3 @c Copyright (C) 1991-2021 Free Software Foundation, Inc.
6 @include configdoc.texi
7 @c (configdoc.texi is generated by the Makefile)
13 @macro gcctabopt{body}
19 @c Configure for the generation of man pages
47 @dircategory Software development
49 * Ld: (ld). The GNU linker.
54 This file documents the @sc{gnu} linker LD
55 @ifset VERSION_PACKAGE
56 @value{VERSION_PACKAGE}
58 version @value{VERSION}.
60 Copyright @copyright{} 1991-2021 Free Software Foundation, Inc.
62 Permission is granted to copy, distribute and/or modify this document
63 under the terms of the GNU Free Documentation License, Version 1.3
64 or any later version published by the Free Software Foundation;
65 with no Invariant Sections, with no Front-Cover Texts, and with no
66 Back-Cover Texts. A copy of the license is included in the
67 section entitled ``GNU Free Documentation License''.
71 @setchapternewpage odd
72 @settitle The GNU linker
77 @ifset VERSION_PACKAGE
78 @subtitle @value{VERSION_PACKAGE}
80 @subtitle Version @value{VERSION}
81 @author Steve Chamberlain
82 @author Ian Lance Taylor
87 \hfill Red Hat Inc\par
88 \hfill nickc\@credhat.com, doc\@redhat.com\par
89 \hfill {\it The GNU linker}\par
90 \hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
92 \global\parindent=0pt % Steve likes it this way.
95 @vskip 0pt plus 1filll
96 @c man begin COPYRIGHT
97 Copyright @copyright{} 1991-2021 Free Software Foundation, Inc.
99 Permission is granted to copy, distribute and/or modify this document
100 under the terms of the GNU Free Documentation License, Version 1.3
101 or any later version published by the Free Software Foundation;
102 with no Invariant Sections, with no Front-Cover Texts, and with no
103 Back-Cover Texts. A copy of the license is included in the
104 section entitled ``GNU Free Documentation License''.
110 @c FIXME: Talk about importance of *order* of args, cmds to linker!
115 This file documents the @sc{gnu} linker ld
116 @ifset VERSION_PACKAGE
117 @value{VERSION_PACKAGE}
119 version @value{VERSION}.
121 This document is distributed under the terms of the GNU Free
122 Documentation License version 1.3. A copy of the license is included
123 in the section entitled ``GNU Free Documentation License''.
126 * Overview:: Overview
127 * Invocation:: Invocation
128 * Scripts:: Linker Scripts
129 * Plugins:: Linker Plugins
131 * Machine Dependent:: Machine Dependent Features
135 * H8/300:: ld and the H8/300
138 * Renesas:: ld and other Renesas micros
141 * ARM:: ld and the ARM family
144 * M68HC11/68HC12:: ld and the Motorola 68HC11 and 68HC12 families
147 * HPPA ELF32:: ld and HPPA 32-bit ELF
150 * M68K:: ld and Motorola 68K family
153 * MIPS:: ld and MIPS family
156 * PowerPC ELF32:: ld and PowerPC 32-bit ELF Support
159 * PowerPC64 ELF64:: ld and PowerPC64 64-bit ELF Support
162 * S/390 ELF:: ld and S/390 ELF Support
165 * SPU ELF:: ld and SPU ELF Support
168 * TI COFF:: ld and the TI COFF
171 * Win32:: ld and WIN32 (cygwin/mingw)
174 * Xtensa:: ld and Xtensa Processors
177 @ifclear SingleFormat
180 @c Following blank line required for remaining bug in makeinfo conds/menus
182 * Reporting Bugs:: Reporting Bugs
183 * MRI:: MRI Compatible Script Files
184 * GNU Free Documentation License:: GNU Free Documentation License
185 * LD Index:: LD Index
192 @cindex @sc{gnu} linker
193 @cindex what is this?
196 @c man begin SYNOPSIS
197 ld [@b{options}] @var{objfile} @dots{}
201 ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and
202 the Info entries for @file{binutils} and
207 @c man begin DESCRIPTION
209 @command{ld} combines a number of object and archive files, relocates
210 their data and ties up symbol references. Usually the last step in
211 compiling a program is to run @command{ld}.
213 @command{ld} accepts Linker Command Language files written in
214 a superset of AT&T's Link Editor Command Language syntax,
215 to provide explicit and total control over the linking process.
219 This man page does not describe the command language; see the
220 @command{ld} entry in @code{info} for full details on the command
221 language and on other aspects of the GNU linker.
224 @ifclear SingleFormat
225 This version of @command{ld} uses the general purpose BFD libraries
226 to operate on object files. This allows @command{ld} to read, combine, and
227 write object files in many different formats---for example, COFF or
228 @code{a.out}. Different formats may be linked together to produce any
229 available kind of object file. @xref{BFD}, for more information.
232 Aside from its flexibility, the @sc{gnu} linker is more helpful than other
233 linkers in providing diagnostic information. Many linkers abandon
234 execution immediately upon encountering an error; whenever possible,
235 @command{ld} continues executing, allowing you to identify other errors
236 (or, in some cases, to get an output file in spite of the error).
243 @c man begin DESCRIPTION
245 The @sc{gnu} linker @command{ld} is meant to cover a broad range of situations,
246 and to be as compatible as possible with other linkers. As a result,
247 you have many choices to control its behavior.
253 * Options:: Command-line Options
254 * Environment:: Environment Variables
258 @section Command-line Options
266 The linker supports a plethora of command-line options, but in actual
267 practice few of them are used in any particular context.
268 @cindex standard Unix system
269 For instance, a frequent use of @command{ld} is to link standard Unix
270 object files on a standard, supported Unix system. On such a system, to
271 link a file @code{hello.o}:
274 ld -o @var{output} /lib/crt0.o hello.o -lc
277 This tells @command{ld} to produce a file called @var{output} as the
278 result of linking the file @code{/lib/crt0.o} with @code{hello.o} and
279 the library @code{libc.a}, which will come from the standard search
280 directories. (See the discussion of the @samp{-l} option below.)
282 Some of the command-line options to @command{ld} may be specified at any
283 point in the command line. However, options which refer to files, such
284 as @samp{-l} or @samp{-T}, cause the file to be read at the point at
285 which the option appears in the command line, relative to the object
286 files and other file options. Repeating non-file options with a
287 different argument will either have no further effect, or override prior
288 occurrences (those further to the left on the command line) of that
289 option. Options which may be meaningfully specified more than once are
290 noted in the descriptions below.
293 Non-option arguments are object files or archives which are to be linked
294 together. They may follow, precede, or be mixed in with command-line
295 options, except that an object file argument may not be placed between
296 an option and its argument.
298 Usually the linker is invoked with at least one object file, but you can
299 specify other forms of binary input files using @samp{-l}, @samp{-R},
300 and the script command language. If @emph{no} binary input files at all
301 are specified, the linker does not produce any output, and issues the
302 message @samp{No input files}.
304 If the linker cannot recognize the format of an object file, it will
305 assume that it is a linker script. A script specified in this way
306 augments the main linker script used for the link (either the default
307 linker script or the one specified by using @samp{-T}). This feature
308 permits the linker to link against a file which appears to be an object
309 or an archive, but actually merely defines some symbol values, or uses
310 @code{INPUT} or @code{GROUP} to load other objects. Specifying a
311 script in this way merely augments the main linker script, with the
312 extra commands placed after the main script; use the @samp{-T} option
313 to replace the default linker script entirely, but note the effect of
314 the @code{INSERT} command. @xref{Scripts}.
316 For options whose names are a single letter,
317 option arguments must either follow the option letter without intervening
318 whitespace, or be given as separate arguments immediately following the
319 option that requires them.
321 For options whose names are multiple letters, either one dash or two can
322 precede the option name; for example, @samp{-trace-symbol} and
323 @samp{--trace-symbol} are equivalent. Note---there is one exception to
324 this rule. Multiple letter options that start with a lower case 'o' can
325 only be preceded by two dashes. This is to reduce confusion with the
326 @samp{-o} option. So for example @samp{-omagic} sets the output file
327 name to @samp{magic} whereas @samp{--omagic} sets the NMAGIC flag on the
330 Arguments to multiple-letter options must either be separated from the
331 option name by an equals sign, or be given as separate arguments
332 immediately following the option that requires them. For example,
333 @samp{--trace-symbol foo} and @samp{--trace-symbol=foo} are equivalent.
334 Unique abbreviations of the names of multiple-letter options are
337 Note---if the linker is being invoked indirectly, via a compiler driver
338 (e.g. @samp{gcc}) then all the linker command-line options should be
339 prefixed by @samp{-Wl,} (or whatever is appropriate for the particular
340 compiler driver) like this:
343 gcc -Wl,--start-group foo.o bar.o -Wl,--end-group
346 This is important, because otherwise the compiler driver program may
347 silently drop the linker options, resulting in a bad link. Confusion
348 may also arise when passing options that require values through a
349 driver, as the use of a space between option and argument acts as
350 a separator, and causes the driver to pass only the option to the linker
351 and the argument to the compiler. In this case, it is simplest to use
352 the joined forms of both single- and multiple-letter options, such as:
355 gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map
358 Here is a table of the generic command-line switches accepted by the GNU
362 @include at-file.texi
364 @kindex -a @var{keyword}
365 @item -a @var{keyword}
366 This option is supported for HP/UX compatibility. The @var{keyword}
367 argument must be one of the strings @samp{archive}, @samp{shared}, or
368 @samp{default}. @samp{-aarchive} is functionally equivalent to
369 @samp{-Bstatic}, and the other two keywords are functionally equivalent
370 to @samp{-Bdynamic}. This option may be used any number of times.
372 @kindex --audit @var{AUDITLIB}
373 @item --audit @var{AUDITLIB}
374 Adds @var{AUDITLIB} to the @code{DT_AUDIT} entry of the dynamic section.
375 @var{AUDITLIB} is not checked for existence, nor will it use the DT_SONAME
376 specified in the library. If specified multiple times @code{DT_AUDIT}
377 will contain a colon separated list of audit interfaces to use. If the linker
378 finds an object with an audit entry while searching for shared libraries,
379 it will add a corresponding @code{DT_DEPAUDIT} entry in the output file.
380 This option is only meaningful on ELF platforms supporting the rtld-audit
383 @ifclear SingleFormat
384 @cindex binary input format
385 @kindex -b @var{format}
386 @kindex --format=@var{format}
389 @item -b @var{input-format}
390 @itemx --format=@var{input-format}
391 @command{ld} may be configured to support more than one kind of object
392 file. If your @command{ld} is configured this way, you can use the
393 @samp{-b} option to specify the binary format for input object files
394 that follow this option on the command line. Even when @command{ld} is
395 configured to support alternative object formats, you don't usually need
396 to specify this, as @command{ld} should be configured to expect as a
397 default input format the most usual format on each machine.
398 @var{input-format} is a text string, the name of a particular format
399 supported by the BFD libraries. (You can list the available binary
400 formats with @samp{objdump -i}.)
403 You may want to use this option if you are linking files with an unusual
404 binary format. You can also use @samp{-b} to switch formats explicitly (when
405 linking object files of different formats), by including
406 @samp{-b @var{input-format}} before each group of object files in a
409 The default format is taken from the environment variable
414 You can also define the input format from a script, using the command
417 see @ref{Format Commands}.
421 @kindex -c @var{MRI-cmdfile}
422 @kindex --mri-script=@var{MRI-cmdfile}
423 @cindex compatibility, MRI
424 @item -c @var{MRI-commandfile}
425 @itemx --mri-script=@var{MRI-commandfile}
426 For compatibility with linkers produced by MRI, @command{ld} accepts script
427 files written in an alternate, restricted command language, described in
429 @ref{MRI,,MRI Compatible Script Files}.
432 the MRI Compatible Script Files section of GNU ld documentation.
434 Introduce MRI script files with
435 the option @samp{-c}; use the @samp{-T} option to run linker
436 scripts written in the general-purpose @command{ld} scripting language.
437 If @var{MRI-cmdfile} does not exist, @command{ld} looks for it in the directories
438 specified by any @samp{-L} options.
440 @cindex common allocation
447 These three options are equivalent; multiple forms are supported for
448 compatibility with other linkers. They assign space to common symbols
449 even if a relocatable output file is specified (with @samp{-r}). The
450 script command @code{FORCE_COMMON_ALLOCATION} has the same effect.
451 @xref{Miscellaneous Commands}.
453 @kindex --depaudit @var{AUDITLIB}
454 @kindex -P @var{AUDITLIB}
455 @item --depaudit @var{AUDITLIB}
456 @itemx -P @var{AUDITLIB}
457 Adds @var{AUDITLIB} to the @code{DT_DEPAUDIT} entry of the dynamic section.
458 @var{AUDITLIB} is not checked for existence, nor will it use the DT_SONAME
459 specified in the library. If specified multiple times @code{DT_DEPAUDIT}
460 will contain a colon separated list of audit interfaces to use. This
461 option is only meaningful on ELF platforms supporting the rtld-audit interface.
462 The -P option is provided for Solaris compatibility.
464 @kindex --enable-non-contiguous-regions
465 @item --enable-non-contiguous-regions
466 This option avoids generating an error if an input section does not
467 fit a matching output section. The linker tries to allocate the input
468 section to subseque nt matching output sections, and generates an
469 error only if no output section is large enough. This is useful when
470 several non-contiguous memory regions are available and the input
471 section does not require a particular one. The order in which input
472 sections are evaluated does not change, for instance:
476 MEM1 (rwx) : ORIGIN : 0x1000, LENGTH = 0x14
477 MEM2 (rwx) : ORIGIN : 0x1000, LENGTH = 0x40
478 MEM3 (rwx) : ORIGIN : 0x2000, LENGTH = 0x40
481 mem1 : @{ *(.data.*); @} > MEM1
482 mem2 : @{ *(.data.*); @} > MEM2
483 mem3 : @{ *(.data.*); @} > MEM2
491 results in .data.1 affected to mem1, and .data.2 and .data.3
492 affected to mem2, even though .data.3 would fit in mem3.
495 This option is incompatible with INSERT statements because it changes
496 the way input sections are mapped to output sections.
498 @kindex --enable-non-contiguous-regions-warnings
499 @item --enable-non-contiguous-regions-warnings
500 This option enables warnings when
501 @code{--enable-non-contiguous-regions} allows possibly unexpected
502 matches in sections mapping, potentially leading to silently
503 discarding a section instead of failing because it does not fit any
506 @cindex entry point, from command line
507 @kindex -e @var{entry}
508 @kindex --entry=@var{entry}
510 @itemx --entry=@var{entry}
511 Use @var{entry} as the explicit symbol for beginning execution of your
512 program, rather than the default entry point. If there is no symbol
513 named @var{entry}, the linker will try to parse @var{entry} as a number,
514 and use that as the entry address (the number will be interpreted in
515 base 10; you may use a leading @samp{0x} for base 16, or a leading
516 @samp{0} for base 8). @xref{Entry Point}, for a discussion of defaults
517 and other ways of specifying the entry point.
519 @kindex --exclude-libs
520 @item --exclude-libs @var{lib},@var{lib},...
521 Specifies a list of archive libraries from which symbols should not be automatically
522 exported. The library names may be delimited by commas or colons. Specifying
523 @code{--exclude-libs ALL} excludes symbols in all archive libraries from
524 automatic export. This option is available only for the i386 PE targeted
525 port of the linker and for ELF targeted ports. For i386 PE, symbols
526 explicitly listed in a .def file are still exported, regardless of this
527 option. For ELF targeted ports, symbols affected by this option will
528 be treated as hidden.
530 @kindex --exclude-modules-for-implib
531 @item --exclude-modules-for-implib @var{module},@var{module},...
532 Specifies a list of object files or archive members, from which symbols
533 should not be automatically exported, but which should be copied wholesale
534 into the import library being generated during the link. The module names
535 may be delimited by commas or colons, and must match exactly the filenames
536 used by @command{ld} to open the files; for archive members, this is simply
537 the member name, but for object files the name listed must include and
538 match precisely any path used to specify the input file on the linker's
539 command-line. This option is available only for the i386 PE targeted port
540 of the linker. Symbols explicitly listed in a .def file are still exported,
541 regardless of this option.
543 @cindex dynamic symbol table
545 @kindex --export-dynamic
546 @kindex --no-export-dynamic
548 @itemx --export-dynamic
549 @itemx --no-export-dynamic
550 When creating a dynamically linked executable, using the @option{-E}
551 option or the @option{--export-dynamic} option causes the linker to add
552 all symbols to the dynamic symbol table. The dynamic symbol table is the
553 set of symbols which are visible from dynamic objects at run time.
555 If you do not use either of these options (or use the
556 @option{--no-export-dynamic} option to restore the default behavior), the
557 dynamic symbol table will normally contain only those symbols which are
558 referenced by some dynamic object mentioned in the link.
560 If you use @code{dlopen} to load a dynamic object which needs to refer
561 back to the symbols defined by the program, rather than some other
562 dynamic object, then you will probably need to use this option when
563 linking the program itself.
565 You can also use the dynamic list to control what symbols should
566 be added to the dynamic symbol table if the output format supports it.
567 See the description of @samp{--dynamic-list}.
569 Note that this option is specific to ELF targeted ports. PE targets
570 support a similar function to export all symbols from a DLL or EXE; see
571 the description of @samp{--export-all-symbols} below.
573 @kindex --export-dynamic-symbol=@var{glob}
574 @cindex export dynamic symbol
575 @item --export-dynamic-symbol=@var{glob}
576 When creating a dynamically linked executable, symbols matching
577 @var{glob} will be added to the dynamic symbol table. When creating a
578 shared library, references to symbols matching @var{glob} will not be
579 bound to the definitions within the shared library. This option is a
580 no-op when creating a shared library and @samp{-Bsymbolic} or
581 @samp{--dynamic-list} are not specified. This option is only meaningful
582 on ELF platforms which support shared libraries.
584 @kindex --export-dynamic-symbol-list=@var{file}
585 @cindex export dynamic symbol list
586 @item --export-dynamic-symbol-list=@var{file}
587 Specify a @samp{--export-dynamic-symbol} for each pattern in the file.
588 The format of the file is the same as the version node without
589 scope and node name. See @ref{VERSION} for more information.
591 @ifclear SingleFormat
592 @cindex big-endian objects
596 Link big-endian objects. This affects the default output format.
598 @cindex little-endian objects
601 Link little-endian objects. This affects the default output format.
604 @kindex -f @var{name}
605 @kindex --auxiliary=@var{name}
607 @itemx --auxiliary=@var{name}
608 When creating an ELF shared object, set the internal DT_AUXILIARY field
609 to the specified name. This tells the dynamic linker that the symbol
610 table of the shared object should be used as an auxiliary filter on the
611 symbol table of the shared object @var{name}.
613 If you later link a program against this filter object, then, when you
614 run the program, the dynamic linker will see the DT_AUXILIARY field. If
615 the dynamic linker resolves any symbols from the filter object, it will
616 first check whether there is a definition in the shared object
617 @var{name}. If there is one, it will be used instead of the definition
618 in the filter object. The shared object @var{name} need not exist.
619 Thus the shared object @var{name} may be used to provide an alternative
620 implementation of certain functions, perhaps for debugging or for
621 machine-specific performance.
623 This option may be specified more than once. The DT_AUXILIARY entries
624 will be created in the order in which they appear on the command line.
626 @kindex -F @var{name}
627 @kindex --filter=@var{name}
629 @itemx --filter=@var{name}
630 When creating an ELF shared object, set the internal DT_FILTER field to
631 the specified name. This tells the dynamic linker that the symbol table
632 of the shared object which is being created should be used as a filter
633 on the symbol table of the shared object @var{name}.
635 If you later link a program against this filter object, then, when you
636 run the program, the dynamic linker will see the DT_FILTER field. The
637 dynamic linker will resolve symbols according to the symbol table of the
638 filter object as usual, but it will actually link to the definitions
639 found in the shared object @var{name}. Thus the filter object can be
640 used to select a subset of the symbols provided by the object
643 Some older linkers used the @option{-F} option throughout a compilation
644 toolchain for specifying object-file format for both input and output
646 @ifclear SingleFormat
647 The @sc{gnu} linker uses other mechanisms for this purpose: the
648 @option{-b}, @option{--format}, @option{--oformat} options, the
649 @code{TARGET} command in linker scripts, and the @code{GNUTARGET}
650 environment variable.
652 The @sc{gnu} linker will ignore the @option{-F} option when not
653 creating an ELF shared object.
655 @cindex finalization function
656 @kindex -fini=@var{name}
657 @item -fini=@var{name}
658 When creating an ELF executable or shared object, call NAME when the
659 executable or shared object is unloaded, by setting DT_FINI to the
660 address of the function. By default, the linker uses @code{_fini} as
661 the function to call.
665 Ignored. Provided for compatibility with other tools.
667 @kindex -G @var{value}
668 @kindex --gpsize=@var{value}
671 @itemx --gpsize=@var{value}
672 Set the maximum size of objects to be optimized using the GP register to
673 @var{size}. This is only meaningful for object file formats such as
674 MIPS ELF that support putting large and small objects into different
675 sections. This is ignored for other object file formats.
677 @cindex runtime library name
678 @kindex -h @var{name}
679 @kindex -soname=@var{name}
681 @itemx -soname=@var{name}
682 When creating an ELF shared object, set the internal DT_SONAME field to
683 the specified name. When an executable is linked with a shared object
684 which has a DT_SONAME field, then when the executable is run the dynamic
685 linker will attempt to load the shared object specified by the DT_SONAME
686 field rather than the using the file name given to the linker.
689 @cindex incremental link
691 Perform an incremental link (same as option @samp{-r}).
693 @cindex initialization function
694 @kindex -init=@var{name}
695 @item -init=@var{name}
696 When creating an ELF executable or shared object, call NAME when the
697 executable or shared object is loaded, by setting DT_INIT to the address
698 of the function. By default, the linker uses @code{_init} as the
701 @cindex archive files, from cmd line
702 @kindex -l @var{namespec}
703 @kindex --library=@var{namespec}
704 @item -l @var{namespec}
705 @itemx --library=@var{namespec}
706 Add the archive or object file specified by @var{namespec} to the
707 list of files to link. This option may be used any number of times.
708 If @var{namespec} is of the form @file{:@var{filename}}, @command{ld}
709 will search the library path for a file called @var{filename}, otherwise it
710 will search the library path for a file called @file{lib@var{namespec}.a}.
712 On systems which support shared libraries, @command{ld} may also search for
713 files other than @file{lib@var{namespec}.a}. Specifically, on ELF
714 and SunOS systems, @command{ld} will search a directory for a library
715 called @file{lib@var{namespec}.so} before searching for one called
716 @file{lib@var{namespec}.a}. (By convention, a @code{.so} extension
717 indicates a shared library.) Note that this behavior does not apply
718 to @file{:@var{filename}}, which always specifies a file called
721 The linker will search an archive only once, at the location where it is
722 specified on the command line. If the archive defines a symbol which
723 was undefined in some object which appeared before the archive on the
724 command line, the linker will include the appropriate file(s) from the
725 archive. However, an undefined symbol in an object appearing later on
726 the command line will not cause the linker to search the archive again.
728 See the @option{-(} option for a way to force the linker to search
729 archives multiple times.
731 You may list the same archive multiple times on the command line.
734 This type of archive searching is standard for Unix linkers. However,
735 if you are using @command{ld} on AIX, note that it is different from the
736 behaviour of the AIX linker.
739 @cindex search directory, from cmd line
741 @kindex --library-path=@var{dir}
742 @item -L @var{searchdir}
743 @itemx --library-path=@var{searchdir}
744 Add path @var{searchdir} to the list of paths that @command{ld} will search
745 for archive libraries and @command{ld} control scripts. You may use this
746 option any number of times. The directories are searched in the order
747 in which they are specified on the command line. Directories specified
748 on the command line are searched before the default directories. All
749 @option{-L} options apply to all @option{-l} options, regardless of the
750 order in which the options appear. @option{-L} options do not affect
751 how @command{ld} searches for a linker script unless @option{-T}
754 If @var{searchdir} begins with @code{=} or @code{$SYSROOT}, then this
755 prefix will be replaced by the @dfn{sysroot prefix}, controlled by the
756 @samp{--sysroot} option, or specified when the linker is configured.
759 The default set of paths searched (without being specified with
760 @samp{-L}) depends on which emulation mode @command{ld} is using, and in
761 some cases also on how it was configured. @xref{Environment}.
764 The paths can also be specified in a link script with the
765 @code{SEARCH_DIR} command. Directories specified this way are searched
766 at the point in which the linker script appears in the command line.
769 @kindex -m @var{emulation}
770 @item -m @var{emulation}
771 Emulate the @var{emulation} linker. You can list the available
772 emulations with the @samp{--verbose} or @samp{-V} options.
774 If the @samp{-m} option is not used, the emulation is taken from the
775 @code{LDEMULATION} environment variable, if that is defined.
777 Otherwise, the default emulation depends upon how the linker was
785 Print a link map to the standard output. A link map provides
786 information about the link, including the following:
790 Where object files are mapped into memory.
792 How common symbols are allocated.
794 All archive members included in the link, with a mention of the symbol
795 which caused the archive member to be brought in.
797 The values assigned to symbols.
799 Note - symbols whose values are computed by an expression which
800 involves a reference to a previous value of the same symbol may not
801 have correct result displayed in the link map. This is because the
802 linker discards intermediate results and only retains the final value
803 of an expression. Under such circumstances the linker will display
804 the final value enclosed by square brackets. Thus for example a
805 linker script containing:
813 will produce the following output in the link map if the @option{-M}
818 [0x0000000c] foo = (foo * 0x4)
819 [0x0000000c] foo = (foo + 0x8)
822 See @ref{Expressions} for more information about expressions in linker
826 How GNU properties are merged.
828 When the linker merges input .note.gnu.property sections into one output
829 .note.gnu.property section, some properties are removed or updated.
830 These actions are reported in the link map. For example:
833 Removed property 0xc0000002 to merge foo.o (0x1) and bar.o (not found)
836 This indicates that property 0xc0000002 is removed from output when
837 merging properties in @file{foo.o}, whose property 0xc0000002 value
838 is 0x1, and @file{bar.o}, which doesn't have property 0xc0000002.
841 Updated property 0xc0010001 (0x1) to merge foo.o (0x1) and bar.o (0x1)
844 This indicates that property 0xc0010001 value is updated to 0x1 in output
845 when merging properties in @file{foo.o}, whose 0xc0010001 property value
846 is 0x1, and @file{bar.o}, whose 0xc0010001 property value is 0x1.
849 @cindex link map discarded
850 @kindex --print-map-discarded
851 @kindex --no-print-map-discarded
852 @item --print-map-discarded
853 @itemx --no-print-map-discarded
854 Print (or do not print) the list of discarded and garbage collected sections
855 in the link map. Enabled by default.
858 @cindex read-only text
863 Turn off page alignment of sections, and disable linking against shared
864 libraries. If the output format supports Unix style magic numbers,
865 mark the output as @code{NMAGIC}.
869 @cindex read/write from cmd line
873 Set the text and data sections to be readable and writable. Also, do
874 not page-align the data segment, and disable linking against shared
875 libraries. If the output format supports Unix style magic numbers,
876 mark the output as @code{OMAGIC}. Note: Although a writable text section
877 is allowed for PE-COFF targets, it does not conform to the format
878 specification published by Microsoft.
883 This option negates most of the effects of the @option{-N} option. It
884 sets the text section to be read-only, and forces the data segment to
885 be page-aligned. Note - this option does not enable linking against
886 shared libraries. Use @option{-Bdynamic} for this.
888 @kindex -o @var{output}
889 @kindex --output=@var{output}
890 @cindex naming the output file
891 @item -o @var{output}
892 @itemx --output=@var{output}
893 Use @var{output} as the name for the program produced by @command{ld}; if this
894 option is not specified, the name @file{a.out} is used by default. The
895 script command @code{OUTPUT} can also specify the output file name.
897 @kindex --dependency-file=@var{depfile}
898 @cindex dependency file
899 @item --dependency-file=@var{depfile}
900 Write a @dfn{dependency file} to @var{depfile}. This file contains a rule
901 suitable for @code{make} describing the output file and all the input files
902 that were read to produce it. The output is similar to the compiler's
903 output with @samp{-M -MP} (@pxref{Preprocessor Options,, Options
904 Controlling the Preprocessor, gcc.info, Using the GNU Compiler
905 Collection}). Note that there is no option like the compiler's @samp{-MM},
906 to exclude ``system files'' (which is not a well-specified concept in the
907 linker, unlike ``system headers'' in the compiler). So the output from
908 @samp{--dependency-file} is always specific to the exact state of the
909 installation where it was produced, and should not be copied into
910 distributed makefiles without careful editing.
912 @kindex -O @var{level}
913 @cindex generating optimized output
915 If @var{level} is a numeric values greater than zero @command{ld} optimizes
916 the output. This might take significantly longer and therefore probably
917 should only be enabled for the final binary. At the moment this
918 option only affects ELF shared library generation. Future releases of
919 the linker may make more use of this option. Also currently there is
920 no difference in the linker's behaviour for different non-zero values
921 of this option. Again this may change with future releases.
923 @kindex -plugin @var{name}
924 @item -plugin @var{name}
925 Involve a plugin in the linking process. The @var{name} parameter is
926 the absolute filename of the plugin. Usually this parameter is
927 automatically added by the complier, when using link time
928 optimization, but users can also add their own plugins if they so
931 Note that the location of the compiler originated plugins is different
932 from the place where the @command{ar}, @command{nm} and
933 @command{ranlib} programs search for their plugins. In order for
934 those commands to make use of a compiler based plugin it must first be
935 copied into the @file{$@{libdir@}/bfd-plugins} directory. All gcc
936 based linker plugins are backward compatible, so it is sufficient to
937 just copy in the newest one.
940 @cindex push state governing input file handling
942 The @option{--push-state} allows one to preserve the current state of the
943 flags which govern the input file handling so that they can all be
944 restored with one corresponding @option{--pop-state} option.
946 The option which are covered are: @option{-Bdynamic}, @option{-Bstatic},
947 @option{-dn}, @option{-dy}, @option{-call_shared}, @option{-non_shared},
948 @option{-static}, @option{-N}, @option{-n}, @option{--whole-archive},
949 @option{--no-whole-archive}, @option{-r}, @option{-Ur},
950 @option{--copy-dt-needed-entries}, @option{--no-copy-dt-needed-entries},
951 @option{--as-needed}, @option{--no-as-needed}, and @option{-a}.
953 One target for this option are specifications for @file{pkg-config}. When
954 used with the @option{--libs} option all possibly needed libraries are
955 listed and then possibly linked with all the time. It is better to return
956 something as follows:
959 -Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
963 @cindex pop state governing input file handling
965 Undoes the effect of --push-state, restores the previous values of the
966 flags governing input file handling.
969 @kindex --emit-relocs
970 @cindex retain relocations in final executable
973 Leave relocation sections and contents in fully linked executables.
974 Post link analysis and optimization tools may need this information in
975 order to perform correct modifications of executables. This results
976 in larger executables.
978 This option is currently only supported on ELF platforms.
980 @kindex --force-dynamic
981 @cindex forcing the creation of dynamic sections
982 @item --force-dynamic
983 Force the output file to have dynamic sections. This option is specific
987 @cindex relocatable output
989 @kindex --relocatable
992 Generate relocatable output---i.e., generate an output file that can in
993 turn serve as input to @command{ld}. This is often called @dfn{partial
994 linking}. As a side effect, in environments that support standard Unix
995 magic numbers, this option also sets the output file's magic number to
997 @c ; see @option{-N}.
998 If this option is not specified, an absolute file is produced. When
999 linking C++ programs, this option @emph{will not} resolve references to
1000 constructors; to do that, use @samp{-Ur}.
1002 When an input file does not have the same format as the output file,
1003 partial linking is only supported if that input file does not contain any
1004 relocations. Different output formats can have further restrictions; for
1005 example some @code{a.out}-based formats do not support partial linking
1006 with input files in other formats at all.
1008 This option does the same thing as @samp{-i}.
1010 @kindex -R @var{file}
1011 @kindex --just-symbols=@var{file}
1012 @cindex symbol-only input
1013 @item -R @var{filename}
1014 @itemx --just-symbols=@var{filename}
1015 Read symbol names and their addresses from @var{filename}, but do not
1016 relocate it or include it in the output. This allows your output file
1017 to refer symbolically to absolute locations of memory defined in other
1018 programs. You may use this option more than once.
1020 For compatibility with other ELF linkers, if the @option{-R} option is
1021 followed by a directory name, rather than a file name, it is treated as
1022 the @option{-rpath} option.
1026 @cindex strip all symbols
1029 Omit all symbol information from the output file.
1032 @kindex --strip-debug
1033 @cindex strip debugger symbols
1035 @itemx --strip-debug
1036 Omit debugger symbol information (but not all symbols) from the output file.
1038 @kindex --strip-discarded
1039 @kindex --no-strip-discarded
1040 @item --strip-discarded
1041 @itemx --no-strip-discarded
1042 Omit (or do not omit) global symbols defined in discarded sections.
1047 @cindex input files, displaying
1050 Print the names of the input files as @command{ld} processes them. If
1051 @samp{-t} is given twice then members within archives are also printed.
1052 @samp{-t} output is useful to generate a list of all the object files
1053 and scripts involved in linking, for example, when packaging files for
1054 a linker bug report.
1056 @kindex -T @var{script}
1057 @kindex --script=@var{script}
1058 @cindex script files
1059 @item -T @var{scriptfile}
1060 @itemx --script=@var{scriptfile}
1061 Use @var{scriptfile} as the linker script. This script replaces
1062 @command{ld}'s default linker script (rather than adding to it), so
1063 @var{commandfile} must specify everything necessary to describe the
1064 output file. @xref{Scripts}. If @var{scriptfile} does not exist in
1065 the current directory, @code{ld} looks for it in the directories
1066 specified by any preceding @samp{-L} options. Multiple @samp{-T}
1069 @kindex -dT @var{script}
1070 @kindex --default-script=@var{script}
1071 @cindex script files
1072 @item -dT @var{scriptfile}
1073 @itemx --default-script=@var{scriptfile}
1074 Use @var{scriptfile} as the default linker script. @xref{Scripts}.
1076 This option is similar to the @option{--script} option except that
1077 processing of the script is delayed until after the rest of the
1078 command line has been processed. This allows options placed after the
1079 @option{--default-script} option on the command line to affect the
1080 behaviour of the linker script, which can be important when the linker
1081 command line cannot be directly controlled by the user. (eg because
1082 the command line is being constructed by another tool, such as
1085 @kindex -u @var{symbol}
1086 @kindex --undefined=@var{symbol}
1087 @cindex undefined symbol
1088 @item -u @var{symbol}
1089 @itemx --undefined=@var{symbol}
1090 Force @var{symbol} to be entered in the output file as an undefined
1091 symbol. Doing this may, for example, trigger linking of additional
1092 modules from standard libraries. @samp{-u} may be repeated with
1093 different option arguments to enter additional undefined symbols. This
1094 option is equivalent to the @code{EXTERN} linker script command.
1096 If this option is being used to force additional modules to be pulled
1097 into the link, and if it is an error for the symbol to remain
1098 undefined, then the option @option{--require-defined} should be used
1101 @kindex --require-defined=@var{symbol}
1102 @cindex symbols, require defined
1103 @cindex defined symbol
1104 @item --require-defined=@var{symbol}
1105 Require that @var{symbol} is defined in the output file. This option
1106 is the same as option @option{--undefined} except that if @var{symbol}
1107 is not defined in the output file then the linker will issue an error
1108 and exit. The same effect can be achieved in a linker script by using
1109 @code{EXTERN}, @code{ASSERT} and @code{DEFINED} together. This option
1110 can be used multiple times to require additional symbols.
1113 @cindex constructors
1115 For anything other than C++ programs, this option is equivalent to
1116 @samp{-r}: it generates relocatable output---i.e., an output file that can in
1117 turn serve as input to @command{ld}. When linking C++ programs, @samp{-Ur}
1118 @emph{does} resolve references to constructors, unlike @samp{-r}.
1119 It does not work to use @samp{-Ur} on files that were themselves linked
1120 with @samp{-Ur}; once the constructor table has been built, it cannot
1121 be added to. Use @samp{-Ur} only for the last partial link, and
1122 @samp{-r} for the others.
1124 @kindex --orphan-handling=@var{MODE}
1125 @cindex orphan sections
1126 @cindex sections, orphan
1127 @item --orphan-handling=@var{MODE}
1128 Control how orphan sections are handled. An orphan section is one not
1129 specifically mentioned in a linker script. @xref{Orphan Sections}.
1131 @var{MODE} can have any of the following values:
1135 Orphan sections are placed into a suitable output section following
1136 the strategy described in @ref{Orphan Sections}. The option
1137 @samp{--unique} also affects how sections are placed.
1140 All orphan sections are discarded, by placing them in the
1141 @samp{/DISCARD/} section (@pxref{Output Section Discarding}).
1144 The linker will place the orphan section as for @code{place} and also
1148 The linker will exit with an error if any orphan section is found.
1151 The default if @samp{--orphan-handling} is not given is @code{place}.
1153 @kindex --unique[=@var{SECTION}]
1154 @item --unique[=@var{SECTION}]
1155 Creates a separate output section for every input section matching
1156 @var{SECTION}, or if the optional wildcard @var{SECTION} argument is
1157 missing, for every orphan input section. An orphan section is one not
1158 specifically mentioned in a linker script. You may use this option
1159 multiple times on the command line; It prevents the normal merging of
1160 input sections with the same name, overriding output section assignments
1170 Display the version number for @command{ld}. The @option{-V} option also
1171 lists the supported emulations.
1174 @kindex --discard-all
1175 @cindex deleting local symbols
1177 @itemx --discard-all
1178 Delete all local symbols.
1181 @kindex --discard-locals
1182 @cindex local symbols, deleting
1184 @itemx --discard-locals
1185 Delete all temporary local symbols. (These symbols start with
1186 system-specific local label prefixes, typically @samp{.L} for ELF systems
1187 or @samp{L} for traditional a.out systems.)
1189 @kindex -y @var{symbol}
1190 @kindex --trace-symbol=@var{symbol}
1191 @cindex symbol tracing
1192 @item -y @var{symbol}
1193 @itemx --trace-symbol=@var{symbol}
1194 Print the name of each linked file in which @var{symbol} appears. This
1195 option may be given any number of times. On many systems it is necessary
1196 to prepend an underscore.
1198 This option is useful when you have an undefined symbol in your link but
1199 don't know where the reference is coming from.
1201 @kindex -Y @var{path}
1203 Add @var{path} to the default library search path. This option exists
1204 for Solaris compatibility.
1206 @kindex -z @var{keyword}
1207 @item -z @var{keyword}
1208 The recognized keywords are:
1212 Always generate BND prefix in PLT entries. Supported for Linux/x86_64.
1214 @item call-nop=prefix-addr
1215 @itemx call-nop=suffix-nop
1216 @itemx call-nop=prefix-@var{byte}
1217 @itemx call-nop=suffix-@var{byte}
1218 Specify the 1-byte @code{NOP} padding when transforming indirect call
1219 to a locally defined function, foo, via its GOT slot.
1220 @option{call-nop=prefix-addr} generates @code{0x67 call foo}.
1221 @option{call-nop=suffix-nop} generates @code{call foo 0x90}.
1222 @option{call-nop=prefix-@var{byte}} generates @code{@var{byte} call foo}.
1223 @option{call-nop=suffix-@var{byte}} generates @code{call foo @var{byte}}.
1224 Supported for i386 and x86_64.
1226 @item cet-report=none
1227 @itemx cet-report=warning
1228 @itemx cet-report=error
1229 Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_IBT and
1230 GNU_PROPERTY_X86_FEATURE_1_SHSTK properties in input .note.gnu.property
1231 section. @option{cet-report=none}, which is the default, will make the
1232 linker not report missing properties in input files.
1233 @option{cet-report=warning} will make the linker issue a warning for
1234 missing properties in input files. @option{cet-report=error} will make
1235 the linker issue an error for missing properties in input files.
