Make info fun|var|types interruptable.
[deliverable/binutils-gdb.git] / ld / ld.texinfo
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1\input texinfo
2@setfilename ld.info
b90efa5b 3@c Copyright (C) 1991-2015 Free Software Foundation, Inc.
252b5132 4@syncodeindex ky cp
dff70155 5@c man begin INCLUDE
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6@include configdoc.texi
7@c (configdoc.texi is generated by the Makefile)
c428fa83 8@include bfdver.texi
dff70155 9@c man end
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10
11@c @smallbook
12
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13@macro gcctabopt{body}
14@code{\body\}
15@end macro
16
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17@c man begin NAME
18@ifset man
19@c Configure for the generation of man pages
20@set UsesEnvVars
21@set GENERIC
0285c67d 22@set ARM
ac145307 23@set C6X
49fa1e15 24@set H8300
0285c67d 25@set HPPA
0285c67d 26@set I960
0285c67d 27@set M68HC11
7fb9f789 28@set M68K
833794fc 29@set MIPS
3c3bdf30 30@set MMIX
2469cfa2 31@set MSP430
35c08157 32@set NDS32
78058a5e 33@set NIOSII
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34@set POWERPC
35@set POWERPC64
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36@set Renesas
37@set SPU
38@set TICOFF
2ca22b03 39@set WIN32
e0001a05 40@set XTENSA
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41@end ifset
42@c man end
43
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44@ifnottex
45@dircategory Software development
46@direntry
252b5132 47* Ld: (ld). The GNU linker.
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48@end direntry
49@end ifnottex
252b5132 50
0e9517a9 51@copying
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52This file documents the @sc{gnu} linker LD
53@ifset VERSION_PACKAGE
54@value{VERSION_PACKAGE}
55@end ifset
56version @value{VERSION}.
252b5132 57
b90efa5b 58Copyright @copyright{} 1991-2015 Free Software Foundation, Inc.
252b5132 59
cf055d54 60Permission is granted to copy, distribute and/or modify this document
793c5807 61under the terms of the GNU Free Documentation License, Version 1.3
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62or any later version published by the Free Software Foundation;
63with no Invariant Sections, with no Front-Cover Texts, and with no
64Back-Cover Texts. A copy of the license is included in the
36f63dca 65section entitled ``GNU Free Documentation License''.
0e9517a9 66@end copying
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67@iftex
68@finalout
69@setchapternewpage odd
71ba23f6 70@settitle The GNU linker
252b5132 71@titlepage
71ba23f6 72@title The GNU linker
252b5132 73@sp 1
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74@subtitle @code{ld}
75@ifset VERSION_PACKAGE
76@subtitle @value{VERSION_PACKAGE}
77@end ifset
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78@subtitle Version @value{VERSION}
79@author Steve Chamberlain
80@author Ian Lance Taylor
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81@page
82
83@tex
84{\parskip=0pt
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85\hfill Red Hat Inc\par
86\hfill nickc\@credhat.com, doc\@redhat.com\par
71ba23f6 87\hfill {\it The GNU linker}\par
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88\hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
89}
90\global\parindent=0pt % Steve likes it this way.
91@end tex
92
93@vskip 0pt plus 1filll
0285c67d 94@c man begin COPYRIGHT
b90efa5b 95Copyright @copyright{} 1991-2015 Free Software Foundation, Inc.
252b5132 96
0285c67d 97Permission is granted to copy, distribute and/or modify this document
793c5807 98under the terms of the GNU Free Documentation License, Version 1.3
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99or any later version published by the Free Software Foundation;
100with no Invariant Sections, with no Front-Cover Texts, and with no
101Back-Cover Texts. A copy of the license is included in the
36f63dca 102section entitled ``GNU Free Documentation License''.
0285c67d 103@c man end
252b5132 104
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105@end titlepage
106@end iftex
4ecceb71 107@contents
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108@c FIXME: Talk about importance of *order* of args, cmds to linker!
109
84ec0e6d 110@ifnottex
252b5132 111@node Top
71ba23f6 112@top LD
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113This file documents the @sc{gnu} linker ld
114@ifset VERSION_PACKAGE
115@value{VERSION_PACKAGE}
116@end ifset
117version @value{VERSION}.
252b5132 118
cf055d54 119This document is distributed under the terms of the GNU Free
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120Documentation License version 1.3. A copy of the license is included
121in the section entitled ``GNU Free Documentation License''.
cf055d54 122
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123@menu
124* Overview:: Overview
125* Invocation:: Invocation
126* Scripts:: Linker Scripts
127@ifset GENERIC
128* Machine Dependent:: Machine Dependent Features
129@end ifset
130@ifclear GENERIC
131@ifset H8300
132* H8/300:: ld and the H8/300
133@end ifset
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134@ifset Renesas
135* Renesas:: ld and other Renesas micros
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136@end ifset
137@ifset I960
138* i960:: ld and the Intel 960 family
139@end ifset
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140@ifset ARM
141* ARM:: ld and the ARM family
142@end ifset
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143@ifset M68HC11
144* M68HC11/68HC12:: ld and the Motorola 68HC11 and 68HC12 families
145@end ifset
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146@ifset HPPA
147* HPPA ELF32:: ld and HPPA 32-bit ELF
148@end ifset
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149@ifset M68K
150* M68K:: ld and Motorola 68K family
151@end ifset
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152@ifset MIPS
153* MIPS:: ld and MIPS family
154@end ifset
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155@ifset POWERPC
156* PowerPC ELF32:: ld and PowerPC 32-bit ELF Support
157@end ifset
158@ifset POWERPC64
159* PowerPC64 ELF64:: ld and PowerPC64 64-bit ELF Support
160@end ifset
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161@ifset SPU
162* SPU ELF:: ld and SPU ELF Support
163@end ifset
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164@ifset TICOFF
165* TI COFF:: ld and the TI COFF
166@end ifset
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167@ifset WIN32
168* Win32:: ld and WIN32 (cygwin/mingw)
169@end ifset
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170@ifset XTENSA
171* Xtensa:: ld and Xtensa Processors
172@end ifset
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173@end ifclear
174@ifclear SingleFormat
175* BFD:: BFD
176@end ifclear
177@c Following blank line required for remaining bug in makeinfo conds/menus
178
179* Reporting Bugs:: Reporting Bugs
180* MRI:: MRI Compatible Script Files
704c465c 181* GNU Free Documentation License:: GNU Free Documentation License
370b66a1 182* LD Index:: LD Index
252b5132 183@end menu
84ec0e6d 184@end ifnottex
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185
186@node Overview
187@chapter Overview
188
189@cindex @sc{gnu} linker
190@cindex what is this?
0285c67d 191
0879a67a 192@ifset man
0285c67d 193@c man begin SYNOPSIS
ff5dcc92 194ld [@b{options}] @var{objfile} @dots{}
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195@c man end
196
197@c man begin SEEALSO
198ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and
199the Info entries for @file{binutils} and
200@file{ld}.
201@c man end
202@end ifset
203
204@c man begin DESCRIPTION
205
ff5dcc92 206@command{ld} combines a number of object and archive files, relocates
252b5132 207their data and ties up symbol references. Usually the last step in
ff5dcc92 208compiling a program is to run @command{ld}.
252b5132 209
ff5dcc92 210@command{ld} accepts Linker Command Language files written in
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211a superset of AT&T's Link Editor Command Language syntax,
212to provide explicit and total control over the linking process.
213
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214@ifset man
215@c For the man only
ece2d90e 216This man page does not describe the command language; see the
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217@command{ld} entry in @code{info} for full details on the command
218language and on other aspects of the GNU linker.
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219@end ifset
220
252b5132 221@ifclear SingleFormat
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222This version of @command{ld} uses the general purpose BFD libraries
223to operate on object files. This allows @command{ld} to read, combine, and
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224write object files in many different formats---for example, COFF or
225@code{a.out}. Different formats may be linked together to produce any
226available kind of object file. @xref{BFD}, for more information.
227@end ifclear
228
229Aside from its flexibility, the @sc{gnu} linker is more helpful than other
230linkers in providing diagnostic information. Many linkers abandon
231execution immediately upon encountering an error; whenever possible,
ff5dcc92 232@command{ld} continues executing, allowing you to identify other errors
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233(or, in some cases, to get an output file in spite of the error).
234
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235@c man end
236
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237@node Invocation
238@chapter Invocation
239
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240@c man begin DESCRIPTION
241
ff5dcc92 242The @sc{gnu} linker @command{ld} is meant to cover a broad range of situations,
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243and to be as compatible as possible with other linkers. As a result,
244you have many choices to control its behavior.
245
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246@c man end
247
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248@ifset UsesEnvVars
249@menu
250* Options:: Command Line Options
251* Environment:: Environment Variables
252@end menu
253
254@node Options
255@section Command Line Options
256@end ifset
257
258@cindex command line
259@cindex options
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260
261@c man begin OPTIONS
262
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263The linker supports a plethora of command-line options, but in actual
264practice few of them are used in any particular context.
265@cindex standard Unix system
ff5dcc92 266For instance, a frequent use of @command{ld} is to link standard Unix
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267object files on a standard, supported Unix system. On such a system, to
268link a file @code{hello.o}:
269
270@smallexample
271ld -o @var{output} /lib/crt0.o hello.o -lc
272@end smallexample
273
ff5dcc92 274This tells @command{ld} to produce a file called @var{output} as the
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275result of linking the file @code{/lib/crt0.o} with @code{hello.o} and
276the library @code{libc.a}, which will come from the standard search
277directories. (See the discussion of the @samp{-l} option below.)
278
ff5dcc92 279Some of the command-line options to @command{ld} may be specified at any
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280point in the command line. However, options which refer to files, such
281as @samp{-l} or @samp{-T}, cause the file to be read at the point at
282which the option appears in the command line, relative to the object
283files and other file options. Repeating non-file options with a
284different argument will either have no further effect, or override prior
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285occurrences (those further to the left on the command line) of that
286option. Options which may be meaningfully specified more than once are
287noted in the descriptions below.
288
289@cindex object files
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290Non-option arguments are object files or archives which are to be linked
291together. They may follow, precede, or be mixed in with command-line
292options, except that an object file argument may not be placed between
293an option and its argument.
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294
295Usually the linker is invoked with at least one object file, but you can
296specify other forms of binary input files using @samp{-l}, @samp{-R},
297and the script command language. If @emph{no} binary input files at all
298are specified, the linker does not produce any output, and issues the
299message @samp{No input files}.
300
36f63dca 301If the linker cannot recognize the format of an object file, it will
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302assume that it is a linker script. A script specified in this way
303augments the main linker script used for the link (either the default
304linker script or the one specified by using @samp{-T}). This feature
305permits the linker to link against a file which appears to be an object
306or an archive, but actually merely defines some symbol values, or uses
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307@code{INPUT} or @code{GROUP} to load other objects. Specifying a
308script in this way merely augments the main linker script, with the
309extra commands placed after the main script; use the @samp{-T} option
310to replace the default linker script entirely, but note the effect of
311the @code{INSERT} command. @xref{Scripts}.
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312
313For options whose names are a single letter,
314option arguments must either follow the option letter without intervening
315whitespace, or be given as separate arguments immediately following the
316option that requires them.
317
318For options whose names are multiple letters, either one dash or two can
e4897a32 319precede the option name; for example, @samp{-trace-symbol} and
36f63dca 320@samp{--trace-symbol} are equivalent. Note---there is one exception to
e4897a32 321this rule. Multiple letter options that start with a lower case 'o' can
ba1be17e 322only be preceded by two dashes. This is to reduce confusion with the
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323@samp{-o} option. So for example @samp{-omagic} sets the output file
324name to @samp{magic} whereas @samp{--omagic} sets the NMAGIC flag on the
325output.
326
327Arguments to multiple-letter options must either be separated from the
328option name by an equals sign, or be given as separate arguments
329immediately following the option that requires them. For example,
330@samp{--trace-symbol foo} and @samp{--trace-symbol=foo} are equivalent.
331Unique abbreviations of the names of multiple-letter options are
332accepted.
252b5132 333
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334Note---if the linker is being invoked indirectly, via a compiler driver
335(e.g. @samp{gcc}) then all the linker command line options should be
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336prefixed by @samp{-Wl,} (or whatever is appropriate for the particular
337compiler driver) like this:
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338
339@smallexample
2509a395 340 gcc -Wl,--start-group foo.o bar.o -Wl,--end-group
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341@end smallexample
342
343This is important, because otherwise the compiler driver program may
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344silently drop the linker options, resulting in a bad link. Confusion
345may also arise when passing options that require values through a
346driver, as the use of a space between option and argument acts as
347a separator, and causes the driver to pass only the option to the linker
348and the argument to the compiler. In this case, it is simplest to use
349the joined forms of both single- and multiple-letter options, such as:
350
351@smallexample
352 gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map
353@end smallexample
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354
355Here is a table of the generic command line switches accepted by the GNU
356linker:
357
ff5dcc92 358@table @gcctabopt
38fc1cb1 359@include at-file.texi
dff70155 360
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361@kindex -a @var{keyword}
362@item -a @var{keyword}
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363This option is supported for HP/UX compatibility. The @var{keyword}
364argument must be one of the strings @samp{archive}, @samp{shared}, or
365@samp{default}. @samp{-aarchive} is functionally equivalent to
366@samp{-Bstatic}, and the other two keywords are functionally equivalent
367to @samp{-Bdynamic}. This option may be used any number of times.
368
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369@kindex --audit @var{AUDITLIB}
370@item --audit @var{AUDITLIB}
371Adds @var{AUDITLIB} to the @code{DT_AUDIT} entry of the dynamic section.
372@var{AUDITLIB} is not checked for existence, nor will it use the DT_SONAME
373specified in the library. If specified multiple times @code{DT_AUDIT}
374will contain a colon separated list of audit interfaces to use. If the linker
375finds an object with an audit entry while searching for shared libraries,
9d5777a3 376it will add a corresponding @code{DT_DEPAUDIT} entry in the output file.
7ee314fa 377This option is only meaningful on ELF platforms supporting the rtld-audit
9d5777a3 378interface.
7ee314fa 379
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380@ifset I960
381@cindex architectures
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382@kindex -A @var{arch}
383@item -A @var{architecture}
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384@kindex --architecture=@var{arch}
385@itemx --architecture=@var{architecture}
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386In the current release of @command{ld}, this option is useful only for the
387Intel 960 family of architectures. In that @command{ld} configuration, the
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388@var{architecture} argument identifies the particular architecture in
389the 960 family, enabling some safeguards and modifying the
ff5dcc92 390archive-library search path. @xref{i960,,@command{ld} and the Intel 960
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391family}, for details.
392
ff5dcc92 393Future releases of @command{ld} may support similar functionality for
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394other architecture families.
395@end ifset
396
397@ifclear SingleFormat
398@cindex binary input format
399@kindex -b @var{format}
400@kindex --format=@var{format}
401@cindex input format
402@cindex input format
403@item -b @var{input-format}
404@itemx --format=@var{input-format}
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405@command{ld} may be configured to support more than one kind of object
406file. If your @command{ld} is configured this way, you can use the
252b5132 407@samp{-b} option to specify the binary format for input object files
ff5dcc92 408that follow this option on the command line. Even when @command{ld} is
252b5132 409configured to support alternative object formats, you don't usually need
ff5dcc92 410to specify this, as @command{ld} should be configured to expect as a
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411default input format the most usual format on each machine.
412@var{input-format} is a text string, the name of a particular format
413supported by the BFD libraries. (You can list the available binary
414formats with @samp{objdump -i}.)
415@xref{BFD}.
416
417You may want to use this option if you are linking files with an unusual
418binary format. You can also use @samp{-b} to switch formats explicitly (when
419linking object files of different formats), by including
420@samp{-b @var{input-format}} before each group of object files in a
a1ab1d2a 421particular format.
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422
423The default format is taken from the environment variable
424@code{GNUTARGET}.
425@ifset UsesEnvVars
426@xref{Environment}.
427@end ifset
428You can also define the input format from a script, using the command
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429@code{TARGET};
430@ifclear man
431see @ref{Format Commands}.
432@end ifclear
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433@end ifclear
434
435@kindex -c @var{MRI-cmdfile}
436@kindex --mri-script=@var{MRI-cmdfile}
437@cindex compatibility, MRI
438@item -c @var{MRI-commandfile}
439@itemx --mri-script=@var{MRI-commandfile}
ff5dcc92 440For compatibility with linkers produced by MRI, @command{ld} accepts script
252b5132 441files written in an alternate, restricted command language, described in
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442@ifclear man
443@ref{MRI,,MRI Compatible Script Files}.
444@end ifclear
445@ifset man
446the MRI Compatible Script Files section of GNU ld documentation.
447@end ifset
448Introduce MRI script files with
252b5132 449the option @samp{-c}; use the @samp{-T} option to run linker
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450scripts written in the general-purpose @command{ld} scripting language.
451If @var{MRI-cmdfile} does not exist, @command{ld} looks for it in the directories
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452specified by any @samp{-L} options.
453
454@cindex common allocation
455@kindex -d
456@kindex -dc
457@kindex -dp
a1ab1d2a 458@item -d
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459@itemx -dc
460@itemx -dp
461These three options are equivalent; multiple forms are supported for
462compatibility with other linkers. They assign space to common symbols
463even if a relocatable output file is specified (with @samp{-r}). The
464script command @code{FORCE_COMMON_ALLOCATION} has the same effect.
465@xref{Miscellaneous Commands}.
466
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467@kindex --depaudit @var{AUDITLIB}
468@kindex -P @var{AUDITLIB}
469@item --depaudit @var{AUDITLIB}
470@itemx -P @var{AUDITLIB}
471Adds @var{AUDITLIB} to the @code{DT_DEPAUDIT} entry of the dynamic section.
472@var{AUDITLIB} is not checked for existence, nor will it use the DT_SONAME
473specified in the library. If specified multiple times @code{DT_DEPAUDIT}
474will contain a colon separated list of audit interfaces to use. This
475option is only meaningful on ELF platforms supporting the rtld-audit interface.
9d5777a3 476The -P option is provided for Solaris compatibility.
7ee314fa 477
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478@cindex entry point, from command line
479@kindex -e @var{entry}
480@kindex --entry=@var{entry}
a1ab1d2a 481@item -e @var{entry}
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482@itemx --entry=@var{entry}
483Use @var{entry} as the explicit symbol for beginning execution of your
484program, rather than the default entry point. If there is no symbol
485named @var{entry}, the linker will try to parse @var{entry} as a number,
486and use that as the entry address (the number will be interpreted in
487base 10; you may use a leading @samp{0x} for base 16, or a leading
488@samp{0} for base 8). @xref{Entry Point}, for a discussion of defaults
489and other ways of specifying the entry point.
490
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491@kindex --exclude-libs
492@item --exclude-libs @var{lib},@var{lib},...
493Specifies a list of archive libraries from which symbols should not be automatically
e1c37eb5 494exported. The library names may be delimited by commas or colons. Specifying
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495@code{--exclude-libs ALL} excludes symbols in all archive libraries from
496automatic export. This option is available only for the i386 PE targeted
497port of the linker and for ELF targeted ports. For i386 PE, symbols
498explicitly listed in a .def file are still exported, regardless of this
499option. For ELF targeted ports, symbols affected by this option will
500be treated as hidden.
501
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502@kindex --exclude-modules-for-implib
503@item --exclude-modules-for-implib @var{module},@var{module},...
504Specifies a list of object files or archive members, from which symbols
505should not be automatically exported, but which should be copied wholesale
506into the import library being generated during the link. The module names
507may be delimited by commas or colons, and must match exactly the filenames
508used by @command{ld} to open the files; for archive members, this is simply
509the member name, but for object files the name listed must include and
510match precisely any path used to specify the input file on the linker's
511command-line. This option is available only for the i386 PE targeted port
512of the linker. Symbols explicitly listed in a .def file are still exported,
513regardless of this option.
514
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515@cindex dynamic symbol table
516@kindex -E
517@kindex --export-dynamic
267e2722 518@kindex --no-export-dynamic
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519@item -E
520@itemx --export-dynamic
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521@itemx --no-export-dynamic
522When creating a dynamically linked executable, using the @option{-E}
523option or the @option{--export-dynamic} option causes the linker to add
524all symbols to the dynamic symbol table. The dynamic symbol table is the
525set of symbols which are visible from dynamic objects at run time.
526
527If you do not use either of these options (or use the
528@option{--no-export-dynamic} option to restore the default behavior), the
529dynamic symbol table will normally contain only those symbols which are
530referenced by some dynamic object mentioned in the link.
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531
532If you use @code{dlopen} to load a dynamic object which needs to refer
533back to the symbols defined by the program, rather than some other
534dynamic object, then you will probably need to use this option when
535linking the program itself.
536
55255dae 537You can also use the dynamic list to control what symbols should
cb840a31 538be added to the dynamic symbol table if the output format supports it.
55255dae 539See the description of @samp{--dynamic-list}.
cb840a31 540
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541Note that this option is specific to ELF targeted ports. PE targets
542support a similar function to export all symbols from a DLL or EXE; see
543the description of @samp{--export-all-symbols} below.
544
36f63dca 545@ifclear SingleFormat
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546@cindex big-endian objects
547@cindex endianness
548@kindex -EB
549@item -EB
550Link big-endian objects. This affects the default output format.
551
552@cindex little-endian objects
553@kindex -EL
554@item -EL
555Link little-endian objects. This affects the default output format.
36f63dca 556@end ifclear
252b5132 557
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558@kindex -f @var{name}
559@kindex --auxiliary=@var{name}
560@item -f @var{name}
561@itemx --auxiliary=@var{name}
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562When creating an ELF shared object, set the internal DT_AUXILIARY field
563to the specified name. This tells the dynamic linker that the symbol
564table of the shared object should be used as an auxiliary filter on the
565symbol table of the shared object @var{name}.
566
567If you later link a program against this filter object, then, when you
568run the program, the dynamic linker will see the DT_AUXILIARY field. If
569the dynamic linker resolves any symbols from the filter object, it will
570first check whether there is a definition in the shared object
571@var{name}. If there is one, it will be used instead of the definition
572in the filter object. The shared object @var{name} need not exist.
573Thus the shared object @var{name} may be used to provide an alternative
574implementation of certain functions, perhaps for debugging or for
575machine specific performance.
576
577This option may be specified more than once. The DT_AUXILIARY entries
578will be created in the order in which they appear on the command line.
579
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580@kindex -F @var{name}
581@kindex --filter=@var{name}
252b5132 582@item -F @var{name}
2509a395 583@itemx --filter=@var{name}
252b5132
RH
584When creating an ELF shared object, set the internal DT_FILTER field to
585the specified name. This tells the dynamic linker that the symbol table
586of the shared object which is being created should be used as a filter
587on the symbol table of the shared object @var{name}.
588
589If you later link a program against this filter object, then, when you
590run the program, the dynamic linker will see the DT_FILTER field. The
591dynamic linker will resolve symbols according to the symbol table of the
592filter object as usual, but it will actually link to the definitions
593found in the shared object @var{name}. Thus the filter object can be
594used to select a subset of the symbols provided by the object
595@var{name}.
596
ff5dcc92 597Some older linkers used the @option{-F} option throughout a compilation
252b5132 598toolchain for specifying object-file format for both input and output
36f63dca
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599object files.
600@ifclear SingleFormat
601The @sc{gnu} linker uses other mechanisms for this purpose: the
ece2d90e 602@option{-b}, @option{--format}, @option{--oformat} options, the
252b5132 603@code{TARGET} command in linker scripts, and the @code{GNUTARGET}
36f63dca
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604environment variable.
605@end ifclear
606The @sc{gnu} linker will ignore the @option{-F} option when not
607creating an ELF shared object.
252b5132 608
3dbf70a2 609@cindex finalization function
2509a395
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610@kindex -fini=@var{name}
611@item -fini=@var{name}
3dbf70a2
MM
612When creating an ELF executable or shared object, call NAME when the
613executable or shared object is unloaded, by setting DT_FINI to the
614address of the function. By default, the linker uses @code{_fini} as
615the function to call.
616
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617@kindex -g
618@item -g
619Ignored. Provided for compatibility with other tools.
620
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621@kindex -G @var{value}
622@kindex --gpsize=@var{value}
252b5132 623@cindex object size
2509a395 624@item -G @var{value}
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625@itemx --gpsize=@var{value}
626Set the maximum size of objects to be optimized using the GP register to
627@var{size}. This is only meaningful for object file formats such as
e8044f35 628MIPS ELF that support putting large and small objects into different
252b5132
RH
629sections. This is ignored for other object file formats.
630
631@cindex runtime library name
2509a395 632@kindex -h @var{name}
252b5132 633@kindex -soname=@var{name}
2509a395 634@item -h @var{name}
252b5132
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635@itemx -soname=@var{name}
636When creating an ELF shared object, set the internal DT_SONAME field to
637the specified name. When an executable is linked with a shared object
638which has a DT_SONAME field, then when the executable is run the dynamic
639linker will attempt to load the shared object specified by the DT_SONAME
640field rather than the using the file name given to the linker.
641
642@kindex -i
643@cindex incremental link
644@item -i
645Perform an incremental link (same as option @samp{-r}).
646
3dbf70a2 647@cindex initialization function
2509a395
SL
648@kindex -init=@var{name}
649@item -init=@var{name}
3dbf70a2
MM
650When creating an ELF executable or shared object, call NAME when the
651executable or shared object is loaded, by setting DT_INIT to the address
652of the function. By default, the linker uses @code{_init} as the
653function to call.
654
252b5132 655@cindex archive files, from cmd line
2509a395 656@kindex -l @var{namespec}
bcb674cf 657@kindex --library=@var{namespec}
2509a395 658@item -l @var{namespec}
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RS
659@itemx --library=@var{namespec}
660Add the archive or object file specified by @var{namespec} to the
661list of files to link. This option may be used any number of times.
662If @var{namespec} is of the form @file{:@var{filename}}, @command{ld}
07d8eb55 663will search the library path for a file called @var{filename}, otherwise it
bcb674cf 664will search the library path for a file called @file{lib@var{namespec}.a}.
252b5132 665
ff5dcc92 666On systems which support shared libraries, @command{ld} may also search for
bcb674cf
RS
667files other than @file{lib@var{namespec}.a}. Specifically, on ELF
668and SunOS systems, @command{ld} will search a directory for a library
669called @file{lib@var{namespec}.so} before searching for one called
670@file{lib@var{namespec}.a}. (By convention, a @code{.so} extension
671indicates a shared library.) Note that this behavior does not apply
672to @file{:@var{filename}}, which always specifies a file called
673@var{filename}.
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674
675The linker will search an archive only once, at the location where it is
676specified on the command line. If the archive defines a symbol which
677was undefined in some object which appeared before the archive on the
678command line, the linker will include the appropriate file(s) from the
679archive. However, an undefined symbol in an object appearing later on
680the command line will not cause the linker to search the archive again.
681
ff5dcc92 682See the @option{-(} option for a way to force the linker to search
252b5132
RH
683archives multiple times.
684
685You may list the same archive multiple times on the command line.
686
687@ifset GENERIC
688This type of archive searching is standard for Unix linkers. However,
ff5dcc92 689if you are using @command{ld} on AIX, note that it is different from the
252b5132
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690behaviour of the AIX linker.
691@end ifset
692
693@cindex search directory, from cmd line
2509a395 694@kindex -L @var{dir}
252b5132 695@kindex --library-path=@var{dir}
2509a395 696@item -L @var{searchdir}
252b5132 697@itemx --library-path=@var{searchdir}
ff5dcc92
SC
698Add path @var{searchdir} to the list of paths that @command{ld} will search
699for archive libraries and @command{ld} control scripts. You may use this
252b5132
RH
700option any number of times. The directories are searched in the order
701in which they are specified on the command line. Directories specified
702on the command line are searched before the default directories. All
ff5dcc92 703@option{-L} options apply to all @option{-l} options, regardless of the
7d24f02c
KH
704order in which the options appear. @option{-L} options do not affect
705how @command{ld} searches for a linker script unless @option{-T}
706option is specified.
252b5132 707
9c8ebd6a 708If @var{searchdir} begins with @code{=}, then the @code{=} will be replaced
b3b9c41d
HPN
709by the @dfn{sysroot prefix}, controlled by the @samp{--sysroot} option, or
710specified when the linker is configured.
9c8ebd6a 711
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RH
712@ifset UsesEnvVars
713The default set of paths searched (without being specified with
ff5dcc92 714@samp{-L}) depends on which emulation mode @command{ld} is using, and in
252b5132
RH
715some cases also on how it was configured. @xref{Environment}.
716@end ifset
717
718The paths can also be specified in a link script with the
719@code{SEARCH_DIR} command. Directories specified this way are searched
720at the point in which the linker script appears in the command line.
721
722@cindex emulation
723@kindex -m @var{emulation}
2509a395 724@item -m @var{emulation}
252b5132
RH
725Emulate the @var{emulation} linker. You can list the available
726emulations with the @samp{--verbose} or @samp{-V} options.
727
728If the @samp{-m} option is not used, the emulation is taken from the
729@code{LDEMULATION} environment variable, if that is defined.
730
731Otherwise, the default emulation depends upon how the linker was
732configured.
733
734@cindex link map
735@kindex -M
736@kindex --print-map
737@item -M
738@itemx --print-map
739Print a link map to the standard output. A link map provides
740information about the link, including the following:
741
742@itemize @bullet
743@item
3b83e13a 744Where object files are mapped into memory.
252b5132
RH
745@item
746How common symbols are allocated.
747@item
748All archive members included in the link, with a mention of the symbol
749which caused the archive member to be brought in.
3b83e13a
NC
750@item
751The values assigned to symbols.
752
753Note - symbols whose values are computed by an expression which
754involves a reference to a previous value of the same symbol may not
755have correct result displayed in the link map. This is because the
756linker discards intermediate results and only retains the final value
757of an expression. Under such circumstances the linker will display
758the final value enclosed by square brackets. Thus for example a
759linker script containing:
760
761@smallexample
762 foo = 1
763 foo = foo * 4
764 foo = foo + 8
765@end smallexample
766
767will produce the following output in the link map if the @option{-M}
768option is used:
769
770@smallexample
771 0x00000001 foo = 0x1
772 [0x0000000c] foo = (foo * 0x4)
773 [0x0000000c] foo = (foo + 0x8)
774@end smallexample
775
776See @ref{Expressions} for more information about expressions in linker
777scripts.
252b5132
RH
778@end itemize
779
780@kindex -n
781@cindex read-only text
782@cindex NMAGIC
783@kindex --nmagic
784@item -n
785@itemx --nmagic
90f5d9d9
JZ
786Turn off page alignment of sections, and disable linking against shared
787libraries. If the output format supports Unix style magic numbers,
788mark the output as @code{NMAGIC}.
252b5132
RH
789
790@kindex -N
791@kindex --omagic
792@cindex read/write from cmd line
793@cindex OMAGIC
a1ab1d2a 794@item -N
252b5132
RH
795@itemx --omagic
796Set the text and data sections to be readable and writable. Also, do
63fd3b82
NC
797not page-align the data segment, and disable linking against shared
798libraries. If the output format supports Unix style magic numbers,
4d8907ac
DS
799mark the output as @code{OMAGIC}. Note: Although a writable text section
800is allowed for PE-COFF targets, it does not conform to the format
801specification published by Microsoft.
63fd3b82
NC
802
803@kindex --no-omagic
804@cindex OMAGIC
805@item --no-omagic
806This option negates most of the effects of the @option{-N} option. It
807sets the text section to be read-only, and forces the data segment to
808be page-aligned. Note - this option does not enable linking against
809shared libraries. Use @option{-Bdynamic} for this.
252b5132
RH
810
811@kindex -o @var{output}
812@kindex --output=@var{output}
813@cindex naming the output file
814@item -o @var{output}
815@itemx --output=@var{output}
ff5dcc92 816Use @var{output} as the name for the program produced by @command{ld}; if this
252b5132
RH
817option is not specified, the name @file{a.out} is used by default. The
818script command @code{OUTPUT} can also specify the output file name.
819
820@kindex -O @var{level}
821@cindex generating optimized output
822@item -O @var{level}
ff5dcc92 823If @var{level} is a numeric values greater than zero @command{ld} optimizes
252b5132 824the output. This might take significantly longer and therefore probably
98c503ac
NC
825should only be enabled for the final binary. At the moment this
826option only affects ELF shared library generation. Future releases of
827the linker may make more use of this option. Also currently there is
828no difference in the linker's behaviour for different non-zero values
829of this option. Again this may change with future releases.
252b5132 830
26278bb8
UD
831@kindex --push-state
832@cindex push state governing input file handling
833@item --push-state
834The @option{--push-state} allows to preserve the current state of the
835flags which govern the input file handling so that they can all be
836restored with one corresponding @option{--pop-state} option.
837
838The option which are covered are: @option{-Bdynamic}, @option{-Bstatic},
839@option{-dn}, @option{-dy}, @option{-call_shared}, @option{-non_shared},
840@option{-static}, @option{-N}, @option{-n}, @option{--whole-archive},
841@option{--no-whole-archive}, @option{-r}, @option{-Ur},
842@option{--copy-dt-needed-entries}, @option{--no-copy-dt-needed-entries},
843@option{--as-needed}, @option{--no-as-needed}, and @option{-a}.
844
845One target for this option are specifications for @file{pkg-config}. When
846used with the @option{--libs} option all possibly needed libraries are
847listed and then possibly linked with all the time. It is better to return
848something as follows:
849
850@smallexample
851-Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
852@end smallexample
853
854@kindex --pop-state
855@cindex pop state governing input file handling
856Undoes the effect of --push-state, restores the previous values of the
857flags governing input file handling.
858
a712da20
NC
859@kindex -q
860@kindex --emit-relocs
861@cindex retain relocations in final executable
862@item -q
863@itemx --emit-relocs
ba1be17e 864Leave relocation sections and contents in fully linked executables.
a712da20
NC
865Post link analysis and optimization tools may need this information in
866order to perform correct modifications of executables. This results
867in larger executables.
868
dbab7a7b
NC
869This option is currently only supported on ELF platforms.
870
4f471f39
RS
871@kindex --force-dynamic
872@cindex forcing the creation of dynamic sections
873@item --force-dynamic
874Force the output file to have dynamic sections. This option is specific
875to VxWorks targets.
876
252b5132
RH
877@cindex partial link
878@cindex relocatable output
879@kindex -r
1049f94e 880@kindex --relocatable
252b5132 881@item -r
1049f94e 882@itemx --relocatable
252b5132 883Generate relocatable output---i.e., generate an output file that can in
ff5dcc92 884turn serve as input to @command{ld}. This is often called @dfn{partial
252b5132
RH
885linking}. As a side effect, in environments that support standard Unix
886magic numbers, this option also sets the output file's magic number to
887@code{OMAGIC}.
ff5dcc92 888@c ; see @option{-N}.
252b5132
RH
889If this option is not specified, an absolute file is produced. When
890linking C++ programs, this option @emph{will not} resolve references to
891constructors; to do that, use @samp{-Ur}.
892
62bf86b4
HPN
893When an input file does not have the same format as the output file,
894partial linking is only supported if that input file does not contain any
895relocations. Different output formats can have further restrictions; for
896example some @code{a.out}-based formats do not support partial linking
897with input files in other formats at all.
898
252b5132
RH
899This option does the same thing as @samp{-i}.
900
901@kindex -R @var{file}
902@kindex --just-symbols=@var{file}
903@cindex symbol-only input
904@item -R @var{filename}
905@itemx --just-symbols=@var{filename}
906Read symbol names and their addresses from @var{filename}, but do not
907relocate it or include it in the output. This allows your output file
908to refer symbolically to absolute locations of memory defined in other
909programs. You may use this option more than once.
910
ff5dcc92 911For compatibility with other ELF linkers, if the @option{-R} option is
252b5132 912followed by a directory name, rather than a file name, it is treated as
ff5dcc92 913the @option{-rpath} option.
252b5132
RH
914
915@kindex -s
916@kindex --strip-all
917@cindex strip all symbols
a1ab1d2a 918@item -s
252b5132
RH
919@itemx --strip-all
920Omit all symbol information from the output file.
921
922@kindex -S
923@kindex --strip-debug
924@cindex strip debugger symbols
a1ab1d2a 925@item -S
252b5132
RH
926@itemx --strip-debug
927Omit debugger symbol information (but not all symbols) from the output file.
928
929@kindex -t
930@kindex --trace
931@cindex input files, displaying
a1ab1d2a 932@item -t
252b5132 933@itemx --trace
ff5dcc92 934Print the names of the input files as @command{ld} processes them.
252b5132
RH
935
936@kindex -T @var{script}
937@kindex --script=@var{script}
938@cindex script files
939@item -T @var{scriptfile}
940@itemx --script=@var{scriptfile}
941Use @var{scriptfile} as the linker script. This script replaces
ff5dcc92 942@command{ld}'s default linker script (rather than adding to it), so
252b5132 943@var{commandfile} must specify everything necessary to describe the
114283d8
NC
944output file. @xref{Scripts}. If @var{scriptfile} does not exist in
945the current directory, @code{ld} looks for it in the directories
946specified by any preceding @samp{-L} options. Multiple @samp{-T}
947options accumulate.
252b5132 948
14be8564
L
949@kindex -dT @var{script}
950@kindex --default-script=@var{script}
951@cindex script files
952@item -dT @var{scriptfile}
953@itemx --default-script=@var{scriptfile}
954Use @var{scriptfile} as the default linker script. @xref{Scripts}.
955
956This option is similar to the @option{--script} option except that
957processing of the script is delayed until after the rest of the
958command line has been processed. This allows options placed after the
959@option{--default-script} option on the command line to affect the
960behaviour of the linker script, which can be important when the linker
961command line cannot be directly controlled by the user. (eg because
962the command line is being constructed by another tool, such as
963@samp{gcc}).
964
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RH
965@kindex -u @var{symbol}
966@kindex --undefined=@var{symbol}
967@cindex undefined symbol
968@item -u @var{symbol}
969@itemx --undefined=@var{symbol}
970Force @var{symbol} to be entered in the output file as an undefined
971symbol. Doing this may, for example, trigger linking of additional
972modules from standard libraries. @samp{-u} may be repeated with
973different option arguments to enter additional undefined symbols. This
974option is equivalent to the @code{EXTERN} linker script command.
975
976@kindex -Ur
977@cindex constructors
a1ab1d2a 978@item -Ur
252b5132
RH
979For anything other than C++ programs, this option is equivalent to
980@samp{-r}: it generates relocatable output---i.e., an output file that can in
ff5dcc92 981turn serve as input to @command{ld}. When linking C++ programs, @samp{-Ur}
252b5132
RH
982@emph{does} resolve references to constructors, unlike @samp{-r}.
983It does not work to use @samp{-Ur} on files that were themselves linked
984with @samp{-Ur}; once the constructor table has been built, it cannot
985be added to. Use @samp{-Ur} only for the last partial link, and
986@samp{-r} for the others.
987
577a0623
AM
988@kindex --unique[=@var{SECTION}]
989@item --unique[=@var{SECTION}]
990Creates a separate output section for every input section matching
991@var{SECTION}, or if the optional wildcard @var{SECTION} argument is
992missing, for every orphan input section. An orphan section is one not
993specifically mentioned in a linker script. You may use this option
994multiple times on the command line; It prevents the normal merging of
995input sections with the same name, overriding output section assignments
996in a linker script.
a854a4a7 997
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RH
998@kindex -v
999@kindex -V
1000@kindex --version
1001@cindex version
1002@item -v
1003@itemx --version
1004@itemx -V
ff5dcc92 1005Display the version number for @command{ld}. The @option{-V} option also
252b5132
RH
1006lists the supported emulations.
1007
1008@kindex -x
1009@kindex --discard-all
1010@cindex deleting local symbols
1011@item -x
1012@itemx --discard-all
1013Delete all local symbols.
1014
1015@kindex -X
1016@kindex --discard-locals
1017@cindex local symbols, deleting
a1ab1d2a 1018@item -X
252b5132 1019@itemx --discard-locals
3c68c38f
BW
1020Delete all temporary local symbols. (These symbols start with
1021system-specific local label prefixes, typically @samp{.L} for ELF systems
1022or @samp{L} for traditional a.out systems.)
252b5132
RH
1023
1024@kindex -y @var{symbol}
1025@kindex --trace-symbol=@var{symbol}
1026@cindex symbol tracing
1027@item -y @var{symbol}
1028@itemx --trace-symbol=@var{symbol}
1029Print the name of each linked file in which @var{symbol} appears. This
1030option may be given any number of times. On many systems it is necessary
1031to prepend an underscore.
1032
1033This option is useful when you have an undefined symbol in your link but
1034don't know where the reference is coming from.
1035
1036@kindex -Y @var{path}
1037@item -Y @var{path}
1038Add @var{path} to the default library search path. This option exists
1039for Solaris compatibility.
1040
1041@kindex -z @var{keyword}
1042@item -z @var{keyword}
cd6d6c15
NC
1043The recognized keywords are:
1044@table @samp
1045
1046@item combreloc
1047Combines multiple reloc sections and sorts them to make dynamic symbol
1048lookup caching possible.
1049
1050@item defs
560e09e9 1051Disallows undefined symbols in object files. Undefined symbols in
07f3b6ad 1052shared libraries are still allowed.
cd6d6c15 1053
6aa29e7b
JJ
1054@item execstack
1055Marks the object as requiring executable stack.
1056
b039ef04
L
1057@item global
1058This option is only meaningful when building a shared object. It makes
1059the symbols defined by this shared object available for symbol resolution
1060of subsequently loaded libraries.
1061
cd6d6c15
NC
1062@item initfirst
1063This option is only meaningful when building a shared object.
1064It marks the object so that its runtime initialization will occur
1065before the runtime initialization of any other objects brought into
1066the process at the same time. Similarly the runtime finalization of
1067the object will occur after the runtime finalization of any other
1068objects.
1069
1070@item interpose
1071Marks the object that its symbol table interposes before all symbols
1072but the primary executable.
1073
5fa222e4
AM
1074@item lazy
1075When generating an executable or shared library, mark it to tell the
1076dynamic linker to defer function call resolution to the point when
1077the function is called (lazy binding), rather than at load time.
1078Lazy binding is the default.
1079
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NC
1080@item loadfltr
1081Marks the object that its filters be processed immediately at
1082runtime.
1083
1084@item muldefs
1085Allows multiple definitions.
1086
1087@item nocombreloc
1088Disables multiple reloc sections combining.
1089
1090@item nocopyreloc
daf220f0
AM
1091Disable linker generated .dynbss variables used in place of variables
1092defined in shared libraries. May result in dynamic text relocations.
