\input texinfo
@setfilename ld.info
@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-@c 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+@c 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
+@c Free Software Foundation, Inc.
@syncodeindex ky cp
+@c man begin INCLUDE
@include configdoc.texi
@c (configdoc.texi is generated by the Makefile)
-@include ldver.texi
+@include bfdver.texi
+@c man end
@c @smallbook
@c Configure for the generation of man pages
@set UsesEnvVars
@set GENERIC
-@set A29K
-@set ARC
@set ARM
-@set D10V
-@set D30V
-@set H8/300
-@set H8/500
+@set H8300
@set HPPA
-@set I370
-@set I80386
-@set I860
@set I960
-@set M32R
@set M68HC11
-@set M680X0
-@set MCORE
-@set MIPS
+@set M68K
@set MMIX
@set MSP430
-@set PDP11
-@set PJ
-@set SH
-@set SPARC
-@set TIC54X
-@set V850
-@set VAX
+@set POWERPC
+@set POWERPC64
+@set Renesas
+@set SPU
+@set TICOFF
@set WIN32
@set XTENSA
@end ifset
@end format
@end ifinfo
-@ifinfo
-This file documents the @sc{gnu} linker LD version @value{VERSION}.
-
-Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
-2001, 2002, 2003, 2004 Free Software Foundation, Inc.
+@copying
+This file documents the @sc{gnu} linker LD
+@ifset VERSION_PACKAGE
+@value{VERSION_PACKAGE}
+@end ifset
+version @value{VERSION}.
-@ignore
+Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
+2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.1
+under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no Front-Cover Texts, and with no
Back-Cover Texts. A copy of the license is included in the
section entitled ``GNU Free Documentation License''.
-
-Permission is granted to process this file through Tex and print the
-results, provided the printed document carries copying permission
-notice identical to this one except for the removal of this paragraph
-(this paragraph not being relevant to the printed manual).
-
-@end ignore
-@end ifinfo
+@end copying
@iftex
@finalout
@setchapternewpage odd
-@settitle Using LD, the GNU linker
+@settitle The GNU linker
@titlepage
-@title Using ld
-@subtitle The GNU linker
+@title The GNU linker
@sp 1
-@subtitle @code{ld} version 2
+@subtitle @code{ld}
+@ifset VERSION_PACKAGE
+@subtitle @value{VERSION_PACKAGE}
+@end ifset
@subtitle Version @value{VERSION}
@author Steve Chamberlain
@author Ian Lance Taylor
{\parskip=0pt
\hfill Red Hat Inc\par
\hfill nickc\@credhat.com, doc\@redhat.com\par
-\hfill {\it Using LD, the GNU linker}\par
+\hfill {\it The GNU linker}\par
\hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
}
\global\parindent=0pt % Steve likes it this way.
@vskip 0pt plus 1filll
@c man begin COPYRIGHT
Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001,
-2002, 2003, 2004 Free Software Foundation, Inc.
+2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
-under the terms of the GNU Free Documentation License, Version 1.1
+under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no Front-Cover Texts, and with no
Back-Cover Texts. A copy of the license is included in the
@end titlepage
@end iftex
+@contents
@c FIXME: Talk about importance of *order* of args, cmds to linker!
@ifnottex
@node Top
-@top Using ld
-This file documents the @sc{gnu} linker ld version @value{VERSION}.
+@top LD
+This file documents the @sc{gnu} linker ld
+@ifset VERSION_PACKAGE
+@value{VERSION_PACKAGE}
+@end ifset
+version @value{VERSION}.
This document is distributed under the terms of the GNU Free
-Documentation License. A copy of the license is included in the
-section entitled ``GNU Free Documentation License''.
+Documentation License version 1.3. A copy of the license is included
+in the section entitled ``GNU Free Documentation License''.
@menu
* Overview:: Overview
@ifset M68HC11
* M68HC11/68HC12:: ld and the Motorola 68HC11 and 68HC12 families
@end ifset
+@ifset M68K
+* M68K:: ld and Motorola 68K family
+@end ifset
+@ifset POWERPC
+* PowerPC ELF32:: ld and PowerPC 32-bit ELF Support
+@end ifset
+@ifset POWERPC64
+* PowerPC64 ELF64:: ld and PowerPC64 64-bit ELF Support
+@end ifset
+@ifset SPU
+* SPU ELF:: ld and SPU ELF Support
+@end ifset
@ifset TICOFF
* TI COFF:: ld and the TI COFF
@end ifset
* Reporting Bugs:: Reporting Bugs
* MRI:: MRI Compatible Script Files
* GNU Free Documentation License:: GNU Free Documentation License
-* Index:: Index
+* LD Index:: LD Index
@end menu
@end ifnottex
@ifset man
@c For the man only
-This man page does not describe the command language; see the
-@command{ld} entry in @code{info}, or the manual
-ld: the GNU linker, for full details on the command language and
-on other aspects of the GNU linker.
+This man page does not describe the command language; see the
+@command{ld} entry in @code{info} for full details on the command
+language and on other aspects of the GNU linker.
@end ifset
@ifclear SingleFormat
linker script or the one specified by using @samp{-T}). This feature
permits the linker to link against a file which appears to be an object
or an archive, but actually merely defines some symbol values, or uses
-@code{INPUT} or @code{GROUP} to load other objects. Note that
-specifying a script in this way merely augments the main linker script;
-use the @samp{-T} option to replace the default linker script entirely.
-@xref{Scripts}.
+@code{INPUT} or @code{GROUP} to load other objects. Specifying a
+script in this way merely augments the main linker script, with the
+extra commands placed after the main script; use the @samp{-T} option
+to replace the default linker script entirely, but note the effect of
+the @code{INSERT} command. @xref{Scripts}.
For options whose names are a single letter,
option arguments must either follow the option letter without intervening
precede the option name; for example, @samp{-trace-symbol} and
@samp{--trace-symbol} are equivalent. Note---there is one exception to
this rule. Multiple letter options that start with a lower case 'o' can
-only be preceeded by two dashes. This is to reduce confusion with the
+only be preceded by two dashes. This is to reduce confusion with the
@samp{-o} option. So for example @samp{-omagic} sets the output file
name to @samp{magic} whereas @samp{--omagic} sets the NMAGIC flag on the
output.
linker:
@table @gcctabopt
+@include at-file.texi
+
@kindex -a@var{keyword}
@item -a@var{keyword}
This option is supported for HP/UX compatibility. The @var{keyword}
@kindex --exclude-libs
@item --exclude-libs @var{lib},@var{lib},...
Specifies a list of archive libraries from which symbols should not be automatically
-exported. The library names may be delimited by commas or colons. Specifying
+exported. The library names may be delimited by commas or colons. Specifying
@code{--exclude-libs ALL} excludes symbols in all archive libraries from
automatic export. This option is available only for the i386 PE targeted
port of the linker and for ELF targeted ports. For i386 PE, symbols
option. For ELF targeted ports, symbols affected by this option will
be treated as hidden.
+@kindex --exclude-modules-for-implib
+@item --exclude-modules-for-implib @var{module},@var{module},...
+Specifies a list of object files or archive members, from which symbols
+should not be automatically exported, but which should be copied wholesale
+into the import library being generated during the link. The module names
+may be delimited by commas or colons, and must match exactly the filenames
+used by @command{ld} to open the files; for archive members, this is simply
+the member name, but for object files the name listed must include and
+match precisely any path used to specify the input file on the linker's
+command-line. This option is available only for the i386 PE targeted port
+of the linker. Symbols explicitly listed in a .def file are still exported,
+regardless of this option.
+
@cindex dynamic symbol table
@kindex -E
@kindex --export-dynamic
dynamic object, then you will probably need to use this option when
linking the program itself.
-You can also use the version script to control what symbols should
+You can also use the dynamic list to control what symbols should
be added to the dynamic symbol table if the output format supports it.
-See the description of @samp{--version-script} in @ref{VERSION}.
+See the description of @samp{--dynamic-list}.
@ifclear SingleFormat
@cindex big-endian objects
object files.
@ifclear SingleFormat
The @sc{gnu} linker uses other mechanisms for this purpose: the
-@option{-b}, @option{--format}, @option{--oformat} options, the
+@option{-b}, @option{--format}, @option{--oformat} options, the
@code{TARGET} command in linker scripts, and the @code{GNUTARGET}
environment variable.
@end ifclear
function to call.
@cindex archive files, from cmd line
-@kindex -l@var{archive}
-@kindex --library=@var{archive}
-@item -l@var{archive}
-@itemx --library=@var{archive}
-Add archive file @var{archive} to the list of files to link. This
-option may be used any number of times. @command{ld} will search its
-path-list for occurrences of @code{lib@var{archive}.a} for every
-@var{archive} specified.
+@kindex -l@var{namespec}
+@kindex --library=@var{namespec}
+@item -l@var{namespec}
+@itemx --library=@var{namespec}
+Add the archive or object file specified by @var{namespec} to the
+list of files to link. This option may be used any number of times.
+If @var{namespec} is of the form @file{:@var{filename}}, @command{ld}
+will search the library path for a file called @var{filename}, otherise it
+will search the library path for a file called @file{lib@var{namespec}.a}.
On systems which support shared libraries, @command{ld} may also search for
-libraries with extensions other than @code{.a}. Specifically, on ELF
-and SunOS systems, @command{ld} will search a directory for a library with
-an extension of @code{.so} before searching for one with an extension of
-@code{.a}. By convention, a @code{.so} extension indicates a shared
-library.
+files other than @file{lib@var{namespec}.a}. Specifically, on ELF
+and SunOS systems, @command{ld} will search a directory for a library
+called @file{lib@var{namespec}.so} before searching for one called
+@file{lib@var{namespec}.a}. (By convention, a @code{.so} extension
+indicates a shared library.) Note that this behavior does not apply
+to @file{:@var{filename}}, which always specifies a file called
+@var{filename}.
The linker will search an archive only once, at the location where it is
specified on the command line. If the archive defines a symbol which
@itemize @bullet
@item
-Where object files and symbols are mapped into memory.
+Where object files are mapped into memory.
@item
How common symbols are allocated.
@item
All archive members included in the link, with a mention of the symbol
which caused the archive member to be brought in.
+@item
+The values assigned to symbols.
+
+Note - symbols whose values are computed by an expression which
+involves a reference to a previous value of the same symbol may not
+have correct result displayed in the link map. This is because the
+linker discards intermediate results and only retains the final value
+of an expression. Under such circumstances the linker will display
+the final value enclosed by square brackets. Thus for example a
+linker script containing:
+
+@smallexample
+ foo = 1
+ foo = foo * 4
+ foo = foo + 8
+@end smallexample
+
+will produce the following output in the link map if the @option{-M}
+option is used:
+
+@smallexample
+ 0x00000001 foo = 0x1
+ [0x0000000c] foo = (foo * 0x4)
+ [0x0000000c] foo = (foo + 0x8)
+@end smallexample
+
+See @ref{Expressions} for more information about expressions in linker
+scripts.
@end itemize
@kindex -n
@item -O @var{level}
If @var{level} is a numeric values greater than zero @command{ld} optimizes
the output. This might take significantly longer and therefore probably
-should only be enabled for the final binary.
+should only be enabled for the final binary. At the moment this
+option only affects ELF shared library generation. Future releases of
+the linker may make more use of this option. Also currently there is
+no difference in the linker's behaviour for different non-zero values
+of this option. Again this may change with future releases.
@kindex -q
@kindex --emit-relocs
@cindex retain relocations in final executable
@item -q
@itemx --emit-relocs
-Leave relocation sections and contents in fully linked exececutables.
+Leave relocation sections and contents in fully linked executables.
Post link analysis and optimization tools may need this information in
order to perform correct modifications of executables. This results
in larger executables.
This option is currently only supported on ELF platforms.
