\input texinfo
@setfilename ld.info
@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-@c 2001, 2002, 2003 Free Software Foundation, Inc.
+@c 2001, 2002, 2003, 2004, 2005, 2006, 2007 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 MSP430
@set PDP11
@set PJ
+@set POWERPC
+@set POWERPC64
@set SH
@set SPARC
@set TIC54X
@end ifinfo
@ifinfo
-This file documents the @sc{gnu} linker LD version @value{VERSION}.
+This file documents the @sc{gnu} linker LD
+@ifset VERSION_PACKAGE
+@value{VERSION_PACKAGE}
+@end ifset
+version @value{VERSION}.
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
-2001, 2002, 2003 Free Software Foundation, Inc.
+2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
@ignore
@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 Free Software Foundation, Inc.
+2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
@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
@ifset HPPA
* HPPA ELF32:: ld and HPPA 32-bit ELF
@end ifset
+@ifset M68HC11
+* M68HC11/68HC12:: ld and the Motorola 68HC11 and 68HC12 families
+@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 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
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}
@samp{0} for base 8). @xref{Entry Point}, for a discussion of defaults
and other ways of specifying the entry point.
+@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
+@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
+explicitly listed in a .def file are still exported, regardless of this
+option. For ELF targeted ports, symbols affected by this option will
+be treated as hidden.
+
@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
@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
Set the text and data sections to be readable and writable. Also, do
not page-align the data segment, and disable linking against shared
libraries. If the output format supports Unix style magic numbers,
-mark the output as @code{OMAGIC}.
+mark the output as @code{OMAGIC}. Note: Although a writable text section
+is allowed for PE-COFF targets, it does not conform to the format
+specification published by Microsoft.
@kindex --no-omagic
@cindex OMAGIC
@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}
@kindex -z @var{keyword}
@item -z @var{keyword}
-The recognized keywords are @code{initfirst}, @code{interpose},
-@code{loadfltr}, @code{nodefaultlib}, @code{nodelete}, @code{nodlopen},
-@code{nodump}, @code{now}, @code{origin}, @code{combreloc}, @code{nocombreloc}
-and @code{nocopyreloc}.
-The other keywords are
-ignored for Solaris compatibility. @code{initfirst} marks the object
-to be initialized first at runtime before any other objects.
-@code{interpose} marks the object that its symbol table interposes
-before all symbols but the primary executable. @code{loadfltr} marks
-the object that its filtees be processed immediately at runtime.
-@code{nodefaultlib} marks the object that the search for dependencies
-of this object will ignore any default library search paths.
-@code{nodelete} marks the object shouldn't be unloaded at runtime.
-@code{nodlopen} marks the object not available to @code{dlopen}.
-@code{nodump} marks the object can not be dumped by @code{dldump}.
-@code{now} marks the object with the non-lazy runtime binding.
-@code{origin} marks the object may contain $ORIGIN.
-@code{defs} disallows undefined symbols.
-@code{muldefs} allows multiple definitions.
-@code{combreloc} combines multiple reloc sections and sorts them
-to make dynamic symbol lookup caching possible.
-@code{nocombreloc} disables multiple reloc sections combining.
-@code{nocopyreloc} disables production of copy relocs.
+The recognized keywords are:
+@table @samp
+
+@item combreloc
+Combines multiple reloc sections and sorts them to make dynamic symbol
+lookup caching possible.
+
+@item defs
+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
+before the runtime initialization of any other objects brought into
+the process at the same time. Similarly the runtime finalization of
+the object will occur after the runtime finalization of any other
+objects.
+
+@item interpose
+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 muldefs
+Allows multiple definitions.
+
+@item nocombreloc
+Disables multiple reloc sections combining.
+
+@item nocopyreloc
+Disables production of copy relocs.
+
+@item nodefaultlib
+Marks the object that the search for dependencies of this object will
+ignore any default library search paths.
+
+@item nodelete
+Marks the object shouldn't be unloaded at runtime.
+
+@item nodlopen
+Marks the object not available to @code{dlopen}.
+
+@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
+when the shared library is linked to using dlopen, instead of
+deferring function call resolution to the point when the function is
+first called.
+
+@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.
@kindex -(
@cindex groups of archives
so the @samp{--accept-unknown-input-arch} option has been added to
restore the old behaviour.
+@kindex --as-needed
+@kindex --no-as-needed
+@item --as-needed
+@itemx --no-as-needed
+This option affects ELF DT_NEEDED tags for dynamic libraries mentioned
+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.
+@option{--no-as-needed} restores the default behaviour.
+
+@kindex --add-needed
+@kindex --no-add-needed
+@item --add-needed
+@itemx --no-add-needed
+This option affects the treatment of dynamic libraries from ELF
+DT_NEEDED tags in dynamic libraries mentioned on the command line after
+the @option{--no-add-needed} option. Normally, the linker will add
+a DT_NEEDED tag for each dynamic library from DT_NEEDED tags.