1236 Note that @option{ibt} will turn off the missing
1237 GNU_PROPERTY_X86_FEATURE_1_IBT property report and @option{shstk} will
1238 turn off the missing GNU_PROPERTY_X86_FEATURE_1_SHSTK property report.
1239 Supported for Linux/i386 and Linux/x86_64.
1243 Combine multiple dynamic relocation sections and sort to improve
1244 dynamic symbol lookup caching. Do not do this if @samp{nocombreloc}.
1248 Generate common symbols with STT_COMMON type during a relocatable
1249 link. Use STT_OBJECT type if @samp{nocommon}.
1251 @item common-page-size=@var{value}
1252 Set the page size most commonly used to @var{value}. Memory image
1253 layout will be optimized to minimize memory pages if the system is
1254 using pages of this size.
1257 Report unresolved symbol references from regular object files. This
1258 is done even if the linker is creating a non-symbolic shared library.
1259 This option is the inverse of @samp{-z undefs}.
1261 @item dynamic-undefined-weak
1262 @itemx nodynamic-undefined-weak
1263 Make undefined weak symbols dynamic when building a dynamic object,
1264 if they are referenced from a regular object file and not forced local
1265 by symbol visibility or versioning. Do not make them dynamic if
1266 @samp{nodynamic-undefined-weak}. If neither option is given, a target
1267 may default to either option being in force, or make some other
1268 selection of undefined weak symbols dynamic. Not all targets support
1272 Marks the object as requiring executable stack.
1275 This option is only meaningful when building a shared object. It makes
1276 the symbols defined by this shared object available for symbol resolution
1277 of subsequently loaded libraries.
1280 This option is only meaningful when building a dynamic executable.
1281 This option marks the executable as requiring global auditing by
1282 setting the @code{DF_1_GLOBAUDIT} bit in the @code{DT_FLAGS_1} dynamic
1283 tag. Global auditing requires that any auditing library defined via
1284 the @option{--depaudit} or @option{-P} command-line options be run for
1285 all dynamic objects loaded by the application.
1288 Generate Intel Indirect Branch Tracking (IBT) enabled PLT entries.
1289 Supported for Linux/i386 and Linux/x86_64.
1292 Generate GNU_PROPERTY_X86_FEATURE_1_IBT in .note.gnu.property section
1293 to indicate compatibility with IBT. This also implies @option{ibtplt}.
1294 Supported for Linux/i386 and Linux/x86_64.
1297 This option is only meaningful when building a shared object.
1298 It marks the object so that its runtime initialization will occur
1299 before the runtime initialization of any other objects brought into
1300 the process at the same time. Similarly the runtime finalization of
1301 the object will occur after the runtime finalization of any other
1305 Specify that the dynamic loader should modify its symbol search order
1306 so that symbols in this shared library interpose all other shared
1307 libraries not so marked.
1311 When generating a shared library or other dynamically loadable ELF
1312 object mark it as one that should (by default) only ever be loaded once,
1313 and only in the main namespace (when using @code{dlmopen}). This is
1314 primarily used to mark fundamental libraries such as libc, libpthread et
1315 al which do not usually function correctly unless they are the sole instances
1316 of themselves. This behaviour can be overridden by the @code{dlmopen} caller
1317 and does not apply to certain loading mechanisms (such as audit libraries).
1320 Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U48 in .note.gnu.property section
1321 to indicate compatibility with Intel LAM_U48. Supported for Linux/x86_64.
1324 Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U57 in .note.gnu.property section
1325 to indicate compatibility with Intel LAM_U57. Supported for Linux/x86_64.
1327 @item lam-u48-report=none
1328 @itemx lam-u48-report=warning
1329 @itemx lam-u48-report=error
1330 Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U48
1331 property in input .note.gnu.property section.
1332 @option{lam-u48-report=none}, which is the default, will make the
1333 linker not report missing properties in input files.
1334 @option{lam-u48-report=warning} will make the linker issue a warning for
1335 missing properties in input files. @option{lam-u48-report=error} will
1336 make the linker issue an error for missing properties in input files.
1337 Supported for Linux/x86_64.
1339 @item lam-u57-report=none
1340 @itemx lam-u57-report=warning
1341 @itemx lam-u57-report=error
1342 Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U57
1343 property in input .note.gnu.property section.
1344 @option{lam-u57-report=none}, which is the default, will make the
1345 linker not report missing properties in input files.
1346 @option{lam-u57-report=warning} will make the linker issue a warning for
1347 missing properties in input files. @option{lam-u57-report=error} will
1348 make the linker issue an error for missing properties in input files.
1349 Supported for Linux/x86_64.
1351 @item lam-report=none
1352 @itemx lam-report=warning
1353 @itemx lam-report=error
1354 Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U48 and
1355 GNU_PROPERTY_X86_FEATURE_1_LAM_U57 properties in input .note.gnu.property
1356 section. @option{lam-report=none}, which is the default, will make the
1357 linker not report missing properties in input files.
1358 @option{lam-report=warning} will make the linker issue a warning for
1359 missing properties in input files. @option{lam-report=error} will make
1360 the linker issue an error for missing properties in input files.
1361 Supported for Linux/x86_64.
1364 When generating an executable or shared library, mark it to tell the
1365 dynamic linker to defer function call resolution to the point when
1366 the function is called (lazy binding), rather than at load time.
1367 Lazy binding is the default.
1370 Specify that the object's filters be processed immediately at runtime.
1372 @item max-page-size=@var{value}
1373 Set the maximum memory page size supported to @var{value}.
1376 Allow multiple definitions.
1379 Disable linker generated .dynbss variables used in place of variables
1380 defined in shared libraries. May result in dynamic text relocations.
1383 Specify that the dynamic loader search for dependencies of this object
1384 should ignore any default library search paths.
1387 Specify that the object shouldn't be unloaded at runtime.
1390 Specify that the object is not available to @code{dlopen}.
1393 Specify that the object can not be dumped by @code{dldump}.
1396 Marks the object as not requiring executable stack.
1398 @item noextern-protected-data
1399 Don't treat protected data symbols as external when building a shared
1400 library. This option overrides the linker backend default. It can be
1401 used to work around incorrect relocations against protected data symbols
1402 generated by compiler. Updates on protected data symbols by another
1403 module aren't visible to the resulting shared library. Supported for
1406 @item noreloc-overflow
1407 Disable relocation overflow check. This can be used to disable
1408 relocation overflow check if there will be no dynamic relocation
1409 overflow at run-time. Supported for x86_64.
1412 When generating an executable or shared library, mark it to tell the
1413 dynamic linker to resolve all symbols when the program is started, or
1414 when the shared library is loaded by dlopen, instead of deferring
1415 function call resolution to the point when the function is first
1419 Specify that the object requires @samp{$ORIGIN} handling in paths.
1423 Create an ELF @code{PT_GNU_RELRO} segment header in the object. This
1424 specifies a memory segment that should be made read-only after
1425 relocation, if supported. Specifying @samp{common-page-size} smaller
1426 than the system page size will render this protection ineffective.
1427 Don't create an ELF @code{PT_GNU_RELRO} segment if @samp{norelro}.
1430 @itemx noseparate-code
1431 Create separate code @code{PT_LOAD} segment header in the object. This
1432 specifies a memory segment that should contain only instructions and must
1433 be in wholly disjoint pages from any other data. Don't create separate
1434 code @code{PT_LOAD} segment if @samp{noseparate-code} is used.
1437 @itemx nounique-symbol
1438 Avoid duplicated local symbol names in the symbol string table. Append
1439 ".@code{number}" to duplicated local symbol names if @samp{unique-symbol}
1440 is used. @option{nounique-symbol} is the default.
1443 Generate GNU_PROPERTY_X86_FEATURE_1_SHSTK in .note.gnu.property section
1444 to indicate compatibility with Intel Shadow Stack. Supported for
1445 Linux/i386 and Linux/x86_64.
1447 @item stack-size=@var{value}
1448 Specify a stack size for an ELF @code{PT_GNU_STACK} segment.
1449 Specifying zero will override any default non-zero sized
1450 @code{PT_GNU_STACK} segment creation.
1452 @item start-stop-visibility=@var{value}
1454 @cindex ELF symbol visibility
1455 Specify the ELF symbol visibility for synthesized
1456 @code{__start_SECNAME} and @code{__stop_SECNAME} symbols (@pxref{Input
1457 Section Example}). @var{value} must be exactly @samp{default},
1458 @samp{internal}, @samp{hidden}, or @samp{protected}. If no @samp{-z
1459 start-stop-visibility} option is given, @samp{protected} is used for
1460 compatibility with historical practice. However, it's highly
1461 recommended to use @samp{-z start-stop-visibility=hidden} in new
1462 programs and shared libraries so that these symbols are not exported
1463 between shared objects, which is not usually what's intended.
1468 Report an error if DT_TEXTREL is set, i.e., if the position-independent
1469 or shared object has dynamic relocations in read-only sections. Don't
1470 report an error if @samp{notext} or @samp{textoff}.
1473 Do not report unresolved symbol references from regular object files,
1474 either when creating an executable, or when creating a shared library.
1475 This option is the inverse of @samp{-z defs}.
1477 @item x86-64-baseline
1481 Specify the x86-64 ISA level needed in .note.gnu.property section.
1482 @option{x86-64-baseline} generates @code{GNU_PROPERTY_X86_ISA_1_BASELINE}.
1483 @option{x86-64-v2} generates @code{GNU_PROPERTY_X86_ISA_1_V2}.
1484 @option{x86-64-v3} generates @code{GNU_PROPERTY_X86_ISA_1_V3}.
1485 @option{x86-64-v4} generates @code{GNU_PROPERTY_X86_ISA_1_V4}.
1486 Supported for Linux/i386 and Linux/x86_64.
1490 Other keywords are ignored for Solaris compatibility.
1493 @cindex groups of archives
1494 @item -( @var{archives} -)
1495 @itemx --start-group @var{archives} --end-group
1496 The @var{archives} should be a list of archive files. They may be
1497 either explicit file names, or @samp{-l} options.
1499 The specified archives are searched repeatedly until no new undefined
1500 references are created. Normally, an archive is searched only once in
1501 the order that it is specified on the command line. If a symbol in that
1502 archive is needed to resolve an undefined symbol referred to by an
1503 object in an archive that appears later on the command line, the linker
1504 would not be able to resolve that reference. By grouping the archives,
1505 they will all be searched repeatedly until all possible references are
1508 Using this option has a significant performance cost. It is best to use
1509 it only when there are unavoidable circular references between two or
1512 @kindex --accept-unknown-input-arch
1513 @kindex --no-accept-unknown-input-arch
1514 @item --accept-unknown-input-arch
1515 @itemx --no-accept-unknown-input-arch
1516 Tells the linker to accept input files whose architecture cannot be
1517 recognised. The assumption is that the user knows what they are doing
1518 and deliberately wants to link in these unknown input files. This was
1519 the default behaviour of the linker, before release 2.14. The default
1520 behaviour from release 2.14 onwards is to reject such input files, and
1521 so the @samp{--accept-unknown-input-arch} option has been added to
1522 restore the old behaviour.
1525 @kindex --no-as-needed
1527 @itemx --no-as-needed
1528 This option affects ELF DT_NEEDED tags for dynamic libraries mentioned
1529 on the command line after the @option{--as-needed} option. Normally
1530 the linker will add a DT_NEEDED tag for each dynamic library mentioned
1531 on the command line, regardless of whether the library is actually
1532 needed or not. @option{--as-needed} causes a DT_NEEDED tag to only be
1533 emitted for a library that @emph{at that point in the link} satisfies a
1534 non-weak undefined symbol reference from a regular object file or, if
1535 the library is not found in the DT_NEEDED lists of other needed libraries, a
1536 non-weak undefined symbol reference from another needed dynamic library.
1537 Object files or libraries appearing on the command line @emph{after}
1538 the library in question do not affect whether the library is seen as
1539 needed. This is similar to the rules for extraction of object files
1540 from archives. @option{--no-as-needed} restores the default behaviour.
1542 @kindex --add-needed
1543 @kindex --no-add-needed
1545 @itemx --no-add-needed
1546 These two options have been deprecated because of the similarity of
1547 their names to the @option{--as-needed} and @option{--no-as-needed}
1548 options. They have been replaced by @option{--copy-dt-needed-entries}
1549 and @option{--no-copy-dt-needed-entries}.
1551 @kindex -assert @var{keyword}
1552 @item -assert @var{keyword}
1553 This option is ignored for SunOS compatibility.
1557 @kindex -call_shared
1561 Link against dynamic libraries. This is only meaningful on platforms
1562 for which shared libraries are supported. This option is normally the
1563 default on such platforms. The different variants of this option are
1564 for compatibility with various systems. You may use this option
1565 multiple times on the command line: it affects library searching for
1566 @option{-l} options which follow it.
1570 Set the @code{DF_1_GROUP} flag in the @code{DT_FLAGS_1} entry in the dynamic
1571 section. This causes the runtime linker to handle lookups in this
1572 object and its dependencies to be performed only inside the group.
1573 @option{--unresolved-symbols=report-all} is implied. This option is
1574 only meaningful on ELF platforms which support shared libraries.
1584 Do not link against shared libraries. This is only meaningful on
1585 platforms for which shared libraries are supported. The different
1586 variants of this option are for compatibility with various systems. You
1587 may use this option multiple times on the command line: it affects
1588 library searching for @option{-l} options which follow it. This
1589 option also implies @option{--unresolved-symbols=report-all}. This
1590 option can be used with @option{-shared}. Doing so means that a
1591 shared library is being created but that all of the library's external
1592 references must be resolved by pulling in entries from static
1597 When creating a shared library, bind references to global symbols to the
1598 definition within the shared library, if any. Normally, it is possible
1599 for a program linked against a shared library to override the definition
1600 within the shared library. This option is only meaningful on ELF
1601 platforms which support shared libraries.
1603 @kindex -Bsymbolic-functions
1604 @item -Bsymbolic-functions
1605 When creating a shared library, bind references to global function
1606 symbols to the definition within the shared library, if any.
1607 This option is only meaningful on ELF platforms which support shared
1610 @kindex --dynamic-list=@var{dynamic-list-file}
1611 @item --dynamic-list=@var{dynamic-list-file}
1612 Specify the name of a dynamic list file to the linker. This is
1613 typically used when creating shared libraries to specify a list of
1614 global symbols whose references shouldn't be bound to the definition
1615 within the shared library, or creating dynamically linked executables
1616 to specify a list of symbols which should be added to the symbol table
1617 in the executable. This option is only meaningful on ELF platforms
1618 which support shared libraries.
1620 The format of the dynamic list is the same as the version node without
1621 scope and node name. See @ref{VERSION} for more information.
1623 @kindex --dynamic-list-data
1624 @item --dynamic-list-data
1625 Include all global data symbols to the dynamic list.
1627 @kindex --dynamic-list-cpp-new
1628 @item --dynamic-list-cpp-new
1629 Provide the builtin dynamic list for C++ operator new and delete. It
1630 is mainly useful for building shared libstdc++.
1632 @kindex --dynamic-list-cpp-typeinfo
1633 @item --dynamic-list-cpp-typeinfo
1634 Provide the builtin dynamic list for C++ runtime type identification.
1636 @kindex --check-sections
1637 @kindex --no-check-sections
1638 @item --check-sections
1639 @itemx --no-check-sections
1640 Asks the linker @emph{not} to check section addresses after they have
1641 been assigned to see if there are any overlaps. Normally the linker will
1642 perform this check, and if it finds any overlaps it will produce
1643 suitable error messages. The linker does know about, and does make
1644 allowances for sections in overlays. The default behaviour can be
1645 restored by using the command-line switch @option{--check-sections}.
1646 Section overlap is not usually checked for relocatable links. You can
1647 force checking in that case by using the @option{--check-sections}
1650 @kindex --copy-dt-needed-entries
1651 @kindex --no-copy-dt-needed-entries
1652 @item --copy-dt-needed-entries
1653 @itemx --no-copy-dt-needed-entries
1654 This option affects the treatment of dynamic libraries referred to
1655 by DT_NEEDED tags @emph{inside} ELF dynamic libraries mentioned on the
1656 command line. Normally the linker won't add a DT_NEEDED tag to the
1657 output binary for each library mentioned in a DT_NEEDED tag in an
1658 input dynamic library. With @option{--copy-dt-needed-entries}
1659 specified on the command line however any dynamic libraries that
1660 follow it will have their DT_NEEDED entries added. The default
1661 behaviour can be restored with @option{--no-copy-dt-needed-entries}.
1663 This option also has an effect on the resolution of symbols in dynamic
1664 libraries. With @option{--copy-dt-needed-entries} dynamic libraries
1665 mentioned on the command line will be recursively searched, following
1666 their DT_NEEDED tags to other libraries, in order to resolve symbols
1667 required by the output binary. With the default setting however
1668 the searching of dynamic libraries that follow it will stop with the
1669 dynamic library itself. No DT_NEEDED links will be traversed to resolve
1672 @cindex cross reference table
1675 Output a cross reference table. If a linker map file is being
1676 generated, the cross reference table is printed to the map file.
1677 Otherwise, it is printed on the standard output.
1679 The format of the table is intentionally simple, so that it may be
1680 easily processed by a script if necessary. The symbols are printed out,
1681 sorted by name. For each symbol, a list of file names is given. If the
1682 symbol is defined, the first file listed is the location of the
1683 definition. If the symbol is defined as a common value then any files
1684 where this happens appear next. Finally any files that reference the
1687 @cindex ctf variables
1688 @kindex --ctf-variables
1689 @kindex --no-ctf-variables
1690 @item --ctf-variables
1691 @item --no-ctf-variables
1692 The CTF debuginfo format supports a section which encodes the names and
1693 types of variables found in the program which do not appear in any symbol
1694 table. These variables clearly cannot be looked up by address by
1695 conventional debuggers, so the space used for their types and names is
1696 usually wasted: the types are usually small but the names are often not.
1697 @option{--ctf-variables} causes the generation of such a section.
1698 The default behaviour can be restored with @option{--no-ctf-variables}.
1700 @cindex ctf type sharing
1701 @kindex --ctf-share-types
1702 @item --ctf-share-types=@var{method}
1703 Adjust the method used to share types between translation units in CTF.
1706 @item share-unconflicted
1707 Put all types that do not have ambiguous definitions into the shared dictionary,
1708 where debuggers can easily access them, even if they only occur in one
1709 translation unit. This is the default.
1711 @item share-duplicated
1712 Put only types that occur in multiple translation units into the shared
1713 dictionary: types with only one definition go into per-translation-unit
1714 dictionaries. Types with ambiguous definitions in multiple translation units
1715 always go into per-translation-unit dictionaries. This tends to make the CTF
1716 larger, but may reduce the amount of CTF in the shared dictionary. For very
1717 large projects this may speed up opening the CTF and save memory in the CTF
1718 consumer at runtime.
1721 @cindex common allocation
1722 @kindex --no-define-common
1723 @item --no-define-common
1724 This option inhibits the assignment of addresses to common symbols.
1725 The script command @code{INHIBIT_COMMON_ALLOCATION} has the same effect.
1726 @xref{Miscellaneous Commands}.
1728 The @samp{--no-define-common} option allows decoupling
1729 the decision to assign addresses to Common symbols from the choice
1730 of the output file type; otherwise a non-Relocatable output type
1731 forces assigning addresses to Common symbols.
1732 Using @samp{--no-define-common} allows Common symbols that are referenced
1733 from a shared library to be assigned addresses only in the main program.
1734 This eliminates the unused duplicate space in the shared library,
1735 and also prevents any possible confusion over resolving to the wrong
1736 duplicate when there are many dynamic modules with specialized search
1737 paths for runtime symbol resolution.
1739 @cindex group allocation in linker script
1740 @cindex section groups
1742 @kindex --force-group-allocation
1743 @item --force-group-allocation
1744 This option causes the linker to place section group members like
1745 normal input sections, and to delete the section groups. This is the
1746 default behaviour for a final link but this option can be used to
1747 change the behaviour of a relocatable link (@samp{-r}). The script
1748 command @code{FORCE_GROUP_ALLOCATION} has the same
1749 effect. @xref{Miscellaneous Commands}.
1751 @cindex symbols, from command line
1752 @kindex --defsym=@var{symbol}=@var{exp}
1753 @item --defsym=@var{symbol}=@var{expression}
1754 Create a global symbol in the output file, containing the absolute
1755 address given by @var{expression}. You may use this option as many
1756 times as necessary to define multiple symbols in the command line. A
1757 limited form of arithmetic is supported for the @var{expression} in this
1758 context: you may give a hexadecimal constant or the name of an existing
1759 symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
1760 constants or symbols. If you need more elaborate expressions, consider
1761 using the linker command language from a script (@pxref{Assignments}).
1762 @emph{Note:} there should be no white space between @var{symbol}, the
1763 equals sign (``@key{=}''), and @var{expression}.
1765 The linker processes @samp{--defsym} arguments and @samp{-T} arguments
1766 in order, placing @samp{--defsym} before @samp{-T} will define the
1767 symbol before the linker script from @samp{-T} is processed, while
1768 placing @samp{--defsym} after @samp{-T} will define the symbol after
1769 the linker script has been processed. This difference has
1770 consequences for expressions within the linker script that use the
1771 @samp{--defsym} symbols, which order is correct will depend on what
1772 you are trying to achieve.
1774 @cindex demangling, from command line
1775 @kindex --demangle[=@var{style}]
1776 @kindex --no-demangle
1777 @item --demangle[=@var{style}]
1778 @itemx --no-demangle
1779 These options control whether to demangle symbol names in error messages
1780 and other output. When the linker is told to demangle, it tries to
1781 present symbol names in a readable fashion: it strips leading
1782 underscores if they are used by the object file format, and converts C++
1783 mangled symbol names into user readable names. Different compilers have
1784 different mangling styles. The optional demangling style argument can be used
1785 to choose an appropriate demangling style for your compiler. The linker will
1786 demangle by default unless the environment variable @samp{COLLECT_NO_DEMANGLE}
1787 is set. These options may be used to override the default.
1789 @cindex dynamic linker, from command line
1790 @kindex -I@var{file}
1791 @kindex --dynamic-linker=@var{file}
1793 @itemx --dynamic-linker=@var{file}
1794 Set the name of the dynamic linker. This is only meaningful when
1795 generating dynamically linked ELF executables. The default dynamic
1796 linker is normally correct; don't use this unless you know what you are
1799 @kindex --no-dynamic-linker
1800 @item --no-dynamic-linker
1801 When producing an executable file, omit the request for a dynamic
1802 linker to be used at load-time. This is only meaningful for ELF
1803 executables that contain dynamic relocations, and usually requires
1804 entry point code that is capable of processing these relocations.
1806 @kindex --embedded-relocs
1807 @item --embedded-relocs
1808 This option is similar to the @option{--emit-relocs} option except
1809 that the relocs are stored in a target-specific section. This option
1810 is only supported by the @samp{BFIN}, @samp{CR16} and @emph{M68K}
1813 @kindex --disable-multiple-abs-defs
1814 @item --disable-multiple-abs-defs
1815 Do not allow multiple definitions with symbols included
1816 in filename invoked by -R or --just-symbols
1818 @kindex --fatal-warnings
1819 @kindex --no-fatal-warnings
1820 @item --fatal-warnings
1821 @itemx --no-fatal-warnings
1822 Treat all warnings as errors. The default behaviour can be restored
1823 with the option @option{--no-fatal-warnings}.
1825 @kindex --force-exe-suffix
1826 @item --force-exe-suffix
1827 Make sure that an output file has a .exe suffix.
1829 If a successfully built fully linked output file does not have a
1830 @code{.exe} or @code{.dll} suffix, this option forces the linker to copy
1831 the output file to one of the same name with a @code{.exe} suffix. This
1832 option is useful when using unmodified Unix makefiles on a Microsoft
1833 Windows host, since some versions of Windows won't run an image unless
1834 it ends in a @code{.exe} suffix.
1836 @kindex --gc-sections
1837 @kindex --no-gc-sections
1838 @cindex garbage collection
1840 @itemx --no-gc-sections
1841 Enable garbage collection of unused input sections. It is ignored on
1842 targets that do not support this option. The default behaviour (of not
1843 performing this garbage collection) can be restored by specifying
1844 @samp{--no-gc-sections} on the command line. Note that garbage
1845 collection for COFF and PE format targets is supported, but the
1846 implementation is currently considered to be experimental.
1848 @samp{--gc-sections} decides which input sections are used by
1849 examining symbols and relocations. The section containing the entry
1850 symbol and all sections containing symbols undefined on the
1851 command-line will be kept, as will sections containing symbols
1852 referenced by dynamic objects. Note that when building shared
1853 libraries, the linker must assume that any visible symbol is
1854 referenced. Once this initial set of sections has been determined,
1855 the linker recursively marks as used any section referenced by their
1856 relocations. See @samp{--entry}, @samp{--undefined}, and
1857 @samp{--gc-keep-exported}.
1859 This option can be set when doing a partial link (enabled with option
1860 @samp{-r}). In this case the root of symbols kept must be explicitly
1861 specified either by one of the options @samp{--entry},
1862 @samp{--undefined}, or @samp{--gc-keep-exported} or by a @code{ENTRY}
1863 command in the linker script.
1865 As a GNU extension, ELF input sections marked with the
1866 @code{SHF_GNU_RETAIN} flag will not be garbage collected.
1868 @kindex --print-gc-sections
1869 @kindex --no-print-gc-sections
1870 @cindex garbage collection
1871 @item --print-gc-sections
1872 @itemx --no-print-gc-sections
1873 List all sections removed by garbage collection. The listing is
1874 printed on stderr. This option is only effective if garbage
1875 collection has been enabled via the @samp{--gc-sections}) option. The
1876 default behaviour (of not listing the sections that are removed) can
1877 be restored by specifying @samp{--no-print-gc-sections} on the command
1880 @kindex --gc-keep-exported
1881 @cindex garbage collection
1882 @item --gc-keep-exported
1883 When @samp{--gc-sections} is enabled, this option prevents garbage
1884 collection of unused input sections that contain global symbols having
1885 default or protected visibility. This option is intended to be used for
1886 executables where unreferenced sections would otherwise be garbage
1887 collected regardless of the external visibility of contained symbols.
1888 Note that this option has no effect when linking shared objects since
1889 it is already the default behaviour. This option is only supported for
1892 @kindex --print-output-format
1893 @cindex output format
1894 @item --print-output-format
1895 Print the name of the default output format (perhaps influenced by
1896 other command-line options). This is the string that would appear
1897 in an @code{OUTPUT_FORMAT} linker script command (@pxref{File Commands}).
1899 @kindex --print-memory-usage
1900 @cindex memory usage
1901 @item --print-memory-usage
1902 Print used size, total size and used size of memory regions created with
1903 the @ref{MEMORY} command. This is useful on embedded targets to have a
1904 quick view of amount of free memory. The format of the output has one
1905 headline and one line per region. It is both human readable and easily
1906 parsable by tools. Here is an example of an output:
1909 Memory region Used Size Region Size %age Used
1910 ROM: 256 KB 1 MB 25.00%
1911 RAM: 32 B 2 GB 0.00%
1918 Print a summary of the command-line options on the standard output and exit.
1920 @kindex --target-help
1922 Print a summary of all target-specific options on the standard output and exit.
1924 @kindex -Map=@var{mapfile}
1925 @item -Map=@var{mapfile}
1926 Print a link map to the file @var{mapfile}. See the description of the
1927 @option{-M} option, above. If @var{mapfile} is just the character
1928 @code{-} then the map will be written to stdout.
1930 Specifying a directory as @var{mapfile} causes the linker map to be
1931 written as a file inside the directory. Normally name of the file
1932 inside the directory is computed as the basename of the @var{output}
1933 file with @code{.map} appended. If however the special character
1934 @code{%} is used then this will be replaced by the full path of the
1935 output file. Additionally if there are any characters after the
1936 @var{%} symbol then @code{.map} will no longer be appended.
1939 -o foo.exe -Map=bar [Creates ./bar]
1940 -o ../dir/foo.exe -Map=bar [Creates ./bar]
1941 -o foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
1942 -o ../dir2/foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
1943 -o foo.exe -Map=% [Creates ./foo.exe.map]
1944 -o ../dir/foo.exe -Map=% [Creates ../dir/foo.exe.map]
1945 -o foo.exe -Map=%.bar [Creates ./foo.exe.bar]
1946 -o ../dir/foo.exe -Map=%.bar [Creates ../dir/foo.exe.bar]
1947 -o ../dir2/foo.exe -Map=../dir/% [Creates ../dir/../dir2/foo.exe.map]
1948 -o ../dir2/foo.exe -Map=../dir/%.bar [Creates ../dir/../dir2/foo.exe.bar]
1951 It is an error to specify more than one @code{%} character.
1953 If the map file already exists then it will be overwritten by this
1956 @cindex memory usage
1957 @kindex --no-keep-memory
1958 @item --no-keep-memory
1959 @command{ld} normally optimizes for speed over memory usage by caching the
1960 symbol tables of input files in memory. This option tells @command{ld} to
1961 instead optimize for memory usage, by rereading the symbol tables as
1962 necessary. This may be required if @command{ld} runs out of memory space
1963 while linking a large executable.
1965 @kindex --no-undefined
1968 @item --no-undefined
1970 Report unresolved symbol references from regular object files. This
1971 is done even if the linker is creating a non-symbolic shared library.
1972 The switch @option{--[no-]allow-shlib-undefined} controls the
1973 behaviour for reporting unresolved references found in shared
1974 libraries being linked in.
1976 The effects of this option can be reverted by using @code{-z undefs}.
1978 @kindex --allow-multiple-definition
1980 @item --allow-multiple-definition
1982 Normally when a symbol is defined multiple times, the linker will
1983 report a fatal error. These options allow multiple definitions and the
1984 first definition will be used.
1986 @kindex --allow-shlib-undefined
1987 @kindex --no-allow-shlib-undefined
1988 @item --allow-shlib-undefined
1989 @itemx --no-allow-shlib-undefined
1990 Allows or disallows undefined symbols in shared libraries.
1991 This switch is similar to @option{--no-undefined} except that it
1992 determines the behaviour when the undefined symbols are in a
1993 shared library rather than a regular object file. It does not affect
1994 how undefined symbols in regular object files are handled.
1996 The default behaviour is to report errors for any undefined symbols
1997 referenced in shared libraries if the linker is being used to create
1998 an executable, but to allow them if the linker is being used to create
2001 The reasons for allowing undefined symbol references in shared
2002 libraries specified at link time are that:
2006 A shared library specified at link time may not be the same as the one
2007 that is available at load time, so the symbol might actually be
2008 resolvable at load time.
2010 There are some operating systems, eg BeOS and HPPA, where undefined
2011 symbols in shared libraries are normal.
2013 The BeOS kernel for example patches shared libraries at load time to
2014 select whichever function is most appropriate for the current
2015 architecture. This is used, for example, to dynamically select an
2016 appropriate memset function.
2019 @kindex --error-handling-script=@var{scriptname}
2020 @item --error-handling-script=@var{scriptname}
2021 If this option is provided then the linker will invoke
2022 @var{scriptname} whenever an error is encountered. Currently however
2023 only two kinds of error are supported: missing symbols and missing
2024 libraries. Two arguments will be passed to script: the keyword
2025 ``undefined-symbol'' or `missing-lib'' and the @var{name} of the
2026 undefined symbol or missing library. The intention is that the script
2027 will provide suggestions to the user as to where the symbol or library
2028 might be found. After the script has finished then the normal linker
2029 error message will be displayed.
2031 The availability of this option is controlled by a configure time
2032 switch, so it may not be present in specific implementations.
2034 @kindex --no-undefined-version
2035 @item --no-undefined-version
2036 Normally when a symbol has an undefined version, the linker will ignore
2037 it. This option disallows symbols with undefined version and a fatal error
2038 will be issued instead.
2040 @kindex --default-symver
2041 @item --default-symver
2042 Create and use a default symbol version (the soname) for unversioned
2045 @kindex --default-imported-symver
2046 @item --default-imported-symver
2047 Create and use a default symbol version (the soname) for unversioned
2050 @kindex --no-warn-mismatch
2051 @item --no-warn-mismatch
2052 Normally @command{ld} will give an error if you try to link together input
2053 files that are mismatched for some reason, perhaps because they have
2054 been compiled for different processors or for different endiannesses.
2055 This option tells @command{ld} that it should silently permit such possible
2056 errors. This option should only be used with care, in cases when you
2057 have taken some special action that ensures that the linker errors are
2060 @kindex --no-warn-search-mismatch
2061 @item --no-warn-search-mismatch
2062 Normally @command{ld} will give a warning if it finds an incompatible
2063 library during a library search. This option silences the warning.
2065 @kindex --no-whole-archive
2066 @item --no-whole-archive
2067 Turn off the effect of the @option{--whole-archive} option for subsequent
2070 @cindex output file after errors
2071 @kindex --noinhibit-exec
2072 @item --noinhibit-exec
2073 Retain the executable output file whenever it is still usable.
2074 Normally, the linker will not produce an output file if it encounters
2075 errors during the link process; it exits without writing an output file
2076 when it issues any error whatsoever.
2080 Only search library directories explicitly specified on the
2081 command line. Library directories specified in linker scripts
2082 (including linker scripts specified on the command line) are ignored.
2084 @ifclear SingleFormat
2085 @kindex --oformat=@var{output-format}
2086 @item --oformat=@var{output-format}
2087 @command{ld} may be configured to support more than one kind of object
2088 file. If your @command{ld} is configured this way, you can use the
2089 @samp{--oformat} option to specify the binary format for the output
2090 object file. Even when @command{ld} is configured to support alternative
2091 object formats, you don't usually need to specify this, as @command{ld}
2092 should be configured to produce as a default output format the most
2093 usual format on each machine. @var{output-format} is a text string, the
2094 name of a particular format supported by the BFD libraries. (You can
2095 list the available binary formats with @samp{objdump -i}.) The script
2096 command @code{OUTPUT_FORMAT} can also specify the output format, but
2097 this option overrides it. @xref{BFD}.
2100 @kindex --out-implib
2101 @item --out-implib @var{file}
2102 Create an import library in @var{file} corresponding to the executable
2103 the linker is generating (eg. a DLL or ELF program). This import
2104 library (which should be called @code{*.dll.a} or @code{*.a} for DLLs)
2105 may be used to link clients against the generated executable; this
2106 behaviour makes it possible to skip a separate import library creation
2107 step (eg. @code{dlltool} for DLLs). This option is only available for
2108 the i386 PE and ELF targetted ports of the linker.
2111 @kindex --pic-executable
2113 @itemx --pic-executable
2114 @cindex position independent executables
2115 Create a position independent executable. This is currently only supported on
2116 ELF platforms. Position independent executables are similar to shared
2117 libraries in that they are relocated by the dynamic linker to the virtual
2118 address the OS chooses for them (which can vary between invocations). Like
2119 normal dynamically linked executables they can be executed and symbols
2120 defined in the executable cannot be overridden by shared libraries.
2124 This option is ignored for Linux compatibility.
2128 This option is ignored for SVR4 compatibility.
2131 @cindex synthesizing linker
2132 @cindex relaxing addressing modes
2136 An option with machine dependent effects.
2138 This option is only supported on a few targets.
2141 @xref{H8/300,,@command{ld} and the H8/300}.
2144 @xref{Xtensa,, @command{ld} and Xtensa Processors}.
2147 @xref{M68HC11/68HC12,,@command{ld} and the 68HC11 and 68HC12}.
2150 @xref{Nios II,,@command{ld} and the Altera Nios II}.
2153 @xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}.
2156 On some platforms the @option{--relax} option performs target specific,
2157 global optimizations that become possible when the linker resolves
2158 addressing in the program, such as relaxing address modes,
2159 synthesizing new instructions, selecting shorter version of current
2160 instructions, and combining constant values.
2162 On some platforms these link time global optimizations may make symbolic
2163 debugging of the resulting executable impossible.
2165 This is known to be the case for the Matsushita MN10200 and MN10300
2166 family of processors.
2169 On platforms where the feature is supported, the option
2170 @option{--no-relax} will disable it.
2172 On platforms where the feature is not supported, both @option{--relax}
2173 and @option{--no-relax} are accepted, but ignored.
2175 @cindex retaining specified symbols
2176 @cindex stripping all but some symbols
2177 @cindex symbols, retaining selectively
2178 @kindex --retain-symbols-file=@var{filename}
2179 @item --retain-symbols-file=@var{filename}
2180 Retain @emph{only} the symbols listed in the file @var{filename},
2181 discarding all others. @var{filename} is simply a flat file, with one
2182 symbol name per line. This option is especially useful in environments
2186 where a large global symbol table is accumulated gradually, to conserve
2189 @samp{--retain-symbols-file} does @emph{not} discard undefined symbols,
2190 or symbols needed for relocations.
2192 You may only specify @samp{--retain-symbols-file} once in the command
2193 line. It overrides @samp{-s} and @samp{-S}.
2196 @item -rpath=@var{dir}
2197 @cindex runtime library search path
2198 @kindex -rpath=@var{dir}
2199 Add a directory to the runtime library search path. This is used when
2200 linking an ELF executable with shared objects. All @option{-rpath}
2201 arguments are concatenated and passed to the runtime linker, which uses
2202 them to locate shared objects at runtime.
2204 The @option{-rpath} option is also used when locating shared objects which
2205 are needed by shared objects explicitly included in the link; see the
2206 description of the @option{-rpath-link} option. Searching @option{-rpath}
2207 in this way is only supported by native linkers and cross linkers which
2208 have been configured with the @option{--with-sysroot} option.
2210 If @option{-rpath} is not used when linking an ELF executable, the
2211 contents of the environment variable @code{LD_RUN_PATH} will be used if it
2214 The @option{-rpath} option may also be used on SunOS. By default, on
2215 SunOS, the linker will form a runtime search path out of all the
2216 @option{-L} options it is given. If a @option{-rpath} option is used, the
2217 runtime search path will be formed exclusively using the @option{-rpath}
2218 options, ignoring the @option{-L} options. This can be useful when using
2219 gcc, which adds many @option{-L} options which may be on NFS mounted
2222 For compatibility with other ELF linkers, if the @option{-R} option is
2223 followed by a directory name, rather than a file name, it is treated as
2224 the @option{-rpath} option.
2228 @cindex link-time runtime library search path
2229 @kindex -rpath-link=@var{dir}
2230 @item -rpath-link=@var{dir}
2231 When using ELF or SunOS, one shared library may require another. This
2232 happens when an @code{ld -shared} link includes a shared library as one
2235 When the linker encounters such a dependency when doing a non-shared,
2236 non-relocatable link, it will automatically try to locate the required
2237 shared library and include it in the link, if it is not included
2238 explicitly. In such a case, the @option{-rpath-link} option
2239 specifies the first set of directories to search. The
2240 @option{-rpath-link} option may specify a sequence of directory names
2241 either by specifying a list of names separated by colons, or by
2242 appearing multiple times.
2244 The tokens @var{$ORIGIN} and @var{$LIB} can appear in these search
2245 directories. They will be replaced by the full path to the directory
2246 containing the program or shared object in the case of @var{$ORIGIN}
2247 and either @samp{lib} - for 32-bit binaries - or @samp{lib64} - for
2248 64-bit binaries - in the case of @var{$LIB}.
2250 The alternative form of these tokens - @var{$@{ORIGIN@}} and
2251 @var{$@{LIB@}} can also be used. The token @var{$PLATFORM} is not
2254 This option should be used with caution as it overrides the search path
2255 that may have been hard compiled into a shared library. In such a case it
2256 is possible to use unintentionally a different search path than the
2257 runtime linker would do.
2259 The linker uses the following search paths to locate required shared
2264 Any directories specified by @option{-rpath-link} options.
2266 Any directories specified by @option{-rpath} options. The difference
2267 between @option{-rpath} and @option{-rpath-link} is that directories
2268 specified by @option{-rpath} options are included in the executable and
2269 used at runtime, whereas the @option{-rpath-link} option is only effective
2270 at link time. Searching @option{-rpath} in this way is only supported
2271 by native linkers and cross linkers which have been configured with
2272 the @option{--with-sysroot} option.
2274 On an ELF system, for native linkers, if the @option{-rpath} and
2275 @option{-rpath-link} options were not used, search the contents of the
2276 environment variable @code{LD_RUN_PATH}.
