\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
@ifset H8300
* H8/300:: ld and the H8/300
@end ifset
-@ifset Hitachi
-* Hitachi:: ld and other Hitachi micros
+@ifset Renesas
+* Renesas:: ld and other Renesas micros
@end ifset
@ifset I960
* i960:: ld and the Intel 960 family
@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 TICOFF
* TI COFF:: ld and the TI COFF
@end ifset
@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
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
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 reference from regular objects.
+@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}.
@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
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
@itemx --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}. The default behaviour (of not performing this garbage
+collection) can be restored by specifying @samp{--no-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
this option overrides it. @xref{BFD}.
@end ifclear
+@kindex -pie
+@kindex --pic-executable
+@item -pie
+@itemx --pic-executable
+@cindex position independent executables
+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 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.
+
@kindex -qmagic
@item -qmagic
This option is ignored for Linux compatibility.
@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
On some platforms, the @samp{--relax} option performs global
optimizations that become possible when the linker resolves addressing
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
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
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}
+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 --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
+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
+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
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 ``Charateristics'' 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
+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]
@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 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
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}
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
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,
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}
@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
@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 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} instrcutions 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
@end ifset
@ifclear GENERIC
-@ifset Hitachi
+@ifset Renesas
@c This stuff is pointless to say unless you're especially concerned
-@c with Hitachi chips; don't enable it for generic case, please.
-@node Hitachi
-@chapter @command{ld} and Other Hitachi Chips
+@c with Renesas chips; don't enable it for generic case, please.
+@node Renesas
+@chapter @command{ld} and Other Renesas Chips
-@command{ld} also supports the H8/300H, the H8/500, and the Hitachi SH. No
-special features, commands, or command-line options are required for
-these chips.
+@command{ld} also supports the Renesas (formerly Hitachi) H8/300H,
+H8/500, and SH chips. No special features, commands, or command-line
+options are required for these chips.
@end ifset
@end ifclear
@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.
+
+@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
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
+
@ifclear GENERIC
@lowersections
@end ifclear
@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
projects / deliverable / binutils-gdb.git / blobdiff