+@kindex --force-dynamic
+@cindex forcing the creation of dynamic sections
+@item --force-dynamic
+Force the output file to have dynamic sections. This option is specific
+to VxWorks targets.
+
@cindex partial link
@cindex relocatable output
@kindex -r
specified by any preceding @samp{-L} options. Multiple @samp{-T}
options accumulate.
+@kindex -dT @var{script}
+@kindex --default-script=@var{script}
+@cindex script files
+@item -dT @var{scriptfile}
+@itemx --default-script=@var{scriptfile}
+Use @var{scriptfile} as the default linker script. @xref{Scripts}.
+
+This option is similar to the @option{--script} option except that
+processing of the script is delayed until after the rest of the
+command line has been processed. This allows options placed after the
+@option{--default-script} option on the command line to affect the
+behaviour of the linker script, which can be important when the linker
+command line cannot be directly controlled by the user. (eg because
+the command line is being constructed by another tool, such as
+@samp{gcc}).
+
@kindex -u @var{symbol}
@kindex --undefined=@var{symbol}
@cindex undefined symbol
@kindex -X
@kindex --discard-locals
@cindex local symbols, deleting
-@cindex L, deleting symbols beginning
@item -X
@itemx --discard-locals
-Delete all temporary local symbols. For most targets, this is all local
-symbols whose names begin with @samp{L}.
+Delete all temporary local symbols. (These symbols start with
+system-specific local label prefixes, typically @samp{.L} for ELF systems
+or @samp{L} for traditional a.out systems.)
@kindex -y @var{symbol}
@kindex --trace-symbol=@var{symbol}
Disallows undefined symbols in object files. Undefined symbols in
shared libraries are still allowed.
+@item execstack
+Marks the object as requiring executable stack.
+
@item initfirst
This option is only meaningful when building a shared object.
It marks the object so that its runtime initialization will occur
Marks the object that its symbol table interposes before all symbols
but the primary executable.
+@item lazy
+When generating an executable or shared library, mark it to tell the
+dynamic linker to defer function call resolution to the point when
+the function is called (lazy binding), rather than at load time.
+Lazy binding is the default.
+
@item loadfltr
Marks the object that its filters be processed immediately at
runtime.
@item nodump
Marks the object can not be dumped by @code{dldump}.
+@item noexecstack
+Marks the object as not requiring executable stack.
+
+@item norelro
+Don't create an ELF @code{PT_GNU_RELRO} segment header in the object.
+
@item now
When generating an executable or shared library, mark it to tell the
dynamic linker to resolve all symbols when the program is started, or
@item origin
Marks the object may contain $ORIGIN.
+@item relro
+Create an ELF @code{PT_GNU_RELRO} segment header in the object.
+
+@item max-page-size=@var{value}
+Set the emulation maximum page size to @var{value}.
+
+@item common-page-size=@var{value}
+Set the emulation common page size to @var{value}.
+
@end table
-Other keywords are ignored for Solaris compatibility.
+Other keywords are ignored for Solaris compatibility.
@kindex -(
@cindex groups of archives
on the command line after the @option{--as-needed} option. Normally,
the linker will add a DT_NEEDED tag for each dynamic library mentioned
on the command line, regardless of whether the library is actually
-needed. @option{--as-needed} causes DT_NEEDED tags to only be emitted
-for libraries that satisfy some symbol reference from regular objects
-which is undefined at the point that the library was linked.
+needed. @option{--as-needed} causes a DT_NEEDED tag to only be emitted
+for a library that satisfies a symbol reference from regular objects
+which is undefined at the point that the library was linked, or, if
+the library is not found in the DT_NEEDED lists of other libraries
+linked up to that point, a reference from another dynamic library.
@option{--no-as-needed} restores the default behaviour.
@kindex --add-needed
variants of this option are for compatibility with various systems. You
may use this option multiple times on the command line: it affects
library searching for @option{-l} options which follow it. This
-option also implies @option{--unresolved-symbols=report-all}.
+option also implies @option{--unresolved-symbols=report-all}. This
+option can be used with @option{-shared}. Doing so means that a
+shared library is being created but that all of the library's external
+references must be resolved by pulling in entries from static
+libraries.
@kindex -Bsymbolic
@item -Bsymbolic
within the shared library. This option is only meaningful on ELF
platforms which support shared libraries.
+@kindex -Bsymbolic-functions
+@item -Bsymbolic-functions
+When creating a shared library, bind references to global function
+symbols to the definition within the shared library, if any.
+This option is only meaningful on ELF platforms which support shared
+libraries.
+
+@kindex --dynamic-list=@var{dynamic-list-file}
+@item --dynamic-list=@var{dynamic-list-file}
+Specify the name of a dynamic list file to the linker. This is
+typically used when creating shared libraries to specify a list of
+global symbols whose references shouldn't be bound to the definition
+within the shared library, or creating dynamically linked executables
+to specify a list of symbols which should be added to the symbol table
+in the executable. This option is only meaningful on ELF platforms
+which support shared libraries.
+
+The format of the dynamic list is the same as the version node without
+scope and node name. See @ref{VERSION} for more information.
+
+@kindex --dynamic-list-data
+@item --dynamic-list-data
+Include all global data symbols to the dynamic list.
+
+@kindex --dynamic-list-cpp-new
+@item --dynamic-list-cpp-new
+Provide the builtin dynamic list for C++ operator new and delete. It
+is mainly useful for building shared libstdc++.
+
+@kindex --dynamic-list-cpp-typeinfo
+@item --dynamic-list-cpp-typeinfo
+Provide the builtin dynamic list for C++ runtime type identification.
+
@kindex --check-sections
@kindex --no-check-sections
@item --check-sections
@itemx --no-check-sections
Asks the linker @emph{not} to check section addresses after they have
-been assigned to see if there any overlaps. Normally the linker will
+been assigned to see if there are any overlaps. Normally the linker will
perform this check, and if it finds any overlaps it will produce
suitable error messages. The linker does know about, and does make
allowances for sections in overlays. The default behaviour can be
restored by using the command line switch @option{--check-sections}.
+Section overlap is not usually checked for relocatable links. You can
+force checking in that case by using the @option{--check-sections}
+option.
@cindex cross reference table
@kindex --cref
linker is normally correct; don't use this unless you know what you are
doing.
-
@kindex --fatal-warnings
+@kindex --no-fatal-warnings
@item --fatal-warnings
-Treat all warnings as errors.
+@itemx --no-fatal-warnings
+Treat all warnings as errors. The default behaviour can be restored
+with the option @option{--no-fatal-warnings}.
@kindex --force-exe-suffix
@item --force-exe-suffix
@kindex --gc-sections
@kindex --no-gc-sections
@cindex garbage collection
-@item --no-gc-sections
-@itemx --gc-sections
+@item --gc-sections
+@itemx --no-gc-sections
Enable garbage collection of unused input sections. It is ignored on
-targets that do not support this option. This option is not compatible
-with @samp{-r}. The default behaviour (of not performing this garbage
-collection) can be restored by specifying @samp{--no-gc-sections} on
-the command line.
+targets that do not support this option. The default behaviour (of not
+performing this garbage collection) can be restored by specifying
+@samp{--no-gc-sections} on the command line.
+
+@samp{--gc-sections} decides which input sections are used by
+examining symbols and relocations. The section containing the entry
+symbol and all sections containing symbols undefined on the
+command-line will be kept, as will sections containing symbols
+referenced by dynamic objects. Note that when building shared
+libraries, the linker must assume that any visible symbol is
+referenced. Once this initial set of sections has been determined,
+the linker recursively marks as used any section referenced by their
+relocations. See @samp{--entry} and @samp{--undefined}.
+
+This option can be set when doing a partial link (enabled with option
+@samp{-r}). In this case the root of symbols kept must be explicitely
+specified either by an @samp{--entry} or @samp{--undefined} option or by
+a @code{ENTRY} command in the linker script.
+
+@kindex --print-gc-sections
+@kindex --no-print-gc-sections
+@cindex garbage collection
+@item --print-gc-sections
+@itemx --no-print-gc-sections
+List all sections removed by garbage collection. The listing is
+printed on stderr. This option is only effective if garbage
+collection has been enabled via the @samp{--gc-sections}) option. The
+default behaviour (of not listing the sections that are removed) can
+be restored by specifying @samp{--no-print-gc-sections} on the command
+line.
@cindex help
@cindex usage
is done even if the linker is creating a non-symbolic shared library.
The switch @option{--[no-]allow-shlib-undefined} controls the
behaviour for reporting unresolved references found in shared
-libraries being linked in.
+libraries being linked in.
@kindex --allow-multiple-definition
@kindex -z muldefs
@kindex --no-allow-shlib-undefined
@item --allow-shlib-undefined
@itemx --no-allow-shlib-undefined
-Allows (the default) or disallows undefined symbols in shared libraries.
+Allows or disallows undefined symbols in shared libraries.
This switch is similar to @option{--no-undefined} except that it
determines the behaviour when the undefined symbols are in a
shared library rather than a regular object file. It does not affect
how undefined symbols in regular object files are handled.
-The reason that @option{--allow-shlib-undefined} is the default is that
-the shared library being specified at link time may not be the same as
-the one that is available at load time, so the symbols might actually be
-resolvable at load time. Plus there are some systems, (eg BeOS) where
-undefined symbols in shared libraries is normal. (The kernel patches
-them at load time to select which function is most appropriate
-for the current architecture. This is used for example to dynamically
-select an appropriate memset function). Apparently it is also normal
-for HPPA shared libraries to have undefined symbols.
+The default behaviour is to report errors for any undefined symbols
+referenced in shared libraries if the linker is being used to create
+an executable, but to allow them if the linker is being used to create
+a shared library.
+
+The reasons for allowing undefined symbol references in shared
+libraries specified at link time are that:
+
+@itemize @bullet
+@item
+A shared library specified at link time may not be the same as the one
+that is available at load time, so the symbol might actually be
+resolvable at load time.
+@item
+There are some operating systems, eg BeOS and HPPA, where undefined
+symbols in shared libraries are normal.
+
+The BeOS kernel for example patches shared libraries at load time to
+select whichever function is most appropriate for the current
+architecture. This is used, for example, to dynamically select an
+appropriate memset function.
+@end itemize
@kindex --no-undefined-version
@item --no-undefined-version
have taken some special action that ensures that the linker errors are
inappropriate.
+@kindex --no-warn-search-mismatch
+@item --no-warn-search-mismatch
+Normally @command{ld} will give a warning if it finds an incompatible
+library during a library search. This option silences the warning.
+
@kindex --no-whole-archive
@item --no-whole-archive
Turn off the effect of the @option{--whole-archive} option for subsequent
@ifset M68HC11
@xref{M68HC11/68HC12,,@command{ld} and the 68HC11 and 68HC12}.
@end ifset
+@ifset POWERPC
+@xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}.
+@end ifset
On some platforms, the @samp{--relax} option performs global
optimizations that become possible when the linker resolves addressing
runtime search path will be formed exclusively using the @option{-rpath}
options, ignoring the @option{-L} options. This can be useful when using
gcc, which adds many @option{-L} options which may be on NFS mounted
-filesystems.
+file systems.
For compatibility with other ELF linkers, if the @option{-R} option is
followed by a directory name, rather than a file name, it is treated as
runtime linker would do.
The linker uses the following search paths to locate required shared
-libraries.
+libraries:
@enumerate
@item
Any directories specified by @option{-rpath-link} options.
between @option{-rpath} and @option{-rpath-link} is that directories
specified by @option{-rpath} options are included in the executable and
used at runtime, whereas the @option{-rpath-link} option is only effective
-at link time. It is for the native linker only.
+at link time. Searching @option{-rpath} in this way is only supported
+by native linkers and cross linkers which have been configured with
+the @option{--with-sysroot} option.
@item
-On an ELF system, if the @option{-rpath} and @code{rpath-link} options
-were not used, search the contents of the environment variable
-@code{LD_RUN_PATH}. It is for the native linker only.