2278 On SunOS, if the @option{-rpath} option was not used, search any
2279 directories specified using @option{-L} options.
2281 For a native linker, search the contents of the environment
2282 variable @code{LD_LIBRARY_PATH}.
2284 For a native ELF linker, the directories in @code{DT_RUNPATH} or
2285 @code{DT_RPATH} of a shared library are searched for shared
2286 libraries needed by it. The @code{DT_RPATH} entries are ignored if
2287 @code{DT_RUNPATH} entries exist.
2289 The default directories, normally @file{/lib} and @file{/usr/lib}.
2291 For a linker for a Linux system, if the file @file{/etc/ld.so.conf}
2292 exists, the list of directories found in that file. Note: the path
2293 to this file is prefixed with the @code{sysroot} value, if that is
2294 defined, and then any @code{prefix} string if the linker was
2295 configured with the @command{--prefix=<path>} option.
2297 For a native linker on a FreeBSD system, any directories specified by
2298 the @code{_PATH_ELF_HINTS} macro defined in the @file{elf-hints.h}
2301 Any directories specifed by a @code{SEARCH_DIR} command in the
2302 linker script being used.
2305 If the required shared library is not found, the linker will issue a
2306 warning and continue with the link.
2313 @cindex shared libraries
2314 Create a shared library. This is currently only supported on ELF, XCOFF
2315 and SunOS platforms. On SunOS, the linker will automatically create a
2316 shared library if the @option{-e} option is not used and there are
2317 undefined symbols in the link.
2319 @kindex --sort-common
2321 @itemx --sort-common=ascending
2322 @itemx --sort-common=descending
2323 This option tells @command{ld} to sort the common symbols by alignment in
2324 ascending or descending order when it places them in the appropriate output
2325 sections. The symbol alignments considered are sixteen-byte or larger,
2326 eight-byte, four-byte, two-byte, and one-byte. This is to prevent gaps
2327 between symbols due to alignment constraints. If no sorting order is
2328 specified, then descending order is assumed.
2330 @kindex --sort-section=name
2331 @item --sort-section=name
2332 This option will apply @code{SORT_BY_NAME} to all wildcard section
2333 patterns in the linker script.
2335 @kindex --sort-section=alignment
2336 @item --sort-section=alignment
2337 This option will apply @code{SORT_BY_ALIGNMENT} to all wildcard section
2338 patterns in the linker script.
2340 @kindex --spare-dynamic-tags
2341 @item --spare-dynamic-tags=@var{count}
2342 This option specifies the number of empty slots to leave in the
2343 .dynamic section of ELF shared objects. Empty slots may be needed by
2344 post processing tools, such as the prelinker. The default is 5.
2346 @kindex --split-by-file
2347 @item --split-by-file[=@var{size}]
2348 Similar to @option{--split-by-reloc} but creates a new output section for
2349 each input file when @var{size} is reached. @var{size} defaults to a
2350 size of 1 if not given.
2352 @kindex --split-by-reloc
2353 @item --split-by-reloc[=@var{count}]
2354 Tries to creates extra sections in the output file so that no single
2355 output section in the file contains more than @var{count} relocations.
2356 This is useful when generating huge relocatable files for downloading into
2357 certain real time kernels with the COFF object file format; since COFF
2358 cannot represent more than 65535 relocations in a single section. Note
2359 that this will fail to work with object file formats which do not
2360 support arbitrary sections. The linker will not split up individual
2361 input sections for redistribution, so if a single input section contains
2362 more than @var{count} relocations one output section will contain that
2363 many relocations. @var{count} defaults to a value of 32768.
2367 Compute and display statistics about the operation of the linker, such
2368 as execution time and memory usage.
2370 @kindex --sysroot=@var{directory}
2371 @item --sysroot=@var{directory}
2372 Use @var{directory} as the location of the sysroot, overriding the
2373 configure-time default. This option is only supported by linkers
2374 that were configured using @option{--with-sysroot}.
2378 This is used by COFF/PE based targets to create a task-linked object
2379 file where all of the global symbols have been converted to statics.
2381 @kindex --traditional-format
2382 @cindex traditional format
2383 @item --traditional-format
2384 For some targets, the output of @command{ld} is different in some ways from
2385 the output of some existing linker. This switch requests @command{ld} to
2386 use the traditional format instead.
2389 For example, on SunOS, @command{ld} combines duplicate entries in the
2390 symbol string table. This can reduce the size of an output file with
2391 full debugging information by over 30 percent. Unfortunately, the SunOS
2392 @code{dbx} program can not read the resulting program (@code{gdb} has no
2393 trouble). The @samp{--traditional-format} switch tells @command{ld} to not
2394 combine duplicate entries.
2396 @kindex --section-start=@var{sectionname}=@var{org}
2397 @item --section-start=@var{sectionname}=@var{org}
2398 Locate a section in the output file at the absolute
2399 address given by @var{org}. You may use this option as many
2400 times as necessary to locate multiple sections in the command
2402 @var{org} must be a single hexadecimal integer;
2403 for compatibility with other linkers, you may omit the leading
2404 @samp{0x} usually associated with hexadecimal values. @emph{Note:} there
2405 should be no white space between @var{sectionname}, the equals
2406 sign (``@key{=}''), and @var{org}.
2408 @kindex -Tbss=@var{org}
2409 @kindex -Tdata=@var{org}
2410 @kindex -Ttext=@var{org}
2411 @cindex segment origins, cmd line
2412 @item -Tbss=@var{org}
2413 @itemx -Tdata=@var{org}
2414 @itemx -Ttext=@var{org}
2415 Same as @option{--section-start}, with @code{.bss}, @code{.data} or
2416 @code{.text} as the @var{sectionname}.
2418 @kindex -Ttext-segment=@var{org}
2419 @item -Ttext-segment=@var{org}
2420 @cindex text segment origin, cmd line
2421 When creating an ELF executable, it will set the address of the first
2422 byte of the text segment.
2424 @kindex -Trodata-segment=@var{org}
2425 @item -Trodata-segment=@var{org}
2426 @cindex rodata segment origin, cmd line
2427 When creating an ELF executable or shared object for a target where
2428 the read-only data is in its own segment separate from the executable
2429 text, it will set the address of the first byte of the read-only data segment.
2431 @kindex -Tldata-segment=@var{org}
2432 @item -Tldata-segment=@var{org}
2433 @cindex ldata segment origin, cmd line
2434 When creating an ELF executable or shared object for x86-64 medium memory
2435 model, it will set the address of the first byte of the ldata segment.
2437 @kindex --unresolved-symbols
2438 @item --unresolved-symbols=@var{method}
2439 Determine how to handle unresolved symbols. There are four possible
2440 values for @samp{method}:
2444 Do not report any unresolved symbols.
2447 Report all unresolved symbols. This is the default.
2449 @item ignore-in-object-files
2450 Report unresolved symbols that are contained in shared libraries, but
2451 ignore them if they come from regular object files.
2453 @item ignore-in-shared-libs
2454 Report unresolved symbols that come from regular object files, but
2455 ignore them if they come from shared libraries. This can be useful
2456 when creating a dynamic binary and it is known that all the shared
2457 libraries that it should be referencing are included on the linker's
2461 The behaviour for shared libraries on their own can also be controlled
2462 by the @option{--[no-]allow-shlib-undefined} option.
2464 Normally the linker will generate an error message for each reported
2465 unresolved symbol but the option @option{--warn-unresolved-symbols}
2466 can change this to a warning.
2468 @kindex --verbose[=@var{NUMBER}]
2469 @cindex verbose[=@var{NUMBER}]
2471 @itemx --verbose[=@var{NUMBER}]
2472 Display the version number for @command{ld} and list the linker emulations
2473 supported. Display which input files can and cannot be opened. Display
2474 the linker script being used by the linker. If the optional @var{NUMBER}
2475 argument > 1, plugin symbol status will also be displayed.
2477 @kindex --version-script=@var{version-scriptfile}
2478 @cindex version script, symbol versions
2479 @item --version-script=@var{version-scriptfile}
2480 Specify the name of a version script to the linker. This is typically
2481 used when creating shared libraries to specify additional information
2482 about the version hierarchy for the library being created. This option
2483 is only fully supported on ELF platforms which support shared libraries;
2484 see @ref{VERSION}. It is partially supported on PE platforms, which can
2485 use version scripts to filter symbol visibility in auto-export mode: any
2486 symbols marked @samp{local} in the version script will not be exported.
2489 @kindex --warn-common
2490 @cindex warnings, on combining symbols
2491 @cindex combining symbols, warnings on
2493 Warn when a common symbol is combined with another common symbol or with
2494 a symbol definition. Unix linkers allow this somewhat sloppy practice,
2495 but linkers on some other operating systems do not. This option allows
2496 you to find potential problems from combining global symbols.
2497 Unfortunately, some C libraries use this practice, so you may get some
2498 warnings about symbols in the libraries as well as in your programs.
2500 There are three kinds of global symbols, illustrated here by C examples:
2504 A definition, which goes in the initialized data section of the output
2508 An undefined reference, which does not allocate space.
2509 There must be either a definition or a common symbol for the
2513 A common symbol. If there are only (one or more) common symbols for a
2514 variable, it goes in the uninitialized data area of the output file.
2515 The linker merges multiple common symbols for the same variable into a
2516 single symbol. If they are of different sizes, it picks the largest
2517 size. The linker turns a common symbol into a declaration, if there is
2518 a definition of the same variable.
2521 The @samp{--warn-common} option can produce five kinds of warnings.
2522 Each warning consists of a pair of lines: the first describes the symbol
2523 just encountered, and the second describes the previous symbol
2524 encountered with the same name. One or both of the two symbols will be
2529 Turning a common symbol into a reference, because there is already a
2530 definition for the symbol.
2532 @var{file}(@var{section}): warning: common of `@var{symbol}'
2533 overridden by definition
2534 @var{file}(@var{section}): warning: defined here
2538 Turning a common symbol into a reference, because a later definition for
2539 the symbol is encountered. This is the same as the previous case,
2540 except that the symbols are encountered in a different order.
2542 @var{file}(@var{section}): warning: definition of `@var{symbol}'
2544 @var{file}(@var{section}): warning: common is here
2548 Merging a common symbol with a previous same-sized common symbol.
2550 @var{file}(@var{section}): warning: multiple common
2552 @var{file}(@var{section}): warning: previous common is here
2556 Merging a common symbol with a previous larger common symbol.
2558 @var{file}(@var{section}): warning: common of `@var{symbol}'
2559 overridden by larger common
2560 @var{file}(@var{section}): warning: larger common is here
2564 Merging a common symbol with a previous smaller common symbol. This is
2565 the same as the previous case, except that the symbols are
2566 encountered in a different order.
2568 @var{file}(@var{section}): warning: common of `@var{symbol}'
2569 overriding smaller common
2570 @var{file}(@var{section}): warning: smaller common is here
2574 @kindex --warn-constructors
2575 @item --warn-constructors
2576 Warn if any global constructors are used. This is only useful for a few
2577 object file formats. For formats like COFF or ELF, the linker can not
2578 detect the use of global constructors.
2580 @kindex --warn-multiple-gp
2581 @item --warn-multiple-gp
2582 Warn if multiple global pointer values are required in the output file.
2583 This is only meaningful for certain processors, such as the Alpha.
2584 Specifically, some processors put large-valued constants in a special
2585 section. A special register (the global pointer) points into the middle
2586 of this section, so that constants can be loaded efficiently via a
2587 base-register relative addressing mode. Since the offset in
2588 base-register relative mode is fixed and relatively small (e.g., 16
2589 bits), this limits the maximum size of the constant pool. Thus, in
2590 large programs, it is often necessary to use multiple global pointer
2591 values in order to be able to address all possible constants. This
2592 option causes a warning to be issued whenever this case occurs.
2595 @cindex warnings, on undefined symbols
2596 @cindex undefined symbols, warnings on
2598 Only warn once for each undefined symbol, rather than once per module
2601 @kindex --warn-section-align
2602 @cindex warnings, on section alignment
2603 @cindex section alignment, warnings on
2604 @item --warn-section-align
2605 Warn if the address of an output section is changed because of
2606 alignment. Typically, the alignment will be set by an input section.
2607 The address will only be changed if it not explicitly specified; that
2608 is, if the @code{SECTIONS} command does not specify a start address for
2609 the section (@pxref{SECTIONS}).
2611 @kindex --warn-textrel
2612 @item --warn-textrel
2613 Warn if the linker adds DT_TEXTREL to a position-independent executable
2616 @kindex --warn-alternate-em
2617 @item --warn-alternate-em
2618 Warn if an object has alternate ELF machine code.
2620 @kindex --warn-unresolved-symbols
2621 @item --warn-unresolved-symbols
2622 If the linker is going to report an unresolved symbol (see the option
2623 @option{--unresolved-symbols}) it will normally generate an error.
2624 This option makes it generate a warning instead.
2626 @kindex --error-unresolved-symbols
2627 @item --error-unresolved-symbols
2628 This restores the linker's default behaviour of generating errors when
2629 it is reporting unresolved symbols.
2631 @kindex --whole-archive
2632 @cindex including an entire archive
2633 @item --whole-archive
2634 For each archive mentioned on the command line after the
2635 @option{--whole-archive} option, include every object file in the archive
2636 in the link, rather than searching the archive for the required object
2637 files. This is normally used to turn an archive file into a shared
2638 library, forcing every object to be included in the resulting shared
2639 library. This option may be used more than once.
2641 Two notes when using this option from gcc: First, gcc doesn't know
2642 about this option, so you have to use @option{-Wl,-whole-archive}.
2643 Second, don't forget to use @option{-Wl,-no-whole-archive} after your
2644 list of archives, because gcc will add its own list of archives to
2645 your link and you may not want this flag to affect those as well.
2647 @kindex --wrap=@var{symbol}
2648 @item --wrap=@var{symbol}
2649 Use a wrapper function for @var{symbol}. Any undefined reference to
2650 @var{symbol} will be resolved to @code{__wrap_@var{symbol}}. Any
2651 undefined reference to @code{__real_@var{symbol}} will be resolved to
2654 This can be used to provide a wrapper for a system function. The
2655 wrapper function should be called @code{__wrap_@var{symbol}}. If it
2656 wishes to call the system function, it should call
2657 @code{__real_@var{symbol}}.
2659 Here is a trivial example:
2663 __wrap_malloc (size_t c)
2665 printf ("malloc called with %zu\n", c);
2666 return __real_malloc (c);
2670 If you link other code with this file using @option{--wrap malloc}, then
2671 all calls to @code{malloc} will call the function @code{__wrap_malloc}
2672 instead. The call to @code{__real_malloc} in @code{__wrap_malloc} will
2673 call the real @code{malloc} function.
2675 You may wish to provide a @code{__real_malloc} function as well, so that
2676 links without the @option{--wrap} option will succeed. If you do this,
2677 you should not put the definition of @code{__real_malloc} in the same
2678 file as @code{__wrap_malloc}; if you do, the assembler may resolve the
2679 call before the linker has a chance to wrap it to @code{malloc}.
2681 Only undefined references are replaced by the linker. So, translation unit
2682 internal references to @var{symbol} are not resolved to
2683 @code{__wrap_@var{symbol}}. In the next example, the call to @code{f} in
2684 @code{g} is not resolved to @code{__wrap_f}.
2700 @kindex --eh-frame-hdr
2701 @kindex --no-eh-frame-hdr
2702 @item --eh-frame-hdr
2703 @itemx --no-eh-frame-hdr
2704 Request (@option{--eh-frame-hdr}) or suppress
2705 (@option{--no-eh-frame-hdr}) the creation of @code{.eh_frame_hdr}
2706 section and ELF @code{PT_GNU_EH_FRAME} segment header.
2708 @kindex --ld-generated-unwind-info
2709 @item --no-ld-generated-unwind-info
2710 Request creation of @code{.eh_frame} unwind info for linker
2711 generated code sections like PLT. This option is on by default
2712 if linker generated unwind info is supported.
2714 @kindex --enable-new-dtags
2715 @kindex --disable-new-dtags
2716 @item --enable-new-dtags
2717 @itemx --disable-new-dtags
2718 This linker can create the new dynamic tags in ELF. But the older ELF
2719 systems may not understand them. If you specify
2720 @option{--enable-new-dtags}, the new dynamic tags will be created as needed
2721 and older dynamic tags will be omitted.
2722 If you specify @option{--disable-new-dtags}, no new dynamic tags will be
2723 created. By default, the new dynamic tags are not created. Note that
2724 those options are only available for ELF systems.
2726 @kindex --hash-size=@var{number}
2727 @item --hash-size=@var{number}
2728 Set the default size of the linker's hash tables to a prime number
2729 close to @var{number}. Increasing this value can reduce the length of
2730 time it takes the linker to perform its tasks, at the expense of
2731 increasing the linker's memory requirements. Similarly reducing this
2732 value can reduce the memory requirements at the expense of speed.
2734 @kindex --hash-style=@var{style}
2735 @item --hash-style=@var{style}
2736 Set the type of linker's hash table(s). @var{style} can be either
2737 @code{sysv} for classic ELF @code{.hash} section, @code{gnu} for
2738 new style GNU @code{.gnu.hash} section or @code{both} for both
2739 the classic ELF @code{.hash} and new style GNU @code{.gnu.hash}
2740 hash tables. The default depends upon how the linker was configured,
2741 but for most Linux based systems it will be @code{both}.
2743 @kindex --compress-debug-sections=none
2744 @kindex --compress-debug-sections=zlib
2745 @kindex --compress-debug-sections=zlib-gnu
2746 @kindex --compress-debug-sections=zlib-gabi
2747 @item --compress-debug-sections=none
2748 @itemx --compress-debug-sections=zlib
2749 @itemx --compress-debug-sections=zlib-gnu
2750 @itemx --compress-debug-sections=zlib-gabi
2751 On ELF platforms, these options control how DWARF debug sections are
2752 compressed using zlib.
2754 @option{--compress-debug-sections=none} doesn't compress DWARF debug
2755 sections. @option{--compress-debug-sections=zlib-gnu} compresses
2756 DWARF debug sections and renames them to begin with @samp{.zdebug}
2757 instead of @samp{.debug}. @option{--compress-debug-sections=zlib-gabi}
2758 also compresses DWARF debug sections, but rather than renaming them it
2759 sets the SHF_COMPRESSED flag in the sections' headers.
2761 The @option{--compress-debug-sections=zlib} option is an alias for
2762 @option{--compress-debug-sections=zlib-gabi}.
2764 Note that this option overrides any compression in input debug
2765 sections, so if a binary is linked with @option{--compress-debug-sections=none}
2766 for example, then any compressed debug sections in input files will be
2767 uncompressed before they are copied into the output binary.
2769 The default compression behaviour varies depending upon the target
2770 involved and the configure options used to build the toolchain. The
2771 default can be determined by examining the output from the linker's
2772 @option{--help} option.
2774 @kindex --reduce-memory-overheads
2775 @item --reduce-memory-overheads
2776 This option reduces memory requirements at ld runtime, at the expense of
2777 linking speed. This was introduced to select the old O(n^2) algorithm
2778 for link map file generation, rather than the new O(n) algorithm which uses
2779 about 40% more memory for symbol storage.
2781 Another effect of the switch is to set the default hash table size to
2782 1021, which again saves memory at the cost of lengthening the linker's
2783 run time. This is not done however if the @option{--hash-size} switch
2786 The @option{--reduce-memory-overheads} switch may be also be used to
2787 enable other tradeoffs in future versions of the linker.
2790 @kindex --build-id=@var{style}
2792 @itemx --build-id=@var{style}
2793 Request the creation of a @code{.note.gnu.build-id} ELF note section
2794 or a @code{.buildid} COFF section. The contents of the note are
2795 unique bits identifying this linked file. @var{style} can be
2796 @code{uuid} to use 128 random bits, @code{sha1} to use a 160-bit
2797 @sc{SHA1} hash on the normative parts of the output contents,
2798 @code{md5} to use a 128-bit @sc{MD5} hash on the normative parts of
2799 the output contents, or @code{0x@var{hexstring}} to use a chosen bit
2800 string specified as an even number of hexadecimal digits (@code{-} and
2801 @code{:} characters between digit pairs are ignored). If @var{style}
2802 is omitted, @code{sha1} is used.
2804 The @code{md5} and @code{sha1} styles produces an identifier
2805 that is always the same in an identical output file, but will be
2806 unique among all nonidentical output files. It is not intended
2807 to be compared as a checksum for the file's contents. A linked
2808 file may be changed later by other tools, but the build ID bit
2809 string identifying the original linked file does not change.
2811 Passing @code{none} for @var{style} disables the setting from any
2812 @code{--build-id} options earlier on the command line.
2817 @subsection Options Specific to i386 PE Targets
2819 @c man begin OPTIONS
2821 The i386 PE linker supports the @option{-shared} option, which causes
2822 the output to be a dynamically linked library (DLL) instead of a
2823 normal executable. You should name the output @code{*.dll} when you
2824 use this option. In addition, the linker fully supports the standard
2825 @code{*.def} files, which may be specified on the linker command line
2826 like an object file (in fact, it should precede archives it exports
2827 symbols from, to ensure that they get linked in, just like a normal
2830 In addition to the options common to all targets, the i386 PE linker
2831 support additional command-line options that are specific to the i386
2832 PE target. Options that take values may be separated from their
2833 values by either a space or an equals sign.
2837 @kindex --add-stdcall-alias
2838 @item --add-stdcall-alias
2839 If given, symbols with a stdcall suffix (@@@var{nn}) will be exported
2840 as-is and also with the suffix stripped.
2841 [This option is specific to the i386 PE targeted port of the linker]
2844 @item --base-file @var{file}
2845 Use @var{file} as the name of a file in which to save the base
2846 addresses of all the relocations needed for generating DLLs with
2848 [This is an i386 PE specific option]
2852 Create a DLL instead of a regular executable. You may also use
2853 @option{-shared} or specify a @code{LIBRARY} in a given @code{.def}
2855 [This option is specific to the i386 PE targeted port of the linker]
2857 @kindex --enable-long-section-names
2858 @kindex --disable-long-section-names
2859 @item --enable-long-section-names
2860 @itemx --disable-long-section-names
2861 The PE variants of the COFF object format add an extension that permits
2862 the use of section names longer than eight characters, the normal limit
2863 for COFF. By default, these names are only allowed in object files, as
2864 fully-linked executable images do not carry the COFF string table required
2865 to support the longer names. As a GNU extension, it is possible to
2866 allow their use in executable images as well, or to (probably pointlessly!)
2867 disallow it in object files, by using these two options. Executable images
2868 generated with these long section names are slightly non-standard, carrying
2869 as they do a string table, and may generate confusing output when examined
2870 with non-GNU PE-aware tools, such as file viewers and dumpers. However,
2871 GDB relies on the use of PE long section names to find Dwarf-2 debug
2872 information sections in an executable image at runtime, and so if neither
2873 option is specified on the command-line, @command{ld} will enable long
2874 section names, overriding the default and technically correct behaviour,
2875 when it finds the presence of debug information while linking an executable
2876 image and not stripping symbols.
2877 [This option is valid for all PE targeted ports of the linker]
2879 @kindex --enable-stdcall-fixup
2880 @kindex --disable-stdcall-fixup
2881 @item --enable-stdcall-fixup
2882 @itemx --disable-stdcall-fixup
2883 If the link finds a symbol that it cannot resolve, it will attempt to
2884 do ``fuzzy linking'' by looking for another defined symbol that differs
2885 only in the format of the symbol name (cdecl vs stdcall) and will
2886 resolve that symbol by linking to the match. For example, the
2887 undefined symbol @code{_foo} might be linked to the function
2888 @code{_foo@@12}, or the undefined symbol @code{_bar@@16} might be linked
2889 to the function @code{_bar}. When the linker does this, it prints a
2890 warning, since it normally should have failed to link, but sometimes
2891 import libraries generated from third-party dlls may need this feature
2892 to be usable. If you specify @option{--enable-stdcall-fixup}, this
2893 feature is fully enabled and warnings are not printed. If you specify
2894 @option{--disable-stdcall-fixup}, this feature is disabled and such
2895 mismatches are considered to be errors.
2896 [This option is specific to the i386 PE targeted port of the linker]
2898 @kindex --leading-underscore
2899 @kindex --no-leading-underscore
2900 @item --leading-underscore
2901 @itemx --no-leading-underscore
2902 For most targets default symbol-prefix is an underscore and is defined
2903 in target's description. By this option it is possible to
2904 disable/enable the default underscore symbol-prefix.
2906 @cindex DLLs, creating
2907 @kindex --export-all-symbols
2908 @item --export-all-symbols
2909 If given, all global symbols in the objects used to build a DLL will
2910 be exported by the DLL. Note that this is the default if there
2911 otherwise wouldn't be any exported symbols. When symbols are
2912 explicitly exported via DEF files or implicitly exported via function
2913 attributes, the default is to not export anything else unless this
2914 option is given. Note that the symbols @code{DllMain@@12},
2915 @code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and
2916 @code{impure_ptr} will not be automatically
2917 exported. Also, symbols imported from other DLLs will not be
2918 re-exported, nor will symbols specifying the DLL's internal layout
2919 such as those beginning with @code{_head_} or ending with
2920 @code{_iname}. In addition, no symbols from @code{libgcc},
2921 @code{libstd++}, @code{libmingw32}, or @code{crtX.o} will be exported.
2922 Symbols whose names begin with @code{__rtti_} or @code{__builtin_} will
2923 not be exported, to help with C++ DLLs. Finally, there is an
2924 extensive list of cygwin-private symbols that are not exported
2925 (obviously, this applies on when building DLLs for cygwin targets).
2926 These cygwin-excludes are: @code{_cygwin_dll_entry@@12},
2927 @code{_cygwin_crt0_common@@8}, @code{_cygwin_noncygwin_dll_entry@@12},
2928 @code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll},
2929 @code{cygwin_premain0}, @code{cygwin_premain1}, @code{cygwin_premain2},
2930 @code{cygwin_premain3}, and @code{environ}.
2931 [This option is specific to the i386 PE targeted port of the linker]
2933 @kindex --exclude-symbols
2934 @item --exclude-symbols @var{symbol},@var{symbol},...
2935 Specifies a list of symbols which should not be automatically
2936 exported. The symbol names may be delimited by commas or colons.
2937 [This option is specific to the i386 PE targeted port of the linker]
2939 @kindex --exclude-all-symbols
2940 @item --exclude-all-symbols
2941 Specifies no symbols should be automatically exported.
2942 [This option is specific to the i386 PE targeted port of the linker]
2944 @kindex --file-alignment
2945 @item --file-alignment
2946 Specify the file alignment. Sections in the file will always begin at
2947 file offsets which are multiples of this number. This defaults to
2949 [This option is specific to the i386 PE targeted port of the linker]
2953 @item --heap @var{reserve}
2954 @itemx --heap @var{reserve},@var{commit}
2955 Specify the number of bytes of memory to reserve (and optionally commit)
2956 to be used as heap for this program. The default is 1MB reserved, 4K
2958 [This option is specific to the i386 PE targeted port of the linker]
2961 @kindex --image-base
2962 @item --image-base @var{value}
2963 Use @var{value} as the base address of your program or dll. This is
2964 the lowest memory location that will be used when your program or dll
2965 is loaded. To reduce the need to relocate and improve performance of
2966 your dlls, each should have a unique base address and not overlap any
2967 other dlls. The default is 0x400000 for executables, and 0x10000000
2969 [This option is specific to the i386 PE targeted port of the linker]
2973 If given, the stdcall suffixes (@@@var{nn}) will be stripped from
2974 symbols before they are exported.
2975 [This option is specific to the i386 PE targeted port of the linker]
2977 @kindex --large-address-aware
2978 @item --large-address-aware
2979 If given, the appropriate bit in the ``Characteristics'' field of the COFF
2980 header is set to indicate that this executable supports virtual addresses
2981 greater than 2 gigabytes. This should be used in conjunction with the /3GB
2982 or /USERVA=@var{value} megabytes switch in the ``[operating systems]''
2983 section of the BOOT.INI. Otherwise, this bit has no effect.
2984 [This option is specific to PE targeted ports of the linker]
2986 @kindex --disable-large-address-aware
2987 @item --disable-large-address-aware
2988 Reverts the effect of a previous @samp{--large-address-aware} option.
2989 This is useful if @samp{--large-address-aware} is always set by the compiler
2990 driver (e.g. Cygwin gcc) and the executable does not support virtual
2991 addresses greater than 2 gigabytes.
2992 [This option is specific to PE targeted ports of the linker]
2994 @kindex --major-image-version
2995 @item --major-image-version @var{value}
2996 Sets the major number of the ``image version''. Defaults to 1.
2997 [This option is specific to the i386 PE targeted port of the linker]
2999 @kindex --major-os-version
3000 @item --major-os-version @var{value}
3001 Sets the major number of the ``os version''. Defaults to 4.
3002 [This option is specific to the i386 PE targeted port of the linker]
3004 @kindex --major-subsystem-version
3005 @item --major-subsystem-version @var{value}
3006 Sets the major number of the ``subsystem version''. Defaults to 4.
3007 [This option is specific to the i386 PE targeted port of the linker]
3009 @kindex --minor-image-version
3010 @item --minor-image-version @var{value}
3011 Sets the minor number of the ``image version''. Defaults to 0.
3012 [This option is specific to the i386 PE targeted port of the linker]
3014 @kindex --minor-os-version
3015 @item --minor-os-version @var{value}
3016 Sets the minor number of the ``os version''. Defaults to 0.
3017 [This option is specific to the i386 PE targeted port of the linker]
3019 @kindex --minor-subsystem-version
3020 @item --minor-subsystem-version @var{value}
3021 Sets the minor number of the ``subsystem version''. Defaults to 0.
3022 [This option is specific to the i386 PE targeted port of the linker]
3024 @cindex DEF files, creating
3025 @cindex DLLs, creating
3026 @kindex --output-def
3027 @item --output-def @var{file}
3028 The linker will create the file @var{file} which will contain a DEF
3029 file corresponding to the DLL the linker is generating. This DEF file
3030 (which should be called @code{*.def}) may be used to create an import
3031 library with @code{dlltool} or may be used as a reference to
3032 automatically or implicitly exported symbols.
3033 [This option is specific to the i386 PE targeted port of the linker]
3035 @cindex DLLs, creating
3036 @kindex --enable-auto-image-base
3037 @item --enable-auto-image-base
3038 @itemx --enable-auto-image-base=@var{value}
3039 Automatically choose the image base for DLLs, optionally starting with base
3040 @var{value}, unless one is specified using the @code{--image-base} argument.
3041 By using a hash generated from the dllname to create unique image bases
3042 for each DLL, in-memory collisions and relocations which can delay program
3043 execution are avoided.
3044 [This option is specific to the i386 PE targeted port of the linker]
3046 @kindex --disable-auto-image-base
3047 @item --disable-auto-image-base
3048 Do not automatically generate a unique image base. If there is no
3049 user-specified image base (@code{--image-base}) then use the platform
3051 [This option is specific to the i386 PE targeted port of the linker]
3053 @cindex DLLs, linking to
3054 @kindex --dll-search-prefix
3055 @item --dll-search-prefix @var{string}
3056 When linking dynamically to a dll without an import library,
3057 search for @code{<string><basename>.dll} in preference to
3058 @code{lib<basename>.dll}. This behaviour allows easy distinction
3059 between DLLs built for the various "subplatforms": native, cygwin,
3060 uwin, pw, etc. For instance, cygwin DLLs typically use
3061 @code{--dll-search-prefix=cyg}.
3062 [This option is specific to the i386 PE targeted port of the linker]
3064 @kindex --enable-auto-import
3065 @item --enable-auto-import
3066 Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for
3067 DATA imports from DLLs, thus making it possible to bypass the dllimport
3068 mechanism on the user side and to reference unmangled symbol names.
3069 [This option is specific to the i386 PE targeted port of the linker]
3071 The following remarks pertain to the original implementation of the
3072 feature and are obsolete nowadays for Cygwin and MinGW targets.
3074 Note: Use of the 'auto-import' extension will cause the text section
3075 of the image file to be made writable. This does not conform to the
3076 PE-COFF format specification published by Microsoft.
3078 Note - use of the 'auto-import' extension will also cause read only
3079 data which would normally be placed into the .rdata section to be
3080 placed into the .data section instead. This is in order to work
3081 around a problem with consts that is described here:
3082 http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
3084 Using 'auto-import' generally will 'just work' -- but sometimes you may
3087 "variable '<var>' can't be auto-imported. Please read the
3088 documentation for ld's @code{--enable-auto-import} for details."
3090 This message occurs when some (sub)expression accesses an address
3091 ultimately given by the sum of two constants (Win32 import tables only
3092 allow one). Instances where this may occur include accesses to member
3093 fields of struct variables imported from a DLL, as well as using a
3094 constant index into an array variable imported from a DLL. Any
3095 multiword variable (arrays, structs, long long, etc) may trigger
3096 this error condition. However, regardless of the exact data type
3097 of the offending exported variable, ld will always detect it, issue
3098 the warning, and exit.
3100 There are several ways to address this difficulty, regardless of the
3101 data type of the exported variable:
3103 One way is to use --enable-runtime-pseudo-reloc switch. This leaves the task
3104 of adjusting references in your client code for runtime environment, so
3105 this method works only when runtime environment supports this feature.
3107 A second solution is to force one of the 'constants' to be a variable --
3108 that is, unknown and un-optimizable at compile time. For arrays,
3109 there are two possibilities: a) make the indexee (the array's address)
3110 a variable, or b) make the 'constant' index a variable. Thus:
3113 extern type extern_array[];
3115 @{ volatile type *t=extern_array; t[1] @}
3121 extern type extern_array[];
3123 @{ volatile int t=1; extern_array[t] @}
3126 For structs (and most other multiword data types) the only option
3127 is to make the struct itself (or the long long, or the ...) variable:
3130 extern struct s extern_struct;
3131 extern_struct.field -->
3132 @{ volatile struct s *t=&extern_struct; t->field @}
3138 extern long long extern_ll;
3140 @{ volatile long long * local_ll=&extern_ll; *local_ll @}
3143 A third method of dealing with this difficulty is to abandon
3144 'auto-import' for the offending symbol and mark it with
3145 @code{__declspec(dllimport)}. However, in practice that
3146 requires using compile-time #defines to indicate whether you are
3147 building a DLL, building client code that will link to the DLL, or
3148 merely building/linking to a static library. In making the choice
3149 between the various methods of resolving the 'direct address with
3150 constant offset' problem, you should consider typical real-world usage:
3158 void main(int argc, char **argv)@{
3159 printf("%d\n",arr[1]);
3169 void main(int argc, char **argv)@{
3170 /* This workaround is for win32 and cygwin; do not "optimize" */
3171 volatile int *parr = arr;
3172 printf("%d\n",parr[1]);
3179 /* Note: auto-export is assumed (no __declspec(dllexport)) */
3180 #if (defined(_WIN32) || defined(__CYGWIN__)) && \
3181 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
3182 #define FOO_IMPORT __declspec(dllimport)
3186 extern FOO_IMPORT int arr[];
3189 void main(int argc, char **argv)@{
3190 printf("%d\n",arr[1]);
3194 A fourth way to avoid this problem is to re-code your
3195 library to use a functional interface rather than a data interface
3196 for the offending variables (e.g. set_foo() and get_foo() accessor
3199 @kindex --disable-auto-import
3200 @item --disable-auto-import
3201 Do not attempt to do sophisticated linking of @code{_symbol} to
3202 @code{__imp__symbol} for DATA imports from DLLs.
3203 [This option is specific to the i386 PE targeted port of the linker]
3205 @kindex --enable-runtime-pseudo-reloc
3206 @item --enable-runtime-pseudo-reloc
3207 If your code contains expressions described in --enable-auto-import section,
3208 that is, DATA imports from DLL with non-zero offset, this switch will create
3209 a vector of 'runtime pseudo relocations' which can be used by runtime
3210 environment to adjust references to such data in your client code.
3211 [This option is specific to the i386 PE targeted port of the linker]
3213 @kindex --disable-runtime-pseudo-reloc
3214 @item --disable-runtime-pseudo-reloc
3215 Do not create pseudo relocations for non-zero offset DATA imports from DLLs.
3216 [This option is specific to the i386 PE targeted port of the linker]
3218 @kindex --enable-extra-pe-debug
3219 @item --enable-extra-pe-debug
3220 Show additional debug info related to auto-import symbol thunking.
3221 [This option is specific to the i386 PE targeted port of the linker]
3223 @kindex --section-alignment
3224 @item --section-alignment
3225 Sets the section alignment. Sections in memory will always begin at
3226 addresses which are a multiple of this number. Defaults to 0x1000.
3227 [This option is specific to the i386 PE targeted port of the linker]
3231 @item --stack @var{reserve}
3232 @itemx --stack @var{reserve},@var{commit}
3233 Specify the number of bytes of memory to reserve (and optionally commit)
3234 to be used as stack for this program. The default is 2MB reserved, 4K
3236 [This option is specific to the i386 PE targeted port of the linker]
3239 @item --subsystem @var{which}
3240 @itemx --subsystem @var{which}:@var{major}
3241 @itemx --subsystem @var{which}:@var{major}.@var{minor}
3242 Specifies the subsystem under which your program will execute. The
3243 legal values for @var{which} are @code{native}, @code{windows},
3244 @code{console}, @code{posix}, and @code{xbox}. You may optionally set
3245 the subsystem version also. Numeric values are also accepted for
3247 [This option is specific to the i386 PE targeted port of the linker]
3249 The following options set flags in the @code{DllCharacteristics} field
3250 of the PE file header:
3251 [These options are specific to PE targeted ports of the linker]
3253 @kindex --high-entropy-va
3254 @item --high-entropy-va
3255 @itemx --disable-high-entropy-va
3256 Image is compatible with 64-bit address space layout randomization
3257 (ASLR). This option is enabled by default for 64-bit PE images.
3259 This option also implies @option{--dynamicbase} and
3260 @option{--enable-reloc-section}.
3262 @kindex --dynamicbase
3264 @itemx --disable-dynamicbase
3265 The image base address may be relocated using address space layout
3266 randomization (ASLR). This feature was introduced with MS Windows
3267 Vista for i386 PE targets. This option is enabled by default but
3268 can be disabled via the @option{--disable-dynamicbase} option.
3269 This option also implies @option{--enable-reloc-section}.
3271 @kindex --forceinteg
3273 @itemx --disable-forceinteg
3274 Code integrity checks are enforced. This option is disabled by
3279 @item --disable-nxcompat
3280 The image is compatible with the Data Execution Prevention.
3281 This feature was introduced with MS Windows XP SP2 for i386 PE
3282 targets. The option is enabled by default.
3284 @kindex --no-isolation
3285 @item --no-isolation
3286 @itemx --disable-no-isolation
3287 Although the image understands isolation, do not isolate the image.
3288 This option is disabled by default.
3292 @itemx --disable-no-seh
3293 The image does not use SEH. No SE handler may be called from
3294 this image. This option is disabled by default.
3298 @itemx --disable-no-bind
3299 Do not bind this image. This option is disabled by default.
3303 @itemx --disable-wdmdriver
3304 The driver uses the MS Windows Driver Model. This option is disabled
3309 @itemx --disable-tsaware
3310 The image is Terminal Server aware. This option is disabled by
3313 @kindex --insert-timestamp
3314 @item --insert-timestamp
3315 @itemx --no-insert-timestamp
3316 Insert a real timestamp into the image. This is the default behaviour
3317 as it matches legacy code and it means that the image will work with
3318 other, proprietary tools. The problem with this default is that it
3319 will result in slightly different images being produced each time the
3320 same sources are linked. The option @option{--no-insert-timestamp}
3321 can be used to insert a zero value for the timestamp, this ensuring
3322 that binaries produced from identical sources will compare
3325 @kindex --enable-reloc-section
3326 @item --enable-reloc-section
3327 @itemx --disable-reloc-section
3328 Create the base relocation table, which is necessary if the image
3329 is loaded at a different image base than specified in the PE header.
3330 This option is enabled by default.
3336 @subsection Options specific to C6X uClinux targets
3338 @c man begin OPTIONS
3340 The C6X uClinux target uses a binary format called DSBT to support shared
3341 libraries. Each shared library in the system needs to have a unique index;
3342 all executables use an index of 0.