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1093
1094@item nodefaultlib
1095Marks the object that the search for dependencies of this object will
1096ignore any default library search paths.
1097
1098@item nodelete
1099Marks the object shouldn't be unloaded at runtime.
1100
1101@item nodlopen
1102Marks the object not available to @code{dlopen}.
1103
1104@item nodump
1105Marks the object can not be dumped by @code{dldump}.
1106
6aa29e7b
JJ
1107@item noexecstack
1108Marks the object as not requiring executable stack.
1109
8dfef1bd
L
1110@item text
1111Treat DT_TEXTREL in shared object as error.
1112
1113@item notext
1114Don't treat DT_TEXTREL in shared object as error.
1115
1116@item textoff
1117Don't treat DT_TEXTREL in shared object as error.
1118
6aa29e7b
JJ
1119@item norelro
1120Don't create an ELF @code{PT_GNU_RELRO} segment header in the object.
1121
cd6d6c15
NC
1122@item now
1123When generating an executable or shared library, mark it to tell the
1124dynamic linker to resolve all symbols when the program is started, or
1125when the shared library is linked to using dlopen, instead of
1126deferring function call resolution to the point when the function is
1127first called.
1128
1129@item origin
1130Marks the object may contain $ORIGIN.
1131
6aa29e7b
JJ
1132@item relro
1133Create an ELF @code{PT_GNU_RELRO} segment header in the object.
1134
24718e3b
L
1135@item max-page-size=@var{value}
1136Set the emulation maximum page size to @var{value}.
1137
1138@item common-page-size=@var{value}
1139Set the emulation common page size to @var{value}.
1140
04c3a755
NS
1141@item stack-size=@var{value}
1142Specify a stack size for in an ELF @code{PT_GNU_STACK} segment.
1143Specifying zero will override any default non-zero sized
1144@code{PT_GNU_STACK} segment creation.
1145
d258b828
IZ
1146@item bndplt
1147Always generate BND prefix in PLT entries. Supported for Linux/x86_64.
1148
889c2a67
L
1149@item noextern-protected-data
1150Don't treat protected data symbol as external when building shared
1151library. This option overrides linker backend default. It can be used
1152to workaround incorrect relocations against protected data symbols
1153generated by compiler. Updates on protected data symbols by another
1154module aren't visibile to the resulting shared library. Supported for
1155i386 and x86-64.
1156
cd6d6c15
NC
1157@end table
1158
ece2d90e 1159Other keywords are ignored for Solaris compatibility.
252b5132
RH
1160
1161@kindex -(
1162@cindex groups of archives
1163@item -( @var{archives} -)
1164@itemx --start-group @var{archives} --end-group
1165The @var{archives} should be a list of archive files. They may be
1166either explicit file names, or @samp{-l} options.
1167
1168The specified archives are searched repeatedly until no new undefined
1169references are created. Normally, an archive is searched only once in
1170the order that it is specified on the command line. If a symbol in that
1171archive is needed to resolve an undefined symbol referred to by an
1172object in an archive that appears later on the command line, the linker
1173would not be able to resolve that reference. By grouping the archives,
1174they all be searched repeatedly until all possible references are
1175resolved.
1176
1177Using this option has a significant performance cost. It is best to use
1178it only when there are unavoidable circular references between two or
1179more archives.
1180
69da35b5
NC
1181@kindex --accept-unknown-input-arch
1182@kindex --no-accept-unknown-input-arch
1183@item --accept-unknown-input-arch
1184@itemx --no-accept-unknown-input-arch
1185Tells the linker to accept input files whose architecture cannot be
2ca22b03 1186recognised. The assumption is that the user knows what they are doing
69da35b5
NC
1187and deliberately wants to link in these unknown input files. This was
1188the default behaviour of the linker, before release 2.14. The default
1189behaviour from release 2.14 onwards is to reject such input files, and
1190so the @samp{--accept-unknown-input-arch} option has been added to
1191restore the old behaviour.
2ca22b03 1192
4a43e768
AM
1193@kindex --as-needed
1194@kindex --no-as-needed
1195@item --as-needed
1196@itemx --no-as-needed
1197This option affects ELF DT_NEEDED tags for dynamic libraries mentioned
ddbb8a31 1198on the command line after the @option{--as-needed} option. Normally
4a43e768
AM
1199the linker will add a DT_NEEDED tag for each dynamic library mentioned
1200on the command line, regardless of whether the library is actually
ddbb8a31 1201needed or not. @option{--as-needed} causes a DT_NEEDED tag to only be
ffa9430d
AM
1202emitted for a library that @emph{at that point in the link} satisfies a
1203non-weak undefined symbol reference from a regular object file or, if
1240be6b
AM
1204the library is not found in the DT_NEEDED lists of other needed libraries, a
1205non-weak undefined symbol reference from another needed dynamic library.
ffa9430d
AM
1206Object files or libraries appearing on the command line @emph{after}
1207the library in question do not affect whether the library is seen as
1208needed. This is similar to the rules for extraction of object files
1209from archives. @option{--no-as-needed} restores the default behaviour.
4a43e768 1210
e56f61be
L
1211@kindex --add-needed
1212@kindex --no-add-needed
1213@item --add-needed
1214@itemx --no-add-needed
ddbb8a31
NC
1215These two options have been deprecated because of the similarity of
1216their names to the @option{--as-needed} and @option{--no-as-needed}
1217options. They have been replaced by @option{--copy-dt-needed-entries}
1218and @option{--no-copy-dt-needed-entries}.
e56f61be 1219
252b5132
RH
1220@kindex -assert @var{keyword}
1221@item -assert @var{keyword}
1222This option is ignored for SunOS compatibility.
1223
1224@kindex -Bdynamic
1225@kindex -dy
1226@kindex -call_shared
1227@item -Bdynamic
1228@itemx -dy
1229@itemx -call_shared
1230Link against dynamic libraries. This is only meaningful on platforms
1231for which shared libraries are supported. This option is normally the
1232default on such platforms. The different variants of this option are
1233for compatibility with various systems. You may use this option
1234multiple times on the command line: it affects library searching for
da8bce14 1235@option{-l} options which follow it.
252b5132 1236
a1ab1d2a
UD
1237@kindex -Bgroup
1238@item -Bgroup
1239Set the @code{DF_1_GROUP} flag in the @code{DT_FLAGS_1} entry in the dynamic
1240section. This causes the runtime linker to handle lookups in this
1241object and its dependencies to be performed only inside the group.
560e09e9
NC
1242@option{--unresolved-symbols=report-all} is implied. This option is
1243only meaningful on ELF platforms which support shared libraries.
a1ab1d2a 1244
252b5132
RH
1245@kindex -Bstatic
1246@kindex -dn
1247@kindex -non_shared
1248@kindex -static
a1ab1d2a 1249@item -Bstatic
252b5132
RH
1250@itemx -dn
1251@itemx -non_shared
1252@itemx -static
1253Do not link against shared libraries. This is only meaningful on
1254platforms for which shared libraries are supported. The different
1255variants of this option are for compatibility with various systems. You
1256may use this option multiple times on the command line: it affects
560e09e9 1257library searching for @option{-l} options which follow it. This
e9156f74
NC
1258option also implies @option{--unresolved-symbols=report-all}. This
1259option can be used with @option{-shared}. Doing so means that a
1260shared library is being created but that all of the library's external
1261references must be resolved by pulling in entries from static
ece2d90e 1262libraries.
252b5132
RH
1263
1264@kindex -Bsymbolic
1265@item -Bsymbolic
1266When creating a shared library, bind references to global symbols to the
1267definition within the shared library, if any. Normally, it is possible
1268for a program linked against a shared library to override the definition
1269within the shared library. This option is only meaningful on ELF
1270platforms which support shared libraries.
1271
40b36307
L
1272@kindex -Bsymbolic-functions
1273@item -Bsymbolic-functions
1274When creating a shared library, bind references to global function
c0065db7 1275symbols to the definition within the shared library, if any.
40b36307
L
1276This option is only meaningful on ELF platforms which support shared
1277libraries.
1278
55255dae
L
1279@kindex --dynamic-list=@var{dynamic-list-file}
1280@item --dynamic-list=@var{dynamic-list-file}
1281Specify the name of a dynamic list file to the linker. This is
1282typically used when creating shared libraries to specify a list of
1283global symbols whose references shouldn't be bound to the definition
1284within the shared library, or creating dynamically linked executables
1285to specify a list of symbols which should be added to the symbol table
1286in the executable. This option is only meaningful on ELF platforms
1287which support shared libraries.
1288
1289The format of the dynamic list is the same as the version node without
1290scope and node name. See @ref{VERSION} for more information.
1291
40b36307
L
1292@kindex --dynamic-list-data
1293@item --dynamic-list-data
1294Include all global data symbols to the dynamic list.
1295
1296@kindex --dynamic-list-cpp-new
1297@item --dynamic-list-cpp-new
1298Provide the builtin dynamic list for C++ operator new and delete. It
1299is mainly useful for building shared libstdc++.
1300
0b8a70d9
L
1301@kindex --dynamic-list-cpp-typeinfo
1302@item --dynamic-list-cpp-typeinfo
1303Provide the builtin dynamic list for C++ runtime type identification.
1304
252b5132
RH
1305@kindex --check-sections
1306@kindex --no-check-sections
1307@item --check-sections
308b1ffd 1308@itemx --no-check-sections
252b5132 1309Asks the linker @emph{not} to check section addresses after they have
7d816a17 1310been assigned to see if there are any overlaps. Normally the linker will
252b5132
RH
1311perform this check, and if it finds any overlaps it will produce
1312suitable error messages. The linker does know about, and does make
1313allowances for sections in overlays. The default behaviour can be
560e09e9 1314restored by using the command line switch @option{--check-sections}.
02b0b1aa
NS
1315Section overlap is not usually checked for relocatable links. You can
1316force checking in that case by using the @option{--check-sections}
1317option.
252b5132 1318
ddbb8a31
NC
1319@kindex --copy-dt-needed-entries
1320@kindex --no-copy-dt-needed-entries
1321@item --copy-dt-needed-entries
1322@itemx --no-copy-dt-needed-entries
9d5777a3 1323This option affects the treatment of dynamic libraries referred to
ddbb8a31 1324by DT_NEEDED tags @emph{inside} ELF dynamic libraries mentioned on the
08efffb8 1325command line. Normally the linker won't add a DT_NEEDED tag to the
ddbb8a31 1326output binary for each library mentioned in a DT_NEEDED tag in an
08efffb8 1327input dynamic library. With @option{--copy-dt-needed-entries}
ddbb8a31 1328specified on the command line however any dynamic libraries that
08efffb8
MM
1329follow it will have their DT_NEEDED entries added. The default
1330behaviour can be restored with @option{--no-copy-dt-needed-entries}.
ddbb8a31
NC
1331
1332This option also has an effect on the resolution of symbols in dynamic
08efffb8
MM
1333libraries. With @option{--copy-dt-needed-entries} dynamic libraries
1334mentioned on the command line will be recursively searched, following
1335their DT_NEEDED tags to other libraries, in order to resolve symbols
1336required by the output binary. With the default setting however
1337the searching of dynamic libraries that follow it will stop with the
1338dynamic library itself. No DT_NEEDED links will be traversed to resolve
ddbb8a31
NC
1339symbols.
1340
252b5132
RH
1341@cindex cross reference table
1342@kindex --cref
1343@item --cref
1344Output a cross reference table. If a linker map file is being
1345generated, the cross reference table is printed to the map file.
1346Otherwise, it is printed on the standard output.
1347
1348The format of the table is intentionally simple, so that it may be
1349easily processed by a script if necessary. The symbols are printed out,
1350sorted by name. For each symbol, a list of file names is given. If the
1351symbol is defined, the first file listed is the location of the
049c1c8e
NC
1352definition. If the symbol is defined as a common value then any files
1353where this happens appear next. Finally any files that reference the
1354symbol are listed.
252b5132 1355
4818e05f
AM
1356@cindex common allocation
1357@kindex --no-define-common
1358@item --no-define-common
1359This option inhibits the assignment of addresses to common symbols.
1360The script command @code{INHIBIT_COMMON_ALLOCATION} has the same effect.
1361@xref{Miscellaneous Commands}.
1362
1363The @samp{--no-define-common} option allows decoupling
1364the decision to assign addresses to Common symbols from the choice
1365of the output file type; otherwise a non-Relocatable output type
1366forces assigning addresses to Common symbols.
1367Using @samp{--no-define-common} allows Common symbols that are referenced
1368from a shared library to be assigned addresses only in the main program.
1369This eliminates the unused duplicate space in the shared library,
1370and also prevents any possible confusion over resolving to the wrong
1371duplicate when there are many dynamic modules with specialized search
1372paths for runtime symbol resolution.
1373
252b5132 1374@cindex symbols, from command line
2509a395
SL
1375@kindex --defsym=@var{symbol}=@var{exp}
1376@item --defsym=@var{symbol}=@var{expression}
252b5132
RH
1377Create a global symbol in the output file, containing the absolute
1378address given by @var{expression}. You may use this option as many
1379times as necessary to define multiple symbols in the command line. A
1380limited form of arithmetic is supported for the @var{expression} in this
1381context: you may give a hexadecimal constant or the name of an existing
1382symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
1383constants or symbols. If you need more elaborate expressions, consider
66bc8739
AM
1384using the linker command language from a script (@pxref{Assignments}).
1385@emph{Note:} there should be no white space between @var{symbol}, the
1386equals sign (``@key{=}''), and @var{expression}.
252b5132
RH
1387
1388@cindex demangling, from command line
28c309a2 1389@kindex --demangle[=@var{style}]
252b5132 1390@kindex --no-demangle
28c309a2 1391@item --demangle[=@var{style}]
252b5132
RH
1392@itemx --no-demangle
1393These options control whether to demangle symbol names in error messages
1394and other output. When the linker is told to demangle, it tries to
1395present symbol names in a readable fashion: it strips leading
1396underscores if they are used by the object file format, and converts C++
a1ab1d2a
UD
1397mangled symbol names into user readable names. Different compilers have
1398different mangling styles. The optional demangling style argument can be used
1399to choose an appropriate demangling style for your compiler. The linker will
28c309a2
NC
1400demangle by default unless the environment variable @samp{COLLECT_NO_DEMANGLE}
1401is set. These options may be used to override the default.
252b5132
RH
1402
1403@cindex dynamic linker, from command line
506eee22 1404@kindex -I@var{file}
2509a395
SL
1405@kindex --dynamic-linker=@var{file}
1406@item -I@var{file}
1407@itemx --dynamic-linker=@var{file}
252b5132
RH
1408Set the name of the dynamic linker. This is only meaningful when
1409generating dynamically linked ELF executables. The default dynamic
1410linker is normally correct; don't use this unless you know what you are
1411doing.
1412
7ce691ae 1413@kindex --fatal-warnings
0fe58ccd 1414@kindex --no-fatal-warnings
7ce691ae 1415@item --fatal-warnings
0fe58ccd
NC
1416@itemx --no-fatal-warnings
1417Treat all warnings as errors. The default behaviour can be restored
1418with the option @option{--no-fatal-warnings}.
7ce691ae 1419
252b5132
RH
1420@kindex --force-exe-suffix
1421@item --force-exe-suffix
1422Make sure that an output file has a .exe suffix.
1423
1424If a successfully built fully linked output file does not have a
1425@code{.exe} or @code{.dll} suffix, this option forces the linker to copy
1426the output file to one of the same name with a @code{.exe} suffix. This
1427option is useful when using unmodified Unix makefiles on a Microsoft
1428Windows host, since some versions of Windows won't run an image unless
1429it ends in a @code{.exe} suffix.
1430
1431@kindex --gc-sections
1432@kindex --no-gc-sections
1433@cindex garbage collection
c17d87de
NC
1434@item --gc-sections
1435@itemx --no-gc-sections
252b5132 1436Enable garbage collection of unused input sections. It is ignored on
ac69cbc6 1437targets that do not support this option. The default behaviour (of not
b3549761
NC
1438performing this garbage collection) can be restored by specifying
1439@samp{--no-gc-sections} on the command line.
252b5132 1440
d5465ba2
AM
1441@samp{--gc-sections} decides which input sections are used by
1442examining symbols and relocations. The section containing the entry
1443symbol and all sections containing symbols undefined on the
1444command-line will be kept, as will sections containing symbols
1445referenced by dynamic objects. Note that when building shared
1446libraries, the linker must assume that any visible symbol is
1447referenced. Once this initial set of sections has been determined,
1448the linker recursively marks as used any section referenced by their
1449relocations. See @samp{--entry} and @samp{--undefined}.
1450
ac69cbc6 1451This option can be set when doing a partial link (enabled with option
9d5777a3 1452@samp{-r}). In this case the root of symbols kept must be explicitly
ac69cbc6
TG
1453specified either by an @samp{--entry} or @samp{--undefined} option or by
1454a @code{ENTRY} command in the linker script.
1455
c17d87de
NC
1456@kindex --print-gc-sections
1457@kindex --no-print-gc-sections
1458@cindex garbage collection
1459@item --print-gc-sections
1460@itemx --no-print-gc-sections
1461List all sections removed by garbage collection. The listing is
1462printed on stderr. This option is only effective if garbage
1463collection has been enabled via the @samp{--gc-sections}) option. The
1464default behaviour (of not listing the sections that are removed) can
1465be restored by specifying @samp{--no-print-gc-sections} on the command
1466line.
1467
30824704
RM
1468@kindex --print-output-format
1469@cindex output format
1470@item --print-output-format
1471Print the name of the default output format (perhaps influenced by
1472other command-line options). This is the string that would appear
1473in an @code{OUTPUT_FORMAT} linker script command (@pxref{File Commands}).
1474
252b5132
RH
1475@cindex help
1476@cindex usage
1477@kindex --help
1478@item --help
1479Print a summary of the command-line options on the standard output and exit.
1480
ea20a7da
CC
1481@kindex --target-help
1482@item --target-help
1483Print a summary of all target specific options on the standard output and exit.
1484
2509a395
SL
1485@kindex -Map=@var{mapfile}
1486@item -Map=@var{mapfile}
252b5132 1487Print a link map to the file @var{mapfile}. See the description of the
560e09e9 1488@option{-M} option, above.
252b5132
RH
1489
1490@cindex memory usage
1491@kindex --no-keep-memory
1492@item --no-keep-memory
ff5dcc92
SC
1493@command{ld} normally optimizes for speed over memory usage by caching the
1494symbol tables of input files in memory. This option tells @command{ld} to
252b5132 1495instead optimize for memory usage, by rereading the symbol tables as
ff5dcc92 1496necessary. This may be required if @command{ld} runs out of memory space
252b5132
RH
1497while linking a large executable.
1498
1499@kindex --no-undefined
a1ab1d2a 1500@kindex -z defs
252b5132 1501@item --no-undefined
a1ab1d2a 1502@itemx -z defs
560e09e9
NC
1503Report unresolved symbol references from regular object files. This
1504is done even if the linker is creating a non-symbolic shared library.
1505The switch @option{--[no-]allow-shlib-undefined} controls the
1506behaviour for reporting unresolved references found in shared
ece2d90e 1507libraries being linked in.
252b5132 1508
aa713662
L
1509@kindex --allow-multiple-definition
1510@kindex -z muldefs
1511@item --allow-multiple-definition
1512@itemx -z muldefs
1513Normally when a symbol is defined multiple times, the linker will
1514report a fatal error. These options allow multiple definitions and the
1515first definition will be used.
1516
b79e8c78 1517@kindex --allow-shlib-undefined
ae9a127f 1518@kindex --no-allow-shlib-undefined
b79e8c78 1519@item --allow-shlib-undefined
ae9a127f 1520@itemx --no-allow-shlib-undefined
903249d7 1521Allows or disallows undefined symbols in shared libraries.
560e09e9
NC
1522This switch is similar to @option{--no-undefined} except that it
1523determines the behaviour when the undefined symbols are in a
1524shared library rather than a regular object file. It does not affect
1525how undefined symbols in regular object files are handled.
1526
903249d7
NC
1527The default behaviour is to report errors for any undefined symbols
1528referenced in shared libraries if the linker is being used to create
1529an executable, but to allow them if the linker is being used to create
1530a shared library.
1531
1532The reasons for allowing undefined symbol references in shared
1533libraries specified at link time are that:
1534
1535@itemize @bullet
1536@item
1537A shared library specified at link time may not be the same as the one
1538that is available at load time, so the symbol might actually be
1539resolvable at load time.
1540@item
1541There are some operating systems, eg BeOS and HPPA, where undefined
1542symbols in shared libraries are normal.
1543
1544The BeOS kernel for example patches shared libraries at load time to
1545select whichever function is most appropriate for the current
1546architecture. This is used, for example, to dynamically select an
1547appropriate memset function.
1548@end itemize
b79e8c78 1549
31941635
L
1550@kindex --no-undefined-version
1551@item --no-undefined-version
1552Normally when a symbol has an undefined version, the linker will ignore
1553it. This option disallows symbols with undefined version and a fatal error
1554will be issued instead.
1555
3e3b46e5
PB
1556@kindex --default-symver
1557@item --default-symver
1558Create and use a default symbol version (the soname) for unversioned
fc0e6df6
PB
1559exported symbols.
1560
1561@kindex --default-imported-symver
1562@item --default-imported-symver
1563Create and use a default symbol version (the soname) for unversioned
1564imported symbols.
3e3b46e5 1565
252b5132
RH
1566@kindex --no-warn-mismatch
1567@item --no-warn-mismatch
ff5dcc92 1568Normally @command{ld} will give an error if you try to link together input
252b5132
RH
1569files that are mismatched for some reason, perhaps because they have
1570been compiled for different processors or for different endiannesses.
ff5dcc92 1571This option tells @command{ld} that it should silently permit such possible
252b5132
RH
1572errors. This option should only be used with care, in cases when you
1573have taken some special action that ensures that the linker errors are
1574inappropriate.
1575
fe7929ce
AM
1576@kindex --no-warn-search-mismatch
1577@item --no-warn-search-mismatch
1578Normally @command{ld} will give a warning if it finds an incompatible
1579library during a library search. This option silences the warning.
1580
252b5132
RH
1581@kindex --no-whole-archive
1582@item --no-whole-archive
ff5dcc92 1583Turn off the effect of the @option{--whole-archive} option for subsequent
252b5132
RH
1584archive files.
1585
1586@cindex output file after errors
1587@kindex --noinhibit-exec
1588@item --noinhibit-exec
1589Retain the executable output file whenever it is still usable.
1590Normally, the linker will not produce an output file if it encounters
1591errors during the link process; it exits without writing an output file
1592when it issues any error whatsoever.
1593
0a9c1c8e
CD
1594@kindex -nostdlib
1595@item -nostdlib
1596Only search library directories explicitly specified on the
1597command line. Library directories specified in linker scripts
1598(including linker scripts specified on the command line) are ignored.
1599
252b5132 1600@ifclear SingleFormat
2509a395
SL
1601@kindex --oformat=@var{output-format}
1602@item --oformat=@var{output-format}
ff5dcc92
SC
1603@command{ld} may be configured to support more than one kind of object
1604file. If your @command{ld} is configured this way, you can use the
252b5132 1605@samp{--oformat} option to specify the binary format for the output
ff5dcc92
SC
1606object file. Even when @command{ld} is configured to support alternative
1607object formats, you don't usually need to specify this, as @command{ld}
252b5132
RH
1608should be configured to produce as a default output format the most
1609usual format on each machine. @var{output-format} is a text string, the
1610name of a particular format supported by the BFD libraries. (You can
1611list the available binary formats with @samp{objdump -i}.) The script
1612command @code{OUTPUT_FORMAT} can also specify the output format, but
1613this option overrides it. @xref{BFD}.
1614@end ifclear
1615
36af4a4e
JJ
1616@kindex -pie
1617@kindex --pic-executable
1618@item -pie
1619@itemx --pic-executable
1620@cindex position independent executables
1621Create a position independent executable. This is currently only supported on
1622ELF platforms. Position independent executables are similar to shared
1623libraries in that they are relocated by the dynamic linker to the virtual
7e7d5768 1624address the OS chooses for them (which can vary between invocations). Like
36af4a4e
JJ
1625normal dynamically linked executables they can be executed and symbols
1626defined in the executable cannot be overridden by shared libraries.
1627
252b5132
RH
1628@kindex -qmagic
1629@item -qmagic
1630This option is ignored for Linux compatibility.
1631
1632@kindex -Qy
1633@item -Qy
1634This option is ignored for SVR4 compatibility.
1635
1636@kindex --relax
1637@cindex synthesizing linker
1638@cindex relaxing addressing modes
28d5f677 1639@cindex --no-relax
252b5132 1640@item --relax
28d5f677 1641@itemx --no-relax
a1ab1d2a 1642An option with machine dependent effects.
252b5132
RH
1643@ifset GENERIC
1644This option is only supported on a few targets.
1645@end ifset
1646@ifset H8300
ff5dcc92 1647@xref{H8/300,,@command{ld} and the H8/300}.
252b5132
RH
1648@end ifset
1649@ifset I960
ff5dcc92 1650@xref{i960,, @command{ld} and the Intel 960 family}.
252b5132 1651@end ifset
e0001a05
NC
1652@ifset XTENSA
1653@xref{Xtensa,, @command{ld} and Xtensa Processors}.
1654@end ifset
93fd0973
SC
1655@ifset M68HC11
1656@xref{M68HC11/68HC12,,@command{ld} and the 68HC11 and 68HC12}.
1657@end ifset
78058a5e
SL
1658@ifset NIOSII
1659@xref{Nios II,,@command{ld} and the Altera Nios II}.
1660@end ifset
2a60a7a8
AM
1661@ifset POWERPC
1662@xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}.
1663@end ifset
252b5132 1664
28d5f677
NC
1665On some platforms the @samp{--relax} option performs target specific,
1666global optimizations that become possible when the linker resolves
1667addressing in the program, such as relaxing address modes,
1668synthesizing new instructions, selecting shorter version of current
11e7fd74 1669instructions, and combining constant values.
252b5132
RH
1670
1671On some platforms these link time global optimizations may make symbolic
1672debugging of the resulting executable impossible.
1673@ifset GENERIC
28d5f677
NC
1674This is known to be the case for the Matsushita MN10200 and MN10300
1675family of processors.
252b5132
RH
1676@end ifset
1677
1678@ifset GENERIC
1679On platforms where this is not supported, @samp{--relax} is accepted,
1680but ignored.
1681@end ifset
1682
28d5f677
NC
1683On platforms where @samp{--relax} is accepted the option
1684@samp{--no-relax} can be used to disable the feature.
1685
252b5132
RH
1686@cindex retaining specified symbols
1687@cindex stripping all but some symbols
1688@cindex symbols, retaining selectively
2509a395
SL
1689@kindex --retain-symbols-file=@var{filename}
1690@item --retain-symbols-file=@var{filename}
252b5132
RH
1691Retain @emph{only} the symbols listed in the file @var{filename},
1692discarding all others. @var{filename} is simply a flat file, with one
1693symbol name per line. This option is especially useful in environments
1694@ifset GENERIC
1695(such as VxWorks)
1696@end ifset
1697where a large global symbol table is accumulated gradually, to conserve
1698run-time memory.
1699
1700@samp{--retain-symbols-file} does @emph{not} discard undefined symbols,
1701or symbols needed for relocations.
1702
1703You may only specify @samp{--retain-symbols-file} once in the command
1704line. It overrides @samp{-s} and @samp{-S}.
1705
1706@ifset GENERIC
2509a395 1707@item -rpath=@var{dir}
252b5132 1708@cindex runtime library search path
2509a395 1709@kindex -rpath=@var{dir}
252b5132 1710Add a directory to the runtime library search path. This is used when
ff5dcc92 1711linking an ELF executable with shared objects. All @option{-rpath}
252b5132 1712arguments are concatenated and passed to the runtime linker, which uses
ff5dcc92 1713them to locate shared objects at runtime. The @option{-rpath} option is
252b5132
RH
1714also used when locating shared objects which are needed by shared
1715objects explicitly included in the link; see the description of the
ff5dcc92 1716@option{-rpath-link} option. If @option{-rpath} is not used when linking an
252b5132
RH
1717ELF executable, the contents of the environment variable
1718@code{LD_RUN_PATH} will be used if it is defined.
1719
ff5dcc92 1720The @option{-rpath} option may also be used on SunOS. By default, on
252b5132 1721SunOS, the linker will form a runtime search patch out of all the
ff5dcc92
SC
1722@option{-L} options it is given. If a @option{-rpath} option is used, the
1723runtime search path will be formed exclusively using the @option{-rpath}
1724options, ignoring the @option{-L} options. This can be useful when using
1725gcc, which adds many @option{-L} options which may be on NFS mounted
b45619c0 1726file systems.
252b5132 1727
ff5dcc92 1728For compatibility with other ELF linkers, if the @option{-R} option is
252b5132 1729followed by a directory name, rather than a file name, it is treated as
ff5dcc92 1730the @option{-rpath} option.
252b5132
RH
1731@end ifset
1732
1733@ifset GENERIC
1734@cindex link-time runtime library search path
2509a395
SL
1735@kindex -rpath-link=@var{dir}
1736@item -rpath-link=@var{dir}
252b5132
RH
1737When using ELF or SunOS, one shared library may require another. This
1738happens when an @code{ld -shared} link includes a shared library as one
1739of the input files.
1740
1741When the linker encounters such a dependency when doing a non-shared,
1742non-relocatable link, it will automatically try to locate the required
1743shared library and include it in the link, if it is not included
ff5dcc92 1744explicitly. In such a case, the @option{-rpath-link} option
252b5132 1745specifies the first set of directories to search. The
ff5dcc92 1746@option{-rpath-link} option may specify a sequence of directory names
252b5132
RH
1747either by specifying a list of names separated by colons, or by
1748appearing multiple times.
1749
28c309a2
NC
1750This option should be used with caution as it overrides the search path
1751that may have been hard compiled into a shared library. In such a case it
1752is possible to use unintentionally a different search path than the
1753runtime linker would do.
1754
252b5132 1755The linker uses the following search paths to locate required shared
ece2d90e 1756libraries:
252b5132
RH
1757@enumerate
1758@item
ff5dcc92 1759Any directories specified by @option{-rpath-link} options.
252b5132 1760@item
ff5dcc92
SC
1761Any directories specified by @option{-rpath} options. The difference
1762between @option{-rpath} and @option{-rpath-link} is that directories
1763specified by @option{-rpath} options are included in the executable and
1764used at runtime, whereas the @option{-rpath-link} option is only effective
ece2d90e
NC
1765at link time. Searching @option{-rpath} in this way is only supported
1766by native linkers and cross linkers which have been configured with
1767the @option{--with-sysroot} option.
252b5132 1768@item
e2a83dd0
NC
1769On an ELF system, for native linkers, if the @option{-rpath} and
1770@option{-rpath-link} options were not used, search the contents of the
1771environment variable @code{LD_RUN_PATH}.
252b5132 1772@item
ff5dcc92
SC
1773On SunOS, if the @option{-rpath} option was not used, search any
1774directories specified using @option{-L} options.
252b5132 1775@item
a1b8d843 1776For a native linker, search the contents of the environment
e2a83dd0 1777variable @code{LD_LIBRARY_PATH}.
252b5132 1778@item
ec4eb78a
L
1779For a native ELF linker, the directories in @code{DT_RUNPATH} or
1780@code{DT_RPATH} of a shared library are searched for shared
1781libraries needed by it. The @code{DT_RPATH} entries are ignored if
1782@code{DT_RUNPATH} entries exist.
1783@item
252b5132
RH
1784The default directories, normally @file{/lib} and @file{/usr/lib}.
1785@item
1786For a native linker on an ELF system, if the file @file{/etc/ld.so.conf}
1787exists, the list of directories found in that file.
1788@end enumerate
1789
1790If the required shared library is not found, the linker will issue a
1791warning and continue with the link.
1792@end ifset
1793
1794@kindex -shared
1795@kindex -Bshareable
1796@item -shared
1797@itemx -Bshareable
1798@cindex shared libraries
1799Create a shared library. This is currently only supported on ELF, XCOFF
1800and SunOS platforms. On SunOS, the linker will automatically create a
ff5dcc92 1801shared library if the @option{-e} option is not used and there are
252b5132
RH
1802undefined symbols in the link.
1803
252b5132 1804@kindex --sort-common
2509a395
SL
1805@item --sort-common
1806@itemx --sort-common=ascending
1807@itemx --sort-common=descending
de7dd2bd
NC
1808This option tells @command{ld} to sort the common symbols by alignment in
1809ascending or descending order when it places them in the appropriate output
1810sections. The symbol alignments considered are sixteen-byte or larger,
1811eight-byte, four-byte, two-byte, and one-byte. This is to prevent gaps
1812between symbols due to alignment constraints. If no sorting order is
1813specified, then descending order is assumed.
252b5132 1814
2509a395
SL
1815@kindex --sort-section=name
1816@item --sort-section=name
bcaa7b3e
L
1817This option will apply @code{SORT_BY_NAME} to all wildcard section
1818patterns in the linker script.
1819
2509a395
SL
1820@kindex --sort-section=alignment
1821@item --sort-section=alignment
bcaa7b3e
L
1822This option will apply @code{SORT_BY_ALIGNMENT} to all wildcard section
1823patterns in the linker script.
1824
252b5132 1825@kindex --split-by-file
2509a395 1826@item --split-by-file[=@var{size}]
ff5dcc92 1827Similar to @option{--split-by-reloc} but creates a new output section for
a854a4a7
AM
1828each input file when @var{size} is reached. @var{size} defaults to a
1829size of 1 if not given.
252b5132
RH
1830
1831@kindex --split-by-reloc
2509a395 1832@item --split-by-reloc[=@var{count}]
a854a4a7 1833Tries to creates extra sections in the output file so that no single
252b5132 1834output section in the file contains more than @var{count} relocations.
a854a4a7 1835This is useful when generating huge relocatable files for downloading into
252b5132
RH
1836certain real time kernels with the COFF object file format; since COFF
1837cannot represent more than 65535 relocations in a single section. Note
1838that this will fail to work with object file formats which do not
1839support arbitrary sections. The linker will not split up individual
1840input sections for redistribution, so if a single input section contains
1841more than @var{count} relocations one output section will contain that
a854a4a7 1842many relocations. @var{count} defaults to a value of 32768.
252b5132
RH
1843
1844@kindex --stats
1845@item --stats
1846Compute and display statistics about the operation of the linker, such
1847as execution time and memory usage.
1848
2509a395 1849@kindex --sysroot=@var{directory}
e2243057
RS
1850@item --sysroot=@var{directory}
1851Use @var{directory} as the location of the sysroot, overriding the
1852configure-time default. This option is only supported by linkers
1853that were configured using @option{--with-sysroot}.
1854
252b5132
RH
1855@kindex --traditional-format
1856@cindex traditional format
1857@item --traditional-format
ff5dcc92
SC
1858For some targets, the output of @command{ld} is different in some ways from
1859the output of some existing linker. This switch requests @command{ld} to
252b5132
RH
1860use the traditional format instead.
1861
1862@cindex dbx
ff5dcc92 1863For example, on SunOS, @command{ld} combines duplicate entries in the
252b5132
RH
1864symbol string table. This can reduce the size of an output file with
1865full debugging information by over 30 percent. Unfortunately, the SunOS
1866@code{dbx} program can not read the resulting program (@code{gdb} has no
ff5dcc92 1867trouble). The @samp{--traditional-format} switch tells @command{ld} to not
252b5132
RH
1868combine duplicate entries.
1869
2509a395
SL
1870@kindex --section-start=@var{sectionname}=@var{org}
1871@item --section-start=@var{sectionname}=@var{org}
176355da
NC
1872Locate a section in the output file at the absolute
1873address given by @var{org}. You may use this option as many
1874times as necessary to locate multiple sections in the command
1875line.
1876@var{org} must be a single hexadecimal integer;
1877for compatibility with other linkers, you may omit the leading
1878@samp{0x} usually associated with hexadecimal values. @emph{Note:} there
1879should be no white space between @var{sectionname}, the equals
1880sign (``@key{=}''), and @var{org}.
1881
2509a395
SL
1882@kindex -Tbss=@var{org}
1883@kindex -Tdata=@var{org}
1884@kindex -Ttext=@var{org}
252b5132 1885@cindex segment origins, cmd line
2509a395
SL
1886@item -Tbss=@var{org}
1887@itemx -Tdata=@var{org}
1888@itemx -Ttext=@var{org}
1889Same as @option{--section-start}, with @code{.bss}, @code{.data} or
a6e02871 1890@code{.text} as the @var{sectionname}.
252b5132 1891
2509a395
SL
1892@kindex -Ttext-segment=@var{org}
1893@item -Ttext-segment=@var{org}
258795f5 1894@cindex text segment origin, cmd line
2b8c06a3
L
1895When creating an ELF executable, it will set the address of the first
1896byte of the text segment.
258795f5 1897
9d5777a3
RM
1898@kindex -Trodata-segment=@var{org}
1899@item -Trodata-segment=@var{org}
1900@cindex rodata segment origin, cmd line
1901When creating an ELF executable or shared object for a target where
1902the read-only data is in its own segment separate from the executable
1903text, it will set the address of the first byte of the read-only data segment.
1904
0d705e9f
AM
1905@kindex -Tldata-segment=@var{org}
1906@item -Tldata-segment=@var{org}
1907@cindex ldata segment origin, cmd line
1908When creating an ELF executable or shared object for x86-64 medium memory
1909model, it will set the address of the first byte of the ldata segment.
1910
560e09e9
NC
1911@kindex --unresolved-symbols
1912@item --unresolved-symbols=@var{method}
1913Determine how to handle unresolved symbols. There are four possible
1914values for @samp{method}:
1915
1916@table @samp
1917@item ignore-all
da8bce14 1918Do not report any unresolved symbols.
560e09e9
NC
1919
1920@item report-all
da8bce14 1921Report all unresolved symbols. This is the default.
560e09e9
NC
1922
1923@item ignore-in-object-files
1924Report unresolved symbols that are contained in shared libraries, but
1925ignore them if they come from regular object files.
1926
1927@item ignore-in-shared-libs
1928Report unresolved symbols that come from regular object files, but
1929ignore them if they come from shared libraries. This can be useful
1930when creating a dynamic binary and it is known that all the shared
1931libraries that it should be referencing are included on the linker's
1932command line.
1933@end table
1934
1935The behaviour for shared libraries on their own can also be controlled
1936by the @option{--[no-]allow-shlib-undefined} option.
1937
1938Normally the linker will generate an error message for each reported
1939unresolved symbol but the option @option{--warn-unresolved-symbols}
1940can change this to a warning.
1941
1715a13c
L
1942@kindex --verbose[=@var{NUMBER}]
1943@cindex verbose[=@var{NUMBER}]
252b5132 1944@item --dll-verbose
1715a13c 1945@itemx --verbose[=@var{NUMBER}]
ff5dcc92 1946Display the version number for @command{ld} and list the linker emulations
252b5132 1947supported. Display which input files can and cannot be opened. Display
1715a13c
L
1948the linker script being used by the linker. If the optional @var{NUMBER}
1949argument > 1, plugin symbol status will also be displayed.
252b5132
RH
1950
1951@kindex --version-script=@var{version-scriptfile}
1952@cindex version script, symbol versions
2509a395 1953@item --version-script=@var{version-scriptfile}
252b5132
RH
1954Specify the name of a version script to the linker. This is typically
1955used when creating shared libraries to specify additional information
36f63dca 1956about the version hierarchy for the library being created. This option
09e2aba4
DK
1957is only fully supported on ELF platforms which support shared libraries;
1958see @ref{VERSION}. It is partially supported on PE platforms, which can
1959use version scripts to filter symbol visibility in auto-export mode: any
1960symbols marked @samp{local} in the version script will not be exported.
1961@xref{WIN32}.
252b5132 1962
7ce691ae 1963@kindex --warn-common
252b5132
RH
1964@cindex warnings, on combining symbols
1965@cindex combining symbols, warnings on
1966@item --warn-common
1967Warn when a common symbol is combined with another common symbol or with
11e7fd74 1968a symbol definition. Unix linkers allow this somewhat sloppy practice,
252b5132
RH
1969but linkers on some other operating systems do not. This option allows
1970you to find potential problems from combining global symbols.
11e7fd74 1971Unfortunately, some C libraries use this practice, so you may get some
252b5132
RH
1972warnings about symbols in the libraries as well as in your programs.
1973
1974There are three kinds of global symbols, illustrated here by C examples:
1975
1976@table @samp
1977@item int i = 1;
1978A definition, which goes in the initialized data section of the output
1979file.
1980
1981@item extern int i;
1982An undefined reference, which does not allocate space.
1983There must be either a definition or a common symbol for the
1984variable somewhere.
1985
1986@item int i;
1987A common symbol. If there are only (one or more) common symbols for a
1988variable, it goes in the uninitialized data area of the output file.
1989The linker merges multiple common symbols for the same variable into a
1990single symbol. If they are of different sizes, it picks the largest
1991size. The linker turns a common symbol into a declaration, if there is
1992a definition of the same variable.
1993@end table
1994
1995The @samp{--warn-common} option can produce five kinds of warnings.
1996Each warning consists of a pair of lines: the first describes the symbol
1997just encountered, and the second describes the previous symbol
1998encountered with the same name. One or both of the two symbols will be
1999a common symbol.
2000
2001@enumerate
2002@item
2003Turning a common symbol into a reference, because there is already a
2004definition for the symbol.
2005@smallexample
2006@var{file}(@var{section}): warning: common of `@var{symbol}'
2007 overridden by definition
2008@var{file}(@var{section}): warning: defined here
2009@end smallexample
2010
2011@item
2012Turning a common symbol into a reference, because a later definition for
2013the symbol is encountered. This is the same as the previous case,
2014except that the symbols are encountered in a different order.
2015@smallexample
2016@var{file}(@var{section}): warning: definition of `@var{symbol}'
2017 overriding common
2018@var{file}(@var{section}): warning: common is here
2019@end smallexample
2020
2021@item
2022Merging a common symbol with a previous same-sized common symbol.
2023@smallexample
2024@var{file}(@var{section}): warning: multiple common
2025 of `@var{symbol}'
2026@var{file}(@var{section}): warning: previous common is here
2027@end smallexample
2028
2029@item
2030Merging a common symbol with a previous larger common symbol.
2031@smallexample
2032@var{file}(@var{section}): warning: common of `@var{symbol}'
2033 overridden by larger common
2034@var{file}(@var{section}): warning: larger common is here
2035@end smallexample
2036
2037@item
2038Merging a common symbol with a previous smaller common symbol. This is
2039the same as the previous case, except that the symbols are
2040encountered in a different order.