+On an ELF system, for native linkers, if the @option{-rpath} and
+@option{-rpath-link} options were not used, search the contents of the
+environment variable @code{LD_RUN_PATH}.
@item
On SunOS, if the @option{-rpath} option was not used, search any
directories specified using @option{-L} options.
@item
-For a native linker, the contents of the environment variable
-@code{LD_LIBRARY_PATH}.
+For a native linker, the search the contents of the environment
+variable @code{LD_LIBRARY_PATH}.
@item
For a native ELF linker, the directories in @code{DT_RUNPATH} or
@code{DT_RPATH} of a shared library are searched for shared
shared library if the @option{-e} option is not used and there are
undefined symbols in the link.
-@item --sort-common
+@item --sort-common [= ascending | descending]
@kindex --sort-common
-This option tells @command{ld} to sort the common symbols by size when it
-places them in the appropriate output sections. First come all the one
-byte symbols, then all the two byte, then all the four byte, and then
-everything else. This is to prevent gaps between symbols due to
-alignment constraints.
+This option tells @command{ld} to sort the common symbols by alignment in
+ascending or descending order when it places them in the appropriate output
+sections. The symbol alignments considered are sixteen-byte or larger,
+eight-byte, four-byte, two-byte, and one-byte. This is to prevent gaps
+between symbols due to alignment constraints. If no sorting order is
+specified, then descending order is assumed.
@kindex --sort-section name
@item --sort-section name
Same as --section-start, with @code{.bss}, @code{.data} or
@code{.text} as the @var{sectionname}.
+@kindex -Ttext-segment @var{org}
+@itemx -Ttext-segment @var{org}
+@cindex text segment origin, cmd line
+When creating an ELF executable or shared object, it will set the address
+of the first byte of the text segment.
+
@kindex --unresolved-symbols
@item --unresolved-symbols=@var{method}
Determine how to handle unresolved symbols. There are four possible
@kindex --warn-shared-textrel
@item --warn-shared-textrel
-Warn if the linker adds a DT_TEXTREL to a shared object.
+Warn if the linker adds a DT_TEXTREL to a shared object.
@kindex --warn-unresolved-symbols
@item --warn-unresolved-symbols
file as @code{__wrap_malloc}; if you do, the assembler may resolve the
call before the linker has a chance to wrap it to @code{malloc}.
+@kindex --eh-frame-hdr
+@item --eh-frame-hdr
+Request creation of @code{.eh_frame_hdr} section and ELF
+@code{PT_GNU_EH_FRAME} segment header.
+
@kindex --enable-new-dtags
@kindex --disable-new-dtags
@item --enable-new-dtags
those options are only available for ELF systems.
@kindex --hash-size=@var{number}
+@item --hash-size=@var{number}
Set the default size of the linker's hash tables to a prime number
close to @var{number}. Increasing this value can reduce the length of
time it takes the linker to perform its tasks, at the expense of
increasing the linker's memory requirements. Similarly reducing this
value can reduce the memory requirements at the expense of speed.
+@kindex --hash-style=@var{style}
+@item --hash-style=@var{style}
+Set the type of linker's hash table(s). @var{style} can be either
+@code{sysv} for classic ELF @code{.hash} section, @code{gnu} for
+new style GNU @code{.gnu.hash} section or @code{both} for both
+the classic ELF @code{.hash} and new style GNU @code{.gnu.hash}
+hash tables. The default is @code{sysv}.
+
@kindex --reduce-memory-overheads
@item --reduce-memory-overheads
This option reduces memory requirements at ld runtime, at the expense of
-linking speed. This was introduced to to select the old O(n^2) algorithm
+linking speed. This was introduced to select the old O(n^2) algorithm
for link map file generation, rather than the new O(n) algorithm which uses
about 40% more memory for symbol storage.
-Another affect of the switch is to set the default hash table size to
+Another effect of the switch is to set the default hash table size to
1021, which again saves memory at the cost of lengthening the linker's
run time. This is not done however if the @option{--hash-size} switch
has been used.
The @option{--reduce-memory-overheads} switch may be also be used to
enable other tradeoffs in future versions of the linker.
+@kindex --build-id
+@kindex --build-id=@var{style}
+@item --build-id
+@itemx --build-id=@var{style}
+Request creation of @code{.note.gnu.build-id} ELF note section.
+The contents of the note are unique bits identifying this linked
+file. @var{style} can be @code{uuid} to use 128 random bits,
+@code{sha1} to use a 160-bit @sc{SHA1} hash on the normative
+parts of the output contents, @code{md5} to use a 128-bit
+@sc{MD5} hash on the normative parts of the output contents, or
+@code{0x@var{hexstring}} to use a chosen bit string specified as
+an even number of hexadecimal digits (@code{-} and @code{:}
+characters between digit pairs are ignored). If @var{style} is
+omitted, @code{sha1} is used.
+
+The @code{md5} and @code{sha1} styles produces an identifier
+that is always the same in an identical output file, but will be
+unique among all nonidentical output files. It is not intended
+to be compared as a checksum for the file's contents. A linked
+file may be changed later by other tools, but the build ID bit
+string identifying the original linked file does not change.
+
+Passing @code{none} for @var{style} disables the setting from any
+@code{--build-id} options earlier on the command line.
@end table
@c man end
file.
[This option is specific to the i386 PE targeted port of the linker]
+@kindex --enable-long-section-names
+@kindex --disable-long-section-names
+@item --enable-long-section-names
+@itemx --disable-long-section-names
+The PE variants of the Coff object format add an extension that permits
+the use of section names longer than eight characters, the normal limit
+for Coff. By default, these names are only allowed in object files, as
+fully-linked executable images do not carry the Coff string table required
+to support the longer names. As a GNU extension, it is possible to
+allow their use in executable images as well, or to (probably pointlessly!)
+disallow it in object files, by using these two options. Executable images
+generated with these long section names are slightly non-standard, carrying
+as they do a string table, and may generate confusing output when examined
+with non-GNU PE-aware tools, such as file viewers and dumpers.
+[This option is valid for all PE targeted ports of the linker]
+
@kindex --enable-stdcall-fixup
@kindex --disable-stdcall-fixup
@item --enable-stdcall-fixup
explicitly exported via DEF files or implicitly exported via function
attributes, the default is to not export anything else unless this
option is given. Note that the symbols @code{DllMain@@12},
-@code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and
+@code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and
@code{impure_ptr} will not be automatically
-exported. Also, symbols imported from other DLLs will not be
-re-exported, nor will symbols specifying the DLL's internal layout
-such as those beginning with @code{_head_} or ending with
-@code{_iname}. In addition, no symbols from @code{libgcc},
+exported. Also, symbols imported from other DLLs will not be
+re-exported, nor will symbols specifying the DLL's internal layout
+such as those beginning with @code{_head_} or ending with
+@code{_iname}. In addition, no symbols from @code{libgcc},
@code{libstd++}, @code{libmingw32}, or @code{crtX.o} will be exported.
Symbols whose names begin with @code{__rtti_} or @code{__builtin_} will
not be exported, to help with C++ DLLs. Finally, there is an
-extensive list of cygwin-private symbols that are not exported
+extensive list of cygwin-private symbols that are not exported
(obviously, this applies on when building DLLs for cygwin targets).
-These cygwin-excludes are: @code{_cygwin_dll_entry@@12},
+These cygwin-excludes are: @code{_cygwin_dll_entry@@12},
@code{_cygwin_crt0_common@@8}, @code{_cygwin_noncygwin_dll_entry@@12},
-@code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll},
+@code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll},
@code{cygwin_premain0}, @code{cygwin_premain1}, @code{cygwin_premain2},
-@code{cygwin_premain3}, and @code{environ}.
+@code{cygwin_premain3}, and @code{environ}.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --exclude-symbols
@kindex --heap
@item --heap @var{reserve}
@itemx --heap @var{reserve},@var{commit}
-Specify the amount of memory to reserve (and optionally commit) to be
-used as heap for this program. The default is 1Mb reserved, 4K
+Specify the number of bytes of memory to reserve (and optionally commit)
+to be used as heap for this program. The default is 1Mb reserved, 4K
committed.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --large-address-aware
@item --large-address-aware
-If given, the appropriate bit in the ``Charateristics'' field of the COFF
+If given, the appropriate bit in the ``Characteristics'' field of the COFF
header is set to indicate that this executable supports virtual addresses
-greater than 2 gigabytes. This should be used in conjuction with the /3GB
+greater than 2 gigabytes. This should be used in conjunction with the /3GB
or /USERVA=@var{value} megabytes switch in the ``[operating systems]''
section of the BOOT.INI. Otherwise, this bit has no effect.
[This option is specific to PE targeted ports of the linker]
@kindex --dll-search-prefix
@item --dll-search-prefix @var{string}
When linking dynamically to a dll without an import library,
-search for @code{<string><basename>.dll} in preference to
+search for @code{<string><basename>.dll} in preference to
@code{lib<basename>.dll}. This behaviour allows easy distinction
between DLLs built for the various "subplatforms": native, cygwin,
uwin, pw, etc. For instance, cygwin DLLs typically use
-@code{--dll-search-prefix=cyg}.
+@code{--dll-search-prefix=cyg}.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --enable-auto-import
@item --enable-auto-import
-Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for
-DATA imports from DLLs, and create the necessary thunking symbols when
+Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for
+DATA imports from DLLs, and create the necessary thunking symbols when
building the import libraries with those DATA exports. Note: Use of the
'auto-import' extension will cause the text section of the image file
to be made writable. This does not conform to the PE-COFF format
specification published by Microsoft.
+Note - use of the 'auto-import' extension will also cause read only
+data which would normally be placed into the .rdata section to be
+placed into the .data section instead. This is in order to work
+around a problem with consts that is described here:
+http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
+
Using 'auto-import' generally will 'just work' -- but sometimes you may
see this message:
-"variable '<var>' can't be auto-imported. Please read the
+"variable '<var>' can't be auto-imported. Please read the
documentation for ld's @code{--enable-auto-import} for details."
-This message occurs when some (sub)expression accesses an address
-ultimately given by the sum of two constants (Win32 import tables only
-allow one). Instances where this may occur include accesses to member
-fields of struct variables imported from a DLL, as well as using a
-constant index into an array variable imported from a DLL. Any
+This message occurs when some (sub)expression accesses an address
+ultimately given by the sum of two constants (Win32 import tables only
+allow one). Instances where this may occur include accesses to member
+fields of struct variables imported from a DLL, as well as using a
+constant index into an array variable imported from a DLL. Any
multiword variable (arrays, structs, long long, etc) may trigger
this error condition. However, regardless of the exact data type
of the offending exported variable, ld will always detect it, issue
of adjusting references in your client code for runtime environment, so
this method works only when runtime environment supports this feature.
-A second solution is to force one of the 'constants' to be a variable --
-that is, unknown and un-optimizable at compile time. For arrays,
-there are two possibilities: a) make the indexee (the array's address)
+A second solution is to force one of the 'constants' to be a variable --
+that is, unknown and un-optimizable at compile time. For arrays,
+there are two possibilities: a) make the indexee (the array's address)
a variable, or b) make the 'constant' index a variable. Thus:
@example
extern type extern_array[];
-extern_array[1] -->
+extern_array[1] -->
@{ volatile type *t=extern_array; t[1] @}
@end example
@example
extern type extern_array[];
-extern_array[1] -->
+extern_array[1] -->
@{ volatile int t=1; extern_array[t] @}
@end example
-For structs (and most other multiword data types) the only option
+For structs (and most other multiword data types) the only option
is to make the struct itself (or the long long, or the ...) variable:
@example
extern struct s extern_struct;
-extern_struct.field -->
+extern_struct.field -->
@{ volatile struct s *t=&extern_struct; t->field @}
@end example
@end example
A third method of dealing with this difficulty is to abandon
-'auto-import' for the offending symbol and mark it with
+'auto-import' for the offending symbol and mark it with
@code{__declspec(dllimport)}. However, in practise that
requires using compile-time #defines to indicate whether you are
-building a DLL, building client code that will link to the DLL, or
-merely building/linking to a static library. In making the choice
-between the various methods of resolving the 'direct address with
+building a DLL, building client code that will link to the DLL, or
+merely building/linking to a static library. In making the choice
+between the various methods of resolving the 'direct address with
constant offset' problem, you should consider typical real-world usage:
Original:
@}
@end example
-A fourth way to avoid this problem is to re-code your
+A fourth way to avoid this problem is to re-code your
library to use a functional interface rather than a data interface
for the offending variables (e.g. set_foo() and get_foo() accessor
functions).
