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@end smallexample

@item
Merging a common symbol with a previous larger common symbol.
@smallexample
@var{file}(@var{section}): warning: common of `@var{symbol}'
   overridden by larger common
@var{file}(@var{section}): warning: larger common is here
@end smallexample

@item
Merging a common symbol with a previous smaller common symbol.  This is
the same as the previous case, except that the symbols are
encountered in a different order.
@smallexample
@var{file}(@var{section}): warning: common of `@var{symbol}'
   overriding smaller common
@var{file}(@var{section}): warning: smaller common is here
@end smallexample
@end enumerate

@kindex --warn-constructors
@item --warn-constructors
Warn if any global constructors are used.  This is only useful for a few
object file formats.  For formats like COFF or ELF, the linker can not
detect the use of global constructors.

@kindex --warn-multiple-gp
@item --warn-multiple-gp
Warn if multiple global pointer values are required in the output file.
This is only meaningful for certain processors, such as the Alpha.
Specifically, some processors put large-valued constants in a special
section.  A special register (the global pointer) points into the middle
of this section, so that constants can be loaded efficiently via a
base-register relative addressing mode.  Since the offset in
base-register relative mode is fixed and relatively small (e.g., 16
bits), this limits the maximum size of the constant pool.  Thus, in
large programs, it is often necessary to use multiple global pointer
values in order to be able to address all possible constants.  This
option causes a warning to be issued whenever this case occurs.

@kindex --warn-once
@cindex warnings, on undefined symbols
@cindex undefined symbols, warnings on
@item --warn-once
Only warn once for each undefined symbol, rather than once per module
which refers to it.

@kindex --warn-section-align
@cindex warnings, on section alignment
@cindex section alignment, warnings on
@item --warn-section-align
Warn if the address of an output section is changed because of
alignment.  Typically, the alignment will be set by an input section.
The address will only be changed if it not explicitly specified; that
is, if the @code{SECTIONS} command does not specify a start address for
the section (@pxref{SECTIONS}).

@kindex --whole-archive
@cindex including an entire archive
@item --whole-archive
For each archive mentioned on the command line after the
@code{--whole-archive} option, include every object file in the archive
in the link, rather than searching the archive for the required object
files.  This is normally used to turn an archive file into a shared
library, forcing every object to be included in the resulting shared
library.  This option may be used more than once.

Two notes when using this option from gcc: First, gcc doesn't know
about this option, so you have to use @code{-Wl,-whole-archive}.
Second, don't forget to use @code{-Wl,-no-whole-archive} after your
list of archives, because gcc will add its own list of archives to
your link and you may not want this flag to affect those as well.

@kindex --wrap
@item --wrap @var{symbol}
Use a wrapper function for @var{symbol}.  Any undefined reference to
@var{symbol} will be resolved to @code{__wrap_@var{symbol}}.  Any
undefined reference to @code{__real_@var{symbol}} will be resolved to
@var{symbol}.

This can be used to provide a wrapper for a system function.  The
wrapper function should be called @code{__wrap_@var{symbol}}.  If it
wishes to call the system function, it should call
@code{__real_@var{symbol}}.

Here is a trivial example:

@smallexample
void *
__wrap_malloc (int c)
@{
  printf ("malloc called with %ld\n", c);
  return __real_malloc (c);
@}
@end smallexample

If you link other code with this file using @code{--wrap malloc}, then
all calls to @code{malloc} will call the function @code{__wrap_malloc}
instead.  The call to @code{__real_malloc} in @code{__wrap_malloc} will
call the real @code{malloc} function.

You may wish to provide a @code{__real_malloc} function as well, so that
links without the @code{--wrap} option will succeed.  If you do this,
you should not put the definition of @code{__real_malloc} in the same
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 --enable-new-dtags
@kindex --disable-new-dtags
@item --enable-new-dtags
@itemx --disable-new-dtags
This linker can create the new dynamic tags in ELF. But the older ELF
systems may not understand them. If you specify
@code{--enable-new-dtags}, the dynamic tags will be created as needed.
If you specify @code{--disable-new-dtags}, no new dynamic tags will be
created. By default, the new dynamic tags are not created. Note that
those options are only available for ELF systems.