2041@smallexample
2042@var{file}(@var{section}): warning: common of `@var{symbol}'
2043 overriding smaller common
2044@var{file}(@var{section}): warning: smaller common is here
2045@end smallexample
2046@end enumerate
2047
2048@kindex --warn-constructors
2049@item --warn-constructors
2050Warn if any global constructors are used. This is only useful for a few
2051object file formats. For formats like COFF or ELF, the linker can not
2052detect the use of global constructors.
2053
2054@kindex --warn-multiple-gp
2055@item --warn-multiple-gp
2056Warn if multiple global pointer values are required in the output file.
2057This is only meaningful for certain processors, such as the Alpha.
2058Specifically, some processors put large-valued constants in a special
2059section. A special register (the global pointer) points into the middle
2060of this section, so that constants can be loaded efficiently via a
2061base-register relative addressing mode. Since the offset in
2062base-register relative mode is fixed and relatively small (e.g., 16
2063bits), this limits the maximum size of the constant pool. Thus, in
2064large programs, it is often necessary to use multiple global pointer
2065values in order to be able to address all possible constants. This
2066option causes a warning to be issued whenever this case occurs.
2067
2068@kindex --warn-once
2069@cindex warnings, on undefined symbols
2070@cindex undefined symbols, warnings on
2071@item --warn-once
2072Only warn once for each undefined symbol, rather than once per module
2073which refers to it.
2074
3ea60775
NC
2075@kindex --warn-orphan
2076@kindex --no-warn-orphan
2077@cindex warnings, on orphan sections
2078@cindex orphan sections, warnings on
2079@item --warn-orphan
2080The @option{--warn-orphan} option tells the linker to generate a
2081warning message whenever it has to place an orphan section into the
2082output file. @xref{Orphan Sections} The @option{--no-warn-orphan}
2083option restores the default behaviour of just silently placing these
2084sections.
2085
252b5132
RH
2086@kindex --warn-section-align
2087@cindex warnings, on section alignment
2088@cindex section alignment, warnings on
2089@item --warn-section-align
2090Warn if the address of an output section is changed because of
2091alignment. Typically, the alignment will be set by an input section.
2092The address will only be changed if it not explicitly specified; that
2093is, if the @code{SECTIONS} command does not specify a start address for
2094the section (@pxref{SECTIONS}).
2095
8fdd7217
NC
2096@kindex --warn-shared-textrel
2097@item --warn-shared-textrel
ece2d90e 2098Warn if the linker adds a DT_TEXTREL to a shared object.
8fdd7217 2099
a0c402a5
L
2100@kindex --warn-alternate-em
2101@item --warn-alternate-em
2102Warn if an object has alternate ELF machine code.
2103
560e09e9
NC
2104@kindex --warn-unresolved-symbols
2105@item --warn-unresolved-symbols
2106If the linker is going to report an unresolved symbol (see the option
2107@option{--unresolved-symbols}) it will normally generate an error.
2108This option makes it generate a warning instead.
2109
2110@kindex --error-unresolved-symbols
2111@item --error-unresolved-symbols
2112This restores the linker's default behaviour of generating errors when
2113it is reporting unresolved symbols.
2114
252b5132
RH
2115@kindex --whole-archive
2116@cindex including an entire archive
2117@item --whole-archive
2118For each archive mentioned on the command line after the
ff5dcc92 2119@option{--whole-archive} option, include every object file in the archive
252b5132
RH
2120in the link, rather than searching the archive for the required object
2121files. This is normally used to turn an archive file into a shared
2122library, forcing every object to be included in the resulting shared
2123library. This option may be used more than once.
2124
7ec229ce 2125Two notes when using this option from gcc: First, gcc doesn't know
ff5dcc92
SC
2126about this option, so you have to use @option{-Wl,-whole-archive}.
2127Second, don't forget to use @option{-Wl,-no-whole-archive} after your
7ec229ce
DD
2128list of archives, because gcc will add its own list of archives to
2129your link and you may not want this flag to affect those as well.
2130
2509a395
SL
2131@kindex --wrap=@var{symbol}
2132@item --wrap=@var{symbol}
252b5132
RH
2133Use a wrapper function for @var{symbol}. Any undefined reference to
2134@var{symbol} will be resolved to @code{__wrap_@var{symbol}}. Any
2135undefined reference to @code{__real_@var{symbol}} will be resolved to
2136@var{symbol}.
2137
2138This can be used to provide a wrapper for a system function. The
2139wrapper function should be called @code{__wrap_@var{symbol}}. If it
2140wishes to call the system function, it should call
2141@code{__real_@var{symbol}}.
2142
2143Here is a trivial example:
2144
2145@smallexample
2146void *
cc2f008e 2147__wrap_malloc (size_t c)
252b5132 2148@{
cc2f008e 2149 printf ("malloc called with %zu\n", c);
252b5132
RH
2150 return __real_malloc (c);
2151@}
2152@end smallexample
2153
ff5dcc92 2154If you link other code with this file using @option{--wrap malloc}, then
252b5132
RH
2155all calls to @code{malloc} will call the function @code{__wrap_malloc}
2156instead. The call to @code{__real_malloc} in @code{__wrap_malloc} will
2157call the real @code{malloc} function.
2158
2159You may wish to provide a @code{__real_malloc} function as well, so that
ff5dcc92 2160links without the @option{--wrap} option will succeed. If you do this,
252b5132
RH
2161you should not put the definition of @code{__real_malloc} in the same
2162file as @code{__wrap_malloc}; if you do, the assembler may resolve the
2163call before the linker has a chance to wrap it to @code{malloc}.
2164
6aa29e7b
JJ
2165@kindex --eh-frame-hdr
2166@item --eh-frame-hdr
2167Request creation of @code{.eh_frame_hdr} section and ELF
2168@code{PT_GNU_EH_FRAME} segment header.
2169
e41b3a13
JJ
2170@kindex --ld-generated-unwind-info
2171@item --no-ld-generated-unwind-info
2172Request creation of @code{.eh_frame} unwind info for linker
2173generated code sections like PLT. This option is on by default
2174if linker generated unwind info is supported.
2175
6c1439be
L
2176@kindex --enable-new-dtags
2177@kindex --disable-new-dtags
2178@item --enable-new-dtags
2179@itemx --disable-new-dtags
2180This linker can create the new dynamic tags in ELF. But the older ELF
2181systems may not understand them. If you specify
b1b00fcc
MF
2182@option{--enable-new-dtags}, the new dynamic tags will be created as needed
2183and older dynamic tags will be omitted.
ff5dcc92 2184If you specify @option{--disable-new-dtags}, no new dynamic tags will be
6c1439be
L
2185created. By default, the new dynamic tags are not created. Note that
2186those options are only available for ELF systems.
2187
2d643429 2188@kindex --hash-size=@var{number}
e185dd51 2189@item --hash-size=@var{number}
2d643429
NC
2190Set the default size of the linker's hash tables to a prime number
2191close to @var{number}. Increasing this value can reduce the length of
2192time it takes the linker to perform its tasks, at the expense of
2193increasing the linker's memory requirements. Similarly reducing this
2194value can reduce the memory requirements at the expense of speed.
2195
fdc90cb4
JJ
2196@kindex --hash-style=@var{style}
2197@item --hash-style=@var{style}
2198Set the type of linker's hash table(s). @var{style} can be either
2199@code{sysv} for classic ELF @code{.hash} section, @code{gnu} for
2200new style GNU @code{.gnu.hash} section or @code{both} for both
2201the classic ELF @code{.hash} and new style GNU @code{.gnu.hash}
2202hash tables. The default is @code{sysv}.
2203
0ce398f1
L
2204@kindex --compress-debug-sections=none
2205@kindex --compress-debug-sections=zlib
2206@kindex --compress-debug-sections=zlib-gnu
2207@kindex --compress-debug-sections=zlib-gabi
2208@item --compress-debug-sections=none
2209@itemx --compress-debug-sections=zlib
2210@itemx --compress-debug-sections=zlib-gnu
2211@itemx --compress-debug-sections=zlib-gabi
2212On ELF platforms , these options control how DWARF debug sections are
2213compressed using zlib. @option{--compress-debug-sections=none} doesn't
2214compress DWARF debug sections. @option{--compress-debug-sections=zlib}
2215and @option{--compress-debug-sections=zlib-gnu} compress DWARF debug
2216sections and rename debug section names to begin with @samp{.zdebug}
2217instead of @samp{.debug}. @option{--compress-debug-sections=zlib-gabi}
2218compresses DWARF debug sections with SHF_COMPRESSED from the ELF ABI.
2219
35835446
JR
2220@kindex --reduce-memory-overheads
2221@item --reduce-memory-overheads
2222This option reduces memory requirements at ld runtime, at the expense of
f2a8f148 2223linking speed. This was introduced to select the old O(n^2) algorithm
35835446 2224for link map file generation, rather than the new O(n) algorithm which uses
2d643429
NC
2225about 40% more memory for symbol storage.
2226
4f9c04f7 2227Another effect of the switch is to set the default hash table size to
2d643429 22281021, which again saves memory at the cost of lengthening the linker's
a85785bc 2229run time. This is not done however if the @option{--hash-size} switch
2d643429
NC
2230has been used.
2231
2232The @option{--reduce-memory-overheads} switch may be also be used to
2233enable other tradeoffs in future versions of the linker.
35835446 2234
c0065db7
RM
2235@kindex --build-id
2236@kindex --build-id=@var{style}
2237@item --build-id
2238@itemx --build-id=@var{style}
61e2488c
JT
2239Request the creation of a @code{.note.gnu.build-id} ELF note section
2240or a @code{.build-id} COFF section. The contents of the note are
2241unique bits identifying this linked file. @var{style} can be
2242@code{uuid} to use 128 random bits, @code{sha1} to use a 160-bit
2243@sc{SHA1} hash on the normative parts of the output contents,
2244@code{md5} to use a 128-bit @sc{MD5} hash on the normative parts of
2245the output contents, or @code{0x@var{hexstring}} to use a chosen bit
2246string specified as an even number of hexadecimal digits (@code{-} and
2247@code{:} characters between digit pairs are ignored). If @var{style}
2248is omitted, @code{sha1} is used.
24382dca
RM
2249
2250The @code{md5} and @code{sha1} styles produces an identifier
2251that is always the same in an identical output file, but will be
2252unique among all nonidentical output files. It is not intended
2253to be compared as a checksum for the file's contents. A linked
2254file may be changed later by other tools, but the build ID bit
2255string identifying the original linked file does not change.
c0065db7
RM
2256
2257Passing @code{none} for @var{style} disables the setting from any
2258@code{--build-id} options earlier on the command line.
252b5132
RH
2259@end table
2260
0285c67d
NC
2261@c man end
2262
36f63dca 2263@subsection Options Specific to i386 PE Targets
252b5132 2264
0285c67d
NC
2265@c man begin OPTIONS
2266
ff5dcc92 2267The i386 PE linker supports the @option{-shared} option, which causes
252b5132
RH
2268the output to be a dynamically linked library (DLL) instead of a
2269normal executable. You should name the output @code{*.dll} when you
2270use this option. In addition, the linker fully supports the standard
2271@code{*.def} files, which may be specified on the linker command line
2272like an object file (in fact, it should precede archives it exports
2273symbols from, to ensure that they get linked in, just like a normal
2274object file).
2275
2276In addition to the options common to all targets, the i386 PE linker
2277support additional command line options that are specific to the i386
2278PE target. Options that take values may be separated from their
2279values by either a space or an equals sign.
2280
ff5dcc92 2281@table @gcctabopt
252b5132
RH
2282
2283@kindex --add-stdcall-alias
2284@item --add-stdcall-alias
2285If given, symbols with a stdcall suffix (@@@var{nn}) will be exported
2286as-is and also with the suffix stripped.
bb10df36 2287[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2288
2289@kindex --base-file
2290@item --base-file @var{file}
2291Use @var{file} as the name of a file in which to save the base
2292addresses of all the relocations needed for generating DLLs with
2293@file{dlltool}.
bb10df36 2294[This is an i386 PE specific option]
252b5132
RH
2295
2296@kindex --dll
2297@item --dll
2298Create a DLL instead of a regular executable. You may also use
ff5dcc92 2299@option{-shared} or specify a @code{LIBRARY} in a given @code{.def}
252b5132 2300file.
bb10df36 2301[This option is specific to the i386 PE targeted port of the linker]
252b5132 2302
88183869
DK
2303@kindex --enable-long-section-names
2304@kindex --disable-long-section-names
2305@item --enable-long-section-names
2306@itemx --disable-long-section-names
2307The PE variants of the Coff object format add an extension that permits
2308the use of section names longer than eight characters, the normal limit
2309for Coff. By default, these names are only allowed in object files, as
2310fully-linked executable images do not carry the Coff string table required
2311to support the longer names. As a GNU extension, it is possible to
2312allow their use in executable images as well, or to (probably pointlessly!)
2313disallow it in object files, by using these two options. Executable images
2314generated with these long section names are slightly non-standard, carrying
2315as they do a string table, and may generate confusing output when examined
9d5777a3
RM
2316with non-GNU PE-aware tools, such as file viewers and dumpers. However,
2317GDB relies on the use of PE long section names to find Dwarf-2 debug
3efd345c
DK
2318information sections in an executable image at runtime, and so if neither
2319option is specified on the command-line, @command{ld} will enable long
2320section names, overriding the default and technically correct behaviour,
2321when it finds the presence of debug information while linking an executable
2322image and not stripping symbols.
88183869
DK
2323[This option is valid for all PE targeted ports of the linker]
2324
252b5132
RH
2325@kindex --enable-stdcall-fixup
2326@kindex --disable-stdcall-fixup
2327@item --enable-stdcall-fixup
2328@itemx --disable-stdcall-fixup
2329If the link finds a symbol that it cannot resolve, it will attempt to
36f63dca 2330do ``fuzzy linking'' by looking for another defined symbol that differs
252b5132
RH
2331only in the format of the symbol name (cdecl vs stdcall) and will
2332resolve that symbol by linking to the match. For example, the
2333undefined symbol @code{_foo} might be linked to the function
2334@code{_foo@@12}, or the undefined symbol @code{_bar@@16} might be linked
2335to the function @code{_bar}. When the linker does this, it prints a
2336warning, since it normally should have failed to link, but sometimes
2337import libraries generated from third-party dlls may need this feature
ff5dcc92 2338to be usable. If you specify @option{--enable-stdcall-fixup}, this
252b5132 2339feature is fully enabled and warnings are not printed. If you specify
ff5dcc92 2340@option{--disable-stdcall-fixup}, this feature is disabled and such
252b5132 2341mismatches are considered to be errors.
bb10df36 2342[This option is specific to the i386 PE targeted port of the linker]
252b5132 2343
522f09cd
KT
2344@kindex --leading-underscore
2345@kindex --no-leading-underscore
2346@item --leading-underscore
2347@itemx --no-leading-underscore
2348For most targets default symbol-prefix is an underscore and is defined
2349in target's description. By this option it is possible to
2350disable/enable the default underscore symbol-prefix.
2351
252b5132
RH
2352@cindex DLLs, creating
2353@kindex --export-all-symbols
2354@item --export-all-symbols
2355If given, all global symbols in the objects used to build a DLL will
2356be exported by the DLL. Note that this is the default if there
2357otherwise wouldn't be any exported symbols. When symbols are
2358explicitly exported via DEF files or implicitly exported via function
2359attributes, the default is to not export anything else unless this
2360option is given. Note that the symbols @code{DllMain@@12},
ece2d90e 2361@code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and
b044cda1 2362@code{impure_ptr} will not be automatically
ece2d90e
NC
2363exported. Also, symbols imported from other DLLs will not be
2364re-exported, nor will symbols specifying the DLL's internal layout
2365such as those beginning with @code{_head_} or ending with
2366@code{_iname}. In addition, no symbols from @code{libgcc},
b044cda1
CW
2367@code{libstd++}, @code{libmingw32}, or @code{crtX.o} will be exported.
2368Symbols whose names begin with @code{__rtti_} or @code{__builtin_} will
2369not be exported, to help with C++ DLLs. Finally, there is an
ece2d90e 2370extensive list of cygwin-private symbols that are not exported
b044cda1 2371(obviously, this applies on when building DLLs for cygwin targets).
ece2d90e 2372These cygwin-excludes are: @code{_cygwin_dll_entry@@12},
b044cda1 2373@code{_cygwin_crt0_common@@8}, @code{_cygwin_noncygwin_dll_entry@@12},
ece2d90e 2374@code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll},
b044cda1 2375@code{cygwin_premain0}, @code{cygwin_premain1}, @code{cygwin_premain2},
ece2d90e 2376@code{cygwin_premain3}, and @code{environ}.
bb10df36 2377[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2378
2379@kindex --exclude-symbols
1d0a3c9c 2380@item --exclude-symbols @var{symbol},@var{symbol},...
252b5132
RH
2381Specifies a list of symbols which should not be automatically
2382exported. The symbol names may be delimited by commas or colons.
bb10df36 2383[This option is specific to the i386 PE targeted port of the linker]
252b5132 2384
2927aaca
NC
2385@kindex --exclude-all-symbols
2386@item --exclude-all-symbols
2387Specifies no symbols should be automatically exported.
2388[This option is specific to the i386 PE targeted port of the linker]
2389
252b5132
RH
2390@kindex --file-alignment
2391@item --file-alignment
2392Specify the file alignment. Sections in the file will always begin at
2393file offsets which are multiples of this number. This defaults to
2394512.
bb10df36 2395[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2396
2397@cindex heap size
2398@kindex --heap
2399@item --heap @var{reserve}
2400@itemx --heap @var{reserve},@var{commit}
a00b50c5 2401Specify the number of bytes of memory to reserve (and optionally commit)
fe6d7d6a 2402to be used as heap for this program. The default is 1MB reserved, 4K
252b5132 2403committed.
bb10df36 2404[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2405
2406@cindex image base
2407@kindex --image-base
2408@item --image-base @var{value}
2409Use @var{value} as the base address of your program or dll. This is
2410the lowest memory location that will be used when your program or dll
2411is loaded. To reduce the need to relocate and improve performance of
2412your dlls, each should have a unique base address and not overlap any
2413other dlls. The default is 0x400000 for executables, and 0x10000000
2414for dlls.
bb10df36 2415[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2416
2417@kindex --kill-at
2418@item --kill-at
2419If given, the stdcall suffixes (@@@var{nn}) will be stripped from
2420symbols before they are exported.
bb10df36 2421[This option is specific to the i386 PE targeted port of the linker]
252b5132 2422
26d2d8a2
BF
2423@kindex --large-address-aware
2424@item --large-address-aware
b45619c0 2425If given, the appropriate bit in the ``Characteristics'' field of the COFF
26d2d8a2 2426header is set to indicate that this executable supports virtual addresses
b45619c0 2427greater than 2 gigabytes. This should be used in conjunction with the /3GB
26d2d8a2
BF
2428or /USERVA=@var{value} megabytes switch in the ``[operating systems]''
2429section of the BOOT.INI. Otherwise, this bit has no effect.
2430[This option is specific to PE targeted ports of the linker]
2431
f69a2f97
NC
2432@kindex --disable-large-address-aware
2433@item --disable-large-address-aware
2434Reverts the effect of a previous @samp{--large-address-aware} option.
2435This is useful if @samp{--large-address-aware} is always set by the compiler
2436driver (e.g. Cygwin gcc) and the executable does not support virtual
2437addresses greater than 2 gigabytes.
2438[This option is specific to PE targeted ports of the linker]
2439
252b5132
RH
2440@kindex --major-image-version
2441@item --major-image-version @var{value}
36f63dca 2442Sets the major number of the ``image version''. Defaults to 1.
bb10df36 2443[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2444
2445@kindex --major-os-version
2446@item --major-os-version @var{value}
36f63dca 2447Sets the major number of the ``os version''. Defaults to 4.
bb10df36 2448[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2449
2450@kindex --major-subsystem-version
2451@item --major-subsystem-version @var{value}
36f63dca 2452Sets the major number of the ``subsystem version''. Defaults to 4.
bb10df36 2453[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2454
2455@kindex --minor-image-version
2456@item --minor-image-version @var{value}
36f63dca 2457Sets the minor number of the ``image version''. Defaults to 0.
bb10df36 2458[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2459
2460@kindex --minor-os-version
2461@item --minor-os-version @var{value}
36f63dca 2462Sets the minor number of the ``os version''. Defaults to 0.
bb10df36 2463[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2464
2465@kindex --minor-subsystem-version
2466@item --minor-subsystem-version @var{value}
36f63dca 2467Sets the minor number of the ``subsystem version''. Defaults to 0.
bb10df36 2468[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2469
2470@cindex DEF files, creating
2471@cindex DLLs, creating
2472@kindex --output-def
2473@item --output-def @var{file}
2474The linker will create the file @var{file} which will contain a DEF
2475file corresponding to the DLL the linker is generating. This DEF file
2476(which should be called @code{*.def}) may be used to create an import
2477library with @code{dlltool} or may be used as a reference to
2478automatically or implicitly exported symbols.
bb10df36 2479[This option is specific to the i386 PE targeted port of the linker]
252b5132 2480
b044cda1
CW
2481@cindex DLLs, creating
2482@kindex --out-implib
2483@item --out-implib @var{file}
2484The linker will create the file @var{file} which will contain an
2485import lib corresponding to the DLL the linker is generating. This
2486import lib (which should be called @code{*.dll.a} or @code{*.a}
560e09e9 2487may be used to link clients against the generated DLL; this behaviour
b044cda1
CW
2488makes it possible to skip a separate @code{dlltool} import library
2489creation step.
bb10df36 2490[This option is specific to the i386 PE targeted port of the linker]
b044cda1
CW
2491
2492@kindex --enable-auto-image-base
2493@item --enable-auto-image-base
d0e6d77b
CF
2494@itemx --enable-auto-image-base=@var{value}
2495Automatically choose the image base for DLLs, optionally starting with base
2496@var{value}, unless one is specified using the @code{--image-base} argument.
2497By using a hash generated from the dllname to create unique image bases
2498for each DLL, in-memory collisions and relocations which can delay program
2499execution are avoided.
bb10df36 2500[This option is specific to the i386 PE targeted port of the linker]
b044cda1
CW
2501
2502@kindex --disable-auto-image-base
2503@item --disable-auto-image-base
2504Do not automatically generate a unique image base. If there is no
2505user-specified image base (@code{--image-base}) then use the platform
2506default.
bb10df36 2507[This option is specific to the i386 PE targeted port of the linker]
b044cda1
CW
2508
2509@cindex DLLs, linking to
2510@kindex --dll-search-prefix
2511@item --dll-search-prefix @var{string}
489d0400 2512When linking dynamically to a dll without an import library,
ece2d90e 2513search for @code{<string><basename>.dll} in preference to
560e09e9 2514@code{lib<basename>.dll}. This behaviour allows easy distinction
b044cda1
CW
2515between DLLs built for the various "subplatforms": native, cygwin,
2516uwin, pw, etc. For instance, cygwin DLLs typically use
ece2d90e 2517@code{--dll-search-prefix=cyg}.
bb10df36 2518[This option is specific to the i386 PE targeted port of the linker]
b044cda1
CW
2519
2520@kindex --enable-auto-import
2521@item --enable-auto-import
ece2d90e
NC
2522Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for
2523DATA imports from DLLs, and create the necessary thunking symbols when
4d8907ac
DS
2524building the import libraries with those DATA exports. Note: Use of the
2525'auto-import' extension will cause the text section of the image file
2526to be made writable. This does not conform to the PE-COFF format
2527specification published by Microsoft.
2528
e2a83dd0
NC
2529Note - use of the 'auto-import' extension will also cause read only
2530data which would normally be placed into the .rdata section to be
2531placed into the .data section instead. This is in order to work
2532around a problem with consts that is described here:
2533http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
2534
4d8907ac
DS
2535Using 'auto-import' generally will 'just work' -- but sometimes you may
2536see this message:
0d888aac 2537
ece2d90e 2538"variable '<var>' can't be auto-imported. Please read the
0d888aac
CW
2539documentation for ld's @code{--enable-auto-import} for details."
2540
ece2d90e
NC
2541This message occurs when some (sub)expression accesses an address
2542ultimately given by the sum of two constants (Win32 import tables only
c0065db7
RM
2543allow one). Instances where this may occur include accesses to member
2544fields of struct variables imported from a DLL, as well as using a
2545constant index into an array variable imported from a DLL. Any
2f8d8971
NC
2546multiword variable (arrays, structs, long long, etc) may trigger
2547this error condition. However, regardless of the exact data type
2548of the offending exported variable, ld will always detect it, issue
2549the warning, and exit.
2550
2551There are several ways to address this difficulty, regardless of the
2552data type of the exported variable:
0d888aac 2553
2fa9fc65
NC
2554One way is to use --enable-runtime-pseudo-reloc switch. This leaves the task
2555of adjusting references in your client code for runtime environment, so
560e09e9 2556this method works only when runtime environment supports this feature.
2fa9fc65 2557
c0065db7
RM
2558A second solution is to force one of the 'constants' to be a variable --
2559that is, unknown and un-optimizable at compile time. For arrays,
2560there are two possibilities: a) make the indexee (the array's address)
0d888aac
CW
2561a variable, or b) make the 'constant' index a variable. Thus:
2562
2563@example
2564extern type extern_array[];
c0065db7 2565extern_array[1] -->
0d888aac
CW
2566 @{ volatile type *t=extern_array; t[1] @}
2567@end example
2568
2569or
2570
2571@example
2572extern type extern_array[];
c0065db7 2573extern_array[1] -->
0d888aac
CW
2574 @{ volatile int t=1; extern_array[t] @}
2575@end example
2576
c0065db7 2577For structs (and most other multiword data types) the only option
2f8d8971 2578is to make the struct itself (or the long long, or the ...) variable:
0d888aac
CW
2579
2580@example
2581extern struct s extern_struct;
c0065db7 2582extern_struct.field -->
0d888aac
CW
2583 @{ volatile struct s *t=&extern_struct; t->field @}
2584@end example
2585
c406afaf
NC
2586or
2587
2588@example
2589extern long long extern_ll;
2590extern_ll -->
2591 @{ volatile long long * local_ll=&extern_ll; *local_ll @}
2592@end example
2593
2fa9fc65 2594A third method of dealing with this difficulty is to abandon
c0065db7 2595'auto-import' for the offending symbol and mark it with
11e7fd74 2596@code{__declspec(dllimport)}. However, in practice that
0d888aac 2597requires using compile-time #defines to indicate whether you are
c0065db7
RM
2598building a DLL, building client code that will link to the DLL, or
2599merely building/linking to a static library. In making the choice
2600between the various methods of resolving the 'direct address with
0d888aac
CW
2601constant offset' problem, you should consider typical real-world usage:
2602
2603Original:
2604@example
2605--foo.h
2606extern int arr[];
2607--foo.c
2608#include "foo.h"
2609void main(int argc, char **argv)@{
2610 printf("%d\n",arr[1]);
2611@}
2612@end example
2613
2614Solution 1:
2615@example
2616--foo.h
2617extern int arr[];
2618--foo.c
2619#include "foo.h"
2620void main(int argc, char **argv)@{
2621 /* This workaround is for win32 and cygwin; do not "optimize" */
2622 volatile int *parr = arr;
2623 printf("%d\n",parr[1]);
2624@}
2625@end example
2626
2627Solution 2:
2628@example
2629--foo.h
2630/* Note: auto-export is assumed (no __declspec(dllexport)) */
2631#if (defined(_WIN32) || defined(__CYGWIN__)) && \
2632 !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
2633#define FOO_IMPORT __declspec(dllimport)
2634#else
2635#define FOO_IMPORT
2636#endif
2637extern FOO_IMPORT int arr[];
2638--foo.c
2639#include "foo.h"
2640void main(int argc, char **argv)@{
2641 printf("%d\n",arr[1]);
2642@}
2643@end example
2644
c0065db7 2645A fourth way to avoid this problem is to re-code your
0d888aac
CW
2646library to use a functional interface rather than a data interface
2647for the offending variables (e.g. set_foo() and get_foo() accessor
2648functions).
bb10df36 2649[This option is specific to the i386 PE targeted port of the linker]
b044cda1
CW
2650
2651@kindex --disable-auto-import
2652@item --disable-auto-import
c0065db7 2653Do not attempt to do sophisticated linking of @code{_symbol} to
b044cda1 2654@code{__imp__symbol} for DATA imports from DLLs.
bb10df36 2655[This option is specific to the i386 PE targeted port of the linker]
b044cda1 2656
2fa9fc65
NC
2657@kindex --enable-runtime-pseudo-reloc
2658@item --enable-runtime-pseudo-reloc
2659If your code contains expressions described in --enable-auto-import section,
2660that is, DATA imports from DLL with non-zero offset, this switch will create
2661a vector of 'runtime pseudo relocations' which can be used by runtime
c0065db7 2662environment to adjust references to such data in your client code.
bb10df36 2663[This option is specific to the i386 PE targeted port of the linker]
2fa9fc65
NC
2664
2665@kindex --disable-runtime-pseudo-reloc
2666@item --disable-runtime-pseudo-reloc
2667Do not create pseudo relocations for non-zero offset DATA imports from
676ee43b 2668DLLs.
bb10df36 2669[This option is specific to the i386 PE targeted port of the linker]
2fa9fc65 2670
b044cda1
CW
2671@kindex --enable-extra-pe-debug
2672@item --enable-extra-pe-debug
2673Show additional debug info related to auto-import symbol thunking.
bb10df36 2674[This option is specific to the i386 PE targeted port of the linker]
b044cda1 2675
252b5132
RH
2676@kindex --section-alignment
2677@item --section-alignment
2678Sets the section alignment. Sections in memory will always begin at
2679addresses which are a multiple of this number. Defaults to 0x1000.
bb10df36 2680[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2681
2682@cindex stack size
2683@kindex --stack
2684@item --stack @var{reserve}
2685@itemx --stack @var{reserve},@var{commit}
a00b50c5 2686Specify the number of bytes of memory to reserve (and optionally commit)
fe6d7d6a 2687to be used as stack for this program. The default is 2MB reserved, 4K
252b5132 2688committed.
bb10df36 2689[This option is specific to the i386 PE targeted port of the linker]
252b5132
RH
2690
2691@kindex --subsystem
2692@item --subsystem @var{which}
2693@itemx --subsystem @var{which}:@var{major}
2694@itemx --subsystem @var{which}:@var{major}.@var{minor}
2695Specifies the subsystem under which your program will execute. The
2696legal values for @var{which} are @code{native}, @code{windows},
33f362e1
NC
2697@code{console}, @code{posix}, and @code{xbox}. You may optionally set
2698the subsystem version also. Numeric values are also accepted for
2699@var{which}.
bb10df36 2700[This option is specific to the i386 PE targeted port of the linker]
252b5132 2701
2f563b51
DK
2702The following options set flags in the @code{DllCharacteristics} field
2703of the PE file header:
2704[These options are specific to PE targeted ports of the linker]
2705
2d5c3743
NC
2706@kindex --high-entropy-va
2707@item --high-entropy-va
2708Image is compatible with 64-bit address space layout randomization
2709(ASLR).
2710
2f563b51
DK
2711@kindex --dynamicbase
2712@item --dynamicbase
2713The image base address may be relocated using address space layout
2714randomization (ASLR). This feature was introduced with MS Windows
2715Vista for i386 PE targets.
2716
2717@kindex --forceinteg
2718@item --forceinteg
2719Code integrity checks are enforced.
2720
2721@kindex --nxcompat
2722@item --nxcompat
2723The image is compatible with the Data Execution Prevention.
2724This feature was introduced with MS Windows XP SP2 for i386 PE targets.
2725
2726@kindex --no-isolation
2727@item --no-isolation
2728Although the image understands isolation, do not isolate the image.
2729
2730@kindex --no-seh
2731@item --no-seh
2732The image does not use SEH. No SE handler may be called from
2733this image.
2734
2735@kindex --no-bind
2736@item --no-bind
2737Do not bind this image.
2738
2739@kindex --wdmdriver
2740@item --wdmdriver
2741The driver uses the MS Windows Driver Model.
9d5777a3 2742
2f563b51
DK
2743@kindex --tsaware
2744@item --tsaware
2745The image is Terminal Server aware.
2746
0cb112f7
CF
2747@kindex --insert-timestamp
2748@item --insert-timestamp
eeb14e5a
LZ
2749@itemx --no-insert-timestamp
2750Insert a real timestamp into the image. This is the default behaviour
2751as it matches legacy code and it means that the image will work with
2752other, proprietary tools. The problem with this default is that it
2753will result in slightly different images being produced each tiem the
2754same sources are linked. The option @option{--no-insert-timestamp}
2755can be used to insert a zero value for the timestamp, this ensuring
2756that binaries produced from indentical sources will compare
2757identically.
252b5132
RH
2758@end table
2759
0285c67d
NC
2760@c man end
2761
ac145307
BS
2762@ifset C6X
2763@subsection Options specific to C6X uClinux targets
2764
2765@c man begin OPTIONS
2766
2767The C6X uClinux target uses a binary format called DSBT to support shared
2768libraries. Each shared library in the system needs to have a unique index;
2769all executables use an index of 0.
2770
2771@table @gcctabopt
2772
2773@kindex --dsbt-size
2774@item --dsbt-size @var{size}
2775This option sets the number of entires in the DSBT of the current executable
2776or shared library to @var{size}. The default is to create a table with 64
2777entries.
2778
2779@kindex --dsbt-index
2780@item --dsbt-index @var{index}
2781This option sets the DSBT index of the current executable or shared library
2782to @var{index}. The default is 0, which is appropriate for generating
2783executables. If a shared library is generated with a DSBT index of 0, the
2784@code{R_C6000_DSBT_INDEX} relocs are copied into the output file.
2785
fbd9ad90
PB
2786@kindex --no-merge-exidx-entries
2787The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent
2788exidx entries in frame unwind info.
2789
ac145307
BS
2790@end table
2791
2792@c man end
2793@end ifset
2794
93fd0973
SC
2795@ifset M68HC11
2796@subsection Options specific to Motorola 68HC11 and 68HC12 targets
2797
2798@c man begin OPTIONS
2799
2800The 68HC11 and 68HC12 linkers support specific options to control the
2801memory bank switching mapping and trampoline code generation.
2802
2803@table @gcctabopt
2804
2805@kindex --no-trampoline
2806@item --no-trampoline
2807This option disables the generation of trampoline. By default a trampoline
2808is generated for each far function which is called using a @code{jsr}
2809instruction (this happens when a pointer to a far function is taken).
2810
2811@kindex --bank-window
2812@item --bank-window @var{name}
2813This option indicates to the linker the name of the memory region in
2814the @samp{MEMORY} specification that describes the memory bank window.
2815The definition of such region is then used by the linker to compute
2816paging and addresses within the memory window.
2817
2818@end table
2819
2820@c man end
2821@end ifset
2822
7fb9f789
NC
2823@ifset M68K
2824@subsection Options specific to Motorola 68K target
2825
2826@c man begin OPTIONS
2827
2828The following options are supported to control handling of GOT generation
2829when linking for 68K targets.
2830
2831@table @gcctabopt
2832
2833@kindex --got
2834@item --got=@var{type}
2835This option tells the linker which GOT generation scheme to use.
2836@var{type} should be one of @samp{single}, @samp{negative},
2837@samp{multigot} or @samp{target}. For more information refer to the
2838Info entry for @file{ld}.
2839
2840@end table
2841
2842@c man end
2843@end ifset
2844
833794fc
MR
2845@ifset MIPS
2846@subsection Options specific to MIPS targets
2847
2848@c man begin OPTIONS
2849
2850The following options are supported to control microMIPS instruction
2851generation when linking for MIPS targets.
2852
2853@table @gcctabopt
2854
2855@kindex --insn32
2856@item --insn32
2857@kindex --no-insn32
2858@itemx --no-insn32
2859These options control the choice of microMIPS instructions used in code
2860generated by the linker, such as that in the PLT or lazy binding stubs,
2861or in relaxation. If @samp{--insn32} is used, then the linker only uses
286232-bit instruction encodings. By default or if @samp{--no-insn32} is
2863used, all instruction encodings are used, including 16-bit ones where
2864possible.
2865
2866@end table
2867
2868@c man end
2869@end ifset
2870
252b5132
RH
2871@ifset UsesEnvVars
2872@node Environment
2873@section Environment Variables
2874
0285c67d
NC
2875@c man begin ENVIRONMENT
2876
560e09e9 2877You can change the behaviour of @command{ld} with the environment variables
36f63dca
NC
2878@ifclear SingleFormat
2879@code{GNUTARGET},
2880@end ifclear
2881@code{LDEMULATION} and @code{COLLECT_NO_DEMANGLE}.
252b5132 2882
36f63dca 2883@ifclear SingleFormat
252b5132
RH
2884@kindex GNUTARGET
2885@cindex default input format
2886@code{GNUTARGET} determines the input-file object format if you don't
2887use @samp{-b} (or its synonym @samp{--format}). Its value should be one
2888of the BFD names for an input format (@pxref{BFD}). If there is no
ff5dcc92 2889@code{GNUTARGET} in the environment, @command{ld} uses the natural format
252b5132
RH
2890of the target. If @code{GNUTARGET} is set to @code{default} then BFD
2891attempts to discover the input format by examining binary input files;
2892this method often succeeds, but there are potential ambiguities, since
2893there is no method of ensuring that the magic number used to specify
2894object-file formats is unique. However, the configuration procedure for
2895BFD on each system places the conventional format for that system first
2896in the search-list, so ambiguities are resolved in favor of convention.
36f63dca 2897@end ifclear
252b5132
RH
2898
2899@kindex LDEMULATION
2900@cindex default emulation
2901@cindex emulation, default
2902@code{LDEMULATION} determines the default emulation if you don't use the
2903@samp{-m} option. The emulation can affect various aspects of linker
2904behaviour, particularly the default linker script. You can list the
2905available emulations with the @samp{--verbose} or @samp{-V} options. If
2906the @samp{-m} option is not used, and the @code{LDEMULATION} environment
2907variable is not defined, the default emulation depends upon how the
2908linker was configured.
252b5132
RH
2909
2910@kindex COLLECT_NO_DEMANGLE
2911@cindex demangling, default
2912Normally, the linker will default to demangling symbols. However, if
2913@code{COLLECT_NO_DEMANGLE} is set in the environment, then it will
2914default to not demangling symbols. This environment variable is used in
2915a similar fashion by the @code{gcc} linker wrapper program. The default
2916may be overridden by the @samp{--demangle} and @samp{--no-demangle}
2917options.
2918
0285c67d
NC
2919@c man end
2920@end ifset
2921
252b5132
RH
2922@node Scripts
2923@chapter Linker Scripts
2924
2925@cindex scripts
2926@cindex linker scripts
2927@cindex command files
2928Every link is controlled by a @dfn{linker script}. This script is
2929written in the linker command language.
2930
2931The main purpose of the linker script is to describe how the sections in
2932the input files should be mapped into the output file, and to control
2933the memory layout of the output file. Most linker scripts do nothing
2934more than this. However, when necessary, the linker script can also
2935direct the linker to perform many other operations, using the commands
2936described below.
2937
2938The linker always uses a linker script. If you do not supply one
2939yourself, the linker will use a default script that is compiled into the
2940linker executable. You can use the @samp{--verbose} command line option
2941to display the default linker script. Certain command line options,
2942such as @samp{-r} or @samp{-N}, will affect the default linker script.
2943
2944You may supply your own linker script by using the @samp{-T} command
2945line option. When you do this, your linker script will replace the
2946default linker script.
2947
2948You may also use linker scripts implicitly by naming them as input files
2949to the linker, as though they were files to be linked. @xref{Implicit
2950Linker Scripts}.
2951
2952@menu
2953* Basic Script Concepts:: Basic Linker Script Concepts
2954* Script Format:: Linker Script Format
2955* Simple Example:: Simple Linker Script Example
2956* Simple Commands:: Simple Linker Script Commands
2957* Assignments:: Assigning Values to Symbols
2958* SECTIONS:: SECTIONS Command
2959* MEMORY:: MEMORY Command
2960* PHDRS:: PHDRS Command
2961* VERSION:: VERSION Command
2962* Expressions:: Expressions in Linker Scripts
2963* Implicit Linker Scripts:: Implicit Linker Scripts
2964@end menu
2965
2966@node Basic Script Concepts
2967@section Basic Linker Script Concepts
2968@cindex linker script concepts
2969We need to define some basic concepts and vocabulary in order to
2970describe the linker script language.
2971
2972The linker combines input files into a single output file. The output
2973file and each input file are in a special data format known as an
2974@dfn{object file format}. Each file is called an @dfn{object file}.
2975The output file is often called an @dfn{executable}, but for our
2976purposes we will also call it an object file. Each object file has,
2977among other things, a list of @dfn{sections}. We sometimes refer to a
2978section in an input file as an @dfn{input section}; similarly, a section
2979in the output file is an @dfn{output section}.
2980
2981Each section in an object file has a name and a size. Most sections
2982also have an associated block of data, known as the @dfn{section
56dd11f0 2983contents}. A section may be marked as @dfn{loadable}, which means that
252b5132
RH
2984the contents should be loaded into memory when the output file is run.
2985A section with no contents may be @dfn{allocatable}, which means that an
2986area in memory should be set aside, but nothing in particular should be
2987loaded there (in some cases this memory must be zeroed out). A section
2988which is neither loadable nor allocatable typically contains some sort
2989of debugging information.
2990
2991Every loadable or allocatable output section has two addresses. The
2992first is the @dfn{VMA}, or virtual memory address. This is the address
2993the section will have when the output file is run. The second is the
2994@dfn{LMA}, or load memory address. This is the address at which the
2995section will be loaded. In most cases the two addresses will be the
2996same. An example of when they might be different is when a data section
2997is loaded into ROM, and then copied into RAM when the program starts up
2998(this technique is often used to initialize global variables in a ROM
2999based system). In this case the ROM address would be the LMA, and the
3000RAM address would be the VMA.
3001
3002You can see the sections in an object file by using the @code{objdump}
3003program with the @samp{-h} option.
3004
3005Every object file also has a list of @dfn{symbols}, known as the
3006@dfn{symbol table}. A symbol may be defined or undefined. Each symbol
3007has a name, and each defined symbol has an address, among other
3008information. If you compile a C or C++ program into an object file, you
3009will get a defined symbol for every defined function and global or
3010static variable. Every undefined function or global variable which is
3011referenced in the input file will become an undefined symbol.
3012
3013You can see the symbols in an object file by using the @code{nm}
3014program, or by using the @code{objdump} program with the @samp{-t}
3015option.
