or state in or with each Opaque copy
4946 a publicly-accessible computer-network location containing a complete
4947 Transparent copy of the Document, free of added material, which the
4948 general network-using public has access to download anonymously at no
4949 charge using public-standard network protocols. If you use the latter
4950 option, you must take reasonably prudent steps, when you begin
4951 distribution of Opaque copies in quantity, to ensure that this
4952 Transparent copy will remain thus accessible at the stated location
4953 until at least one year after the last time you distribute an Opaque
4954 copy (directly or through your agents or retailers) of that edition to
4957 It is requested, but not required, that you contact the authors of the
4958 Document well before redistributing any large number of copies, to give
4959 them a chance to provide you with an updated version of the Document.
4964 You may copy and distribute a Modified Version of the Document under
4965 the conditions of sections 2 and 3 above, provided that you release
4966 the Modified Version under precisely this License, with the Modified
4967 Version filling the role of the Document, thus licensing distribution
4968 and modification of the Modified Version to whoever possesses a copy
4969 of it. In addition, you must do these things in the Modified Version:
4971 A. Use in the Title Page (and on the covers, if any) a title distinct
4972 from that of the Document, and from those of previous versions
4973 (which should, if there were any, be listed in the History section
4974 of the Document). You may use the same title as a previous version
4975 if the original publisher of that version gives permission.
4976 B. List on the Title Page, as authors, one or more persons or entities
4977 responsible for authorship of the modifications in the Modified
4978 Version, together with at least five of the principal authors of the
4979 Document (all of its principal authors, if it has less than five).
4980 C. State on the Title page the name of the publisher of the
4981 Modified Version, as the publisher.
4982 D. Preserve all the copyright notices of the Document.
4983 E. Add an appropriate copyright notice for your modifications
4984 adjacent to the other copyright notices.
4985 F. Include, immediately after the copyright notices, a license notice
4986 giving the public permission to use the Modified Version under the
4987 terms of this License, in the form shown in the Addendum below.
4988 G. Preserve in that license notice the full lists of Invariant Sections
4989 and required Cover Texts given in the Document's license notice.
4990 H. Include an unaltered copy of this License.
4991 I. Preserve the section entitled "History", and its title, and add to
4992 it an item stating at least the title, year, new authors, and
4993 publisher of the Modified Version as given on the Title Page. If
4994 there is no section entitled "History" in the Document, create one
4995 stating the title, year, authors, and publisher of the Document as
4996 given on its Title Page, then add an item describing the Modified
4997 Version as stated in the previous sentence.
4998 J. Preserve the network location, if any, given in the Document for
4999 public access to a Transparent copy of the Document, and likewise
5000 the network locations given in the Document for previous versions
5001 it was based on. These may be placed in the "History" section.
5002 You may omit a network location for a work that was published at
5003 least four years before the Document itself, or if the original
5004 publisher of the version it refers to gives permission.
5005 K. In any section entitled "Acknowledgements" or "Dedications",
5006 preserve the section's title, and preserve in the section all the
5007 substance and tone of each of the contributor acknowledgements
5008 and/or dedications given therein.
5009 L. Preserve all the Invariant Sections of the Document,
5010 unaltered in their text and in their titles. Section numbers
5011 or the equivalent are not considered part of the section titles.
5012 M. Delete any section entitled "Endorsements". Such a section
5013 may not be included in the Modified Version.
5014 N. Do not retitle any existing section as "Endorsements"
5015 or to conflict in title with any Invariant Section.
5017 If the Modified Version includes new front-matter sections or
5018 appendices that qualify as Secondary Sections and contain no material
5019 copied from the Document, you may at your option designate some or all
5020 of these sections as invariant. To do this, add their titles to the
5021 list of Invariant Sections in the Modified Version's license notice.
5022 These titles must be distinct from any other section titles.
5024 You may add a section entitled "Endorsements", provided it contains
5025 nothing but endorsements of your Modified Version by various
5026 parties--for example, statements of peer review or that the text has
5027 been approved by an organization as the authoritative definition of a
5030 You may add a passage of up to five words as a Front-Cover Text, and a
5031 passage of up to 25 words as a Back-Cover Text, to the end of the list
5032 of Cover Texts in the Modified Version. Only one passage of
5033 Front-Cover Text and one of Back-Cover Text may be added by (or
5034 through arrangements made by) any one entity. If the Document already
5035 includes a cover text for the same cover, previously added by you or
5036 by arrangement made by the same entity you are acting on behalf of,
5037 you may not add another; but you may replace the old one, on explicit
5038 permission from the previous publisher that added the old one.
5040 The author(s) and publisher(s) of the Document do not by this License
5041 give permission to use their names for publicity for or to assert or
5042 imply endorsement of any Modified Version.
5045 5. COMBINING DOCUMENTS
5047 You may combine the Document with other documents released under this
5048 License, under the terms defined in section 4 above for modified
5049 versions, provided that you include in the combination all of the
5050 Invariant Sections of all of the original documents, unmodified, and
5051 list them all as Invariant Sections of your combined work in its
5054 The combined work need only contain one copy of this License, and
5055 multiple identical Invariant Sections may be replaced with a single
5056 copy. If there are multiple Invariant Sections with the same name but
5057 different contents, make the title of each such section unique by
5058 adding at the end of it, in parentheses, the name of the original
5059 author or publisher of that section if known, or else a unique number.