@kindex --disable-auto-import
@item --disable-auto-import
-Do not attempt to do sophisticated linking of @code{_symbol} to
+Do not attempt to do sophisticated linking of @code{_symbol} to
@code{__imp__symbol} for DATA imports from DLLs.
[This option is specific to the i386 PE targeted port of the linker]
If your code contains expressions described in --enable-auto-import section,
that is, DATA imports from DLL with non-zero offset, this switch will create
a vector of 'runtime pseudo relocations' which can be used by runtime
-environment to adjust references to such data in your client code.
+environment to adjust references to such data in your client code.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --disable-runtime-pseudo-reloc
@kindex --stack
@item --stack @var{reserve}
@itemx --stack @var{reserve},@var{commit}
-Specify the amount of memory to reserve (and optionally commit) to be
-used as stack for this program. The default is 2Mb reserved, 4K
+Specify the number of bytes of memory to reserve (and optionally commit)
+to be used as stack for this program. The default is 2Mb reserved, 4K
committed.
[This option is specific to the i386 PE targeted port of the linker]
@c man end
@end ifset
+@ifset M68K
+@subsection Options specific to Motorola 68K target
+
+@c man begin OPTIONS
+
+The following options are supported to control handling of GOT generation
+when linking for 68K targets.
+
+@table @gcctabopt
+
+@kindex --got
+@item --got=@var{type}
+This option tells the linker which GOT generation scheme to use.
+@var{type} should be one of @samp{single}, @samp{negative},
+@samp{multigot} or @samp{target}. For more information refer to the
+Info entry for @file{ld}.
+
+@end table
+
+@c man end
+@end ifset
+
@ifset UsesEnvVars
@node Environment
@section Environment Variables
with the @option{-L} option. You can nest calls to @code{INCLUDE} up to
10 levels deep.
+You can place @code{INCLUDE} directives at the top level, in @code{MEMORY} or
+@code{SECTIONS} commands, or in output section descriptions.
+
@item INPUT(@var{file}, @var{file}, @dots{})
@itemx INPUT(@var{file} @var{file} @dots{})
@kindex INPUT(@var{files})
@item OUTPUT(@var{filename})
@kindex OUTPUT(@var{filename})
-@cindex output file name in linker scripot
+@cindex output file name in linker script
The @code{OUTPUT} command names the output file. Using
@code{OUTPUT(@var{filename})} in the linker script is exactly like using
@samp{-o @var{filename}} on the command line (@pxref{Options,,Command
command-line option: to make @code{ld} omit the assignment of addresses
to common symbols even for a non-relocatable output file.
+@item INSERT [ AFTER | BEFORE ] @var{output_section}
+@kindex INSERT
+@cindex insert user script into default script
+This command is typically used in a script specified by @samp{-T} to
+augment the default @code{SECTIONS} with, for example, overlays. It
+inserts all prior linker script statements after (or before)
+@var{output_section}, and also causes @samp{-T} to not override the
+default linker script. The exact insertion point is as for orphan
+sections. @xref{Location Counter}. The insertion happens after the
+linker has mapped input sections to output sections. Prior to the
+insertion, since @samp{-T} scripts are parsed before the default
+linker script, statements in the @samp{-T} script occur before the
+default linker script statements in the internal linker representation
+of the script. In particular, input section assignments will be made
+to @samp{-T} output sections before those in the default script. Here
+is an example of how a @samp{-T} script using @code{INSERT} might look:
+
+@smallexample
+SECTIONS
+@{
+ OVERLAY :
+ @{
+ .ov1 @{ ov1*(.text) @}
+ .ov2 @{ ov2*(.text) @}
+ @}
+@}
+INSERT AFTER .text;
+@end smallexample
+
@item NOCROSSREFS(@var{section} @var{section} @dots{})
@kindex NOCROSSREFS(@var{sections})
@cindex cross references
@cindex symbol definition, scripts
@cindex variables, defining
You may assign a value to a symbol in a linker script. This will define
-the symbol as a global symbol.
+the symbol and place it into the symbol table with a global scope.
@menu
* Simple Assignments:: Simple Assignments
* PROVIDE:: PROVIDE
+* PROVIDE_HIDDEN:: PROVIDE_HIDDEN
+* Source Code Reference:: How to use a linker script defined symbol in source code
@end menu
@node Simple Assignments
If the program references @samp{etext} but does not define it, the
linker will use the definition in the linker script.
+@node PROVIDE_HIDDEN
+@subsection PROVIDE_HIDDEN
+@cindex PROVIDE_HIDDEN
+Similar to @code{PROVIDE}. For ELF targeted ports, the symbol will be
+hidden and won't be exported.
+
+@node Source Code Reference
+@subsection Source Code Reference
+
+Accessing a linker script defined variable from source code is not
+intuitive. In particular a linker script symbol is not equivalent to
+a variable declaration in a high level language, it is instead a
+symbol that does not have a value.
+
+Before going further, it is important to note that compilers often
+transform names in the source code into different names when they are
+stored in the symbol table. For example, Fortran compilers commonly
+prepend or append an underscore, and C++ performs extensive @samp{name
+mangling}. Therefore there might be a discrepancy between the name
+of a variable as it is used in source code and the name of the same
+variable as it is defined in a linker script. For example in C a
+linker script variable might be referred to as:
+
+@smallexample
+ extern int foo;
+@end smallexample
+
+But in the linker script it might be defined as:
+
+@smallexample
+ _foo = 1000;
+@end smallexample
+
+In the remaining examples however it is assumed that no name
+transformation has taken place.
+
+When a symbol is declared in a high level language such as C, two
+things happen. The first is that the compiler reserves enough space
+in the program's memory to hold the @emph{value} of the symbol. The
+second is that the compiler creates an entry in the program's symbol
+table which holds the symbol's @emph{address}. ie the symbol table
+contains the address of the block of memory holding the symbol's
+value. So for example the following C declaration, at file scope:
+
+@smallexample
+ int foo = 1000;
+@end smallexample
+
+creates a entry called @samp{foo} in the symbol table. This entry
+holds the address of an @samp{int} sized block of memory where the
+number 1000 is initially stored.
+
+When a program references a symbol the compiler generates code that
+first accesses the symbol table to find the address of the symbol's
+memory block and then code to read the value from that memory block.
+So:
+
+@smallexample
+ foo = 1;
+@end smallexample
+
+looks up the symbol @samp{foo} in the symbol table, gets the address
+associated with this symbol and then writes the value 1 into that
+address. Whereas:
+
+@smallexample
+ int * a = & foo;
+@end smallexample
+
+looks up the symbol @samp{foo} in the symbol table, gets it address
+and then copies this address into the block of memory associated with
+the variable @samp{a}.
+
+Linker scripts symbol declarations, by contrast, create an entry in
+the symbol table but do not assign any memory to them. Thus they are
+an address without a value. So for example the linker script definition:
+
+@smallexample
+ foo = 1000;
+@end smallexample
+
+creates an entry in the symbol table called @samp{foo} which holds
+the address of memory location 1000, but nothing special is stored at
+address 1000. This means that you cannot access the @emph{value} of a
+linker script defined symbol - it has no value - all you can do is
+access the @emph{address} of a linker script defined symbol.
+
+Hence when you are using a linker script defined symbol in source code
+you should always take the address of the symbol, and never attempt to
+use its value. For example suppose you want to copy the contents of a
+section of memory called .ROM into a section called .FLASH and the
+linker script contains these declarations:
+
+@smallexample
+@group
+ start_of_ROM = .ROM;
+ end_of_ROM = .ROM + sizeof (.ROM) - 1;
+ start_of_FLASH = .FLASH;
+@end group
+@end smallexample
+
+Then the C source code to perform the copy would be:
+
+@smallexample
+@group
+ extern char start_of_ROM, end_of_ROM, start_of_FLASH;
+
+ memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);
+@end group
+@end smallexample
+
+Note the use of the @samp{&} operators. These are correct.
+
@node SECTIONS
@section SECTIONS Command
@kindex SECTIONS
@smallexample
@group
@var{section} [@var{address}] [(@var{type})] :
- [AT(@var{lma})] [SUBALIGN(@var{subsection_align})]
+ [AT(@var{lma})] [ALIGN(@var{section_align})] [SUBALIGN(@var{subsection_align})]
@{
@var{output-section-command}
@var{output-section-command}
match all files except the ones specified in the EXCLUDE_FILE list. For
example:
@smallexample
-(*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors))
+*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
@end smallexample
will cause all .ctors sections from all files except @file{crtend.o} and
@file{otherfile.o} to be included.
data.o(.data)
@end smallexample
+You can also specify files within archives by writing a pattern
+matching the archive, a colon, then the pattern matching the file,
+with no whitespace around the colon.
+
+@table @samp
+@item archive:file
+matches file within archive
+@item archive:
+matches the whole archive
+@item :file
+matches file but not one in an archive
+@end table
+
+Either one or both of @samp{archive} and @samp{file} can contain shell
+wildcards. On DOS based file systems, the linker will assume that a
+single letter followed by a colon is a drive specifier, so
+@samp{c:myfile.o} is a simple file specification, not @samp{myfile.o}
+within an archive called @samp{c}. @samp{archive:file} filespecs may
+also be used within an @code{EXCLUDE_FILE} list, but may not appear in
+other linker script contexts. For instance, you cannot extract a file
+from an archive by using @samp{archive:file} in an @code{INPUT}
+command.
+
If you use a file name without a list of sections, then all sections in
the input file will be included in the output section. This is not
commonly done, but it may by useful on occasion. For example:
data.o
@end smallexample
-When you use a file name which does not contain any wild card
+When you use a file name which is not an @samp{archive:file} specifier
+and does not contain any wild card
characters, the linker will first see if you also specified the file
name on the linker command line or in an @code{INPUT} command. If you
did not, the linker will attempt to open the file as an input file, as
It will sort the input sections by alignment first, then by name if 2
sections have the same alignment.
@item
-@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
+@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
treated the same as @code{SORT_BY_NAME} (wildcard section pattern).
@item
@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern))
@cindex discarding sections
@cindex sections, discarding
@cindex removing sections
-The linker will not create output section which do not have any
-contents. This is for convenience when referring to input sections that
-may or may not be present in any of the input files. For example:
+The linker will not create output sections with no contents. This is
+for convenience when referring to input sections that may or may not
+be present in any of the input files. For example:
@smallexample
-.foo @{ *(.foo) @}
+.foo : @{ *(.foo) @}
@end smallexample
@noindent
will only create a @samp{.foo} section in the output file if there is a
-@samp{.foo} section in at least one input file.
+@samp{.foo} section in at least one input file, and if the input
+sections are not all empty. Other link script directives that allocate
+space in an output section will also create the output section.
-If you use anything other than an input section description as an output
-section command, such as a symbol assignment, then the output section
-will always be created, even if there are no matching input sections.
+The linker will ignore address assignments (@pxref{Output Section Address})
+on discarded output sections, except when the linker script defines
+symbols in the output section. In that case the linker will obey
+the address assignments, possibly advancing dot even though the
+section is discarded.