3016
3017@node Script Format
3018@section Linker Script Format
3019@cindex linker script format
3020Linker scripts are text files.
3021
3022You write a linker script as a series of commands. Each command is
3023either a keyword, possibly followed by arguments, or an assignment to a
3024symbol. You may separate commands using semicolons. Whitespace is
3025generally ignored.
3026
3027Strings such as file or format names can normally be entered directly.
3028If the file name contains a character such as a comma which would
3029otherwise serve to separate file names, you may put the file name in
3030double quotes. There is no way to use a double quote character in a
3031file name.
3032
3033You may include comments in linker scripts just as in C, delimited by
3034@samp{/*} and @samp{*/}. As in C, comments are syntactically equivalent
3035to whitespace.
3036
3037@node Simple Example
3038@section Simple Linker Script Example
3039@cindex linker script example
3040@cindex example of linker script
3041Many linker scripts are fairly simple.
3042
3043The simplest possible linker script has just one command:
3044@samp{SECTIONS}. You use the @samp{SECTIONS} command to describe the
3045memory layout of the output file.
3046
3047The @samp{SECTIONS} command is a powerful command. Here we will
3048describe a simple use of it. Let's assume your program consists only of
3049code, initialized data, and uninitialized data. These will be in the
3050@samp{.text}, @samp{.data}, and @samp{.bss} sections, respectively.
3051Let's assume further that these are the only sections which appear in
3052your input files.
3053
3054For this example, let's say that the code should be loaded at address
30550x10000, and that the data should start at address 0x8000000. Here is a
3056linker script which will do that:
3057@smallexample
3058SECTIONS
3059@{
3060 . = 0x10000;
3061 .text : @{ *(.text) @}
3062 . = 0x8000000;
3063 .data : @{ *(.data) @}
3064 .bss : @{ *(.bss) @}
3065@}
3066@end smallexample
3067
3068You write the @samp{SECTIONS} command as the keyword @samp{SECTIONS},
3069followed by a series of symbol assignments and output section
3070descriptions enclosed in curly braces.
3071
252b5132
RH
3072The first line inside the @samp{SECTIONS} command of the above example
3073sets the value of the special symbol @samp{.}, which is the location
3074counter. If you do not specify the address of an output section in some
3075other way (other ways are described later), the address is set from the
3076current value of the location counter. The location counter is then
3077incremented by the size of the output section. At the start of the
3078@samp{SECTIONS} command, the location counter has the value @samp{0}.
3079
3080The second line defines an output section, @samp{.text}. The colon is
3081required syntax which may be ignored for now. Within the curly braces
3082after the output section name, you list the names of the input sections
3083which should be placed into this output section. The @samp{*} is a
3084wildcard which matches any file name. The expression @samp{*(.text)}
3085means all @samp{.text} input sections in all input files.
3086
3087Since the location counter is @samp{0x10000} when the output section
3088@samp{.text} is defined, the linker will set the address of the
3089@samp{.text} section in the output file to be @samp{0x10000}.
3090
3091The remaining lines define the @samp{.data} and @samp{.bss} sections in
3092the output file. The linker will place the @samp{.data} output section
3093at address @samp{0x8000000}. After the linker places the @samp{.data}
3094output section, the value of the location counter will be
3095@samp{0x8000000} plus the size of the @samp{.data} output section. The
3096effect is that the linker will place the @samp{.bss} output section
58434bc1 3097immediately after the @samp{.data} output section in memory.
252b5132
RH
3098
3099The linker will ensure that each output section has the required
3100alignment, by increasing the location counter if necessary. In this
3101example, the specified addresses for the @samp{.text} and @samp{.data}
3102sections will probably satisfy any alignment constraints, but the linker
3103may have to create a small gap between the @samp{.data} and @samp{.bss}
3104sections.
3105
3106That's it! That's a simple and complete linker script.
3107
3108@node Simple Commands
3109@section Simple Linker Script Commands
3110@cindex linker script simple commands
3111In this section we describe the simple linker script commands.
3112
3113@menu
3114* Entry Point:: Setting the entry point
3115* File Commands:: Commands dealing with files
3116@ifclear SingleFormat
3117* Format Commands:: Commands dealing with object file formats
3118@end ifclear
3119
4a93e180 3120* REGION_ALIAS:: Assign alias names to memory regions
252b5132
RH
3121* Miscellaneous Commands:: Other linker script commands
3122@end menu
3123
3124@node Entry Point
36f63dca 3125@subsection Setting the Entry Point
252b5132
RH
3126@kindex ENTRY(@var{symbol})
3127@cindex start of execution
3128@cindex first instruction
3129@cindex entry point
3130The first instruction to execute in a program is called the @dfn{entry
3131point}. You can use the @code{ENTRY} linker script command to set the
3132entry point. The argument is a symbol name:
3133@smallexample
3134ENTRY(@var{symbol})
3135@end smallexample
3136
3137There are several ways to set the entry point. The linker will set the
3138entry point by trying each of the following methods in order, and
3139stopping when one of them succeeds:
3140@itemize @bullet
a1ab1d2a 3141@item
252b5132 3142the @samp{-e} @var{entry} command-line option;
a1ab1d2a 3143@item
252b5132 3144the @code{ENTRY(@var{symbol})} command in a linker script;
a1ab1d2a 3145@item
3ab904c4
NC
3146the value of a target specific symbol, if it is defined; For many
3147targets this is @code{start}, but PE and BeOS based systems for example
3148check a list of possible entry symbols, matching the first one found.
a1ab1d2a 3149@item
252b5132 3150the address of the first byte of the @samp{.text} section, if present;
a1ab1d2a 3151@item
252b5132
RH
3152The address @code{0}.
3153@end itemize
3154
3155@node File Commands
36f63dca 3156@subsection Commands Dealing with Files
252b5132
RH
3157@cindex linker script file commands
3158Several linker script commands deal with files.
3159
3160@table @code
3161@item INCLUDE @var{filename}
3162@kindex INCLUDE @var{filename}
3163@cindex including a linker script
3164Include the linker script @var{filename} at this point. The file will
3165be searched for in the current directory, and in any directory specified
ff5dcc92 3166with the @option{-L} option. You can nest calls to @code{INCLUDE} up to
252b5132
RH
316710 levels deep.
3168
4006703d
NS
3169You can place @code{INCLUDE} directives at the top level, in @code{MEMORY} or
3170@code{SECTIONS} commands, or in output section descriptions.
3171
252b5132
RH
3172@item INPUT(@var{file}, @var{file}, @dots{})
3173@itemx INPUT(@var{file} @var{file} @dots{})
3174@kindex INPUT(@var{files})
3175@cindex input files in linker scripts
3176@cindex input object files in linker scripts
3177@cindex linker script input object files
3178The @code{INPUT} command directs the linker to include the named files
3179in the link, as though they were named on the command line.
3180
3181For example, if you always want to include @file{subr.o} any time you do
3182a link, but you can't be bothered to put it on every link command line,
3183then you can put @samp{INPUT (subr.o)} in your linker script.
3184
3185In fact, if you like, you can list all of your input files in the linker
3186script, and then invoke the linker with nothing but a @samp{-T} option.
3187
e3f2db7f
AO
3188In case a @dfn{sysroot prefix} is configured, and the filename starts
3189with the @samp{/} character, and the script being processed was
3190located inside the @dfn{sysroot prefix}, the filename will be looked
3191for in the @dfn{sysroot prefix}. Otherwise, the linker will try to
3192open the file in the current directory. If it is not found, the
cad60a33
HPN
3193linker will search through the archive library search path.
3194The @dfn{sysroot prefix} can also be forced by specifying @code{=}
3195as the first character in the filename path. See also the
e3f2db7f 3196description of @samp{-L} in @ref{Options,,Command Line Options}.
252b5132 3197
ff5dcc92 3198If you use @samp{INPUT (-l@var{file})}, @command{ld} will transform the
252b5132
RH
3199name to @code{lib@var{file}.a}, as with the command line argument
3200@samp{-l}.
3201
3202When you use the @code{INPUT} command in an implicit linker script, the
3203files will be included in the link at the point at which the linker
3204script file is included. This can affect archive searching.
3205
3206@item GROUP(@var{file}, @var{file}, @dots{})
3207@itemx GROUP(@var{file} @var{file} @dots{})
3208@kindex GROUP(@var{files})
3209@cindex grouping input files
3210The @code{GROUP} command is like @code{INPUT}, except that the named
3211files should all be archives, and they are searched repeatedly until no
3212new undefined references are created. See the description of @samp{-(}
3213in @ref{Options,,Command Line Options}.
3214
b717d30e
JJ
3215@item AS_NEEDED(@var{file}, @var{file}, @dots{})
3216@itemx AS_NEEDED(@var{file} @var{file} @dots{})
3217@kindex AS_NEEDED(@var{files})
3218This construct can appear only inside of the @code{INPUT} or @code{GROUP}
3219commands, among other filenames. The files listed will be handled
3220as if they appear directly in the @code{INPUT} or @code{GROUP} commands,
3221with the exception of ELF shared libraries, that will be added only
3222when they are actually needed. This construct essentially enables
3223@option{--as-needed} option for all the files listed inside of it
3224and restores previous @option{--as-needed} resp. @option{--no-as-needed}
3225setting afterwards.
3226
252b5132
RH
3227@item OUTPUT(@var{filename})
3228@kindex OUTPUT(@var{filename})
b45619c0 3229@cindex output file name in linker script
252b5132
RH
3230The @code{OUTPUT} command names the output file. Using
3231@code{OUTPUT(@var{filename})} in the linker script is exactly like using
3232@samp{-o @var{filename}} on the command line (@pxref{Options,,Command
3233Line Options}). If both are used, the command line option takes
3234precedence.
3235
3236You can use the @code{OUTPUT} command to define a default name for the
3237output file other than the usual default of @file{a.out}.
3238
3239@item SEARCH_DIR(@var{path})
3240@kindex SEARCH_DIR(@var{path})
3241@cindex library search path in linker script
3242@cindex archive search path in linker script
3243@cindex search path in linker script
3244The @code{SEARCH_DIR} command adds @var{path} to the list of paths where
ff5dcc92 3245@command{ld} looks for archive libraries. Using
252b5132
RH
3246@code{SEARCH_DIR(@var{path})} is exactly like using @samp{-L @var{path}}
3247on the command line (@pxref{Options,,Command Line Options}). If both
3248are used, then the linker will search both paths. Paths specified using
3249the command line option are searched first.
3250
3251@item STARTUP(@var{filename})
3252@kindex STARTUP(@var{filename})
3253@cindex first input file
3254The @code{STARTUP} command is just like the @code{INPUT} command, except
3255that @var{filename} will become the first input file to be linked, as
3256though it were specified first on the command line. This may be useful
3257when using a system in which the entry point is always the start of the
3258first file.
3259@end table
3260
3261@ifclear SingleFormat
3262@node Format Commands
36f63dca 3263@subsection Commands Dealing with Object File Formats
252b5132
RH
3264A couple of linker script commands deal with object file formats.
3265
3266@table @code
3267@item OUTPUT_FORMAT(@var{bfdname})
3268@itemx OUTPUT_FORMAT(@var{default}, @var{big}, @var{little})
3269@kindex OUTPUT_FORMAT(@var{bfdname})
3270@cindex output file format in linker script
3271The @code{OUTPUT_FORMAT} command names the BFD format to use for the
3272output file (@pxref{BFD}). Using @code{OUTPUT_FORMAT(@var{bfdname})} is
024531e2 3273exactly like using @samp{--oformat @var{bfdname}} on the command line
252b5132
RH
3274(@pxref{Options,,Command Line Options}). If both are used, the command
3275line option takes precedence.
3276
3277You can use @code{OUTPUT_FORMAT} with three arguments to use different
3278formats based on the @samp{-EB} and @samp{-EL} command line options.
3279This permits the linker script to set the output format based on the
3280desired endianness.
3281
3282If neither @samp{-EB} nor @samp{-EL} are used, then the output format
3283will be the first argument, @var{default}. If @samp{-EB} is used, the
3284output format will be the second argument, @var{big}. If @samp{-EL} is
3285used, the output format will be the third argument, @var{little}.
3286
3287For example, the default linker script for the MIPS ELF target uses this
3288command:
3289@smallexample
3290OUTPUT_FORMAT(elf32-bigmips, elf32-bigmips, elf32-littlemips)
3291@end smallexample
3292This says that the default format for the output file is
3293@samp{elf32-bigmips}, but if the user uses the @samp{-EL} command line
3294option, the output file will be created in the @samp{elf32-littlemips}
3295format.
3296
3297@item TARGET(@var{bfdname})
3298@kindex TARGET(@var{bfdname})
3299@cindex input file format in linker script
3300The @code{TARGET} command names the BFD format to use when reading input
3301files. It affects subsequent @code{INPUT} and @code{GROUP} commands.
3302This command is like using @samp{-b @var{bfdname}} on the command line
3303(@pxref{Options,,Command Line Options}). If the @code{TARGET} command
3304is used but @code{OUTPUT_FORMAT} is not, then the last @code{TARGET}
3305command is also used to set the format for the output file. @xref{BFD}.
3306@end table
3307@end ifclear
3308
4a93e180
NC
3309@node REGION_ALIAS
3310@subsection Assign alias names to memory regions
3311@kindex REGION_ALIAS(@var{alias}, @var{region})
3312@cindex region alias
3313@cindex region names
3314
3315Alias names can be added to existing memory regions created with the
3316@ref{MEMORY} command. Each name corresponds to at most one memory region.
3317
3318@smallexample
3319REGION_ALIAS(@var{alias}, @var{region})
3320@end smallexample
3321
3322The @code{REGION_ALIAS} function creates an alias name @var{alias} for the
3323memory region @var{region}. This allows a flexible mapping of output sections
3324to memory regions. An example follows.
3325
3326Suppose we have an application for embedded systems which come with various
3327memory storage devices. All have a general purpose, volatile memory @code{RAM}
3328that allows code execution or data storage. Some may have a read-only,
3329non-volatile memory @code{ROM} that allows code execution and read-only data
3330access. The last variant is a read-only, non-volatile memory @code{ROM2} with
3331read-only data access and no code execution capability. We have four output
3332sections:
3333
3334@itemize @bullet
3335@item
3336@code{.text} program code;
3337@item
3338@code{.rodata} read-only data;
3339@item
3340@code{.data} read-write initialized data;
3341@item
3342@code{.bss} read-write zero initialized data.
3343@end itemize
3344
3345The goal is to provide a linker command file that contains a system independent
3346part defining the output sections and a system dependent part mapping the
3347output sections to the memory regions available on the system. Our embedded
3348systems come with three different memory setups @code{A}, @code{B} and
3349@code{C}:
3350@multitable @columnfractions .25 .25 .25 .25
3351@item Section @tab Variant A @tab Variant B @tab Variant C
9d5777a3 3352@item .text @tab RAM @tab ROM @tab ROM
4a93e180
NC
3353@item .rodata @tab RAM @tab ROM @tab ROM2
3354@item .data @tab RAM @tab RAM/ROM @tab RAM/ROM2
3355@item .bss @tab RAM @tab RAM @tab RAM
3356@end multitable
3357The notation @code{RAM/ROM} or @code{RAM/ROM2} means that this section is
3358loaded into region @code{ROM} or @code{ROM2} respectively. Please note that
3359the load address of the @code{.data} section starts in all three variants at
3360the end of the @code{.rodata} section.
3361
3362The base linker script that deals with the output sections follows. It
3363includes the system dependent @code{linkcmds.memory} file that describes the
3364memory layout:
3365@smallexample
3366INCLUDE linkcmds.memory
3367
3368SECTIONS
3369 @{
3370 .text :
3371 @{
3372 *(.text)
3373 @} > REGION_TEXT
3374 .rodata :
3375 @{
3376 *(.rodata)
3377 rodata_end = .;
3378 @} > REGION_RODATA
3379 .data : AT (rodata_end)
3380 @{
3381 data_start = .;
3382 *(.data)
3383 @} > REGION_DATA
3384 data_size = SIZEOF(.data);
3385 data_load_start = LOADADDR(.data);
3386 .bss :
3387 @{
3388 *(.bss)
3389 @} > REGION_BSS
3390 @}
3391@end smallexample
3392
3393Now we need three different @code{linkcmds.memory} files to define memory
3394regions and alias names. The content of @code{linkcmds.memory} for the three
3395variants @code{A}, @code{B} and @code{C}:
3396@table @code
3397@item A
3398Here everything goes into the @code{RAM}.
3399@smallexample
3400MEMORY
3401 @{
3402 RAM : ORIGIN = 0, LENGTH = 4M
3403 @}
3404
3405REGION_ALIAS("REGION_TEXT", RAM);
3406REGION_ALIAS("REGION_RODATA", RAM);
3407REGION_ALIAS("REGION_DATA", RAM);
3408REGION_ALIAS("REGION_BSS", RAM);
3409@end smallexample
3410@item B
3411Program code and read-only data go into the @code{ROM}. Read-write data goes
3412into the @code{RAM}. An image of the initialized data is loaded into the
3413@code{ROM} and will be copied during system start into the @code{RAM}.
3414@smallexample
3415MEMORY
3416 @{
3417 ROM : ORIGIN = 0, LENGTH = 3M
3418 RAM : ORIGIN = 0x10000000, LENGTH = 1M
3419 @}
3420
3421REGION_ALIAS("REGION_TEXT", ROM);
3422REGION_ALIAS("REGION_RODATA", ROM);
3423REGION_ALIAS("REGION_DATA", RAM);
3424REGION_ALIAS("REGION_BSS", RAM);
3425@end smallexample
3426@item C
3427Program code goes into the @code{ROM}. Read-only data goes into the
3428@code{ROM2}. Read-write data goes into the @code{RAM}. An image of the
3429initialized data is loaded into the @code{ROM2} and will be copied during
3430system start into the @code{RAM}.
3431@smallexample
3432MEMORY
3433 @{
3434 ROM : ORIGIN = 0, LENGTH = 2M
3435 ROM2 : ORIGIN = 0x10000000, LENGTH = 1M
3436 RAM : ORIGIN = 0x20000000, LENGTH = 1M
3437 @}
3438
3439REGION_ALIAS("REGION_TEXT", ROM);
3440REGION_ALIAS("REGION_RODATA", ROM2);
3441REGION_ALIAS("REGION_DATA", RAM);
3442REGION_ALIAS("REGION_BSS", RAM);
3443@end smallexample
3444@end table
3445
3446It is possible to write a common system initialization routine to copy the
3447@code{.data} section from @code{ROM} or @code{ROM2} into the @code{RAM} if
3448necessary:
3449@smallexample
3450#include <string.h>
3451
3452extern char data_start [];
3453extern char data_size [];
3454extern char data_load_start [];
3455
3456void copy_data(void)
3457@{
3458 if (data_start != data_load_start)
3459 @{
3460 memcpy(data_start, data_load_start, (size_t) data_size);
3461 @}
3462@}
3463@end smallexample
3464
252b5132 3465@node Miscellaneous Commands
36f63dca 3466@subsection Other Linker Script Commands
252b5132
RH
3467There are a few other linker scripts commands.
3468
3469@table @code
3470@item ASSERT(@var{exp}, @var{message})
3471@kindex ASSERT
3472@cindex assertion in linker script
3473Ensure that @var{exp} is non-zero. If it is zero, then exit the linker
3474with an error code, and print @var{message}.
3475
3476@item EXTERN(@var{symbol} @var{symbol} @dots{})
3477@kindex EXTERN
3478@cindex undefined symbol in linker script
3479Force @var{symbol} to be entered in the output file as an undefined
3480symbol. Doing this may, for example, trigger linking of additional
3481modules from standard libraries. You may list several @var{symbol}s for
3482each @code{EXTERN}, and you may use @code{EXTERN} multiple times. This
3483command has the same effect as the @samp{-u} command-line option.
3484
3485@item FORCE_COMMON_ALLOCATION
3486@kindex FORCE_COMMON_ALLOCATION
3487@cindex common allocation in linker script
3488This command has the same effect as the @samp{-d} command-line option:
ff5dcc92 3489to make @command{ld} assign space to common symbols even if a relocatable
252b5132
RH
3490output file is specified (@samp{-r}).
3491
4818e05f
AM
3492@item INHIBIT_COMMON_ALLOCATION
3493@kindex INHIBIT_COMMON_ALLOCATION
3494@cindex common allocation in linker script
3495This command has the same effect as the @samp{--no-define-common}
3496command-line option: to make @code{ld} omit the assignment of addresses
3497to common symbols even for a non-relocatable output file.
3498
53d25da6
AM
3499@item INSERT [ AFTER | BEFORE ] @var{output_section}
3500@kindex INSERT
3501@cindex insert user script into default script
3502This command is typically used in a script specified by @samp{-T} to
3503augment the default @code{SECTIONS} with, for example, overlays. It
3504inserts all prior linker script statements after (or before)
3505@var{output_section}, and also causes @samp{-T} to not override the
3506default linker script. The exact insertion point is as for orphan
3507sections. @xref{Location Counter}. The insertion happens after the
3508linker has mapped input sections to output sections. Prior to the
3509insertion, since @samp{-T} scripts are parsed before the default
3510linker script, statements in the @samp{-T} script occur before the
3511default linker script statements in the internal linker representation
3512of the script. In particular, input section assignments will be made
3513to @samp{-T} output sections before those in the default script. Here
3514is an example of how a @samp{-T} script using @code{INSERT} might look:
3515
3516@smallexample
3517SECTIONS
3518@{
3519 OVERLAY :
3520 @{
3521 .ov1 @{ ov1*(.text) @}
3522 .ov2 @{ ov2*(.text) @}
3523 @}
3524@}
3525INSERT AFTER .text;
3526@end smallexample
3527
252b5132
RH
3528@item NOCROSSREFS(@var{section} @var{section} @dots{})
3529@kindex NOCROSSREFS(@var{sections})
3530@cindex cross references
ff5dcc92 3531This command may be used to tell @command{ld} to issue an error about any
252b5132
RH
3532references among certain output sections.
3533
3534In certain types of programs, particularly on embedded systems when
3535using overlays, when one section is loaded into memory, another section
3536will not be. Any direct references between the two sections would be
3537errors. For example, it would be an error if code in one section called
3538a function defined in the other section.
3539
3540The @code{NOCROSSREFS} command takes a list of output section names. If
ff5dcc92 3541@command{ld} detects any cross references between the sections, it reports
252b5132
RH
3542an error and returns a non-zero exit status. Note that the
3543@code{NOCROSSREFS} command uses output section names, not input section
3544names.
3545
3546@ifclear SingleFormat
3547@item OUTPUT_ARCH(@var{bfdarch})
3548@kindex OUTPUT_ARCH(@var{bfdarch})
3549@cindex machine architecture
3550@cindex architecture
3551Specify a particular output machine architecture. The argument is one
3552of the names used by the BFD library (@pxref{BFD}). You can see the
3553architecture of an object file by using the @code{objdump} program with
3554the @samp{-f} option.
3555@end ifclear
01554a74
AM
3556
3557@item LD_FEATURE(@var{string})
3558@kindex LD_FEATURE(@var{string})
3559This command may be used to modify @command{ld} behavior. If
3560@var{string} is @code{"SANE_EXPR"} then absolute symbols and numbers
3561in a script are simply treated as numbers everywhere.
3562@xref{Expression Section}.
252b5132
RH
3563@end table
3564
3565@node Assignments
3566@section Assigning Values to Symbols
3567@cindex assignment in scripts
3568@cindex symbol definition, scripts
3569@cindex variables, defining
3570You may assign a value to a symbol in a linker script. This will define
73ae6183 3571the symbol and place it into the symbol table with a global scope.
252b5132
RH
3572
3573@menu
3574* Simple Assignments:: Simple Assignments
eb8476a6 3575* HIDDEN:: HIDDEN
252b5132 3576* PROVIDE:: PROVIDE
7af8e998 3577* PROVIDE_HIDDEN:: PROVIDE_HIDDEN
73ae6183 3578* Source Code Reference:: How to use a linker script defined symbol in source code
252b5132
RH
3579@end menu
3580
3581@node Simple Assignments
3582@subsection Simple Assignments
3583
3584You may assign to a symbol using any of the C assignment operators:
3585
3586@table @code
3587@item @var{symbol} = @var{expression} ;
3588@itemx @var{symbol} += @var{expression} ;
3589@itemx @var{symbol} -= @var{expression} ;
3590@itemx @var{symbol} *= @var{expression} ;
3591@itemx @var{symbol} /= @var{expression} ;
3592@itemx @var{symbol} <<= @var{expression} ;
3593@itemx @var{symbol} >>= @var{expression} ;
3594@itemx @var{symbol} &= @var{expression} ;
3595@itemx @var{symbol} |= @var{expression} ;
3596@end table
3597
3598The first case will define @var{symbol} to the value of
3599@var{expression}. In the other cases, @var{symbol} must already be
3600defined, and the value will be adjusted accordingly.
3601
3602The special symbol name @samp{.} indicates the location counter. You
b5666f2f 3603may only use this within a @code{SECTIONS} command. @xref{Location Counter}.
252b5132
RH
3604
3605The semicolon after @var{expression} is required.
3606
3607Expressions are defined below; see @ref{Expressions}.
3608
3609You may write symbol assignments as commands in their own right, or as
3610statements within a @code{SECTIONS} command, or as part of an output
3611section description in a @code{SECTIONS} command.
3612
3613The section of the symbol will be set from the section of the
3614expression; for more information, see @ref{Expression Section}.
3615
3616Here is an example showing the three different places that symbol
3617assignments may be used:
3618
3619@smallexample
3620floating_point = 0;
3621SECTIONS
3622@{
3623 .text :
3624 @{
3625 *(.text)
3626 _etext = .;
3627 @}
156e34dd 3628 _bdata = (. + 3) & ~ 3;
252b5132
RH
3629 .data : @{ *(.data) @}
3630@}
3631@end smallexample
3632@noindent
3633In this example, the symbol @samp{floating_point} will be defined as
3634zero. The symbol @samp{_etext} will be defined as the address following
3635the last @samp{.text} input section. The symbol @samp{_bdata} will be
3636defined as the address following the @samp{.text} output section aligned
3637upward to a 4 byte boundary.
3638
eb8476a6
MR
3639@node HIDDEN
3640@subsection HIDDEN
3641@cindex HIDDEN
3642For ELF targeted ports, define a symbol that will be hidden and won't be
3643exported. The syntax is @code{HIDDEN(@var{symbol} = @var{expression})}.
3644
3645Here is the example from @ref{Simple Assignments}, rewritten to use
3646@code{HIDDEN}:
3647
3648@smallexample
3649HIDDEN(floating_point = 0);
3650SECTIONS
3651@{
3652 .text :
3653 @{
3654 *(.text)
3655 HIDDEN(_etext = .);
3656 @}
3657 HIDDEN(_bdata = (. + 3) & ~ 3);
3658 .data : @{ *(.data) @}
3659@}
3660@end smallexample
3661@noindent
3662In this case none of the three symbols will be visible outside this module.
3663
252b5132
RH
3664@node PROVIDE
3665@subsection PROVIDE
3666@cindex PROVIDE
3667In some cases, it is desirable for a linker script to define a symbol
3668only if it is referenced and is not defined by any object included in
3669the link. For example, traditional linkers defined the symbol
3670@samp{etext}. However, ANSI C requires that the user be able to use
3671@samp{etext} as a function name without encountering an error. The
3672@code{PROVIDE} keyword may be used to define a symbol, such as
3673@samp{etext}, only if it is referenced but not defined. The syntax is
3674@code{PROVIDE(@var{symbol} = @var{expression})}.
3675
3676Here is an example of using @code{PROVIDE} to define @samp{etext}:
3677@smallexample
3678SECTIONS
3679@{
3680 .text :
3681 @{
3682 *(.text)
3683 _etext = .;
3684 PROVIDE(etext = .);
3685 @}
3686@}
3687@end smallexample
3688
3689In this example, if the program defines @samp{_etext} (with a leading
3690underscore), the linker will give a multiple definition error. If, on
3691the other hand, the program defines @samp{etext} (with no leading
3692underscore), the linker will silently use the definition in the program.
3693If the program references @samp{etext} but does not define it, the
3694linker will use the definition in the linker script.
3695
7af8e998
L
3696@node PROVIDE_HIDDEN
3697@subsection PROVIDE_HIDDEN
3698@cindex PROVIDE_HIDDEN
3699Similar to @code{PROVIDE}. For ELF targeted ports, the symbol will be
3700hidden and won't be exported.
3701
73ae6183
NC
3702@node Source Code Reference
3703@subsection Source Code Reference
3704
3705Accessing a linker script defined variable from source code is not
3706intuitive. In particular a linker script symbol is not equivalent to
3707a variable declaration in a high level language, it is instead a
3708symbol that does not have a value.
3709
3710Before going further, it is important to note that compilers often
3711transform names in the source code into different names when they are
3712stored in the symbol table. For example, Fortran compilers commonly
3713prepend or append an underscore, and C++ performs extensive @samp{name
3714mangling}. Therefore there might be a discrepancy between the name
3715of a variable as it is used in source code and the name of the same
3716variable as it is defined in a linker script. For example in C a
3717linker script variable might be referred to as:
3718
3719@smallexample
3720 extern int foo;
3721@end smallexample
3722
3723But in the linker script it might be defined as:
3724
3725@smallexample
3726 _foo = 1000;
3727@end smallexample
3728
3729In the remaining examples however it is assumed that no name
3730transformation has taken place.
3731
3732When a symbol is declared in a high level language such as C, two
3733things happen. The first is that the compiler reserves enough space
3734in the program's memory to hold the @emph{value} of the symbol. The
3735second is that the compiler creates an entry in the program's symbol
3736table which holds the symbol's @emph{address}. ie the symbol table
3737contains the address of the block of memory holding the symbol's
3738value. So for example the following C declaration, at file scope:
3739
3740@smallexample
3741 int foo = 1000;
3742@end smallexample
3743
10bf6894 3744creates an entry called @samp{foo} in the symbol table. This entry
73ae6183
NC
3745holds the address of an @samp{int} sized block of memory where the
3746number 1000 is initially stored.
3747
3748When a program references a symbol the compiler generates code that
3749first accesses the symbol table to find the address of the symbol's
3750memory block and then code to read the value from that memory block.
3751So:
3752
3753@smallexample
3754 foo = 1;
3755@end smallexample
3756
3757looks up the symbol @samp{foo} in the symbol table, gets the address
3758associated with this symbol and then writes the value 1 into that
3759address. Whereas:
3760
3761@smallexample
3762 int * a = & foo;
3763@end smallexample
3764
10bf6894 3765looks up the symbol @samp{foo} in the symbol table, gets its address
73ae6183
NC
3766and then copies this address into the block of memory associated with
3767the variable @samp{a}.
3768
3769Linker scripts symbol declarations, by contrast, create an entry in
3770the symbol table but do not assign any memory to them. Thus they are
3771an address without a value. So for example the linker script definition:
3772
3773@smallexample
3774 foo = 1000;
3775@end smallexample
3776
3777creates an entry in the symbol table called @samp{foo} which holds
3778the address of memory location 1000, but nothing special is stored at
3779address 1000. This means that you cannot access the @emph{value} of a
3780linker script defined symbol - it has no value - all you can do is
3781access the @emph{address} of a linker script defined symbol.
3782
3783Hence when you are using a linker script defined symbol in source code
3784you should always take the address of the symbol, and never attempt to
3785use its value. For example suppose you want to copy the contents of a
3786section of memory called .ROM into a section called .FLASH and the
3787linker script contains these declarations:
3788
3789@smallexample
3790@group
3791 start_of_ROM = .ROM;
3792 end_of_ROM = .ROM + sizeof (.ROM) - 1;
3793 start_of_FLASH = .FLASH;
3794@end group
3795@end smallexample
3796
3797Then the C source code to perform the copy would be:
3798
3799@smallexample
3800@group
3801 extern char start_of_ROM, end_of_ROM, start_of_FLASH;
c0065db7 3802
73ae6183
NC
3803 memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);
3804@end group
3805@end smallexample
3806
3807Note the use of the @samp{&} operators. These are correct.
3808
252b5132 3809@node SECTIONS
36f63dca 3810@section SECTIONS Command
252b5132
RH
3811@kindex SECTIONS
3812The @code{SECTIONS} command tells the linker how to map input sections
3813into output sections, and how to place the output sections in memory.
3814
3815The format of the @code{SECTIONS} command is:
3816@smallexample
3817SECTIONS
3818@{
3819 @var{sections-command}
3820 @var{sections-command}
3821 @dots{}
3822@}
3823@end smallexample
3824
3825Each @var{sections-command} may of be one of the following:
3826
3827@itemize @bullet
3828@item
3829an @code{ENTRY} command (@pxref{Entry Point,,Entry command})
3830@item
3831a symbol assignment (@pxref{Assignments})
3832@item
3833an output section description
3834@item
3835an overlay description
3836@end itemize
3837
3838The @code{ENTRY} command and symbol assignments are permitted inside the
3839@code{SECTIONS} command for convenience in using the location counter in
3840those commands. This can also make the linker script easier to
3841understand because you can use those commands at meaningful points in
3842the layout of the output file.
3843
3844Output section descriptions and overlay descriptions are described
3845below.
3846
3847If you do not use a @code{SECTIONS} command in your linker script, the
3848linker will place each input section into an identically named output
3849section in the order that the sections are first encountered in the
3850input files. If all input sections are present in the first file, for
3851example, the order of sections in the output file will match the order
3852in the first input file. The first section will be at address zero.
3853
3854@menu
3855* Output Section Description:: Output section description
3856* Output Section Name:: Output section name
3857* Output Section Address:: Output section address
3858* Input Section:: Input section description
3859* Output Section Data:: Output section data
3860* Output Section Keywords:: Output section keywords
3861* Output Section Discarding:: Output section discarding
3862* Output Section Attributes:: Output section attributes
3863* Overlay Description:: Overlay description
3864@end menu
3865
3866@node Output Section Description
36f63dca 3867@subsection Output Section Description
252b5132
RH
3868The full description of an output section looks like this:
3869@smallexample
a1ab1d2a 3870@group
7e7d5768 3871@var{section} [@var{address}] [(@var{type})] :
0c71d759 3872 [AT(@var{lma})]
1eec346e 3873 [ALIGN(@var{section_align}) | ALIGN_WITH_INPUT]
0c71d759
NC
3874 [SUBALIGN(@var{subsection_align})]
3875 [@var{constraint}]
252b5132
RH
3876 @{
3877 @var{output-section-command}
3878 @var{output-section-command}
3879 @dots{}
abc9061b 3880 @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}] [,]
252b5132
RH
3881@end group
3882@end smallexample
3883
3884Most output sections do not use most of the optional section attributes.
3885
3886The whitespace around @var{section} is required, so that the section
3887name is unambiguous. The colon and the curly braces are also required.
abc9061b
CC
3888The comma at the end may be required if a @var{fillexp} is used and
3889the next @var{sections-command} looks like a continuation of the expression.
252b5132
RH
3890The line breaks and other white space are optional.
3891
3892Each @var{output-section-command} may be one of the following:
3893
3894@itemize @bullet
3895@item
3896a symbol assignment (@pxref{Assignments})
3897@item
3898an input section description (@pxref{Input Section})
3899@item
3900data values to include directly (@pxref{Output Section Data})
3901@item
3902a special output section keyword (@pxref{Output Section Keywords})
3903@end itemize
3904
3905@node Output Section Name
36f63dca 3906@subsection Output Section Name
252b5132
RH
3907@cindex name, section
3908@cindex section name
3909The name of the output section is @var{section}. @var{section} must
3910meet the constraints of your output format. In formats which only
3911support a limited number of sections, such as @code{a.out}, the name
3912must be one of the names supported by the format (@code{a.out}, for
3913example, allows only @samp{.text}, @samp{.data} or @samp{.bss}). If the
3914output format supports any number of sections, but with numbers and not
3915names (as is the case for Oasys), the name should be supplied as a
3916quoted numeric string. A section name may consist of any sequence of
3917characters, but a name which contains any unusual characters such as
3918commas must be quoted.
3919
3920The output section name @samp{/DISCARD/} is special; @ref{Output Section
3921Discarding}.
3922
3923@node Output Section Address
2a16d82a 3924@subsection Output Section Address
252b5132
RH
3925@cindex address, section
3926@cindex section address
3927The @var{address} is an expression for the VMA (the virtual memory
ea5cae92
NC
3928address) of the output section. This address is optional, but if it
3929is provided then the output address will be set exactly as specified.
3930
3931If the output address is not specified then one will be chosen for the
3932section, based on the heuristic below. This address will be adjusted
3933to fit the alignment requirement of the output section. The
3934alignment requirement is the strictest alignment of any input section
3935contained within the output section.
3936
3937The output section address heuristic is as follows:
3938
3939@itemize @bullet
3940@item
3941If an output memory @var{region} is set for the section then it
3942is added to this region and its address will be the next free address
3943in that region.
3944
3945@item
3946If the MEMORY command has been used to create a list of memory
3947regions then the first region which has attributes compatible with the
3948section is selected to contain it. The section's output address will
3949be the next free address in that region; @ref{MEMORY}.
3950
3951@item
3952If no memory regions were specified, or none match the section then
3953the output address will be based on the current value of the location
3954counter.
3955@end itemize
3956
3957@noindent
3958For example:
3959
252b5132
RH
3960@smallexample
3961.text . : @{ *(.text) @}
3962@end smallexample
ea5cae92 3963
252b5132
RH
3964@noindent
3965and
ea5cae92 3966
252b5132
RH
3967@smallexample
3968.text : @{ *(.text) @}
3969@end smallexample
ea5cae92 3970
252b5132
RH
3971@noindent
3972are subtly different. The first will set the address of the
3973@samp{.text} output section to the current value of the location
3974counter. The second will set it to the current value of the location
ea5cae92
NC
3975counter aligned to the strictest alignment of any of the @samp{.text}
3976input sections.
252b5132
RH
3977
3978The @var{address} may be an arbitrary expression; @ref{Expressions}.
3979For example, if you want to align the section on a 0x10 byte boundary,
3980so that the lowest four bits of the section address are zero, you could
3981do something like this:
3982@smallexample
3983.text ALIGN(0x10) : @{ *(.text) @}
3984@end smallexample
3985@noindent
3986This works because @code{ALIGN} returns the current location counter
3987aligned upward to the specified value.
3988
3989Specifying @var{address} for a section will change the value of the
6ce340f1
NC
3990location counter, provided that the section is non-empty. (Empty
3991sections are ignored).
252b5132
RH
3992
3993@node Input Section
36f63dca 3994@subsection Input Section Description
252b5132
RH
3995@cindex input sections
3996@cindex mapping input sections to output sections
3997The most common output section command is an input section description.
3998
3999The input section description is the most basic linker script operation.
4000You use output sections to tell the linker how to lay out your program
4001in memory. You use input section descriptions to tell the linker how to
4002map the input files into your memory layout.
4003
4004@menu
4005* Input Section Basics:: Input section basics
4006* Input Section Wildcards:: Input section wildcard patterns
4007* Input Section Common:: Input section for common symbols
4008* Input Section Keep:: Input section and garbage collection
4009* Input Section Example:: Input section example
4010@end menu
4011
4012@node Input Section Basics
36f63dca 4013@subsubsection Input Section Basics
252b5132
RH
4014@cindex input section basics
4015An input section description consists of a file name optionally followed
4016by a list of section names in parentheses.
4017
4018The file name and the section name may be wildcard patterns, which we
4019describe further below (@pxref{Input Section Wildcards}).
4020
4021The most common input section description is to include all input
4022sections with a particular name in the output section. For example, to
4023include all input @samp{.text} sections, you would write:
4024@smallexample
4025*(.text)
4026@end smallexample
4027@noindent
18625d54
CM
4028Here the @samp{*} is a wildcard which matches any file name. To exclude a list
4029of files from matching the file name wildcard, EXCLUDE_FILE may be used to
4030match all files except the ones specified in the EXCLUDE_FILE list. For
4031example:
252b5132 4032@smallexample
b4346c09 4033*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
252b5132 4034@end smallexample
765b7cbe
JB
4035will cause all .ctors sections from all files except @file{crtend.o} and
4036@file{otherfile.o} to be included.
252b5132
RH
4037
4038There are two ways to include more than one section:
4039@smallexample
4040*(.text .rdata)
4041*(.text) *(.rdata)
4042@end smallexample
4043@noindent
4044The difference between these is the order in which the @samp{.text} and
4045@samp{.rdata} input sections will appear in the output section. In the
b6bf44ba
AM
4046first example, they will be intermingled, appearing in the same order as
4047they are found in the linker input. In the second example, all
252b5132
RH
4048@samp{.text} input sections will appear first, followed by all
4049@samp{.rdata} input sections.
4050
4051You can specify a file name to include sections from a particular file.
4052You would do this if one or more of your files contain special data that
4053needs to be at a particular location in memory. For example:
4054@smallexample
4055data.o(.data)
4056@end smallexample
4057
ae17ab41
CM
4058To refine the sections that are included based on the section flags
4059of an input section, INPUT_SECTION_FLAGS may be used.
4060
4061Here is a simple example for using Section header flags for ELF sections:
4062
4063@smallexample
4064@group
4065SECTIONS @{
4066 .text : @{ INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) @}
4067 .text2 : @{ INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) @}
4068@}
4069@end group
4070@end smallexample
4071
4072In this example, the output section @samp{.text} will be comprised of any
4073input section matching the name *(.text) whose section header flags
4074@code{SHF_MERGE} and @code{SHF_STRINGS} are set. The output section
4075@samp{.text2} will be comprised of any input section matching the name *(.text)
4076whose section header flag @code{SHF_WRITE} is clear.
4077
967928e9
AM
4078You can also specify files within archives by writing a pattern
4079matching the archive, a colon, then the pattern matching the file,
4080with no whitespace around the colon.
4081
4082@table @samp
4083@item archive:file
4084matches file within archive
4085@item archive:
4086matches the whole archive
4087@item :file
4088matches file but not one in an archive
4089@end table
4090
4091Either one or both of @samp{archive} and @samp{file} can contain shell
4092wildcards. On DOS based file systems, the linker will assume that a
4093single letter followed by a colon is a drive specifier, so
4094@samp{c:myfile.o} is a simple file specification, not @samp{myfile.o}
4095within an archive called @samp{c}. @samp{archive:file} filespecs may
4096also be used within an @code{EXCLUDE_FILE} list, but may not appear in
4097other linker script contexts. For instance, you cannot extract a file
4098from an archive by using @samp{archive:file} in an @code{INPUT}
4099command.