+@option{--no-add-needed} causes DT_NEEDED tags will never be emitted
+for those libraries from DT_NEEDED tags. @option{--add-needed} restores
+the default behaviour.
+
@kindex -assert @var{keyword}
@item -assert @var{keyword}
This option is ignored for SunOS compatibility.
Set the @code{DF_1_GROUP} flag in the @code{DT_FLAGS_1} entry in the dynamic
section. This causes the runtime linker to handle lookups in this
object and its dependencies to be performed only inside the group.
-@option{--no-undefined} is implied. This option is only meaningful on ELF
-platforms which support shared libraries.
+@option{--unresolved-symbols=report-all} is implied. This option is
+only meaningful on ELF platforms which support shared libraries.
@kindex -Bstatic
@kindex -dn
platforms for which shared libraries are supported. The different
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.
+library searching for @option{-l} options which follow it. This
+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 @samp{--check-sections}.
+restored by using the command line switch @option{--check-sections}.
@cindex cross reference table
@kindex --cref
linker is normally correct; don't use this unless you know what you are
doing.
-@cindex MIPS embedded PIC code
-@kindex --embedded-relocs
-@item --embedded-relocs
-This option is only meaningful when linking MIPS embedded PIC code,
-generated by the -membedded-pic option to the @sc{gnu} compiler and
-assembler. It causes the linker to create a table which may be used at
-runtime to relocate any data which was statically initialized to pointer
-values. See the code in testsuite/ld-empic for details.
-
@kindex --fatal-warnings
@item --fatal-warnings
@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}, nor should it be used with dynamic linking. The default
-behaviour (of not performing this garbage collection) can be restored by
-specifying @samp{--no-gc-sections} on the command line.
+with @samp{-r} or @samp{--emit-relocs}. The default behaviour (of not
+performing this garbage collection) can be restored by specifying
+@samp{--no-gc-sections} on the command line.
+
+@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
@kindex -Map
@item -Map @var{mapfile}
Print a link map to the file @var{mapfile}. See the description of the
-@samp{-M} option, above.
+@option{-M} option, above.
@cindex memory usage
@kindex --no-keep-memory
@kindex -z defs
@item --no-undefined
@itemx -z defs
-Normally when creating a non-symbolic shared library, undefined symbols
-are allowed and left to be resolved by the runtime loader. This option
-disallows such undefined symbols if they come from regular object
-files. The switch @samp{--no-allow-shlib-undefined} controls the
-behaviour for shared objects being linked into the shared library.
+Report unresolved symbol references from regular object files. This
+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.
@kindex --allow-multiple-definition
@kindex -z muldefs
@kindex --no-allow-shlib-undefined
@item --allow-shlib-undefined
@itemx --no-allow-shlib-undefined
-Allow (the default) or disallow undefined symbols in shared objects.
-The setting of this switch overrides @samp{--no-undefined} where
-shared objects are concerned. Thus if @samp{--no-undefined} is set
-but @samp{--no-allow-shlib-undefined} is not, the net result will be
-that undefined symbols in regular object files will trigger an error,
-but undefined symbols in shared objects will be ignored.
-
-The reason that @samp{--allow-shlib-undefined} is the default is that
-the shared object being specified at link time may not be the same one
-that is available at load time, so the symbols might actually be
+Allows (the default) 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 since the kernel
-patches them at load time to select which function is most appropriate
-for the current architecture. eg. to dynamically select an appropriate
-memset function. Apparently it is also normal for HPPA shared
-libraries to have undefined symbols.
+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.
@kindex --no-undefined-version
@item --no-undefined-version
it. This option disallows symbols with undefined version and a fatal error
will be issued instead.
+@kindex --default-symver
+@item --default-symver
+Create and use a default symbol version (the soname) for unversioned
+exported symbols.
+
+@kindex --default-imported-symver
+@item --default-imported-symver
+Create and use a default symbol version (the soname) for unversioned
+imported symbols.
+
@kindex --no-warn-mismatch
@item --no-warn-mismatch
Normally @command{ld} will give an error if you try to link together input
@ifset XTENSA
@xref{Xtensa,, @command{ld} and Xtensa Processors}.
@end ifset
+@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
everything else. This is to prevent gaps between symbols due to
alignment constraints.
+@kindex --sort-section name
+@item --sort-section name
+This option will apply @code{SORT_BY_NAME} to all wildcard section
+patterns in the linker script.
+
+@kindex --sort-section alignment
+@item --sort-section alignment
+This option will apply @code{SORT_BY_ALIGNMENT} to all wildcard section
+patterns in the linker script.