@cindex /DISCARD/
The special output section name @samp{/DISCARD/} may be used to discard
@smallexample
@group
@var{section} [@var{address}] [(@var{type})] :
- [AT(@var{lma})] [SUBALIGN(@var{subsection_align})]
+ [AT(@var{lma})] [ALIGN(@var{section_align})] [SUBALIGN(@var{subsection_align})]
@{
@var{output-section-command}
@var{output-section-command}
@menu
* Output Section Type:: Output section type
* Output Section LMA:: Output section LMA
+* Forced Output Alignment:: Forced Output Alignment
* Forced Input Alignment:: Forced Input Alignment
* Output Section Region:: Output section region
* Output Section Phdr:: Output section phdr
an output section description sets the VMA (@pxref{Output Section
Address}).
-The linker will normally set the LMA equal to the VMA. You can change
-that by using the @code{AT} keyword. The expression @var{lma} that
-follows the @code{AT} keyword specifies the load address of the
-section.
+The expression @var{lma} that follows the @code{AT} keyword specifies
+the load address of the section.
Alternatively, with @samp{AT>@var{lma_region}} expression, you may
specify a memory region for the section's load address. @xref{MEMORY}.
Note that if the section has not had a VMA assigned to it then the
linker will use the @var{lma_region} as the VMA region as well.
+
+If neither @code{AT} nor @code{AT>} is specified for an allocatable
+section, the linker will set the LMA such that the difference between
+VMA and LMA for the section is the same as the preceding output
+section in the same region. If there is no preceding output section
+or the section is not allocatable, the linker will set the LMA equal
+to the VMA.
@xref{Output Section Region}.
@cindex ROM initialized data
@end group
@end smallexample
+@node Forced Output Alignment
+@subsubsection Forced Output Alignment
+@kindex ALIGN(@var{section_align})
+@cindex forcing output section alignment
+@cindex output section alignment
+You can increase an output section's alignment by using ALIGN.
+
@node Forced Input Alignment
@subsubsection Forced Input Alignment
@kindex SUBALIGN(@var{subsection_align})
NOCROSSREFS}.
For each section within the @code{OVERLAY}, the linker automatically
-defines two symbols. The symbol @code{__load_start_@var{secname}} is
+provides two symbols. The symbol @code{__load_start_@var{secname}} is
defined as the starting load address of the section. The symbol
@code{__load_stop_@var{secname}} is defined as the final load address of
the section. Any characters within @var{secname} which are not legal
This will define both @samp{.text0} and @samp{.text1} to start at
address 0x1000. @samp{.text0} will be loaded at address 0x4000, and
@samp{.text1} will be loaded immediately after @samp{.text0}. The
-following symbols will be defined: @code{__load_start_text0},
+following symbols will be defined if referenced: @code{__load_start_text0},
@code{__load_stop_text0}, @code{__load_start_text1},
@code{__load_stop_text1}.
@smallexample
@group
.text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
- __load_start_text0 = LOADADDR (.text0);
- __load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0);
+ PROVIDE (__load_start_text0 = LOADADDR (.text0));
+ PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0));
.text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
- __load_start_text1 = LOADADDR (.text1);
- __load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1);
+ PROVIDE (__load_start_text1 = LOADADDR (.text1));
+ PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1));
. = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
@end group
@end smallexample
region, the linker will issue an error message.
It is possible to access the origin and length of a memory in an
-expression via the @code{ORIGIN(@var{memory})} and
+expression via the @code{ORIGIN(@var{memory})} and
@code{LENGTH(@var{memory})} functions:
@smallexample
@group
- _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
+ _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
@end group
@end smallexample
VERS_2.0 @{
bar1; bar2;
+ extern "C++" @{
+ ns::*;
+ "int f(int, double)";
+ @}
@} VERS_1.2;
@end smallexample
symbol whose name begins with @samp{old}, @samp{original}, or @samp{new}
is matched. The wildcard patterns available are the same as those used
in the shell when matching filenames (also known as ``globbing'').
+However, if you specify the symbol name inside double quotes, then the
+name is treated as literal, rather than as a glob pattern.
Next, the version script defines node @samp{VERS_1.2}. This node
depends upon @samp{VERS_1.1}. The script binds the symbol @samp{foo2}
specifically bound to a version node, it will effectively bind it to an
unspecified base version of the library. You can bind all otherwise
unspecified symbols to a given version node by using @samp{global: *;}
-somewhere in the version script.
+somewhere in the version script. Note that it's slightly crazy to use
+wildcards in a global spec except on the last version node. Global
+wildcards elsewhere run the risk of accidentally adding symbols to the
+set exported for an old version. That's wrong since older versions
+ought to have a fixed set of symbols.
The names of the version nodes have no specific meaning other than what
they might suggest to the person reading them. The @samp{2.0} version
could just as well have appeared in between @samp{1.1} and @samp{1.2}.
However, this would be a confusing way to write a version script.
-Node name can be omited, provided it is the only version node
+Node name can be omitted, provided it is the only version node
in the version script. Such version script doesn't assign any versions to
symbols, only selects which symbols will be globally visible out and which
won't.
VERSION extern "lang" @{ version-script-commands @}
@end smallexample
-The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
+The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
The linker will iterate over the list of symbols at the link time and
demangle them according to @samp{lang} before matching them to the
patterns specified in @samp{version-script-commands}.
+Demangled names may contains spaces and other special characters. As
+described above, you can use a glob pattern to match demangled names,
+or you can use a double-quoted string to match the string exactly. In
+the latter case, be aware that minor differences (such as differing
+whitespace) between the version script and the demangler output will
+cause a mismatch. As the exact string generated by the demangler
+might change in the future, even if the mangled name does not, you
+should check that all of your version directives are behaving as you
+expect when you upgrade.
+
@node Expressions
@section Expressions in Linker Scripts
@cindex expressions
@menu
* Constants:: Constants
* Symbols:: Symbol Names
+* Orphan Sections:: Orphan Sections
* Location Counter:: The Location Counter
* Operators:: Operators
* Evaluation:: Evaluation
As in C, the linker considers an integer beginning with @samp{0} to be
octal, and an integer beginning with @samp{0x} or @samp{0X} to be
-hexadecimal. The linker considers other integers to be decimal.
+hexadecimal. Alternatively the linker accepts suffixes of @samp{h} or
+@samp{H} for hexadeciaml, @samp{o} or @samp{O} for octal, @samp{b} or
+@samp{B} for binary and @samp{d} or @samp{D} for decimal. Any integer
+value without a prefix or a suffix is considered to be decimal.
@cindex scaled integers
@cindex K and M integer suffixes
${\rm 1024}$ or ${\rm 1024}^2$
@end tex
@c END TEXI2ROFF-KILL
-respectively. For example, the following all refer to the same quantity:
+respectively. For example, the following
+all refer to the same quantity:
+
@smallexample
_fourk_1 = 4K;
_fourk_2 = 4096;
_fourk_3 = 0x1000;
+_fourk_4 = 10000o;
@end smallexample
+Note - the @code{K} and @code{M} suffixes cannot be used in
+conjunction with the base suffixes mentioned above.
+
@node Symbols
@subsection Symbol Names
@cindex symbol names
to delimit symbols with spaces. For example, @samp{A-B} is one symbol,
whereas @samp{A - B} is an expression involving subtraction.
+@node Orphan Sections
+@subsection Orphan Sections
+@cindex orphan
+Orphan sections are sections present in the input files which
+are not explicitly placed into the output file by the linker
+script. The linker will still copy these sections into the
+output file, but it has to guess as to where they should be
+placed. The linker uses a simple heuristic to do this. It
+attempts to place orphan sections after non-orphan sections of the
+same attribute, such as code vs data, loadable vs non-loadable, etc.
+If there is not enough room to do this then it places
+at the end of the file.
+
+For ELF targets, the attribute of the section includes section type as
+well as section flag.
+
+If an orphaned section's name is representable as a C identifier then
+the linker will automatically @pxref{PROVIDE} two symbols:
+__start_SECNAME and __end_SECNAME, where SECNAME is the name of the
+section. These indicate the start address and end address of the
+orphaned section respectively. Note: most section names are not
+representable as C identifiers because they contain a @samp{.}
+character.
+
@node Location Counter
@subsection The Location Counter
@kindex .
@cindex holes
Assigning a value to @code{.} will cause the location counter to be
moved. This may be used to create holes in the output section. The
-location counter may never be moved backwards.
+location counter may not be moved backwards inside an output section,
+and may not be moved backwards outside of an output section if so
+doing creates areas with overlapping LMAs.
@smallexample
SECTIONS
The builtin function @code{NEXT} is closely related to @code{ALIGN}.
+@item ALIGNOF(@var{section})
+@kindex ALIGNOF(@var{section})
+@cindex section alignment
+Return the alignment in bytes of the named @var{section}, if that section has
+been allocated. If the section has not been allocated when this is
+evaluated, the linker will report an error. In the following example,
+the alignment of the @code{.output} section is stored as the first
+value in that section.
+@smallexample
+@group
+SECTIONS@{ @dots{}
+ .output @{
+ LONG (ALIGNOF (.output))
+ @dots{}
+ @}
+@dots{} @}
+@end group
+@end smallexample
+
@item BLOCK(@var{exp})
@kindex BLOCK(@var{exp})
This is a synonym for @code{ALIGN}, for compatibility with older linker
@ifset HPPA
* HPPA ELF32:: @command{ld} and HPPA 32-bit ELF
@end ifset
+@ifset M68K
+* M68K:: @command{ld} and the Motorola 68K family
+@end ifset
@ifset MMIX
* MMIX:: @command{ld} and MMIX
@end ifset
@ifset M68HC11
* M68HC11/68HC12:: @code{ld} and the Motorola 68HC11 and 68HC12 families
@end ifset
+@ifset POWERPC
+* PowerPC ELF32:: @command{ld} and PowerPC 32-bit ELF Support
+@end ifset
+@ifset POWERPC64
+* PowerPC64 ELF64:: @command{ld} and PowerPC64 64-bit ELF Support
+@end ifset
+@ifset SPU
+* SPU ELF:: @command{ld} and SPU ELF Support
+@end ifset
@ifset TICOFF
* TI COFF:: @command{ld} and TI COFF
@end ifset
top page of memory).
@item bit manipulation instructions
-@command{ld} finds all bit manipulation instructions like @code{band, bclr,
+@command{ld} finds all bit manipulation instructions like @code{band, bclr,
biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor}
-which use 32 bit and 16 bit absolute address form, but refer to the top
+which use 32 bit and 16 bit absolute address form, but refer to the top
page of memory, and changes them to use the 8 bit address form.
(That is: the linker turns @samp{bset #xx:3,@code{@@}@var{aa}:32} into
-@samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
+@samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
the top page of memory).
@item system control instructions
-@command{ld} finds all @code{ldc.w, stc.w} instrcutions which use the
-32 bit absolute address form, but refer to the top page of memory, and
+@command{ld} finds all @code{ldc.w, stc.w} instructions which use the
+32 bit absolute address form, but refer to the top page of memory, and
changes them to use 16 bit address form.
(That is: the linker turns @samp{ldc.w @code{@@}@var{aa}:32,ccr} into
-@samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
+@samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
the top page of memory).
@end table
@cindex trampoline generation on M68HC12
For 68HC11 and 68HC12, @command{ld} can generate trampoline code to
call a far function using a normal @code{jsr} instruction. The linker
-will also change the relocation to some far function to use the
+will also change the relocation to some far function to use the
trampoline address instead of the function address. This is typically the
case when a pointer to a function is taken. The pointer will in fact
point to the function trampoline.
@cindex ARM interworking support
@kindex --support-old-code
For the ARM, @command{ld} will generate code stubs to allow functions calls
-betweem ARM and Thumb code. These stubs only work with code that has
+between ARM and Thumb code. These stubs only work with code that has
been compiled and assembled with the @samp{-mthumb-interwork} command
line option. If it is necessary to link with old ARM object files or
libraries, which have not been compiled with the -mthumb-interwork
branched to using a BX instruction, and the program will start
executing in Thumb mode straight away.