4100
252b5132
RH
4101If you use a file name without a list of sections, then all sections in
4102the input file will be included in the output section. This is not
4103commonly done, but it may by useful on occasion. For example:
4104@smallexample
4105data.o
4106@end smallexample
4107
967928e9
AM
4108When you use a file name which is not an @samp{archive:file} specifier
4109and does not contain any wild card
252b5132
RH
4110characters, the linker will first see if you also specified the file
4111name on the linker command line or in an @code{INPUT} command. If you
4112did not, the linker will attempt to open the file as an input file, as
4113though it appeared on the command line. Note that this differs from an
4114@code{INPUT} command, because the linker will not search for the file in
4115the archive search path.
4116
4117@node Input Section Wildcards
36f63dca 4118@subsubsection Input Section Wildcard Patterns
252b5132
RH
4119@cindex input section wildcards
4120@cindex wildcard file name patterns
4121@cindex file name wildcard patterns
4122@cindex section name wildcard patterns
4123In an input section description, either the file name or the section
4124name or both may be wildcard patterns.
4125
4126The file name of @samp{*} seen in many examples is a simple wildcard
4127pattern for the file name.
4128
4129The wildcard patterns are like those used by the Unix shell.
4130
4131@table @samp
4132@item *
4133matches any number of characters
4134@item ?
4135matches any single character
4136@item [@var{chars}]
4137matches a single instance of any of the @var{chars}; the @samp{-}
4138character may be used to specify a range of characters, as in
4139@samp{[a-z]} to match any lower case letter
4140@item \
4141quotes the following character
4142@end table
4143
4144When a file name is matched with a wildcard, the wildcard characters
4145will not match a @samp{/} character (used to separate directory names on
4146Unix). A pattern consisting of a single @samp{*} character is an
4147exception; it will always match any file name, whether it contains a
4148@samp{/} or not. In a section name, the wildcard characters will match
4149a @samp{/} character.
4150
4151File name wildcard patterns only match files which are explicitly
4152specified on the command line or in an @code{INPUT} command. The linker
4153does not search directories to expand wildcards.
4154
4155If a file name matches more than one wildcard pattern, or if a file name
4156appears explicitly and is also matched by a wildcard pattern, the linker
4157will use the first match in the linker script. For example, this
4158sequence of input section descriptions is probably in error, because the
4159@file{data.o} rule will not be used:
4160@smallexample
4161.data : @{ *(.data) @}
4162.data1 : @{ data.o(.data) @}
4163@end smallexample
4164
bcaa7b3e 4165@cindex SORT_BY_NAME
252b5132
RH
4166Normally, the linker will place files and sections matched by wildcards
4167in the order in which they are seen during the link. You can change
bcaa7b3e
L
4168this by using the @code{SORT_BY_NAME} keyword, which appears before a wildcard
4169pattern in parentheses (e.g., @code{SORT_BY_NAME(.text*)}). When the
4170@code{SORT_BY_NAME} keyword is used, the linker will sort the files or sections
252b5132
RH
4171into ascending order by name before placing them in the output file.
4172
bcaa7b3e
L
4173@cindex SORT_BY_ALIGNMENT
4174@code{SORT_BY_ALIGNMENT} is very similar to @code{SORT_BY_NAME}. The
4175difference is @code{SORT_BY_ALIGNMENT} will sort sections into
1ae5c3ae 4176descending order by alignment before placing them in the output file.
ee83b8a6
NC
4177Larger alignments are placed before smaller alignments in order to
4178reduce the amount of padding necessary.
bcaa7b3e 4179
02ecc8e9
L
4180@cindex SORT_BY_INIT_PRIORITY
4181@code{SORT_BY_INIT_PRIORITY} is very similar to @code{SORT_BY_NAME}. The
4182difference is @code{SORT_BY_INIT_PRIORITY} will sort sections into
4183ascending order by numerical value of the GCC init_priority attribute
4184encoded in the section name before placing them in the output file.
4185
bcaa7b3e
L
4186@cindex SORT
4187@code{SORT} is an alias for @code{SORT_BY_NAME}.
4188
4189When there are nested section sorting commands in linker script, there
4190can be at most 1 level of nesting for section sorting commands.
4191
4192@enumerate
4193@item
4194@code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)).
1ae5c3ae 4195It will sort the input sections by name first, then by alignment if two
bcaa7b3e
L
4196sections have the same name.
4197@item
4198@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)).
1ae5c3ae 4199It will sort the input sections by alignment first, then by name if two
bcaa7b3e
L
4200sections have the same alignment.
4201@item
c0065db7 4202@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
bcaa7b3e
L
4203treated the same as @code{SORT_BY_NAME} (wildcard section pattern).
4204@item
4205@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern))
4206is treated the same as @code{SORT_BY_ALIGNMENT} (wildcard section pattern).
4207@item
4208All other nested section sorting commands are invalid.
4209@end enumerate
4210
4211When both command line section sorting option and linker script
4212section sorting command are used, section sorting command always
4213takes precedence over the command line option.
4214
4215If the section sorting command in linker script isn't nested, the
4216command line option will make the section sorting command to be
4217treated as nested sorting command.
4218
4219@enumerate
4220@item
4221@code{SORT_BY_NAME} (wildcard section pattern ) with
4222@option{--sort-sections alignment} is equivalent to
4223@code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)).
4224@item
4225@code{SORT_BY_ALIGNMENT} (wildcard section pattern) with
4226@option{--sort-section name} is equivalent to
4227@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)).
4228@end enumerate
4229
4230If the section sorting command in linker script is nested, the
4231command line option will be ignored.
4232
eda680f8
L
4233@cindex SORT_NONE
4234@code{SORT_NONE} disables section sorting by ignoring the command line
4235section sorting option.
4236
252b5132
RH
4237If you ever get confused about where input sections are going, use the
4238@samp{-M} linker option to generate a map file. The map file shows
4239precisely how input sections are mapped to output sections.
4240
4241This example shows how wildcard patterns might be used to partition
4242files. This linker script directs the linker to place all @samp{.text}
4243sections in @samp{.text} and all @samp{.bss} sections in @samp{.bss}.
4244The linker will place the @samp{.data} section from all files beginning
4245with an upper case character in @samp{.DATA}; for all other files, the
4246linker will place the @samp{.data} section in @samp{.data}.
4247@smallexample
4248@group
4249SECTIONS @{
4250 .text : @{ *(.text) @}
4251 .DATA : @{ [A-Z]*(.data) @}
4252 .data : @{ *(.data) @}
4253 .bss : @{ *(.bss) @}
4254@}
4255@end group
4256@end smallexample
4257
4258@node Input Section Common
36f63dca 4259@subsubsection Input Section for Common Symbols
252b5132
RH
4260@cindex common symbol placement
4261@cindex uninitialized data placement
4262A special notation is needed for common symbols, because in many object
4263file formats common symbols do not have a particular input section. The
4264linker treats common symbols as though they are in an input section
4265named @samp{COMMON}.
4266
4267You may use file names with the @samp{COMMON} section just as with any
4268other input sections. You can use this to place common symbols from a
4269particular input file in one section while common symbols from other
4270input files are placed in another section.
4271
4272In most cases, common symbols in input files will be placed in the
4273@samp{.bss} section in the output file. For example:
4274@smallexample
4275.bss @{ *(.bss) *(COMMON) @}
4276@end smallexample
4277
4278@cindex scommon section
4279@cindex small common symbols
4280Some object file formats have more than one type of common symbol. For
4281example, the MIPS ELF object file format distinguishes standard common
4282symbols and small common symbols. In this case, the linker will use a
4283different special section name for other types of common symbols. In
4284the case of MIPS ELF, the linker uses @samp{COMMON} for standard common
4285symbols and @samp{.scommon} for small common symbols. This permits you
4286to map the different types of common symbols into memory at different
4287locations.
4288
4289@cindex [COMMON]
4290You will sometimes see @samp{[COMMON]} in old linker scripts. This
4291notation is now considered obsolete. It is equivalent to
4292@samp{*(COMMON)}.
4293
4294@node Input Section Keep
36f63dca 4295@subsubsection Input Section and Garbage Collection
252b5132
RH
4296@cindex KEEP
4297@cindex garbage collection
4298When link-time garbage collection is in use (@samp{--gc-sections}),
a1ab1d2a 4299it is often useful to mark sections that should not be eliminated.
252b5132
RH
4300This is accomplished by surrounding an input section's wildcard entry
4301with @code{KEEP()}, as in @code{KEEP(*(.init))} or
bcaa7b3e 4302@code{KEEP(SORT_BY_NAME(*)(.ctors))}.
252b5132
RH
4303
4304@node Input Section Example
36f63dca 4305@subsubsection Input Section Example
252b5132
RH
4306The following example is a complete linker script. It tells the linker
4307to read all of the sections from file @file{all.o} and place them at the
4308start of output section @samp{outputa} which starts at location
4309@samp{0x10000}. All of section @samp{.input1} from file @file{foo.o}
4310follows immediately, in the same output section. All of section
4311@samp{.input2} from @file{foo.o} goes into output section
4312@samp{outputb}, followed by section @samp{.input1} from @file{foo1.o}.
4313All of the remaining @samp{.input1} and @samp{.input2} sections from any
4314files are written to output section @samp{outputc}.
4315
4316@smallexample
4317@group
4318SECTIONS @{
4319 outputa 0x10000 :
4320 @{
4321 all.o
4322 foo.o (.input1)
4323 @}
36f63dca
NC
4324@end group
4325@group
252b5132
RH
4326 outputb :
4327 @{
4328 foo.o (.input2)
4329 foo1.o (.input1)
4330 @}
36f63dca
NC
4331@end group
4332@group
252b5132
RH
4333 outputc :
4334 @{
4335 *(.input1)
4336 *(.input2)
4337 @}
4338@}
4339@end group
a1ab1d2a 4340@end smallexample
252b5132
RH
4341
4342@node Output Section Data
36f63dca 4343@subsection Output Section Data
252b5132
RH
4344@cindex data
4345@cindex section data
4346@cindex output section data
4347@kindex BYTE(@var{expression})
4348@kindex SHORT(@var{expression})
4349@kindex LONG(@var{expression})
4350@kindex QUAD(@var{expression})
4351@kindex SQUAD(@var{expression})
4352You can include explicit bytes of data in an output section by using
4353@code{BYTE}, @code{SHORT}, @code{LONG}, @code{QUAD}, or @code{SQUAD} as
4354an output section command. Each keyword is followed by an expression in
4355parentheses providing the value to store (@pxref{Expressions}). The
4356value of the expression is stored at the current value of the location
4357counter.
4358
4359The @code{BYTE}, @code{SHORT}, @code{LONG}, and @code{QUAD} commands
4360store one, two, four, and eight bytes (respectively). After storing the
4361bytes, the location counter is incremented by the number of bytes
4362stored.
4363
4364For example, this will store the byte 1 followed by the four byte value
4365of the symbol @samp{addr}:
4366@smallexample
4367BYTE(1)
4368LONG(addr)
4369@end smallexample
4370
4371When using a 64 bit host or target, @code{QUAD} and @code{SQUAD} are the
4372same; they both store an 8 byte, or 64 bit, value. When both host and
4373target are 32 bits, an expression is computed as 32 bits. In this case
4374@code{QUAD} stores a 32 bit value zero extended to 64 bits, and
4375@code{SQUAD} stores a 32 bit value sign extended to 64 bits.
4376
4377If the object file format of the output file has an explicit endianness,
4378which is the normal case, the value will be stored in that endianness.
4379When the object file format does not have an explicit endianness, as is
4380true of, for example, S-records, the value will be stored in the
4381endianness of the first input object file.
4382
36f63dca 4383Note---these commands only work inside a section description and not
2b5fc1f5
NC
4384between them, so the following will produce an error from the linker:
4385@smallexample
4386SECTIONS @{@ .text : @{@ *(.text) @}@ LONG(1) .data : @{@ *(.data) @}@ @}@
4387@end smallexample
4388whereas this will work:
4389@smallexample
4390SECTIONS @{@ .text : @{@ *(.text) ; LONG(1) @}@ .data : @{@ *(.data) @}@ @}@
4391@end smallexample
4392
252b5132
RH
4393@kindex FILL(@var{expression})
4394@cindex holes, filling
4395@cindex unspecified memory
4396You may use the @code{FILL} command to set the fill pattern for the
4397current section. It is followed by an expression in parentheses. Any
4398otherwise unspecified regions of memory within the section (for example,
4399gaps left due to the required alignment of input sections) are filled
a139d329 4400with the value of the expression, repeated as
252b5132
RH
4401necessary. A @code{FILL} statement covers memory locations after the
4402point at which it occurs in the section definition; by including more
4403than one @code{FILL} statement, you can have different fill patterns in
4404different parts of an output section.
4405
4406This example shows how to fill unspecified regions of memory with the
563e308f 4407value @samp{0x90}:
252b5132 4408@smallexample
563e308f 4409FILL(0x90909090)
252b5132
RH
4410@end smallexample
4411
4412The @code{FILL} command is similar to the @samp{=@var{fillexp}} output
9673c93c 4413section attribute, but it only affects the
252b5132
RH
4414part of the section following the @code{FILL} command, rather than the
4415entire section. If both are used, the @code{FILL} command takes
9673c93c 4416precedence. @xref{Output Section Fill}, for details on the fill
a139d329 4417expression.
252b5132
RH
4418
4419@node Output Section Keywords
36f63dca 4420@subsection Output Section Keywords
252b5132
RH
4421There are a couple of keywords which can appear as output section
4422commands.
4423
4424@table @code
4425@kindex CREATE_OBJECT_SYMBOLS
4426@cindex input filename symbols
4427@cindex filename symbols
4428@item CREATE_OBJECT_SYMBOLS
4429The command tells the linker to create a symbol for each input file.
4430The name of each symbol will be the name of the corresponding input
4431file. The section of each symbol will be the output section in which
4432the @code{CREATE_OBJECT_SYMBOLS} command appears.
4433
4434This is conventional for the a.out object file format. It is not
4435normally used for any other object file format.
4436
4437@kindex CONSTRUCTORS
4438@cindex C++ constructors, arranging in link
4439@cindex constructors, arranging in link
4440@item CONSTRUCTORS
4441When linking using the a.out object file format, the linker uses an
4442unusual set construct to support C++ global constructors and
4443destructors. When linking object file formats which do not support
4444arbitrary sections, such as ECOFF and XCOFF, the linker will
4445automatically recognize C++ global constructors and destructors by name.
4446For these object file formats, the @code{CONSTRUCTORS} command tells the
4447linker to place constructor information in the output section where the
4448@code{CONSTRUCTORS} command appears. The @code{CONSTRUCTORS} command is
4449ignored for other object file formats.
4450
4451The symbol @w{@code{__CTOR_LIST__}} marks the start of the global
7e69709c
AM
4452constructors, and the symbol @w{@code{__CTOR_END__}} marks the end.
4453Similarly, @w{@code{__DTOR_LIST__}} and @w{@code{__DTOR_END__}} mark
4454the start and end of the global destructors. The
252b5132
RH
4455first word in the list is the number of entries, followed by the address
4456of each constructor or destructor, followed by a zero word. The
4457compiler must arrange to actually run the code. For these object file
4458formats @sc{gnu} C++ normally calls constructors from a subroutine
4459@code{__main}; a call to @code{__main} is automatically inserted into
4460the startup code for @code{main}. @sc{gnu} C++ normally runs
4461destructors either by using @code{atexit}, or directly from the function
4462@code{exit}.
4463
4464For object file formats such as @code{COFF} or @code{ELF} which support
4465arbitrary section names, @sc{gnu} C++ will normally arrange to put the
4466addresses of global constructors and destructors into the @code{.ctors}
4467and @code{.dtors} sections. Placing the following sequence into your
4468linker script will build the sort of table which the @sc{gnu} C++
4469runtime code expects to see.
4470
4471@smallexample
4472 __CTOR_LIST__ = .;
4473 LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
4474 *(.ctors)
4475 LONG(0)
4476 __CTOR_END__ = .;
4477 __DTOR_LIST__ = .;
4478 LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
4479 *(.dtors)
4480 LONG(0)
4481 __DTOR_END__ = .;
4482@end smallexample
4483
4484If you are using the @sc{gnu} C++ support for initialization priority,
4485which provides some control over the order in which global constructors
4486are run, you must sort the constructors at link time to ensure that they
4487are executed in the correct order. When using the @code{CONSTRUCTORS}
bcaa7b3e
L
4488command, use @samp{SORT_BY_NAME(CONSTRUCTORS)} instead. When using the
4489@code{.ctors} and @code{.dtors} sections, use @samp{*(SORT_BY_NAME(.ctors))} and
4490@samp{*(SORT_BY_NAME(.dtors))} instead of just @samp{*(.ctors)} and
252b5132
RH
4491@samp{*(.dtors)}.
4492
4493Normally the compiler and linker will handle these issues automatically,
4494and you will not need to concern yourself with them. However, you may
4495need to consider this if you are using C++ and writing your own linker
4496scripts.
4497
4498@end table
4499
4500@node Output Section Discarding
36f63dca 4501@subsection Output Section Discarding
252b5132
RH
4502@cindex discarding sections
4503@cindex sections, discarding
4504@cindex removing sections
2edab91c
AM
4505The linker will not normally create output sections with no contents.
4506This is for convenience when referring to input sections that may or
4507may not be present in any of the input files. For example:
252b5132 4508@smallexample
49c13adb 4509.foo : @{ *(.foo) @}
252b5132
RH
4510@end smallexample
4511@noindent
4512will only create a @samp{.foo} section in the output file if there is a
74541ad4
AM
4513@samp{.foo} section in at least one input file, and if the input
4514sections are not all empty. Other link script directives that allocate
2edab91c
AM
4515space in an output section will also create the output section. So
4516too will assignments to dot even if the assignment does not create
4517space, except for @samp{. = 0}, @samp{. = . + 0}, @samp{. = sym},
4518@samp{. = . + sym} and @samp{. = ALIGN (. != 0, expr, 1)} when
4519@samp{sym} is an absolute symbol of value 0 defined in the script.
4520This allows you to force output of an empty section with @samp{. = .}.
74541ad4 4521
a0976ea4 4522The linker will ignore address assignments (@pxref{Output Section Address})
74541ad4
AM
4523on discarded output sections, except when the linker script defines
4524symbols in the output section. In that case the linker will obey
a0976ea4
AM
4525the address assignments, possibly advancing dot even though the
4526section is discarded.
252b5132
RH
4527
4528@cindex /DISCARD/
4529The special output section name @samp{/DISCARD/} may be used to discard
4530input sections. Any input sections which are assigned to an output
4531section named @samp{/DISCARD/} are not included in the output file.
4532
4533@node Output Section Attributes
36f63dca 4534@subsection Output Section Attributes
252b5132
RH
4535@cindex output section attributes
4536We showed above that the full description of an output section looked
4537like this:
0c71d759 4538
252b5132 4539@smallexample
a1ab1d2a 4540@group
7e7d5768 4541@var{section} [@var{address}] [(@var{type})] :
0c71d759
NC
4542 [AT(@var{lma})]
4543 [ALIGN(@var{section_align})]
4544 [SUBALIGN(@var{subsection_align})]
4545 [@var{constraint}]
252b5132
RH
4546 @{
4547 @var{output-section-command}
4548 @var{output-section-command}
4549 @dots{}
562d3460 4550 @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}]
252b5132
RH
4551@end group
4552@end smallexample
0c71d759 4553
252b5132
RH
4554We've already described @var{section}, @var{address}, and
4555@var{output-section-command}. In this section we will describe the
4556remaining section attributes.
4557
a1ab1d2a 4558@menu
252b5132
RH
4559* Output Section Type:: Output section type
4560* Output Section LMA:: Output section LMA
bbf115d3 4561* Forced Output Alignment:: Forced Output Alignment
7e7d5768 4562* Forced Input Alignment:: Forced Input Alignment
0c71d759 4563* Output Section Constraint:: Output section constraint
252b5132
RH
4564* Output Section Region:: Output section region
4565* Output Section Phdr:: Output section phdr
4566* Output Section Fill:: Output section fill
4567@end menu
4568
4569@node Output Section Type
36f63dca 4570@subsubsection Output Section Type
252b5132
RH
4571Each output section may have a type. The type is a keyword in
4572parentheses. The following types are defined:
4573
4574@table @code
4575@item NOLOAD
4576The section should be marked as not loadable, so that it will not be
4577loaded into memory when the program is run.
4578@item DSECT
4579@itemx COPY
4580@itemx INFO
4581@itemx OVERLAY
4582These type names are supported for backward compatibility, and are
4583rarely used. They all have the same effect: the section should be
4584marked as not allocatable, so that no memory is allocated for the
4585section when the program is run.
4586@end table
4587
4588@kindex NOLOAD
4589@cindex prevent unnecessary loading
4590@cindex loading, preventing
4591The linker normally sets the attributes of an output section based on
4592the input sections which map into it. You can override this by using
4593the section type. For example, in the script sample below, the
4594@samp{ROM} section is addressed at memory location @samp{0} and does not
2e76e85a 4595need to be loaded when the program is run.
252b5132
RH
4596@smallexample
4597@group
4598SECTIONS @{
4599 ROM 0 (NOLOAD) : @{ @dots{} @}
4600 @dots{}
4601@}
4602@end group
4603@end smallexample
4604
4605@node Output Section LMA
36f63dca 4606@subsubsection Output Section LMA
562d3460 4607@kindex AT>@var{lma_region}
252b5132
RH
4608@kindex AT(@var{lma})
4609@cindex load address
4610@cindex section load address
4611Every section has a virtual address (VMA) and a load address (LMA); see
ea5cae92
NC
4612@ref{Basic Script Concepts}. The virtual address is specified by the
4613@pxref{Output Section Address} described earlier. The load address is
4614specified by the @code{AT} or @code{AT>} keywords. Specifying a load
4615address is optional.
6bdafbeb 4616
ea5cae92
NC
4617The @code{AT} keyword takes an expression as an argument. This
4618specifies the exact load address of the section. The @code{AT>} keyword
4619takes the name of a memory region as an argument. @xref{MEMORY}. The
4620load address of the section is set to the next free address in the
4621region, aligned to the section's alignment requirements.
dc0b6aa0
AM
4622
4623If neither @code{AT} nor @code{AT>} is specified for an allocatable
ea5cae92
NC
4624section, the linker will use the following heuristic to determine the
4625load address:
4626
4627@itemize @bullet
4628@item
4629If the section has a specific VMA address, then this is used as
4630the LMA address as well.
4631
4632@item
4633If the section is not allocatable then its LMA is set to its VMA.
4634
4635@item
4636Otherwise if a memory region can be found that is compatible
4637with the current section, and this region contains at least one
4638section, then the LMA is set so the difference between the
4639VMA and LMA is the same as the difference between the VMA and LMA of
4640the last section in the located region.
4641
4642@item
4643If no memory regions have been declared then a default region
4644that covers the entire address space is used in the previous step.
4645
4646@item
4647If no suitable region could be found, or there was no previous
4648section then the LMA is set equal to the VMA.
4649@end itemize
252b5132
RH
4650
4651@cindex ROM initialized data
4652@cindex initialized data in ROM
4653This feature is designed to make it easy to build a ROM image. For
4654example, the following linker script creates three output sections: one
4655called @samp{.text}, which starts at @code{0x1000}, one called
4656@samp{.mdata}, which is loaded at the end of the @samp{.text} section
4657even though its VMA is @code{0x2000}, and one called @samp{.bss} to hold
4658uninitialized data at address @code{0x3000}. The symbol @code{_data} is
4659defined with the value @code{0x2000}, which shows that the location
4660counter holds the VMA value, not the LMA value.
4661
4662@smallexample
4663@group
4664SECTIONS
4665 @{
4666 .text 0x1000 : @{ *(.text) _etext = . ; @}
a1ab1d2a 4667 .mdata 0x2000 :
252b5132
RH
4668 AT ( ADDR (.text) + SIZEOF (.text) )
4669 @{ _data = . ; *(.data); _edata = . ; @}
4670 .bss 0x3000 :
4671 @{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;@}
4672@}
4673@end group
4674@end smallexample
4675
4676The run-time initialization code for use with a program generated with
4677this linker script would include something like the following, to copy
4678the initialized data from the ROM image to its runtime address. Notice
4679how this code takes advantage of the symbols defined by the linker
4680script.
4681
4682@smallexample
4683@group
4684extern char _etext, _data, _edata, _bstart, _bend;
4685char *src = &_etext;
4686char *dst = &_data;
4687
ea5cae92
NC
4688/* ROM has data at end of text; copy it. */
4689while (dst < &_edata)
252b5132 4690 *dst++ = *src++;
252b5132 4691
ea5cae92 4692/* Zero bss. */
252b5132
RH
4693for (dst = &_bstart; dst< &_bend; dst++)
4694 *dst = 0;
4695@end group
4696@end smallexample
4697
bbf115d3
L
4698@node Forced Output Alignment
4699@subsubsection Forced Output Alignment
4700@kindex ALIGN(@var{section_align})
4701@cindex forcing output section alignment
4702@cindex output section alignment
1eec346e 4703You can increase an output section's alignment by using ALIGN. As an
13075d04
SH
4704alternative you can enforce that the difference between the VMA and LMA remains
4705intact throughout this output section with the ALIGN_WITH_INPUT attribute.
bbf115d3 4706
7e7d5768
AM
4707@node Forced Input Alignment
4708@subsubsection Forced Input Alignment
4709@kindex SUBALIGN(@var{subsection_align})
4710@cindex forcing input section alignment
4711@cindex input section alignment
4712You can force input section alignment within an output section by using
4713SUBALIGN. The value specified overrides any alignment given by input
4714sections, whether larger or smaller.
4715
0c71d759
NC
4716@node Output Section Constraint
4717@subsubsection Output Section Constraint
4718@kindex ONLY_IF_RO
4719@kindex ONLY_IF_RW
4720@cindex constraints on output sections
4721You can specify that an output section should only be created if all
4722of its input sections are read-only or all of its input sections are
4723read-write by using the keyword @code{ONLY_IF_RO} and
4724@code{ONLY_IF_RW} respectively.
4725
252b5132 4726@node Output Section Region
36f63dca 4727@subsubsection Output Section Region
252b5132
RH
4728@kindex >@var{region}
4729@cindex section, assigning to memory region
4730@cindex memory regions and sections
4731You can assign a section to a previously defined region of memory by
4732using @samp{>@var{region}}. @xref{MEMORY}.
4733
4734Here is a simple example:
4735@smallexample
4736@group
4737MEMORY @{ rom : ORIGIN = 0x1000, LENGTH = 0x1000 @}
4738SECTIONS @{ ROM : @{ *(.text) @} >rom @}
4739@end group
4740@end smallexample
4741
4742@node Output Section Phdr
36f63dca 4743@subsubsection Output Section Phdr
252b5132
RH
4744@kindex :@var{phdr}
4745@cindex section, assigning to program header
4746@cindex program headers and sections
4747You can assign a section to a previously defined program segment by
4748using @samp{:@var{phdr}}. @xref{PHDRS}. If a section is assigned to
4749one or more segments, then all subsequent allocated sections will be
4750assigned to those segments as well, unless they use an explicitly
4751@code{:@var{phdr}} modifier. You can use @code{:NONE} to tell the
4752linker to not put the section in any segment at all.
4753
4754Here is a simple example:
4755@smallexample
4756@group
4757PHDRS @{ text PT_LOAD ; @}
4758SECTIONS @{ .text : @{ *(.text) @} :text @}
4759@end group
4760@end smallexample
4761
4762@node Output Section Fill
36f63dca 4763@subsubsection Output Section Fill
252b5132
RH
4764@kindex =@var{fillexp}
4765@cindex section fill pattern
4766@cindex fill pattern, entire section
4767You can set the fill pattern for an entire section by using
4768@samp{=@var{fillexp}}. @var{fillexp} is an expression
4769(@pxref{Expressions}). Any otherwise unspecified regions of memory
4770within the output section (for example, gaps left due to the required
a139d329
AM
4771alignment of input sections) will be filled with the value, repeated as
4772necessary. If the fill expression is a simple hex number, ie. a string
9673c93c 4773of hex digit starting with @samp{0x} and without a trailing @samp{k} or @samp{M}, then
a139d329
AM
4774an arbitrarily long sequence of hex digits can be used to specify the
4775fill pattern; Leading zeros become part of the pattern too. For all
9673c93c 4776other cases, including extra parentheses or a unary @code{+}, the fill
a139d329
AM
4777pattern is the four least significant bytes of the value of the
4778expression. In all cases, the number is big-endian.
252b5132
RH
4779
4780You can also change the fill value with a @code{FILL} command in the
9673c93c 4781output section commands; (@pxref{Output Section Data}).
252b5132
RH
4782
4783Here is a simple example:
4784@smallexample
4785@group
563e308f 4786SECTIONS @{ .text : @{ *(.text) @} =0x90909090 @}
252b5132
RH
4787@end group
4788@end smallexample
4789
4790@node Overlay Description
36f63dca 4791@subsection Overlay Description
252b5132
RH
4792@kindex OVERLAY
4793@cindex overlays
4794An overlay description provides an easy way to describe sections which
4795are to be loaded as part of a single memory image but are to be run at
4796the same memory address. At run time, some sort of overlay manager will
4797copy the overlaid sections in and out of the runtime memory address as
4798required, perhaps by simply manipulating addressing bits. This approach
4799can be useful, for example, when a certain region of memory is faster
4800than another.
4801
4802Overlays are described using the @code{OVERLAY} command. The
4803@code{OVERLAY} command is used within a @code{SECTIONS} command, like an
4804output section description. The full syntax of the @code{OVERLAY}
4805command is as follows:
4806@smallexample
4807@group
4808OVERLAY [@var{start}] : [NOCROSSREFS] [AT ( @var{ldaddr} )]
4809 @{
4810 @var{secname1}
4811 @{
4812 @var{output-section-command}
4813 @var{output-section-command}
4814 @dots{}
4815 @} [:@var{phdr}@dots{}] [=@var{fill}]
4816 @var{secname2}
4817 @{
4818 @var{output-section-command}
4819 @var{output-section-command}
4820 @dots{}
4821 @} [:@var{phdr}@dots{}] [=@var{fill}]
4822 @dots{}
abc9061b 4823 @} [>@var{region}] [:@var{phdr}@dots{}] [=@var{fill}] [,]
252b5132
RH
4824@end group
4825@end smallexample
4826
4827Everything is optional except @code{OVERLAY} (a keyword), and each
4828section must have a name (@var{secname1} and @var{secname2} above). The
4829section definitions within the @code{OVERLAY} construct are identical to
11e7fd74 4830those within the general @code{SECTIONS} construct (@pxref{SECTIONS}),
252b5132
RH
4831except that no addresses and no memory regions may be defined for
4832sections within an @code{OVERLAY}.
4833
abc9061b
CC
4834The comma at the end may be required if a @var{fill} is used and
4835the next @var{sections-command} looks like a continuation of the expression.
4836
252b5132
RH
4837The sections are all defined with the same starting address. The load
4838addresses of the sections are arranged such that they are consecutive in
4839memory starting at the load address used for the @code{OVERLAY} as a
4840whole (as with normal section definitions, the load address is optional,
4841and defaults to the start address; the start address is also optional,
4842and defaults to the current value of the location counter).
4843
56dd11f0
NC
4844If the @code{NOCROSSREFS} keyword is used, and there are any
4845references among the sections, the linker will report an error. Since
4846the sections all run at the same address, it normally does not make
4847sense for one section to refer directly to another.
4848@xref{Miscellaneous Commands, NOCROSSREFS}.
252b5132
RH
4849
4850For each section within the @code{OVERLAY}, the linker automatically
34711ca3 4851provides two symbols. The symbol @code{__load_start_@var{secname}} is
252b5132
RH
4852defined as the starting load address of the section. The symbol
4853@code{__load_stop_@var{secname}} is defined as the final load address of
4854the section. Any characters within @var{secname} which are not legal
4855within C identifiers are removed. C (or assembler) code may use these
4856symbols to move the overlaid sections around as necessary.
4857
4858At the end of the overlay, the value of the location counter is set to
4859the start address of the overlay plus the size of the largest section.
4860
4861Here is an example. Remember that this would appear inside a
4862@code{SECTIONS} construct.
4863@smallexample
4864@group
4865 OVERLAY 0x1000 : AT (0x4000)
4866 @{
4867 .text0 @{ o1/*.o(.text) @}
4868 .text1 @{ o2/*.o(.text) @}
4869 @}
4870@end group
4871@end smallexample
4872@noindent
4873This will define both @samp{.text0} and @samp{.text1} to start at
4874address 0x1000. @samp{.text0} will be loaded at address 0x4000, and
4875@samp{.text1} will be loaded immediately after @samp{.text0}. The
34711ca3 4876following symbols will be defined if referenced: @code{__load_start_text0},
252b5132
RH
4877@code{__load_stop_text0}, @code{__load_start_text1},
4878@code{__load_stop_text1}.
4879
4880C code to copy overlay @code{.text1} into the overlay area might look
4881like the following.
4882
4883@smallexample
4884@group
4885 extern char __load_start_text1, __load_stop_text1;
4886 memcpy ((char *) 0x1000, &__load_start_text1,
4887 &__load_stop_text1 - &__load_start_text1);
4888@end group
4889@end smallexample
4890
4891Note that the @code{OVERLAY} command is just syntactic sugar, since
4892everything it does can be done using the more basic commands. The above
4893example could have been written identically as follows.
4894
4895@smallexample
4896@group
4897 .text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
34711ca3
AM
4898 PROVIDE (__load_start_text0 = LOADADDR (.text0));
4899 PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0));
252b5132 4900 .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
34711ca3
AM
4901 PROVIDE (__load_start_text1 = LOADADDR (.text1));
4902 PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1));
252b5132
RH
4903 . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
4904@end group
4905@end smallexample
4906
4907@node MEMORY
36f63dca 4908@section MEMORY Command
252b5132
RH
4909@kindex MEMORY
4910@cindex memory regions
4911@cindex regions of memory
4912@cindex allocating memory
4913@cindex discontinuous memory
4914The linker's default configuration permits allocation of all available
4915memory. You can override this by using the @code{MEMORY} command.
4916
4917The @code{MEMORY} command describes the location and size of blocks of
4918memory in the target. You can use it to describe which memory regions
4919may be used by the linker, and which memory regions it must avoid. You
4920can then assign sections to particular memory regions. The linker will
4921set section addresses based on the memory regions, and will warn about
4922regions that become too full. The linker will not shuffle sections
4923around to fit into the available regions.
4924
4925A linker script may contain at most one use of the @code{MEMORY}
4926command. However, you can define as many blocks of memory within it as
4927you wish. The syntax is:
4928@smallexample
4929@group
a1ab1d2a 4930MEMORY
252b5132
RH
4931 @{
4932 @var{name} [(@var{attr})] : ORIGIN = @var{origin}, LENGTH = @var{len}
4933 @dots{}
4934 @}
4935@end group
4936@end smallexample
4937
4938The @var{name} is a name used in the linker script to refer to the
4939region. The region name has no meaning outside of the linker script.
4940Region names are stored in a separate name space, and will not conflict
4941with symbol names, file names, or section names. Each memory region
4a93e180
NC
4942must have a distinct name within the @code{MEMORY} command. However you can
4943add later alias names to existing memory regions with the @ref{REGION_ALIAS}
9d5777a3 4944command.
252b5132
RH
4945
4946@cindex memory region attributes
4947The @var{attr} string is an optional list of attributes that specify
4948whether to use a particular memory region for an input section which is
4949not explicitly mapped in the linker script. As described in
4950@ref{SECTIONS}, if you do not specify an output section for some input
4951section, the linker will create an output section with the same name as
4952the input section. If you define region attributes, the linker will use
4953them to select the memory region for the output section that it creates.
4954
4955The @var{attr} string must consist only of the following characters:
4956@table @samp
4957@item R
4958Read-only section
4959@item W
4960Read/write section
4961@item X
4962Executable section
4963@item A
4964Allocatable section
4965@item I
4966Initialized section
4967@item L
4968Same as @samp{I}
4969@item !
c09e9a8c 4970Invert the sense of any of the attributes that follow
252b5132
RH
4971@end table
4972
4973If a unmapped section matches any of the listed attributes other than
4974@samp{!}, it will be placed in the memory region. The @samp{!}
4975attribute reverses this test, so that an unmapped section will be placed
4976in the memory region only if it does not match any of the listed
4977attributes.
4978
4979@kindex ORIGIN =
4980@kindex o =
4981@kindex org =
9cd6d51a
NC
4982The @var{origin} is an numerical expression for the start address of
4983the memory region. The expression must evaluate to a constant and it
4984cannot involve any symbols. The keyword @code{ORIGIN} may be
4985abbreviated to @code{org} or @code{o} (but not, for example,
4986@code{ORG}).
252b5132
RH
4987
4988@kindex LENGTH =
4989@kindex len =
4990@kindex l =
4991The @var{len} is an expression for the size in bytes of the memory
4992region. As with the @var{origin} expression, the expression must
9cd6d51a
NC
4993be numerical only and must evaluate to a constant. The keyword
4994@code{LENGTH} may be abbreviated to @code{len} or @code{l}.
252b5132
RH
4995
4996In the following example, we specify that there are two memory regions
4997available for allocation: one starting at @samp{0} for 256 kilobytes,
4998and the other starting at @samp{0x40000000} for four megabytes. The
4999linker will place into the @samp{rom} memory region every section which
5000is not explicitly mapped into a memory region, and is either read-only
5001or executable. The linker will place other sections which are not
5002explicitly mapped into a memory region into the @samp{ram} memory
5003region.
5004
5005@smallexample
5006@group
a1ab1d2a 5007MEMORY
252b5132
RH
5008 @{
5009 rom (rx) : ORIGIN = 0, LENGTH = 256K
5010 ram (!rx) : org = 0x40000000, l = 4M
5011 @}
5012@end group
5013@end smallexample
5014
5015Once you define a memory region, you can direct the linker to place
5016specific output sections into that memory region by using the
5017@samp{>@var{region}} output section attribute. For example, if you have
5018a memory region named @samp{mem}, you would use @samp{>mem} in the
5019output section definition. @xref{Output Section Region}. If no address
5020was specified for the output section, the linker will set the address to
5021the next available address within the memory region. If the combined
5022output sections directed to a memory region are too large for the
5023region, the linker will issue an error message.
5024
3ec57632 5025It is possible to access the origin and length of a memory in an
c0065db7 5026expression via the @code{ORIGIN(@var{memory})} and
3ec57632
NC
5027@code{LENGTH(@var{memory})} functions:
5028
5029@smallexample
5030@group
c0065db7 5031 _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
3ec57632
NC
5032@end group
5033@end smallexample
5034
252b5132
RH
5035@node PHDRS
5036@section PHDRS Command
5037@kindex PHDRS
5038@cindex program headers
5039@cindex ELF program headers
5040@cindex program segments
5041@cindex segments, ELF
5042The ELF object file format uses @dfn{program headers}, also knows as
5043@dfn{segments}. The program headers describe how the program should be
5044loaded into memory. You can print them out by using the @code{objdump}
5045program with the @samp{-p} option.
5046
5047When you run an ELF program on a native ELF system, the system loader
5048reads the program headers in order to figure out how to load the
5049program. This will only work if the program headers are set correctly.
5050This manual does not describe the details of how the system loader
5051interprets program headers; for more information, see the ELF ABI.
5052
5053The linker will create reasonable program headers by default. However,
5054in some cases, you may need to specify the program headers more
5055precisely. You may use the @code{PHDRS} command for this purpose. When
5056the linker sees the @code{PHDRS} command in the linker script, it will
5057not create any program headers other than the ones specified.
5058
5059The linker only pays attention to the @code{PHDRS} command when
5060generating an ELF output file. In other cases, the linker will simply
5061ignore @code{PHDRS}.
5062
5063This is the syntax of the @code{PHDRS} command. The words @code{PHDRS},
5064@code{FILEHDR}, @code{AT}, and @code{FLAGS} are keywords.
5065
5066@smallexample
5067@group
5068PHDRS
5069@{
5070 @var{name} @var{type} [ FILEHDR ] [ PHDRS ] [ AT ( @var{address} ) ]
5071 [ FLAGS ( @var{flags} ) ] ;
5072@}
5073@end group
5074@end smallexample
5075
5076The @var{name} is used only for reference in the @code{SECTIONS} command
5077of the linker script. It is not put into the output file. Program
5078header names are stored in a separate name space, and will not conflict
5079with symbol names, file names, or section names. Each program header
5c1a3f0f
NS
5080must have a distinct name. The headers are processed in order and it
5081is usual for them to map to sections in ascending load address order.
252b5132
RH
5082
5083Certain program header types describe segments of memory which the
5084system loader will load from the file. In the linker script, you
5085specify the contents of these segments by placing allocatable output
5086sections in the segments. You use the @samp{:@var{phdr}} output section
5087attribute to place a section in a particular segment. @xref{Output
5088Section Phdr}.
5089
5090It is normal to put certain sections in more than one segment. This
5091merely implies that one segment of memory contains another. You may
5092repeat @samp{:@var{phdr}}, using it once for each segment which should
5093contain the section.
5094
5095If you place a section in one or more segments using @samp{:@var{phdr}},
5096then the linker will place all subsequent allocatable sections which do
5097not specify @samp{:@var{phdr}} in the same segments. This is for
5098convenience, since generally a whole set of contiguous sections will be
5099placed in a single segment. You can use @code{:NONE} to override the
5100default segment and tell the linker to not put the section in any
5101segment at all.
5102
5103@kindex FILEHDR
5104@kindex PHDRS
5c1a3f0f 5105You may use the @code{FILEHDR} and @code{PHDRS} keywords after
252b5132
RH
5106the program header type to further describe the contents of the segment.
5107The @code{FILEHDR} keyword means that the segment should include the ELF
5108file header. The @code{PHDRS} keyword means that the segment should
5c1a3f0f 5109include the ELF program headers themselves. If applied to a loadable
4100cea3
AM
5110segment (@code{PT_LOAD}), all prior loadable segments must have one of
5111these keywords.
252b5132
RH
5112
5113The @var{type} may be one of the following. The numbers indicate the
5114value of the keyword.
5115
5116@table @asis
5117@item @code{PT_NULL} (0)
5118Indicates an unused program header.
5119
5120@item @code{PT_LOAD} (1)
5121Indicates that this program header describes a segment to be loaded from
5122the file.
5123
5124@item @code{PT_DYNAMIC} (2)
5125Indicates a segment where dynamic linking information can be found.