+
@kindex --split-by-file
@item --split-by-file [@var{size}]
Similar to @option{--split-by-reloc} but creates a new output section for
Compute and display statistics about the operation of the linker, such
as execution time and memory usage.
+@kindex --sysroot
+@item --sysroot=@var{directory}
+Use @var{directory} as the location of the sysroot, overriding the
+configure-time default. This option is only supported by linkers
+that were configured using @option{--with-sysroot}.
+
@kindex --traditional-format
@cindex traditional format
@item --traditional-format
Same as --section-start, with @code{.bss}, @code{.data} or
@code{.text} as the @var{sectionname}.
+@kindex --unresolved-symbols
+@item --unresolved-symbols=@var{method}
+Determine how to handle unresolved symbols. There are four possible
+values for @samp{method}:
+
+@table @samp
+@item ignore-all
+Do not report any unresolved symbols.
+
+@item report-all
+Report all unresolved symbols. This is the default.
+
+@item ignore-in-object-files
+Report unresolved symbols that are contained in shared libraries, but
+ignore them if they come from regular object files.
+
+@item ignore-in-shared-libs
+Report unresolved symbols that come from regular object files, but
+ignore them if they come from shared libraries. This can be useful
+when creating a dynamic binary and it is known that all the shared
+libraries that it should be referencing are included on the linker's
+command line.
+@end table
+
+The behaviour for shared libraries on their own can also be controlled
+by the @option{--[no-]allow-shlib-undefined} option.
+
+Normally the linker will generate an error message for each reported
+unresolved symbol but the option @option{--warn-unresolved-symbols}
+can change this to a warning.
+
@kindex --verbose
@cindex verbose
@item --dll-verbose
@cindex combining symbols, warnings on
@item --warn-common
Warn when a common symbol is combined with another common symbol or with
-a symbol definition. Unix linkers allow this somewhat sloppy practice,
+a symbol definition. Unix linkers allow this somewhat sloppy practise,
but linkers on some other operating systems do not. This option allows
you to find potential problems from combining global symbols.
-Unfortunately, some C libraries use this practice, so you may get some
+Unfortunately, some C libraries use this practise, so you may get some
warnings about symbols in the libraries as well as in your programs.
There are three kinds of global symbols, illustrated here by C examples:
is, if the @code{SECTIONS} command does not specify a start address for
the section (@pxref{SECTIONS}).
+@kindex --warn-shared-textrel
+@item --warn-shared-textrel
+Warn if the linker adds a DT_TEXTREL to a shared object.
+
+@kindex --warn-unresolved-symbols
+@item --warn-unresolved-symbols
+If the linker is going to report an unresolved symbol (see the option
+@option{--unresolved-symbols}) it will normally generate an error.
+This option makes it generate a warning instead.
+
+@kindex --error-unresolved-symbols
+@item --error-unresolved-symbols
+This restores the linker's default behaviour of generating errors when
+it is reporting unresolved symbols.
+
@kindex --whole-archive
@cindex including an entire archive
@item --whole-archive
@smallexample
void *
-__wrap_malloc (int c)
+__wrap_malloc (size_t c)
@{
- printf ("malloc called with %ld\n", c);
+ printf ("malloc called with %zu\n", c);
return __real_malloc (c);
@}
@end smallexample
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
created. By default, the new dynamic tags are not created. Note that
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 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 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.
+
@end table
@c man end
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
exported. The symbol names may be delimited by commas or colons.
[This option is specific to the i386 PE targeted port of the linker]
-@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
-@code{--exclude-libs ALL} excludes symbols in all archive libraries from
-automatic export. Symbols explicitly listed in a .def file are still exported,
-regardless of this option.
-[This option is specific to the i386 PE targeted port of the linker]
-
@kindex --file-alignment
@item --file-alignment
Specify the file alignment. Sections in the file will always begin at
symbols before they are exported.
[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 ``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 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 --major-image-version
@item --major-image-version @var{value}
Sets the major number of the ``image version''. Defaults to 1.
The linker will create the file @var{file} which will contain an
import lib corresponding to the DLL the linker is generating. This
import lib (which should be called @code{*.dll.a} or @code{*.a}
-may be used to link clients against the generated DLL; this behavior
+may be used to link clients against the generated DLL; this behaviour
makes it possible to skip a separate @code{dlltool} import library
creation step.
[This option is specific to the i386 PE targeted port 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
-@code{lib<basename>.dll}. This behavior allows easy distinction
+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
-building the import libraries with those DATA exports. This generally
-will 'just work' -- but sometimes you may see this message:
+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.
-"variable '<var>' can't be auto-imported. Please read the
+Using 'auto-import' generally will 'just work' -- but sometimes you may
+see this message:
+
+"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
+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
One way is to use --enable-runtime-pseudo-reloc switch. This leaves the task
of adjusting references in your client code for runtime environment, so
-this method works only when runtime environtment supports this feature.