3347 @item --dsbt-size @var{size}
3348 This option sets the number of entries in the DSBT of the current executable
3349 or shared library to @var{size}. The default is to create a table with 64
3352 @kindex --dsbt-index
3353 @item --dsbt-index @var{index}
3354 This option sets the DSBT index of the current executable or shared library
3355 to @var{index}. The default is 0, which is appropriate for generating
3356 executables. If a shared library is generated with a DSBT index of 0, the
3357 @code{R_C6000_DSBT_INDEX} relocs are copied into the output file.
3359 @kindex --no-merge-exidx-entries
3360 The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent
3361 exidx entries in frame unwind info.
3369 @subsection Options specific to C-SKY targets
3371 @c man begin OPTIONS
3375 @kindex --branch-stub on C-SKY
3377 This option enables linker branch relaxation by inserting branch stub
3378 sections when needed to extend the range of branches. This option is
3379 usually not required since C-SKY supports branch and call instructions that
3380 can access the full memory range and branch relaxation is normally handled by
3381 the compiler or assembler.
3383 @kindex --stub-group-size on C-SKY
3384 @item --stub-group-size=@var{N}
3385 This option allows finer control of linker branch stub creation.
3386 It sets the maximum size of a group of input sections that can
3387 be handled by one stub section. A negative value of @var{N} locates
3388 stub sections after their branches, while a positive value allows stub
3389 sections to appear either before or after the branches. Values of
3390 @samp{1} or @samp{-1} indicate that the
3391 linker should choose suitable defaults.
3399 @subsection Options specific to Motorola 68HC11 and 68HC12 targets
3401 @c man begin OPTIONS
3403 The 68HC11 and 68HC12 linkers support specific options to control the
3404 memory bank switching mapping and trampoline code generation.
3408 @kindex --no-trampoline
3409 @item --no-trampoline
3410 This option disables the generation of trampoline. By default a trampoline
3411 is generated for each far function which is called using a @code{jsr}
3412 instruction (this happens when a pointer to a far function is taken).
3414 @kindex --bank-window
3415 @item --bank-window @var{name}
3416 This option indicates to the linker the name of the memory region in
3417 the @samp{MEMORY} specification that describes the memory bank window.
3418 The definition of such region is then used by the linker to compute
3419 paging and addresses within the memory window.
3427 @subsection Options specific to Motorola 68K target
3429 @c man begin OPTIONS
3431 The following options are supported to control handling of GOT generation
3432 when linking for 68K targets.
3437 @item --got=@var{type}
3438 This option tells the linker which GOT generation scheme to use.
3439 @var{type} should be one of @samp{single}, @samp{negative},
3440 @samp{multigot} or @samp{target}. For more information refer to the
3441 Info entry for @file{ld}.
3449 @subsection Options specific to MIPS targets
3451 @c man begin OPTIONS
3453 The following options are supported to control microMIPS instruction
3454 generation and branch relocation checks for ISA mode transitions when
3455 linking for MIPS targets.
3463 These options control the choice of microMIPS instructions used in code
3464 generated by the linker, such as that in the PLT or lazy binding stubs,
3465 or in relaxation. If @samp{--insn32} is used, then the linker only uses
3466 32-bit instruction encodings. By default or if @samp{--no-insn32} is
3467 used, all instruction encodings are used, including 16-bit ones where
3470 @kindex --ignore-branch-isa
3471 @item --ignore-branch-isa
3472 @kindex --no-ignore-branch-isa
3473 @itemx --no-ignore-branch-isa
3474 These options control branch relocation checks for invalid ISA mode
3475 transitions. If @samp{--ignore-branch-isa} is used, then the linker
3476 accepts any branch relocations and any ISA mode transition required
3477 is lost in relocation calculation, except for some cases of @code{BAL}
3478 instructions which meet relaxation conditions and are converted to
3479 equivalent @code{JALX} instructions as the associated relocation is
3480 calculated. By default or if @samp{--no-ignore-branch-isa} is used
3481 a check is made causing the loss of an ISA mode transition to produce
3484 @kindex --compact-branches
3485 @item --compact-branches
3486 @kindex --no-compact-branches
3487 @itemx --no-compact-branches
3488 These options control the generation of compact instructions by the linker
3489 in the PLT entries for MIPS R6.
3498 @subsection Options specific to PDP11 targets
3500 @c man begin OPTIONS
3502 For the pdp11-aout target, three variants of the output format can be
3503 produced as selected by the following options. The default variant
3504 for pdp11-aout is the @samp{--omagic} option, whereas for other
3505 targets @samp{--nmagic} is the default. The @samp{--imagic} option is
3506 defined only for the pdp11-aout target, while the others are described
3507 here as they apply to the pdp11-aout target.
3516 Mark the output as @code{OMAGIC} (0407) in the @file{a.out} header to
3517 indicate that the text segment is not to be write-protected and
3518 shared. Since the text and data sections are both readable and
3519 writable, the data section is allocated immediately contiguous after
3520 the text segment. This is the oldest format for PDP11 executable
3521 programs and is the default for @command{ld} on PDP11 Unix systems
3522 from the beginning through 2.11BSD.
3529 Mark the output as @code{NMAGIC} (0410) in the @file{a.out} header to
3530 indicate that when the output file is executed, the text portion will
3531 be read-only and shareable among all processes executing the same
3532 file. This involves moving the data areas up to the first possible 8K
3533 byte page boundary following the end of the text. This option creates
3534 a @emph{pure executable} format.
3541 Mark the output as @code{IMAGIC} (0411) in the @file{a.out} header to
3542 indicate that when the output file is executed, the program text and
3543 data areas will be loaded into separate address spaces using the split
3544 instruction and data space feature of the memory management unit in
3545 larger models of the PDP11. This doubles the address space available
3546 to the program. The text segment is again pure, write-protected, and
3547 shareable. The only difference in the output format between this
3548 option and the others, besides the magic number, is that both the text
3549 and data sections start at location 0. The @samp{-z} option selected
3550 this format in 2.11BSD. This option creates a @emph{separate
3556 Equivalent to @samp{--nmagic} for pdp11-aout.
3565 @section Environment Variables
3567 @c man begin ENVIRONMENT
3569 You can change the behaviour of @command{ld} with the environment variables
3570 @ifclear SingleFormat
3573 @code{LDEMULATION} and @code{COLLECT_NO_DEMANGLE}.
3575 @ifclear SingleFormat
3577 @cindex default input format
3578 @code{GNUTARGET} determines the input-file object format if you don't
3579 use @samp{-b} (or its synonym @samp{--format}). Its value should be one
3580 of the BFD names for an input format (@pxref{BFD}). If there is no
3581 @code{GNUTARGET} in the environment, @command{ld} uses the natural format
3582 of the target. If @code{GNUTARGET} is set to @code{default} then BFD
3583 attempts to discover the input format by examining binary input files;
3584 this method often succeeds, but there are potential ambiguities, since
3585 there is no method of ensuring that the magic number used to specify
3586 object-file formats is unique. However, the configuration procedure for
3587 BFD on each system places the conventional format for that system first
3588 in the search-list, so ambiguities are resolved in favor of convention.
3592 @cindex default emulation
3593 @cindex emulation, default
3594 @code{LDEMULATION} determines the default emulation if you don't use the
3595 @samp{-m} option. The emulation can affect various aspects of linker
3596 behaviour, particularly the default linker script. You can list the
3597 available emulations with the @samp{--verbose} or @samp{-V} options. If
3598 the @samp{-m} option is not used, and the @code{LDEMULATION} environment
3599 variable is not defined, the default emulation depends upon how the
3600 linker was configured.
3602 @kindex COLLECT_NO_DEMANGLE
3603 @cindex demangling, default
3604 Normally, the linker will default to demangling symbols. However, if
3605 @code{COLLECT_NO_DEMANGLE} is set in the environment, then it will
3606 default to not demangling symbols. This environment variable is used in
3607 a similar fashion by the @code{gcc} linker wrapper program. The default
3608 may be overridden by the @samp{--demangle} and @samp{--no-demangle}
3615 @chapter Linker Scripts
3618 @cindex linker scripts
3619 @cindex command files
3620 Every link is controlled by a @dfn{linker script}. This script is
3621 written in the linker command language.
3623 The main purpose of the linker script is to describe how the sections in
3624 the input files should be mapped into the output file, and to control
3625 the memory layout of the output file. Most linker scripts do nothing
3626 more than this. However, when necessary, the linker script can also
3627 direct the linker to perform many other operations, using the commands
3630 The linker always uses a linker script. If you do not supply one
3631 yourself, the linker will use a default script that is compiled into the
3632 linker executable. You can use the @samp{--verbose} command-line option
3633 to display the default linker script. Certain command-line options,
3634 such as @samp{-r} or @samp{-N}, will affect the default linker script.
3636 You may supply your own linker script by using the @samp{-T} command
3637 line option. When you do this, your linker script will replace the
3638 default linker script.
3640 You may also use linker scripts implicitly by naming them as input files
3641 to the linker, as though they were files to be linked. @xref{Implicit
3645 * Basic Script Concepts:: Basic Linker Script Concepts
3646 * Script Format:: Linker Script Format
3647 * Simple Example:: Simple Linker Script Example
3648 * Simple Commands:: Simple Linker Script Commands
3649 * Assignments:: Assigning Values to Symbols
3650 * SECTIONS:: SECTIONS Command
3651 * MEMORY:: MEMORY Command
3652 * PHDRS:: PHDRS Command
3653 * VERSION:: VERSION Command
3654 * Expressions:: Expressions in Linker Scripts
3655 * Implicit Linker Scripts:: Implicit Linker Scripts
3658 @node Basic Script Concepts
3659 @section Basic Linker Script Concepts
3660 @cindex linker script concepts
3661 We need to define some basic concepts and vocabulary in order to
3662 describe the linker script language.
3664 The linker combines input files into a single output file. The output
3665 file and each input file are in a special data format known as an
3666 @dfn{object file format}. Each file is called an @dfn{object file}.
3667 The output file is often called an @dfn{executable}, but for our
3668 purposes we will also call it an object file. Each object file has,
3669 among other things, a list of @dfn{sections}. We sometimes refer to a
3670 section in an input file as an @dfn{input section}; similarly, a section
3671 in the output file is an @dfn{output section}.
3673 Each section in an object file has a name and a size. Most sections
3674 also have an associated block of data, known as the @dfn{section
3675 contents}. A section may be marked as @dfn{loadable}, which means that
3676 the contents should be loaded into memory when the output file is run.
3677 A section with no contents may be @dfn{allocatable}, which means that an
3678 area in memory should be set aside, but nothing in particular should be
3679 loaded there (in some cases this memory must be zeroed out). A section
3680 which is neither loadable nor allocatable typically contains some sort
3681 of debugging information.
3683 Every loadable or allocatable output section has two addresses. The
3684 first is the @dfn{VMA}, or virtual memory address. This is the address
3685 the section will have when the output file is run. The second is the
3686 @dfn{LMA}, or load memory address. This is the address at which the
3687 section will be loaded. In most cases the two addresses will be the
3688 same. An example of when they might be different is when a data section
3689 is loaded into ROM, and then copied into RAM when the program starts up
3690 (this technique is often used to initialize global variables in a ROM
3691 based system). In this case the ROM address would be the LMA, and the
3692 RAM address would be the VMA.
3694 You can see the sections in an object file by using the @code{objdump}
3695 program with the @samp{-h} option.
3697 Every object file also has a list of @dfn{symbols}, known as the
3698 @dfn{symbol table}. A symbol may be defined or undefined. Each symbol
3699 has a name, and each defined symbol has an address, among other
3700 information. If you compile a C or C++ program into an object file, you
3701 will get a defined symbol for every defined function and global or
3702 static variable. Every undefined function or global variable which is
3703 referenced in the input file will become an undefined symbol.
3705 You can see the symbols in an object file by using the @code{nm}
3706 program, or by using the @code{objdump} program with the @samp{-t}
3710 @section Linker Script Format
3711 @cindex linker script format
3712 Linker scripts are text files.
3714 You write a linker script as a series of commands. Each command is
3715 either a keyword, possibly followed by arguments, or an assignment to a
3716 symbol. You may separate commands using semicolons. Whitespace is
3719 Strings such as file or format names can normally be entered directly.
3720 If the file name contains a character such as a comma which would
3721 otherwise serve to separate file names, you may put the file name in
3722 double quotes. There is no way to use a double quote character in a
3725 You may include comments in linker scripts just as in C, delimited by
3726 @samp{/*} and @samp{*/}. As in C, comments are syntactically equivalent
3729 @node Simple Example
3730 @section Simple Linker Script Example
3731 @cindex linker script example
3732 @cindex example of linker script
3733 Many linker scripts are fairly simple.
3735 The simplest possible linker script has just one command:
3736 @samp{SECTIONS}. You use the @samp{SECTIONS} command to describe the
3737 memory layout of the output file.
3739 The @samp{SECTIONS} command is a powerful command. Here we will
3740 describe a simple use of it. Let's assume your program consists only of
3741 code, initialized data, and uninitialized data. These will be in the
3742 @samp{.text}, @samp{.data}, and @samp{.bss} sections, respectively.
3743 Let's assume further that these are the only sections which appear in
3746 For this example, let's say that the code should be loaded at address
3747 0x10000, and that the data should start at address 0x8000000. Here is a
3748 linker script which will do that:
3753 .text : @{ *(.text) @}
3755 .data : @{ *(.data) @}
3756 .bss : @{ *(.bss) @}
3760 You write the @samp{SECTIONS} command as the keyword @samp{SECTIONS},
3761 followed by a series of symbol assignments and output section
3762 descriptions enclosed in curly braces.
3764 The first line inside the @samp{SECTIONS} command of the above example
3765 sets the value of the special symbol @samp{.}, which is the location
3766 counter. If you do not specify the address of an output section in some
3767 other way (other ways are described later), the address is set from the
3768 current value of the location counter. The location counter is then
3769 incremented by the size of the output section. At the start of the
3770 @samp{SECTIONS} command, the location counter has the value @samp{0}.
3772 The second line defines an output section, @samp{.text}. The colon is
3773 required syntax which may be ignored for now. Within the curly braces
3774 after the output section name, you list the names of the input sections
3775 which should be placed into this output section. The @samp{*} is a
3776 wildcard which matches any file name. The expression @samp{*(.text)}
3777 means all @samp{.text} input sections in all input files.
3779 Since the location counter is @samp{0x10000} when the output section
3780 @samp{.text} is defined, the linker will set the address of the
3781 @samp{.text} section in the output file to be @samp{0x10000}.
3783 The remaining lines define the @samp{.data} and @samp{.bss} sections in
3784 the output file. The linker will place the @samp{.data} output section
3785 at address @samp{0x8000000}. After the linker places the @samp{.data}
3786 output section, the value of the location counter will be
3787 @samp{0x8000000} plus the size of the @samp{.data} output section. The
3788 effect is that the linker will place the @samp{.bss} output section
3789 immediately after the @samp{.data} output section in memory.
3791 The linker will ensure that each output section has the required
3792 alignment, by increasing the location counter if necessary. In this
3793 example, the specified addresses for the @samp{.text} and @samp{.data}
3794 sections will probably satisfy any alignment constraints, but the linker
3795 may have to create a small gap between the @samp{.data} and @samp{.bss}
3798 That's it! That's a simple and complete linker script.
3800 @node Simple Commands
3801 @section Simple Linker Script Commands
3802 @cindex linker script simple commands
3803 In this section we describe the simple linker script commands.
3806 * Entry Point:: Setting the entry point
3807 * File Commands:: Commands dealing with files
3808 @ifclear SingleFormat
3809 * Format Commands:: Commands dealing with object file formats
3812 * REGION_ALIAS:: Assign alias names to memory regions
3813 * Miscellaneous Commands:: Other linker script commands
3817 @subsection Setting the Entry Point
3818 @kindex ENTRY(@var{symbol})
3819 @cindex start of execution
3820 @cindex first instruction
3822 The first instruction to execute in a program is called the @dfn{entry
3823 point}. You can use the @code{ENTRY} linker script command to set the
3824 entry point. The argument is a symbol name:
3829 There are several ways to set the entry point. The linker will set the
3830 entry point by trying each of the following methods in order, and
3831 stopping when one of them succeeds:
3834 the @samp{-e} @var{entry} command-line option;
3836 the @code{ENTRY(@var{symbol})} command in a linker script;
3838 the value of a target-specific symbol, if it is defined; For many
3839 targets this is @code{start}, but PE- and BeOS-based systems for example
3840 check a list of possible entry symbols, matching the first one found.
3842 the address of the first byte of the @samp{.text} section, if present;
3844 The address @code{0}.
3848 @subsection Commands Dealing with Files
3849 @cindex linker script file commands
3850 Several linker script commands deal with files.
3853 @item INCLUDE @var{filename}
3854 @kindex INCLUDE @var{filename}
3855 @cindex including a linker script
3856 Include the linker script @var{filename} at this point. The file will
3857 be searched for in the current directory, and in any directory specified
3858 with the @option{-L} option. You can nest calls to @code{INCLUDE} up to
3861 You can place @code{INCLUDE} directives at the top level, in @code{MEMORY} or
3862 @code{SECTIONS} commands, or in output section descriptions.
3864 @item INPUT(@var{file}, @var{file}, @dots{})
3865 @itemx INPUT(@var{file} @var{file} @dots{})
3866 @kindex INPUT(@var{files})
3867 @cindex input files in linker scripts
3868 @cindex input object files in linker scripts
3869 @cindex linker script input object files
3870 The @code{INPUT} command directs the linker to include the named files
3871 in the link, as though they were named on the command line.
3873 For example, if you always want to include @file{subr.o} any time you do
3874 a link, but you can't be bothered to put it on every link command line,
3875 then you can put @samp{INPUT (subr.o)} in your linker script.
3877 In fact, if you like, you can list all of your input files in the linker
3878 script, and then invoke the linker with nothing but a @samp{-T} option.
3880 In case a @dfn{sysroot prefix} is configured, and the filename starts
3881 with the @samp{/} character, and the script being processed was
3882 located inside the @dfn{sysroot prefix}, the filename will be looked
3883 for in the @dfn{sysroot prefix}. The @dfn{sysroot prefix} can also be forced by specifying
3884 @code{=} as the first character in the filename path, or prefixing the
3885 filename path with @code{$SYSROOT}. See also the description of
3886 @samp{-L} in @ref{Options,,Command-line Options}.
3888 If a @dfn{sysroot prefix} is not used then the linker will try to open
3889 the file in the directory containing the linker script. If it is not
3890 found the linker will then search the current directory. If it is still
3891 not found the linker will search through the archive library search
3894 If you use @samp{INPUT (-l@var{file})}, @command{ld} will transform the
3895 name to @code{lib@var{file}.a}, as with the command-line argument
3898 When you use the @code{INPUT} command in an implicit linker script, the
3899 files will be included in the link at the point at which the linker
3900 script file is included. This can affect archive searching.
3902 @item GROUP(@var{file}, @var{file}, @dots{})
3903 @itemx GROUP(@var{file} @var{file} @dots{})
3904 @kindex GROUP(@var{files})
3905 @cindex grouping input files
3906 The @code{GROUP} command is like @code{INPUT}, except that the named
3907 files should all be archives, and they are searched repeatedly until no
3908 new undefined references are created. See the description of @samp{-(}
3909 in @ref{Options,,Command-line Options}.
3911 @item AS_NEEDED(@var{file}, @var{file}, @dots{})
3912 @itemx AS_NEEDED(@var{file} @var{file} @dots{})
3913 @kindex AS_NEEDED(@var{files})
3914 This construct can appear only inside of the @code{INPUT} or @code{GROUP}
3915 commands, among other filenames. The files listed will be handled
3916 as if they appear directly in the @code{INPUT} or @code{GROUP} commands,
3917 with the exception of ELF shared libraries, that will be added only
3918 when they are actually needed. This construct essentially enables
3919 @option{--as-needed} option for all the files listed inside of it
3920 and restores previous @option{--as-needed} resp. @option{--no-as-needed}
3923 @item OUTPUT(@var{filename})
3924 @kindex OUTPUT(@var{filename})
3925 @cindex output file name in linker script
3926 The @code{OUTPUT} command names the output file. Using
3927 @code{OUTPUT(@var{filename})} in the linker script is exactly like using
3928 @samp{-o @var{filename}} on the command line (@pxref{Options,,Command
3929 Line Options}). If both are used, the command-line option takes
3932 You can use the @code{OUTPUT} command to define a default name for the
3933 output file other than the usual default of @file{a.out}.
3935 @item SEARCH_DIR(@var{path})
3936 @kindex SEARCH_DIR(@var{path})
3937 @cindex library search path in linker script
3938 @cindex archive search path in linker script
3939 @cindex search path in linker script
3940 The @code{SEARCH_DIR} command adds @var{path} to the list of paths where
3941 @command{ld} looks for archive libraries. Using
3942 @code{SEARCH_DIR(@var{path})} is exactly like using @samp{-L @var{path}}
3943 on the command line (@pxref{Options,,Command-line Options}). If both
3944 are used, then the linker will search both paths. Paths specified using
3945 the command-line option are searched first.
3947 @item STARTUP(@var{filename})
3948 @kindex STARTUP(@var{filename})
3949 @cindex first input file
3950 The @code{STARTUP} command is just like the @code{INPUT} command, except
3951 that @var{filename} will become the first input file to be linked, as
3952 though it were specified first on the command line. This may be useful
3953 when using a system in which the entry point is always the start of the
3957 @ifclear SingleFormat
3958 @node Format Commands
3959 @subsection Commands Dealing with Object File Formats
3960 A couple of linker script commands deal with object file formats.
3963 @item OUTPUT_FORMAT(@var{bfdname})
3964 @itemx OUTPUT_FORMAT(@var{default}, @var{big}, @var{little})
3965 @kindex OUTPUT_FORMAT(@var{bfdname})
3966 @cindex output file format in linker script
3967 The @code{OUTPUT_FORMAT} command names the BFD format to use for the
3968 output file (@pxref{BFD}). Using @code{OUTPUT_FORMAT(@var{bfdname})} is
3969 exactly like using @samp{--oformat @var{bfdname}} on the command line
3970 (@pxref{Options,,Command-line Options}). If both are used, the command
3971 line option takes precedence.
3973 You can use @code{OUTPUT_FORMAT} with three arguments to use different
3974 formats based on the @samp{-EB} and @samp{-EL} command-line options.
3975 This permits the linker script to set the output format based on the
3978 If neither @samp{-EB} nor @samp{-EL} are used, then the output format
3979 will be the first argument, @var{default}. If @samp{-EB} is used, the
3980 output format will be the second argument, @var{big}. If @samp{-EL} is
3981 used, the output format will be the third argument, @var{little}.
3983 For example, the default linker script for the MIPS ELF target uses this
3986 OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips)
3988 This says that the default format for the output file is
3989 @samp{elf32-bigmips}, but if the user uses the @samp{-EL} command-line
3990 option, the output file will be created in the @samp{elf32-littlemips}
3993 @item TARGET(@var{bfdname})
3994 @kindex TARGET(@var{bfdname})
3995 @cindex input file format in linker script
3996 The @code{TARGET} command names the BFD format to use when reading input
3997 files. It affects subsequent @code{INPUT} and @code{GROUP} commands.
3998 This command is like using @samp{-b @var{bfdname}} on the command line
3999 (@pxref{Options,,Command-line Options}). If the @code{TARGET} command
4000 is used but @code{OUTPUT_FORMAT} is not, then the last @code{TARGET}
4001 command is also used to set the format for the output file. @xref{BFD}.
4006 @subsection Assign alias names to memory regions
4007 @kindex REGION_ALIAS(@var{alias}, @var{region})
4008 @cindex region alias
4009 @cindex region names
4011 Alias names can be added to existing memory regions created with the
4012 @ref{MEMORY} command. Each name corresponds to at most one memory region.
4015 REGION_ALIAS(@var{alias}, @var{region})
4018 The @code{REGION_ALIAS} function creates an alias name @var{alias} for the
4019 memory region @var{region}. This allows a flexible mapping of output sections
4020 to memory regions. An example follows.
4022 Suppose we have an application for embedded systems which come with various
4023 memory storage devices. All have a general purpose, volatile memory @code{RAM}
4024 that allows code execution or data storage. Some may have a read-only,
4025 non-volatile memory @code{ROM} that allows code execution and read-only data
4026 access. The last variant is a read-only, non-volatile memory @code{ROM2} with
4027 read-only data access and no code execution capability. We have four output
4032 @code{.text} program code;
4034 @code{.rodata} read-only data;
4036 @code{.data} read-write initialized data;
4038 @code{.bss} read-write zero initialized data.
4041 The goal is to provide a linker command file that contains a system independent
4042 part defining the output sections and a system dependent part mapping the
4043 output sections to the memory regions available on the system. Our embedded
4044 systems come with three different memory setups @code{A}, @code{B} and
4046 @multitable @columnfractions .25 .25 .25 .25
4047 @item Section @tab Variant A @tab Variant B @tab Variant C
4048 @item .text @tab RAM @tab ROM @tab ROM
4049 @item .rodata @tab RAM @tab ROM @tab ROM2
4050 @item .data @tab RAM @tab RAM/ROM @tab RAM/ROM2
4051 @item .bss @tab RAM @tab RAM @tab RAM
4053 The notation @code{RAM/ROM} or @code{RAM/ROM2} means that this section is
4054 loaded into region @code{ROM} or @code{ROM2} respectively. Please note that
4055 the load address of the @code{.data} section starts in all three variants at
4056 the end of the @code{.rodata} section.
4058 The base linker script that deals with the output sections follows. It
4059 includes the system dependent @code{linkcmds.memory} file that describes the
4062 INCLUDE linkcmds.memory
4075 .data : AT (rodata_end)
4080 data_size = SIZEOF(.data);
4081 data_load_start = LOADADDR(.data);
4089 Now we need three different @code{linkcmds.memory} files to define memory
4090 regions and alias names. The content of @code{linkcmds.memory} for the three
4091 variants @code{A}, @code{B} and @code{C}:
4094 Here everything goes into the @code{RAM}.
4098 RAM : ORIGIN = 0, LENGTH = 4M
4101 REGION_ALIAS("REGION_TEXT", RAM);
4102 REGION_ALIAS("REGION_RODATA", RAM);
4103 REGION_ALIAS("REGION_DATA", RAM);
4104 REGION_ALIAS("REGION_BSS", RAM);
4107 Program code and read-only data go into the @code{ROM}. Read-write data goes
4108 into the @code{RAM}. An image of the initialized data is loaded into the
4109 @code{ROM} and will be copied during system start into the @code{RAM}.
4113 ROM : ORIGIN = 0, LENGTH = 3M
4114 RAM : ORIGIN = 0x10000000, LENGTH = 1M
4117 REGION_ALIAS("REGION_TEXT", ROM);
4118 REGION_ALIAS("REGION_RODATA", ROM);
4119 REGION_ALIAS("REGION_DATA", RAM);
4120 REGION_ALIAS("REGION_BSS", RAM);
4123 Program code goes into the @code{ROM}. Read-only data goes into the
4124 @code{ROM2}. Read-write data goes into the @code{RAM}. An image of the
4125 initialized data is loaded into the @code{ROM2} and will be copied during
4126 system start into the @code{RAM}.
4130 ROM : ORIGIN = 0, LENGTH = 2M
4131 ROM2 : ORIGIN = 0x10000000, LENGTH = 1M
4132 RAM : ORIGIN = 0x20000000, LENGTH = 1M
4135 REGION_ALIAS("REGION_TEXT", ROM);
4136 REGION_ALIAS("REGION_RODATA", ROM2);
4137 REGION_ALIAS("REGION_DATA", RAM);
4138 REGION_ALIAS("REGION_BSS", RAM);
4142 It is possible to write a common system initialization routine to copy the
4143 @code{.data} section from @code{ROM} or @code{ROM2} into the @code{RAM} if
4148 extern char data_start [];
4149 extern char data_size [];
4150 extern char data_load_start [];
4152 void copy_data(void)
4154 if (data_start != data_load_start)
4156 memcpy(data_start, data_load_start, (size_t) data_size);
4161 @node Miscellaneous Commands
4162 @subsection Other Linker Script Commands
4163 There are a few other linker scripts commands.
4166 @item ASSERT(@var{exp}, @var{message})
4168 @cindex assertion in linker script
4169 Ensure that @var{exp} is non-zero. If it is zero, then exit the linker
4170 with an error code, and print @var{message}.
4172 Note that assertions are checked before the final stages of linking
4173 take place. This means that expressions involving symbols PROVIDEd
4174 inside section definitions will fail if the user has not set values
4175 for those symbols. The only exception to this rule is PROVIDEd
4176 symbols that just reference dot. Thus an assertion like this:
4181 PROVIDE (__stack = .);
4182 PROVIDE (__stack_size = 0x100);
4183 ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack");
4187 will fail if @code{__stack_size} is not defined elsewhere. Symbols
4188 PROVIDEd outside of section definitions are evaluated earlier, so they
4189 can be used inside ASSERTions. Thus:
4192 PROVIDE (__stack_size = 0x100);
4195 PROVIDE (__stack = .);
4196 ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack");
4202 @item EXTERN(@var{symbol} @var{symbol} @dots{})
4204 @cindex undefined symbol in linker script
4205 Force @var{symbol} to be entered in the output file as an undefined
4206 symbol. Doing this may, for example, trigger linking of additional
4207 modules from standard libraries. You may list several @var{symbol}s for
4208 each @code{EXTERN}, and you may use @code{EXTERN} multiple times. This
4209 command has the same effect as the @samp{-u} command-line option.
4211 @item FORCE_COMMON_ALLOCATION
4212 @kindex FORCE_COMMON_ALLOCATION
4213 @cindex common allocation in linker script
4214 This command has the same effect as the @samp{-d} command-line option:
4215 to make @command{ld} assign space to common symbols even if a relocatable
4216 output file is specified (@samp{-r}).
4218 @item INHIBIT_COMMON_ALLOCATION
4219 @kindex INHIBIT_COMMON_ALLOCATION
4220 @cindex common allocation in linker script
4221 This command has the same effect as the @samp{--no-define-common}
4222 command-line option: to make @code{ld} omit the assignment of addresses
4223 to common symbols even for a non-relocatable output file.
4225 @item FORCE_GROUP_ALLOCATION
4226 @kindex FORCE_GROUP_ALLOCATION
4227 @cindex group allocation in linker script
4228 @cindex section groups
4230 This command has the same effect as the
4231 @samp{--force-group-allocation} command-line option: to make
4232 @command{ld} place section group members like normal input sections,
4233 and to delete the section groups even if a relocatable output file is
4234 specified (@samp{-r}).
4236 @item INSERT [ AFTER | BEFORE ] @var{output_section}
4238 @cindex insert user script into default script
4239 This command is typically used in a script specified by @samp{-T} to
4240 augment the default @code{SECTIONS} with, for example, overlays. It
4241 inserts all prior linker script statements after (or before)
4242 @var{output_section}, and also causes @samp{-T} to not override the
4243 default linker script. The exact insertion point is as for orphan
4244 sections. @xref{Location Counter}. The insertion happens after the
4245 linker has mapped input sections to output sections. Prior to the
4246 insertion, since @samp{-T} scripts are parsed before the default
4247 linker script, statements in the @samp{-T} script occur before the
4248 default linker script statements in the internal linker representation
4249 of the script. In particular, input section assignments will be made
4250 to @samp{-T} output sections before those in the default script. Here
4251 is an example of how a @samp{-T} script using @code{INSERT} might look:
4258 .ov1 @{ ov1*(.text) @}
4259 .ov2 @{ ov2*(.text) @}
4265 @item NOCROSSREFS(@var{section} @var{section} @dots{})
4266 @kindex NOCROSSREFS(@var{sections})
4267 @cindex cross references
4268 This command may be used to tell @command{ld} to issue an error about any
4269 references among certain output sections.
4271 In certain types of programs, particularly on embedded systems when
4272 using overlays, when one section is loaded into memory, another section
4273 will not be. Any direct references between the two sections would be
4274 errors. For example, it would be an error if code in one section called
4275 a function defined in the other section.
4277 The @code{NOCROSSREFS} command takes a list of output section names. If
4278 @command{ld} detects any cross references between the sections, it reports
4279 an error and returns a non-zero exit status. Note that the
4280 @code{NOCROSSREFS} command uses output section names, not input section
4283 @item NOCROSSREFS_TO(@var{tosection} @var{fromsection} @dots{})
4284 @kindex NOCROSSREFS_TO(@var{tosection} @var{fromsections})
4285 @cindex cross references
4286 This command may be used to tell @command{ld} to issue an error about any
4287 references to one section from a list of other sections.
4289 The @code{NOCROSSREFS} command is useful when ensuring that two or more
4290 output sections are entirely independent but there are situations where
4291 a one-way dependency is needed. For example, in a multi-core application
4292 there may be shared code that can be called from each core but for safety
4293 must never call back.
4295 The @code{NOCROSSREFS_TO} command takes a list of output section names.
4296 The first section can not be referenced from any of the other sections.
4297 If @command{ld} detects any references to the first section from any of
4298 the other sections, it reports an error and returns a non-zero exit
4299 status. Note that the @code{NOCROSSREFS_TO} command uses output section
4300 names, not input section names.
4302 @ifclear SingleFormat
4303 @item OUTPUT_ARCH(@var{bfdarch})
4304 @kindex OUTPUT_ARCH(@var{bfdarch})
4305 @cindex machine architecture
4306 @cindex architecture
4307 Specify a particular output machine architecture. The argument is one
4308 of the names used by the BFD library (@pxref{BFD}). You can see the
4309 architecture of an object file by using the @code{objdump} program with
4310 the @samp{-f} option.
4313 @item LD_FEATURE(@var{string})
4314 @kindex LD_FEATURE(@var{string})
4315 This command may be used to modify @command{ld} behavior. If
4316 @var{string} is @code{"SANE_EXPR"} then absolute symbols and numbers
4317 in a script are simply treated as numbers everywhere.
4318 @xref{Expression Section}.
4322 @section Assigning Values to Symbols
4323 @cindex assignment in scripts
4324 @cindex symbol definition, scripts
4325 @cindex variables, defining
4326 You may assign a value to a symbol in a linker script. This will define
4327 the symbol and place it into the symbol table with a global scope.
4330 * Simple Assignments:: Simple Assignments
4333 * PROVIDE_HIDDEN:: PROVIDE_HIDDEN
4334 * Source Code Reference:: How to use a linker script defined symbol in source code
4337 @node Simple Assignments
4338 @subsection Simple Assignments
4340 You may assign to a symbol using any of the C assignment operators:
4343 @item @var{symbol} = @var{expression} ;
4344 @itemx @var{symbol} += @var{expression} ;
4345 @itemx @var{symbol} -= @var{expression} ;
4346 @itemx @var{symbol} *= @var{expression} ;
4347 @itemx @var{symbol} /= @var{expression} ;
4348 @itemx @var{symbol} <<= @var{expression} ;
4349 @itemx @var{symbol} >>= @var{expression} ;
4350 @itemx @var{symbol} &= @var{expression} ;
4351 @itemx @var{symbol} |= @var{expression} ;
4354 The first case will define @var{symbol} to the value of
4355 @var{expression}. In the other cases, @var{symbol} must already be
4356 defined, and the value will be adjusted accordingly.
4358 The special symbol name @samp{.} indicates the location counter. You
4359 may only use this within a @code{SECTIONS} command. @xref{Location Counter}.
4361 The semicolon after @var{expression} is required.
4363 Expressions are defined below; see @ref{Expressions}.
4365 You may write symbol assignments as commands in their own right, or as
4366 statements within a @code{SECTIONS} command, or as part of an output
4367 section description in a @code{SECTIONS} command.
4369 The section of the symbol will be set from the section of the
4370 expression; for more information, see @ref{Expression Section}.
4372 Here is an example showing the three different places that symbol
4373 assignments may be used:
4384 _bdata = (. + 3) & ~ 3;
4385 .data : @{ *(.data) @}
4389 In this example, the symbol @samp{floating_point} will be defined as
4390 zero. The symbol @samp{_etext} will be defined as the address following
4391 the last @samp{.text} input section. The symbol @samp{_bdata} will be
4392 defined as the address following the @samp{.text} output section aligned
4393 upward to a 4 byte boundary.
4398 For ELF targeted ports, define a symbol that will be hidden and won't be
4399 exported. The syntax is @code{HIDDEN(@var{symbol} = @var{expression})}.
4401 Here is the example from @ref{Simple Assignments}, rewritten to use
4405 HIDDEN(floating_point = 0);
4413 HIDDEN(_bdata = (. + 3) & ~ 3);
4414 .data : @{ *(.data) @}
4418 In this case none of the three symbols will be visible outside this module.
4423 In some cases, it is desirable for a linker script to define a symbol
4424 only if it is referenced and is not defined by any object included in
4425 the link. For example, traditional linkers defined the symbol
4426 @samp{etext}. However, ANSI C requires that the user be able to use
4427 @samp{etext} as a function name without encountering an error. The
4428 @code{PROVIDE} keyword may be used to define a symbol, such as
4429 @samp{etext}, only if it is referenced but not defined. The syntax is
4430 @code{PROVIDE(@var{symbol} = @var{expression})}.
4432 Here is an example of using @code{PROVIDE} to define @samp{etext}:
4445 In this example, if the program defines @samp{_etext} (with a leading
4446 underscore), the linker will give a multiple definition error. If, on
4447 the other hand, the program defines @samp{etext} (with no leading
4448 underscore), the linker will silently use the definition in the program.
4449 If the program references @samp{etext} but does not define it, the
4450 linker will use the definition in the linker script.
4452 Note - the @code{PROVIDE} directive considers a common symbol to be
4453 defined, even though such a symbol could be combined with the symbol
4454 that the @code{PROVIDE} would create. This is particularly important
4455 when considering constructor and destructor list symbols such as
4456 @samp{__CTOR_LIST__} as these are often defined as common symbols.
4458 @node PROVIDE_HIDDEN
4459 @subsection PROVIDE_HIDDEN
4460 @cindex PROVIDE_HIDDEN
4461 Similar to @code{PROVIDE}. For ELF targeted ports, the symbol will be
4462 hidden and won't be exported.
4464 @node Source Code Reference
4465 @subsection Source Code Reference
4467 Accessing a linker script defined variable from source code is not
4468 intuitive. In particular a linker script symbol is not equivalent to
4469 a variable declaration in a high level language, it is instead a
4470 symbol that does not have a value.
4472 Before going further, it is important to note that compilers often
4473 transform names in the source code into different names when they are
4474 stored in the symbol table. For example, Fortran compilers commonly
4475 prepend or append an underscore, and C++ performs extensive @samp{name
4476 mangling}. Therefore there might be a discrepancy between the name
4477 of a variable as it is used in source code and the name of the same
4478 variable as it is defined in a linker script. For example in C a
4479 linker script variable might be referred to as:
4485 But in the linker script it might be defined as:
4491 In the remaining examples however it is assumed that no name
4492 transformation has taken place.
4494 When a symbol is declared in a high level language such as C, two
4495 things happen. The first is that the compiler reserves enough space
4496 in the program's memory to hold the @emph{value} of the symbol. The
4497 second is that the compiler creates an entry in the program's symbol
4498 table which holds the symbol's @emph{address}. ie the symbol table
4499 contains the address of the block of memory holding the symbol's
4500 value. So for example the following C declaration, at file scope:
4506 creates an entry called @samp{foo} in the symbol table. This entry
4507 holds the address of an @samp{int} sized block of memory where the
4508 number 1000 is initially stored.
4510 When a program references a symbol the compiler generates code that
4511 first accesses the symbol table to find the address of the symbol's
4512 memory block and then code to read the value from that memory block.
4519 looks up the symbol @samp{foo} in the symbol table, gets the address
4520 associated with this symbol and then writes the value 1 into that
4527 looks up the symbol @samp{foo} in the symbol table, gets its address
4528 and then copies this address into the block of memory associated with
4529 the variable @samp{a}.
