\input texinfo
@setfilename ld.info
@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-@c 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+@c 2001, 2002, 2003, 2004, 2005, 2006, 2007 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, 2004 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, 2004 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 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}
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
@cindex retain relocations in final executable
@item -q
@itemx --emit-relocs
-Leave relocation sections and contents in fully linked exececutables.
+Leave relocation sections and contents in fully linked executables.
Post link analysis and optimization tools may need this information in
order to perform correct modifications of executables. This results
in larger executables.
This option is currently only supported on ELF platforms.
+@kindex --force-dynamic
+@cindex forcing the creation of dynamic sections
+@item --force-dynamic
+Force the output file to have dynamic sections. This option is specific
+to VxWorks targets.
+
@cindex partial link
@cindex relocatable output
@kindex -r
specified by any preceding @samp{-L} options. Multiple @samp{-T}
options accumulate.
+@kindex -dT @var{script}
+@kindex --default-script=@var{script}
+@cindex script files
+@item -dT @var{scriptfile}
+@itemx --default-script=@var{scriptfile}
+Use @var{scriptfile} as the default linker script. @xref{Scripts}.
+
+This option is similar to the @option{--script} option except that
+processing of the script is delayed until after the rest of the
+command line has been processed. This allows options placed after the
+@option{--default-script} option on the command line to affect the
+behaviour of the linker script, which can be important when the linker
+command line cannot be directly controlled by the user. (eg because
+the command line is being constructed by another tool, such as
+@samp{gcc}).
+
@kindex -u @var{symbol}
@kindex --undefined=@var{symbol}
@cindex undefined symbol
@kindex -X
@kindex --discard-locals
@cindex local symbols, deleting
-@cindex L, deleting symbols beginning
@item -X
@itemx --discard-locals
-Delete all temporary local symbols. For most targets, this is all local
-symbols whose names begin with @samp{L}.
+Delete all temporary local symbols. (These symbols start with
+system-specific local label prefixes, typically @samp{.L} for ELF systems
+or @samp{L} for traditional a.out systems.)
@kindex -y @var{symbol}
@kindex --trace-symbol=@var{symbol}
Disallows undefined symbols in object files. Undefined symbols in
shared libraries are still allowed.
+@item execstack
+Marks the object as requiring executable stack.
+
@item initfirst
This option is only meaningful when building a shared object.
It marks the object so that its runtime initialization will occur
Marks the object that its symbol table interposes before all symbols
but the primary executable.
+@item lazy
+When generating an executable or shared library, mark it to tell the
+dynamic linker to defer function call resolution to the point when
+the function is called (lazy binding), rather than at load time.
+Lazy binding is the default.
+
@item loadfltr
Marks the object that its filters be processed immediately at
runtime.
@item nodump
Marks the object can not be dumped by @code{dldump}.
+@item noexecstack
+Marks the object as not requiring executable stack.
+
+@item norelro
+Don't create an ELF @code{PT_GNU_RELRO} segment header in the object.
+
@item now
When generating an executable or shared library, mark it to tell the
dynamic linker to resolve all symbols when the program is started, or
@item origin
Marks the object may contain $ORIGIN.
+@item relro
+Create an ELF @code{PT_GNU_RELRO} segment header in the object.
+
+@item max-page-size=@var{value}
+Set the emulation maximum page size to @var{value}.
+
+@item common-page-size=@var{value}
+Set the emulation common page size to @var{value}.
+
@end table
-Other keywords are ignored for Solaris compatibility.
+Other keywords are ignored for Solaris compatibility.
@kindex -(
@cindex groups of archives
variants of this option are for compatibility with various systems. You
may use this option multiple times on the command line: it affects
library searching for @option{-l} options which follow it. This
-option also implies @option{--unresolved-symbols=report-all}.
+option also implies @option{--unresolved-symbols=report-all}. This
+option can be used with @option{-shared}. Doing so means that a
+shared library is being created but that all of the library's external
+references must be resolved by pulling in entries from static
+libraries.
@kindex -Bsymbolic
@item -Bsymbolic
within the shared library. This option is only meaningful on ELF
platforms which support shared libraries.
+@kindex -Bsymbolic-functions
+@item -Bsymbolic-functions
+When creating a shared library, bind references to global function
+symbols to the definition within the shared library, if any.