+@cindex PE import table prefixing
+@kindex --use-nul-prefixed-import-tables
+The @samp{--use-nul-prefixed-import-tables} switch is specifying, that
+the import tables idata4 and idata5 have to be generated with a zero
+elememt prefix for import libraries. This is the old style to generate
+import tables. By default this option is turned off.
+
@cindex BE8
@kindex --be8
The @samp{--be8} switch instructs @command{ld} to generate BE8 format
In the former case, the switch should not be used, and @samp{R_ARM_V4BX}
relocations are ignored.
+@cindex FIX_V4BX_INTERWORKING
+@kindex --fix-v4bx-interworking
+Replace @code{BX rM} instructions identified by @samp{R_ARM_V4BX}
+relocations with a branch to the following veneer:
+
+@smallexample
+TST rM, #1
+MOVEQ PC, rM
+BX Rn
+@end smallexample
+
+This allows generation of libraries/applications that work on ARMv4 cores
+and are still interworking safe. Note that the above veneer clobbers the
+condition flags, so may cause incorrect progrm behavior in rare cases.
+
+@cindex USE_BLX
+@kindex --use-blx
+The @samp{--use-blx} switch enables the linker to use ARM/Thumb
+BLX instructions (available on ARMv5t and above) in various
+situations. Currently it is used to perform calls via the PLT from Thumb
+code using BLX rather than using BX and a mode-switching stub before
+each PLT entry. This should lead to such calls executing slightly faster.
+
+This option is enabled implicitly for SymbianOS, so there is no need to
+specify it if you are using that target.
+
+@cindex VFP11_DENORM_FIX
+@kindex --vfp11-denorm-fix
+The @samp{--vfp11-denorm-fix} switch enables a link-time workaround for a
+bug in certain VFP11 coprocessor hardware, which sometimes allows
+instructions with denorm operands (which must be handled by support code)
+to have those operands overwritten by subsequent instructions before
+the support code can read the intended values.
+
+The bug may be avoided in scalar mode if you allow at least one
+intervening instruction between a VFP11 instruction which uses a register
+and another instruction which writes to the same register, or at least two
+intervening instructions if vector mode is in use. The bug only affects
+full-compliance floating-point mode: you do not need this workaround if
+you are using "runfast" mode. Please contact ARM for further details.
+
+If you know you are using buggy VFP11 hardware, you can
+enable this workaround by specifying the linker option
+@samp{--vfp-denorm-fix=scalar} if you are using the VFP11 scalar
+mode only, or @samp{--vfp-denorm-fix=vector} if you are using
+vector mode (the latter also works for scalar code). The default is
+@samp{--vfp-denorm-fix=none}.
+
+If the workaround is enabled, instructions are scanned for
+potentially-troublesome sequences, and a veneer is created for each
+such sequence which may trigger the erratum. The veneer consists of the
+first instruction of the sequence and a branch back to the subsequent
+instruction. The original instruction is then replaced with a branch to
+the veneer. The extra cycles required to call and return from the veneer
+are sufficient to avoid the erratum in both the scalar and vector cases.
+
+@cindex NO_ENUM_SIZE_WARNING
+@kindex --no-enum-size-warning
+The @option{--no-enum-size-warning} switch prevents the linker from
+warning when linking object files that specify incompatible EABI
+enumeration size attributes. For example, with this switch enabled,
+linking of an object file using 32-bit enumeration values with another
+using enumeration values fitted into the smallest possible space will
+not be diagnosed.
+
+@cindex NO_WCHAR_SIZE_WARNING
+@kindex --no-wchar-size-warning
+The @option{--no-wchar-size-warning} switch prevents the linker from
+warning when linking object files that specify incompatible EABI
+@code{wchar_t} size attributes. For example, with this switch enabled,
+linking of an object file using 32-bit @code{wchar_t} values with another
+using 16-bit @code{wchar_t} values will not be diagnosed.
+
+@cindex PIC_VENEER
+@kindex --pic-veneer
+The @samp{--pic-veneer} switch makes the linker use PIC sequences for
+ARM/Thumb interworking veneers, even if the rest of the binary
+is not PIC. This avoids problems on uClinux targets where
+@samp{--emit-relocs} is used to generate relocatable binaries.
+
+@cindex STUB_GROUP_SIZE
+@kindex --stub-group-size=@var{N}
+The linker will automatically generate and insert small sequences of
+code into a linked ARM ELF executable whenever an attempt is made to
+perform a function call to a symbol that is too far away. The
+placement of these sequences of instructions - called stubs - is
+controlled by the command line option @option{--stub-group-size=N}.
+The placement is important because a poor choice can create a need for
+duplicate stubs, increasing the code sizw. The linker will try to
+group stubs together in order to reduce interruptions to the flow of
+code, but it needs guidance as to how big these groups should be and
+where they should be placed.
+
+The value of @samp{N}, the parameter to the
+@option{--stub-group-size=} option controls where the stub groups are
+placed. If it is negative then all stubs are placed before the first
+branch that needs them. If it is positive then the stubs can be
+placed either before or after the branches that need them. If the
+value of @samp{N} is 1 (either +1 or -1) then the linker will choose
+exactly where to place groups of stubs, using its built in heuristics.
+A value of @samp{N} greater than 1 (or smaller than -1) tells the
+linker that a single group of stubs can service at most @samp{N} bytes
+from the input sections.
+
+The default, if @option{--stub-group-size=} is not specified, is
+@samp{N = +1}.
+
+Farcalls stubs insertion is fully supported for the ARM-EABI target
+only, because it relies on object files properties not present
+otherwise.
+
@ifclear GENERIC
@lowersections
@end ifclear
@end ifclear
@end ifset
+@ifset M68K
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node M68K
+@section @command{ld} and the Motorola 68K family
+
+@cindex Motorola 68K GOT generation
+@kindex --got=@var{type}
+The @samp{--got=@var{type}} option lets you choose the GOT generation scheme.
+The choices are @samp{single}, @samp{negative}, @samp{multigot} and
+@samp{target}. When @samp{target} is selected the linker chooses
+the default GOT generation scheme for the current target.
+@samp{single} tells the linker to generate a single GOT with
+entries only at non-negative offsets.
+@samp{negative} instructs the linker to generate a single GOT with
+entries at both negative and positive offsets. Not all environments
+support such GOTs.
+@samp{multigot} allows the linker to generate several GOTs in the
+output file. All GOT references from a single input object
+file access the same GOT, but references from different input object
+files might access different GOTs. Not all environments support such GOTs.
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
@ifset MMIX
@ifclear GENERIC
@raisesections
this section; it is always set to the program entry, which is at the
symbol @code{Main} for @code{mmo} files.
-Symbols with the prefix @code{__.MMIX.start.}, for example
-@code{__.MMIX.start..text} and @code{__.MMIX.start..data} are special;
-there must be only one each, even if they are local. The default linker
-script uses these to set the default start address of a section.
+Global symbols with the prefix @code{__.MMIX.start.}, for example
+@code{__.MMIX.start..text} and @code{__.MMIX.start..data} are special.
+The default linker script uses these to set the default start address
+of a section.
Initial and trailing multiples of zero-valued 32-bit words in a section,
are left out from an mmo file.
Defines an information memory section (if applicable). Any code in
this section will be uploaded to the MPU.
-@item @samp{.infomemnobits}
+@item @samp{.infomemnobits}
This is the same as the @samp{.infomem} section except that any code
in this section will not be uploaded to the MPU.
@item @samp{.noinit}
Denotes a portion of RAM located above @samp{.bss} section.
-The last two sections are used by gcc.
+The last two sections are used by gcc.
+@end table
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
+@ifset POWERPC
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node PowerPC ELF32
+@section @command{ld} and PowerPC 32-bit ELF Support
+@cindex PowerPC long branches
+@kindex --relax on PowerPC
+Branches on PowerPC processors are limited to a signed 26-bit
+displacement, which may result in @command{ld} giving
+@samp{relocation truncated to fit} errors with very large programs.
+@samp{--relax} enables the generation of trampolines that can access
+the entire 32-bit address space. These trampolines are inserted at
+section boundaries, so may not themselves be reachable if an input
+section exceeds 33M in size.
+
+@cindex PowerPC ELF32 options
+@table @option
+@cindex PowerPC PLT
+@kindex --bss-plt
+@item --bss-plt
+Current PowerPC GCC accepts a @samp{-msecure-plt} option that
+generates code capable of using a newer PLT and GOT layout that has
+the security advantage of no executable section ever needing to be
+writable and no writable section ever being executable. PowerPC
+@command{ld} will generate this layout, including stubs to access the
+PLT, if all input files (including startup and static libraries) were
+compiled with @samp{-msecure-plt}. @samp{--bss-plt} forces the old
+BSS PLT (and GOT layout) which can give slightly better performance.
+
+@kindex --secure-plt
+@item --secure-plt
+@command{ld} will use the new PLT and GOT layout if it is linking new
+@samp{-fpic} or @samp{-fPIC} code, but does not do so automatically
+when linking non-PIC code. This option requests the new PLT and GOT
+layout. A warning will be given if some object file requires the old
+style BSS PLT.
+
+@cindex PowerPC GOT
+@kindex --sdata-got
+@item --sdata-got
+The new secure PLT and GOT are placed differently relative to other
+sections compared to older BSS PLT and GOT placement. The location of
+@code{.plt} must change because the new secure PLT is an initialized
+section while the old PLT is uninitialized. The reason for the
+@code{.got} change is more subtle: The new placement allows
+@code{.got} to be read-only in applications linked with
+@samp{-z relro -z now}. However, this placement means that
+@code{.sdata} cannot always be used in shared libraries, because the
+PowerPC ABI accesses @code{.sdata} in shared libraries from the GOT
+pointer. @samp{--sdata-got} forces the old GOT placement. PowerPC
+GCC doesn't use @code{.sdata} in shared libraries, so this option is
+really only useful for other compilers that may do so.
+
+@cindex PowerPC stub symbols
+@kindex --emit-stub-syms
+@item --emit-stub-syms
+This option causes @command{ld} to label linker stubs with a local
+symbol that encodes the stub type and destination.
+
+@cindex PowerPC TLS optimization
+@kindex --no-tls-optimize
+@item --no-tls-optimize
+PowerPC @command{ld} normally performs some optimization of code
+sequences used to access Thread-Local Storage. Use this option to
+disable the optimization.
+@end table
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
+@ifset POWERPC64
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node PowerPC64 ELF64
+@section @command{ld} and PowerPC64 64-bit ELF Support
+
+@cindex PowerPC64 ELF64 options
+@table @option
+@cindex PowerPC64 stub grouping
+@kindex --stub-group-size
+@item --stub-group-size
+Long branch stubs, PLT call stubs and TOC adjusting stubs are placed
+by @command{ld} in stub sections located between groups of input sections.
+@samp{--stub-group-size} specifies the maximum size of a group of input
+sections handled by one stub section. Since branch offsets are signed,
+a stub section may serve two groups of input sections, one group before
+the stub section, and one group after it. However, when using
+conditional branches that require stubs, it may be better (for branch
+prediction) that stub sections only serve one group of input sections.
+A negative value for @samp{N} chooses this scheme, ensuring that
+branches to stubs always use a negative offset. Two special values of
+@samp{N} are recognized, @samp{1} and @samp{-1}. These both instruct
+@command{ld} to automatically size input section groups for the branch types
+detected, with the same behaviour regarding stub placement as other
+positive or negative values of @samp{N} respectively.
+
+Note that @samp{--stub-group-size} does not split input sections. A
+single input section larger than the group size specified will of course
+create a larger group (of one section). If input sections are too
+large, it may not be possible for a branch to reach its stub.