+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,
A third method of dealing with this difficulty is to abandon
'auto-import' for the offending symbol and mark it with
-@code{__declspec(dllimport)}. However, in practice that
+@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
@kindex --disable-auto-import
@item --disable-auto-import
-Do not attempt to do sophisticalted 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]
@itemx --subsystem @var{which}:@var{major}.@var{minor}
Specifies the subsystem under which your program will execute. The
legal values for @var{which} are @code{native}, @code{windows},
-@code{console}, and @code{posix}. You may optionally set the
-subsystem version also.
+@code{console}, @code{posix}, and @code{xbox}. You may optionally set
+the subsystem version also. Numeric values are also accepted for
+@var{which}.
[This option is specific to the i386 PE targeted port of the linker]
@end table
@c man end
+@ifset M68HC11
+@subsection Options specific to Motorola 68HC11 and 68HC12 targets
+
+@c man begin OPTIONS
+
+The 68HC11 and 68HC12 linkers support specific options to control the
+memory bank switching mapping and trampoline code generation.
+
+@table @gcctabopt
+
+@kindex --no-trampoline
+@item --no-trampoline
+This option disables the generation of trampoline. By default a trampoline
+is generated for each far function which is called using a @code{jsr}
+instruction (this happens when a pointer to a far function is taken).
+
+@kindex --bank-window
+@item --bank-window @var{name}
+This option indicates to the linker the name of the memory region in
+the @samp{MEMORY} specification that describes the memory bank window.
+The definition of such region is then used by the linker to compute
+paging and addresses within the memory window.
+
+@end table
+
+@c man end
+@end ifset
+
@ifset UsesEnvVars
@node Environment
@section Environment Variables
@c man begin ENVIRONMENT
-You can change the behavior of @command{ld} with the environment variables
+You can change the behaviour of @command{ld} with the environment variables
@ifclear SingleFormat
@code{GNUTARGET},
@end ifclear
output section, the value of the location counter will be
@samp{0x8000000} plus the size of the @samp{.data} output section. The
effect is that the linker will place the @samp{.bss} output section
-immediately after the @samp{.data} output section in memory
+immediately after the @samp{.data} output section in memory.
The linker will ensure that each output section has the required
alignment, by increasing the location counter if necessary. In this
new undefined references are created. See the description of @samp{-(}
in @ref{Options,,Command Line Options}.
+@item AS_NEEDED(@var{file}, @var{file}, @dots{})
+@itemx AS_NEEDED(@var{file} @var{file} @dots{})
+@kindex AS_NEEDED(@var{files})
+This construct can appear only inside of the @code{INPUT} or @code{GROUP}
+commands, among other filenames. The files listed will be handled
+as if they appear directly in the @code{INPUT} or @code{GROUP} commands,
+with the exception of ELF shared libraries, that will be added only
+when they are actually needed. This construct essentially enables
+@option{--as-needed} option for all the files listed inside of it
+and restores previous @option{--as-needed} resp. @option{--no-as-needed}
+setting afterwards.
+
@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
@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
defined, and the value will be adjusted accordingly.
The special symbol name @samp{.} indicates the location counter. You
-may only use this within a @code{SECTIONS} command.
+may only use this within a @code{SECTIONS} command. @xref{Location Counter}.
The semicolon after @var{expression} is required.
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}
Discarding}.
@node Output Section Address
-@subsection Output Section Description
+@subsection Output Section Address
@cindex address, section
@cindex section address
The @var{address} is an expression for the VMA (the virtual memory
.data1 : @{ data.o(.data) @}
@end smallexample
-@cindex SORT
+@cindex SORT_BY_NAME
Normally, the linker will place files and sections matched by wildcards
in the order in which they are seen during the link. You can change
-this by using the @code{SORT} keyword, which appears before a wildcard
-pattern in parentheses (e.g., @code{SORT(.text*)}). When the
-@code{SORT} keyword is used, the linker will sort the files or sections
+this by using the @code{SORT_BY_NAME} keyword, which appears before a wildcard
+pattern in parentheses (e.g., @code{SORT_BY_NAME(.text*)}). When the
+@code{SORT_BY_NAME} keyword is used, the linker will sort the files or sections
into ascending order by name before placing them in the output file.
+@cindex SORT_BY_ALIGNMENT
+@code{SORT_BY_ALIGNMENT} is very similar to @code{SORT_BY_NAME}. The
+difference is @code{SORT_BY_ALIGNMENT} will sort sections into
+ascending order by alignment before placing them in the output file.
+
+@cindex SORT
+@code{SORT} is an alias for @code{SORT_BY_NAME}.
+
+When there are nested section sorting commands in linker script, there
+can be at most 1 level of nesting for section sorting commands.
+
+@enumerate
+@item
+@code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)).