+This option is only meaningful on ELF platforms which support shared
+libraries.
+
+@kindex --dynamic-list=@var{dynamic-list-file}
+@item --dynamic-list=@var{dynamic-list-file}
+Specify the name of a dynamic list file to the linker. This is
+typically used when creating shared libraries to specify a list of
+global symbols whose references shouldn't be bound to the definition
+within the shared library, or creating dynamically linked executables
+to specify a list of symbols which should be added to the symbol table
+in the executable. This option is only meaningful on ELF platforms
+which support shared libraries.
+
+The format of the dynamic list is the same as the version node without
+scope and node name. See @ref{VERSION} for more information.
+
+@kindex --dynamic-list-data
+@item --dynamic-list-data
+Include all global data symbols to the dynamic list.
+
+@kindex --dynamic-list-cpp-new
+@item --dynamic-list-cpp-new
+Provide the builtin dynamic list for C++ operator new and delete. It
+is mainly useful for building shared libstdc++.
+
+@kindex --dynamic-list-cpp-typeinfo
+@item --dynamic-list-cpp-typeinfo
+Provide the builtin dynamic list for C++ runtime type identification.
+
@kindex --check-sections
@kindex --no-check-sections
@item --check-sections
@itemx --no-check-sections
Asks the linker @emph{not} to check section addresses after they have
-been assigned to see if there any overlaps. Normally the linker will
+been assigned to see if there are any overlaps. Normally the linker will
perform this check, and if it finds any overlaps it will produce
suitable error messages. The linker does know about, and does make
allowances for sections in overlays. The default behaviour can be
@kindex --gc-sections
@kindex --no-gc-sections
@cindex garbage collection
-@item --no-gc-sections
-@itemx --gc-sections
+@item --gc-sections
+@itemx --no-gc-sections
Enable garbage collection of unused input sections. It is ignored on
targets that do not support this option. This option is not compatible
-with @samp{-r}. The default behaviour (of not performing this garbage
-collection) can be restored by specifying @samp{--no-gc-sections} on
-the command line.
+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
is done even if the linker is creating a non-symbolic shared library.
The switch @option{--[no-]allow-shlib-undefined} controls the
behaviour for reporting unresolved references found in shared
-libraries being linked in.
+libraries being linked in.
@kindex --allow-multiple-definition
@kindex -z muldefs
the one that is available at load time, so the symbols might actually be
resolvable at load time. Plus there are some systems, (eg BeOS) where
undefined symbols in shared libraries is normal. (The kernel patches
-them at load time to select which function is most appropriate
+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.
@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
@kindex --warn-shared-textrel
@item --warn-shared-textrel
-Warn if the linker adds a DT_TEXTREL to a shared object.
+Warn if the linker adds a DT_TEXTREL to a shared object.
@kindex --warn-unresolved-symbols
@item --warn-unresolved-symbols
file as @code{__wrap_malloc}; if you do, the assembler may resolve the
call before the linker has a chance to wrap it to @code{malloc}.
+@kindex --eh-frame-hdr
+@item --eh-frame-hdr
+Request creation of @code{.eh_frame_hdr} section and ELF
+@code{PT_GNU_EH_FRAME} segment header.
+
@kindex --enable-new-dtags
@kindex --disable-new-dtags
@item --enable-new-dtags
those options are only available for ELF systems.
@kindex --hash-size=@var{number}
+@item --hash-size=@var{number}
Set the default size of the linker's hash tables to a prime number
close to @var{number}. Increasing this value can reduce the length of
time it takes the linker to perform its tasks, at the expense of
increasing the linker's memory requirements. Similarly reducing this
value can reduce the memory requirements at the expense of speed.
+@kindex --hash-style=@var{style}
+@item --hash-style=@var{style}
+Set the type of linker's hash table(s). @var{style} can be either
+@code{sysv} for classic ELF @code{.hash} section, @code{gnu} for
+new style GNU @code{.gnu.hash} section or @code{both} for both
+the classic ELF @code{.hash} and new style GNU @code{.gnu.hash}
+hash tables. The default is @code{sysv}.
+
@kindex --reduce-memory-overheads
@item --reduce-memory-overheads
This option reduces memory requirements at ld runtime, at the expense of
-linking speed. This was introduced to to select the old O(n^2) algorithm
+linking speed. This was introduced to select the old O(n^2) algorithm
for link map file generation, rather than the new O(n) algorithm which uses
about 40% more memory for symbol storage.