5126
5127@item @code{PT_INTERP} (3)
5128Indicates a segment where the name of the program interpreter may be
5129found.
5130
5131@item @code{PT_NOTE} (4)
5132Indicates a segment holding note information.
5133
5134@item @code{PT_SHLIB} (5)
5135A reserved program header type, defined but not specified by the ELF
5136ABI.
5137
5138@item @code{PT_PHDR} (6)
5139Indicates a segment where the program headers may be found.
5140
5141@item @var{expression}
5142An expression giving the numeric type of the program header. This may
5143be used for types not defined above.
5144@end table
5145
5146You can specify that a segment should be loaded at a particular address
5147in memory by using an @code{AT} expression. This is identical to the
5148@code{AT} command used as an output section attribute (@pxref{Output
5149Section LMA}). The @code{AT} command for a program header overrides the
5150output section attribute.
5151
5152The linker will normally set the segment flags based on the sections
5153which comprise the segment. You may use the @code{FLAGS} keyword to
5154explicitly specify the segment flags. The value of @var{flags} must be
5155an integer. It is used to set the @code{p_flags} field of the program
5156header.
5157
5158Here is an example of @code{PHDRS}. This shows a typical set of program
5159headers used on a native ELF system.
5160
5161@example
5162@group
5163PHDRS
5164@{
5165 headers PT_PHDR PHDRS ;
5166 interp PT_INTERP ;
5167 text PT_LOAD FILEHDR PHDRS ;
5168 data PT_LOAD ;
5169 dynamic PT_DYNAMIC ;
5170@}
5171
5172SECTIONS
5173@{
5174 . = SIZEOF_HEADERS;
5175 .interp : @{ *(.interp) @} :text :interp
5176 .text : @{ *(.text) @} :text
5177 .rodata : @{ *(.rodata) @} /* defaults to :text */
5178 @dots{}
5179 . = . + 0x1000; /* move to a new page in memory */
5180 .data : @{ *(.data) @} :data
5181 .dynamic : @{ *(.dynamic) @} :data :dynamic
5182 @dots{}
5183@}
5184@end group
5185@end example
5186
5187@node VERSION
5188@section VERSION Command
5189@kindex VERSION @{script text@}
5190@cindex symbol versions
5191@cindex version script
5192@cindex versions of symbols
5193The linker supports symbol versions when using ELF. Symbol versions are
5194only useful when using shared libraries. The dynamic linker can use
5195symbol versions to select a specific version of a function when it runs
5196a program that may have been linked against an earlier version of the
5197shared library.
5198
5199You can include a version script directly in the main linker script, or
5200you can supply the version script as an implicit linker script. You can
5201also use the @samp{--version-script} linker option.
5202
5203The syntax of the @code{VERSION} command is simply
5204@smallexample
5205VERSION @{ version-script-commands @}
5206@end smallexample
5207
5208The format of the version script commands is identical to that used by
5209Sun's linker in Solaris 2.5. The version script defines a tree of
5210version nodes. You specify the node names and interdependencies in the
5211version script. You can specify which symbols are bound to which
5212version nodes, and you can reduce a specified set of symbols to local
5213scope so that they are not globally visible outside of the shared
5214library.
5215
5216The easiest way to demonstrate the version script language is with a few
5217examples.
5218
5219@smallexample
5220VERS_1.1 @{
5221 global:
5222 foo1;
5223 local:
a1ab1d2a
UD
5224 old*;
5225 original*;
5226 new*;
252b5132
RH
5227@};
5228
5229VERS_1.2 @{
5230 foo2;
5231@} VERS_1.1;
5232
5233VERS_2.0 @{
5234 bar1; bar2;
c0065db7 5235 extern "C++" @{
86043bbb 5236 ns::*;
bb1515f2
MF
5237 "f(int, double)";
5238 @};
252b5132
RH
5239@} VERS_1.2;
5240@end smallexample
5241
5242This example version script defines three version nodes. The first
5243version node defined is @samp{VERS_1.1}; it has no other dependencies.
5244The script binds the symbol @samp{foo1} to @samp{VERS_1.1}. It reduces
5245a number of symbols to local scope so that they are not visible outside
313e35ee
AM
5246of the shared library; this is done using wildcard patterns, so that any
5247symbol whose name begins with @samp{old}, @samp{original}, or @samp{new}
5248is matched. The wildcard patterns available are the same as those used
5249in the shell when matching filenames (also known as ``globbing'').
86043bbb
MM
5250However, if you specify the symbol name inside double quotes, then the
5251name is treated as literal, rather than as a glob pattern.
252b5132
RH
5252
5253Next, the version script defines node @samp{VERS_1.2}. This node
5254depends upon @samp{VERS_1.1}. The script binds the symbol @samp{foo2}
5255to the version node @samp{VERS_1.2}.
5256
5257Finally, the version script defines node @samp{VERS_2.0}. This node
5258depends upon @samp{VERS_1.2}. The scripts binds the symbols @samp{bar1}
5259and @samp{bar2} are bound to the version node @samp{VERS_2.0}.
5260
5261When the linker finds a symbol defined in a library which is not
5262specifically bound to a version node, it will effectively bind it to an
5263unspecified base version of the library. You can bind all otherwise
a981ed6f 5264unspecified symbols to a given version node by using @samp{global: *;}
ae5a3597
AM
5265somewhere in the version script. Note that it's slightly crazy to use
5266wildcards in a global spec except on the last version node. Global
5267wildcards elsewhere run the risk of accidentally adding symbols to the
5268set exported for an old version. That's wrong since older versions
5269ought to have a fixed set of symbols.
252b5132
RH
5270
5271The names of the version nodes have no specific meaning other than what
5272they might suggest to the person reading them. The @samp{2.0} version
5273could just as well have appeared in between @samp{1.1} and @samp{1.2}.
5274However, this would be a confusing way to write a version script.
5275
0f6bf451 5276Node name can be omitted, provided it is the only version node
6b9b879a
JJ
5277in the version script. Such version script doesn't assign any versions to
5278symbols, only selects which symbols will be globally visible out and which
5279won't.
5280
5281@smallexample
7c9c73be 5282@{ global: foo; bar; local: *; @};
9d201f2f 5283@end smallexample
6b9b879a 5284
252b5132
RH
5285When you link an application against a shared library that has versioned
5286symbols, the application itself knows which version of each symbol it
5287requires, and it also knows which version nodes it needs from each
5288shared library it is linked against. Thus at runtime, the dynamic
5289loader can make a quick check to make sure that the libraries you have
5290linked against do in fact supply all of the version nodes that the
5291application will need to resolve all of the dynamic symbols. In this
5292way it is possible for the dynamic linker to know with certainty that
5293all external symbols that it needs will be resolvable without having to
5294search for each symbol reference.
5295
5296The symbol versioning is in effect a much more sophisticated way of
5297doing minor version checking that SunOS does. The fundamental problem
5298that is being addressed here is that typically references to external
5299functions are bound on an as-needed basis, and are not all bound when
5300the application starts up. If a shared library is out of date, a
5301required interface may be missing; when the application tries to use
5302that interface, it may suddenly and unexpectedly fail. With symbol
5303versioning, the user will get a warning when they start their program if
5304the libraries being used with the application are too old.
5305
5306There are several GNU extensions to Sun's versioning approach. The
5307first of these is the ability to bind a symbol to a version node in the
5308source file where the symbol is defined instead of in the versioning
5309script. This was done mainly to reduce the burden on the library
5310maintainer. You can do this by putting something like:
5311@smallexample
5312__asm__(".symver original_foo,foo@@VERS_1.1");
5313@end smallexample
5314@noindent
5315in the C source file. This renames the function @samp{original_foo} to
5316be an alias for @samp{foo} bound to the version node @samp{VERS_1.1}.
5317The @samp{local:} directive can be used to prevent the symbol
96a94295
L
5318@samp{original_foo} from being exported. A @samp{.symver} directive
5319takes precedence over a version script.
252b5132
RH
5320
5321The second GNU extension is to allow multiple versions of the same
5322function to appear in a given shared library. In this way you can make
5323an incompatible change to an interface without increasing the major
5324version number of the shared library, while still allowing applications
5325linked against the old interface to continue to function.
5326
5327To do this, you must use multiple @samp{.symver} directives in the
5328source file. Here is an example:
5329
5330@smallexample
5331__asm__(".symver original_foo,foo@@");
5332__asm__(".symver old_foo,foo@@VERS_1.1");
5333__asm__(".symver old_foo1,foo@@VERS_1.2");
5334__asm__(".symver new_foo,foo@@@@VERS_2.0");
5335@end smallexample
5336
5337In this example, @samp{foo@@} represents the symbol @samp{foo} bound to the
5338unspecified base version of the symbol. The source file that contains this
5339example would define 4 C functions: @samp{original_foo}, @samp{old_foo},
5340@samp{old_foo1}, and @samp{new_foo}.
5341
5342When you have multiple definitions of a given symbol, there needs to be
5343some way to specify a default version to which external references to
5344this symbol will be bound. You can do this with the
5345@samp{foo@@@@VERS_2.0} type of @samp{.symver} directive. You can only
5346declare one version of a symbol as the default in this manner; otherwise
5347you would effectively have multiple definitions of the same symbol.
5348
5349If you wish to bind a reference to a specific version of the symbol
5350within the shared library, you can use the aliases of convenience
36f63dca 5351(i.e., @samp{old_foo}), or you can use the @samp{.symver} directive to
252b5132
RH
5352specifically bind to an external version of the function in question.
5353
cb840a31
L
5354You can also specify the language in the version script:
5355
5356@smallexample
5357VERSION extern "lang" @{ version-script-commands @}
5358@end smallexample
5359
c0065db7 5360The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
cb840a31
L
5361The linker will iterate over the list of symbols at the link time and
5362demangle them according to @samp{lang} before matching them to the
bb1515f2
MF
5363patterns specified in @samp{version-script-commands}. The default
5364@samp{lang} is @samp{C}.
cb840a31 5365
86043bbb
MM
5366Demangled names may contains spaces and other special characters. As
5367described above, you can use a glob pattern to match demangled names,
5368or you can use a double-quoted string to match the string exactly. In
5369the latter case, be aware that minor differences (such as differing
5370whitespace) between the version script and the demangler output will
5371cause a mismatch. As the exact string generated by the demangler
5372might change in the future, even if the mangled name does not, you
5373should check that all of your version directives are behaving as you
5374expect when you upgrade.
5375
252b5132
RH
5376@node Expressions
5377@section Expressions in Linker Scripts
5378@cindex expressions
5379@cindex arithmetic
5380The syntax for expressions in the linker script language is identical to
5381that of C expressions. All expressions are evaluated as integers. All
5382expressions are evaluated in the same size, which is 32 bits if both the
5383host and target are 32 bits, and is otherwise 64 bits.
5384
5385You can use and set symbol values in expressions.
5386
5387The linker defines several special purpose builtin functions for use in
5388expressions.
5389
5390@menu
5391* Constants:: Constants
0c71d759 5392* Symbolic Constants:: Symbolic constants
252b5132 5393* Symbols:: Symbol Names
ecca9871 5394* Orphan Sections:: Orphan Sections
252b5132
RH
5395* Location Counter:: The Location Counter
5396* Operators:: Operators
5397* Evaluation:: Evaluation
5398* Expression Section:: The Section of an Expression
5399* Builtin Functions:: Builtin Functions
5400@end menu
5401
5402@node Constants
5403@subsection Constants
5404@cindex integer notation
5405@cindex constants in linker scripts
5406All constants are integers.
5407
5408As in C, the linker considers an integer beginning with @samp{0} to be
5409octal, and an integer beginning with @samp{0x} or @samp{0X} to be
8a308ae8 5410hexadecimal. Alternatively the linker accepts suffixes of @samp{h} or
11e7fd74 5411@samp{H} for hexadecimal, @samp{o} or @samp{O} for octal, @samp{b} or
8a308ae8
NC
5412@samp{B} for binary and @samp{d} or @samp{D} for decimal. Any integer
5413value without a prefix or a suffix is considered to be decimal.
252b5132
RH
5414
5415@cindex scaled integers
5416@cindex K and M integer suffixes
5417@cindex M and K integer suffixes
5418@cindex suffixes for integers
5419@cindex integer suffixes
5420In addition, you can use the suffixes @code{K} and @code{M} to scale a
5421constant by
5422@c TEXI2ROFF-KILL
36f63dca 5423@ifnottex
252b5132
RH
5424@c END TEXI2ROFF-KILL
5425@code{1024} or @code{1024*1024}
5426@c TEXI2ROFF-KILL
36f63dca 5427@end ifnottex
252b5132
RH
5428@tex
5429${\rm 1024}$ or ${\rm 1024}^2$
5430@end tex
5431@c END TEXI2ROFF-KILL
8a308ae8
NC
5432respectively. For example, the following
5433all refer to the same quantity:
5434
252b5132 5435@smallexample
36f63dca
NC
5436_fourk_1 = 4K;
5437_fourk_2 = 4096;
5438_fourk_3 = 0x1000;
8a308ae8 5439_fourk_4 = 10000o;
252b5132
RH
5440@end smallexample
5441
8a308ae8
NC
5442Note - the @code{K} and @code{M} suffixes cannot be used in
5443conjunction with the base suffixes mentioned above.
5444
0c71d759
NC
5445@node Symbolic Constants
5446@subsection Symbolic Constants
5447@cindex symbolic constants
5448@kindex CONSTANT
5449It is possible to refer to target specific constants via the use of
5450the @code{CONSTANT(@var{name})} operator, where @var{name} is one of:
5451
5452@table @code
5453@item MAXPAGESIZE
5454@kindex MAXPAGESIZE
5455The target's maximum page size.
5456
5457@item COMMONPAGESIZE
5458@kindex COMMONPAGESIZE
5459The target's default page size.
5460@end table
5461
5462So for example:
5463
5464@smallexample
9d5777a3 5465 .text ALIGN (CONSTANT (MAXPAGESIZE)) : @{ *(.text) @}
0c71d759
NC
5466@end smallexample
5467
5468will create a text section aligned to the largest page boundary
5469supported by the target.
5470
252b5132
RH
5471@node Symbols
5472@subsection Symbol Names
5473@cindex symbol names
5474@cindex names
5475@cindex quoted symbol names
5476@kindex "
5477Unless quoted, symbol names start with a letter, underscore, or period
5478and may include letters, digits, underscores, periods, and hyphens.
5479Unquoted symbol names must not conflict with any keywords. You can
5480specify a symbol which contains odd characters or has the same name as a
5481keyword by surrounding the symbol name in double quotes:
5482@smallexample
36f63dca
NC
5483"SECTION" = 9;
5484"with a space" = "also with a space" + 10;
252b5132
RH
5485@end smallexample
5486
5487Since symbols can contain many non-alphabetic characters, it is safest
5488to delimit symbols with spaces. For example, @samp{A-B} is one symbol,
5489whereas @samp{A - B} is an expression involving subtraction.
5490
ecca9871
L
5491@node Orphan Sections
5492@subsection Orphan Sections
5493@cindex orphan
5494Orphan sections are sections present in the input files which
5495are not explicitly placed into the output file by the linker
5496script. The linker will still copy these sections into the
5497output file, but it has to guess as to where they should be
5498placed. The linker uses a simple heuristic to do this. It
5499attempts to place orphan sections after non-orphan sections of the
5500same attribute, such as code vs data, loadable vs non-loadable, etc.
5501If there is not enough room to do this then it places
5502at the end of the file.
5503
5504For ELF targets, the attribute of the section includes section type as
5505well as section flag.
5506
41911f68 5507If an orphaned section's name is representable as a C identifier then
a61ca861 5508the linker will automatically @pxref{PROVIDE} two symbols:
9aec8434 5509__start_SECNAME and __stop_SECNAME, where SECNAME is the name of the
41911f68
NC
5510section. These indicate the start address and end address of the
5511orphaned section respectively. Note: most section names are not
5512representable as C identifiers because they contain a @samp{.}
5513character.
5514
252b5132
RH
5515@node Location Counter
5516@subsection The Location Counter
5517@kindex .
5518@cindex dot
5519@cindex location counter
5520@cindex current output location
5521The special linker variable @dfn{dot} @samp{.} always contains the
5522current output location counter. Since the @code{.} always refers to a
5523location in an output section, it may only appear in an expression
5524within a @code{SECTIONS} command. The @code{.} symbol may appear
5525anywhere that an ordinary symbol is allowed in an expression.
5526
5527@cindex holes
5528Assigning a value to @code{.} will cause the location counter to be
5529moved. This may be used to create holes in the output section. The
dc0b6aa0
AM
5530location counter may not be moved backwards inside an output section,
5531and may not be moved backwards outside of an output section if so
5532doing creates areas with overlapping LMAs.
252b5132
RH
5533
5534@smallexample
5535SECTIONS
5536@{
5537 output :
5538 @{
5539 file1(.text)
5540 . = . + 1000;
5541 file2(.text)
5542 . += 1000;
5543 file3(.text)
563e308f 5544 @} = 0x12345678;
252b5132
RH
5545@}
5546@end smallexample
5547@noindent
5548In the previous example, the @samp{.text} section from @file{file1} is
5549located at the beginning of the output section @samp{output}. It is
5550followed by a 1000 byte gap. Then the @samp{.text} section from
5551@file{file2} appears, also with a 1000 byte gap following before the
563e308f 5552@samp{.text} section from @file{file3}. The notation @samp{= 0x12345678}
252b5132
RH
5553specifies what data to write in the gaps (@pxref{Output Section Fill}).
5554
5c6bbab8
NC
5555@cindex dot inside sections
5556Note: @code{.} actually refers to the byte offset from the start of the
5557current containing object. Normally this is the @code{SECTIONS}
69da35b5 5558statement, whose start address is 0, hence @code{.} can be used as an
5c6bbab8
NC
5559absolute address. If @code{.} is used inside a section description
5560however, it refers to the byte offset from the start of that section,
5561not an absolute address. Thus in a script like this:
5562
5563@smallexample
5564SECTIONS
5565@{
5566 . = 0x100
5567 .text: @{
5568 *(.text)
5569 . = 0x200
5570 @}
5571 . = 0x500
5572 .data: @{
5573 *(.data)
5574 . += 0x600
5575 @}
5576@}
5577@end smallexample
5578
5579The @samp{.text} section will be assigned a starting address of 0x100
5580and a size of exactly 0x200 bytes, even if there is not enough data in
5581the @samp{.text} input sections to fill this area. (If there is too
5582much data, an error will be produced because this would be an attempt to
5583move @code{.} backwards). The @samp{.data} section will start at 0x500
5584and it will have an extra 0x600 bytes worth of space after the end of
5585the values from the @samp{.data} input sections and before the end of
5586the @samp{.data} output section itself.
5587
b5666f2f
AM
5588@cindex dot outside sections
5589Setting symbols to the value of the location counter outside of an
5590output section statement can result in unexpected values if the linker
5591needs to place orphan sections. For example, given the following:
5592
5593@smallexample
5594SECTIONS
5595@{
5596 start_of_text = . ;
5597 .text: @{ *(.text) @}
5598 end_of_text = . ;
5599
5600 start_of_data = . ;
5601 .data: @{ *(.data) @}
5602 end_of_data = . ;
5603@}
5604@end smallexample
5605
5606If the linker needs to place some input section, e.g. @code{.rodata},
5607not mentioned in the script, it might choose to place that section
5608between @code{.text} and @code{.data}. You might think the linker
5609should place @code{.rodata} on the blank line in the above script, but
5610blank lines are of no particular significance to the linker. As well,
5611the linker doesn't associate the above symbol names with their
5612sections. Instead, it assumes that all assignments or other
5613statements belong to the previous output section, except for the
5614special case of an assignment to @code{.}. I.e., the linker will
5615place the orphan @code{.rodata} section as if the script was written
5616as follows:
5617
5618@smallexample
5619SECTIONS
5620@{
5621 start_of_text = . ;
5622 .text: @{ *(.text) @}
5623 end_of_text = . ;
5624
5625 start_of_data = . ;
5626 .rodata: @{ *(.rodata) @}
5627 .data: @{ *(.data) @}
5628 end_of_data = . ;
5629@}
5630@end smallexample
5631
5632This may or may not be the script author's intention for the value of
5633@code{start_of_data}. One way to influence the orphan section
5634placement is to assign the location counter to itself, as the linker
5635assumes that an assignment to @code{.} is setting the start address of
5636a following output section and thus should be grouped with that
5637section. So you could write:
5638
5639@smallexample
5640SECTIONS
5641@{
5642 start_of_text = . ;
5643 .text: @{ *(.text) @}
5644 end_of_text = . ;
5645
5646 . = . ;
5647 start_of_data = . ;
5648 .data: @{ *(.data) @}
5649 end_of_data = . ;
5650@}
5651@end smallexample
5652
5653Now, the orphan @code{.rodata} section will be placed between
5654@code{end_of_text} and @code{start_of_data}.
5655
252b5132
RH
5656@need 2000
5657@node Operators
5658@subsection Operators
5659@cindex operators for arithmetic
5660@cindex arithmetic operators
5661@cindex precedence in expressions
5662The linker recognizes the standard C set of arithmetic operators, with
5663the standard bindings and precedence levels:
5664@c TEXI2ROFF-KILL
36f63dca 5665@ifnottex
252b5132
RH
5666@c END TEXI2ROFF-KILL
5667@smallexample
5668precedence associativity Operators Notes
5669(highest)
56701 left ! - ~ (1)
56712 left * / %
56723 left + -
56734 left >> <<
56745 left == != > < <= >=
56756 left &
56767 left |
56778 left &&
56789 left ||
567910 right ? :
568011 right &= += -= *= /= (2)
5681(lowest)
5682@end smallexample
5683Notes:
a1ab1d2a 5684(1) Prefix operators
252b5132
RH
5685(2) @xref{Assignments}.
5686@c TEXI2ROFF-KILL
36f63dca 5687@end ifnottex
252b5132
RH
5688@tex
5689\vskip \baselineskip
5690%"lispnarrowing" is the extra indent used generally for smallexample
5691\hskip\lispnarrowing\vbox{\offinterlineskip
5692\hrule
5693\halign
5694{\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ {\tt #}\ \hfil&\vrule#\cr
5695height2pt&\omit&&\omit&&\omit&\cr
5696&Precedence&& Associativity &&{\rm Operators}&\cr
5697height2pt&\omit&&\omit&&\omit&\cr
5698\noalign{\hrule}
5699height2pt&\omit&&\omit&&\omit&\cr
5700&highest&&&&&\cr
5701% '176 is tilde, '~' in tt font
a1ab1d2a 5702&1&&left&&\qquad- \char'176\ !\qquad\dag&\cr
252b5132
RH
5703&2&&left&&* / \%&\cr
5704&3&&left&&+ -&\cr
5705&4&&left&&>> <<&\cr
5706&5&&left&&== != > < <= >=&\cr
5707&6&&left&&\&&\cr
5708&7&&left&&|&\cr
5709&8&&left&&{\&\&}&\cr
5710&9&&left&&||&\cr
5711&10&&right&&? :&\cr
5712&11&&right&&\qquad\&= += -= *= /=\qquad\ddag&\cr
5713&lowest&&&&&\cr
5714height2pt&\omit&&\omit&&\omit&\cr}
5715\hrule}
5716@end tex
5717@iftex
5718{
5719@obeylines@parskip=0pt@parindent=0pt
5720@dag@quad Prefix operators.
5721@ddag@quad @xref{Assignments}.
5722}
5723@end iftex
5724@c END TEXI2ROFF-KILL
5725
5726@node Evaluation
5727@subsection Evaluation
5728@cindex lazy evaluation
5729@cindex expression evaluation order
5730The linker evaluates expressions lazily. It only computes the value of
5731an expression when absolutely necessary.
5732
5733The linker needs some information, such as the value of the start
5734address of the first section, and the origins and lengths of memory
5735regions, in order to do any linking at all. These values are computed
5736as soon as possible when the linker reads in the linker script.
5737
5738However, other values (such as symbol values) are not known or needed
5739until after storage allocation. Such values are evaluated later, when
5740other information (such as the sizes of output sections) is available
5741for use in the symbol assignment expression.
5742
5743The sizes of sections cannot be known until after allocation, so
5744assignments dependent upon these are not performed until after
5745allocation.
5746
5747Some expressions, such as those depending upon the location counter
5748@samp{.}, must be evaluated during section allocation.
5749
5750If the result of an expression is required, but the value is not
5751available, then an error results. For example, a script like the
5752following
5753@smallexample
5754@group
5755SECTIONS
5756 @{
a1ab1d2a 5757 .text 9+this_isnt_constant :
252b5132
RH
5758 @{ *(.text) @}
5759 @}
5760@end group
5761@end smallexample
5762@noindent
5763will cause the error message @samp{non constant expression for initial
5764address}.
5765
5766@node Expression Section
5767@subsection The Section of an Expression
5768@cindex expression sections
5769@cindex absolute expressions
5770@cindex relative expressions
5771@cindex absolute and relocatable symbols
5772@cindex relocatable and absolute symbols
5773@cindex symbols, relocatable and absolute
7542af2a
AM
5774Addresses and symbols may be section relative, or absolute. A section
5775relative symbol is relocatable. If you request relocatable output
5776using the @samp{-r} option, a further link operation may change the
5777value of a section relative symbol. On the other hand, an absolute
5778symbol will retain the same value throughout any further link
5779operations.
5780
abf4be64
AM
5781Some terms in linker expressions are addresses. This is true of
5782section relative symbols and for builtin functions that return an
5783address, such as @code{ADDR}, @code{LOADADDR}, @code{ORIGIN} and
5784@code{SEGMENT_START}. Other terms are simply numbers, or are builtin
5785functions that return a non-address value, such as @code{LENGTH}.
01554a74
AM
5786One complication is that unless you set @code{LD_FEATURE ("SANE_EXPR")}
5787(@pxref{Miscellaneous Commands}), numbers and absolute symbols are treated
5c3049d2
AM
5788differently depending on their location, for compatibility with older
5789versions of @code{ld}. Expressions appearing outside an output
5790section definition treat all numbers as absolute addresses.
5791Expressions appearing inside an output section definition treat
01554a74
AM
5792absolute symbols as numbers. If @code{LD_FEATURE ("SANE_EXPR")} is
5793given, then absolute symbols and numbers are simply treated as numbers
5794everywhere.
5c3049d2
AM
5795
5796In the following simple example,
252b5132 5797
7542af2a
AM
5798@smallexample
5799@group
5800SECTIONS
5801 @{
5802 . = 0x100;
5803 __executable_start = 0x100;
5804 .data :
5805 @{
5806 . = 0x10;
5807 __data_start = 0x10;
5808 *(.data)
5809 @}
5810 @dots{}
5811 @}
5812@end group
5813@end smallexample
252b5132 5814
7542af2a
AM
5815both @code{.} and @code{__executable_start} are set to the absolute
5816address 0x100 in the first two assignments, then both @code{.} and
5817@code{__data_start} are set to 0x10 relative to the @code{.data}
5818section in the second two assignments.
252b5132 5819
5c3049d2
AM
5820For expressions involving numbers, relative addresses and absolute
5821addresses, ld follows these rules to evaluate terms:
7542af2a
AM
5822
5823@itemize @bullet
5824@item
c05f749e
AM
5825Unary operations on an absolute address or number, and binary
5826operations on two absolute addresses or two numbers, or between one
5827absolute address and a number, apply the operator to the value(s).
5828@item
7542af2a
AM
5829Unary operations on a relative address, and binary operations on two
5830relative addresses in the same section or between one relative address
5831and a number, apply the operator to the offset part of the address(es).
5832@item
c05f749e
AM
5833Other binary operations, that is, between two relative addresses not
5834in the same section, or between a relative address and an absolute
5835address, first convert any non-absolute term to an absolute address
5836before applying the operator.
7542af2a
AM
5837@end itemize
5838
5839The result section of each sub-expression is as follows:
5840
5841@itemize @bullet
5842@item
5843An operation involving only numbers results in a number.
5844@item
5845The result of comparisons, @samp{&&} and @samp{||} is also a number.
5846@item
9bc8bb33 5847The result of other binary arithmetic and logical operations on two
11e7fd74 5848relative addresses in the same section or two absolute addresses
9bc8bb33
AM
5849(after above conversions) is also a number.
5850@item
5851The result of other operations on relative addresses or one
5852relative address and a number, is a relative address in the same
5853section as the relative operand(s).
7542af2a
AM
5854@item
5855The result of other operations on absolute addresses (after above
5856conversions) is an absolute address.
5857@end itemize
252b5132
RH
5858
5859You can use the builtin function @code{ABSOLUTE} to force an expression
5860to be absolute when it would otherwise be relative. For example, to
5861create an absolute symbol set to the address of the end of the output
5862section @samp{.data}:
5863@smallexample
5864SECTIONS
5865 @{
5866 .data : @{ *(.data) _edata = ABSOLUTE(.); @}
5867 @}
5868@end smallexample
5869@noindent
5870If @samp{ABSOLUTE} were not used, @samp{_edata} would be relative to the
5871@samp{.data} section.
5872
7542af2a
AM
5873Using @code{LOADADDR} also forces an expression absolute, since this
5874particular builtin function returns an absolute address.
5875
252b5132
RH
5876@node Builtin Functions
5877@subsection Builtin Functions
5878@cindex functions in expressions
5879The linker script language includes a number of builtin functions for
5880use in linker script expressions.
5881
5882@table @code
5883@item ABSOLUTE(@var{exp})
5884@kindex ABSOLUTE(@var{exp})
5885@cindex expression, absolute
5886Return the absolute (non-relocatable, as opposed to non-negative) value
5887of the expression @var{exp}. Primarily useful to assign an absolute
5888value to a symbol within a section definition, where symbol values are
5889normally section relative. @xref{Expression Section}.
5890
5891@item ADDR(@var{section})
5892@kindex ADDR(@var{section})
5893@cindex section address in expression
7542af2a 5894Return the address (VMA) of the named @var{section}. Your
252b5132 5895script must previously have defined the location of that section. In
7542af2a
AM
5896the following example, @code{start_of_output_1}, @code{symbol_1} and
5897@code{symbol_2} are assigned equivalent values, except that
5898@code{symbol_1} will be relative to the @code{.output1} section while
5899the other two will be absolute:
252b5132
RH
5900@smallexample
5901@group
5902SECTIONS @{ @dots{}
5903 .output1 :
a1ab1d2a 5904 @{
252b5132
RH
5905 start_of_output_1 = ABSOLUTE(.);
5906 @dots{}
5907 @}
5908 .output :
5909 @{
5910 symbol_1 = ADDR(.output1);
5911 symbol_2 = start_of_output_1;
5912 @}
5913@dots{} @}
5914@end group
5915@end smallexample
5916
876f4090
NS
5917@item ALIGN(@var{align})
5918@itemx ALIGN(@var{exp},@var{align})
5919@kindex ALIGN(@var{align})
5920@kindex ALIGN(@var{exp},@var{align})
252b5132
RH
5921@cindex round up location counter
5922@cindex align location counter
876f4090
NS
5923@cindex round up expression
5924@cindex align expression
5925Return the location counter (@code{.}) or arbitrary expression aligned
5926to the next @var{align} boundary. The single operand @code{ALIGN}
5927doesn't change the value of the location counter---it just does
5928arithmetic on it. The two operand @code{ALIGN} allows an arbitrary
5929expression to be aligned upwards (@code{ALIGN(@var{align})} is
5930equivalent to @code{ALIGN(., @var{align})}).
5931
5932Here is an example which aligns the output @code{.data} section to the
5933next @code{0x2000} byte boundary after the preceding section and sets a
5934variable within the section to the next @code{0x8000} boundary after the
5935input sections:
252b5132
RH
5936@smallexample
5937@group
5938SECTIONS @{ @dots{}
5939 .data ALIGN(0x2000): @{
5940 *(.data)
5941 variable = ALIGN(0x8000);
5942 @}
5943@dots{} @}
5944@end group
5945@end smallexample
5946@noindent
5947The first use of @code{ALIGN} in this example specifies the location of
5948a section because it is used as the optional @var{address} attribute of
5949a section definition (@pxref{Output Section Address}). The second use
5950of @code{ALIGN} is used to defines the value of a symbol.
5951
5952The builtin function @code{NEXT} is closely related to @code{ALIGN}.
5953
362c1d1a
NS
5954@item ALIGNOF(@var{section})
5955@kindex ALIGNOF(@var{section})
5956@cindex section alignment
5957Return the alignment in bytes of the named @var{section}, if that section has
5958been allocated. If the section has not been allocated when this is
5959evaluated, the linker will report an error. In the following example,
5960the alignment of the @code{.output} section is stored as the first
5961value in that section.
5962@smallexample
5963@group
5964SECTIONS@{ @dots{}
5965 .output @{
5966 LONG (ALIGNOF (.output))
5967 @dots{}
5968 @}
5969@dots{} @}
5970@end group
5971@end smallexample
5972
252b5132
RH
5973@item BLOCK(@var{exp})
5974@kindex BLOCK(@var{exp})
5975This is a synonym for @code{ALIGN}, for compatibility with older linker
5976scripts. It is most often seen when setting the address of an output
5977section.
5978
2d20f7bf
JJ
5979@item DATA_SEGMENT_ALIGN(@var{maxpagesize}, @var{commonpagesize})
5980@kindex DATA_SEGMENT_ALIGN(@var{maxpagesize}, @var{commonpagesize})
5981This is equivalent to either
5982@smallexample
5983(ALIGN(@var{maxpagesize}) + (. & (@var{maxpagesize} - 1)))
5984@end smallexample
5985or
5986@smallexample
5987(ALIGN(@var{maxpagesize}) + (. & (@var{maxpagesize} - @var{commonpagesize})))
5988@end smallexample
5989@noindent
5990depending on whether the latter uses fewer @var{commonpagesize} sized pages
5991for the data segment (area between the result of this expression and
5992@code{DATA_SEGMENT_END}) than the former or not.
5993If the latter form is used, it means @var{commonpagesize} bytes of runtime
5994memory will be saved at the expense of up to @var{commonpagesize} wasted
5995bytes in the on-disk file.
5996
5997This expression can only be used directly in @code{SECTIONS} commands, not in
5998any output section descriptions and only once in the linker script.
5999@var{commonpagesize} should be less or equal to @var{maxpagesize} and should
6000be the system page size the object wants to be optimized for (while still
6001working on system page sizes up to @var{maxpagesize}).
6002
6003@noindent
6004Example:
6005@smallexample
6006 . = DATA_SEGMENT_ALIGN(0x10000, 0x2000);
6007@end smallexample
6008
6009@item DATA_SEGMENT_END(@var{exp})
6010@kindex DATA_SEGMENT_END(@var{exp})
6011This defines the end of data segment for @code{DATA_SEGMENT_ALIGN}
6012evaluation purposes.
6013
6014@smallexample
6015 . = DATA_SEGMENT_END(.);
6016@end smallexample
6017
a4f5ad88
JJ
6018@item DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
6019@kindex DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
6020This defines the end of the @code{PT_GNU_RELRO} segment when
eec2f3ed 6021@samp{-z relro} option is used.
a4f5ad88
JJ
6022When @samp{-z relro} option is not present, @code{DATA_SEGMENT_RELRO_END}
6023does nothing, otherwise @code{DATA_SEGMENT_ALIGN} is padded so that
6024@var{exp} + @var{offset} is aligned to the most commonly used page
6025boundary for particular target. If present in the linker script,
6026it must always come in between @code{DATA_SEGMENT_ALIGN} and
eec2f3ed
AM
6027@code{DATA_SEGMENT_END}. Evaluates to the second argument plus any
6028padding needed at the end of the @code{PT_GNU_RELRO} segment due to
6029section alignment.
a4f5ad88
JJ
6030
6031@smallexample
6032 . = DATA_SEGMENT_RELRO_END(24, .);
6033@end smallexample
6034
252b5132
RH
6035@item DEFINED(@var{symbol})
6036@kindex DEFINED(@var{symbol})
6037@cindex symbol defaults
6038Return 1 if @var{symbol} is in the linker global symbol table and is
420e579c
HPN
6039defined before the statement using DEFINED in the script, otherwise
6040return 0. You can use this function to provide
252b5132
RH
6041default values for symbols. For example, the following script fragment
6042shows how to set a global symbol @samp{begin} to the first location in
6043the @samp{.text} section---but if a symbol called @samp{begin} already
6044existed, its value is preserved:
6045
6046@smallexample
6047@group
6048SECTIONS @{ @dots{}
6049 .text : @{
6050 begin = DEFINED(begin) ? begin : . ;
6051 @dots{}
6052 @}
6053 @dots{}
6054@}
6055@end group
6056@end smallexample
6057
3ec57632
NC
6058@item LENGTH(@var{memory})
6059@kindex LENGTH(@var{memory})
6060Return the length of the memory region named @var{memory}.
6061
252b5132
RH
6062@item LOADADDR(@var{section})
6063@kindex LOADADDR(@var{section})
6064@cindex section load address in expression
7542af2a 6065Return the absolute LMA of the named @var{section}. (@pxref{Output
252b5132
RH
6066Section LMA}).
6067
2e53f7d6
NC
6068@item LOG2CEIL(@var{exp})
6069@kindex LOG2CEIL(@var{exp})
6070Return the binary logarithm of @var{exp} rounded towards infinity.
6071@code{LOG2CEIL(0)} returns 0.
6072
252b5132
RH
6073@kindex MAX
6074@item MAX(@var{exp1}, @var{exp2})
6075Returns the maximum of @var{exp1} and @var{exp2}.
6076
6077@kindex MIN
6078@item MIN(@var{exp1}, @var{exp2})
6079Returns the minimum of @var{exp1} and @var{exp2}.
6080
6081@item NEXT(@var{exp})
6082@kindex NEXT(@var{exp})
6083@cindex unallocated address, next
6084Return the next unallocated address that is a multiple of @var{exp}.
6085This function is closely related to @code{ALIGN(@var{exp})}; unless you
6086use the @code{MEMORY} command to define discontinuous memory for the
6087output file, the two functions are equivalent.
6088
3ec57632
NC
6089@item ORIGIN(@var{memory})
6090@kindex ORIGIN(@var{memory})
6091Return the origin of the memory region named @var{memory}.
6092
ba916c8a
MM
6093@item SEGMENT_START(@var{segment}, @var{default})
6094@kindex SEGMENT_START(@var{segment}, @var{default})
6095Return the base address of the named @var{segment}. If an explicit
c5da8c7d
NC
6096value has already been given for this segment (with a command-line
6097@samp{-T} option) then that value will be returned otherwise the value
6098will be @var{default}. At present, the @samp{-T} command-line option
6099can only be used to set the base address for the ``text'', ``data'', and
7542af2a 6100``bss'' sections, but you can use @code{SEGMENT_START} with any segment
ba916c8a
MM
6101name.
6102
252b5132
RH
6103@item SIZEOF(@var{section})
6104@kindex SIZEOF(@var{section})
6105@cindex section size
6106Return the size in bytes of the named @var{section}, if that section has
6107been allocated. If the section has not been allocated when this is
6108evaluated, the linker will report an error. In the following example,
6109@code{symbol_1} and @code{symbol_2} are assigned identical values:
6110@smallexample
6111@group
6112SECTIONS@{ @dots{}
6113 .output @{
6114 .start = . ;
6115 @dots{}
6116 .end = . ;
6117 @}
6118 symbol_1 = .end - .start ;
6119 symbol_2 = SIZEOF(.output);
6120@dots{} @}
6121@end group
6122@end smallexample
6123
6124@item SIZEOF_HEADERS
6125@itemx sizeof_headers
6126@kindex SIZEOF_HEADERS
6127@cindex header size
6128Return the size in bytes of the output file's headers. This is
6129information which appears at the start of the output file. You can use
6130this number when setting the start address of the first section, if you
6131choose, to facilitate paging.
6132
6133@cindex not enough room for program headers
6134@cindex program headers, not enough room
6135When producing an ELF output file, if the linker script uses the
6136@code{SIZEOF_HEADERS} builtin function, the linker must compute the
6137number of program headers before it has determined all the section
6138addresses and sizes. If the linker later discovers that it needs
6139additional program headers, it will report an error @samp{not enough
6140room for program headers}. To avoid this error, you must avoid using
6141the @code{SIZEOF_HEADERS} function, or you must rework your linker
6142script to avoid forcing the linker to use additional program headers, or
6143you must define the program headers yourself using the @code{PHDRS}
6144command (@pxref{PHDRS}).
6145@end table
6146
6147@node Implicit Linker Scripts
6148@section Implicit Linker Scripts
6149@cindex implicit linker scripts
6150If you specify a linker input file which the linker can not recognize as
6151an object file or an archive file, it will try to read the file as a
6152linker script. If the file can not be parsed as a linker script, the
6153linker will report an error.
6154
6155An implicit linker script will not replace the default linker script.
6156
6157Typically an implicit linker script would contain only symbol
6158assignments, or the @code{INPUT}, @code{GROUP}, or @code{VERSION}
6159commands.
6160
6161Any input files read because of an implicit linker script will be read
6162at the position in the command line where the implicit linker script was
6163read. This can affect archive searching.
6164
6165@ifset GENERIC
6166@node Machine Dependent
6167@chapter Machine Dependent Features
6168
6169@cindex machine dependencies
ff5dcc92
SC
6170@command{ld} has additional features on some platforms; the following
6171sections describe them. Machines where @command{ld} has no additional
252b5132
RH
6172functionality are not listed.