4531 Linker scripts symbol declarations, by contrast, create an entry in
4532 the symbol table but do not assign any memory to them. Thus they are
4533 an address without a value. So for example the linker script definition:
4539 creates an entry in the symbol table called @samp{foo} which holds
4540 the address of memory location 1000, but nothing special is stored at
4541 address 1000. This means that you cannot access the @emph{value} of a
4542 linker script defined symbol - it has no value - all you can do is
4543 access the @emph{address} of a linker script defined symbol.
4545 Hence when you are using a linker script defined symbol in source code
4546 you should always take the address of the symbol, and never attempt to
4547 use its value. For example suppose you want to copy the contents of a
4548 section of memory called .ROM into a section called .FLASH and the
4549 linker script contains these declarations:
4553 start_of_ROM = .ROM;
4554 end_of_ROM = .ROM + sizeof (.ROM);
4555 start_of_FLASH = .FLASH;
4559 Then the C source code to perform the copy would be:
4563 extern char start_of_ROM, end_of_ROM, start_of_FLASH;
4565 memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);
4569 Note the use of the @samp{&} operators. These are correct.
4570 Alternatively the symbols can be treated as the names of vectors or
4571 arrays and then the code will again work as expected:
4575 extern char start_of_ROM[], end_of_ROM[], start_of_FLASH[];
4577 memcpy (start_of_FLASH, start_of_ROM, end_of_ROM - start_of_ROM);
4581 Note how using this method does not require the use of @samp{&}
4585 @section SECTIONS Command
4587 The @code{SECTIONS} command tells the linker how to map input sections
4588 into output sections, and how to place the output sections in memory.
4590 The format of the @code{SECTIONS} command is:
4594 @var{sections-command}
4595 @var{sections-command}
4600 Each @var{sections-command} may of be one of the following:
4604 an @code{ENTRY} command (@pxref{Entry Point,,Entry command})
4606 a symbol assignment (@pxref{Assignments})
4608 an output section description
4610 an overlay description
4613 The @code{ENTRY} command and symbol assignments are permitted inside the
4614 @code{SECTIONS} command for convenience in using the location counter in
4615 those commands. This can also make the linker script easier to
4616 understand because you can use those commands at meaningful points in
4617 the layout of the output file.
4619 Output section descriptions and overlay descriptions are described
4622 If you do not use a @code{SECTIONS} command in your linker script, the
4623 linker will place each input section into an identically named output
4624 section in the order that the sections are first encountered in the
4625 input files. If all input sections are present in the first file, for
4626 example, the order of sections in the output file will match the order
4627 in the first input file. The first section will be at address zero.
4630 * Output Section Description:: Output section description
4631 * Output Section Name:: Output section name
4632 * Output Section Address:: Output section address
4633 * Input Section:: Input section description
4634 * Output Section Data:: Output section data
4635 * Output Section Keywords:: Output section keywords
4636 * Output Section Discarding:: Output section discarding
4637 * Output Section Attributes:: Output section attributes
4638 * Overlay Description:: Overlay description
4641 @node Output Section Description
4642 @subsection Output Section Description
4643 The full description of an output section looks like this:
4646 @var{section} [@var{address}] [(@var{type})] :
4648 [ALIGN(@var{section_align}) | ALIGN_WITH_INPUT]
4649 [SUBALIGN(@var{subsection_align})]
4652 @var{output-section-command}
4653 @var{output-section-command}
4655 @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}] [,]
4659 Most output sections do not use most of the optional section attributes.
4661 The whitespace around @var{section} is required, so that the section
4662 name is unambiguous. The colon and the curly braces are also required.
4663 The comma at the end may be required if a @var{fillexp} is used and
4664 the next @var{sections-command} looks like a continuation of the expression.
4665 The line breaks and other white space are optional.
4667 Each @var{output-section-command} may be one of the following:
4671 a symbol assignment (@pxref{Assignments})
4673 an input section description (@pxref{Input Section})
4675 data values to include directly (@pxref{Output Section Data})
4677 a special output section keyword (@pxref{Output Section Keywords})
4680 @node Output Section Name
4681 @subsection Output Section Name
4682 @cindex name, section
4683 @cindex section name
4684 The name of the output section is @var{section}. @var{section} must
4685 meet the constraints of your output format. In formats which only
4686 support a limited number of sections, such as @code{a.out}, the name
4687 must be one of the names supported by the format (@code{a.out}, for
4688 example, allows only @samp{.text}, @samp{.data} or @samp{.bss}). If the
4689 output format supports any number of sections, but with numbers and not
4690 names (as is the case for Oasys), the name should be supplied as a
4691 quoted numeric string. A section name may consist of any sequence of
4692 characters, but a name which contains any unusual characters such as
4693 commas must be quoted.
4695 The output section name @samp{/DISCARD/} is special; @ref{Output Section
4698 @node Output Section Address
4699 @subsection Output Section Address
4700 @cindex address, section
4701 @cindex section address
4702 The @var{address} is an expression for the VMA (the virtual memory
4703 address) of the output section. This address is optional, but if it
4704 is provided then the output address will be set exactly as specified.
4706 If the output address is not specified then one will be chosen for the
4707 section, based on the heuristic below. This address will be adjusted
4708 to fit the alignment requirement of the output section. The
4709 alignment requirement is the strictest alignment of any input section
4710 contained within the output section.
4712 The output section address heuristic is as follows:
4716 If an output memory @var{region} is set for the section then it
4717 is added to this region and its address will be the next free address
4721 If the MEMORY command has been used to create a list of memory
4722 regions then the first region which has attributes compatible with the
4723 section is selected to contain it. The section's output address will
4724 be the next free address in that region; @ref{MEMORY}.
4727 If no memory regions were specified, or none match the section then
4728 the output address will be based on the current value of the location
4736 .text . : @{ *(.text) @}
4743 .text : @{ *(.text) @}
4747 are subtly different. The first will set the address of the
4748 @samp{.text} output section to the current value of the location
4749 counter. The second will set it to the current value of the location
4750 counter aligned to the strictest alignment of any of the @samp{.text}
4753 The @var{address} may be an arbitrary expression; @ref{Expressions}.
4754 For example, if you want to align the section on a 0x10 byte boundary,
4755 so that the lowest four bits of the section address are zero, you could
4756 do something like this:
4758 .text ALIGN(0x10) : @{ *(.text) @}
4761 This works because @code{ALIGN} returns the current location counter
4762 aligned upward to the specified value.
4764 Specifying @var{address} for a section will change the value of the
4765 location counter, provided that the section is non-empty. (Empty
4766 sections are ignored).
4769 @subsection Input Section Description
4770 @cindex input sections
4771 @cindex mapping input sections to output sections
4772 The most common output section command is an input section description.
4774 The input section description is the most basic linker script operation.
4775 You use output sections to tell the linker how to lay out your program
4776 in memory. You use input section descriptions to tell the linker how to
4777 map the input files into your memory layout.
4780 * Input Section Basics:: Input section basics
4781 * Input Section Wildcards:: Input section wildcard patterns
4782 * Input Section Common:: Input section for common symbols
4783 * Input Section Keep:: Input section and garbage collection
4784 * Input Section Example:: Input section example
4787 @node Input Section Basics
4788 @subsubsection Input Section Basics
4789 @cindex input section basics
4790 An input section description consists of a file name optionally followed
4791 by a list of section names in parentheses.
4793 The file name and the section name may be wildcard patterns, which we
4794 describe further below (@pxref{Input Section Wildcards}).
4796 The most common input section description is to include all input
4797 sections with a particular name in the output section. For example, to
4798 include all input @samp{.text} sections, you would write:
4803 Here the @samp{*} is a wildcard which matches any file name. To exclude a list
4804 @cindex EXCLUDE_FILE
4805 of files from matching the file name wildcard, EXCLUDE_FILE may be used to
4806 match all files except the ones specified in the EXCLUDE_FILE list. For
4809 EXCLUDE_FILE (*crtend.o *otherfile.o) *(.ctors)
4812 will cause all .ctors sections from all files except @file{crtend.o}
4813 and @file{otherfile.o} to be included. The EXCLUDE_FILE can also be
4814 placed inside the section list, for example:
4816 *(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
4819 The result of this is identically to the previous example. Supporting
4820 two syntaxes for EXCLUDE_FILE is useful if the section list contains
4821 more than one section, as described below.
4823 There are two ways to include more than one section:
4829 The difference between these is the order in which the @samp{.text} and
4830 @samp{.rdata} input sections will appear in the output section. In the
4831 first example, they will be intermingled, appearing in the same order as
4832 they are found in the linker input. In the second example, all
4833 @samp{.text} input sections will appear first, followed by all
4834 @samp{.rdata} input sections.
4836 When using EXCLUDE_FILE with more than one section, if the exclusion
4837 is within the section list then the exclusion only applies to the
4838 immediately following section, for example:
4840 *(EXCLUDE_FILE (*somefile.o) .text .rdata)
4843 will cause all @samp{.text} sections from all files except
4844 @file{somefile.o} to be included, while all @samp{.rdata} sections
4845 from all files, including @file{somefile.o}, will be included. To
4846 exclude the @samp{.rdata} sections from @file{somefile.o} the example
4847 could be modified to:
4849 *(EXCLUDE_FILE (*somefile.o) .text EXCLUDE_FILE (*somefile.o) .rdata)
4852 Alternatively, placing the EXCLUDE_FILE outside of the section list,
4853 before the input file selection, will cause the exclusion to apply for
4854 all sections. Thus the previous example can be rewritten as:
4856 EXCLUDE_FILE (*somefile.o) *(.text .rdata)
4859 You can specify a file name to include sections from a particular file.
4860 You would do this if one or more of your files contain special data that
4861 needs to be at a particular location in memory. For example:
4866 To refine the sections that are included based on the section flags
4867 of an input section, INPUT_SECTION_FLAGS may be used.
4869 Here is a simple example for using Section header flags for ELF sections:
4874 .text : @{ INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) @}
4875 .text2 : @{ INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) @}
4880 In this example, the output section @samp{.text} will be comprised of any
4881 input section matching the name *(.text) whose section header flags
4882 @code{SHF_MERGE} and @code{SHF_STRINGS} are set. The output section
4883 @samp{.text2} will be comprised of any input section matching the name *(.text)
4884 whose section header flag @code{SHF_WRITE} is clear.
4886 You can also specify files within archives by writing a pattern
4887 matching the archive, a colon, then the pattern matching the file,
4888 with no whitespace around the colon.
4892 matches file within archive
4894 matches the whole archive
4896 matches file but not one in an archive
4899 Either one or both of @samp{archive} and @samp{file} can contain shell
4900 wildcards. On DOS based file systems, the linker will assume that a
4901 single letter followed by a colon is a drive specifier, so
4902 @samp{c:myfile.o} is a simple file specification, not @samp{myfile.o}
4903 within an archive called @samp{c}. @samp{archive:file} filespecs may
4904 also be used within an @code{EXCLUDE_FILE} list, but may not appear in
4905 other linker script contexts. For instance, you cannot extract a file
4906 from an archive by using @samp{archive:file} in an @code{INPUT}
4909 If you use a file name without a list of sections, then all sections in
4910 the input file will be included in the output section. This is not
4911 commonly done, but it may by useful on occasion. For example:
4916 When you use a file name which is not an @samp{archive:file} specifier
4917 and does not contain any wild card
4918 characters, the linker will first see if you also specified the file
4919 name on the linker command line or in an @code{INPUT} command. If you
4920 did not, the linker will attempt to open the file as an input file, as
4921 though it appeared on the command line. Note that this differs from an
4922 @code{INPUT} command, because the linker will not search for the file in
4923 the archive search path.
4925 @node Input Section Wildcards
4926 @subsubsection Input Section Wildcard Patterns
4927 @cindex input section wildcards
4928 @cindex wildcard file name patterns
4929 @cindex file name wildcard patterns
4930 @cindex section name wildcard patterns
4931 In an input section description, either the file name or the section
4932 name or both may be wildcard patterns.
4934 The file name of @samp{*} seen in many examples is a simple wildcard
4935 pattern for the file name.
4937 The wildcard patterns are like those used by the Unix shell.
4941 matches any number of characters
4943 matches any single character
4945 matches a single instance of any of the @var{chars}; the @samp{-}
4946 character may be used to specify a range of characters, as in
4947 @samp{[a-z]} to match any lower case letter
4949 quotes the following character
4952 When a file name is matched with a wildcard, the wildcard characters
4953 will not match a @samp{/} character (used to separate directory names on
4954 Unix). A pattern consisting of a single @samp{*} character is an
4955 exception; it will always match any file name, whether it contains a
4956 @samp{/} or not. In a section name, the wildcard characters will match
4957 a @samp{/} character.
4959 File name wildcard patterns only match files which are explicitly
4960 specified on the command line or in an @code{INPUT} command. The linker
4961 does not search directories to expand wildcards.
4963 If a file name matches more than one wildcard pattern, or if a file name
4964 appears explicitly and is also matched by a wildcard pattern, the linker
4965 will use the first match in the linker script. For example, this
4966 sequence of input section descriptions is probably in error, because the
4967 @file{data.o} rule will not be used:
4969 .data : @{ *(.data) @}
4970 .data1 : @{ data.o(.data) @}
4973 @cindex SORT_BY_NAME
4974 Normally, the linker will place files and sections matched by wildcards
4975 in the order in which they are seen during the link. You can change
4976 this by using the @code{SORT_BY_NAME} keyword, which appears before a wildcard
4977 pattern in parentheses (e.g., @code{SORT_BY_NAME(.text*)}). When the
4978 @code{SORT_BY_NAME} keyword is used, the linker will sort the files or sections
4979 into ascending order by name before placing them in the output file.
4981 @cindex SORT_BY_ALIGNMENT
4982 @code{SORT_BY_ALIGNMENT} is similar to @code{SORT_BY_NAME}.
4983 @code{SORT_BY_ALIGNMENT} will sort sections into descending order of
4984 alignment before placing them in the output file. Placing larger
4985 alignments before smaller alignments can reduce the amount of padding
4988 @cindex SORT_BY_INIT_PRIORITY
4989 @code{SORT_BY_INIT_PRIORITY} is also similar to @code{SORT_BY_NAME}.
4990 @code{SORT_BY_INIT_PRIORITY} will sort sections into ascending
4991 numerical order of the GCC init_priority attribute encoded in the
4992 section name before placing them in the output file. In
4993 @code{.init_array.NNNNN} and @code{.fini_array.NNNNN}, @code{NNNNN} is
4994 the init_priority. In @code{.ctors.NNNNN} and @code{.dtors.NNNNN},
4995 @code{NNNNN} is 65535 minus the init_priority.
4998 @code{SORT} is an alias for @code{SORT_BY_NAME}.
5000 When there are nested section sorting commands in linker script, there
5001 can be at most 1 level of nesting for section sorting commands.
5005 @code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)).
5006 It will sort the input sections by name first, then by alignment if two
5007 sections have the same name.
5009 @code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)).
5010 It will sort the input sections by alignment first, then by name if two
5011 sections have the same alignment.
5013 @code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
5014 treated the same as @code{SORT_BY_NAME} (wildcard section pattern).
5016 @code{SORT_BY_ALIGNMENT} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern))
5017 is treated the same as @code{SORT_BY_ALIGNMENT} (wildcard section pattern).
5019 All other nested section sorting commands are invalid.
5022 When both command-line section sorting option and linker script
5023 section sorting command are used, section sorting command always
5024 takes precedence over the command-line option.
5026 If the section sorting command in linker script isn't nested, the
5027 command-line option will make the section sorting command to be
5028 treated as nested sorting command.
5032 @code{SORT_BY_NAME} (wildcard section pattern ) with
5033 @option{--sort-sections alignment} is equivalent to
5034 @code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)).
5036 @code{SORT_BY_ALIGNMENT} (wildcard section pattern) with
5037 @option{--sort-section name} is equivalent to
5038 @code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)).
5041 If the section sorting command in linker script is nested, the
5042 command-line option will be ignored.
5045 @code{SORT_NONE} disables section sorting by ignoring the command-line
5046 section sorting option.
5048 If you ever get confused about where input sections are going, use the
5049 @samp{-M} linker option to generate a map file. The map file shows
5050 precisely how input sections are mapped to output sections.
5052 This example shows how wildcard patterns might be used to partition
5053 files. This linker script directs the linker to place all @samp{.text}
5054 sections in @samp{.text} and all @samp{.bss} sections in @samp{.bss}.
5055 The linker will place the @samp{.data} section from all files beginning
5056 with an upper case character in @samp{.DATA}; for all other files, the
5057 linker will place the @samp{.data} section in @samp{.data}.
5061 .text : @{ *(.text) @}
5062 .DATA : @{ [A-Z]*(.data) @}
5063 .data : @{ *(.data) @}
5064 .bss : @{ *(.bss) @}
5069 @node Input Section Common
5070 @subsubsection Input Section for Common Symbols
5071 @cindex common symbol placement
5072 @cindex uninitialized data placement
5073 A special notation is needed for common symbols, because in many object
5074 file formats common symbols do not have a particular input section. The
5075 linker treats common symbols as though they are in an input section
5076 named @samp{COMMON}.
5078 You may use file names with the @samp{COMMON} section just as with any
5079 other input sections. You can use this to place common symbols from a
5080 particular input file in one section while common symbols from other
5081 input files are placed in another section.
5083 In most cases, common symbols in input files will be placed in the
5084 @samp{.bss} section in the output file. For example:
5086 .bss @{ *(.bss) *(COMMON) @}
5089 @cindex scommon section
5090 @cindex small common symbols
5091 Some object file formats have more than one type of common symbol. For
5092 example, the MIPS ELF object file format distinguishes standard common
5093 symbols and small common symbols. In this case, the linker will use a
5094 different special section name for other types of common symbols. In
5095 the case of MIPS ELF, the linker uses @samp{COMMON} for standard common
5096 symbols and @samp{.scommon} for small common symbols. This permits you
5097 to map the different types of common symbols into memory at different
5101 You will sometimes see @samp{[COMMON]} in old linker scripts. This
5102 notation is now considered obsolete. It is equivalent to
5105 @node Input Section Keep
5106 @subsubsection Input Section and Garbage Collection
5108 @cindex garbage collection
5109 When link-time garbage collection is in use (@samp{--gc-sections}),
5110 it is often useful to mark sections that should not be eliminated.
5111 This is accomplished by surrounding an input section's wildcard entry
5112 with @code{KEEP()}, as in @code{KEEP(*(.init))} or
5113 @code{KEEP(SORT_BY_NAME(*)(.ctors))}.
5115 @node Input Section Example
5116 @subsubsection Input Section Example
5117 The following example is a complete linker script. It tells the linker
5118 to read all of the sections from file @file{all.o} and place them at the
5119 start of output section @samp{outputa} which starts at location
5120 @samp{0x10000}. All of section @samp{.input1} from file @file{foo.o}
5121 follows immediately, in the same output section. All of section
5122 @samp{.input2} from @file{foo.o} goes into output section
5123 @samp{outputb}, followed by section @samp{.input1} from @file{foo1.o}.
5124 All of the remaining @samp{.input1} and @samp{.input2} sections from any
5125 files are written to output section @samp{outputc}.
5153 If an output section's name is the same as the input section's name
5154 and is representable as a C identifier, then the linker will
5155 automatically @pxref{PROVIDE} two symbols: __start_SECNAME and
5156 __stop_SECNAME, where SECNAME is the name of the section. These
5157 indicate the start address and end address of the output section
5158 respectively. Note: most section names are not representable as
5159 C identifiers because they contain a @samp{.} character.
5161 @node Output Section Data
5162 @subsection Output Section Data
5164 @cindex section data
5165 @cindex output section data
5166 @kindex BYTE(@var{expression})
5167 @kindex SHORT(@var{expression})
5168 @kindex LONG(@var{expression})
5169 @kindex QUAD(@var{expression})
5170 @kindex SQUAD(@var{expression})
5171 You can include explicit bytes of data in an output section by using
5172 @code{BYTE}, @code{SHORT}, @code{LONG}, @code{QUAD}, or @code{SQUAD} as
5173 an output section command. Each keyword is followed by an expression in
5174 parentheses providing the value to store (@pxref{Expressions}). The
5175 value of the expression is stored at the current value of the location
5178 The @code{BYTE}, @code{SHORT}, @code{LONG}, and @code{QUAD} commands
5179 store one, two, four, and eight bytes (respectively). After storing the
5180 bytes, the location counter is incremented by the number of bytes
5183 For example, this will store the byte 1 followed by the four byte value
5184 of the symbol @samp{addr}:
5190 When using a 64 bit host or target, @code{QUAD} and @code{SQUAD} are the
5191 same; they both store an 8 byte, or 64 bit, value. When both host and
5192 target are 32 bits, an expression is computed as 32 bits. In this case
5193 @code{QUAD} stores a 32 bit value zero extended to 64 bits, and
5194 @code{SQUAD} stores a 32 bit value sign extended to 64 bits.
5196 If the object file format of the output file has an explicit endianness,
5197 which is the normal case, the value will be stored in that endianness.
5198 When the object file format does not have an explicit endianness, as is
5199 true of, for example, S-records, the value will be stored in the
5200 endianness of the first input object file.
5202 Note---these commands only work inside a section description and not
5203 between them, so the following will produce an error from the linker:
5205 SECTIONS @{@ .text : @{@ *(.text) @}@ LONG(1) .data : @{@ *(.data) @}@ @}@
5207 whereas this will work:
5209 SECTIONS @{@ .text : @{@ *(.text) ; LONG(1) @}@ .data : @{@ *(.data) @}@ @}@
5212 @kindex FILL(@var{expression})
5213 @cindex holes, filling
5214 @cindex unspecified memory
5215 You may use the @code{FILL} command to set the fill pattern for the
5216 current section. It is followed by an expression in parentheses. Any
5217 otherwise unspecified regions of memory within the section (for example,
5218 gaps left due to the required alignment of input sections) are filled
5219 with the value of the expression, repeated as
5220 necessary. A @code{FILL} statement covers memory locations after the
5221 point at which it occurs in the section definition; by including more
5222 than one @code{FILL} statement, you can have different fill patterns in
5223 different parts of an output section.
5225 This example shows how to fill unspecified regions of memory with the
5231 The @code{FILL} command is similar to the @samp{=@var{fillexp}} output
5232 section attribute, but it only affects the
5233 part of the section following the @code{FILL} command, rather than the
5234 entire section. If both are used, the @code{FILL} command takes
5235 precedence. @xref{Output Section Fill}, for details on the fill
5238 @node Output Section Keywords
5239 @subsection Output Section Keywords
5240 There are a couple of keywords which can appear as output section
5244 @kindex CREATE_OBJECT_SYMBOLS
5245 @cindex input filename symbols
5246 @cindex filename symbols
5247 @item CREATE_OBJECT_SYMBOLS
5248 The command tells the linker to create a symbol for each input file.
5249 The name of each symbol will be the name of the corresponding input
5250 file. The section of each symbol will be the output section in which
5251 the @code{CREATE_OBJECT_SYMBOLS} command appears.
5253 This is conventional for the a.out object file format. It is not
5254 normally used for any other object file format.
5256 @kindex CONSTRUCTORS
5257 @cindex C++ constructors, arranging in link
5258 @cindex constructors, arranging in link
5260 When linking using the a.out object file format, the linker uses an
5261 unusual set construct to support C++ global constructors and
5262 destructors. When linking object file formats which do not support
5263 arbitrary sections, such as ECOFF and XCOFF, the linker will
5264 automatically recognize C++ global constructors and destructors by name.
5265 For these object file formats, the @code{CONSTRUCTORS} command tells the
5266 linker to place constructor information in the output section where the
5267 @code{CONSTRUCTORS} command appears. The @code{CONSTRUCTORS} command is
5268 ignored for other object file formats.
5270 The symbol @w{@code{__CTOR_LIST__}} marks the start of the global
5271 constructors, and the symbol @w{@code{__CTOR_END__}} marks the end.
5272 Similarly, @w{@code{__DTOR_LIST__}} and @w{@code{__DTOR_END__}} mark
5273 the start and end of the global destructors. The
5274 first word in the list is the number of entries, followed by the address
5275 of each constructor or destructor, followed by a zero word. The
5276 compiler must arrange to actually run the code. For these object file
5277 formats @sc{gnu} C++ normally calls constructors from a subroutine
5278 @code{__main}; a call to @code{__main} is automatically inserted into
5279 the startup code for @code{main}. @sc{gnu} C++ normally runs
5280 destructors either by using @code{atexit}, or directly from the function
5283 For object file formats such as @code{COFF} or @code{ELF} which support
5284 arbitrary section names, @sc{gnu} C++ will normally arrange to put the
5285 addresses of global constructors and destructors into the @code{.ctors}
5286 and @code{.dtors} sections. Placing the following sequence into your
5287 linker script will build the sort of table which the @sc{gnu} C++
5288 runtime code expects to see.
5292 LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
5297 LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
5303 If you are using the @sc{gnu} C++ support for initialization priority,
5304 which provides some control over the order in which global constructors
5305 are run, you must sort the constructors at link time to ensure that they
5306 are executed in the correct order. When using the @code{CONSTRUCTORS}
5307 command, use @samp{SORT_BY_NAME(CONSTRUCTORS)} instead. When using the
5308 @code{.ctors} and @code{.dtors} sections, use @samp{*(SORT_BY_NAME(.ctors))} and
5309 @samp{*(SORT_BY_NAME(.dtors))} instead of just @samp{*(.ctors)} and
5312 Normally the compiler and linker will handle these issues automatically,
5313 and you will not need to concern yourself with them. However, you may
5314 need to consider this if you are using C++ and writing your own linker
5319 @node Output Section Discarding
5320 @subsection Output Section Discarding
5321 @cindex discarding sections
5322 @cindex sections, discarding
5323 @cindex removing sections
5324 The linker will not normally create output sections with no contents.
5325 This is for convenience when referring to input sections that may or
5326 may not be present in any of the input files. For example:
5328 .foo : @{ *(.foo) @}
5331 will only create a @samp{.foo} section in the output file if there is a
5332 @samp{.foo} section in at least one input file, and if the input
5333 sections are not all empty. Other link script directives that allocate
5334 space in an output section will also create the output section. So
5335 too will assignments to dot even if the assignment does not create
5336 space, except for @samp{. = 0}, @samp{. = . + 0}, @samp{. = sym},
5337 @samp{. = . + sym} and @samp{. = ALIGN (. != 0, expr, 1)} when
5338 @samp{sym} is an absolute symbol of value 0 defined in the script.
5339 This allows you to force output of an empty section with @samp{. = .}.
5341 The linker will ignore address assignments (@pxref{Output Section Address})
5342 on discarded output sections, except when the linker script defines
5343 symbols in the output section. In that case the linker will obey
5344 the address assignments, possibly advancing dot even though the
5345 section is discarded.
5348 The special output section name @samp{/DISCARD/} may be used to discard
5349 input sections. Any input sections which are assigned to an output
5350 section named @samp{/DISCARD/} are not included in the output file.
5352 This can be used to discard input sections marked with the ELF flag
5353 @code{SHF_GNU_RETAIN}, which would otherwise have been saved from linker
5356 Note, sections that match the @samp{/DISCARD/} output section will be
5357 discarded even if they are in an ELF section group which has other
5358 members which are not being discarded. This is deliberate.
5359 Discarding takes precedence over grouping.
5361 @node Output Section Attributes
5362 @subsection Output Section Attributes
5363 @cindex output section attributes
5364 We showed above that the full description of an output section looked
5369 @var{section} [@var{address}] [(@var{type})] :
5371 [ALIGN(@var{section_align}) | ALIGN_WITH_INPUT]
5372 [SUBALIGN(@var{subsection_align})]
5375 @var{output-section-command}
5376 @var{output-section-command}
5378 @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}]
5382 We've already described @var{section}, @var{address}, and
5383 @var{output-section-command}. In this section we will describe the
5384 remaining section attributes.
5387 * Output Section Type:: Output section type
5388 * Output Section LMA:: Output section LMA
5389 * Forced Output Alignment:: Forced Output Alignment
5390 * Forced Input Alignment:: Forced Input Alignment
5391 * Output Section Constraint:: Output section constraint
5392 * Output Section Region:: Output section region
5393 * Output Section Phdr:: Output section phdr
5394 * Output Section Fill:: Output section fill
5397 @node Output Section Type
5398 @subsubsection Output Section Type
5399 Each output section may have a type. The type is a keyword in
5400 parentheses. The following types are defined:
5404 The section should be marked as not loadable, so that it will not be
5405 loaded into memory when the program is run.
5410 These type names are supported for backward compatibility, and are
5411 rarely used. They all have the same effect: the section should be
5412 marked as not allocatable, so that no memory is allocated for the
5413 section when the program is run.
5417 @cindex prevent unnecessary loading
5418 @cindex loading, preventing
5419 The linker normally sets the attributes of an output section based on
5420 the input sections which map into it. You can override this by using
5421 the section type. For example, in the script sample below, the
5422 @samp{ROM} section is addressed at memory location @samp{0} and does not
5423 need to be loaded when the program is run.
5427 ROM 0 (NOLOAD) : @{ @dots{} @}
5433 @node Output Section LMA
5434 @subsubsection Output Section LMA
5435 @kindex AT>@var{lma_region}
5436 @kindex AT(@var{lma})
5437 @cindex load address
5438 @cindex section load address
5439 Every section has a virtual address (VMA) and a load address (LMA); see
5440 @ref{Basic Script Concepts}. The virtual address is specified by the
5441 @pxref{Output Section Address} described earlier. The load address is
5442 specified by the @code{AT} or @code{AT>} keywords. Specifying a load
5443 address is optional.
5445 The @code{AT} keyword takes an expression as an argument. This
5446 specifies the exact load address of the section. The @code{AT>} keyword
5447 takes the name of a memory region as an argument. @xref{MEMORY}. The
5448 load address of the section is set to the next free address in the
5449 region, aligned to the section's alignment requirements.
5451 If neither @code{AT} nor @code{AT>} is specified for an allocatable
5452 section, the linker will use the following heuristic to determine the
5457 If the section has a specific VMA address, then this is used as
5458 the LMA address as well.
5461 If the section is not allocatable then its LMA is set to its VMA.
5464 Otherwise if a memory region can be found that is compatible
5465 with the current section, and this region contains at least one
5466 section, then the LMA is set so the difference between the
5467 VMA and LMA is the same as the difference between the VMA and LMA of
5468 the last section in the located region.
5471 If no memory regions have been declared then a default region
5472 that covers the entire address space is used in the previous step.
5475 If no suitable region could be found, or there was no previous
5476 section then the LMA is set equal to the VMA.
5479 @cindex ROM initialized data
5480 @cindex initialized data in ROM
5481 This feature is designed to make it easy to build a ROM image. For
5482 example, the following linker script creates three output sections: one
5483 called @samp{.text}, which starts at @code{0x1000}, one called
5484 @samp{.mdata}, which is loaded at the end of the @samp{.text} section
5485 even though its VMA is @code{0x2000}, and one called @samp{.bss} to hold
5486 uninitialized data at address @code{0x3000}. The symbol @code{_data} is
5487 defined with the value @code{0x2000}, which shows that the location
5488 counter holds the VMA value, not the LMA value.
5494 .text 0x1000 : @{ *(.text) _etext = . ; @}
5496 AT ( ADDR (.text) + SIZEOF (.text) )
5497 @{ _data = . ; *(.data); _edata = . ; @}
5499 @{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;@}
5504 The run-time initialization code for use with a program generated with
5505 this linker script would include something like the following, to copy
5506 the initialized data from the ROM image to its runtime address. Notice
5507 how this code takes advantage of the symbols defined by the linker
5512 extern char _etext, _data, _edata, _bstart, _bend;
5513 char *src = &_etext;
5516 /* ROM has data at end of text; copy it. */
5517 while (dst < &_edata)
5521 for (dst = &_bstart; dst< &_bend; dst++)
5526 @node Forced Output Alignment
5527 @subsubsection Forced Output Alignment
5528 @kindex ALIGN(@var{section_align})
5529 @cindex forcing output section alignment
5530 @cindex output section alignment
5531 You can increase an output section's alignment by using ALIGN. As an
5532 alternative you can enforce that the difference between the VMA and LMA remains
5533 intact throughout this output section with the ALIGN_WITH_INPUT attribute.
5535 @node Forced Input Alignment
5536 @subsubsection Forced Input Alignment
5537 @kindex SUBALIGN(@var{subsection_align})
5538 @cindex forcing input section alignment
5539 @cindex input section alignment
5540 You can force input section alignment within an output section by using
5541 SUBALIGN. The value specified overrides any alignment given by input
5542 sections, whether larger or smaller.
5544 @node Output Section Constraint
5545 @subsubsection Output Section Constraint
5548 @cindex constraints on output sections
5549 You can specify that an output section should only be created if all
5550 of its input sections are read-only or all of its input sections are
5551 read-write by using the keyword @code{ONLY_IF_RO} and
5552 @code{ONLY_IF_RW} respectively.
5554 @node Output Section Region
5555 @subsubsection Output Section Region
5556 @kindex >@var{region}
5557 @cindex section, assigning to memory region
5558 @cindex memory regions and sections
5559 You can assign a section to a previously defined region of memory by
5560 using @samp{>@var{region}}. @xref{MEMORY}.
5562 Here is a simple example:
5565 MEMORY @{ rom : ORIGIN = 0x1000, LENGTH = 0x1000 @}
5566 SECTIONS @{ ROM : @{ *(.text) @} >rom @}
5570 @node Output Section Phdr
5571 @subsubsection Output Section Phdr
5573 @cindex section, assigning to program header
5574 @cindex program headers and sections
5575 You can assign a section to a previously defined program segment by
5576 using @samp{:@var{phdr}}. @xref{PHDRS}. If a section is assigned to
5577 one or more segments, then all subsequent allocated sections will be
5578 assigned to those segments as well, unless they use an explicitly
5579 @code{:@var{phdr}} modifier. You can use @code{:NONE} to tell the
5580 linker to not put the section in any segment at all.
5582 Here is a simple example:
5585 PHDRS @{ text PT_LOAD ; @}
5586 SECTIONS @{ .text : @{ *(.text) @} :text @}
5590 @node Output Section Fill
5591 @subsubsection Output Section Fill
5592 @kindex =@var{fillexp}
5593 @cindex section fill pattern
5594 @cindex fill pattern, entire section
5595 You can set the fill pattern for an entire section by using
5596 @samp{=@var{fillexp}}. @var{fillexp} is an expression
5597 (@pxref{Expressions}). Any otherwise unspecified regions of memory
5598 within the output section (for example, gaps left due to the required
5599 alignment of input sections) will be filled with the value, repeated as
5600 necessary. If the fill expression is a simple hex number, ie. a string
5601 of hex digit starting with @samp{0x} and without a trailing @samp{k} or @samp{M}, then
5602 an arbitrarily long sequence of hex digits can be used to specify the
5603 fill pattern; Leading zeros become part of the pattern too. For all
5604 other cases, including extra parentheses or a unary @code{+}, the fill
5605 pattern is the four least significant bytes of the value of the
5606 expression. In all cases, the number is big-endian.
5608 You can also change the fill value with a @code{FILL} command in the
5609 output section commands; (@pxref{Output Section Data}).
5611 Here is a simple example:
5614 SECTIONS @{ .text : @{ *(.text) @} =0x90909090 @}
5618 @node Overlay Description
5619 @subsection Overlay Description
5622 An overlay description provides an easy way to describe sections which
5623 are to be loaded as part of a single memory image but are to be run at
5624 the same memory address. At run time, some sort of overlay manager will
5625 copy the overlaid sections in and out of the runtime memory address as
5626 required, perhaps by simply manipulating addressing bits. This approach
5627 can be useful, for example, when a certain region of memory is faster
5630 Overlays are described using the @code{OVERLAY} command. The
5631 @code{OVERLAY} command is used within a @code{SECTIONS} command, like an
5632 output section description. The full syntax of the @code{OVERLAY}
5633 command is as follows:
5636 OVERLAY [@var{start}] : [NOCROSSREFS] [AT ( @var{ldaddr} )]
5640 @var{output-section-command}
5641 @var{output-section-command}
5643 @} [:@var{phdr}@dots{}] [=@var{fill}]
5646 @var{output-section-command}
5647 @var{output-section-command}
5649 @} [:@var{phdr}@dots{}] [=@var{fill}]
5651 @} [>@var{region}] [:@var{phdr}@dots{}] [=@var{fill}] [,]
5655 Everything is optional except @code{OVERLAY} (a keyword), and each
5656 section must have a name (@var{secname1} and @var{secname2} above). The
5657 section definitions within the @code{OVERLAY} construct are identical to
5658 those within the general @code{SECTIONS} construct (@pxref{SECTIONS}),
5659 except that no addresses and no memory regions may be defined for
5660 sections within an @code{OVERLAY}.
5662 The comma at the end may be required if a @var{fill} is used and
5663 the next @var{sections-command} looks like a continuation of the expression.
5665 The sections are all defined with the same starting address. The load
5666 addresses of the sections are arranged such that they are consecutive in
5667 memory starting at the load address used for the @code{OVERLAY} as a
5668 whole (as with normal section definitions, the load address is optional,
5669 and defaults to the start address; the start address is also optional,
5670 and defaults to the current value of the location counter).
5672 If the @code{NOCROSSREFS} keyword is used, and there are any
5673 references among the sections, the linker will report an error. Since
5674 the sections all run at the same address, it normally does not make
5675 sense for one section to refer directly to another.
5676 @xref{Miscellaneous Commands, NOCROSSREFS}.
5678 For each section within the @code{OVERLAY}, the linker automatically
5679 provides two symbols. The symbol @code{__load_start_@var{secname}} is
5680 defined as the starting load address of the section. The symbol
5681 @code{__load_stop_@var{secname}} is defined as the final load address of
5682 the section. Any characters within @var{secname} which are not legal
5683 within C identifiers are removed. C (or assembler) code may use these
5684 symbols to move the overlaid sections around as necessary.
5686 At the end of the overlay, the value of the location counter is set to
5687 the start address of the overlay plus the size of the largest section.
5689 Here is an example. Remember that this would appear inside a
5690 @code{SECTIONS} construct.
5693 OVERLAY 0x1000 : AT (0x4000)
5695 .text0 @{ o1/*.o(.text) @}
5696 .text1 @{ o2/*.o(.text) @}
5701 This will define both @samp{.text0} and @samp{.text1} to start at
5702 address 0x1000. @samp{.text0} will be loaded at address 0x4000, and
5703 @samp{.text1} will be loaded immediately after @samp{.text0}. The
5704 following symbols will be defined if referenced: @code{__load_start_text0},
5705 @code{__load_stop_text0}, @code{__load_start_text1},
5706 @code{__load_stop_text1}.
5708 C code to copy overlay @code{.text1} into the overlay area might look
5713 extern char __load_start_text1, __load_stop_text1;
5714 memcpy ((char *) 0x1000, &__load_start_text1,
5715 &__load_stop_text1 - &__load_start_text1);
5719 Note that the @code{OVERLAY} command is just syntactic sugar, since
5720 everything it does can be done using the more basic commands. The above
5721 example could have been written identically as follows.
5725 .text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
5726 PROVIDE (__load_start_text0 = LOADADDR (.text0));
5727 PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0));
5728 .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
5729 PROVIDE (__load_start_text1 = LOADADDR (.text1));
5730 PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1));
5731 . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
5736 @section MEMORY Command
5738 @cindex memory regions
5739 @cindex regions of memory
5740 @cindex allocating memory
5741 @cindex discontinuous memory
5742 The linker's default configuration permits allocation of all available
5743 memory. You can override this by using the @code{MEMORY} command.
5745 The @code{MEMORY} command describes the location and size of blocks of
5746 memory in the target. You can use it to describe which memory regions
5747 may be used by the linker, and which memory regions it must avoid. You
5748 can then assign sections to particular memory regions. The linker will
5749 set section addresses based on the memory regions, and will warn about
5750 regions that become too full. The linker will not shuffle sections
5751 around to fit into the available regions.
5753 A linker script may contain many uses of the @code{MEMORY} command,
5754 however, all memory blocks defined are treated as if they were
5755 specified inside a single @code{MEMORY} command. The syntax for
5761 @var{name} [(@var{attr})] : ORIGIN = @var{origin}, LENGTH = @var{len}
5767 The @var{name} is a name used in the linker script to refer to the
5768 region. The region name has no meaning outside of the linker script.