-Another affect of the switch is to set the default hash table size to
+Another effect of the switch is to set the default hash table size to
1021, which again saves memory at the cost of lengthening the linker's
run time. This is not done however if the @option{--hash-size} switch
has been used.
explicitly exported via DEF files or implicitly exported via function
attributes, the default is to not export anything else unless this
option is given. Note that the symbols @code{DllMain@@12},
-@code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and
+@code{DllEntryPoint@@0}, @code{DllMainCRTStartup@@12}, and
@code{impure_ptr} will not be automatically
-exported. Also, symbols imported from other DLLs will not be
-re-exported, nor will symbols specifying the DLL's internal layout
-such as those beginning with @code{_head_} or ending with
-@code{_iname}. In addition, no symbols from @code{libgcc},
+exported. Also, symbols imported from other DLLs will not be
+re-exported, nor will symbols specifying the DLL's internal layout
+such as those beginning with @code{_head_} or ending with
+@code{_iname}. In addition, no symbols from @code{libgcc},
@code{libstd++}, @code{libmingw32}, or @code{crtX.o} will be exported.
Symbols whose names begin with @code{__rtti_} or @code{__builtin_} will
not be exported, to help with C++ DLLs. Finally, there is an
-extensive list of cygwin-private symbols that are not exported
+extensive list of cygwin-private symbols that are not exported
(obviously, this applies on when building DLLs for cygwin targets).
-These cygwin-excludes are: @code{_cygwin_dll_entry@@12},
+These cygwin-excludes are: @code{_cygwin_dll_entry@@12},
@code{_cygwin_crt0_common@@8}, @code{_cygwin_noncygwin_dll_entry@@12},
-@code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll},
+@code{_fmode}, @code{_impure_ptr}, @code{cygwin_attach_dll},
@code{cygwin_premain0}, @code{cygwin_premain1}, @code{cygwin_premain2},
-@code{cygwin_premain3}, and @code{environ}.
+@code{cygwin_premain3}, and @code{environ}.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --exclude-symbols
@kindex --large-address-aware
@item --large-address-aware
-If given, the appropriate bit in the ``Charateristics'' field of the COFF
+If given, the appropriate bit in the ``Characteristics'' field of the COFF
header is set to indicate that this executable supports virtual addresses
-greater than 2 gigabytes. This should be used in conjuction with the /3GB
+greater than 2 gigabytes. This should be used in conjunction with the /3GB
or /USERVA=@var{value} megabytes switch in the ``[operating systems]''
section of the BOOT.INI. Otherwise, this bit has no effect.
[This option is specific to PE targeted ports of the linker]
@kindex --dll-search-prefix
@item --dll-search-prefix @var{string}
When linking dynamically to a dll without an import library,
-search for @code{<string><basename>.dll} in preference to
+search for @code{<string><basename>.dll} in preference to
@code{lib<basename>.dll}. This behaviour allows easy distinction
between DLLs built for the various "subplatforms": native, cygwin,
uwin, pw, etc. For instance, cygwin DLLs typically use
-@code{--dll-search-prefix=cyg}.
+@code{--dll-search-prefix=cyg}.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --enable-auto-import
@item --enable-auto-import
-Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for
-DATA imports from DLLs, and create the necessary thunking symbols when
+Do sophisticated linking of @code{_symbol} to @code{__imp__symbol} for
+DATA imports from DLLs, and create the necessary thunking symbols when
building the import libraries with those DATA exports. Note: Use of the
'auto-import' extension will cause the text section of the image file
to be made writable. This does not conform to the PE-COFF format
Using 'auto-import' generally will 'just work' -- but sometimes you may
see this message:
-"variable '<var>' can't be auto-imported. Please read the
+"variable '<var>' can't be auto-imported. Please read the
documentation for ld's @code{--enable-auto-import} for details."
-This message occurs when some (sub)expression accesses an address
-ultimately given by the sum of two constants (Win32 import tables only
+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
@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
@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
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
@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}
@cindex discarding sections
@cindex sections, discarding
@cindex removing sections
-The linker will not create output section which do not have any
-contents. This is for convenience when referring to input sections that
-may or may not be present in any of the input files. For example:
+The linker will not create output sections with no contents. This is
+for convenience when referring to input sections that may or may not
+be present in any of the input files. For example:
@smallexample
-.foo @{ *(.foo) @}
+.foo : @{ *(.foo) @}
@end smallexample
@noindent
will only create a @samp{.foo} section in the output file if there is a
-@samp{.foo} section in at least one input file.