+It will sort the input sections by name first, then by alignment if 2
+sections have the same name.
+@item
+@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)).
+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
+treated the same as @code{SORT_BY_NAME} (wildcard section pattern).
+@item
+@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern))
+is treated the same as @code{SORT_BY_ALIGNMENT} (wildcard section pattern).
+@item
+All other nested section sorting commands are invalid.
+@end enumerate
+
+When both command line section sorting option and linker script
+section sorting command are used, section sorting command always
+takes precedence over the command line option.
+
+If the section sorting command in linker script isn't nested, the
+command line option will make the section sorting command to be
+treated as nested sorting command.
+
+@enumerate
+@item
+@code{SORT_BY_NAME} (wildcard section pattern ) with
+@option{--sort-sections alignment} is equivalent to
+@code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)).
+@item
+@code{SORT_BY_ALIGNMENT} (wildcard section pattern) with
+@option{--sort-section name} is equivalent to
+@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)).
+@end enumerate
+
+If the section sorting command in linker script is nested, the
+command line option will be ignored.
+
If you ever get confused about where input sections are going, use the
@samp{-M} linker option to generate a map file. The map file shows
precisely how input sections are mapped to output sections.
it is often useful to mark sections that should not be eliminated.
This is accomplished by surrounding an input section's wildcard entry
with @code{KEEP()}, as in @code{KEEP(*(.init))} or
-@code{KEEP(SORT(*)(.ctors))}.
+@code{KEEP(SORT_BY_NAME(*)(.ctors))}.
@node Input Section Example
@subsubsection Input Section Example
ignored for other object file formats.
The symbol @w{@code{__CTOR_LIST__}} marks the start of the global
-constructors, and the symbol @w{@code{__DTOR_LIST}} marks the end. The
+constructors, and the symbol @w{@code{__CTOR_END__}} marks the end.
+Similarly, @w{@code{__DTOR_LIST__}} and @w{@code{__DTOR_END__}} mark
+the start and end of the global destructors. The
first word in the list is the number of entries, followed by the address
of each constructor or destructor, followed by a zero word. The
compiler must arrange to actually run the code. For these object file
which provides some control over the order in which global constructors
are run, you must sort the constructors at link time to ensure that they
are executed in the correct order. When using the @code{CONSTRUCTORS}
-command, use @samp{SORT(CONSTRUCTORS)} instead. When using the
-@code{.ctors} and @code{.dtors} sections, use @samp{*(SORT(.ctors))} and
-@samp{*(SORT(.dtors))} instead of just @samp{*(.ctors)} and
+command, use @samp{SORT_BY_NAME(CONSTRUCTORS)} instead. When using the
+@code{.ctors} and @code{.dtors} sections, use @samp{*(SORT_BY_NAME(.ctors))} and
+@samp{*(SORT_BY_NAME(.dtors))} instead of just @samp{*(.ctors)} and
@samp{*(.dtors)}.
Normally the compiler and linker will handle these issues automatically,
@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. Alternatively, with @samp{AT>@var{lma_region}} expression,
-you may specify a memory region for the section's load address. @xref{MEMORY}.
+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
@cindex initialized data in ROM
@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
@kindex ORIGIN =
@kindex o =
@kindex org =
-The @var{origin} is an expression for the start address of the memory
-region. The expression must evaluate to a constant before memory
-allocation is performed, which means that you may not use any section
-relative symbols. The keyword @code{ORIGIN} may be abbreviated to
-@code{org} or @code{o} (but not, for example, @code{ORG}).
+The @var{origin} is an numerical expression for the start address of
+the memory region. The expression must evaluate to a constant and it
+cannot involve any symbols. The keyword @code{ORIGIN} may be
+abbreviated to @code{org} or @code{o} (but not, for example,
+@code{ORG}).
@kindex LENGTH =
@kindex len =
@kindex l =
The @var{len} is an expression for the size in bytes of the memory
region. As with the @var{origin} expression, the expression must
-evaluate to a constant before memory allocation is performed. The
-keyword @code{LENGTH} may be abbreviated to @code{len} or @code{l}.
+be numerical only and must evaluate to a constant. The keyword
+@code{LENGTH} may be abbreviated to @code{len} or @code{l}.
In the following example, we specify that there are two memory regions
available for allocation: one starting at @samp{0} for 256 kilobytes,
output sections directed to a memory region are too large for the
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
+@code{LENGTH(@var{memory})} functions:
+
+@smallexample
+@group
+ _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
+@end group
+@end smallexample
+
@node PHDRS
@section PHDRS Command
@kindex PHDRS
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}
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.
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
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.
+
@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 values from the @samp{.data} input sections and before the end of
the @samp{.data} output section itself.