6173
6174@menu
36f63dca
NC
6175@ifset H8300
6176* H8/300:: @command{ld} and the H8/300
6177@end ifset
6178@ifset I960
6179* i960:: @command{ld} and the Intel 960 family
6180@end ifset
7ca01ed9
NC
6181@ifset M68HC11
6182* M68HC11/68HC12:: @code{ld} and the Motorola 68HC11 and 68HC12 families
6183@end ifset
36f63dca
NC
6184@ifset ARM
6185* ARM:: @command{ld} and the ARM family
6186@end ifset
6187@ifset HPPA
6188* HPPA ELF32:: @command{ld} and HPPA 32-bit ELF
6189@end ifset
7fb9f789
NC
6190@ifset M68K
6191* M68K:: @command{ld} and the Motorola 68K family
6192@end ifset
833794fc
MR
6193@ifset MIPS
6194* MIPS:: @command{ld} and the MIPS family
6195@end ifset
3c3bdf30 6196@ifset MMIX
36f63dca 6197* MMIX:: @command{ld} and MMIX
3c3bdf30 6198@end ifset
2469cfa2 6199@ifset MSP430
36f63dca 6200* MSP430:: @command{ld} and MSP430
2469cfa2 6201@end ifset
35c08157
KLC
6202@ifset NDS32
6203* NDS32:: @command{ld} and NDS32
6204@end ifset
78058a5e
SL
6205@ifset NIOSII
6206* Nios II:: @command{ld} and the Altera Nios II
6207@end ifset
2a60a7a8
AM
6208@ifset POWERPC
6209* PowerPC ELF32:: @command{ld} and PowerPC 32-bit ELF Support
6210@end ifset
6211@ifset POWERPC64
6212* PowerPC64 ELF64:: @command{ld} and PowerPC64 64-bit ELF Support
6213@end ifset
49fa1e15
AM
6214@ifset SPU
6215* SPU ELF:: @command{ld} and SPU ELF Support
6216@end ifset
74459f0e 6217@ifset TICOFF
ff5dcc92 6218* TI COFF:: @command{ld} and TI COFF
74459f0e 6219@end ifset
2ca22b03
NC
6220@ifset WIN32
6221* WIN32:: @command{ld} and WIN32 (cygwin/mingw)
6222@end ifset
e0001a05
NC
6223@ifset XTENSA
6224* Xtensa:: @command{ld} and Xtensa Processors
6225@end ifset
252b5132
RH
6226@end menu
6227@end ifset
6228
252b5132
RH
6229@ifset H8300
6230@ifclear GENERIC
6231@raisesections
6232@end ifclear
6233
6234@node H8/300
ff5dcc92 6235@section @command{ld} and the H8/300
252b5132
RH
6236
6237@cindex H8/300 support
ff5dcc92 6238For the H8/300, @command{ld} can perform these global optimizations when
252b5132
RH
6239you specify the @samp{--relax} command-line option.
6240
6241@table @emph
6242@cindex relaxing on H8/300
6243@item relaxing address modes
ff5dcc92 6244@command{ld} finds all @code{jsr} and @code{jmp} instructions whose
252b5132
RH
6245targets are within eight bits, and turns them into eight-bit
6246program-counter relative @code{bsr} and @code{bra} instructions,
6247respectively.
6248
6249@cindex synthesizing on H8/300
6250@item synthesizing instructions
81f5558e 6251@c FIXME: specifically mov.b, or any mov instructions really? -> mov.b only, at least on H8, H8H, H8S
ff5dcc92 6252@command{ld} finds all @code{mov.b} instructions which use the
252b5132
RH
6253sixteen-bit absolute address form, but refer to the top
6254page of memory, and changes them to use the eight-bit address form.
6255(That is: the linker turns @samp{mov.b @code{@@}@var{aa}:16} into
6256@samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the
6257top page of memory).
1502569c 6258
81f5558e
NC
6259@command{ld} finds all @code{mov} instructions which use the register
6260indirect with 32-bit displacement addressing mode, but use a small
6261displacement inside 16-bit displacement range, and changes them to use
6262the 16-bit displacement form. (That is: the linker turns @samp{mov.b
6263@code{@@}@var{d}:32,ERx} into @samp{mov.b @code{@@}@var{d}:16,ERx}
6264whenever the displacement @var{d} is in the 16 bit signed integer
6265range. Only implemented in ELF-format ld).
6266
1502569c 6267@item bit manipulation instructions
c0065db7 6268@command{ld} finds all bit manipulation instructions like @code{band, bclr,
1502569c 6269biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor}
c0065db7 6270which use 32 bit and 16 bit absolute address form, but refer to the top
1502569c
NC
6271page of memory, and changes them to use the 8 bit address form.
6272(That is: the linker turns @samp{bset #xx:3,@code{@@}@var{aa}:32} into
c0065db7 6273@samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
1502569c
NC
6274the top page of memory).
6275
6276@item system control instructions
c0065db7
RM
6277@command{ld} finds all @code{ldc.w, stc.w} instructions which use the
627832 bit absolute address form, but refer to the top page of memory, and
1502569c
NC
6279changes them to use 16 bit address form.
6280(That is: the linker turns @samp{ldc.w @code{@@}@var{aa}:32,ccr} into
c0065db7 6281@samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
1502569c 6282the top page of memory).
252b5132
RH
6283@end table
6284
6285@ifclear GENERIC
6286@lowersections
6287@end ifclear
6288@end ifset
6289
36f63dca 6290@ifclear GENERIC
c2dcd04e 6291@ifset Renesas
36f63dca 6292@c This stuff is pointless to say unless you're especially concerned
c2dcd04e
NC
6293@c with Renesas chips; don't enable it for generic case, please.
6294@node Renesas
6295@chapter @command{ld} and Other Renesas Chips
36f63dca 6296
c2dcd04e
NC
6297@command{ld} also supports the Renesas (formerly Hitachi) H8/300H,
6298H8/500, and SH chips. No special features, commands, or command-line
6299options are required for these chips.
36f63dca
NC
6300@end ifset
6301@end ifclear
6302
6303@ifset I960
6304@ifclear GENERIC
6305@raisesections
6306@end ifclear
6307
6308@node i960
6309@section @command{ld} and the Intel 960 Family
6310
6311@cindex i960 support
6312
6313You can use the @samp{-A@var{architecture}} command line option to
6314specify one of the two-letter names identifying members of the 960
6315family; the option specifies the desired output target, and warns of any
6316incompatible instructions in the input files. It also modifies the
6317linker's search strategy for archive libraries, to support the use of
6318libraries specific to each particular architecture, by including in the
6319search loop names suffixed with the string identifying the architecture.
6320
6321For example, if your @command{ld} command line included @w{@samp{-ACA}} as
6322well as @w{@samp{-ltry}}, the linker would look (in its built-in search
6323paths, and in any paths you specify with @samp{-L}) for a library with
6324the names
6325
6326@smallexample
6327@group
6328try
6329libtry.a
6330tryca
6331libtryca.a
6332@end group
6333@end smallexample
6334
6335@noindent
6336The first two possibilities would be considered in any event; the last
6337two are due to the use of @w{@samp{-ACA}}.
6338
6339You can meaningfully use @samp{-A} more than once on a command line, since
6340the 960 architecture family allows combination of target architectures; each
6341use will add another pair of name variants to search for when @w{@samp{-l}}
6342specifies a library.
6343
6344@cindex @option{--relax} on i960
6345@cindex relaxing on i960
6346@command{ld} supports the @samp{--relax} option for the i960 family. If
6347you specify @samp{--relax}, @command{ld} finds all @code{balx} and
6348@code{calx} instructions whose targets are within 24 bits, and turns
6349them into 24-bit program-counter relative @code{bal} and @code{cal}
6350instructions, respectively. @command{ld} also turns @code{cal}
6351instructions into @code{bal} instructions when it determines that the
6352target subroutine is a leaf routine (that is, the target subroutine does
6353not itself call any subroutines).
6354
6355@ifclear GENERIC
6356@lowersections
6357@end ifclear
6358@end ifset
6359
6360@ifset ARM
6361@ifclear GENERIC
6362@raisesections
6363@end ifclear
6364
93fd0973
SC
6365@ifset M68HC11
6366@ifclear GENERIC
6367@raisesections
6368@end ifclear
6369
6370@node M68HC11/68HC12
6371@section @command{ld} and the Motorola 68HC11 and 68HC12 families
6372
6373@cindex M68HC11 and 68HC12 support
6374
6375@subsection Linker Relaxation
6376
6377For the Motorola 68HC11, @command{ld} can perform these global
6378optimizations when you specify the @samp{--relax} command-line option.
6379
6380@table @emph
6381@cindex relaxing on M68HC11
6382@item relaxing address modes
6383@command{ld} finds all @code{jsr} and @code{jmp} instructions whose
6384targets are within eight bits, and turns them into eight-bit
6385program-counter relative @code{bsr} and @code{bra} instructions,
6386respectively.
6387
6388@command{ld} also looks at all 16-bit extended addressing modes and
6389transforms them in a direct addressing mode when the address is in
6390page 0 (between 0 and 0x0ff).
6391
6392@item relaxing gcc instruction group
6393When @command{gcc} is called with @option{-mrelax}, it can emit group
6394of instructions that the linker can optimize to use a 68HC11 direct
6395addressing mode. These instructions consists of @code{bclr} or
6396@code{bset} instructions.
6397
6398@end table
6399
6400@subsection Trampoline Generation
6401
6402@cindex trampoline generation on M68HC11
6403@cindex trampoline generation on M68HC12
6404For 68HC11 and 68HC12, @command{ld} can generate trampoline code to
6405call a far function using a normal @code{jsr} instruction. The linker
c0065db7 6406will also change the relocation to some far function to use the
93fd0973
SC
6407trampoline address instead of the function address. This is typically the
6408case when a pointer to a function is taken. The pointer will in fact
6409point to the function trampoline.
6410
6411@ifclear GENERIC
6412@lowersections
6413@end ifclear
6414@end ifset
6415
36f63dca 6416@node ARM
3674e28a 6417@section @command{ld} and the ARM family
36f63dca
NC
6418
6419@cindex ARM interworking support
6420@kindex --support-old-code
6421For the ARM, @command{ld} will generate code stubs to allow functions calls
b45619c0 6422between ARM and Thumb code. These stubs only work with code that has
36f63dca
NC
6423been compiled and assembled with the @samp{-mthumb-interwork} command
6424line option. If it is necessary to link with old ARM object files or
6425libraries, which have not been compiled with the -mthumb-interwork
6426option then the @samp{--support-old-code} command line switch should be
6427given to the linker. This will make it generate larger stub functions
6428which will work with non-interworking aware ARM code. Note, however,
6429the linker does not support generating stubs for function calls to
6430non-interworking aware Thumb code.
6431
6432@cindex thumb entry point
6433@cindex entry point, thumb
6434@kindex --thumb-entry=@var{entry}
6435The @samp{--thumb-entry} switch is a duplicate of the generic
6436@samp{--entry} switch, in that it sets the program's starting address.
6437But it also sets the bottom bit of the address, so that it can be
6438branched to using a BX instruction, and the program will start
6439executing in Thumb mode straight away.
6440
ce11ba6c
KT
6441@cindex PE import table prefixing
6442@kindex --use-nul-prefixed-import-tables
6443The @samp{--use-nul-prefixed-import-tables} switch is specifying, that
6444the import tables idata4 and idata5 have to be generated with a zero
11e7fd74 6445element prefix for import libraries. This is the old style to generate
ce11ba6c
KT
6446import tables. By default this option is turned off.
6447
e489d0ae
PB
6448@cindex BE8
6449@kindex --be8
6450The @samp{--be8} switch instructs @command{ld} to generate BE8 format
080bb7bb
NC
6451executables. This option is only valid when linking big-endian
6452objects - ie ones which have been assembled with the @option{-EB}
6453option. The resulting image will contain big-endian data and
6454little-endian code.
e489d0ae 6455
3674e28a
PB
6456@cindex TARGET1
6457@kindex --target1-rel
6458@kindex --target1-abs
6459The @samp{R_ARM_TARGET1} relocation is typically used for entries in the
6460@samp{.init_array} section. It is interpreted as either @samp{R_ARM_REL32}
6461or @samp{R_ARM_ABS32}, depending on the target. The @samp{--target1-rel}
6462and @samp{--target1-abs} switches override the default.
6463
6464@cindex TARGET2
6465@kindex --target2=@var{type}
6466The @samp{--target2=type} switch overrides the default definition of the
6467@samp{R_ARM_TARGET2} relocation. Valid values for @samp{type}, their
6468meanings, and target defaults are as follows:
6469@table @samp
6470@item rel
eeac373a
PB
6471@samp{R_ARM_REL32} (arm*-*-elf, arm*-*-eabi)
6472@item abs
6473@samp{R_ARM_ABS32} (arm*-*-symbianelf)
3674e28a
PB
6474@item got-rel
6475@samp{R_ARM_GOT_PREL} (arm*-*-linux, arm*-*-*bsd)
6476@end table
6477
319850b4
JB
6478@cindex FIX_V4BX
6479@kindex --fix-v4bx
6480The @samp{R_ARM_V4BX} relocation (defined by the ARM AAELF
6481specification) enables objects compiled for the ARMv4 architecture to be
6482interworking-safe when linked with other objects compiled for ARMv4t, but
6483also allows pure ARMv4 binaries to be built from the same ARMv4 objects.
6484
6485In the latter case, the switch @option{--fix-v4bx} must be passed to the
6486linker, which causes v4t @code{BX rM} instructions to be rewritten as
6487@code{MOV PC,rM}, since v4 processors do not have a @code{BX} instruction.
6488
6489In the former case, the switch should not be used, and @samp{R_ARM_V4BX}
6490relocations are ignored.
6491
845b51d6
PB
6492@cindex FIX_V4BX_INTERWORKING
6493@kindex --fix-v4bx-interworking
6494Replace @code{BX rM} instructions identified by @samp{R_ARM_V4BX}
6495relocations with a branch to the following veneer:
6496
6497@smallexample
6498TST rM, #1
6499MOVEQ PC, rM
6500BX Rn
6501@end smallexample
6502
6503This allows generation of libraries/applications that work on ARMv4 cores
6504and are still interworking safe. Note that the above veneer clobbers the
11e7fd74 6505condition flags, so may cause incorrect program behavior in rare cases.
845b51d6 6506
33bfe774
JB
6507@cindex USE_BLX
6508@kindex --use-blx
6509The @samp{--use-blx} switch enables the linker to use ARM/Thumb
6510BLX instructions (available on ARMv5t and above) in various
6511situations. Currently it is used to perform calls via the PLT from Thumb
6512code using BLX rather than using BX and a mode-switching stub before
6513each PLT entry. This should lead to such calls executing slightly faster.
6514
6515This option is enabled implicitly for SymbianOS, so there is no need to
6516specify it if you are using that target.
6517
c6dd86c6
JB
6518@cindex VFP11_DENORM_FIX
6519@kindex --vfp11-denorm-fix
6520The @samp{--vfp11-denorm-fix} switch enables a link-time workaround for a
6521bug in certain VFP11 coprocessor hardware, which sometimes allows
6522instructions with denorm operands (which must be handled by support code)
6523to have those operands overwritten by subsequent instructions before
6524the support code can read the intended values.
6525
6526The bug may be avoided in scalar mode if you allow at least one
6527intervening instruction between a VFP11 instruction which uses a register
6528and another instruction which writes to the same register, or at least two
6529intervening instructions if vector mode is in use. The bug only affects
6530full-compliance floating-point mode: you do not need this workaround if
6531you are using "runfast" mode. Please contact ARM for further details.
6532
6533If you know you are using buggy VFP11 hardware, you can
6534enable this workaround by specifying the linker option
6535@samp{--vfp-denorm-fix=scalar} if you are using the VFP11 scalar
6536mode only, or @samp{--vfp-denorm-fix=vector} if you are using
6537vector mode (the latter also works for scalar code). The default is
6538@samp{--vfp-denorm-fix=none}.
6539
6540If the workaround is enabled, instructions are scanned for
6541potentially-troublesome sequences, and a veneer is created for each
6542such sequence which may trigger the erratum. The veneer consists of the
6543first instruction of the sequence and a branch back to the subsequent
6544instruction. The original instruction is then replaced with a branch to
6545the veneer. The extra cycles required to call and return from the veneer
6546are sufficient to avoid the erratum in both the scalar and vector cases.
6547
2de70689
MGD
6548@cindex ARM1176 erratum workaround
6549@kindex --fix-arm1176
6550@kindex --no-fix-arm1176
9d5777a3
RM
6551The @samp{--fix-arm1176} switch enables a link-time workaround for an erratum
6552in certain ARM1176 processors. The workaround is enabled by default if you
6553are targeting ARM v6 (excluding ARM v6T2) or earlier. It can be disabled
2de70689
MGD
6554unconditionally by specifying @samp{--no-fix-arm1176}.
6555
9d5777a3 6556Further information is available in the ``ARM1176JZ-S and ARM1176JZF-S
11e7fd74 6557Programmer Advice Notice'' available on the ARM documentation website at:
2de70689
MGD
6558http://infocenter.arm.com/.
6559
bf21ed78
MS
6560@cindex NO_ENUM_SIZE_WARNING
6561@kindex --no-enum-size-warning
726150b7 6562The @option{--no-enum-size-warning} switch prevents the linker from
bf21ed78
MS
6563warning when linking object files that specify incompatible EABI
6564enumeration size attributes. For example, with this switch enabled,
6565linking of an object file using 32-bit enumeration values with another
6566using enumeration values fitted into the smallest possible space will
6567not be diagnosed.
a9dc9481
JM
6568
6569@cindex NO_WCHAR_SIZE_WARNING
6570@kindex --no-wchar-size-warning
6571The @option{--no-wchar-size-warning} switch prevents the linker from
6572warning when linking object files that specify incompatible EABI
6573@code{wchar_t} size attributes. For example, with this switch enabled,
6574linking of an object file using 32-bit @code{wchar_t} values with another
6575using 16-bit @code{wchar_t} values will not be diagnosed.
bf21ed78 6576
726150b7
NC
6577@cindex PIC_VENEER
6578@kindex --pic-veneer
6579The @samp{--pic-veneer} switch makes the linker use PIC sequences for
6580ARM/Thumb interworking veneers, even if the rest of the binary
6581is not PIC. This avoids problems on uClinux targets where
6582@samp{--emit-relocs} is used to generate relocatable binaries.
6583
6584@cindex STUB_GROUP_SIZE
6585@kindex --stub-group-size=@var{N}
6586The linker will automatically generate and insert small sequences of
6587code into a linked ARM ELF executable whenever an attempt is made to
6588perform a function call to a symbol that is too far away. The
6589placement of these sequences of instructions - called stubs - is
6590controlled by the command line option @option{--stub-group-size=N}.
6591The placement is important because a poor choice can create a need for
11e7fd74 6592duplicate stubs, increasing the code size. The linker will try to
726150b7
NC
6593group stubs together in order to reduce interruptions to the flow of
6594code, but it needs guidance as to how big these groups should be and
6595where they should be placed.
6596
6597The value of @samp{N}, the parameter to the
6598@option{--stub-group-size=} option controls where the stub groups are
07d72278 6599placed. If it is negative then all stubs are placed after the first
726150b7
NC
6600branch that needs them. If it is positive then the stubs can be
6601placed either before or after the branches that need them. If the
6602value of @samp{N} is 1 (either +1 or -1) then the linker will choose
6603exactly where to place groups of stubs, using its built in heuristics.
6604A value of @samp{N} greater than 1 (or smaller than -1) tells the
6605linker that a single group of stubs can service at most @samp{N} bytes
6606from the input sections.
6607
6608The default, if @option{--stub-group-size=} is not specified, is
6609@samp{N = +1}.
6610
1a51c1a4
NC
6611Farcalls stubs insertion is fully supported for the ARM-EABI target
6612only, because it relies on object files properties not present
6613otherwise.
6614
1db37fe6
YG
6615@cindex Cortex-A8 erratum workaround
6616@kindex --fix-cortex-a8
6617@kindex --no-fix-cortex-a8
6618The @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}.
6619
6620The erratum only affects Thumb-2 code. Please contact ARM for further details.
6621
68fcca92
JW
6622@cindex Cortex-A53 erratum 835769 workaround
6623@kindex --fix-cortex-a53-835769
6624@kindex --no-fix-cortex-a53-835769
6625The @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}.
6626
6627Please contact ARM for further details.
6628
1db37fe6
YG
6629@kindex --merge-exidx-entries
6630@kindex --no-merge-exidx-entries
6631@cindex Merging exidx entries
6632The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent exidx entries in debuginfo.
6633
6634@kindex --long-plt
6635@cindex 32-bit PLT entries
6636The @samp{--long-plt} option enables the use of 16 byte PLT entries
6637which support up to 4Gb of code. The default is to use 12 byte PLT
6638entries which only support 512Mb of code.
6639
36f63dca
NC
6640@ifclear GENERIC
6641@lowersections
6642@end ifclear
6643@end ifset
6644
6645@ifset HPPA
6646@ifclear GENERIC
6647@raisesections
6648@end ifclear
6649
6650@node HPPA ELF32
6651@section @command{ld} and HPPA 32-bit ELF Support
6652@cindex HPPA multiple sub-space stubs
6653@kindex --multi-subspace
6654When generating a shared library, @command{ld} will by default generate
6655import stubs suitable for use with a single sub-space application.
6656The @samp{--multi-subspace} switch causes @command{ld} to generate export
6657stubs, and different (larger) import stubs suitable for use with
6658multiple sub-spaces.
6659
6660@cindex HPPA stub grouping
6661@kindex --stub-group-size=@var{N}
6662Long branch stubs and import/export stubs are placed by @command{ld} in
6663stub sections located between groups of input sections.
6664@samp{--stub-group-size} specifies the maximum size of a group of input
6665sections handled by one stub section. Since branch offsets are signed,
6666a stub section may serve two groups of input sections, one group before
6667the stub section, and one group after it. However, when using
6668conditional branches that require stubs, it may be better (for branch
6669prediction) that stub sections only serve one group of input sections.
6670A negative value for @samp{N} chooses this scheme, ensuring that
6671branches to stubs always use a negative offset. Two special values of
6672@samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct
6673@command{ld} to automatically size input section groups for the branch types
6674detected, with the same behaviour regarding stub placement as other
6675positive or negative values of @samp{N} respectively.
6676
6677Note that @samp{--stub-group-size} does not split input sections. A
6678single input section larger than the group size specified will of course
6679create a larger group (of one section). If input sections are too
6680large, it may not be possible for a branch to reach its stub.
6681
6682@ifclear GENERIC
6683@lowersections
6684@end ifclear
6685@end ifset
6686
7fb9f789
NC
6687@ifset M68K
6688@ifclear GENERIC
6689@raisesections
6690@end ifclear
6691
6692@node M68K
6693@section @command{ld} and the Motorola 68K family
6694
6695@cindex Motorola 68K GOT generation
6696@kindex --got=@var{type}
6697The @samp{--got=@var{type}} option lets you choose the GOT generation scheme.
6698The choices are @samp{single}, @samp{negative}, @samp{multigot} and
6699@samp{target}. When @samp{target} is selected the linker chooses
6700the default GOT generation scheme for the current target.
6701@samp{single} tells the linker to generate a single GOT with
6702entries only at non-negative offsets.
6703@samp{negative} instructs the linker to generate a single GOT with
6704entries at both negative and positive offsets. Not all environments
6705support such GOTs.
6706@samp{multigot} allows the linker to generate several GOTs in the
6707output file. All GOT references from a single input object
6708file access the same GOT, but references from different input object
6709files might access different GOTs. Not all environments support such GOTs.
6710
6711@ifclear GENERIC
6712@lowersections
6713@end ifclear
6714@end ifset
6715
833794fc
MR
6716@ifset MIPS
6717@ifclear GENERIC
6718@raisesections
6719@end ifclear
6720
6721@node MIPS
6722@section @command{ld} and the MIPS family
6723
6724@cindex MIPS microMIPS instruction choice selection
6725@kindex --insn32
6726@kindex --no-insn32
6727The @samp{--insn32} and @samp{--no-insn32} options control the choice of
6728microMIPS instructions used in code generated by the linker, such as that
6729in the PLT or lazy binding stubs, or in relaxation. If @samp{--insn32} is
6730used, then the linker only uses 32-bit instruction encodings. By default
6731or if @samp{--no-insn32} is used, all instruction encodings are used,
6732including 16-bit ones where possible.
6733
6734@ifclear GENERIC
6735@lowersections
6736@end ifclear
6737@end ifset
6738
36f63dca
NC
6739@ifset MMIX
6740@ifclear GENERIC
6741@raisesections
6742@end ifclear
6743
6744@node MMIX
6745@section @code{ld} and MMIX
6746For MMIX, there is a choice of generating @code{ELF} object files or
6747@code{mmo} object files when linking. The simulator @code{mmix}
6748understands the @code{mmo} format. The binutils @code{objcopy} utility
6749can translate between the two formats.
6750
6751There is one special section, the @samp{.MMIX.reg_contents} section.
6752Contents in this section is assumed to correspond to that of global
6753registers, and symbols referring to it are translated to special symbols,
6754equal to registers. In a final link, the start address of the
6755@samp{.MMIX.reg_contents} section corresponds to the first allocated
6756global register multiplied by 8. Register @code{$255} is not included in
6757this section; it is always set to the program entry, which is at the
6758symbol @code{Main} for @code{mmo} files.
6759
7a2de473
HPN
6760Global symbols with the prefix @code{__.MMIX.start.}, for example
6761@code{__.MMIX.start..text} and @code{__.MMIX.start..data} are special.
6762The default linker script uses these to set the default start address
6763of a section.
36f63dca
NC
6764
6765Initial and trailing multiples of zero-valued 32-bit words in a section,
6766are left out from an mmo file.
6767
6768@ifclear GENERIC
6769@lowersections
6770@end ifclear
6771@end ifset
6772
6773@ifset MSP430
6774@ifclear GENERIC
6775@raisesections
6776@end ifclear
6777
6778@node MSP430
6779@section @code{ld} and MSP430
6780For the MSP430 it is possible to select the MPU architecture. The flag @samp{-m [mpu type]}
6781will select an appropriate linker script for selected MPU type. (To get a list of known MPUs
6782just pass @samp{-m help} option to the linker).
6783
6784@cindex MSP430 extra sections
6785The linker will recognize some extra sections which are MSP430 specific:
6786
6787@table @code
6788@item @samp{.vectors}
6789Defines a portion of ROM where interrupt vectors located.
6790
6791@item @samp{.bootloader}
6792Defines the bootloader portion of the ROM (if applicable). Any code
6793in this section will be uploaded to the MPU.
6794
6795@item @samp{.infomem}
6796Defines an information memory section (if applicable). Any code in
6797this section will be uploaded to the MPU.
6798
c0065db7 6799@item @samp{.infomemnobits}
36f63dca
NC
6800This is the same as the @samp{.infomem} section except that any code
6801in this section will not be uploaded to the MPU.
6802
6803@item @samp{.noinit}
6804Denotes a portion of RAM located above @samp{.bss} section.
6805
c0065db7 6806The last two sections are used by gcc.
36f63dca
NC
6807@end table
6808
6809@ifclear GENERIC
6810@lowersections
6811@end ifclear
6812@end ifset
6813
35c08157
KLC
6814@ifset NDS32
6815@ifclear GENERIC
6816@raisesections
6817@end ifclear
6818
6819@node NDS32
6820@section @code{ld} and NDS32
6821@kindex relaxing on NDS32
6822For NDS32, there are some options to select relaxation behavior. The linker
6823relaxes objects according to these options.
6824
6825@table @code
6826@item @samp{--m[no-]fp-as-gp}
6827Disable/enable fp-as-gp relaxation.
6828
6829@item @samp{--mexport-symbols=FILE}
6830Exporting symbols and their address into FILE as linker script.
6831
6832@item @samp{--m[no-]ex9}
6833Disable/enable link-time EX9 relaxation.
6834
6835@item @samp{--mexport-ex9=FILE}
6836Export the EX9 table after linking.
6837
6838@item @samp{--mimport-ex9=FILE}
6839Import the Ex9 table for EX9 relaxation.
6840
6841@item @samp{--mupdate-ex9}
6842Update the existing EX9 table.
6843
6844@item @samp{--mex9-limit=NUM}
6845Maximum number of entries in the ex9 table.
6846
6847@item @samp{--mex9-loop-aware}
6848Avoid generating the EX9 instruction inside the loop.
6849
6850@item @samp{--m[no-]ifc}
6851Disable/enable the link-time IFC optimization.
6852
6853@item @samp{--mifc-loop-aware}
6854Avoid generating the IFC instruction inside the loop.
6855@end table
6856
6857@ifclear GENERIC
6858@lowersections
6859@end ifclear
6860@end ifset
6861
78058a5e
SL
6862@ifset NIOSII
6863@ifclear GENERIC
6864@raisesections
6865@end ifclear
6866
6867@node Nios II
6868@section @command{ld} and the Altera Nios II
6869@cindex Nios II call relaxation
6870@kindex --relax on Nios II
6871
6872Call and immediate jump instructions on Nios II processors are limited to
6873transferring control to addresses in the same 256MB memory segment,
6874which may result in @command{ld} giving
6875@samp{relocation truncated to fit} errors with very large programs.
6876The command-line option @option{--relax} enables the generation of
6877trampolines that can access the entire 32-bit address space for calls
6878outside the normal @code{call} and @code{jmpi} address range. These
6879trampolines are inserted at section boundaries, so may not themselves
6880be reachable if an input section and its associated call trampolines are
6881larger than 256MB.
6882
6883The @option{--relax} option is enabled by default unless @option{-r}
6884is also specified. You can disable trampoline generation by using the
6885@option{--no-relax} linker option. You can also disable this optimization
6886locally by using the @samp{set .noat} directive in assembly-language
6887source files, as the linker-inserted trampolines use the @code{at}
6888register as a temporary.
6889
6890Note that the linker @option{--relax} option is independent of assembler
6891relaxation options, and that using the GNU assembler's @option{-relax-all}
6892option interferes with the linker's more selective call instruction relaxation.
6893
6894@ifclear GENERIC
6895@lowersections
6896@end ifclear
6897@end ifset
6898
2a60a7a8
AM
6899@ifset POWERPC
6900@ifclear GENERIC
6901@raisesections
6902@end ifclear
6903
6904@node PowerPC ELF32
6905@section @command{ld} and PowerPC 32-bit ELF Support
6906@cindex PowerPC long branches
6907@kindex --relax on PowerPC
6908Branches on PowerPC processors are limited to a signed 26-bit
6909displacement, which may result in @command{ld} giving
6910@samp{relocation truncated to fit} errors with very large programs.
6911@samp{--relax} enables the generation of trampolines that can access
6912the entire 32-bit address space. These trampolines are inserted at
6913section boundaries, so may not themselves be reachable if an input
c8a1f254
NS
6914section exceeds 33M in size. You may combine @samp{-r} and
6915@samp{--relax} to add trampolines in a partial link. In that case
6916both branches to undefined symbols and inter-section branches are also
6917considered potentially out of range, and trampolines inserted.
2a60a7a8
AM
6918
6919@cindex PowerPC ELF32 options
6920@table @option
6921@cindex PowerPC PLT
6922@kindex --bss-plt
6923@item --bss-plt
6924Current PowerPC GCC accepts a @samp{-msecure-plt} option that
6925generates code capable of using a newer PLT and GOT layout that has
6926the security advantage of no executable section ever needing to be
6927writable and no writable section ever being executable. PowerPC
6928@command{ld} will generate this layout, including stubs to access the
6929PLT, if all input files (including startup and static libraries) were
6930compiled with @samp{-msecure-plt}. @samp{--bss-plt} forces the old
6931BSS PLT (and GOT layout) which can give slightly better performance.
6932
016687f8
AM
6933@kindex --secure-plt
6934@item --secure-plt
6935@command{ld} will use the new PLT and GOT layout if it is linking new
6936@samp{-fpic} or @samp{-fPIC} code, but does not do so automatically
6937when linking non-PIC code. This option requests the new PLT and GOT
6938layout. A warning will be given if some object file requires the old
6939style BSS PLT.
6940
2a60a7a8
AM
6941@cindex PowerPC GOT
6942@kindex --sdata-got
6943@item --sdata-got
6944The new secure PLT and GOT are placed differently relative to other
6945sections compared to older BSS PLT and GOT placement. The location of
6946@code{.plt} must change because the new secure PLT is an initialized
6947section while the old PLT is uninitialized. The reason for the
6948@code{.got} change is more subtle: The new placement allows
6949@code{.got} to be read-only in applications linked with
6950@samp{-z relro -z now}. However, this placement means that
6951@code{.sdata} cannot always be used in shared libraries, because the
6952PowerPC ABI accesses @code{.sdata} in shared libraries from the GOT
6953pointer. @samp{--sdata-got} forces the old GOT placement. PowerPC
6954GCC doesn't use @code{.sdata} in shared libraries, so this option is
6955really only useful for other compilers that may do so.
6956
6957@cindex PowerPC stub symbols
6958@kindex --emit-stub-syms
6959@item --emit-stub-syms
6960This option causes @command{ld} to label linker stubs with a local
6961symbol that encodes the stub type and destination.
6962
6963@cindex PowerPC TLS optimization
6964@kindex --no-tls-optimize
6965@item --no-tls-optimize
6966PowerPC @command{ld} normally performs some optimization of code
6967sequences used to access Thread-Local Storage. Use this option to
6968disable the optimization.
6969@end table
6970
6971@ifclear GENERIC
6972@lowersections
6973@end ifclear
6974@end ifset
6975
6976@ifset POWERPC64
6977@ifclear GENERIC
6978@raisesections
6979@end ifclear
6980
6981@node PowerPC64 ELF64
6982@section @command{ld} and PowerPC64 64-bit ELF Support
6983
6984@cindex PowerPC64 ELF64 options
6985@table @option
6986@cindex PowerPC64 stub grouping
6987@kindex --stub-group-size
6988@item --stub-group-size
6989Long branch stubs, PLT call stubs and TOC adjusting stubs are placed
6990by @command{ld} in stub sections located between groups of input sections.
6991@samp{--stub-group-size} specifies the maximum size of a group of input
6992sections handled by one stub section. Since branch offsets are signed,
6993a stub section may serve two groups of input sections, one group before
6994the stub section, and one group after it. However, when using
6995conditional branches that require stubs, it may be better (for branch
6996prediction) that stub sections only serve one group of input sections.
6997A negative value for @samp{N} chooses this scheme, ensuring that
6998branches to stubs always use a negative offset. Two special values of
6999@samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct
7000@command{ld} to automatically size input section groups for the branch types
7001detected, with the same behaviour regarding stub placement as other
7002positive or negative values of @samp{N} respectively.
7003
7004Note that @samp{--stub-group-size} does not split input sections. A
7005single input section larger than the group size specified will of course
7006create a larger group (of one section). If input sections are too
7007large, it may not be possible for a branch to reach its stub.
7008
7009@cindex PowerPC64 stub symbols
7010@kindex --emit-stub-syms
7011@item --emit-stub-syms
7012This option causes @command{ld} to label linker stubs with a local
7013symbol that encodes the stub type and destination.
7014
7015@cindex PowerPC64 dot symbols
7016@kindex --dotsyms
7017@kindex --no-dotsyms
7018@item --dotsyms, --no-dotsyms
7019These two options control how @command{ld} interprets version patterns
7020in a version script. Older PowerPC64 compilers emitted both a
7021function descriptor symbol with the same name as the function, and a
7022code entry symbol with the name prefixed by a dot (@samp{.}). To
7023properly version a function @samp{foo}, the version script thus needs
7024to control both @samp{foo} and @samp{.foo}. The option
7025@samp{--dotsyms}, on by default, automatically adds the required
7026dot-prefixed patterns. Use @samp{--no-dotsyms} to disable this
7027feature.
7028
7029@cindex PowerPC64 TLS optimization
7030@kindex --no-tls-optimize
7031@item --no-tls-optimize
7032PowerPC64 @command{ld} normally performs some optimization of code
7033sequences used to access Thread-Local Storage. Use this option to
7034disable the optimization.
7035
7036@cindex PowerPC64 OPD optimization
7037@kindex --no-opd-optimize
7038@item --no-opd-optimize
7039PowerPC64 @command{ld} normally removes @code{.opd} section entries
7040corresponding to deleted link-once functions, or functions removed by
e7fc76dd 7041the action of @samp{--gc-sections} or linker script @code{/DISCARD/}.
2a60a7a8
AM
7042Use this option to disable @code{.opd} optimization.
7043
7044@cindex PowerPC64 OPD spacing
7045@kindex --non-overlapping-opd
7046@item --non-overlapping-opd
7047Some PowerPC64 compilers have an option to generate compressed
7048@code{.opd} entries spaced 16 bytes apart, overlapping the third word,
7049the static chain pointer (unused in C) with the first word of the next
7050entry. This option expands such entries to the full 24 bytes.
7051
7052@cindex PowerPC64 TOC optimization
7053@kindex --no-toc-optimize
7054@item --no-toc-optimize
7055PowerPC64 @command{ld} normally removes unused @code{.toc} section
7056entries. Such entries are detected by examining relocations that
7057reference the TOC in code sections. A reloc in a deleted code section
7058marks a TOC word as unneeded, while a reloc in a kept code section
7059marks a TOC word as needed. Since the TOC may reference itself, TOC
7060relocs are also examined. TOC words marked as both needed and
7061unneeded will of course be kept. TOC words without any referencing
7062reloc are assumed to be part of a multi-word entry, and are kept or
7063discarded as per the nearest marked preceding word. This works
7064reliably for compiler generated code, but may be incorrect if assembly
7065code is used to insert TOC entries. Use this option to disable the
7066optimization.
7067
7068@cindex PowerPC64 multi-TOC
7069@kindex --no-multi-toc
7070@item --no-multi-toc
794e51c0
AM
7071If given any toc option besides @code{-mcmodel=medium} or
7072@code{-mcmodel=large}, PowerPC64 GCC generates code for a TOC model
7073where TOC
2a60a7a8
AM
7074entries are accessed with a 16-bit offset from r2. This limits the
7075total TOC size to 64K. PowerPC64 @command{ld} extends this limit by
7076grouping code sections such that each group uses less than 64K for its
7077TOC entries, then inserts r2 adjusting stubs between inter-group
7078calls. @command{ld} does not split apart input sections, so cannot
7079help if a single input file has a @code{.toc} section that exceeds
708064K, most likely from linking multiple files with @command{ld -r}.
7081Use this option to turn off this feature.
794e51c0
AM
7082
7083@cindex PowerPC64 TOC sorting
7084@kindex --no-toc-sort
7085@item --no-toc-sort
7086By default, @command{ld} sorts TOC sections so that those whose file
7087happens to have a section called @code{.init} or @code{.fini} are
7088placed first, followed by TOC sections referenced by code generated
7089with PowerPC64 gcc's @code{-mcmodel=small}, and lastly TOC sections
7090referenced only by code generated with PowerPC64 gcc's
7091@code{-mcmodel=medium} or @code{-mcmodel=large} options. Doing this
7092results in better TOC grouping for multi-TOC. Use this option to turn
7093off this feature.
7094
7095@cindex PowerPC64 PLT stub alignment
7096@kindex --plt-align
7097@kindex --no-plt-align
7098@item --plt-align
7099@itemx --no-plt-align
7100Use these options to control whether individual PLT call stubs are
e05fa0ba
AM
7101padded so that they don't cross a 32-byte boundary, or to the
7102specified power of two boundary when using @code{--plt-align=}. Note
7103that this isn't alignment in the usual sense. By default PLT call
7104stubs are packed tightly.
794e51c0
AM
7105
7106@cindex PowerPC64 PLT call stub static chain
7107@kindex --plt-static-chain
7108@kindex --no-plt-static-chain
7109@item --plt-static-chain
7110@itemx --no-plt-static-chain
7111Use these options to control whether PLT call stubs load the static
7112chain pointer (r11). @code{ld} defaults to not loading the static
7113chain since there is never any need to do so on a PLT call.
7114
7115@cindex PowerPC64 PLT call stub thread safety
7116@kindex --plt-thread-safe
7117@kindex --no-plt-thread-safe
7118@item --plt-thread-safe
7119@itemx --no-thread-safe
7120With power7's weakly ordered memory model, it is possible when using
7121lazy binding for ld.so to update a plt entry in one thread and have
7122another thread see the individual plt entry words update in the wrong
7123order, despite ld.so carefully writing in the correct order and using
7124memory write barriers. To avoid this we need some sort of read
7125barrier in the call stub, or use LD_BIND_NOW=1. By default, @code{ld}
7126looks for calls to commonly used functions that create threads, and if
7127seen, adds the necessary barriers. Use these options to change the
7128default behaviour.
2a60a7a8
AM
7129@end table
7130
7131@ifclear GENERIC
7132@lowersections
7133@end ifclear
7134@end ifset
7135
49fa1e15
AM
7136@ifset SPU
7137@ifclear GENERIC
7138@raisesections
7139@end ifclear
7140
7141@node SPU ELF
7142@section @command{ld} and SPU ELF Support
7143
7144@cindex SPU ELF options
7145@table @option
7146
7147@cindex SPU plugins
7148@kindex --plugin
7149@item --plugin
7150This option marks an executable as a PIC plugin module.
7151
7152@cindex SPU overlays
7153@kindex --no-overlays
7154@item --no-overlays
7155Normally, @command{ld} recognizes calls to functions within overlay
7156regions, and redirects such calls to an overlay manager via a stub.
7157@command{ld} also provides a built-in overlay manager. This option
7158turns off all this special overlay handling.
7159
7160@cindex SPU overlay stub symbols
7161@kindex --emit-stub-syms
7162@item --emit-stub-syms
7163This option causes @command{ld} to label overlay stubs with a local
7164symbol that encodes the stub type and destination.
7165
7166@cindex SPU extra overlay stubs
7167@kindex --extra-overlay-stubs
7168@item --extra-overlay-stubs
7169This option causes @command{ld} to add overlay call stubs on all
7170function calls out of overlay regions. Normally stubs are not added
7171on calls to non-overlay regions.
7172
7173@cindex SPU local store size
7174@kindex --local-store=lo:hi
7175@item --local-store=lo:hi
7176@command{ld} usually checks that a final executable for SPU fits in
7177the address range 0 to 256k. This option may be used to change the
7178range. Disable the check entirely with @option{--local-store=0:0}.
7179
c0065db7 7180@cindex SPU
49fa1e15
AM
7181@kindex --stack-analysis
7182@item --stack-analysis
7183SPU local store space is limited. Over-allocation of stack space
7184unnecessarily limits space available for code and data, while
7185under-allocation results in runtime failures. If given this option,
7186@command{ld} will provide an estimate of maximum stack usage.
7187@command{ld} does this by examining symbols in code sections to
7188determine the extents of functions, and looking at function prologues
7189for stack adjusting instructions. A call-graph is created by looking
7190for relocations on branch instructions. The graph is then searched
7191for the maximum stack usage path. Note that this analysis does not
7192find calls made via function pointers, and does not handle recursion
7193and other cycles in the call graph. Stack usage may be
7194under-estimated if your code makes such calls. Also, stack usage for
7195dynamic allocation, e.g. alloca, will not be detected. If a link map
7196is requested, detailed information about each function's stack usage
7197and calls will be given.
7198
c0065db7 7199@cindex SPU
49fa1e15
AM
7200@kindex --emit-stack-syms
7201@item --emit-stack-syms
7202This option, if given along with @option{--stack-analysis} will result
7203in @command{ld} emitting stack sizing symbols for each function.
7204These take the form @code{__stack_<function_name>} for global
7205functions, and @code{__stack_<number>_<function_name>} for static
7206functions. @code{<number>} is the section id in hex. The value of
7207such symbols is the stack requirement for the corresponding function.
