\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
lookup caching possible.
@item defs
-Disallows undefined symbols.
+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.
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 -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
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
@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
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 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
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
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
-@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
(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
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.
+
@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.
@end table
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