+@cindex dot outside sections
+Setting symbols to the value of the location counter outside of an
+output section statement can result in unexpected values if the linker
+needs to place orphan sections. For example, given the following:
+
+@smallexample
+SECTIONS
+@{
+ start_of_text = . ;
+ .text: @{ *(.text) @}
+ end_of_text = . ;
+
+ start_of_data = . ;
+ .data: @{ *(.data) @}
+ end_of_data = . ;
+@}
+@end smallexample
+
+If the linker needs to place some input section, e.g. @code{.rodata},
+not mentioned in the script, it might choose to place that section
+between @code{.text} and @code{.data}. You might think the linker
+should place @code{.rodata} on the blank line in the above script, but
+blank lines are of no particular significance to the linker. As well,
+the linker doesn't associate the above symbol names with their
+sections. Instead, it assumes that all assignments or other
+statements belong to the previous output section, except for the
+special case of an assignment to @code{.}. I.e., the linker will
+place the orphan @code{.rodata} section as if the script was written
+as follows:
+
+@smallexample
+SECTIONS
+@{
+ start_of_text = . ;
+ .text: @{ *(.text) @}
+ end_of_text = . ;
+
+ start_of_data = . ;
+ .rodata: @{ *(.rodata) @}
+ .data: @{ *(.data) @}
+ end_of_data = . ;
+@}
+@end smallexample
+
+This may or may not be the script author's intention for the value of
+@code{start_of_data}. One way to influence the orphan section
+placement is to assign the location counter to itself, as the linker
+assumes that an assignment to @code{.} is setting the start address of
+a following output section and thus should be grouped with that
+section. So you could write:
+
+@smallexample
+SECTIONS
+@{
+ start_of_text = . ;
+ .text: @{ *(.text) @}
+ end_of_text = . ;
+
+ . = . ;
+ start_of_data = . ;
+ .data: @{ *(.data) @}
+ end_of_data = . ;
+@}
+@end smallexample
+
+Now, the orphan @code{.rodata} section will be placed between
+@code{end_of_text} and @code{start_of_data}.
+
@need 2000
@node Operators
@subsection Operators
@end group
@end smallexample
-@item ALIGN(@var{exp})
-@kindex ALIGN(@var{exp})
+@item ALIGN(@var{align})
+@itemx ALIGN(@var{exp},@var{align})
+@kindex ALIGN(@var{align})
+@kindex ALIGN(@var{exp},@var{align})
@cindex round up location counter
@cindex align location counter
-Return the location counter (@code{.}) aligned to the next @var{exp}
-boundary.
-@code{ALIGN} doesn't change the value of the location counter---it just
-does arithmetic on it. Here is an example which aligns the output
-@code{.data} section to the next @code{0x2000} byte boundary after the
-preceding section and sets a variable within the section to the next
-@code{0x8000} boundary after the input sections:
+@cindex round up expression
+@cindex align expression
+Return the location counter (@code{.}) or arbitrary expression aligned
+to the next @var{align} boundary. The single operand @code{ALIGN}
+doesn't change the value of the location counter---it just does
+arithmetic on it. The two operand @code{ALIGN} allows an arbitrary
+expression to be aligned upwards (@code{ALIGN(@var{align})} is
+equivalent to @code{ALIGN(., @var{align})}).
+
+Here is an example which aligns the output @code{.data} section to the
+next @code{0x2000} byte boundary after the preceding section and sets a
+variable within the section to the next @code{0x8000} boundary after the
+input sections:
@smallexample
@group
SECTIONS @{ @dots{}
. = DATA_SEGMENT_END(.);
@end smallexample
+@item DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
+@kindex DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
+This defines the end of the @code{PT_GNU_RELRO} segment when
+@samp{-z relro} option is used. Second argument is returned.
+When @samp{-z relro} option is not present, @code{DATA_SEGMENT_RELRO_END}
+does nothing, otherwise @code{DATA_SEGMENT_ALIGN} is padded so that
+@var{exp} + @var{offset} is aligned to the most commonly used page
+boundary for particular target. If present in the linker script,
+it must always come in between @code{DATA_SEGMENT_ALIGN} and
+@code{DATA_SEGMENT_END}.
+
+@smallexample
+ . = DATA_SEGMENT_RELRO_END(24, .);
+@end smallexample
+
@item DEFINED(@var{symbol})
@kindex DEFINED(@var{symbol})
@cindex symbol defaults
Return 1 if @var{symbol} is in the linker global symbol table and is
-defined, otherwise return 0. You can use this function to provide
+defined before the statement using DEFINED in the script, otherwise
+return 0. You can use this function to provide
default values for symbols. For example, the following script fragment
shows how to set a global symbol @samp{begin} to the first location in
the @samp{.text} section---but if a symbol called @samp{begin} already
@end group
@end smallexample
+@item LENGTH(@var{memory})
+@kindex LENGTH(@var{memory})
+Return the length of the memory region named @var{memory}.