+@samp{.foo} section in at least one input file, and if the input
+sections are not all empty. Other link script directives that allocate
+space in an output section will also create the output section.
-If you use anything other than an input section description as an output
-section command, such as a symbol assignment, then the output section
-will always be created, even if there are no matching input sections.
+The linker will ignore address assignments (@pxref{Output Section Address})
+on discarded output sections, except when the linker script defines
+symbols in the output section. In that case the linker will obey
+the address assignments, possibly advancing dot even though the
+section is discarded.
@cindex /DISCARD/
The special output section name @samp{/DISCARD/} may be used to discard
@smallexample
@group
@var{section} [@var{address}] [(@var{type})] :
- [AT(@var{lma})] [SUBALIGN(@var{subsection_align})]
+ [AT(@var{lma})] [ALIGN(@var{section_align})] [SUBALIGN(@var{subsection_align})]
@{
@var{output-section-command}
@var{output-section-command}
@menu
* Output Section Type:: Output section type
* Output Section LMA:: Output section LMA
+* Forced Output Alignment:: Forced Output Alignment
* Forced Input Alignment:: Forced Input Alignment
* Output Section Region:: Output section region
* Output Section Phdr:: Output section phdr
an output section description sets the VMA (@pxref{Output Section
Address}).
-The linker will normally set the LMA equal to the VMA. You can change
-that by using the @code{AT} keyword. The expression @var{lma} that
-follows the @code{AT} keyword specifies the load address of the
-section.
+The expression @var{lma} that follows the @code{AT} keyword specifies
+the load address of the section.
Alternatively, with @samp{AT>@var{lma_region}} expression, you may
specify a memory region for the section's load address. @xref{MEMORY}.
Note that if the section has not had a VMA assigned to it then the
linker will use the @var{lma_region} as the VMA region as well.
+
+If neither @code{AT} nor @code{AT>} is specified for an allocatable
+section, the linker will set the LMA such that the difference between
+VMA and LMA for the section is the same as the preceding output
+section in the same region. If there is no preceding output section
+or the section is not allocatable, the linker will set the LMA equal
+to the VMA.
@xref{Output Section Region}.
@cindex ROM initialized data
@end group
@end smallexample
+@node Forced Output Alignment
+@subsubsection Forced Output Alignment
+@kindex ALIGN(@var{section_align})
+@cindex forcing output section alignment
+@cindex output section alignment
+You can increase an output section's alignment by using ALIGN.
+
@node Forced Input Alignment
@subsubsection Forced Input Alignment
@kindex SUBALIGN(@var{subsection_align})
NOCROSSREFS}.
For each section within the @code{OVERLAY}, the linker automatically
-defines two symbols. The symbol @code{__load_start_@var{secname}} is
+provides two symbols. The symbol @code{__load_start_@var{secname}} is
defined as the starting load address of the section. The symbol
@code{__load_stop_@var{secname}} is defined as the final load address of
the section. Any characters within @var{secname} which are not legal
This will define both @samp{.text0} and @samp{.text1} to start at
address 0x1000. @samp{.text0} will be loaded at address 0x4000, and
@samp{.text1} will be loaded immediately after @samp{.text0}. The
-following symbols will be defined: @code{__load_start_text0},
+following symbols will be defined if referenced: @code{__load_start_text0},
@code{__load_stop_text0}, @code{__load_start_text1},
@code{__load_stop_text1}.
@smallexample
@group
.text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
- __load_start_text0 = LOADADDR (.text0);
- __load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0);
+ PROVIDE (__load_start_text0 = LOADADDR (.text0));
+ PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0));
.text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
- __load_start_text1 = LOADADDR (.text1);
- __load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1);
+ PROVIDE (__load_start_text1 = LOADADDR (.text1));
+ PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1));
. = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
@end group
@end smallexample
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
@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
the top page of memory).
@item system control instructions
-@command{ld} finds all @code{ldc.w, stc.w} instrcutions which use the
+@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
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
@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
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
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