7208The symbol size will be zero, type @code{STT_NOTYPE}, binding
c0065db7 7209@code{STB_LOCAL}, and section @code{SHN_ABS}.
49fa1e15
AM
7210@end table
7211
7212@ifclear GENERIC
7213@lowersections
7214@end ifclear
7215@end ifset
7216
36f63dca
NC
7217@ifset TICOFF
7218@ifclear GENERIC
7219@raisesections
7220@end ifclear
7221
7222@node TI COFF
7223@section @command{ld}'s Support for Various TI COFF Versions
7224@cindex TI COFF versions
7225@kindex --format=@var{version}
7226The @samp{--format} switch allows selection of one of the various
7227TI COFF versions. The latest of this writing is 2; versions 0 and 1 are
7228also supported. The TI COFF versions also vary in header byte-order
7229format; @command{ld} will read any version or byte order, but the output
7230header format depends on the default specified by the specific target.
7231
7232@ifclear GENERIC
7233@lowersections
7234@end ifclear
7235@end ifset
7236
2ca22b03
NC
7237@ifset WIN32
7238@ifclear GENERIC
7239@raisesections
7240@end ifclear
7241
7242@node WIN32
7243@section @command{ld} and WIN32 (cygwin/mingw)
7244
c0065db7 7245This section describes some of the win32 specific @command{ld} issues.
b45619c0 7246See @ref{Options,,Command Line Options} for detailed description of the
dc8465bf 7247command line options mentioned here.
2ca22b03
NC
7248
7249@table @emph
c0065db7
RM
7250@cindex import libraries
7251@item import libraries
69da35b5 7252The standard Windows linker creates and uses so-called import
2ca22b03 7253libraries, which contains information for linking to dll's. They are
69da35b5
NC
7254regular static archives and are handled as any other static
7255archive. The cygwin and mingw ports of @command{ld} have specific
2ca22b03
NC
7256support for creating such libraries provided with the
7257@samp{--out-implib} command line option.
7258
c0065db7
RM
7259@item exporting DLL symbols
7260@cindex exporting DLL symbols
dc8465bf
NC
7261The cygwin/mingw @command{ld} has several ways to export symbols for dll's.
7262
7263@table @emph
7264@item using auto-export functionality
7265@cindex using auto-export functionality
7266By default @command{ld} exports symbols with the auto-export functionality,
7267which is controlled by the following command line options:
7268
0a5d968e
NC
7269@itemize
7270@item --export-all-symbols [This is the default]
7271@item --exclude-symbols
7272@item --exclude-libs
e1c37eb5 7273@item --exclude-modules-for-implib
09e2aba4 7274@item --version-script
0a5d968e
NC
7275@end itemize
7276
09e2aba4
DK
7277When auto-export is in operation, @command{ld} will export all the non-local
7278(global and common) symbols it finds in a DLL, with the exception of a few
7279symbols known to belong to the system's runtime and libraries. As it will
7280often not be desirable to export all of a DLL's symbols, which may include
7281private functions that are not part of any public interface, the command-line
9d5777a3 7282options listed above may be used to filter symbols out from the list for
09e2aba4
DK
7283exporting. The @samp{--output-def} option can be used in order to see the
7284final list of exported symbols with all exclusions taken into effect.
7285
7286If @samp{--export-all-symbols} is not given explicitly on the
0a5d968e
NC
7287command line, then the default auto-export behavior will be @emph{disabled}
7288if either of the following are true:
7289
7290@itemize
7291@item A DEF file is used.
7292@item Any symbol in any object file was marked with the __declspec(dllexport) attribute.
7293@end itemize
dc8465bf 7294
c0065db7
RM
7295@item using a DEF file
7296@cindex using a DEF file
dc8465bf
NC
7297Another way of exporting symbols is using a DEF file. A DEF file is
7298an ASCII file containing definitions of symbols which should be
7299exported when a dll is created. Usually it is named @samp{<dll
7300name>.def} and is added as any other object file to the linker's
0a5d968e 7301command line. The file's name must end in @samp{.def} or @samp{.DEF}.
dc8465bf
NC
7302
7303@example
7304gcc -o <output> <objectfiles> <dll name>.def
7305@end example
7306
0a5d968e
NC
7307Using a DEF file turns off the normal auto-export behavior, unless the
7308@samp{--export-all-symbols} option is also used.
7309
dc8465bf
NC
7310Here is an example of a DEF file for a shared library called @samp{xyz.dll}:
7311
7312@example
4b5bd4e7 7313LIBRARY "xyz.dll" BASE=0x20000000
dc8465bf
NC
7314
7315EXPORTS
7316foo
7317bar
7318_bar = bar
4b5bd4e7
DS
7319another_foo = abc.dll.afoo
7320var1 DATA
7fcab871
KT
7321doo = foo == foo2
7322eoo DATA == var1
c0065db7 7323@end example
dc8465bf 7324
7fcab871 7325This example defines a DLL with a non-default base address and seven
4b5bd4e7
DS
7326symbols in the export table. The third exported symbol @code{_bar} is an
7327alias for the second. The fourth symbol, @code{another_foo} is resolved
7328by "forwarding" to another module and treating it as an alias for
7329@code{afoo} exported from the DLL @samp{abc.dll}. The final symbol
7fcab871
KT
7330@code{var1} is declared to be a data object. The @samp{doo} symbol in
7331export library is an alias of @samp{foo}, which gets the string name
7332in export table @samp{foo2}. The @samp{eoo} symbol is an data export
7333symbol, which gets in export table the name @samp{var1}.
4b5bd4e7 7334
6b31ad16
DS
7335The optional @code{LIBRARY <name>} command indicates the @emph{internal}
7336name of the output DLL. If @samp{<name>} does not include a suffix,
7337the default library suffix, @samp{.DLL} is appended.
7338
b45619c0
NC
7339When the .DEF file is used to build an application, rather than a
7340library, the @code{NAME <name>} command should be used instead of
6b31ad16 7341@code{LIBRARY}. If @samp{<name>} does not include a suffix, the default
c0065db7 7342executable suffix, @samp{.EXE} is appended.
6b31ad16
DS
7343
7344With either @code{LIBRARY <name>} or @code{NAME <name>} the optional
7345specification @code{BASE = <number>} may be used to specify a
c0065db7 7346non-default base address for the image.
6b31ad16
DS
7347
7348If neither @code{LIBRARY <name>} nor @code{NAME <name>} is specified,
a2877985
DS
7349or they specify an empty string, the internal name is the same as the
7350filename specified on the command line.
6b31ad16 7351
4b5bd4e7
DS
7352The complete specification of an export symbol is:
7353
7354@example
7355EXPORTS
7356 ( ( ( <name1> [ = <name2> ] )
7357 | ( <name1> = <module-name> . <external-name>))
7fcab871 7358 [ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] [== <name3>] ) *
c0065db7 7359@end example
4b5bd4e7
DS
7360
7361Declares @samp{<name1>} as an exported symbol from the DLL, or declares
7362@samp{<name1>} as an exported alias for @samp{<name2>}; or declares
7363@samp{<name1>} as a "forward" alias for the symbol
7364@samp{<external-name>} in the DLL @samp{<module-name>}.
7365Optionally, the symbol may be exported by the specified ordinal
7fcab871
KT
7366@samp{<integer>} alias. The optional @samp{<name3>} is the to be used
7367string in import/export table for the symbol.
4b5bd4e7
DS
7368
7369The optional keywords that follow the declaration indicate:
7370
7371@code{NONAME}: Do not put the symbol name in the DLL's export table. It
7372will still be exported by its ordinal alias (either the value specified
7373by the .def specification or, otherwise, the value assigned by the
7374linker). The symbol name, however, does remain visible in the import
7375library (if any), unless @code{PRIVATE} is also specified.
7376
7377@code{DATA}: The symbol is a variable or object, rather than a function.
7378The import lib will export only an indirect reference to @code{foo} as
7379the symbol @code{_imp__foo} (ie, @code{foo} must be resolved as
7380@code{*_imp__foo}).
7381
7382@code{CONSTANT}: Like @code{DATA}, but put the undecorated @code{foo} as
7383well as @code{_imp__foo} into the import library. Both refer to the
7384read-only import address table's pointer to the variable, not to the
7385variable itself. This can be dangerous. If the user code fails to add
7386the @code{dllimport} attribute and also fails to explicitly add the
7387extra indirection that the use of the attribute enforces, the
7388application will behave unexpectedly.
7389
7390@code{PRIVATE}: Put the symbol in the DLL's export table, but do not put
7391it into the static import library used to resolve imports at link time. The
7392symbol can still be imported using the @code{LoadLibrary/GetProcAddress}
7393API at runtime or by by using the GNU ld extension of linking directly to
7394the DLL without an import library.
c0065db7 7395
4b5bd4e7
DS
7396See ld/deffilep.y in the binutils sources for the full specification of
7397other DEF file statements
dc8465bf
NC
7398
7399@cindex creating a DEF file
7400While linking a shared dll, @command{ld} is able to create a DEF file
7401with the @samp{--output-def <file>} command line option.
0a5d968e
NC
7402
7403@item Using decorations
7404@cindex Using decorations
7405Another way of marking symbols for export is to modify the source code
7406itself, so that when building the DLL each symbol to be exported is
7407declared as:
7408
7409@example
7410__declspec(dllexport) int a_variable
7411__declspec(dllexport) void a_function(int with_args)
7412@end example
7413
7414All such symbols will be exported from the DLL. If, however,
7415any of the object files in the DLL contain symbols decorated in
7416this way, then the normal auto-export behavior is disabled, unless
7417the @samp{--export-all-symbols} option is also used.
7418
7419Note that object files that wish to access these symbols must @emph{not}
c0065db7 7420decorate them with dllexport. Instead, they should use dllimport,
0a5d968e
NC
7421instead:
7422
7423@example
7424__declspec(dllimport) int a_variable
7425__declspec(dllimport) void a_function(int with_args)
7426@end example
7427
c0065db7
RM
7428This complicates the structure of library header files, because
7429when included by the library itself the header must declare the
0a5d968e
NC
7430variables and functions as dllexport, but when included by client
7431code the header must declare them as dllimport. There are a number
c0065db7 7432of idioms that are typically used to do this; often client code can
0a5d968e
NC
7433omit the __declspec() declaration completely. See
7434@samp{--enable-auto-import} and @samp{automatic data imports} for more
b45619c0 7435information.
c0065db7 7436@end table
dc8465bf 7437
2ca22b03
NC
7438@cindex automatic data imports
7439@item automatic data imports
7440The standard Windows dll format supports data imports from dlls only
69da35b5 7441by adding special decorations (dllimport/dllexport), which let the
2ca22b03 7442compiler produce specific assembler instructions to deal with this
c0065db7 7443issue. This increases the effort necessary to port existing Un*x
69da35b5 7444code to these platforms, especially for large
2ca22b03 7445c++ libraries and applications. The auto-import feature, which was
c0065db7 7446initially provided by Paul Sokolovsky, allows one to omit the
b45619c0 7447decorations to achieve a behavior that conforms to that on POSIX/Un*x
c0065db7 7448platforms. This feature is enabled with the @samp{--enable-auto-import}
69da35b5
NC
7449command-line option, although it is enabled by default on cygwin/mingw.
7450The @samp{--enable-auto-import} option itself now serves mainly to
7451suppress any warnings that are ordinarily emitted when linked objects
7452trigger the feature's use.
7453
c0065db7 7454auto-import of variables does not always work flawlessly without
69da35b5
NC
7455additional assistance. Sometimes, you will see this message
7456
c0065db7 7457"variable '<var>' can't be auto-imported. Please read the
69da35b5
NC
7458documentation for ld's @code{--enable-auto-import} for details."
7459
c0065db7
RM
7460The @samp{--enable-auto-import} documentation explains why this error
7461occurs, and several methods that can be used to overcome this difficulty.
7462One of these methods is the @emph{runtime pseudo-relocs} feature, described
69da35b5
NC
7463below.
7464
7465@cindex runtime pseudo-relocation
c0065db7
RM
7466For complex variables imported from DLLs (such as structs or classes),
7467object files typically contain a base address for the variable and an
7468offset (@emph{addend}) within the variable--to specify a particular
7469field or public member, for instance. Unfortunately, the runtime loader used
7470in win32 environments is incapable of fixing these references at runtime
69da35b5 7471without the additional information supplied by dllimport/dllexport decorations.
c0065db7 7472The standard auto-import feature described above is unable to resolve these
69da35b5
NC
7473references.
7474
c0065db7
RM
7475The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
7476be resolved without error, while leaving the task of adjusting the references
7477themselves (with their non-zero addends) to specialized code provided by the
7478runtime environment. Recent versions of the cygwin and mingw environments and
7479compilers provide this runtime support; older versions do not. However, the
7480support is only necessary on the developer's platform; the compiled result will
69da35b5
NC
7481run without error on an older system.
7482
c0065db7
RM
7483@samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
7484enabled as needed.
2ca22b03
NC
7485
7486@cindex direct linking to a dll
7487@item direct linking to a dll
7488The cygwin/mingw ports of @command{ld} support the direct linking,
7489including data symbols, to a dll without the usage of any import
69da35b5 7490libraries. This is much faster and uses much less memory than does the
b45619c0 7491traditional import library method, especially when linking large
c0065db7
RM
7492libraries or applications. When @command{ld} creates an import lib, each
7493function or variable exported from the dll is stored in its own bfd, even
7494though a single bfd could contain many exports. The overhead involved in
69da35b5 7495storing, loading, and processing so many bfd's is quite large, and explains the
c0065db7 7496tremendous time, memory, and storage needed to link against particularly
69da35b5
NC
7497large or complex libraries when using import libs.
7498
c0065db7 7499Linking directly to a dll uses no extra command-line switches other than
69da35b5 7500@samp{-L} and @samp{-l}, because @command{ld} already searches for a number
c0065db7 7501of names to match each library. All that is needed from the developer's
69da35b5
NC
7502perspective is an understanding of this search, in order to force ld to
7503select the dll instead of an import library.
7504
2ca22b03 7505
69da35b5
NC
7506For instance, when ld is called with the argument @samp{-lxxx} it will attempt
7507to find, in the first directory of its search path,
2ca22b03
NC
7508
7509@example
45e948fe
NC
7510libxxx.dll.a
7511xxx.dll.a
7512libxxx.a
7513xxx.lib
69da35b5 7514cygxxx.dll (*)
45e948fe
NC
7515libxxx.dll
7516xxx.dll
2ca22b03
NC
7517@end example
7518
69da35b5
NC
7519before moving on to the next directory in the search path.
7520
c0065db7
RM
7521(*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
7522where @samp{<prefix>} is set by the @command{ld} option
7523@samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
7524file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
69da35b5
NC
7525@samp{cygxxx.dll}.
7526
c0065db7
RM
7527Other win32-based unix environments, such as mingw or pw32, may use other
7528@samp{<prefix>}es, although at present only cygwin makes use of this feature. It
69da35b5
NC
7529was originally intended to help avoid name conflicts among dll's built for the
7530various win32/un*x environments, so that (for example) two versions of a zlib dll
7531could coexist on the same machine.
7532
2ca22b03
NC
7533The generic cygwin/mingw path layout uses a @samp{bin} directory for
7534applications and dll's and a @samp{lib} directory for the import
69da35b5 7535libraries (using cygwin nomenclature):
2ca22b03
NC
7536
7537@example
7538bin/
7539 cygxxx.dll
7540lib/
7541 libxxx.dll.a (in case of dll's)
c0065db7 7542 libxxx.a (in case of static archive)
2ca22b03
NC
7543@end example
7544
c0065db7
RM
7545Linking directly to a dll without using the import library can be
7546done two ways:
2ca22b03
NC
7547
75481. Use the dll directly by adding the @samp{bin} path to the link line
7549@example
7550gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx
c0065db7 7551@end example
2ca22b03 7552
69da35b5
NC
7553However, as the dll's often have version numbers appended to their names
7554(@samp{cygncurses-5.dll}) this will often fail, unless one specifies
7555@samp{-L../bin -lncurses-5} to include the version. Import libs are generally
7556not versioned, and do not have this difficulty.
7557
2ca22b03
NC
75582. Create a symbolic link from the dll to a file in the @samp{lib}
7559directory according to the above mentioned search pattern. This
7560should be used to avoid unwanted changes in the tools needed for
7561making the app/dll.
7562
7563@example
7564ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a]
c0065db7 7565@end example
2ca22b03
NC
7566
7567Then you can link without any make environment changes.
7568
7569@example
7570gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx
c0065db7 7571@end example
69da35b5
NC
7572
7573This technique also avoids the version number problems, because the following is
7574perfectly legal
7575
7576@example
7577bin/
7578 cygxxx-5.dll
7579lib/
c0065db7 7580 libxxx.dll.a -> ../bin/cygxxx-5.dll
69da35b5
NC
7581@end example
7582
dc8465bf 7583Linking directly to a dll without using an import lib will work
69da35b5
NC
7584even when auto-import features are exercised, and even when
7585@samp{--enable-runtime-pseudo-relocs} is used.
7586
7587Given the improvements in speed and memory usage, one might justifiably
45e948fe 7588wonder why import libraries are used at all. There are three reasons:
69da35b5
NC
7589
75901. Until recently, the link-directly-to-dll functionality did @emph{not}
7591work with auto-imported data.
7592
dc8465bf
NC
75932. Sometimes it is necessary to include pure static objects within the
7594import library (which otherwise contains only bfd's for indirection
7595symbols that point to the exports of a dll). Again, the import lib
7596for the cygwin kernel makes use of this ability, and it is not
7597possible to do this without an import lib.
69da35b5 7598
45e948fe
NC
75993. Symbol aliases can only be resolved using an import lib. This is
7600critical when linking against OS-supplied dll's (eg, the win32 API)
7601in which symbols are usually exported as undecorated aliases of their
7602stdcall-decorated assembly names.
7603
69da35b5 7604So, import libs are not going away. But the ability to replace
c0065db7
RM
7605true import libs with a simple symbolic link to (or a copy of)
7606a dll, in many cases, is a useful addition to the suite of tools
7607binutils makes available to the win32 developer. Given the
69da35b5
NC
7608massive improvements in memory requirements during linking, storage
7609requirements, and linking speed, we expect that many developers
7610will soon begin to use this feature whenever possible.
dc8465bf 7611
c0065db7 7612@item symbol aliasing
dc8465bf 7613@table @emph
c0065db7
RM
7614@item adding additional names
7615Sometimes, it is useful to export symbols with additional names.
dc8465bf
NC
7616A symbol @samp{foo} will be exported as @samp{foo}, but it can also be
7617exported as @samp{_foo} by using special directives in the DEF file
7618when creating the dll. This will affect also the optional created
c0065db7 7619import library. Consider the following DEF file:
dc8465bf 7620
c0065db7 7621@example
dc8465bf
NC
7622LIBRARY "xyz.dll" BASE=0x61000000
7623
7624EXPORTS
c0065db7 7625foo
dc8465bf 7626_foo = foo
c0065db7 7627@end example
dc8465bf
NC
7628
7629The line @samp{_foo = foo} maps the symbol @samp{foo} to @samp{_foo}.
7630
7631Another method for creating a symbol alias is to create it in the
7632source code using the "weak" attribute:
7633
c0065db7
RM
7634@example
7635void foo () @{ /* Do something. */; @}
dc8465bf 7636void _foo () __attribute__ ((weak, alias ("foo")));
c0065db7 7637@end example
dc8465bf
NC
7638
7639See the gcc manual for more information about attributes and weak
7640symbols.
7641
7642@item renaming symbols
7643Sometimes it is useful to rename exports. For instance, the cygwin
c0065db7 7644kernel does this regularly. A symbol @samp{_foo} can be exported as
dc8465bf
NC
7645@samp{foo} but not as @samp{_foo} by using special directives in the
7646DEF file. (This will also affect the import library, if it is
c0065db7 7647created). In the following example:
dc8465bf 7648
c0065db7 7649@example
dc8465bf
NC
7650LIBRARY "xyz.dll" BASE=0x61000000
7651
7652EXPORTS
7653_foo = foo
c0065db7 7654@end example
dc8465bf
NC
7655
7656The line @samp{_foo = foo} maps the exported symbol @samp{foo} to
7657@samp{_foo}.
c0065db7 7658@end table
dc8465bf 7659
0a5d968e 7660Note: using a DEF file disables the default auto-export behavior,
c0065db7 7661unless the @samp{--export-all-symbols} command line option is used.
0a5d968e 7662If, however, you are trying to rename symbols, then you should list
c0065db7
RM
7663@emph{all} desired exports in the DEF file, including the symbols
7664that are not being renamed, and do @emph{not} use the
7665@samp{--export-all-symbols} option. If you list only the
7666renamed symbols in the DEF file, and use @samp{--export-all-symbols}
7667to handle the other symbols, then the both the new names @emph{and}
7668the original names for the renamed symbols will be exported.
7669In effect, you'd be aliasing those symbols, not renaming them,
0a5d968e 7670which is probably not what you wanted.
c87db184
CF
7671
7672@cindex weak externals
7673@item weak externals
7674The Windows object format, PE, specifies a form of weak symbols called
7675weak externals. When a weak symbol is linked and the symbol is not
7676defined, the weak symbol becomes an alias for some other symbol. There
7677are three variants of weak externals:
7678@itemize
7679@item Definition is searched for in objects and libraries, historically
7680called lazy externals.
7681@item Definition is searched for only in other objects, not in libraries.
7682This form is not presently implemented.
7683@item No search; the symbol is an alias. This form is not presently
7684implemented.
7685@end itemize
7686As a GNU extension, weak symbols that do not specify an alternate symbol
7687are supported. If the symbol is undefined when linking, the symbol
7688uses a default value.
c1711530
DK
7689
7690@cindex aligned common symbols
7691@item aligned common symbols
7692As a GNU extension to the PE file format, it is possible to specify the
7693desired alignment for a common symbol. This information is conveyed from
7694the assembler or compiler to the linker by means of GNU-specific commands
7695carried in the object file's @samp{.drectve} section, which are recognized
7696by @command{ld} and respected when laying out the common symbols. Native
7697tools will be able to process object files employing this GNU extension,
7698but will fail to respect the alignment instructions, and may issue noisy
7699warnings about unknown linker directives.
5063daf7 7700
2ca22b03
NC
7701@end table
7702
7703@ifclear GENERIC
7704@lowersections
7705@end ifclear
7706@end ifset
7707
e0001a05
NC
7708@ifset XTENSA
7709@ifclear GENERIC
7710@raisesections
7711@end ifclear
7712
7713@node Xtensa
7714@section @code{ld} and Xtensa Processors
7715
7716@cindex Xtensa processors
7717The default @command{ld} behavior for Xtensa processors is to interpret
7718@code{SECTIONS} commands so that lists of explicitly named sections in a
7719specification with a wildcard file will be interleaved when necessary to
7720keep literal pools within the range of PC-relative load offsets. For
7721example, with the command:
7722
7723@smallexample
7724SECTIONS
7725@{
7726 .text : @{
7727 *(.literal .text)
7728 @}
7729@}
7730@end smallexample
7731
7732@noindent
7733@command{ld} may interleave some of the @code{.literal}
7734and @code{.text} sections from different object files to ensure that the
7735literal pools are within the range of PC-relative load offsets. A valid
7736interleaving might place the @code{.literal} sections from an initial
7737group of files followed by the @code{.text} sections of that group of
7738files. Then, the @code{.literal} sections from the rest of the files
7739and the @code{.text} sections from the rest of the files would follow.
e0001a05 7740
43cd72b9 7741@cindex @option{--relax} on Xtensa
e0001a05 7742@cindex relaxing on Xtensa
43cd72b9
BW
7743Relaxation is enabled by default for the Xtensa version of @command{ld} and
7744provides two important link-time optimizations. The first optimization
7745is to combine identical literal values to reduce code size. A redundant
7746literal will be removed and all the @code{L32R} instructions that use it
7747will be changed to reference an identical literal, as long as the
7748location of the replacement literal is within the offset range of all
7749the @code{L32R} instructions. The second optimization is to remove
7750unnecessary overhead from assembler-generated ``longcall'' sequences of
7751@code{L32R}/@code{CALLX@var{n}} when the target functions are within
7752range of direct @code{CALL@var{n}} instructions.
7753
7754For each of these cases where an indirect call sequence can be optimized
7755to a direct call, the linker will change the @code{CALLX@var{n}}
7756instruction to a @code{CALL@var{n}} instruction, remove the @code{L32R}
7757instruction, and remove the literal referenced by the @code{L32R}
7758instruction if it is not used for anything else. Removing the
7759@code{L32R} instruction always reduces code size but can potentially
7760hurt performance by changing the alignment of subsequent branch targets.
7761By default, the linker will always preserve alignments, either by
7762switching some instructions between 24-bit encodings and the equivalent
7763density instructions or by inserting a no-op in place of the @code{L32R}
7764instruction that was removed. If code size is more important than
7765performance, the @option{--size-opt} option can be used to prevent the
7766linker from widening density instructions or inserting no-ops, except in
7767a few cases where no-ops are required for correctness.
7768
7769The following Xtensa-specific command-line options can be used to
7770control the linker:
7771
7772@cindex Xtensa options
7773@table @option
43cd72b9
BW
7774@item --size-opt
7775When optimizing indirect calls to direct calls, optimize for code size
7776more than performance. With this option, the linker will not insert
7777no-ops or widen density instructions to preserve branch target
7778alignment. There may still be some cases where no-ops are required to
7779preserve the correctness of the code.
7780@end table
e0001a05
NC
7781
7782@ifclear GENERIC
7783@lowersections
7784@end ifclear
7785@end ifset
7786
252b5132
RH
7787@ifclear SingleFormat
7788@node BFD
7789@chapter BFD
7790
7791@cindex back end
7792@cindex object file management
7793@cindex object formats available
7794@kindex objdump -i
7795The linker accesses object and archive files using the BFD libraries.
7796These libraries allow the linker to use the same routines to operate on
7797object files whatever the object file format. A different object file
7798format can be supported simply by creating a new BFD back end and adding
7799it to the library. To conserve runtime memory, however, the linker and
7800associated tools are usually configured to support only a subset of the
7801object file formats available. You can use @code{objdump -i}
7802(@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}) to
7803list all the formats available for your configuration.
7804
7805@cindex BFD requirements
7806@cindex requirements for BFD
7807As with most implementations, BFD is a compromise between
7808several conflicting requirements. The major factor influencing
7809BFD design was efficiency: any time used converting between
7810formats is time which would not have been spent had BFD not
7811been involved. This is partly offset by abstraction payback; since
7812BFD simplifies applications and back ends, more time and care
7813may be spent optimizing algorithms for a greater speed.
7814
7815One minor artifact of the BFD solution which you should bear in
7816mind is the potential for information loss. There are two places where
7817useful information can be lost using the BFD mechanism: during
7818conversion and during output. @xref{BFD information loss}.
7819
7820@menu
7821* BFD outline:: How it works: an outline of BFD
7822@end menu
7823
7824@node BFD outline
36f63dca 7825@section How It Works: An Outline of BFD
252b5132
RH
7826@cindex opening object files
7827@include bfdsumm.texi
7828@end ifclear
7829
7830@node Reporting Bugs
7831@chapter Reporting Bugs
ff5dcc92
SC
7832@cindex bugs in @command{ld}
7833@cindex reporting bugs in @command{ld}
252b5132 7834
ff5dcc92 7835Your bug reports play an essential role in making @command{ld} reliable.
252b5132
RH
7836
7837Reporting a bug may help you by bringing a solution to your problem, or
7838it may not. But in any case the principal function of a bug report is
ff5dcc92 7839to help the entire community by making the next version of @command{ld}
252b5132 7840work better. Bug reports are your contribution to the maintenance of
ff5dcc92 7841@command{ld}.
252b5132
RH
7842
7843In order for a bug report to serve its purpose, you must include the
7844information that enables us to fix the bug.
7845
7846@menu
7847* Bug Criteria:: Have you found a bug?
7848* Bug Reporting:: How to report bugs
7849@end menu
7850
7851@node Bug Criteria
36f63dca 7852@section Have You Found a Bug?
252b5132
RH
7853@cindex bug criteria
7854
7855If you are not sure whether you have found a bug, here are some guidelines:
7856
7857@itemize @bullet
7858@cindex fatal signal
7859@cindex linker crash
7860@cindex crash of linker
7861@item
7862If the linker gets a fatal signal, for any input whatever, that is a
ff5dcc92 7863@command{ld} bug. Reliable linkers never crash.
252b5132
RH
7864
7865@cindex error on valid input
7866@item
ff5dcc92 7867If @command{ld} produces an error message for valid input, that is a bug.
252b5132
RH
7868
7869@cindex invalid input
7870@item
ff5dcc92 7871If @command{ld} does not produce an error message for invalid input, that
252b5132
RH
7872may be a bug. In the general case, the linker can not verify that
7873object files are correct.
7874
7875@item
7876If you are an experienced user of linkers, your suggestions for
ff5dcc92 7877improvement of @command{ld} are welcome in any case.
252b5132
RH
7878@end itemize
7879
7880@node Bug Reporting
36f63dca 7881@section How to Report Bugs
252b5132 7882@cindex bug reports
ff5dcc92 7883@cindex @command{ld} bugs, reporting
252b5132
RH
7884
7885A number of companies and individuals offer support for @sc{gnu}
ff5dcc92 7886products. If you obtained @command{ld} from a support organization, we
252b5132
RH
7887recommend you contact that organization first.
7888
7889You can find contact information for many support companies and
7890individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
7891distribution.
7892
ad22bfe8 7893@ifset BUGURL
ff5dcc92 7894Otherwise, send bug reports for @command{ld} to
ad22bfe8
JM
7895@value{BUGURL}.
7896@end ifset
252b5132
RH
7897
7898The fundamental principle of reporting bugs usefully is this:
7899@strong{report all the facts}. If you are not sure whether to state a
7900fact or leave it out, state it!
7901
7902Often people omit facts because they think they know what causes the
7903problem and assume that some details do not matter. Thus, you might
b553b183
NC
7904assume that the name of a symbol you use in an example does not
7905matter. Well, probably it does not, but one cannot be sure. Perhaps
7906the bug is a stray memory reference which happens to fetch from the
7907location where that name is stored in memory; perhaps, if the name
7908were different, the contents of that location would fool the linker
7909into doing the right thing despite the bug. Play it safe and give a
7910specific, complete example. That is the easiest thing for you to do,
c0065db7 7911and the most helpful.
b553b183
NC
7912
7913Keep in mind that the purpose of a bug report is to enable us to fix
7914the bug if it is new to us. Therefore, always write your bug reports
7915on the assumption that the bug has not been reported previously.
252b5132
RH
7916
7917Sometimes people give a few sketchy facts and ask, ``Does this ring a
36f63dca
NC
7918bell?'' This cannot help us fix a bug, so it is basically useless. We
7919respond by asking for enough details to enable us to investigate.
7920You might as well expedite matters by sending them to begin with.
252b5132
RH
7921
7922To enable us to fix the bug, you should include all these things:
7923
7924@itemize @bullet
7925@item
ff5dcc92 7926The version of @command{ld}. @command{ld} announces it if you start it with
252b5132
RH
7927the @samp{--version} argument.
7928
7929Without this, we will not know whether there is any point in looking for
ff5dcc92 7930the bug in the current version of @command{ld}.
252b5132
RH
7931
7932@item
ff5dcc92 7933Any patches you may have applied to the @command{ld} source, including any
252b5132
RH
7934patches made to the @code{BFD} library.
7935
7936@item
7937The type of machine you are using, and the operating system name and
7938version number.
7939
7940@item
ff5dcc92 7941What compiler (and its version) was used to compile @command{ld}---e.g.
252b5132
RH
7942``@code{gcc-2.7}''.
7943
7944@item
7945The command arguments you gave the linker to link your example and
7946observe the bug. To guarantee you will not omit something important,
7947list them all. A copy of the Makefile (or the output from make) is
7948sufficient.
7949
7950If we were to try to guess the arguments, we would probably guess wrong
7951and then we might not encounter the bug.
7952
7953@item
7954A complete input file, or set of input files, that will reproduce the
b553b183
NC
7955bug. It is generally most helpful to send the actual object files
7956provided that they are reasonably small. Say no more than 10K. For
7957bigger files you can either make them available by FTP or HTTP or else
7958state that you are willing to send the object file(s) to whomever
7959requests them. (Note - your email will be going to a mailing list, so
7960we do not want to clog it up with large attachments). But small
7961attachments are best.
252b5132
RH
7962
7963If the source files were assembled using @code{gas} or compiled using
7964@code{gcc}, then it may be OK to send the source files rather than the
7965object files. In this case, be sure to say exactly what version of
7966@code{gas} or @code{gcc} was used to produce the object files. Also say
7967how @code{gas} or @code{gcc} were configured.
7968
7969@item
7970A description of what behavior you observe that you believe is
7971incorrect. For example, ``It gets a fatal signal.''
7972
ff5dcc92 7973Of course, if the bug is that @command{ld} gets a fatal signal, then we
252b5132
RH
7974will certainly notice it. But if the bug is incorrect output, we might
7975not notice unless it is glaringly wrong. You might as well not give us
7976a chance to make a mistake.
7977
7978Even if the problem you experience is a fatal signal, you should still
7979say so explicitly. Suppose something strange is going on, such as, your
b45619c0 7980copy of @command{ld} is out of sync, or you have encountered a bug in the
252b5132
RH
7981C library on your system. (This has happened!) Your copy might crash
7982and ours would not. If you told us to expect a crash, then when ours
7983fails to crash, we would know that the bug was not happening for us. If
7984you had not told us to expect a crash, then we would not be able to draw
7985any conclusion from our observations.
7986
7987@item
ff5dcc92 7988If you wish to suggest changes to the @command{ld} source, send us context
252b5132
RH
7989diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or
7990@samp{-p} option. Always send diffs from the old file to the new file.
ff5dcc92 7991If you even discuss something in the @command{ld} source, refer to it by
252b5132
RH
7992context, not by line number.
7993
7994The line numbers in our development sources will not match those in your
7995sources. Your line numbers would convey no useful information to us.
7996@end itemize
7997
7998Here are some things that are not necessary:
7999
8000@itemize @bullet
8001@item
8002A description of the envelope of the bug.
8003
8004Often people who encounter a bug spend a lot of time investigating
8005which changes to the input file will make the bug go away and which
8006changes will not affect it.
8007
8008This is often time consuming and not very useful, because the way we
8009will find the bug is by running a single example under the debugger
8010with breakpoints, not by pure deduction from a series of examples.
8011We recommend that you save your time for something else.
8012
8013Of course, if you can find a simpler example to report @emph{instead}
8014of the original one, that is a convenience for us. Errors in the
8015output will be easier to spot, running under the debugger will take
8016less time, and so on.
8017
8018However, simplification is not vital; if you do not want to do this,
8019report the bug anyway and send us the entire test case you used.
8020
8021@item
8022A patch for the bug.
8023
8024A patch for the bug does help us if it is a good one. But do not omit
8025the necessary information, such as the test case, on the assumption that
8026a patch is all we need. We might see problems with your patch and decide
8027to fix the problem another way, or we might not understand it at all.
8028
ff5dcc92 8029Sometimes with a program as complicated as @command{ld} it is very hard to
252b5132
RH
8030construct an example that will make the program follow a certain path
8031through the code. If you do not send us the example, we will not be
8032able to construct one, so we will not be able to verify that the bug is
8033fixed.
8034
8035And if we cannot understand what bug you are trying to fix, or why your
8036patch should be an improvement, we will not install it. A test case will
8037help us to understand.
8038
8039@item
8040A guess about what the bug is or what it depends on.
8041
8042Such guesses are usually wrong. Even we cannot guess right about such
8043things without first using the debugger to find the facts.
8044@end itemize
8045
8046@node MRI
8047@appendix MRI Compatible Script Files
8048@cindex MRI compatibility
ff5dcc92
SC
8049To aid users making the transition to @sc{gnu} @command{ld} from the MRI
8050linker, @command{ld} can use MRI compatible linker scripts as an
252b5132
RH
8051alternative to the more general-purpose linker scripting language
8052described in @ref{Scripts}. MRI compatible linker scripts have a much
8053simpler command set than the scripting language otherwise used with
ff5dcc92 8054@command{ld}. @sc{gnu} @command{ld} supports the most commonly used MRI
252b5132
RH
8055linker commands; these commands are described here.
8056
8057In general, MRI scripts aren't of much use with the @code{a.out} object
8058file format, since it only has three sections and MRI scripts lack some
8059features to make use of them.
8060
8061You can specify a file containing an MRI-compatible script using the
8062@samp{-c} command-line option.
8063
8064Each command in an MRI-compatible script occupies its own line; each
8065command line starts with the keyword that identifies the command (though
8066blank lines are also allowed for punctuation). If a line of an
ff5dcc92 8067MRI-compatible script begins with an unrecognized keyword, @command{ld}
252b5132
RH
8068issues a warning message, but continues processing the script.
8069
8070Lines beginning with @samp{*} are comments.
8071
8072You can write these commands using all upper-case letters, or all
8073lower case; for example, @samp{chip} is the same as @samp{CHIP}.
8074The following list shows only the upper-case form of each command.
8075
8076@table @code
8077@cindex @code{ABSOLUTE} (MRI)
8078@item ABSOLUTE @var{secname}
8079@itemx ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
ff5dcc92 8080Normally, @command{ld} includes in the output file all sections from all
252b5132
RH
8081the input files. However, in an MRI-compatible script, you can use the
8082@code{ABSOLUTE} command to restrict the sections that will be present in
8083your output program. If the @code{ABSOLUTE} command is used at all in a
8084script, then only the sections named explicitly in @code{ABSOLUTE}
8085commands will appear in the linker output. You can still use other
8086input sections (whatever you select on the command line, or using
8087@code{LOAD}) to resolve addresses in the output file.
8088
8089@cindex @code{ALIAS} (MRI)
8090@item ALIAS @var{out-secname}, @var{in-secname}
8091Use this command to place the data from input section @var{in-secname}
8092in a section called @var{out-secname} in the linker output file.
8093
8094@var{in-secname} may be an integer.
8095
8096@cindex @code{ALIGN} (MRI)
8097@item ALIGN @var{secname} = @var{expression}
8098Align the section called @var{secname} to @var{expression}. The
8099@var{expression} should be a power of two.
8100
8101@cindex @code{BASE} (MRI)
8102@item BASE @var{expression}
8103Use the value of @var{expression} as the lowest address (other than
8104absolute addresses) in the output file.
8105
8106@cindex @code{CHIP} (MRI)
8107@item CHIP @var{expression}
8108@itemx CHIP @var{expression}, @var{expression}
8109This command does nothing; it is accepted only for compatibility.
8110
8111@cindex @code{END} (MRI)
8112@item END
8113This command does nothing whatever; it's only accepted for compatibility.
8114
8115@cindex @code{FORMAT} (MRI)
8116@item FORMAT @var{output-format}
8117Similar to the @code{OUTPUT_FORMAT} command in the more general linker
a1ab1d2a 8118language, but restricted to one of these output formats:
252b5132
RH
8119
8120@enumerate
a1ab1d2a 8121@item
252b5132
RH
8122S-records, if @var{output-format} is @samp{S}
8123
8124@item
8125IEEE, if @var{output-format} is @samp{IEEE}
8126
8127@item
8128COFF (the @samp{coff-m68k} variant in BFD), if @var{output-format} is
8129@samp{COFF}
8130@end enumerate
8131
8132@cindex @code{LIST} (MRI)
8133@item LIST @var{anything}@dots{}
8134Print (to the standard output file) a link map, as produced by the
ff5dcc92 8135@command{ld} command-line option @samp{-M}.
252b5132
RH
8136
8137The keyword @code{LIST} may be followed by anything on the
8138same line, with no change in its effect.
8139
8140@cindex @code{LOAD} (MRI)
8141@item LOAD @var{filename}
8142@itemx LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
8143Include one or more object file @var{filename} in the link; this has the
ff5dcc92 8144same effect as specifying @var{filename} directly on the @command{ld}
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8145command line.
8146
8147@cindex @code{NAME} (MRI)
8148@item NAME @var{output-name}
ff5dcc92 8149@var{output-name} is the name for the program produced by @command{ld}; the
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8150MRI-compatible command @code{NAME} is equivalent to the command-line
8151option @samp{-o} or the general script language command @code{OUTPUT}.
8152
8153@cindex @code{ORDER} (MRI)
8154@item ORDER @var{secname}, @var{secname}, @dots{} @var{secname}
8155@itemx ORDER @var{secname} @var{secname} @var{secname}
ff5dcc92 8156Normally, @command{ld} orders the sections in its output file in the
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8157order in which they first appear in the input files. In an MRI-compatible
8158script, you can override this ordering with the @code{ORDER} command. The
8159sections you list with @code{ORDER} will appear first in your output
8160file, in the order specified.
8161
8162@cindex @code{PUBLIC} (MRI)
8163@item PUBLIC @var{name}=@var{expression}
8164@itemx PUBLIC @var{name},@var{expression}
8165@itemx PUBLIC @var{name} @var{expression}
8166Supply a value (@var{expression}) for external symbol
8167@var{name} used in the linker input files.
8168
8169@cindex @code{SECT} (MRI)
8170@item SECT @var{secname}, @var{expression}
8171@itemx SECT @var{secname}=@var{expression}
8172@itemx SECT @var{secname} @var{expression}
8173You can use any of these three forms of the @code{SECT} command to
8174specify the start address (@var{expression}) for section @var{secname}.
8175If you have more than one @code{SECT} statement for the same
8176@var{secname}, only the @emph{first} sets the start address.
8177@end table
8178
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8179@node GNU Free Documentation License
8180@appendix GNU Free Documentation License
36f63dca 8181@include fdl.texi
704c465c 8182
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8183@node LD Index
8184@unnumbered LD Index
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8185
8186@printindex cp
8187
8188@tex
7ca01ed9 8189% I think something like @@colophon should be in texinfo. In the
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8190% meantime:
8191\long\def\colophon{\hbox to0pt{}\vfill
8192\centerline{The body of this manual is set in}
8193\centerline{\fontname\tenrm,}
8194\centerline{with headings in {\bf\fontname\tenbf}}
8195\centerline{and examples in {\tt\fontname\tentt}.}
8196\centerline{{\it\fontname\tenit\/} and}
8197\centerline{{\sl\fontname\tensl\/}}
8198\centerline{are used for emphasis.}\vfill}
8199\page\colophon
7ca01ed9 8200% Blame: doc@@cygnus.com, 28mar91.
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8201@end tex
8202
252b5132 8203@bye
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