+
@item LOADADDR(@var{section})
@kindex LOADADDR(@var{section})
@cindex section load address in expression
use the @code{MEMORY} command to define discontinuous memory for the
output file, the two functions are equivalent.
+@item ORIGIN(@var{memory})
+@kindex ORIGIN(@var{memory})
+Return the origin of the memory region named @var{memory}.
+
+@item SEGMENT_START(@var{segment}, @var{default})
+@kindex SEGMENT_START(@var{segment}, @var{default})
+Return the base address of the named @var{segment}. If an explicit
+value has been given for this segment (with a command-line @samp{-T}
+option) that value will be returned; otherwise the value will be
+@var{default}. At present, the @samp{-T} command-line option can only
+be used to set the base address for the ``text'', ``data'', and
+``bss'' sections, but you use @code{SEGMENT_START} with any segment
+name.
+
@item SIZEOF(@var{section})
@kindex SIZEOF(@var{section})
@cindex section size
@ifset MSP430
* MSP430:: @command{ld} and MSP430
@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 TICOFF
* TI COFF:: @command{ld} and TI COFF
@end ifset
(That is: the linker turns @samp{mov.b @code{@@}@var{aa}:16} into
@samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the
top page of memory).
+
+@item bit manipulation instructions
+@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
+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
+the top page of memory).
+
+@item system control instructions
+@command{ld} finds all @code{ldc.w, stc.w} instructions which use the
+32 bit absolute address form, but refer to the top page of memory, and
+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
+the top page of memory).
@end table
@ifclear GENERIC
@raisesections
@end ifclear
+@ifset M68HC11
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node M68HC11/68HC12
+@section @command{ld} and the Motorola 68HC11 and 68HC12 families
+
+@cindex M68HC11 and 68HC12 support
+
+@subsection Linker Relaxation
+
+For the Motorola 68HC11, @command{ld} can perform these global
+optimizations when you specify the @samp{--relax} command-line option.
+
+@table @emph
+@cindex relaxing on M68HC11
+@item relaxing address modes
+@command{ld} finds all @code{jsr} and @code{jmp} instructions whose
+targets are within eight bits, and turns them into eight-bit
+program-counter relative @code{bsr} and @code{bra} instructions,
+respectively.
+
+@command{ld} also looks at all 16-bit extended addressing modes and
+transforms them in a direct addressing mode when the address is in
+page 0 (between 0 and 0x0ff).
+
+@item relaxing gcc instruction group
+When @command{gcc} is called with @option{-mrelax}, it can emit group
+of instructions that the linker can optimize to use a 68HC11 direct
+addressing mode. These instructions consists of @code{bclr} or
+@code{bset} instructions.
+
+@end table
+
+@subsection Trampoline Generation
+
+@cindex trampoline generation on M68HC11
+@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
+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 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.
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
@node ARM
-@section @command{ld}'s Support for Interworking Between ARM and Thumb Code
+@section @command{ld} and the ARM family
@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 BE8
+@kindex --be8
+The @samp{--be8} switch instructs @command{ld} to generate BE8 format
+executables. This option is only valid when linking big-endian objects.
+The resulting image will contain big-endian data and little-endian code.
+
+@cindex TARGET1
+@kindex --target1-rel
+@kindex --target1-abs
+The @samp{R_ARM_TARGET1} relocation is typically used for entries in the
+@samp{.init_array} section. It is interpreted as either @samp{R_ARM_REL32}
+or @samp{R_ARM_ABS32}, depending on the target. The @samp{--target1-rel}
+and @samp{--target1-abs} switches override the default.
+
+@cindex TARGET2
+@kindex --target2=@var{type}
+The @samp{--target2=type} switch overrides the default definition of the
+@samp{R_ARM_TARGET2} relocation. Valid values for @samp{type}, their
+meanings, and target defaults are as follows:
+@table @samp
+@item rel
+@samp{R_ARM_REL32} (arm*-*-elf, arm*-*-eabi)
+@item abs
+@samp{R_ARM_ABS32} (arm*-*-symbianelf)
+@item got-rel
+@samp{R_ARM_GOT_PREL} (arm*-*-linux, arm*-*-*bsd)
+@end table
+
+@cindex FIX_V4BX
+@kindex --fix-v4bx
+The @samp{R_ARM_V4BX} relocation (defined by the ARM AAELF
+specification) enables objects compiled for the ARMv4 architecture to be
+interworking-safe when linked with other objects compiled for ARMv4t, but
+also allows pure ARMv4 binaries to be built from the same ARMv4 objects.
+
+In the latter case, the switch @option{--fix-v4bx} must be passed to the
+linker, which causes v4t @code{BX rM} instructions to be rewritten as
+@code{MOV PC,rM}, since v4 processors do not have a @code{BX} instruction.