+
+@cindex PowerPC64 stub symbols
+@kindex --emit-stub-syms
+@item --emit-stub-syms
+This option causes @command{ld} to label linker stubs with a local
+symbol that encodes the stub type and destination.
+
+@cindex PowerPC64 dot symbols
+@kindex --dotsyms
+@kindex --no-dotsyms
+@item --dotsyms, --no-dotsyms
+These two options control how @command{ld} interprets version patterns
+in a version script. Older PowerPC64 compilers emitted both a
+function descriptor symbol with the same name as the function, and a
+code entry symbol with the name prefixed by a dot (@samp{.}). To
+properly version a function @samp{foo}, the version script thus needs
+to control both @samp{foo} and @samp{.foo}. The option
+@samp{--dotsyms}, on by default, automatically adds the required
+dot-prefixed patterns. Use @samp{--no-dotsyms} to disable this
+feature.
+
+@cindex PowerPC64 TLS optimization
+@kindex --no-tls-optimize
+@item --no-tls-optimize
+PowerPC64 @command{ld} normally performs some optimization of code
+sequences used to access Thread-Local Storage. Use this option to
+disable the optimization.
+
+@cindex PowerPC64 OPD optimization
+@kindex --no-opd-optimize
+@item --no-opd-optimize
+PowerPC64 @command{ld} normally removes @code{.opd} section entries
+corresponding to deleted link-once functions, or functions removed by
+the action of @samp{--gc-sections} or linker script @code{/DISCARD/}.
+Use this option to disable @code{.opd} optimization.
+
+@cindex PowerPC64 OPD spacing
+@kindex --non-overlapping-opd
+@item --non-overlapping-opd
+Some PowerPC64 compilers have an option to generate compressed
+@code{.opd} entries spaced 16 bytes apart, overlapping the third word,
+the static chain pointer (unused in C) with the first word of the next
+entry. This option expands such entries to the full 24 bytes.
+
+@cindex PowerPC64 TOC optimization
+@kindex --no-toc-optimize
+@item --no-toc-optimize
+PowerPC64 @command{ld} normally removes unused @code{.toc} section
+entries. Such entries are detected by examining relocations that
+reference the TOC in code sections. A reloc in a deleted code section
+marks a TOC word as unneeded, while a reloc in a kept code section
+marks a TOC word as needed. Since the TOC may reference itself, TOC
+relocs are also examined. TOC words marked as both needed and
+unneeded will of course be kept. TOC words without any referencing
+reloc are assumed to be part of a multi-word entry, and are kept or
+discarded as per the nearest marked preceding word. This works
+reliably for compiler generated code, but may be incorrect if assembly
+code is used to insert TOC entries. Use this option to disable the
+optimization.
+
+@cindex PowerPC64 multi-TOC
+@kindex --no-multi-toc
+@item --no-multi-toc
+By default, PowerPC64 GCC generates code for a TOC model where TOC
+entries are accessed with a 16-bit offset from r2. This limits the
+total TOC size to 64K. PowerPC64 @command{ld} extends this limit by
+grouping code sections such that each group uses less than 64K for its
+TOC entries, then inserts r2 adjusting stubs between inter-group
+calls. @command{ld} does not split apart input sections, so cannot
+help if a single input file has a @code{.toc} section that exceeds
+64K, most likely from linking multiple files with @command{ld -r}.
+Use this option to turn off this feature.
+@end table
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
+@ifset SPU
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node SPU ELF
+@section @command{ld} and SPU ELF Support
+
+@cindex SPU ELF options
+@table @option
+
+@cindex SPU plugins
+@kindex --plugin
+@item --plugin
+This option marks an executable as a PIC plugin module.
+
+@cindex SPU overlays
+@kindex --no-overlays
+@item --no-overlays
+Normally, @command{ld} recognizes calls to functions within overlay
+regions, and redirects such calls to an overlay manager via a stub.
+@command{ld} also provides a built-in overlay manager. This option
+turns off all this special overlay handling.
+
+@cindex SPU overlay stub symbols
+@kindex --emit-stub-syms
+@item --emit-stub-syms
+This option causes @command{ld} to label overlay stubs with a local
+symbol that encodes the stub type and destination.
+
+@cindex SPU extra overlay stubs
+@kindex --extra-overlay-stubs
+@item --extra-overlay-stubs
+This option causes @command{ld} to add overlay call stubs on all
+function calls out of overlay regions. Normally stubs are not added
+on calls to non-overlay regions.
+
+@cindex SPU local store size
+@kindex --local-store=lo:hi
+@item --local-store=lo:hi
+@command{ld} usually checks that a final executable for SPU fits in
+the address range 0 to 256k. This option may be used to change the
+range. Disable the check entirely with @option{--local-store=0:0}.
+
+@cindex SPU
+@kindex --stack-analysis
+@item --stack-analysis
+SPU local store space is limited. Over-allocation of stack space
+unnecessarily limits space available for code and data, while
+under-allocation results in runtime failures. If given this option,
+@command{ld} will provide an estimate of maximum stack usage.
+@command{ld} does this by examining symbols in code sections to
+determine the extents of functions, and looking at function prologues
+for stack adjusting instructions. A call-graph is created by looking
+for relocations on branch instructions. The graph is then searched
+for the maximum stack usage path. Note that this analysis does not
+find calls made via function pointers, and does not handle recursion
+and other cycles in the call graph. Stack usage may be
+under-estimated if your code makes such calls. Also, stack usage for
+dynamic allocation, e.g. alloca, will not be detected. If a link map
+is requested, detailed information about each function's stack usage
+and calls will be given.
+
+@cindex SPU
+@kindex --emit-stack-syms
+@item --emit-stack-syms
+This option, if given along with @option{--stack-analysis} will result
+in @command{ld} emitting stack sizing symbols for each function.
+These take the form @code{__stack_<function_name>} for global
+functions, and @code{__stack_<number>_<function_name>} for static
+functions. @code{<number>} is the section id in hex. The value of
+such symbols is the stack requirement for the corresponding function.
+The symbol size will be zero, type @code{STT_NOTYPE}, binding
+@code{STB_LOCAL}, and section @code{SHN_ABS}.
@end table
@ifclear GENERIC
@node WIN32
@section @command{ld} and WIN32 (cygwin/mingw)
-This section describes some of the win32 specific @command{ld} issues.
-See @ref{Options,,Command Line Options} for detailed decription of the
+This section describes some of the win32 specific @command{ld} issues.
+See @ref{Options,,Command Line Options} for detailed description of the
command line options mentioned here.
@table @emph
-@cindex import libraries
-@item import libraries
+@cindex import libraries
+@item import libraries
The standard Windows linker creates and uses so-called import
libraries, which contains information for linking to dll's. They are
regular static archives and are handled as any other static
support for creating such libraries provided with the
@samp{--out-implib} command line option.
-@item exporting DLL symbols
-@cindex exporting DLL symbols
+@item exporting DLL symbols
+@cindex exporting DLL symbols
The cygwin/mingw @command{ld} has several ways to export symbols for dll's.
@table @emph
@item --export-all-symbols [This is the default]
@item --exclude-symbols
@item --exclude-libs
+@item --exclude-modules-for-implib
@end itemize
-If, however, @samp{--export-all-symbols} is not given explicitly on the
+If, however, @samp{--export-all-symbols} is not given explicitly on the
command line, then the default auto-export behavior will be @emph{disabled}
if either of the following are true:
@item Any symbol in any object file was marked with the __declspec(dllexport) attribute.
@end itemize
-@item using a DEF file
-@cindex using a DEF file
+@item using a DEF file
+@cindex using a DEF file
Another way of exporting symbols is using a DEF file. A DEF file is
an ASCII file containing definitions of symbols which should be
exported when a dll is created. Usually it is named @samp{<dll
Here is an example of a DEF file for a shared library called @samp{xyz.dll}:
@example
-LIBRARY "xyz.dll" BASE=0x10000000
+LIBRARY "xyz.dll" BASE=0x20000000
EXPORTS
foo
bar
_bar = bar
-@end example
+another_foo = abc.dll.afoo
+var1 DATA
+@end example
+
+This example defines a DLL with a non-default base address and five
+symbols in the export table. The third exported symbol @code{_bar} is an
+alias for the second. The fourth symbol, @code{another_foo} is resolved
+by "forwarding" to another module and treating it as an alias for
+@code{afoo} exported from the DLL @samp{abc.dll}. The final symbol
+@code{var1} is declared to be a data object.
+
+The optional @code{LIBRARY <name>} command indicates the @emph{internal}
+name of the output DLL. If @samp{<name>} does not include a suffix,
+the default library suffix, @samp{.DLL} is appended.
+
+When the .DEF file is used to build an application, rather than a
+library, the @code{NAME <name>} command should be used instead of
+@code{LIBRARY}. If @samp{<name>} does not include a suffix, the default
+executable suffix, @samp{.EXE} is appended.
+
+With either @code{LIBRARY <name>} or @code{NAME <name>} the optional
+specification @code{BASE = <number>} may be used to specify a
+non-default base address for the image.
+
+If neither @code{LIBRARY <name>} nor @code{NAME <name>} is specified,
+or they specify an empty string, the internal name is the same as the
+filename specified on the command line.
+
+The complete specification of an export symbol is:
+
+@example
+EXPORTS
+ ( ( ( <name1> [ = <name2> ] )
+ | ( <name1> = <module-name> . <external-name>))
+ [ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] ) *
+@end example
-This example defines a base address and three symbols. The third
-symbol is an alias for the second. For the complete format
-specification see ld/deffilep.y in the binutils sources.
+Declares @samp{<name1>} as an exported symbol from the DLL, or declares
+@samp{<name1>} as an exported alias for @samp{<name2>}; or declares
+@samp{<name1>} as a "forward" alias for the symbol
+@samp{<external-name>} in the DLL @samp{<module-name>}.
+Optionally, the symbol may be exported by the specified ordinal
+@samp{<integer>} alias.
+
+The optional keywords that follow the declaration indicate:
+
+@code{NONAME}: Do not put the symbol name in the DLL's export table. It
+will still be exported by its ordinal alias (either the value specified
+by the .def specification or, otherwise, the value assigned by the
+linker). The symbol name, however, does remain visible in the import
+library (if any), unless @code{PRIVATE} is also specified.
+
+@code{DATA}: The symbol is a variable or object, rather than a function.
+The import lib will export only an indirect reference to @code{foo} as
+the symbol @code{_imp__foo} (ie, @code{foo} must be resolved as
+@code{*_imp__foo}).
+
+@code{CONSTANT}: Like @code{DATA}, but put the undecorated @code{foo} as
+well as @code{_imp__foo} into the import library. Both refer to the
+read-only import address table's pointer to the variable, not to the
+variable itself. This can be dangerous. If the user code fails to add
+the @code{dllimport} attribute and also fails to explicitly add the
+extra indirection that the use of the attribute enforces, the
+application will behave unexpectedly.
+
+@code{PRIVATE}: Put the symbol in the DLL's export table, but do not put
+it into the static import library used to resolve imports at link time. The
+symbol can still be imported using the @code{LoadLibrary/GetProcAddress}
+API at runtime or by by using the GNU ld extension of linking directly to
+the DLL without an import library.
+
+See ld/deffilep.y in the binutils sources for the full specification of
+other DEF file statements
@cindex creating a DEF file
While linking a shared dll, @command{ld} is able to create a DEF file
the @samp{--export-all-symbols} option is also used.
Note that object files that wish to access these symbols must @emph{not}
-decorate them with dllexport. Instead, they should use dllimport,
+decorate them with dllexport. Instead, they should use dllimport,
instead:
@example
__declspec(dllimport) void a_function(int with_args)
@end example
-This complicates the structure of library header files, because
-when included by the library itself the header must declare the
+This complicates the structure of library header files, because
+when included by the library itself the header must declare the
variables and functions as dllexport, but when included by client
code the header must declare them as dllimport. There are a number
-of idioms that are typically used to do this; often client code can
+of idioms that are typically used to do this; often client code can
omit the __declspec() declaration completely. See
@samp{--enable-auto-import} and @samp{automatic data imports} for more
-imformation.