5769 Region names are stored in a separate name space, and will not conflict
5770 with symbol names, file names, or section names. Each memory region
5771 must have a distinct name within the @code{MEMORY} command. However you can
5772 add later alias names to existing memory regions with the @ref{REGION_ALIAS}
5775 @cindex memory region attributes
5776 The @var{attr} string is an optional list of attributes that specify
5777 whether to use a particular memory region for an input section which is
5778 not explicitly mapped in the linker script. As described in
5779 @ref{SECTIONS}, if you do not specify an output section for some input
5780 section, the linker will create an output section with the same name as
5781 the input section. If you define region attributes, the linker will use
5782 them to select the memory region for the output section that it creates.
5784 The @var{attr} string must consist only of the following characters:
5799 Invert the sense of any of the attributes that follow
5802 If an unmapped section matches any of the listed attributes other than
5803 @samp{!}, it will be placed in the memory region. The @samp{!}
5804 attribute reverses the test for the characters that follow, so that an
5805 unmapped section will be placed in the memory region only if it does
5806 not match any of the attributes listed afterwards. Thus an attribute
5807 string of @samp{RW!X} will match any unmapped section that has either
5808 or both of the @samp{R} and @samp{W} attributes, but only as long as
5809 the section does not also have the @samp{X} attribute.
5814 The @var{origin} is an numerical expression for the start address of
5815 the memory region. The expression must evaluate to a constant and it
5816 cannot involve any symbols. The keyword @code{ORIGIN} may be
5817 abbreviated to @code{org} or @code{o} (but not, for example,
5823 The @var{len} is an expression for the size in bytes of the memory
5824 region. As with the @var{origin} expression, the expression must
5825 be numerical only and must evaluate to a constant. The keyword
5826 @code{LENGTH} may be abbreviated to @code{len} or @code{l}.
5828 In the following example, we specify that there are two memory regions
5829 available for allocation: one starting at @samp{0} for 256 kilobytes,
5830 and the other starting at @samp{0x40000000} for four megabytes. The
5831 linker will place into the @samp{rom} memory region every section which
5832 is not explicitly mapped into a memory region, and is either read-only
5833 or executable. The linker will place other sections which are not
5834 explicitly mapped into a memory region into the @samp{ram} memory
5841 rom (rx) : ORIGIN = 0, LENGTH = 256K
5842 ram (!rx) : org = 0x40000000, l = 4M
5847 Once you define a memory region, you can direct the linker to place
5848 specific output sections into that memory region by using the
5849 @samp{>@var{region}} output section attribute. For example, if you have
5850 a memory region named @samp{mem}, you would use @samp{>mem} in the
5851 output section definition. @xref{Output Section Region}. If no address
5852 was specified for the output section, the linker will set the address to
5853 the next available address within the memory region. If the combined
5854 output sections directed to a memory region are too large for the
5855 region, the linker will issue an error message.
5857 It is possible to access the origin and length of a memory in an
5858 expression via the @code{ORIGIN(@var{memory})} and
5859 @code{LENGTH(@var{memory})} functions:
5863 _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
5868 @section PHDRS Command
5870 @cindex program headers
5871 @cindex ELF program headers
5872 @cindex program segments
5873 @cindex segments, ELF
5874 The ELF object file format uses @dfn{program headers}, also knows as
5875 @dfn{segments}. The program headers describe how the program should be
5876 loaded into memory. You can print them out by using the @code{objdump}
5877 program with the @samp{-p} option.
5879 When you run an ELF program on a native ELF system, the system loader
5880 reads the program headers in order to figure out how to load the
5881 program. This will only work if the program headers are set correctly.
5882 This manual does not describe the details of how the system loader
5883 interprets program headers; for more information, see the ELF ABI.
5885 The linker will create reasonable program headers by default. However,
5886 in some cases, you may need to specify the program headers more
5887 precisely. You may use the @code{PHDRS} command for this purpose. When
5888 the linker sees the @code{PHDRS} command in the linker script, it will
5889 not create any program headers other than the ones specified.
5891 The linker only pays attention to the @code{PHDRS} command when
5892 generating an ELF output file. In other cases, the linker will simply
5893 ignore @code{PHDRS}.
5895 This is the syntax of the @code{PHDRS} command. The words @code{PHDRS},
5896 @code{FILEHDR}, @code{AT}, and @code{FLAGS} are keywords.
5902 @var{name} @var{type} [ FILEHDR ] [ PHDRS ] [ AT ( @var{address} ) ]
5903 [ FLAGS ( @var{flags} ) ] ;
5908 The @var{name} is used only for reference in the @code{SECTIONS} command
5909 of the linker script. It is not put into the output file. Program
5910 header names are stored in a separate name space, and will not conflict
5911 with symbol names, file names, or section names. Each program header
5912 must have a distinct name. The headers are processed in order and it
5913 is usual for them to map to sections in ascending load address order.
5915 Certain program header types describe segments of memory which the
5916 system loader will load from the file. In the linker script, you
5917 specify the contents of these segments by placing allocatable output
5918 sections in the segments. You use the @samp{:@var{phdr}} output section
5919 attribute to place a section in a particular segment. @xref{Output
5922 It is normal to put certain sections in more than one segment. This
5923 merely implies that one segment of memory contains another. You may
5924 repeat @samp{:@var{phdr}}, using it once for each segment which should
5925 contain the section.
5927 If you place a section in one or more segments using @samp{:@var{phdr}},
5928 then the linker will place all subsequent allocatable sections which do
5929 not specify @samp{:@var{phdr}} in the same segments. This is for
5930 convenience, since generally a whole set of contiguous sections will be
5931 placed in a single segment. You can use @code{:NONE} to override the
5932 default segment and tell the linker to not put the section in any
5937 You may use the @code{FILEHDR} and @code{PHDRS} keywords after
5938 the program header type to further describe the contents of the segment.
5939 The @code{FILEHDR} keyword means that the segment should include the ELF
5940 file header. The @code{PHDRS} keyword means that the segment should
5941 include the ELF program headers themselves. If applied to a loadable
5942 segment (@code{PT_LOAD}), all prior loadable segments must have one of
5945 The @var{type} may be one of the following. The numbers indicate the
5946 value of the keyword.
5949 @item @code{PT_NULL} (0)
5950 Indicates an unused program header.
5952 @item @code{PT_LOAD} (1)
5953 Indicates that this program header describes a segment to be loaded from
5956 @item @code{PT_DYNAMIC} (2)
5957 Indicates a segment where dynamic linking information can be found.
5959 @item @code{PT_INTERP} (3)
5960 Indicates a segment where the name of the program interpreter may be
5963 @item @code{PT_NOTE} (4)
5964 Indicates a segment holding note information.
5966 @item @code{PT_SHLIB} (5)
5967 A reserved program header type, defined but not specified by the ELF
5970 @item @code{PT_PHDR} (6)
5971 Indicates a segment where the program headers may be found.
5973 @item @code{PT_TLS} (7)
5974 Indicates a segment containing thread local storage.
5976 @item @var{expression}
5977 An expression giving the numeric type of the program header. This may
5978 be used for types not defined above.
5981 You can specify that a segment should be loaded at a particular address
5982 in memory by using an @code{AT} expression. This is identical to the
5983 @code{AT} command used as an output section attribute (@pxref{Output
5984 Section LMA}). The @code{AT} command for a program header overrides the
5985 output section attribute.
5987 The linker will normally set the segment flags based on the sections
5988 which comprise the segment. You may use the @code{FLAGS} keyword to
5989 explicitly specify the segment flags. The value of @var{flags} must be
5990 an integer. It is used to set the @code{p_flags} field of the program
5993 Here is an example of @code{PHDRS}. This shows a typical set of program
5994 headers used on a native ELF system.
6000 headers PT_PHDR PHDRS ;
6002 text PT_LOAD FILEHDR PHDRS ;
6004 dynamic PT_DYNAMIC ;
6010 .interp : @{ *(.interp) @} :text :interp
6011 .text : @{ *(.text) @} :text
6012 .rodata : @{ *(.rodata) @} /* defaults to :text */
6014 . = . + 0x1000; /* move to a new page in memory */
6015 .data : @{ *(.data) @} :data
6016 .dynamic : @{ *(.dynamic) @} :data :dynamic
6023 @section VERSION Command
6024 @kindex VERSION @{script text@}
6025 @cindex symbol versions
6026 @cindex version script
6027 @cindex versions of symbols
6028 The linker supports symbol versions when using ELF. Symbol versions are
6029 only useful when using shared libraries. The dynamic linker can use
6030 symbol versions to select a specific version of a function when it runs
6031 a program that may have been linked against an earlier version of the
6034 You can include a version script directly in the main linker script, or
6035 you can supply the version script as an implicit linker script. You can
6036 also use the @samp{--version-script} linker option.
6038 The syntax of the @code{VERSION} command is simply
6040 VERSION @{ version-script-commands @}
6043 The format of the version script commands is identical to that used by
6044 Sun's linker in Solaris 2.5. The version script defines a tree of
6045 version nodes. You specify the node names and interdependencies in the
6046 version script. You can specify which symbols are bound to which
6047 version nodes, and you can reduce a specified set of symbols to local
6048 scope so that they are not globally visible outside of the shared
6051 The easiest way to demonstrate the version script language is with a few
6077 This example version script defines three version nodes. The first
6078 version node defined is @samp{VERS_1.1}; it has no other dependencies.
6079 The script binds the symbol @samp{foo1} to @samp{VERS_1.1}. It reduces
6080 a number of symbols to local scope so that they are not visible outside
6081 of the shared library; this is done using wildcard patterns, so that any
6082 symbol whose name begins with @samp{old}, @samp{original}, or @samp{new}
6083 is matched. The wildcard patterns available are the same as those used
6084 in the shell when matching filenames (also known as ``globbing'').
6085 However, if you specify the symbol name inside double quotes, then the
6086 name is treated as literal, rather than as a glob pattern.
6088 Next, the version script defines node @samp{VERS_1.2}. This node
6089 depends upon @samp{VERS_1.1}. The script binds the symbol @samp{foo2}
6090 to the version node @samp{VERS_1.2}.
6092 Finally, the version script defines node @samp{VERS_2.0}. This node
6093 depends upon @samp{VERS_1.2}. The scripts binds the symbols @samp{bar1}
6094 and @samp{bar2} are bound to the version node @samp{VERS_2.0}.
6096 When the linker finds a symbol defined in a library which is not
6097 specifically bound to a version node, it will effectively bind it to an
6098 unspecified base version of the library. You can bind all otherwise
6099 unspecified symbols to a given version node by using @samp{global: *;}
6100 somewhere in the version script. Note that it's slightly crazy to use
6101 wildcards in a global spec except on the last version node. Global
6102 wildcards elsewhere run the risk of accidentally adding symbols to the
6103 set exported for an old version. That's wrong since older versions
6104 ought to have a fixed set of symbols.
6106 The names of the version nodes have no specific meaning other than what
6107 they might suggest to the person reading them. The @samp{2.0} version
6108 could just as well have appeared in between @samp{1.1} and @samp{1.2}.
6109 However, this would be a confusing way to write a version script.
6111 Node name can be omitted, provided it is the only version node
6112 in the version script. Such version script doesn't assign any versions to
6113 symbols, only selects which symbols will be globally visible out and which
6117 @{ global: foo; bar; local: *; @};
6120 When you link an application against a shared library that has versioned
6121 symbols, the application itself knows which version of each symbol it
6122 requires, and it also knows which version nodes it needs from each
6123 shared library it is linked against. Thus at runtime, the dynamic
6124 loader can make a quick check to make sure that the libraries you have
6125 linked against do in fact supply all of the version nodes that the
6126 application will need to resolve all of the dynamic symbols. In this
6127 way it is possible for the dynamic linker to know with certainty that
6128 all external symbols that it needs will be resolvable without having to
6129 search for each symbol reference.
6131 The symbol versioning is in effect a much more sophisticated way of
6132 doing minor version checking that SunOS does. The fundamental problem
6133 that is being addressed here is that typically references to external
6134 functions are bound on an as-needed basis, and are not all bound when
6135 the application starts up. If a shared library is out of date, a
6136 required interface may be missing; when the application tries to use
6137 that interface, it may suddenly and unexpectedly fail. With symbol
6138 versioning, the user will get a warning when they start their program if
6139 the libraries being used with the application are too old.
6141 There are several GNU extensions to Sun's versioning approach. The
6142 first of these is the ability to bind a symbol to a version node in the
6143 source file where the symbol is defined instead of in the versioning
6144 script. This was done mainly to reduce the burden on the library
6145 maintainer. You can do this by putting something like:
6147 __asm__(".symver original_foo,foo@@VERS_1.1");
6150 in the C source file. This renames the function @samp{original_foo} to
6151 be an alias for @samp{foo} bound to the version node @samp{VERS_1.1}.
6152 The @samp{local:} directive can be used to prevent the symbol
6153 @samp{original_foo} from being exported. A @samp{.symver} directive
6154 takes precedence over a version script.
6156 The second GNU extension is to allow multiple versions of the same
6157 function to appear in a given shared library. In this way you can make
6158 an incompatible change to an interface without increasing the major
6159 version number of the shared library, while still allowing applications
6160 linked against the old interface to continue to function.
6162 To do this, you must use multiple @samp{.symver} directives in the
6163 source file. Here is an example:
6166 __asm__(".symver original_foo,foo@@");
6167 __asm__(".symver old_foo,foo@@VERS_1.1");
6168 __asm__(".symver old_foo1,foo@@VERS_1.2");
6169 __asm__(".symver new_foo,foo@@@@VERS_2.0");
6172 In this example, @samp{foo@@} represents the symbol @samp{foo} bound to the
6173 unspecified base version of the symbol. The source file that contains this
6174 example would define 4 C functions: @samp{original_foo}, @samp{old_foo},
6175 @samp{old_foo1}, and @samp{new_foo}.
6177 When you have multiple definitions of a given symbol, there needs to be
6178 some way to specify a default version to which external references to
6179 this symbol will be bound. You can do this with the
6180 @samp{foo@@@@VERS_2.0} type of @samp{.symver} directive. You can only
6181 declare one version of a symbol as the default in this manner; otherwise
6182 you would effectively have multiple definitions of the same symbol.
6184 If you wish to bind a reference to a specific version of the symbol
6185 within the shared library, you can use the aliases of convenience
6186 (i.e., @samp{old_foo}), or you can use the @samp{.symver} directive to
6187 specifically bind to an external version of the function in question.
6189 You can also specify the language in the version script:
6192 VERSION extern "lang" @{ version-script-commands @}
6195 The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
6196 The linker will iterate over the list of symbols at the link time and
6197 demangle them according to @samp{lang} before matching them to the
6198 patterns specified in @samp{version-script-commands}. The default
6199 @samp{lang} is @samp{C}.
6201 Demangled names may contains spaces and other special characters. As
6202 described above, you can use a glob pattern to match demangled names,
6203 or you can use a double-quoted string to match the string exactly. In
6204 the latter case, be aware that minor differences (such as differing
6205 whitespace) between the version script and the demangler output will
6206 cause a mismatch. As the exact string generated by the demangler
6207 might change in the future, even if the mangled name does not, you
6208 should check that all of your version directives are behaving as you
6209 expect when you upgrade.
6212 @section Expressions in Linker Scripts
6215 The syntax for expressions in the linker script language is identical to
6216 that of C expressions. All expressions are evaluated as integers. All
6217 expressions are evaluated in the same size, which is 32 bits if both the
6218 host and target are 32 bits, and is otherwise 64 bits.
6220 You can use and set symbol values in expressions.
6222 The linker defines several special purpose builtin functions for use in
6226 * Constants:: Constants
6227 * Symbolic Constants:: Symbolic constants
6228 * Symbols:: Symbol Names
6229 * Orphan Sections:: Orphan Sections
6230 * Location Counter:: The Location Counter
6231 * Operators:: Operators
6232 * Evaluation:: Evaluation
6233 * Expression Section:: The Section of an Expression
6234 * Builtin Functions:: Builtin Functions
6238 @subsection Constants
6239 @cindex integer notation
6240 @cindex constants in linker scripts
6241 All constants are integers.
6243 As in C, the linker considers an integer beginning with @samp{0} to be
6244 octal, and an integer beginning with @samp{0x} or @samp{0X} to be
6245 hexadecimal. Alternatively the linker accepts suffixes of @samp{h} or
6246 @samp{H} for hexadecimal, @samp{o} or @samp{O} for octal, @samp{b} or
6247 @samp{B} for binary and @samp{d} or @samp{D} for decimal. Any integer
6248 value without a prefix or a suffix is considered to be decimal.
6250 @cindex scaled integers
6251 @cindex K and M integer suffixes
6252 @cindex M and K integer suffixes
6253 @cindex suffixes for integers
6254 @cindex integer suffixes
6255 In addition, you can use the suffixes @code{K} and @code{M} to scale a
6259 @c END TEXI2ROFF-KILL
6260 @code{1024} or @code{1024*1024}
6264 ${\rm 1024}$ or ${\rm 1024}^2$
6266 @c END TEXI2ROFF-KILL
6267 respectively. For example, the following
6268 all refer to the same quantity:
6277 Note - the @code{K} and @code{M} suffixes cannot be used in
6278 conjunction with the base suffixes mentioned above.
6280 @node Symbolic Constants
6281 @subsection Symbolic Constants
6282 @cindex symbolic constants
6284 It is possible to refer to target-specific constants via the use of
6285 the @code{CONSTANT(@var{name})} operator, where @var{name} is one of:
6290 The target's maximum page size.
6292 @item COMMONPAGESIZE
6293 @kindex COMMONPAGESIZE
6294 The target's default page size.
6300 .text ALIGN (CONSTANT (MAXPAGESIZE)) : @{ *(.text) @}
6303 will create a text section aligned to the largest page boundary
6304 supported by the target.
6307 @subsection Symbol Names
6308 @cindex symbol names
6310 @cindex quoted symbol names
6312 Unless quoted, symbol names start with a letter, underscore, or period
6313 and may include letters, digits, underscores, periods, and hyphens.
6314 Unquoted symbol names must not conflict with any keywords. You can
6315 specify a symbol which contains odd characters or has the same name as a
6316 keyword by surrounding the symbol name in double quotes:
6319 "with a space" = "also with a space" + 10;
6322 Since symbols can contain many non-alphabetic characters, it is safest
6323 to delimit symbols with spaces. For example, @samp{A-B} is one symbol,
6324 whereas @samp{A - B} is an expression involving subtraction.
6326 @node Orphan Sections
6327 @subsection Orphan Sections
6329 Orphan sections are sections present in the input files which
6330 are not explicitly placed into the output file by the linker
6331 script. The linker will still copy these sections into the
6332 output file by either finding, or creating a suitable output section
6333 in which to place the orphaned input section.
6335 If the name of an orphaned input section exactly matches the name of
6336 an existing output section, then the orphaned input section will be
6337 placed at the end of that output section.
6339 If there is no output section with a matching name then new output
6340 sections will be created. Each new output section will have the same
6341 name as the orphan section placed within it. If there are multiple
6342 orphan sections with the same name, these will all be combined into
6343 one new output section.
6345 If new output sections are created to hold orphaned input sections,
6346 then the linker must decide where to place these new output sections
6347 in relation to existing output sections. On most modern targets, the
6348 linker attempts to place orphan sections after sections of the same
6349 attribute, such as code vs data, loadable vs non-loadable, etc. If no
6350 sections with matching attributes are found, or your target lacks this
6351 support, the orphan section is placed at the end of the file.
6353 The command-line options @samp{--orphan-handling} and @samp{--unique}
6354 (@pxref{Options,,Command-line Options}) can be used to control which
6355 output sections an orphan is placed in.
6357 @node Location Counter
6358 @subsection The Location Counter
6361 @cindex location counter
6362 @cindex current output location
6363 The special linker variable @dfn{dot} @samp{.} always contains the
6364 current output location counter. Since the @code{.} always refers to a
6365 location in an output section, it may only appear in an expression
6366 within a @code{SECTIONS} command. The @code{.} symbol may appear
6367 anywhere that an ordinary symbol is allowed in an expression.
6370 Assigning a value to @code{.} will cause the location counter to be
6371 moved. This may be used to create holes in the output section. The
6372 location counter may not be moved backwards inside an output section,
6373 and may not be moved backwards outside of an output section if so
6374 doing creates areas with overlapping LMAs.
6390 In the previous example, the @samp{.text} section from @file{file1} is
6391 located at the beginning of the output section @samp{output}. It is
6392 followed by a 1000 byte gap. Then the @samp{.text} section from
6393 @file{file2} appears, also with a 1000 byte gap following before the
6394 @samp{.text} section from @file{file3}. The notation @samp{= 0x12345678}
6395 specifies what data to write in the gaps (@pxref{Output Section Fill}).
6397 @cindex dot inside sections
6398 Note: @code{.} actually refers to the byte offset from the start of the
6399 current containing object. Normally this is the @code{SECTIONS}
6400 statement, whose start address is 0, hence @code{.} can be used as an
6401 absolute address. If @code{.} is used inside a section description
6402 however, it refers to the byte offset from the start of that section,
6403 not an absolute address. Thus in a script like this:
6421 The @samp{.text} section will be assigned a starting address of 0x100
6422 and a size of exactly 0x200 bytes, even if there is not enough data in
6423 the @samp{.text} input sections to fill this area. (If there is too
6424 much data, an error will be produced because this would be an attempt to
6425 move @code{.} backwards). The @samp{.data} section will start at 0x500
6426 and it will have an extra 0x600 bytes worth of space after the end of
6427 the values from the @samp{.data} input sections and before the end of
6428 the @samp{.data} output section itself.
6430 @cindex dot outside sections
6431 Setting symbols to the value of the location counter outside of an
6432 output section statement can result in unexpected values if the linker
6433 needs to place orphan sections. For example, given the following:
6439 .text: @{ *(.text) @}
6443 .data: @{ *(.data) @}
6448 If the linker needs to place some input section, e.g. @code{.rodata},
6449 not mentioned in the script, it might choose to place that section
6450 between @code{.text} and @code{.data}. You might think the linker
6451 should place @code{.rodata} on the blank line in the above script, but
6452 blank lines are of no particular significance to the linker. As well,
6453 the linker doesn't associate the above symbol names with their
6454 sections. Instead, it assumes that all assignments or other
6455 statements belong to the previous output section, except for the
6456 special case of an assignment to @code{.}. I.e., the linker will
6457 place the orphan @code{.rodata} section as if the script was written
6464 .text: @{ *(.text) @}
6468 .rodata: @{ *(.rodata) @}
6469 .data: @{ *(.data) @}
6474 This may or may not be the script author's intention for the value of
6475 @code{start_of_data}. One way to influence the orphan section
6476 placement is to assign the location counter to itself, as the linker
6477 assumes that an assignment to @code{.} is setting the start address of
6478 a following output section and thus should be grouped with that
6479 section. So you could write:
6485 .text: @{ *(.text) @}
6490 .data: @{ *(.data) @}
6495 Now, the orphan @code{.rodata} section will be placed between
6496 @code{end_of_text} and @code{start_of_data}.
6500 @subsection Operators
6501 @cindex operators for arithmetic
6502 @cindex arithmetic operators
6503 @cindex precedence in expressions
6504 The linker recognizes the standard C set of arithmetic operators, with
6505 the standard bindings and precedence levels:
6508 @c END TEXI2ROFF-KILL
6510 precedence associativity Operators Notes
6516 5 left == != > < <= >=
6522 11 right &= += -= *= /= (2)
6526 (1) Prefix operators
6527 (2) @xref{Assignments}.
6531 \vskip \baselineskip
6532 %"lispnarrowing" is the extra indent used generally for smallexample
6533 \hskip\lispnarrowing\vbox{\offinterlineskip
6536 {\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ {\tt #}\ \hfil&\vrule#\cr
6537 height2pt&\omit&&\omit&&\omit&\cr
6538 &Precedence&& Associativity &&{\rm Operators}&\cr
6539 height2pt&\omit&&\omit&&\omit&\cr
6541 height2pt&\omit&&\omit&&\omit&\cr
6543 % '176 is tilde, '~' in tt font
6544 &1&&left&&\qquad- \char'176\ !\qquad\dag&\cr
6545 &2&&left&&* / \%&\cr
6548 &5&&left&&== != > < <= >=&\cr
6551 &8&&left&&{\&\&}&\cr
6554 &11&&right&&\qquad\&= += -= *= /=\qquad\ddag&\cr
6556 height2pt&\omit&&\omit&&\omit&\cr}
6561 @obeylines@parskip=0pt@parindent=0pt
6562 @dag@quad Prefix operators.
6563 @ddag@quad @xref{Assignments}.
6566 @c END TEXI2ROFF-KILL
6569 @subsection Evaluation
6570 @cindex lazy evaluation
6571 @cindex expression evaluation order
6572 The linker evaluates expressions lazily. It only computes the value of
6573 an expression when absolutely necessary.
6575 The linker needs some information, such as the value of the start
6576 address of the first section, and the origins and lengths of memory
6577 regions, in order to do any linking at all. These values are computed
6578 as soon as possible when the linker reads in the linker script.
6580 However, other values (such as symbol values) are not known or needed
6581 until after storage allocation. Such values are evaluated later, when
6582 other information (such as the sizes of output sections) is available
6583 for use in the symbol assignment expression.
6585 The sizes of sections cannot be known until after allocation, so
6586 assignments dependent upon these are not performed until after
6589 Some expressions, such as those depending upon the location counter
6590 @samp{.}, must be evaluated during section allocation.
6592 If the result of an expression is required, but the value is not
6593 available, then an error results. For example, a script like the
6599 .text 9+this_isnt_constant :
6605 will cause the error message @samp{non constant expression for initial
6608 @node Expression Section
6609 @subsection The Section of an Expression
6610 @cindex expression sections
6611 @cindex absolute expressions
6612 @cindex relative expressions
6613 @cindex absolute and relocatable symbols
6614 @cindex relocatable and absolute symbols
6615 @cindex symbols, relocatable and absolute
6616 Addresses and symbols may be section relative, or absolute. A section
6617 relative symbol is relocatable. If you request relocatable output
6618 using the @samp{-r} option, a further link operation may change the
6619 value of a section relative symbol. On the other hand, an absolute
6620 symbol will retain the same value throughout any further link
6623 Some terms in linker expressions are addresses. This is true of
6624 section relative symbols and for builtin functions that return an
6625 address, such as @code{ADDR}, @code{LOADADDR}, @code{ORIGIN} and
6626 @code{SEGMENT_START}. Other terms are simply numbers, or are builtin
6627 functions that return a non-address value, such as @code{LENGTH}.
6628 One complication is that unless you set @code{LD_FEATURE ("SANE_EXPR")}
6629 (@pxref{Miscellaneous Commands}), numbers and absolute symbols are treated
6630 differently depending on their location, for compatibility with older
6631 versions of @code{ld}. Expressions appearing outside an output
6632 section definition treat all numbers as absolute addresses.
6633 Expressions appearing inside an output section definition treat
6634 absolute symbols as numbers. If @code{LD_FEATURE ("SANE_EXPR")} is
6635 given, then absolute symbols and numbers are simply treated as numbers
6638 In the following simple example,
6645 __executable_start = 0x100;
6649 __data_start = 0x10;
6657 both @code{.} and @code{__executable_start} are set to the absolute
6658 address 0x100 in the first two assignments, then both @code{.} and
6659 @code{__data_start} are set to 0x10 relative to the @code{.data}
6660 section in the second two assignments.
6662 For expressions involving numbers, relative addresses and absolute
6663 addresses, ld follows these rules to evaluate terms:
6667 Unary operations on an absolute address or number, and binary
6668 operations on two absolute addresses or two numbers, or between one
6669 absolute address and a number, apply the operator to the value(s).
6671 Unary operations on a relative address, and binary operations on two
6672 relative addresses in the same section or between one relative address
6673 and a number, apply the operator to the offset part of the address(es).
6675 Other binary operations, that is, between two relative addresses not
6676 in the same section, or between a relative address and an absolute
6677 address, first convert any non-absolute term to an absolute address
6678 before applying the operator.
6681 The result section of each sub-expression is as follows:
6685 An operation involving only numbers results in a number.
6687 The result of comparisons, @samp{&&} and @samp{||} is also a number.
6689 The result of other binary arithmetic and logical operations on two
6690 relative addresses in the same section or two absolute addresses
6691 (after above conversions) is also a number when
6692 @code{LD_FEATURE ("SANE_EXPR")} or inside an output section definition
6693 but an absolute address otherwise.
6695 The result of other operations on relative addresses or one
6696 relative address and a number, is a relative address in the same
6697 section as the relative operand(s).
6699 The result of other operations on absolute addresses (after above
6700 conversions) is an absolute address.
6703 You can use the builtin function @code{ABSOLUTE} to force an expression
6704 to be absolute when it would otherwise be relative. For example, to
6705 create an absolute symbol set to the address of the end of the output
6706 section @samp{.data}:
6710 .data : @{ *(.data) _edata = ABSOLUTE(.); @}
6714 If @samp{ABSOLUTE} were not used, @samp{_edata} would be relative to the
6715 @samp{.data} section.
6717 Using @code{LOADADDR} also forces an expression absolute, since this
6718 particular builtin function returns an absolute address.
6720 @node Builtin Functions
6721 @subsection Builtin Functions
6722 @cindex functions in expressions
6723 The linker script language includes a number of builtin functions for
6724 use in linker script expressions.
6727 @item ABSOLUTE(@var{exp})
6728 @kindex ABSOLUTE(@var{exp})
6729 @cindex expression, absolute
6730 Return the absolute (non-relocatable, as opposed to non-negative) value
6731 of the expression @var{exp}. Primarily useful to assign an absolute
6732 value to a symbol within a section definition, where symbol values are
6733 normally section relative. @xref{Expression Section}.
6735 @item ADDR(@var{section})
6736 @kindex ADDR(@var{section})
6737 @cindex section address in expression
6738 Return the address (VMA) of the named @var{section}. Your
6739 script must previously have defined the location of that section. In
6740 the following example, @code{start_of_output_1}, @code{symbol_1} and
6741 @code{symbol_2} are assigned equivalent values, except that
6742 @code{symbol_1} will be relative to the @code{.output1} section while
6743 the other two will be absolute:
6749 start_of_output_1 = ABSOLUTE(.);
6754 symbol_1 = ADDR(.output1);
6755 symbol_2 = start_of_output_1;
6761 @item ALIGN(@var{align})
6762 @itemx ALIGN(@var{exp},@var{align})
6763 @kindex ALIGN(@var{align})
6764 @kindex ALIGN(@var{exp},@var{align})
6765 @cindex round up location counter
6766 @cindex align location counter
6767 @cindex round up expression
6768 @cindex align expression
6769 Return the location counter (@code{.}) or arbitrary expression aligned
6770 to the next @var{align} boundary. The single operand @code{ALIGN}
6771 doesn't change the value of the location counter---it just does
6772 arithmetic on it. The two operand @code{ALIGN} allows an arbitrary
6773 expression to be aligned upwards (@code{ALIGN(@var{align})} is
6774 equivalent to @code{ALIGN(ABSOLUTE(.), @var{align})}).
6776 Here is an example which aligns the output @code{.data} section to the
6777 next @code{0x2000} byte boundary after the preceding section and sets a
6778 variable within the section to the next @code{0x8000} boundary after the
6783 .data ALIGN(0x2000): @{
6785 variable = ALIGN(0x8000);
6791 The first use of @code{ALIGN} in this example specifies the location of
6792 a section because it is used as the optional @var{address} attribute of
6793 a section definition (@pxref{Output Section Address}). The second use
6794 of @code{ALIGN} is used to defines the value of a symbol.
6796 The builtin function @code{NEXT} is closely related to @code{ALIGN}.
6798 @item ALIGNOF(@var{section})
6799 @kindex ALIGNOF(@var{section})
6800 @cindex section alignment
6801 Return the alignment in bytes of the named @var{section}, if that section has
6802 been allocated. If the section has not been allocated when this is
6803 evaluated, the linker will report an error. In the following example,
6804 the alignment of the @code{.output} section is stored as the first
6805 value in that section.
6810 LONG (ALIGNOF (.output))
6817 @item BLOCK(@var{exp})
6818 @kindex BLOCK(@var{exp})
6819 This is a synonym for @code{ALIGN}, for compatibility with older linker
6820 scripts. It is most often seen when setting the address of an output
6823 @item DATA_SEGMENT_ALIGN(@var{maxpagesize}, @var{commonpagesize})
6824 @kindex DATA_SEGMENT_ALIGN(@var{maxpagesize}, @var{commonpagesize})
6825 This is equivalent to either
6827 (ALIGN(@var{maxpagesize}) + (. & (@var{maxpagesize} - 1)))
6831 (ALIGN(@var{maxpagesize})
6832 + ((. + @var{commonpagesize} - 1) & (@var{maxpagesize} - @var{commonpagesize})))
6835 depending on whether the latter uses fewer @var{commonpagesize} sized pages
6836 for the data segment (area between the result of this expression and
6837 @code{DATA_SEGMENT_END}) than the former or not.
6838 If the latter form is used, it means @var{commonpagesize} bytes of runtime
6839 memory will be saved at the expense of up to @var{commonpagesize} wasted
6840 bytes in the on-disk file.
6842 This expression can only be used directly in @code{SECTIONS} commands, not in
6843 any output section descriptions and only once in the linker script.
6844 @var{commonpagesize} should be less or equal to @var{maxpagesize} and should
6845 be the system page size the object wants to be optimized for while still
6846 running on system page sizes up to @var{maxpagesize}. Note however
6847 that @samp{-z relro} protection will not be effective if the system
6848 page size is larger than @var{commonpagesize}.
6853 . = DATA_SEGMENT_ALIGN(0x10000, 0x2000);
6856 @item DATA_SEGMENT_END(@var{exp})
6857 @kindex DATA_SEGMENT_END(@var{exp})
6858 This defines the end of data segment for @code{DATA_SEGMENT_ALIGN}
6859 evaluation purposes.
6862 . = DATA_SEGMENT_END(.);
6865 @item DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
6866 @kindex DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
6867 This defines the end of the @code{PT_GNU_RELRO} segment when
6868 @samp{-z relro} option is used.
6869 When @samp{-z relro} option is not present, @code{DATA_SEGMENT_RELRO_END}
6870 does nothing, otherwise @code{DATA_SEGMENT_ALIGN} is padded so that
6871 @var{exp} + @var{offset} is aligned to the @var{commonpagesize}
6872 argument given to @code{DATA_SEGMENT_ALIGN}. If present in the linker
6873 script, it must be placed between @code{DATA_SEGMENT_ALIGN} and
6874 @code{DATA_SEGMENT_END}. Evaluates to the second argument plus any
6875 padding needed at the end of the @code{PT_GNU_RELRO} segment due to
6879 . = DATA_SEGMENT_RELRO_END(24, .);
6882 @item DEFINED(@var{symbol})
6883 @kindex DEFINED(@var{symbol})
6884 @cindex symbol defaults
6885 Return 1 if @var{symbol} is in the linker global symbol table and is
6886 defined before the statement using DEFINED in the script, otherwise
6887 return 0. You can use this function to provide
6888 default values for symbols. For example, the following script fragment
6889 shows how to set a global symbol @samp{begin} to the first location in
6890 the @samp{.text} section---but if a symbol called @samp{begin} already
6891 existed, its value is preserved:
6897 begin = DEFINED(begin) ? begin : . ;
6905 @item LENGTH(@var{memory})
6906 @kindex LENGTH(@var{memory})
6907 Return the length of the memory region named @var{memory}.
6909 @item LOADADDR(@var{section})
6910 @kindex LOADADDR(@var{section})
6911 @cindex section load address in expression
6912 Return the absolute LMA of the named @var{section}. (@pxref{Output
6915 @item LOG2CEIL(@var{exp})
6916 @kindex LOG2CEIL(@var{exp})
6917 Return the binary logarithm of @var{exp} rounded towards infinity.
6918 @code{LOG2CEIL(0)} returns 0.
6921 @item MAX(@var{exp1}, @var{exp2})
6922 Returns the maximum of @var{exp1} and @var{exp2}.
6925 @item MIN(@var{exp1}, @var{exp2})
6926 Returns the minimum of @var{exp1} and @var{exp2}.
6928 @item NEXT(@var{exp})
6929 @kindex NEXT(@var{exp})
6930 @cindex unallocated address, next
6931 Return the next unallocated address that is a multiple of @var{exp}.
6932 This function is closely related to @code{ALIGN(@var{exp})}; unless you
6933 use the @code{MEMORY} command to define discontinuous memory for the
6934 output file, the two functions are equivalent.
6936 @item ORIGIN(@var{memory})
6937 @kindex ORIGIN(@var{memory})
6938 Return the origin of the memory region named @var{memory}.
6940 @item SEGMENT_START(@var{segment}, @var{default})
6941 @kindex SEGMENT_START(@var{segment}, @var{default})
6942 Return the base address of the named @var{segment}. If an explicit
6943 value has already been given for this segment (with a command-line
6944 @samp{-T} option) then that value will be returned otherwise the value
6945 will be @var{default}. At present, the @samp{-T} command-line option
6946 can only be used to set the base address for the ``text'', ``data'', and
6947 ``bss'' sections, but you can use @code{SEGMENT_START} with any segment
6950 @item SIZEOF(@var{section})
6951 @kindex SIZEOF(@var{section})
6952 @cindex section size
6953 Return the size in bytes of the named @var{section}, if that section has
6954 been allocated. If the section has not been allocated when this is
6955 evaluated, the linker will report an error. In the following example,
6956 @code{symbol_1} and @code{symbol_2} are assigned identical values:
6965 symbol_1 = .end - .start ;
6966 symbol_2 = SIZEOF(.output);
6971 @item SIZEOF_HEADERS
6972 @itemx sizeof_headers
6973 @kindex SIZEOF_HEADERS
6975 Return the size in bytes of the output file's headers. This is
6976 information which appears at the start of the output file. You can use
6977 this number when setting the start address of the first section, if you
6978 choose, to facilitate paging.
6980 @cindex not enough room for program headers
6981 @cindex program headers, not enough room
6982 When producing an ELF output file, if the linker script uses the
6983 @code{SIZEOF_HEADERS} builtin function, the linker must compute the
6984 number of program headers before it has determined all the section
6985 addresses and sizes. If the linker later discovers that it needs
6986 additional program headers, it will report an error @samp{not enough
6987 room for program headers}. To avoid this error, you must avoid using
6988 the @code{SIZEOF_HEADERS} function, or you must rework your linker
6989 script to avoid forcing the linker to use additional program headers, or
6990 you must define the program headers yourself using the @code{PHDRS}
6991 command (@pxref{PHDRS}).
6994 @node Implicit Linker Scripts
6995 @section Implicit Linker Scripts
6996 @cindex implicit linker scripts
6997 If you specify a linker input file which the linker can not recognize as
6998 an object file or an archive file, it will try to read the file as a
6999 linker script. If the file can not be parsed as a linker script, the
7000 linker will report an error.
7002 An implicit linker script will not replace the default linker script.
7004 Typically an implicit linker script would contain only symbol
7005 assignments, or the @code{INPUT}, @code{GROUP}, or @code{VERSION}
7008 Any input files read because of an implicit linker script will be read
7009 at the position in the command line where the implicit linker script was
7010 read. This can affect archive searching.
7013 @chapter Linker Plugins
7016 @cindex linker plugins
7017 The linker can use dynamically loaded plugins to modify its behavior.
7018 For example, the link-time optimization feature that some compilers
7019 support is implemented with a linker plugin.
7021 Currently there is only one plugin shipped by default, but more may
7022 be added here later.
7025 * libdep Plugin:: Static Library Dependencies Plugin
7029 @section Static Library Dependencies Plugin
7030 @cindex static library dependencies
7031 Originally, static libraries were contained in an archive file consisting
7032 just of a collection of relocatable object files. Later they evolved to
7033 optionally include a symbol table, to assist in finding the needed objects
7034 within a library. There their evolution ended, and dynamic libraries
7037 One useful feature of dynamic libraries was that, more than just collecting
7038 multiple objects into a single file, they also included a list of their
7039 dependencies, such that one could specify just the name of a single dynamic
7040 library at link time, and all of its dependencies would be implicitly
7041 referenced as well. But static libraries lacked this feature, so if a
7042 link invocation was switched from using dynamic libraries to static
7043 libraries, the link command would usually fail unless it was rewritten to
7044 explicitly list the dependencies of the static library.