5060 Make the same adjustment to the section titles in the list of
5061 Invariant Sections in the license notice of the combined work.
5063 In the combination, you must combine any sections entitled "History"
5064 in the various original documents, forming one section entitled
5065 "History"; likewise combine any sections entitled "Acknowledgements",
5066 and any sections entitled "Dedications". You must delete all sections
5067 entitled "Endorsements."
5070 6. COLLECTIONS OF DOCUMENTS
5072 You may make a collection consisting of the Document and other documents
5073 released under this License, and replace the individual copies of this
5074 License in the various documents with a single copy that is included in
5075 the collection, provided that you follow the rules of this License for
5076 verbatim copying of each of the documents in all other respects.
5078 You may extract a single document from such a collection, and distribute
5079 it individually under this License, provided you insert a copy of this
5080 License into the extracted document, and follow this License in all
5081 other respects regarding verbatim copying of that document.
5084 7. AGGREGATION WITH INDEPENDENT WORKS
5086 A compilation of the Document or its derivatives with other separate
5087 and independent documents or works, in or on a volume of a storage or
5088 distribution medium, does not as a whole count as a Modified Version
5089 of the Document, provided no compilation copyright is claimed for the
5090 compilation. Such a compilation is called an "aggregate", and this
5091 License does not apply to the other self-contained works thus compiled
5092 with the Document, on account of their being thus compiled, if they
5093 are not themselves derivative works of the Document.
5095 If the Cover Text requirement of section 3 is applicable to these
5096 copies of the Document, then if the Document is less than one quarter
5097 of the entire aggregate, the Document's Cover Texts may be placed on
5098 covers that surround only the Document within the aggregate.
5099 Otherwise they must appear on covers around the whole aggregate.
5104 Translation is considered a kind of modification, so you may
5105 distribute translations of the Document under the terms of section 4.
5106 Replacing Invariant Sections with translations requires special
5107 permission from their copyright holders, but you may include
5108 translations of some or all Invariant Sections in addition to the
5109 original versions of these Invariant Sections. You may include a
5110 translation of this License provided that you also include the
5111 original English version of this License. In case of a disagreement
5112 between the translation and the original English version of this
5113 License, the original English version will prevail.
5118 You may not copy, modify, sublicense, or distribute the Document except
5119 as expressly provided for under this License. Any other attempt to
5120 copy, modify, sublicense or distribute the Document is void, and will
5121 automatically terminate your rights under this License. However,
5122 parties who have received copies, or rights, from you under this
5123 License will not have their licenses terminated so long as such
5124 parties remain in full compliance.
5127 10. FUTURE REVISIONS OF THIS LICENSE
5129 The Free Software Foundation may publish new, revised versions
5130 of the GNU Free Documentation License from time to time. Such new
5131 versions will be similar in spirit to the present version, but may
5132 differ in detail to address new problems or concerns. See
5133 http://www.gnu.org/copyleft/.
5135 Each version of the License is given a distinguishing version number.
5136 If the Document specifies that a particular numbered version of this
5137 License "or any later version" applies to it, you have the option of
5138 following the terms and conditions either of that specified version or
5139 of any later version that has been published (not as a draft) by the
5140 Free Software Foundation. If the Document does not specify a version
5141 number of this License, you may choose any version ever published (not
5142 as a draft) by the Free Software Foundation.
5145 ADDENDUM: How to use this License for your documents
5147 To use this License in a document you have written, include a copy of
5148 the License in the document and put the following copyright and
5149 license notices just after the title page:
5152 Copyright (c) YEAR YOUR NAME.
5153 Permission is granted to copy, distribute and/or modify this document
5154 under the terms of the GNU Free Documentation License, Version 1.1
5155 or any later version published by the Free Software Foundation;
5156 with the Invariant Sections being LIST THEIR TITLES, with the
5157 Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
5158 A copy of the license is included in the section entitled "GNU
5159 Free Documentation License".
5162 If you have no Invariant Sections, write "with no Invariant Sections"
5163 instead of saying which ones are invariant. If you have no
5164 Front-Cover Texts, write "no Front-Cover Texts" instead of
5165 "Front-Cover Texts being LIST"; likewise for Back-Cover Texts.
5167 If your document contains nontrivial examples of program code, we
5168 recommend releasing these examples in parallel under your choice of
5169 free software license, such as the GNU General Public License,
5170 to permit their use in free software.
5178 % I think something like @colophon should be in texinfo. In the
5180 \long\def\colophon{\hbox to0pt{}\vfill
5181 \centerline{The body of this manual is set in}
5182 \centerline{\fontname\tenrm,}
5183 \centerline{with headings in {\bf\fontname\tenbf}}
5184 \centerline{and examples in {\tt\fontname\tentt}.}
5185 \centerline{{\it\fontname\tenit\/} and}
5186 \centerline{{\sl\fontname\tensl\/}}
5187 \centerline{are used for emphasis.}\vfill}
5189 % Blame: doc@cygnus.com, 28mar91.