-@end table
+information.
+@end table
@cindex automatic data imports
@item automatic data imports
The standard Windows dll format supports data imports from dlls only
by adding special decorations (dllimport/dllexport), which let the
compiler produce specific assembler instructions to deal with this
-issue. This increases the effort necessary to port existing Un*x
+issue. This increases the effort necessary to port existing Un*x
code to these platforms, especially for large
c++ libraries and applications. The auto-import feature, which was
-initially provided by Paul Sokolovsky, allows one to omit the
-decorations to archieve a behavior that conforms to that on POSIX/Un*x
-platforms. This feature is enabled with the @samp{--enable-auto-import}
+initially provided by Paul Sokolovsky, allows one to omit the
+decorations to achieve a behavior that conforms to that on POSIX/Un*x
+platforms. This feature is enabled with the @samp{--enable-auto-import}
command-line option, although it is enabled by default on cygwin/mingw.
The @samp{--enable-auto-import} option itself now serves mainly to
suppress any warnings that are ordinarily emitted when linked objects
trigger the feature's use.
-auto-import of variables does not always work flawlessly without
+auto-import of variables does not always work flawlessly without
additional assistance. Sometimes, you will see this message
-"variable '<var>' can't be auto-imported. Please read the
+"variable '<var>' can't be auto-imported. Please read the
documentation for ld's @code{--enable-auto-import} for details."
-The @samp{--enable-auto-import} documentation explains why this error
-occurs, and several methods that can be used to overcome this difficulty.
-One of these methods is the @emph{runtime pseudo-relocs} feature, described
+The @samp{--enable-auto-import} documentation explains why this error
+occurs, and several methods that can be used to overcome this difficulty.
+One of these methods is the @emph{runtime pseudo-relocs} feature, described
below.
@cindex runtime pseudo-relocation
-For complex variables imported from DLLs (such as structs or classes),
-object files typically contain a base address for the variable and an
-offset (@emph{addend}) within the variable--to specify a particular
-field or public member, for instance. Unfortunately, the runtime loader used
-in win32 environments is incapable of fixing these references at runtime
+For complex variables imported from DLLs (such as structs or classes),
+object files typically contain a base address for the variable and an
+offset (@emph{addend}) within the variable--to specify a particular
+field or public member, for instance. Unfortunately, the runtime loader used
+in win32 environments is incapable of fixing these references at runtime
without the additional information supplied by dllimport/dllexport decorations.
-The standard auto-import feature described above is unable to resolve these
+The standard auto-import feature described above is unable to resolve these
references.
-The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
-be resolved without error, while leaving the task of adjusting the references
-themselves (with their non-zero addends) to specialized code provided by the
-runtime environment. Recent versions of the cygwin and mingw environments and
-compilers provide this runtime support; older versions do not. However, the
-support is only necessary on the developer's platform; the compiled result will
+The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
+be resolved without error, while leaving the task of adjusting the references
+themselves (with their non-zero addends) to specialized code provided by the
+runtime environment. Recent versions of the cygwin and mingw environments and
+compilers provide this runtime support; older versions do not. However, the
+support is only necessary on the developer's platform; the compiled result will
run without error on an older system.
-@samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
-enabled as needed.
+@samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
+enabled as needed.
@cindex direct linking to a dll
@item direct linking to a dll
The cygwin/mingw ports of @command{ld} support the direct linking,
including data symbols, to a dll without the usage of any import
libraries. This is much faster and uses much less memory than does the
-traditional import library method, expecially when linking large
-libraries or applications. When @command{ld} creates an import lib, each
-function or variable exported from the dll is stored in its own bfd, even
-though a single bfd could contain many exports. The overhead involved in
+traditional import library method, especially when linking large
+libraries or applications. When @command{ld} creates an import lib, each
+function or variable exported from the dll is stored in its own bfd, even
+though a single bfd could contain many exports. The overhead involved in
storing, loading, and processing so many bfd's is quite large, and explains the
-tremendous time, memory, and storage needed to link against particularly
+tremendous time, memory, and storage needed to link against particularly
large or complex libraries when using import libs.
-Linking directly to a dll uses no extra command-line switches other than
+Linking directly to a dll uses no extra command-line switches other than
@samp{-L} and @samp{-l}, because @command{ld} already searches for a number
-of names to match each library. All that is needed from the developer's
+of names to match each library. All that is needed from the developer's
perspective is an understanding of this search, in order to force ld to
select the dll instead of an import library.
to find, in the first directory of its search path,
@example
-libxxx.dll.a
-xxx.dll.a
-libxxx.a
+libxxx.dll.a
+xxx.dll.a
+libxxx.a
+xxx.lib
cygxxx.dll (*)
-libxxx.dll
-xxx.dll
+libxxx.dll
+xxx.dll
@end example
before moving on to the next directory in the search path.
-(*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
-where @samp{<prefix>} is set by the @command{ld} option
-@samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
-file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
+(*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
+where @samp{<prefix>} is set by the @command{ld} option
+@samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
+file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
@samp{cygxxx.dll}.
-Other win32-based unix environments, such as mingw or pw32, may use other
-@samp{<prefix>}es, although at present only cygwin makes use of this feature. It
+Other win32-based unix environments, such as mingw or pw32, may use other
+@samp{<prefix>}es, although at present only cygwin makes use of this feature. It
was originally intended to help avoid name conflicts among dll's built for the
various win32/un*x environments, so that (for example) two versions of a zlib dll
could coexist on the same machine.
cygxxx.dll
lib/
libxxx.dll.a (in case of dll's)
- libxxx.a (in case of static archive)
+ libxxx.a (in case of static archive)
@end example
-Linking directly to a dll without using the import library can be
-done two ways:
+Linking directly to a dll without using the import library can be
+done two ways:
1. Use the dll directly by adding the @samp{bin} path to the link line
@example
gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx
-@end example
+@end example
However, as the dll's often have version numbers appended to their names
(@samp{cygncurses-5.dll}) this will often fail, unless one specifies
@example
ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a]
-@end example
+@end example
Then you can link without any make environment changes.
@example
gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx
-@end example
+@end example
This technique also avoids the version number problems, because the following is
perfectly legal
bin/
cygxxx-5.dll
lib/
- libxxx.dll.a -> ../bin/cygxxx-5.dll
+ libxxx.dll.a -> ../bin/cygxxx-5.dll
@end example
Linking directly to a dll without using an import lib will work
@samp{--enable-runtime-pseudo-relocs} is used.
Given the improvements in speed and memory usage, one might justifiably
-wonder why import libraries are used at all. There are two reasons:
+wonder why import libraries are used at all. There are three reasons:
1. Until recently, the link-directly-to-dll functionality did @emph{not}
work with auto-imported data.
for the cygwin kernel makes use of this ability, and it is not
possible to do this without an import lib.
+3. Symbol aliases can only be resolved using an import lib. This is
+critical when linking against OS-supplied dll's (eg, the win32 API)
+in which symbols are usually exported as undecorated aliases of their
+stdcall-decorated assembly names.
+
So, import libs are not going away. But the ability to replace
-true import libs with a simple symbolic link to (or a copy of)
-a dll, in most cases, is a useful addition to the suite of tools
-binutils makes available to the win32 developer. Given the
+true import libs with a simple symbolic link to (or a copy of)
+a dll, in many cases, is a useful addition to the suite of tools
+binutils makes available to the win32 developer. Given the
massive improvements in memory requirements during linking, storage
requirements, and linking speed, we expect that many developers
will soon begin to use this feature whenever possible.
-@item symbol aliasing
+@item symbol aliasing
@table @emph
-@item adding additional names
-Sometimes, it is useful to export symbols with additional names.
+@item adding additional names
+Sometimes, it is useful to export symbols with additional names.
A symbol @samp{foo} will be exported as @samp{foo}, but it can also be
exported as @samp{_foo} by using special directives in the DEF file
when creating the dll. This will affect also the optional created
-import library. Consider the following DEF file:
+import library. Consider the following DEF file:
-@example
+@example
LIBRARY "xyz.dll" BASE=0x61000000
EXPORTS
-foo
+foo
_foo = foo
-@end example
+@end example
The line @samp{_foo = foo} maps the symbol @samp{foo} to @samp{_foo}.
Another method for creating a symbol alias is to create it in the
source code using the "weak" attribute:
-@example
-void foo () @{ /* Do something. */; @}
+@example
+void foo () @{ /* Do something. */; @}
void _foo () __attribute__ ((weak, alias ("foo")));
-@end example
+@end example
See the gcc manual for more information about attributes and weak
symbols.
@item renaming symbols
Sometimes it is useful to rename exports. For instance, the cygwin
-kernel does this regularly. A symbol @samp{_foo} can be exported as
+kernel does this regularly. A symbol @samp{_foo} can be exported as
@samp{foo} but not as @samp{_foo} by using special directives in the
DEF file. (This will also affect the import library, if it is
-created). In the following example:
+created). In the following example:
-@example
+@example
LIBRARY "xyz.dll" BASE=0x61000000
EXPORTS
_foo = foo
-@end example
+@end example
The line @samp{_foo = foo} maps the exported symbol @samp{foo} to
@samp{_foo}.
-@end table
+@end table
Note: using a DEF file disables the default auto-export behavior,
-unless the @samp{--export-all-symbols} command line option is used.
+unless the @samp{--export-all-symbols} command line option is used.
If, however, you are trying to rename symbols, then you should list
-@emph{all} desired exports in the DEF file, including the symbols
-that are not being renamed, and do @emph{not} use the
-@samp{--export-all-symbols} option. If you list only the
-renamed symbols in the DEF file, and use @samp{--export-all-symbols}
-to handle the other symbols, then the both the new names @emph{and}
-the original names for the renamed symbols will be exported.
-In effect, you'd be aliasing those symbols, not renaming them,
+@emph{all} desired exports in the DEF file, including the symbols
+that are not being renamed, and do @emph{not} use the
+@samp{--export-all-symbols} option. If you list only the
+renamed symbols in the DEF file, and use @samp{--export-all-symbols}
+to handle the other symbols, then the both the new names @emph{and}
+the original names for the renamed symbols will be exported.
+In effect, you'd be aliasing those symbols, not renaming them,
which is probably not what you wanted.
@cindex weak externals
individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
distribution.
+@ifset BUGURL
Otherwise, send bug reports for @command{ld} to
-@samp{bug-binutils@@gnu.org}.
+@value{BUGURL}.
+@end ifset
The fundamental principle of reporting bugs usefully is this:
@strong{report all the facts}. If you are not sure whether to state a
were different, the contents of that location would fool the linker
into doing the right thing despite the bug. Play it safe and give a
specific, complete example. That is the easiest thing for you to do,
-and the most helpful.
+and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix
the bug if it is new to us. Therefore, always write your bug reports
Even if the problem you experience is a fatal signal, you should still
say so explicitly. Suppose something strange is going on, such as, your
-copy of @command{ld} is out of synch, or you have encountered a bug in the
+copy of @command{ld} is out of sync, or you have encountered a bug in the
C library on your system. (This has happened!) Your copy might crash
and ours would not. If you told us to expect a crash, then when ours
fails to crash, we would know that the bug was not happening for us. If
@var{secname}, only the @emph{first} sets the start address.
@end table
+@node GNU Free Documentation License
+@appendix GNU Free Documentation License
@include fdl.texi
-@node Index
-@unnumbered Index
+@node LD Index
+@unnumbered LD Index
@printindex cp
% Blame: doc@cygnus.com, 28mar91.
@end tex
-
-@contents
@bye
projects / deliverable / binutils-gdb.git / blobdiff