7046 The GNU @command{ar} utility now supports a @option{--record-libdeps} option
7047 to embed dependency lists into static libraries as well, and the @file{libdep}
7048 plugin may be used to read this dependency information at link time. The
7049 dependency information is stored as a single string, carrying @option{-l}
7050 and @option{-L} arguments as they would normally appear in a linker
7051 command line. As such, the information can be written with any text
7052 utility and stored into any archive, even if GNU @command{ar} is not
7053 being used to create the archive. The information is stored in an
7054 archive member named @samp{__.LIBDEP}.
7056 For example, given a library @file{libssl.a} that depends on another
7057 library @file{libcrypto.a} which may be found in @file{/usr/local/lib},
7058 the @samp{__.LIBDEP} member of @file{libssl.a} would contain
7061 -L/usr/local/lib -lcrypto
7065 @node Machine Dependent
7066 @chapter Machine Dependent Features
7068 @cindex machine dependencies
7069 @command{ld} has additional features on some platforms; the following
7070 sections describe them. Machines where @command{ld} has no additional
7071 functionality are not listed.
7075 * H8/300:: @command{ld} and the H8/300
7078 * M68HC11/68HC12:: @code{ld} and the Motorola 68HC11 and 68HC12 families
7081 * ARM:: @command{ld} and the ARM family
7084 * HPPA ELF32:: @command{ld} and HPPA 32-bit ELF
7087 * M68K:: @command{ld} and the Motorola 68K family
7090 * MIPS:: @command{ld} and the MIPS family
7093 * MMIX:: @command{ld} and MMIX
7096 * MSP430:: @command{ld} and MSP430
7099 * NDS32:: @command{ld} and NDS32
7102 * Nios II:: @command{ld} and the Altera Nios II
7105 * PowerPC ELF32:: @command{ld} and PowerPC 32-bit ELF Support
7108 * PowerPC64 ELF64:: @command{ld} and PowerPC64 64-bit ELF Support
7111 * S/390 ELF:: @command{ld} and S/390 ELF Support
7114 * SPU ELF:: @command{ld} and SPU ELF Support
7117 * TI COFF:: @command{ld} and TI COFF
7120 * WIN32:: @command{ld} and WIN32 (cygwin/mingw)
7123 * Xtensa:: @command{ld} and Xtensa Processors
7134 @section @command{ld} and the H8/300
7136 @cindex H8/300 support
7137 For the H8/300, @command{ld} can perform these global optimizations when
7138 you specify the @samp{--relax} command-line option.
7141 @cindex relaxing on H8/300
7142 @item relaxing address modes
7143 @command{ld} finds all @code{jsr} and @code{jmp} instructions whose
7144 targets are within eight bits, and turns them into eight-bit
7145 program-counter relative @code{bsr} and @code{bra} instructions,
7148 @cindex synthesizing on H8/300
7149 @item synthesizing instructions
7150 @c FIXME: specifically mov.b, or any mov instructions really? -> mov.b only, at least on H8, H8H, H8S
7151 @command{ld} finds all @code{mov.b} instructions which use the
7152 sixteen-bit absolute address form, but refer to the top
7153 page of memory, and changes them to use the eight-bit address form.
7154 (That is: the linker turns @samp{mov.b @code{@@}@var{aa}:16} into
7155 @samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the
7156 top page of memory).
7158 @command{ld} finds all @code{mov} instructions which use the register
7159 indirect with 32-bit displacement addressing mode, but use a small
7160 displacement inside 16-bit displacement range, and changes them to use
7161 the 16-bit displacement form. (That is: the linker turns @samp{mov.b
7162 @code{@@}@var{d}:32,ERx} into @samp{mov.b @code{@@}@var{d}:16,ERx}
7163 whenever the displacement @var{d} is in the 16 bit signed integer
7164 range. Only implemented in ELF-format ld).
7166 @item bit manipulation instructions
7167 @command{ld} finds all bit manipulation instructions like @code{band, bclr,
7168 biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor}
7169 which use 32 bit and 16 bit absolute address form, but refer to the top
7170 page of memory, and changes them to use the 8 bit address form.
7171 (That is: the linker turns @samp{bset #xx:3,@code{@@}@var{aa}:32} into
7172 @samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
7173 the top page of memory).
7175 @item system control instructions
7176 @command{ld} finds all @code{ldc.w, stc.w} instructions which use the
7177 32 bit absolute address form, but refer to the top page of memory, and
7178 changes them to use 16 bit address form.
7179 (That is: the linker turns @samp{ldc.w @code{@@}@var{aa}:32,ccr} into
7180 @samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
7181 the top page of memory).
7191 @c This stuff is pointless to say unless you're especially concerned
7192 @c with Renesas chips; don't enable it for generic case, please.
7194 @chapter @command{ld} and Other Renesas Chips
7196 @command{ld} also supports the Renesas (formerly Hitachi) H8/300H,
7197 H8/500, and SH chips. No special features, commands, or command-line
7198 options are required for these chips.
7212 @node M68HC11/68HC12
7213 @section @command{ld} and the Motorola 68HC11 and 68HC12 families
7215 @cindex M68HC11 and 68HC12 support
7217 @subsection Linker Relaxation
7219 For the Motorola 68HC11, @command{ld} can perform these global
7220 optimizations when you specify the @samp{--relax} command-line option.
7223 @cindex relaxing on M68HC11
7224 @item relaxing address modes
7225 @command{ld} finds all @code{jsr} and @code{jmp} instructions whose
7226 targets are within eight bits, and turns them into eight-bit
7227 program-counter relative @code{bsr} and @code{bra} instructions,
7230 @command{ld} also looks at all 16-bit extended addressing modes and
7231 transforms them in a direct addressing mode when the address is in
7232 page 0 (between 0 and 0x0ff).
7234 @item relaxing gcc instruction group
7235 When @command{gcc} is called with @option{-mrelax}, it can emit group
7236 of instructions that the linker can optimize to use a 68HC11 direct
7237 addressing mode. These instructions consists of @code{bclr} or
7238 @code{bset} instructions.
7242 @subsection Trampoline Generation
7244 @cindex trampoline generation on M68HC11
7245 @cindex trampoline generation on M68HC12
7246 For 68HC11 and 68HC12, @command{ld} can generate trampoline code to
7247 call a far function using a normal @code{jsr} instruction. The linker
7248 will also change the relocation to some far function to use the
7249 trampoline address instead of the function address. This is typically the
7250 case when a pointer to a function is taken. The pointer will in fact
7251 point to the function trampoline.
7259 @section @command{ld} and the ARM family
7261 @cindex ARM interworking support
7262 @kindex --support-old-code
7263 For the ARM, @command{ld} will generate code stubs to allow functions calls
7264 between ARM and Thumb code. These stubs only work with code that has
7265 been compiled and assembled with the @samp{-mthumb-interwork} command
7266 line option. If it is necessary to link with old ARM object files or
7267 libraries, which have not been compiled with the -mthumb-interwork
7268 option then the @samp{--support-old-code} command-line switch should be
7269 given to the linker. This will make it generate larger stub functions
7270 which will work with non-interworking aware ARM code. Note, however,
7271 the linker does not support generating stubs for function calls to
7272 non-interworking aware Thumb code.
7274 @cindex thumb entry point
7275 @cindex entry point, thumb
7276 @kindex --thumb-entry=@var{entry}
7277 The @samp{--thumb-entry} switch is a duplicate of the generic
7278 @samp{--entry} switch, in that it sets the program's starting address.
7279 But it also sets the bottom bit of the address, so that it can be
7280 branched to using a BX instruction, and the program will start
7281 executing in Thumb mode straight away.
7283 @cindex PE import table prefixing
7284 @kindex --use-nul-prefixed-import-tables
7285 The @samp{--use-nul-prefixed-import-tables} switch is specifying, that
7286 the import tables idata4 and idata5 have to be generated with a zero
7287 element prefix for import libraries. This is the old style to generate
7288 import tables. By default this option is turned off.
7292 The @samp{--be8} switch instructs @command{ld} to generate BE8 format
7293 executables. This option is only valid when linking big-endian
7294 objects - ie ones which have been assembled with the @option{-EB}
7295 option. The resulting image will contain big-endian data and
7299 @kindex --target1-rel
7300 @kindex --target1-abs
7301 The @samp{R_ARM_TARGET1} relocation is typically used for entries in the
7302 @samp{.init_array} section. It is interpreted as either @samp{R_ARM_REL32}
7303 or @samp{R_ARM_ABS32}, depending on the target. The @samp{--target1-rel}
7304 and @samp{--target1-abs} switches override the default.
7307 @kindex --target2=@var{type}
7308 The @samp{--target2=type} switch overrides the default definition of the
7309 @samp{R_ARM_TARGET2} relocation. Valid values for @samp{type}, their
7310 meanings, and target defaults are as follows:
7313 @samp{R_ARM_REL32} (arm*-*-elf, arm*-*-eabi)
7315 @samp{R_ARM_ABS32} (arm*-*-symbianelf)
7317 @samp{R_ARM_GOT_PREL} (arm*-*-linux, arm*-*-*bsd)
7322 The @samp{R_ARM_V4BX} relocation (defined by the ARM AAELF
7323 specification) enables objects compiled for the ARMv4 architecture to be
7324 interworking-safe when linked with other objects compiled for ARMv4t, but
7325 also allows pure ARMv4 binaries to be built from the same ARMv4 objects.
7327 In the latter case, the switch @option{--fix-v4bx} must be passed to the
7328 linker, which causes v4t @code{BX rM} instructions to be rewritten as
7329 @code{MOV PC,rM}, since v4 processors do not have a @code{BX} instruction.
7331 In the former case, the switch should not be used, and @samp{R_ARM_V4BX}
7332 relocations are ignored.
7334 @cindex FIX_V4BX_INTERWORKING
7335 @kindex --fix-v4bx-interworking
7336 Replace @code{BX rM} instructions identified by @samp{R_ARM_V4BX}
7337 relocations with a branch to the following veneer:
7345 This allows generation of libraries/applications that work on ARMv4 cores
7346 and are still interworking safe. Note that the above veneer clobbers the
7347 condition flags, so may cause incorrect program behavior in rare cases.
7351 The @samp{--use-blx} switch enables the linker to use ARM/Thumb
7352 BLX instructions (available on ARMv5t and above) in various
7353 situations. Currently it is used to perform calls via the PLT from Thumb
7354 code using BLX rather than using BX and a mode-switching stub before
7355 each PLT entry. This should lead to such calls executing slightly faster.
7357 This option is enabled implicitly for SymbianOS, so there is no need to
7358 specify it if you are using that target.
7360 @cindex VFP11_DENORM_FIX
7361 @kindex --vfp11-denorm-fix
7362 The @samp{--vfp11-denorm-fix} switch enables a link-time workaround for a
7363 bug in certain VFP11 coprocessor hardware, which sometimes allows
7364 instructions with denorm operands (which must be handled by support code)
7365 to have those operands overwritten by subsequent instructions before
7366 the support code can read the intended values.
7368 The bug may be avoided in scalar mode if you allow at least one
7369 intervening instruction between a VFP11 instruction which uses a register
7370 and another instruction which writes to the same register, or at least two
7371 intervening instructions if vector mode is in use. The bug only affects
7372 full-compliance floating-point mode: you do not need this workaround if
7373 you are using "runfast" mode. Please contact ARM for further details.
7375 If you know you are using buggy VFP11 hardware, you can
7376 enable this workaround by specifying the linker option
7377 @samp{--vfp-denorm-fix=scalar} if you are using the VFP11 scalar
7378 mode only, or @samp{--vfp-denorm-fix=vector} if you are using
7379 vector mode (the latter also works for scalar code). The default is
7380 @samp{--vfp-denorm-fix=none}.
7382 If the workaround is enabled, instructions are scanned for
7383 potentially-troublesome sequences, and a veneer is created for each
7384 such sequence which may trigger the erratum. The veneer consists of the
7385 first instruction of the sequence and a branch back to the subsequent
7386 instruction. The original instruction is then replaced with a branch to
7387 the veneer. The extra cycles required to call and return from the veneer
7388 are sufficient to avoid the erratum in both the scalar and vector cases.
7390 @cindex ARM1176 erratum workaround
7391 @kindex --fix-arm1176
7392 @kindex --no-fix-arm1176
7393 The @samp{--fix-arm1176} switch enables a link-time workaround for an erratum
7394 in certain ARM1176 processors. The workaround is enabled by default if you
7395 are targeting ARM v6 (excluding ARM v6T2) or earlier. It can be disabled
7396 unconditionally by specifying @samp{--no-fix-arm1176}.
7398 Further information is available in the ``ARM1176JZ-S and ARM1176JZF-S
7399 Programmer Advice Notice'' available on the ARM documentation website at:
7400 http://infocenter.arm.com/.
7402 @cindex STM32L4xx erratum workaround
7403 @kindex --fix-stm32l4xx-629360
7405 The @samp{--fix-stm32l4xx-629360} switch enables a link-time
7406 workaround for a bug in the bus matrix / memory controller for some of
7407 the STM32 Cortex-M4 based products (STM32L4xx). When accessing
7408 off-chip memory via the affected bus for bus reads of 9 words or more,
7409 the bus can generate corrupt data and/or abort. These are only
7410 core-initiated accesses (not DMA), and might affect any access:
7411 integer loads such as LDM, POP and floating-point loads such as VLDM,
7412 VPOP. Stores are not affected.
7414 The bug can be avoided by splitting memory accesses into the
7415 necessary chunks to keep bus reads below 8 words.
7417 The workaround is not enabled by default, this is equivalent to use
7418 @samp{--fix-stm32l4xx-629360=none}. If you know you are using buggy
7419 STM32L4xx hardware, you can enable the workaround by specifying the
7420 linker option @samp{--fix-stm32l4xx-629360}, or the equivalent
7421 @samp{--fix-stm32l4xx-629360=default}.
7423 If the workaround is enabled, instructions are scanned for
7424 potentially-troublesome sequences, and a veneer is created for each
7425 such sequence which may trigger the erratum. The veneer consists in a
7426 replacement sequence emulating the behaviour of the original one and a
7427 branch back to the subsequent instruction. The original instruction is
7428 then replaced with a branch to the veneer.
7430 The workaround does not always preserve the memory access order for
7431 the LDMDB instruction, when the instruction loads the PC.
7433 The workaround is not able to handle problematic instructions when
7434 they are in the middle of an IT block, since a branch is not allowed
7435 there. In that case, the linker reports a warning and no replacement
7438 The workaround is not able to replace problematic instructions with a
7439 PC-relative branch instruction if the @samp{.text} section is too
7440 large. In that case, when the branch that replaces the original code
7441 cannot be encoded, the linker reports a warning and no replacement
7444 @cindex NO_ENUM_SIZE_WARNING
7445 @kindex --no-enum-size-warning
7446 The @option{--no-enum-size-warning} switch prevents the linker from
7447 warning when linking object files that specify incompatible EABI
7448 enumeration size attributes. For example, with this switch enabled,
7449 linking of an object file using 32-bit enumeration values with another
7450 using enumeration values fitted into the smallest possible space will
7453 @cindex NO_WCHAR_SIZE_WARNING
7454 @kindex --no-wchar-size-warning
7455 The @option{--no-wchar-size-warning} switch prevents the linker from
7456 warning when linking object files that specify incompatible EABI
7457 @code{wchar_t} size attributes. For example, with this switch enabled,
7458 linking of an object file using 32-bit @code{wchar_t} values with another
7459 using 16-bit @code{wchar_t} values will not be diagnosed.
7462 @kindex --pic-veneer
7463 The @samp{--pic-veneer} switch makes the linker use PIC sequences for
7464 ARM/Thumb interworking veneers, even if the rest of the binary
7465 is not PIC. This avoids problems on uClinux targets where
7466 @samp{--emit-relocs} is used to generate relocatable binaries.
7468 @cindex STUB_GROUP_SIZE
7469 @kindex --stub-group-size=@var{N}
7470 The linker will automatically generate and insert small sequences of
7471 code into a linked ARM ELF executable whenever an attempt is made to
7472 perform a function call to a symbol that is too far away. The
7473 placement of these sequences of instructions - called stubs - is
7474 controlled by the command-line option @option{--stub-group-size=N}.
7475 The placement is important because a poor choice can create a need for
7476 duplicate stubs, increasing the code size. The linker will try to
7477 group stubs together in order to reduce interruptions to the flow of
7478 code, but it needs guidance as to how big these groups should be and
7479 where they should be placed.
7481 The value of @samp{N}, the parameter to the
7482 @option{--stub-group-size=} option controls where the stub groups are
7483 placed. If it is negative then all stubs are placed after the first
7484 branch that needs them. If it is positive then the stubs can be
7485 placed either before or after the branches that need them. If the
7486 value of @samp{N} is 1 (either +1 or -1) then the linker will choose
7487 exactly where to place groups of stubs, using its built in heuristics.
7488 A value of @samp{N} greater than 1 (or smaller than -1) tells the
7489 linker that a single group of stubs can service at most @samp{N} bytes
7490 from the input sections.
7492 The default, if @option{--stub-group-size=} is not specified, is
7495 Farcalls stubs insertion is fully supported for the ARM-EABI target
7496 only, because it relies on object files properties not present
7499 @cindex Cortex-A8 erratum workaround
7500 @kindex --fix-cortex-a8
7501 @kindex --no-fix-cortex-a8
7502 The @samp{--fix-cortex-a8} switch enables a link-time workaround for an erratum in certain Cortex-A8 processors. The workaround is enabled by default if you are targeting the ARM v7-A architecture profile. It can be enabled otherwise by specifying @samp{--fix-cortex-a8}, or disabled unconditionally by specifying @samp{--no-fix-cortex-a8}.
7504 The erratum only affects Thumb-2 code. Please contact ARM for further details.
7506 @cindex Cortex-A53 erratum 835769 workaround
7507 @kindex --fix-cortex-a53-835769
7508 @kindex --no-fix-cortex-a53-835769
7509 The @samp{--fix-cortex-a53-835769} switch enables a link-time workaround for erratum 835769 present on certain early revisions of Cortex-A53 processors. The workaround is disabled by default. It can be enabled by specifying @samp{--fix-cortex-a53-835769}, or disabled unconditionally by specifying @samp{--no-fix-cortex-a53-835769}.
7511 Please contact ARM for further details.
7513 @kindex --merge-exidx-entries
7514 @kindex --no-merge-exidx-entries
7515 @cindex Merging exidx entries
7516 The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent exidx entries in debuginfo.
7519 @cindex 32-bit PLT entries
7520 The @samp{--long-plt} option enables the use of 16 byte PLT entries
7521 which support up to 4Gb of code. The default is to use 12 byte PLT
7522 entries which only support 512Mb of code.
7524 @kindex --no-apply-dynamic-relocs
7525 @cindex AArch64 rela addend
7526 The @samp{--no-apply-dynamic-relocs} option makes AArch64 linker do not apply
7527 link-time values for dynamic relocations.
7529 @cindex Placement of SG veneers
7530 All SG veneers are placed in the special output section @code{.gnu.sgstubs}.
7531 Its start address must be set, either with the command-line option
7532 @samp{--section-start} or in a linker script, to indicate where to place these
7535 @kindex --cmse-implib
7536 @cindex Secure gateway import library
7537 The @samp{--cmse-implib} option requests that the import libraries
7538 specified by the @samp{--out-implib} and @samp{--in-implib} options are
7539 secure gateway import libraries, suitable for linking a non-secure
7540 executable against secure code as per ARMv8-M Security Extensions.
7542 @kindex --in-implib=@var{file}
7543 @cindex Input import library
7544 The @samp{--in-implib=file} specifies an input import library whose symbols
7545 must keep the same address in the executable being produced. A warning is
7546 given if no @samp{--out-implib} is given but new symbols have been introduced
7547 in the executable that should be listed in its import library. Otherwise, if
7548 @samp{--out-implib} is specified, the symbols are added to the output import
7549 library. A warning is also given if some symbols present in the input import
7550 library have disappeared from the executable. This option is only effective
7551 for Secure Gateway import libraries, ie. when @samp{--cmse-implib} is
7565 @section @command{ld} and HPPA 32-bit ELF Support
7566 @cindex HPPA multiple sub-space stubs
7567 @kindex --multi-subspace
7568 When generating a shared library, @command{ld} will by default generate
7569 import stubs suitable for use with a single sub-space application.
7570 The @samp{--multi-subspace} switch causes @command{ld} to generate export
7571 stubs, and different (larger) import stubs suitable for use with
7572 multiple sub-spaces.
7574 @cindex HPPA stub grouping
7575 @kindex --stub-group-size=@var{N}
7576 Long branch stubs and import/export stubs are placed by @command{ld} in
7577 stub sections located between groups of input sections.
7578 @samp{--stub-group-size} specifies the maximum size of a group of input
7579 sections handled by one stub section. Since branch offsets are signed,
7580 a stub section may serve two groups of input sections, one group before
7581 the stub section, and one group after it. However, when using
7582 conditional branches that require stubs, it may be better (for branch
7583 prediction) that stub sections only serve one group of input sections.
7584 A negative value for @samp{N} chooses this scheme, ensuring that
7585 branches to stubs always use a negative offset. Two special values of
7586 @samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct
7587 @command{ld} to automatically size input section groups for the branch types
7588 detected, with the same behaviour regarding stub placement as other
7589 positive or negative values of @samp{N} respectively.
7591 Note that @samp{--stub-group-size} does not split input sections. A
7592 single input section larger than the group size specified will of course
7593 create a larger group (of one section). If input sections are too
7594 large, it may not be possible for a branch to reach its stub.
7607 @section @command{ld} and the Motorola 68K family
7609 @cindex Motorola 68K GOT generation
7610 @kindex --got=@var{type}
7611 The @samp{--got=@var{type}} option lets you choose the GOT generation scheme.
7612 The choices are @samp{single}, @samp{negative}, @samp{multigot} and
7613 @samp{target}. When @samp{target} is selected the linker chooses
7614 the default GOT generation scheme for the current target.
7615 @samp{single} tells the linker to generate a single GOT with
7616 entries only at non-negative offsets.
7617 @samp{negative} instructs the linker to generate a single GOT with
7618 entries at both negative and positive offsets. Not all environments
7620 @samp{multigot} allows the linker to generate several GOTs in the
7621 output file. All GOT references from a single input object
7622 file access the same GOT, but references from different input object
7623 files might access different GOTs. Not all environments support such GOTs.
7636 @section @command{ld} and the MIPS family
7638 @cindex MIPS microMIPS instruction choice selection
7641 The @samp{--insn32} and @samp{--no-insn32} options control the choice of
7642 microMIPS instructions used in code generated by the linker, such as that
7643 in the PLT or lazy binding stubs, or in relaxation. If @samp{--insn32} is
7644 used, then the linker only uses 32-bit instruction encodings. By default
7645 or if @samp{--no-insn32} is used, all instruction encodings are used,
7646 including 16-bit ones where possible.
7648 @cindex MIPS branch relocation check control
7649 @kindex --ignore-branch-isa
7650 @kindex --no-ignore-branch-isa
7651 The @samp{--ignore-branch-isa} and @samp{--no-ignore-branch-isa} options
7652 control branch relocation checks for invalid ISA mode transitions. If
7653 @samp{--ignore-branch-isa} is used, then the linker accepts any branch
7654 relocations and any ISA mode transition required is lost in relocation
7655 calculation, except for some cases of @code{BAL} instructions which meet
7656 relaxation conditions and are converted to equivalent @code{JALX}
7657 instructions as the associated relocation is calculated. By default
7658 or if @samp{--no-ignore-branch-isa} is used a check is made causing
7659 the loss of an ISA mode transition to produce an error.
7672 @section @code{ld} and MMIX
7673 For MMIX, there is a choice of generating @code{ELF} object files or
7674 @code{mmo} object files when linking. The simulator @code{mmix}
7675 understands the @code{mmo} format. The binutils @code{objcopy} utility
7676 can translate between the two formats.
7678 There is one special section, the @samp{.MMIX.reg_contents} section.
7679 Contents in this section is assumed to correspond to that of global
7680 registers, and symbols referring to it are translated to special symbols,
7681 equal to registers. In a final link, the start address of the
7682 @samp{.MMIX.reg_contents} section corresponds to the first allocated
7683 global register multiplied by 8. Register @code{$255} is not included in
7684 this section; it is always set to the program entry, which is at the
7685 symbol @code{Main} for @code{mmo} files.
7687 Global symbols with the prefix @code{__.MMIX.start.}, for example
7688 @code{__.MMIX.start..text} and @code{__.MMIX.start..data} are special.
7689 The default linker script uses these to set the default start address
7692 Initial and trailing multiples of zero-valued 32-bit words in a section,
7693 are left out from an mmo file.
7706 @section @code{ld} and MSP430
7707 For the MSP430 it is possible to select the MPU architecture. The flag @samp{-m [mpu type]}
7708 will select an appropriate linker script for selected MPU type. (To get a list of known MPUs
7709 just pass @samp{-m help} option to the linker).
7711 @cindex MSP430 extra sections
7712 The linker will recognize some extra sections which are MSP430 specific:
7715 @item @samp{.vectors}
7716 Defines a portion of ROM where interrupt vectors located.
7718 @item @samp{.bootloader}
7719 Defines the bootloader portion of the ROM (if applicable). Any code
7720 in this section will be uploaded to the MPU.
7722 @item @samp{.infomem}
7723 Defines an information memory section (if applicable). Any code in
7724 this section will be uploaded to the MPU.
7726 @item @samp{.infomemnobits}
7727 This is the same as the @samp{.infomem} section except that any code
7728 in this section will not be uploaded to the MPU.
7730 @item @samp{.noinit}
7731 Denotes a portion of RAM located above @samp{.bss} section.
7733 The last two sections are used by gcc.
7737 @cindex MSP430 Options
7738 @kindex --code-region
7739 @item --code-region=[either,lower,upper,none]
7740 This will transform .text* sections to [either,lower,upper].text* sections. The
7741 argument passed to GCC for -mcode-region is propagated to the linker
7744 @kindex --data-region
7745 @item --data-region=[either,lower,upper,none]
7746 This will transform .data*, .bss* and .rodata* sections to
7747 [either,lower,upper].[data,bss,rodata]* sections. The argument passed to GCC
7748 for -mdata-region is propagated to the linker using this option.
7750 @kindex --disable-sec-transformation
7751 @item --disable-sec-transformation
7752 Prevent the transformation of sections as specified by the @code{--code-region}
7753 and @code{--data-region} options.
7754 This is useful if you are compiling and linking using a single call to the GCC
7755 wrapper, and want to compile the source files using -m[code,data]-region but
7756 not transform the sections for prebuilt libraries and objects.
7770 @section @code{ld} and NDS32
7771 @kindex relaxing on NDS32
7772 For NDS32, there are some options to select relaxation behavior. The linker
7773 relaxes objects according to these options.
7776 @item @samp{--m[no-]fp-as-gp}
7777 Disable/enable fp-as-gp relaxation.
7779 @item @samp{--mexport-symbols=FILE}
7780 Exporting symbols and their address into FILE as linker script.
7782 @item @samp{--m[no-]ex9}
7783 Disable/enable link-time EX9 relaxation.
7785 @item @samp{--mexport-ex9=FILE}
7786 Export the EX9 table after linking.
7788 @item @samp{--mimport-ex9=FILE}
7789 Import the Ex9 table for EX9 relaxation.
7791 @item @samp{--mupdate-ex9}
7792 Update the existing EX9 table.
7794 @item @samp{--mex9-limit=NUM}
7795 Maximum number of entries in the ex9 table.
7797 @item @samp{--mex9-loop-aware}
7798 Avoid generating the EX9 instruction inside the loop.
7800 @item @samp{--m[no-]ifc}
7801 Disable/enable the link-time IFC optimization.
7803 @item @samp{--mifc-loop-aware}
7804 Avoid generating the IFC instruction inside the loop.
7818 @section @command{ld} and the Altera Nios II
7819 @cindex Nios II call relaxation
7820 @kindex --relax on Nios II
7822 Call and immediate jump instructions on Nios II processors are limited to
7823 transferring control to addresses in the same 256MB memory segment,
7824 which may result in @command{ld} giving
7825 @samp{relocation truncated to fit} errors with very large programs.
7826 The command-line option @option{--relax} enables the generation of
7827 trampolines that can access the entire 32-bit address space for calls
7828 outside the normal @code{call} and @code{jmpi} address range. These
7829 trampolines are inserted at section boundaries, so may not themselves
7830 be reachable if an input section and its associated call trampolines are
7833 The @option{--relax} option is enabled by default unless @option{-r}
7834 is also specified. You can disable trampoline generation by using the
7835 @option{--no-relax} linker option. You can also disable this optimization
7836 locally by using the @samp{set .noat} directive in assembly-language
7837 source files, as the linker-inserted trampolines use the @code{at}
7838 register as a temporary.
7840 Note that the linker @option{--relax} option is independent of assembler
7841 relaxation options, and that using the GNU assembler's @option{-relax-all}
7842 option interferes with the linker's more selective call instruction relaxation.
7855 @section @command{ld} and PowerPC 32-bit ELF Support
7856 @cindex PowerPC long branches
7857 @kindex --relax on PowerPC
7858 Branches on PowerPC processors are limited to a signed 26-bit
7859 displacement, which may result in @command{ld} giving
7860 @samp{relocation truncated to fit} errors with very large programs.
7861 @samp{--relax} enables the generation of trampolines that can access
7862 the entire 32-bit address space. These trampolines are inserted at
7863 section boundaries, so may not themselves be reachable if an input
7864 section exceeds 33M in size. You may combine @samp{-r} and
7865 @samp{--relax} to add trampolines in a partial link. In that case
7866 both branches to undefined symbols and inter-section branches are also
7867 considered potentially out of range, and trampolines inserted.
7869 @cindex PowerPC ELF32 options
7874 Current PowerPC GCC accepts a @samp{-msecure-plt} option that
7875 generates code capable of using a newer PLT and GOT layout that has
7876 the security advantage of no executable section ever needing to be
7877 writable and no writable section ever being executable. PowerPC
7878 @command{ld} will generate this layout, including stubs to access the
7879 PLT, if all input files (including startup and static libraries) were
7880 compiled with @samp{-msecure-plt}. @samp{--bss-plt} forces the old
7881 BSS PLT (and GOT layout) which can give slightly better performance.
7883 @kindex --secure-plt
7885 @command{ld} will use the new PLT and GOT layout if it is linking new
7886 @samp{-fpic} or @samp{-fPIC} code, but does not do so automatically
7887 when linking non-PIC code. This option requests the new PLT and GOT
7888 layout. A warning will be given if some object file requires the old
7894 The new secure PLT and GOT are placed differently relative to other
7895 sections compared to older BSS PLT and GOT placement. The location of
7896 @code{.plt} must change because the new secure PLT is an initialized
7897 section while the old PLT is uninitialized. The reason for the
7898 @code{.got} change is more subtle: The new placement allows
7899 @code{.got} to be read-only in applications linked with
7900 @samp{-z relro -z now}. However, this placement means that
7901 @code{.sdata} cannot always be used in shared libraries, because the
7902 PowerPC ABI accesses @code{.sdata} in shared libraries from the GOT
7903 pointer. @samp{--sdata-got} forces the old GOT placement. PowerPC
7904 GCC doesn't use @code{.sdata} in shared libraries, so this option is
7905 really only useful for other compilers that may do so.
7907 @cindex PowerPC stub symbols
7908 @kindex --emit-stub-syms
7909 @item --emit-stub-syms
7910 This option causes @command{ld} to label linker stubs with a local
7911 symbol that encodes the stub type and destination.
7913 @cindex PowerPC TLS optimization
7914 @kindex --no-tls-optimize
7915 @item --no-tls-optimize
7916 PowerPC @command{ld} normally performs some optimization of code
7917 sequences used to access Thread-Local Storage. Use this option to
7918 disable the optimization.
7931 @node PowerPC64 ELF64
7932 @section @command{ld} and PowerPC64 64-bit ELF Support
7934 @cindex PowerPC64 ELF64 options
7936 @cindex PowerPC64 stub grouping
7937 @kindex --stub-group-size
7938 @item --stub-group-size
7939 Long branch stubs, PLT call stubs and TOC adjusting stubs are placed
7940 by @command{ld} in stub sections located between groups of input sections.
7941 @samp{--stub-group-size} specifies the maximum size of a group of input
7942 sections handled by one stub section. Since branch offsets are signed,
7943 a stub section may serve two groups of input sections, one group before
7944 the stub section, and one group after it. However, when using
7945 conditional branches that require stubs, it may be better (for branch
7946 prediction) that stub sections only serve one group of input sections.
7947 A negative value for @samp{N} chooses this scheme, ensuring that
7948 branches to stubs always use a negative offset. Two special values of
7949 @samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct
7950 @command{ld} to automatically size input section groups for the branch types
7951 detected, with the same behaviour regarding stub placement as other
7952 positive or negative values of @samp{N} respectively.
7954 Note that @samp{--stub-group-size} does not split input sections. A
7955 single input section larger than the group size specified will of course
7956 create a larger group (of one section). If input sections are too
7957 large, it may not be possible for a branch to reach its stub.
7959 @cindex PowerPC64 stub symbols
7960 @kindex --emit-stub-syms
7961 @item --emit-stub-syms
7962 This option causes @command{ld} to label linker stubs with a local
7963 symbol that encodes the stub type and destination.
7965 @cindex PowerPC64 dot symbols
7967 @kindex --no-dotsyms
7970 These two options control how @command{ld} interprets version patterns
7971 in a version script. Older PowerPC64 compilers emitted both a
7972 function descriptor symbol with the same name as the function, and a
7973 code entry symbol with the name prefixed by a dot (@samp{.}). To
7974 properly version a function @samp{foo}, the version script thus needs
7975 to control both @samp{foo} and @samp{.foo}. The option
7976 @samp{--dotsyms}, on by default, automatically adds the required
7977 dot-prefixed patterns. Use @samp{--no-dotsyms} to disable this
7980 @cindex PowerPC64 register save/restore functions
7981 @kindex --save-restore-funcs
7982 @kindex --no-save-restore-funcs
7983 @item --save-restore-funcs
7984 @itemx --no-save-restore-funcs
7985 These two options control whether PowerPC64 @command{ld} automatically
7986 provides out-of-line register save and restore functions used by
7987 @samp{-Os} code. The default is to provide any such referenced
7988 function for a normal final link, and to not do so for a relocatable
7991 @cindex PowerPC64 TLS optimization
7992 @kindex --no-tls-optimize
7993 @item --no-tls-optimize
7994 PowerPC64 @command{ld} normally performs some optimization of code
7995 sequences used to access Thread-Local Storage. Use this option to
7996 disable the optimization.
7998 @cindex PowerPC64 __tls_get_addr optimization
7999 @kindex --tls-get-addr-optimize
8000 @kindex --no-tls-get-addr-optimize
8001 @kindex --tls-get-addr-regsave
8002 @kindex --no-tls-get-addr-regsave
8003 @item --tls-get-addr-optimize
8004 @itemx --no-tls-get-addr-optimize
8005 These options control how PowerPC64 @command{ld} uses a special
8006 stub to call __tls_get_addr. PowerPC64 glibc 2.22 and later support
8007 an optimization that allows the second and subsequent calls to
8008 @code{__tls_get_addr} for a given symbol to be resolved by the special
8009 stub without calling in to glibc. By default the linker enables
8010 generation of the stub when glibc advertises the availability of
8012 Using @option{--tls-get-addr-optimize} with an older glibc won't do
8013 much besides slow down your applications, but may be useful if linking
8014 an application against an older glibc with the expectation that it
8015 will normally be used on systems having a newer glibc.
8016 @option{--tls-get-addr-regsave} forces generation of a stub that saves
8017 and restores volatile registers around the call into glibc. Normally,
8018 this is done when the linker detects a call to __tls_get_addr_desc.
8019 Such calls then go via the register saving stub to __tls_get_addr_opt.
8020 @option{--no-tls-get-addr-regsave} disables generation of the
8023 @cindex PowerPC64 OPD optimization
8024 @kindex --no-opd-optimize
8025 @item --no-opd-optimize
8026 PowerPC64 @command{ld} normally removes @code{.opd} section entries
8027 corresponding to deleted link-once functions, or functions removed by
8028 the action of @samp{--gc-sections} or linker script @code{/DISCARD/}.
8029 Use this option to disable @code{.opd} optimization.
8031 @cindex PowerPC64 OPD spacing
8032 @kindex --non-overlapping-opd
8033 @item --non-overlapping-opd
8034 Some PowerPC64 compilers have an option to generate compressed
8035 @code{.opd} entries spaced 16 bytes apart, overlapping the third word,
8036 the static chain pointer (unused in C) with the first word of the next
8037 entry. This option expands such entries to the full 24 bytes.
8039 @cindex PowerPC64 TOC optimization
8040 @kindex --no-toc-optimize
8041 @item --no-toc-optimize
8042 PowerPC64 @command{ld} normally removes unused @code{.toc} section
8043 entries. Such entries are detected by examining relocations that
8044 reference the TOC in code sections. A reloc in a deleted code section
8045 marks a TOC word as unneeded, while a reloc in a kept code section
8046 marks a TOC word as needed. Since the TOC may reference itself, TOC
8047 relocs are also examined. TOC words marked as both needed and
8048 unneeded will of course be kept. TOC words without any referencing
8049 reloc are assumed to be part of a multi-word entry, and are kept or
8050 discarded as per the nearest marked preceding word. This works
8051 reliably for compiler generated code, but may be incorrect if assembly
8052 code is used to insert TOC entries. Use this option to disable the
8055 @cindex PowerPC64 inline PLT call optimization
8056 @kindex --no-inline-optimize
8057 @item --no-inline-optimize
8058 PowerPC64 @command{ld} normally replaces inline PLT call sequences
8059 marked with @code{R_PPC64_PLTSEQ}, @code{R_PPC64_PLTCALL},
8060 @code{R_PPC64_PLT16_HA} and @code{R_PPC64_PLT16_LO_DS} relocations by
8061 a number of @code{nop}s and a direct call when the function is defined
8062 locally and can't be overridden by some other definition. This option
8063 disables that optimization.
8065 @cindex PowerPC64 multi-TOC
8066 @kindex --no-multi-toc
8067 @item --no-multi-toc
8068 If given any toc option besides @code{-mcmodel=medium} or
8069 @code{-mcmodel=large}, PowerPC64 GCC generates code for a TOC model
8071 entries are accessed with a 16-bit offset from r2. This limits the
8072 total TOC size to 64K. PowerPC64 @command{ld} extends this limit by
8073 grouping code sections such that each group uses less than 64K for its
8074 TOC entries, then inserts r2 adjusting stubs between inter-group
8075 calls. @command{ld} does not split apart input sections, so cannot
8076 help if a single input file has a @code{.toc} section that exceeds
8077 64K, most likely from linking multiple files with @command{ld -r}.
8078 Use this option to turn off this feature.
8080 @cindex PowerPC64 TOC sorting
8081 @kindex --no-toc-sort
8083 By default, @command{ld} sorts TOC sections so that those whose file
8084 happens to have a section called @code{.init} or @code{.fini} are
8085 placed first, followed by TOC sections referenced by code generated
8086 with PowerPC64 gcc's @code{-mcmodel=small}, and lastly TOC sections
8087 referenced only by code generated with PowerPC64 gcc's
8088 @code{-mcmodel=medium} or @code{-mcmodel=large} options. Doing this
8089 results in better TOC grouping for multi-TOC. Use this option to turn
8092 @cindex PowerPC64 PLT stub alignment
8094 @kindex --no-plt-align
8096 @itemx --no-plt-align
8097 Use these options to control whether individual PLT call stubs are
8098 aligned to a 32-byte boundary, or to the specified power of two
8099 boundary when using @code{--plt-align=}. A negative value may be
8100 specified to pad PLT call stubs so that they do not cross the
8101 specified power of two boundary (or the minimum number of boundaries
8102 if a PLT stub is so large that it must cross a boundary). By default
8103 PLT call stubs are aligned to 32-byte boundaries.
8105 @cindex PowerPC64 PLT call stub static chain
8106 @kindex --plt-static-chain
8107 @kindex --no-plt-static-chain
8108 @item --plt-static-chain
8109 @itemx --no-plt-static-chain
8110 Use these options to control whether PLT call stubs load the static
8111 chain pointer (r11). @code{ld} defaults to not loading the static
8112 chain since there is never any need to do so on a PLT call.
