\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 Free Software Foundation, Inc.
@syncodeindex ky cp
@include configdoc.texi
@c (configdoc.texi is generated by the Makefile)
This file documents the @sc{gnu} linker LD version @value{VERSION}.
Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
-2001, 2002, 2003 Free Software Foundation, Inc.
+2001, 2002, 2003, 2004 Free Software Foundation, Inc.
@ignore
@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 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
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 partial link
@cindex relocatable output
@kindex -r
-@kindex --relocateable
+@kindex --relocatable
@item -r
-@itemx --relocateable
+@itemx --relocatable
Generate relocatable output---i.e., generate an output file that can in
turn serve as input to @command{ld}. This is often called @dfn{partial
linking}. As a side effect, in environments that support standard Unix
@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 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 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 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.
+
+@end table
+
+Other keywords are ignored for Solaris compatibility.
@kindex -(
@cindex groups of archives
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}.
@kindex -Bsymbolic
@item -Bsymbolic
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
@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
Create a position independent executable. This is currently only supported on
ELF platforms. Position independent executables are similar to shared
libraries in that they are relocated by the dynamic linker to the virtual
-address OS chooses for them (which can varry between invocations), like
+address the OS chooses for them (which can vary between invocations). Like
normal dynamically linked executables they can be executed and symbols
defined in the executable cannot be overridden by shared libraries.
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-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
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]
@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
+@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}.
@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:
+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.
+
+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."
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]
@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
The full description of an output section looks like this:
@smallexample
@group
-@var{section} [@var{address}] [(@var{type})] : [AT(@var{lma})]
+@var{section} [@var{address}] [(@var{type})] :
+ [AT(@var{lma})] [SUBALIGN(@var{subsection_align})]
@{
@var{output-section-command}
@var{output-section-command}
like this:
@smallexample
@group
-@var{section} [@var{address}] [(@var{type})] : [AT(@var{lma})]
+@var{section} [@var{address}] [(@var{type})] :
+ [AT(@var{lma})] [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 Input Alignment:: Forced Input Alignment
* Output Section Region:: Output section region
* Output Section Phdr:: Output section phdr
* Output Section Fill:: Output section fill
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}.
+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.
+@xref{Output Section Region}.
@cindex ROM initialized data
@cindex initialized data in ROM
@end group
@end smallexample
+@node Forced Input Alignment
+@subsubsection Forced Input Alignment
+@kindex SUBALIGN(@var{subsection_align})
+@cindex forcing input section alignment
+@cindex input section alignment
+You can force input section alignment within an output section by using
+SUBALIGN. The value specified overrides any alignment given by input
+sections, whether larger or smaller.
+
@node Output Section Region
@subsubsection Output Section Region
@kindex >@var{region}
@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{}
@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
@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.
@end table
projects / deliverable / binutils-gdb.git / blobdiff