+
+In the former case, the switch should not be used, and @samp{R_ARM_V4BX}
+relocations are ignored.
+
+@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 @samp{--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.
+
@ifclear GENERIC
@lowersections
@end ifclear
@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.
+
+@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 scrip @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 TICOFF
@ifclear GENERIC
@raisesections
@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
+See @ref{Options,,Command Line Options} for detailed description of the
command line options mentioned here.
@table @emph
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
+another_foo = abc.dll.afoo
+var1 DATA
@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.
+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
+
+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
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.
+information.
@end table
@cindex automatic data imports
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
+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
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
+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
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.
@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
+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
@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 the renamed symbols will be exported.
+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
+@item weak externals
+The Windows object format, PE, specifies a form of weak symbols called
+weak externals. When a weak symbol is linked and the symbol is not
+defined, the weak symbol becomes an alias for some other symbol. There
+are three variants of weak externals:
+@itemize
+@item Definition is searched for in objects and libraries, historically
+called lazy externals.
+@item Definition is searched for only in other objects, not in libraries.
+This form is not presently implemented.
+@item No search; the symbol is an alias. This form is not presently
+implemented.
+@end itemize
+As a GNU extension, weak symbols that do not specify an alternate symbol
+are supported. If the symbol is undefined when linking, the symbol
+uses a default value.
@end table
@ifclear GENERIC
group of files followed by the @code{.text} sections of that group of
files. Then, the @code{.literal} sections from the rest of the files
and the @code{.text} sections from the rest of the files would follow.
-The non-interleaved order can still be specified as:
-@smallexample
-SECTIONS
-@{
- .text : @{
- *(.literal) *(.text)
- @}
-@}
-@end smallexample
-
-@cindex @code{--relax} on Xtensa
+@cindex @option{--relax} on Xtensa
@cindex relaxing on Xtensa
+Relaxation is enabled by default for the Xtensa version of @command{ld} and
+provides two important link-time optimizations. The first optimization
+is to combine identical literal values to reduce code size. A redundant
+literal will be removed and all the @code{L32R} instructions that use it
+will be changed to reference an identical literal, as long as the
+location of the replacement literal is within the offset range of all
+the @code{L32R} instructions. The second optimization is to remove
+unnecessary overhead from assembler-generated ``longcall'' sequences of
+@code{L32R}/@code{CALLX@var{n}} when the target functions are within
+range of direct @code{CALL@var{n}} instructions.
+
+For each of these cases where an indirect call sequence can be optimized
+to a direct call, the linker will change the @code{CALLX@var{n}}
+instruction to a @code{CALL@var{n}} instruction, remove the @code{L32R}
+instruction, and remove the literal referenced by the @code{L32R}
+instruction if it is not used for anything else. Removing the
+@code{L32R} instruction always reduces code size but can potentially
+hurt performance by changing the alignment of subsequent branch targets.
+By default, the linker will always preserve alignments, either by
+switching some instructions between 24-bit encodings and the equivalent
+density instructions or by inserting a no-op in place of the @code{L32R}
+instruction that was removed. If code size is more important than
+performance, the @option{--size-opt} option can be used to prevent the
+linker from widening density instructions or inserting no-ops, except in
+a few cases where no-ops are required for correctness.
+
+The following Xtensa-specific command-line options can be used to
+control the linker:
+
+@cindex Xtensa options
+@table @option
@kindex --no-relax
-The Xtensa version of @command{ld} enables the @option{--relax} option by
-default to attempt to reduce space in the output image by combining
-literals with identical values. It also provides the
-@option{--no-relax} option to disable this optimization. When enabled,
-the relaxation algorithm ensures that a literal will only be merged with
-another literal when the new merged literal location is within the
-offset range of all of its uses.
-
-The relaxation mechanism will also attempt to optimize
-assembler-generated ``longcall'' sequences of
-@code{L32R}/@code{CALLX@var{n}} when the target is known to fit into a
-@code{CALL@var{n}} instruction encoding. The current optimization
-converts the sequence into @code{NOP}/@code{CALL@var{n}} and removes the
-literal referenced by the @code{L32R} instruction.
+@item --no-relax
+Since the Xtensa version of @code{ld} enables the @option{--relax} option
+by default, the @option{--no-relax} option is provided to disable
+relaxation.
+
+@item --size-opt
+When optimizing indirect calls to direct calls, optimize for code size
+more than performance. With this option, the linker will not insert
+no-ops or widen density instructions to preserve branch target
+alignment. There may still be some cases where no-ops are required to
+preserve the correctness of the code.
+@end table
@ifclear GENERIC
@lowersections
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
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
@include fdl.texi
-@node Index
-@unnumbered Index
+@node LD Index
+@unnumbered LD Index
@printindex cp
projects / deliverable / binutils-gdb.git / blobdiff