8114 @cindex PowerPC64 PLT call stub thread safety
8115 @kindex --plt-thread-safe
8116 @kindex --no-plt-thread-safe
8117 @item --plt-thread-safe
8118 @itemx --no-plt-thread-safe
8119 With power7's weakly ordered memory model, it is possible when using
8120 lazy binding for ld.so to update a plt entry in one thread and have
8121 another thread see the individual plt entry words update in the wrong
8122 order, despite ld.so carefully writing in the correct order and using
8123 memory write barriers. To avoid this we need some sort of read
8124 barrier in the call stub, or use LD_BIND_NOW=1. By default, @code{ld}
8125 looks for calls to commonly used functions that create threads, and if
8126 seen, adds the necessary barriers. Use these options to change the
8129 @cindex PowerPC64 ELFv2 PLT localentry optimization
8130 @kindex --plt-localentry
8131 @kindex --no-plt-localentry
8132 @item --plt-localentry
8133 @itemx --no-localentry
8134 ELFv2 functions with localentry:0 are those with a single entry point,
8135 ie. global entry == local entry, and that have no requirement on r2
8136 (the TOC/GOT pointer) or r12, and guarantee r2 is unchanged on return.
8137 Such an external function can be called via the PLT without saving r2
8138 or restoring it on return, avoiding a common load-hit-store for small
8139 functions. The optimization is attractive, with up to 40% reduction
8140 in execution time for a small function, but can result in symbol
8141 interposition failures. Also, minor changes in a shared library,
8142 including system libraries, can cause a function that was localentry:0
8143 to become localentry:8. This will result in a dynamic loader
8144 complaint and failure to run. The option is experimental, use with
8145 care. @option{--no-plt-localentry} is the default.
8147 @cindex PowerPC64 Power10 stubs
8148 @kindex --power10-stubs
8149 @kindex --no-power10-stubs
8150 @item --power10-stubs
8151 @itemx --no-power10-stubs
8152 When PowerPC64 @command{ld} links input object files containing
8153 relocations used on power10 prefixed instructions it normally creates
8154 linkage stubs (PLT call and long branch) using power10 instructions
8155 for @code{@@notoc} PLT calls where @code{r2} is not known. The
8156 power10 notoc stubs are smaller and faster, so are preferred for
8157 power10. @option{--power10-stubs} and @option{--no-power10-stubs}
8158 allow you to override the linker's selection of stub instructions.
8159 @option{--power10-stubs=auto} allows the user to select the default
8174 @section @command{ld} and S/390 ELF Support
8176 @cindex S/390 ELF options
8180 @kindex --s390-pgste
8182 This option marks the result file with a @code{PT_S390_PGSTE}
8183 segment. The Linux kernel is supposed to allocate 4k page tables for
8184 binaries marked that way.
8198 @section @command{ld} and SPU ELF Support
8200 @cindex SPU ELF options
8206 This option marks an executable as a PIC plugin module.
8208 @cindex SPU overlays
8209 @kindex --no-overlays
8211 Normally, @command{ld} recognizes calls to functions within overlay
8212 regions, and redirects such calls to an overlay manager via a stub.
8213 @command{ld} also provides a built-in overlay manager. This option
8214 turns off all this special overlay handling.
8216 @cindex SPU overlay stub symbols
8217 @kindex --emit-stub-syms
8218 @item --emit-stub-syms
8219 This option causes @command{ld} to label overlay stubs with a local
8220 symbol that encodes the stub type and destination.
8222 @cindex SPU extra overlay stubs
8223 @kindex --extra-overlay-stubs
8224 @item --extra-overlay-stubs
8225 This option causes @command{ld} to add overlay call stubs on all
8226 function calls out of overlay regions. Normally stubs are not added
8227 on calls to non-overlay regions.
8229 @cindex SPU local store size
8230 @kindex --local-store=lo:hi
8231 @item --local-store=lo:hi
8232 @command{ld} usually checks that a final executable for SPU fits in
8233 the address range 0 to 256k. This option may be used to change the
8234 range. Disable the check entirely with @option{--local-store=0:0}.
8237 @kindex --stack-analysis
8238 @item --stack-analysis
8239 SPU local store space is limited. Over-allocation of stack space
8240 unnecessarily limits space available for code and data, while
8241 under-allocation results in runtime failures. If given this option,
8242 @command{ld} will provide an estimate of maximum stack usage.
8243 @command{ld} does this by examining symbols in code sections to
8244 determine the extents of functions, and looking at function prologues
8245 for stack adjusting instructions. A call-graph is created by looking
8246 for relocations on branch instructions. The graph is then searched
8247 for the maximum stack usage path. Note that this analysis does not
8248 find calls made via function pointers, and does not handle recursion
8249 and other cycles in the call graph. Stack usage may be
8250 under-estimated if your code makes such calls. Also, stack usage for
8251 dynamic allocation, e.g. alloca, will not be detected. If a link map
8252 is requested, detailed information about each function's stack usage
8253 and calls will be given.
8256 @kindex --emit-stack-syms
8257 @item --emit-stack-syms
8258 This option, if given along with @option{--stack-analysis} will result
8259 in @command{ld} emitting stack sizing symbols for each function.
8260 These take the form @code{__stack_<function_name>} for global
8261 functions, and @code{__stack_<number>_<function_name>} for static
8262 functions. @code{<number>} is the section id in hex. The value of
8263 such symbols is the stack requirement for the corresponding function.
8264 The symbol size will be zero, type @code{STT_NOTYPE}, binding
8265 @code{STB_LOCAL}, and section @code{SHN_ABS}.
8279 @section @command{ld}'s Support for Various TI COFF Versions
8280 @cindex TI COFF versions
8281 @kindex --format=@var{version}
8282 The @samp{--format} switch allows selection of one of the various
8283 TI COFF versions. The latest of this writing is 2; versions 0 and 1 are
8284 also supported. The TI COFF versions also vary in header byte-order
8285 format; @command{ld} will read any version or byte order, but the output
8286 header format depends on the default specified by the specific target.
8299 @section @command{ld} and WIN32 (cygwin/mingw)
8301 This section describes some of the win32 specific @command{ld} issues.
8302 See @ref{Options,,Command-line Options} for detailed description of the
8303 command-line options mentioned here.
8306 @cindex import libraries
8307 @item import libraries
8308 The standard Windows linker creates and uses so-called import
8309 libraries, which contains information for linking to dll's. They are
8310 regular static archives and are handled as any other static
8311 archive. The cygwin and mingw ports of @command{ld} have specific
8312 support for creating such libraries provided with the
8313 @samp{--out-implib} command-line option.
8315 @item exporting DLL symbols
8316 @cindex exporting DLL symbols
8317 The cygwin/mingw @command{ld} has several ways to export symbols for dll's.
8320 @item using auto-export functionality
8321 @cindex using auto-export functionality
8322 By default @command{ld} exports symbols with the auto-export functionality,
8323 which is controlled by the following command-line options:
8326 @item --export-all-symbols [This is the default]
8327 @item --exclude-symbols
8328 @item --exclude-libs
8329 @item --exclude-modules-for-implib
8330 @item --version-script
8333 When auto-export is in operation, @command{ld} will export all the non-local
8334 (global and common) symbols it finds in a DLL, with the exception of a few
8335 symbols known to belong to the system's runtime and libraries. As it will
8336 often not be desirable to export all of a DLL's symbols, which may include
8337 private functions that are not part of any public interface, the command-line
8338 options listed above may be used to filter symbols out from the list for
8339 exporting. The @samp{--output-def} option can be used in order to see the
8340 final list of exported symbols with all exclusions taken into effect.
8342 If @samp{--export-all-symbols} is not given explicitly on the
8343 command line, then the default auto-export behavior will be @emph{disabled}
8344 if either of the following are true:
8347 @item A DEF file is used.
8348 @item Any symbol in any object file was marked with the __declspec(dllexport) attribute.
8351 @item using a DEF file
8352 @cindex using a DEF file
8353 Another way of exporting symbols is using a DEF file. A DEF file is
8354 an ASCII file containing definitions of symbols which should be
8355 exported when a dll is created. Usually it is named @samp{<dll
8356 name>.def} and is added as any other object file to the linker's
8357 command line. The file's name must end in @samp{.def} or @samp{.DEF}.
8360 gcc -o <output> <objectfiles> <dll name>.def
8363 Using a DEF file turns off the normal auto-export behavior, unless the
8364 @samp{--export-all-symbols} option is also used.
8366 Here is an example of a DEF file for a shared library called @samp{xyz.dll}:
8369 LIBRARY "xyz.dll" BASE=0x20000000
8375 another_foo = abc.dll.afoo
8381 This example defines a DLL with a non-default base address and seven
8382 symbols in the export table. The third exported symbol @code{_bar} is an
8383 alias for the second. The fourth symbol, @code{another_foo} is resolved
8384 by "forwarding" to another module and treating it as an alias for
8385 @code{afoo} exported from the DLL @samp{abc.dll}. The final symbol
8386 @code{var1} is declared to be a data object. The @samp{doo} symbol in
8387 export library is an alias of @samp{foo}, which gets the string name
8388 in export table @samp{foo2}. The @samp{eoo} symbol is an data export
8389 symbol, which gets in export table the name @samp{var1}.
8391 The optional @code{LIBRARY <name>} command indicates the @emph{internal}
8392 name of the output DLL. If @samp{<name>} does not include a suffix,
8393 the default library suffix, @samp{.DLL} is appended.
8395 When the .DEF file is used to build an application, rather than a
8396 library, the @code{NAME <name>} command should be used instead of
8397 @code{LIBRARY}. If @samp{<name>} does not include a suffix, the default
8398 executable suffix, @samp{.EXE} is appended.
8400 With either @code{LIBRARY <name>} or @code{NAME <name>} the optional
8401 specification @code{BASE = <number>} may be used to specify a
8402 non-default base address for the image.
8404 If neither @code{LIBRARY <name>} nor @code{NAME <name>} is specified,
8405 or they specify an empty string, the internal name is the same as the
8406 filename specified on the command line.
8408 The complete specification of an export symbol is:
8412 ( ( ( <name1> [ = <name2> ] )
8413 | ( <name1> = <module-name> . <external-name>))
8414 [ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] [== <name3>] ) *
8417 Declares @samp{<name1>} as an exported symbol from the DLL, or declares
8418 @samp{<name1>} as an exported alias for @samp{<name2>}; or declares
8419 @samp{<name1>} as a "forward" alias for the symbol
8420 @samp{<external-name>} in the DLL @samp{<module-name>}.
8421 Optionally, the symbol may be exported by the specified ordinal
8422 @samp{<integer>} alias. The optional @samp{<name3>} is the to be used
8423 string in import/export table for the symbol.
8425 The optional keywords that follow the declaration indicate:
8427 @code{NONAME}: Do not put the symbol name in the DLL's export table. It
8428 will still be exported by its ordinal alias (either the value specified
8429 by the .def specification or, otherwise, the value assigned by the
8430 linker). The symbol name, however, does remain visible in the import
8431 library (if any), unless @code{PRIVATE} is also specified.
8433 @code{DATA}: The symbol is a variable or object, rather than a function.
8434 The import lib will export only an indirect reference to @code{foo} as
8435 the symbol @code{_imp__foo} (ie, @code{foo} must be resolved as
8438 @code{CONSTANT}: Like @code{DATA}, but put the undecorated @code{foo} as
8439 well as @code{_imp__foo} into the import library. Both refer to the
8440 read-only import address table's pointer to the variable, not to the
8441 variable itself. This can be dangerous. If the user code fails to add
8442 the @code{dllimport} attribute and also fails to explicitly add the
8443 extra indirection that the use of the attribute enforces, the
8444 application will behave unexpectedly.
8446 @code{PRIVATE}: Put the symbol in the DLL's export table, but do not put
8447 it into the static import library used to resolve imports at link time. The
8448 symbol can still be imported using the @code{LoadLibrary/GetProcAddress}
8449 API at runtime or by using the GNU ld extension of linking directly to
8450 the DLL without an import library.
8452 See ld/deffilep.y in the binutils sources for the full specification of
8453 other DEF file statements
8455 @cindex creating a DEF file
8456 While linking a shared dll, @command{ld} is able to create a DEF file
8457 with the @samp{--output-def <file>} command-line option.
8459 @item Using decorations
8460 @cindex Using decorations
8461 Another way of marking symbols for export is to modify the source code
8462 itself, so that when building the DLL each symbol to be exported is
8466 __declspec(dllexport) int a_variable
8467 __declspec(dllexport) void a_function(int with_args)
8470 All such symbols will be exported from the DLL. If, however,
8471 any of the object files in the DLL contain symbols decorated in
8472 this way, then the normal auto-export behavior is disabled, unless
8473 the @samp{--export-all-symbols} option is also used.
8475 Note that object files that wish to access these symbols must @emph{not}
8476 decorate them with dllexport. Instead, they should use dllimport,
8480 __declspec(dllimport) int a_variable
8481 __declspec(dllimport) void a_function(int with_args)
8484 This complicates the structure of library header files, because
8485 when included by the library itself the header must declare the
8486 variables and functions as dllexport, but when included by client
8487 code the header must declare them as dllimport. There are a number
8488 of idioms that are typically used to do this; often client code can
8489 omit the __declspec() declaration completely. See
8490 @samp{--enable-auto-import} and @samp{automatic data imports} for more
8494 @cindex automatic data imports
8495 @item automatic data imports
8496 The standard Windows dll format supports data imports from dlls only
8497 by adding special decorations (dllimport/dllexport), which let the
8498 compiler produce specific assembler instructions to deal with this
8499 issue. This increases the effort necessary to port existing Un*x
8500 code to these platforms, especially for large
8501 c++ libraries and applications. The auto-import feature, which was
8502 initially provided by Paul Sokolovsky, allows one to omit the
8503 decorations to achieve a behavior that conforms to that on POSIX/Un*x
8504 platforms. This feature is enabled with the @samp{--enable-auto-import}
8505 command-line option, although it is enabled by default on cygwin/mingw.
8506 The @samp{--enable-auto-import} option itself now serves mainly to
8507 suppress any warnings that are ordinarily emitted when linked objects
8508 trigger the feature's use.
8510 auto-import of variables does not always work flawlessly without
8511 additional assistance. Sometimes, you will see this message
8513 "variable '<var>' can't be auto-imported. Please read the
8514 documentation for ld's @code{--enable-auto-import} for details."
8516 The @samp{--enable-auto-import} documentation explains why this error
8517 occurs, and several methods that can be used to overcome this difficulty.
8518 One of these methods is the @emph{runtime pseudo-relocs} feature, described
8521 @cindex runtime pseudo-relocation
8522 For complex variables imported from DLLs (such as structs or classes),
8523 object files typically contain a base address for the variable and an
8524 offset (@emph{addend}) within the variable--to specify a particular
8525 field or public member, for instance. Unfortunately, the runtime loader used
8526 in win32 environments is incapable of fixing these references at runtime
8527 without the additional information supplied by dllimport/dllexport decorations.
8528 The standard auto-import feature described above is unable to resolve these
8531 The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
8532 be resolved without error, while leaving the task of adjusting the references
8533 themselves (with their non-zero addends) to specialized code provided by the
8534 runtime environment. Recent versions of the cygwin and mingw environments and
8535 compilers provide this runtime support; older versions do not. However, the
8536 support is only necessary on the developer's platform; the compiled result will
8537 run without error on an older system.
8539 @samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
8542 @cindex direct linking to a dll
8543 @item direct linking to a dll
8544 The cygwin/mingw ports of @command{ld} support the direct linking,
8545 including data symbols, to a dll without the usage of any import
8546 libraries. This is much faster and uses much less memory than does the
8547 traditional import library method, especially when linking large
8548 libraries or applications. When @command{ld} creates an import lib, each
8549 function or variable exported from the dll is stored in its own bfd, even
8550 though a single bfd could contain many exports. The overhead involved in
8551 storing, loading, and processing so many bfd's is quite large, and explains the
8552 tremendous time, memory, and storage needed to link against particularly
8553 large or complex libraries when using import libs.
8555 Linking directly to a dll uses no extra command-line switches other than
8556 @samp{-L} and @samp{-l}, because @command{ld} already searches for a number
8557 of names to match each library. All that is needed from the developer's
8558 perspective is an understanding of this search, in order to force ld to
8559 select the dll instead of an import library.
8562 For instance, when ld is called with the argument @samp{-lxxx} it will attempt
8563 to find, in the first directory of its search path,
8576 before moving on to the next directory in the search path.
8578 (*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
8579 where @samp{<prefix>} is set by the @command{ld} option
8580 @samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
8581 file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
8584 Other win32-based unix environments, such as mingw or pw32, may use other
8585 @samp{<prefix>}es, although at present only cygwin makes use of this feature. It
8586 was originally intended to help avoid name conflicts among dll's built for the
8587 various win32/un*x environments, so that (for example) two versions of a zlib dll
8588 could coexist on the same machine.
8590 The generic cygwin/mingw path layout uses a @samp{bin} directory for
8591 applications and dll's and a @samp{lib} directory for the import
8592 libraries (using cygwin nomenclature):
8598 libxxx.dll.a (in case of dll's)
8599 libxxx.a (in case of static archive)
8602 Linking directly to a dll without using the import library can be
8605 1. Use the dll directly by adding the @samp{bin} path to the link line
8607 gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx
8610 However, as the dll's often have version numbers appended to their names
8611 (@samp{cygncurses-5.dll}) this will often fail, unless one specifies
8612 @samp{-L../bin -lncurses-5} to include the version. Import libs are generally
8613 not versioned, and do not have this difficulty.
8615 2. Create a symbolic link from the dll to a file in the @samp{lib}
8616 directory according to the above mentioned search pattern. This
8617 should be used to avoid unwanted changes in the tools needed for
8621 ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a]
8624 Then you can link without any make environment changes.
8627 gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx
8630 This technique also avoids the version number problems, because the following is
8637 libxxx.dll.a -> ../bin/cygxxx-5.dll
8640 Linking directly to a dll without using an import lib will work
8641 even when auto-import features are exercised, and even when
8642 @samp{--enable-runtime-pseudo-relocs} is used.
8644 Given the improvements in speed and memory usage, one might justifiably
8645 wonder why import libraries are used at all. There are three reasons:
8647 1. Until recently, the link-directly-to-dll functionality did @emph{not}
8648 work with auto-imported data.
8650 2. Sometimes it is necessary to include pure static objects within the
8651 import library (which otherwise contains only bfd's for indirection
8652 symbols that point to the exports of a dll). Again, the import lib
8653 for the cygwin kernel makes use of this ability, and it is not
8654 possible to do this without an import lib.
8656 3. Symbol aliases can only be resolved using an import lib. This is
8657 critical when linking against OS-supplied dll's (eg, the win32 API)
8658 in which symbols are usually exported as undecorated aliases of their
8659 stdcall-decorated assembly names.
8661 So, import libs are not going away. But the ability to replace
8662 true import libs with a simple symbolic link to (or a copy of)
8663 a dll, in many cases, is a useful addition to the suite of tools
8664 binutils makes available to the win32 developer. Given the
8665 massive improvements in memory requirements during linking, storage
8666 requirements, and linking speed, we expect that many developers
8667 will soon begin to use this feature whenever possible.
8669 @item symbol aliasing
8671 @item adding additional names
8672 Sometimes, it is useful to export symbols with additional names.
8673 A symbol @samp{foo} will be exported as @samp{foo}, but it can also be
8674 exported as @samp{_foo} by using special directives in the DEF file
8675 when creating the dll. This will affect also the optional created
8676 import library. Consider the following DEF file:
8679 LIBRARY "xyz.dll" BASE=0x61000000
8686 The line @samp{_foo = foo} maps the symbol @samp{foo} to @samp{_foo}.
8688 Another method for creating a symbol alias is to create it in the
8689 source code using the "weak" attribute:
8692 void foo () @{ /* Do something. */; @}
8693 void _foo () __attribute__ ((weak, alias ("foo")));
8696 See the gcc manual for more information about attributes and weak
8699 @item renaming symbols
8700 Sometimes it is useful to rename exports. For instance, the cygwin
8701 kernel does this regularly. A symbol @samp{_foo} can be exported as
8702 @samp{foo} but not as @samp{_foo} by using special directives in the
8703 DEF file. (This will also affect the import library, if it is
8704 created). In the following example:
8707 LIBRARY "xyz.dll" BASE=0x61000000
8713 The line @samp{_foo = foo} maps the exported symbol @samp{foo} to
8717 Note: using a DEF file disables the default auto-export behavior,
8718 unless the @samp{--export-all-symbols} command-line option is used.
8719 If, however, you are trying to rename symbols, then you should list
8720 @emph{all} desired exports in the DEF file, including the symbols
8721 that are not being renamed, and do @emph{not} use the
8722 @samp{--export-all-symbols} option. If you list only the
8723 renamed symbols in the DEF file, and use @samp{--export-all-symbols}
8724 to handle the other symbols, then the both the new names @emph{and}
8725 the original names for the renamed symbols will be exported.
8726 In effect, you'd be aliasing those symbols, not renaming them,
8727 which is probably not what you wanted.
8729 @cindex weak externals
8730 @item weak externals
8731 The Windows object format, PE, specifies a form of weak symbols called
8732 weak externals. When a weak symbol is linked and the symbol is not
8733 defined, the weak symbol becomes an alias for some other symbol. There
8734 are three variants of weak externals:
8736 @item Definition is searched for in objects and libraries, historically
8737 called lazy externals.
8738 @item Definition is searched for only in other objects, not in libraries.
8739 This form is not presently implemented.
8740 @item No search; the symbol is an alias. This form is not presently
8743 As a GNU extension, weak symbols that do not specify an alternate symbol
8744 are supported. If the symbol is undefined when linking, the symbol
8745 uses a default value.
8747 @cindex aligned common symbols
8748 @item aligned common symbols
8749 As a GNU extension to the PE file format, it is possible to specify the
8750 desired alignment for a common symbol. This information is conveyed from
8751 the assembler or compiler to the linker by means of GNU-specific commands
8752 carried in the object file's @samp{.drectve} section, which are recognized
8753 by @command{ld} and respected when laying out the common symbols. Native
8754 tools will be able to process object files employing this GNU extension,
8755 but will fail to respect the alignment instructions, and may issue noisy
8756 warnings about unknown linker directives.
8771 @section @code{ld} and Xtensa Processors
8773 @cindex Xtensa processors
8774 The default @command{ld} behavior for Xtensa processors is to interpret
8775 @code{SECTIONS} commands so that lists of explicitly named sections in a
8776 specification with a wildcard file will be interleaved when necessary to
8777 keep literal pools within the range of PC-relative load offsets. For
8778 example, with the command:
8790 @command{ld} may interleave some of the @code{.literal}
8791 and @code{.text} sections from different object files to ensure that the
8792 literal pools are within the range of PC-relative load offsets. A valid
8793 interleaving might place the @code{.literal} sections from an initial
8794 group of files followed by the @code{.text} sections of that group of
8795 files. Then, the @code{.literal} sections from the rest of the files
8796 and the @code{.text} sections from the rest of the files would follow.
8798 @cindex @option{--relax} on Xtensa
8799 @cindex relaxing on Xtensa
8800 Relaxation is enabled by default for the Xtensa version of @command{ld} and
8801 provides two important link-time optimizations. The first optimization
8802 is to combine identical literal values to reduce code size. A redundant
8803 literal will be removed and all the @code{L32R} instructions that use it
8804 will be changed to reference an identical literal, as long as the
8805 location of the replacement literal is within the offset range of all
8806 the @code{L32R} instructions. The second optimization is to remove
8807 unnecessary overhead from assembler-generated ``longcall'' sequences of
8808 @code{L32R}/@code{CALLX@var{n}} when the target functions are within
8809 range of direct @code{CALL@var{n}} instructions.
8811 For each of these cases where an indirect call sequence can be optimized
8812 to a direct call, the linker will change the @code{CALLX@var{n}}
8813 instruction to a @code{CALL@var{n}} instruction, remove the @code{L32R}
8814 instruction, and remove the literal referenced by the @code{L32R}
8815 instruction if it is not used for anything else. Removing the
8816 @code{L32R} instruction always reduces code size but can potentially
8817 hurt performance by changing the alignment of subsequent branch targets.
8818 By default, the linker will always preserve alignments, either by
8819 switching some instructions between 24-bit encodings and the equivalent
8820 density instructions or by inserting a no-op in place of the @code{L32R}
8821 instruction that was removed. If code size is more important than
8822 performance, the @option{--size-opt} option can be used to prevent the
8823 linker from widening density instructions or inserting no-ops, except in
8824 a few cases where no-ops are required for correctness.
8826 The following Xtensa-specific command-line options can be used to
8829 @cindex Xtensa options
8832 When optimizing indirect calls to direct calls, optimize for code size
8833 more than performance. With this option, the linker will not insert
8834 no-ops or widen density instructions to preserve branch target
8835 alignment. There may still be some cases where no-ops are required to
8836 preserve the correctness of the code.
8838 @item --abi-windowed
8840 Choose ABI for the output object and for the generated PLT code.
8841 PLT code inserted by the linker must match ABI of the output object
8842 because windowed and call0 ABI use incompatible function call
8844 Default ABI is chosen by the ABI tag in the @code{.xtensa.info} section
8845 of the first input object.
8846 A warning is issued if ABI tags of input objects do not match each other
8847 or the chosen output object ABI.
8855 @ifclear SingleFormat
8860 @cindex object file management
8861 @cindex object formats available
8863 The linker accesses object and archive files using the BFD libraries.
8864 These libraries allow the linker to use the same routines to operate on
8865 object files whatever the object file format. A different object file
8866 format can be supported simply by creating a new BFD back end and adding
8867 it to the library. To conserve runtime memory, however, the linker and
8868 associated tools are usually configured to support only a subset of the
8869 object file formats available. You can use @code{objdump -i}
8870 (@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}) to
8871 list all the formats available for your configuration.
8873 @cindex BFD requirements
8874 @cindex requirements for BFD
8875 As with most implementations, BFD is a compromise between
8876 several conflicting requirements. The major factor influencing
8877 BFD design was efficiency: any time used converting between
8878 formats is time which would not have been spent had BFD not
8879 been involved. This is partly offset by abstraction payback; since
8880 BFD simplifies applications and back ends, more time and care
8881 may be spent optimizing algorithms for a greater speed.
8883 One minor artifact of the BFD solution which you should bear in
8884 mind is the potential for information loss. There are two places where
8885 useful information can be lost using the BFD mechanism: during
8886 conversion and during output. @xref{BFD information loss}.
8889 * BFD outline:: How it works: an outline of BFD
8893 @section How It Works: An Outline of BFD
8894 @cindex opening object files
8895 @include bfdsumm.texi
8898 @node Reporting Bugs
8899 @chapter Reporting Bugs
8900 @cindex bugs in @command{ld}
8901 @cindex reporting bugs in @command{ld}
8903 Your bug reports play an essential role in making @command{ld} reliable.
8905 Reporting a bug may help you by bringing a solution to your problem, or
8906 it may not. But in any case the principal function of a bug report is
8907 to help the entire community by making the next version of @command{ld}
8908 work better. Bug reports are your contribution to the maintenance of
8911 In order for a bug report to serve its purpose, you must include the
8912 information that enables us to fix the bug.
8915 * Bug Criteria:: Have you found a bug?
8916 * Bug Reporting:: How to report bugs
8920 @section Have You Found a Bug?
8921 @cindex bug criteria
8923 If you are not sure whether you have found a bug, here are some guidelines:
8926 @cindex fatal signal
8927 @cindex linker crash
8928 @cindex crash of linker
8930 If the linker gets a fatal signal, for any input whatever, that is a
8931 @command{ld} bug. Reliable linkers never crash.
8933 @cindex error on valid input
8935 If @command{ld} produces an error message for valid input, that is a bug.
8937 @cindex invalid input
8939 If @command{ld} does not produce an error message for invalid input, that
8940 may be a bug. In the general case, the linker can not verify that
8941 object files are correct.
8944 If you are an experienced user of linkers, your suggestions for
8945 improvement of @command{ld} are welcome in any case.
8949 @section How to Report Bugs
8951 @cindex @command{ld} bugs, reporting
8953 A number of companies and individuals offer support for @sc{gnu}
8954 products. If you obtained @command{ld} from a support organization, we
8955 recommend you contact that organization first.
8957 You can find contact information for many support companies and
8958 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
8962 Otherwise, send bug reports for @command{ld} to
8966 The fundamental principle of reporting bugs usefully is this:
8967 @strong{report all the facts}. If you are not sure whether to state a
8968 fact or leave it out, state it!
8970 Often people omit facts because they think they know what causes the
8971 problem and assume that some details do not matter. Thus, you might
8972 assume that the name of a symbol you use in an example does not
8973 matter. Well, probably it does not, but one cannot be sure. Perhaps
8974 the bug is a stray memory reference which happens to fetch from the
8975 location where that name is stored in memory; perhaps, if the name
8976 were different, the contents of that location would fool the linker
8977 into doing the right thing despite the bug. Play it safe and give a
8978 specific, complete example. That is the easiest thing for you to do,
8979 and the most helpful.
8981 Keep in mind that the purpose of a bug report is to enable us to fix
8982 the bug if it is new to us. Therefore, always write your bug reports
8983 on the assumption that the bug has not been reported previously.
8985 Sometimes people give a few sketchy facts and ask, ``Does this ring a
8986 bell?'' This cannot help us fix a bug, so it is basically useless. We
8987 respond by asking for enough details to enable us to investigate.
8988 You might as well expedite matters by sending them to begin with.
8990 To enable us to fix the bug, you should include all these things:
8994 The version of @command{ld}. @command{ld} announces it if you start it with
8995 the @samp{--version} argument.
8997 Without this, we will not know whether there is any point in looking for
8998 the bug in the current version of @command{ld}.
9001 Any patches you may have applied to the @command{ld} source, including any
9002 patches made to the @code{BFD} library.
9005 The type of machine you are using, and the operating system name and
9009 What compiler (and its version) was used to compile @command{ld}---e.g.
9013 The command arguments you gave the linker to link your example and
9014 observe the bug. To guarantee you will not omit something important,
9015 list them all. A copy of the Makefile (or the output from make) is
9018 If we were to try to guess the arguments, we would probably guess wrong
9019 and then we might not encounter the bug.
9022 A complete input file, or set of input files, that will reproduce the
9023 bug. It is generally most helpful to send the actual object files
9024 provided that they are reasonably small. Say no more than 10K. For
9025 bigger files you can either make them available by FTP or HTTP or else
9026 state that you are willing to send the object file(s) to whomever
9027 requests them. (Note - your email will be going to a mailing list, so
9028 we do not want to clog it up with large attachments). But small
9029 attachments are best.
9031 If the source files were assembled using @code{gas} or compiled using
9032 @code{gcc}, then it may be OK to send the source files rather than the
9033 object files. In this case, be sure to say exactly what version of
9034 @code{gas} or @code{gcc} was used to produce the object files. Also say
9035 how @code{gas} or @code{gcc} were configured.
9038 A description of what behavior you observe that you believe is
9039 incorrect. For example, ``It gets a fatal signal.''
9041 Of course, if the bug is that @command{ld} gets a fatal signal, then we
9042 will certainly notice it. But if the bug is incorrect output, we might
9043 not notice unless it is glaringly wrong. You might as well not give us
9044 a chance to make a mistake.
9046 Even if the problem you experience is a fatal signal, you should still
9047 say so explicitly. Suppose something strange is going on, such as, your
9048 copy of @command{ld} is out of sync, or you have encountered a bug in the
9049 C library on your system. (This has happened!) Your copy might crash
9050 and ours would not. If you told us to expect a crash, then when ours
9051 fails to crash, we would know that the bug was not happening for us. If
9052 you had not told us to expect a crash, then we would not be able to draw
9053 any conclusion from our observations.
9056 If you wish to suggest changes to the @command{ld} source, send us context
9057 diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or
9058 @samp{-p} option. Always send diffs from the old file to the new file.
9059 If you even discuss something in the @command{ld} source, refer to it by
9060 context, not by line number.
9062 The line numbers in our development sources will not match those in your
9063 sources. Your line numbers would convey no useful information to us.
9066 Here are some things that are not necessary:
9070 A description of the envelope of the bug.
9072 Often people who encounter a bug spend a lot of time investigating
9073 which changes to the input file will make the bug go away and which
9074 changes will not affect it.
9076 This is often time consuming and not very useful, because the way we
9077 will find the bug is by running a single example under the debugger
9078 with breakpoints, not by pure deduction from a series of examples.
9079 We recommend that you save your time for something else.
9081 Of course, if you can find a simpler example to report @emph{instead}
9082 of the original one, that is a convenience for us. Errors in the
9083 output will be easier to spot, running under the debugger will take
9084 less time, and so on.
9086 However, simplification is not vital; if you do not want to do this,
9087 report the bug anyway and send us the entire test case you used.
9090 A patch for the bug.
9092 A patch for the bug does help us if it is a good one. But do not omit
9093 the necessary information, such as the test case, on the assumption that
9094 a patch is all we need. We might see problems with your patch and decide
9095 to fix the problem another way, or we might not understand it at all.
9097 Sometimes with a program as complicated as @command{ld} it is very hard to
9098 construct an example that will make the program follow a certain path
9099 through the code. If you do not send us the example, we will not be
9100 able to construct one, so we will not be able to verify that the bug is
9103 And if we cannot understand what bug you are trying to fix, or why your
9104 patch should be an improvement, we will not install it. A test case will
9105 help us to understand.
9108 A guess about what the bug is or what it depends on.
9110 Such guesses are usually wrong. Even we cannot guess right about such
9111 things without first using the debugger to find the facts.
9115 @appendix MRI Compatible Script Files
9116 @cindex MRI compatibility
9117 To aid users making the transition to @sc{gnu} @command{ld} from the MRI
9118 linker, @command{ld} can use MRI compatible linker scripts as an
9119 alternative to the more general-purpose linker scripting language
9120 described in @ref{Scripts}. MRI compatible linker scripts have a much
9121 simpler command set than the scripting language otherwise used with
9122 @command{ld}. @sc{gnu} @command{ld} supports the most commonly used MRI
9123 linker commands; these commands are described here.
9125 In general, MRI scripts aren't of much use with the @code{a.out} object
9126 file format, since it only has three sections and MRI scripts lack some
9127 features to make use of them.
9129 You can specify a file containing an MRI-compatible script using the
9130 @samp{-c} command-line option.
9132 Each command in an MRI-compatible script occupies its own line; each
9133 command line starts with the keyword that identifies the command (though
9134 blank lines are also allowed for punctuation). If a line of an
9135 MRI-compatible script begins with an unrecognized keyword, @command{ld}
9136 issues a warning message, but continues processing the script.
9138 Lines beginning with @samp{*} are comments.
9140 You can write these commands using all upper-case letters, or all
9141 lower case; for example, @samp{chip} is the same as @samp{CHIP}.
9142 The following list shows only the upper-case form of each command.
9145 @cindex @code{ABSOLUTE} (MRI)
9146 @item ABSOLUTE @var{secname}
9147 @itemx ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
9148 Normally, @command{ld} includes in the output file all sections from all
9149 the input files. However, in an MRI-compatible script, you can use the
9150 @code{ABSOLUTE} command to restrict the sections that will be present in
9151 your output program. If the @code{ABSOLUTE} command is used at all in a
9152 script, then only the sections named explicitly in @code{ABSOLUTE}
9153 commands will appear in the linker output. You can still use other
9154 input sections (whatever you select on the command line, or using
9155 @code{LOAD}) to resolve addresses in the output file.
9157 @cindex @code{ALIAS} (MRI)
9158 @item ALIAS @var{out-secname}, @var{in-secname}
9159 Use this command to place the data from input section @var{in-secname}
9160 in a section called @var{out-secname} in the linker output file.
9162 @var{in-secname} may be an integer.
9164 @cindex @code{ALIGN} (MRI)
9165 @item ALIGN @var{secname} = @var{expression}
9166 Align the section called @var{secname} to @var{expression}. The
9167 @var{expression} should be a power of two.
9169 @cindex @code{BASE} (MRI)
9170 @item BASE @var{expression}
9171 Use the value of @var{expression} as the lowest address (other than
9172 absolute addresses) in the output file.
9174 @cindex @code{CHIP} (MRI)
9175 @item CHIP @var{expression}
9176 @itemx CHIP @var{expression}, @var{expression}
9177 This command does nothing; it is accepted only for compatibility.
9179 @cindex @code{END} (MRI)
9181 This command does nothing whatever; it's only accepted for compatibility.
9183 @cindex @code{FORMAT} (MRI)
9184 @item FORMAT @var{output-format}
9185 Similar to the @code{OUTPUT_FORMAT} command in the more general linker
9186 language, but restricted to S-records, if @var{output-format} is @samp{S}
9188 @cindex @code{LIST} (MRI)
9189 @item LIST @var{anything}@dots{}
9190 Print (to the standard output file) a link map, as produced by the
9191 @command{ld} command-line option @samp{-M}.
9193 The keyword @code{LIST} may be followed by anything on the
9194 same line, with no change in its effect.
9196 @cindex @code{LOAD} (MRI)
9197 @item LOAD @var{filename}
9198 @itemx LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
9199 Include one or more object file @var{filename} in the link; this has the
9200 same effect as specifying @var{filename} directly on the @command{ld}
9203 @cindex @code{NAME} (MRI)
9204 @item NAME @var{output-name}
9205 @var{output-name} is the name for the program produced by @command{ld}; the
9206 MRI-compatible command @code{NAME} is equivalent to the command-line
9207 option @samp{-o} or the general script language command @code{OUTPUT}.
9209 @cindex @code{ORDER} (MRI)
9210 @item ORDER @var{secname}, @var{secname}, @dots{} @var{secname}
9211 @itemx ORDER @var{secname} @var{secname} @var{secname}
9212 Normally, @command{ld} orders the sections in its output file in the
9213 order in which they first appear in the input files. In an MRI-compatible
9214 script, you can override this ordering with the @code{ORDER} command. The
9215 sections you list with @code{ORDER} will appear first in your output
9216 file, in the order specified.
9218 @cindex @code{PUBLIC} (MRI)
9219 @item PUBLIC @var{name}=@var{expression}
9220 @itemx PUBLIC @var{name},@var{expression}
9221 @itemx PUBLIC @var{name} @var{expression}
9222 Supply a value (@var{expression}) for external symbol
9223 @var{name} used in the linker input files.
9225 @cindex @code{SECT} (MRI)
9226 @item SECT @var{secname}, @var{expression}
9227 @itemx SECT @var{secname}=@var{expression}
9228 @itemx SECT @var{secname} @var{expression}
9229 You can use any of these three forms of the @code{SECT} command to
9230 specify the start address (@var{expression}) for section @var{secname}.
9231 If you have more than one @code{SECT} statement for the same
9232 @var{secname}, only the @emph{first} sets the start address.
9235 @node GNU Free Documentation License
9236 @appendix GNU Free Documentation License
9240 @unnumbered LD Index
9245 % I think something like @@colophon should be in texinfo. In the
9247 \long\def\colophon{\hbox to0pt{}\vfill
9248 \centerline{The body of this manual is set in}
9249 \centerline{\fontname\tenrm,}
9250 \centerline{with headings in {\bf\fontname\tenbf}}
9251 \centerline{and examples in {\tt\fontname\tentt}.}
9252 \centerline{{\it\fontname\tenit\/} and}
9253 \centerline{{\sl\fontname\tensl\/}}
9254 \centerline{are used for emphasis.}\vfill}
9256 % Blame: doc@@cygnus.com, 28mar91.