@end table

@subsection Options specific to i386 PE targets

The i386 PE linker supports the @code{-shared} option, which causes
the output to be a dynamically linked library (DLL) instead of a
normal executable.  You should name the output @code{*.dll} when you
use this option.  In addition, the linker fully supports the standard
@code{*.def} files, which may be specified on the linker command line
like an object file (in fact, it should precede archives it exports
symbols from, to ensure that they get linked in, just like a normal
object file).

In addition to the options common to all targets, the i386 PE linker
support additional command line options that are specific to the i386
PE target.  Options that take values may be separated from their
values by either a space or an equals sign.

@table @code

@kindex --add-stdcall-alias
@item --add-stdcall-alias
If given, symbols with a stdcall suffix (@@@var{nn}) will be exported
as-is and also with the suffix stripped.

@kindex --base-file
@item --base-file @var{file}
Use @var{file} as the name of a file in which to save the base
addresses of all the relocations needed for generating DLLs with
@file{dlltool}.

@kindex --dll
@item --dll
Create a DLL instead of a regular executable.  You may also use
@code{-shared} or specify a @code{LIBRARY} in a given @code{.def}
file.

@kindex --enable-stdcall-fixup
@kindex --disable-stdcall-fixup
@item --enable-stdcall-fixup
@itemx --disable-stdcall-fixup
If the link finds a symbol that it cannot resolve, it will attempt to
do "fuzzy linking" by looking for another defined symbol that differs
only in the format of the symbol name (cdecl vs stdcall) and will
resolve that symbol by linking to the match.  For example, the
undefined symbol @code{_foo} might be linked to the function
@code{_foo@@12}, or the undefined symbol @code{_bar@@16} might be linked
to the function @code{_bar}.  When the linker does this, it prints a
warning, since it normally should have failed to link, but sometimes
import libraries generated from third-party dlls may need this feature
to be usable.  If you specify @code{--enable-stdcall-fixup}, this
feature is fully enabled and warnings are not printed.  If you specify
@code{--disable-stdcall-fixup}, this feature is disabled and such
mismatches are considered to be errors.

@cindex DLLs, creating
@kindex --export-all-symbols
@item --export-all-symbols
If given, all global symbols in the objects used to build a DLL will
be exported by the DLL.  Note that this is the default if there
otherwise wouldn't be any exported symbols.  When symbols are
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}, and @code{impure_ptr} will not be automatically
exported.

@kindex --exclude-symbols
@item --exclude-symbols @var{symbol},@var{symbol},...
Specifies a list of symbols which should not be automatically
exported.  The symbol names may be delimited by commas or colons.

@kindex --file-alignment
@item --file-alignment
Specify the file alignment.  Sections in the file will always begin at
file offsets which are multiples of this number.  This defaults to
512.

@cindex heap size
@kindex --heap
@item --heap @var{reserve}
@itemx --heap @var{reserve},@var{commit}
Specify the amount of memory to reserve (and optionally commit) to be
used as heap for this program.  The default is 1Mb reserved, 4K
committed.

@cindex image base
@kindex --image-base
@item --image-base @var{value}
Use @var{value} as the base address of your program or dll.  This is
the lowest memory location that will be used when your program or dll
is loaded.  To reduce the need to relocate and improve performance of
your dlls, each should have a unique base address and not overlap any
other dlls.  The default is 0x400000 for executables, and 0x10000000
for dlls.

@kindex --kill-at
@item --kill-at
If given, the stdcall suffixes (@@@var{nn}) will be stripped from
symbols before they are exported.

@kindex --major-image-version
@item --major-image-version @var{value}
Sets the major number of the "image version".  Defaults to 1.

@kindex --major-os-version
@item --major-os-version @var{value}
Sets the major number of the "os version".  Defaults to 4.

@kindex --major-subsystem-version
@item --major-subsystem-version @var{value}
Sets the major number of the "subsystem version".  Defaults to 4.

@kindex --minor-image-version
@item --minor-image-version @var{value}
Sets the minor number of the "image version".  Defaults to 0.

@kindex --minor-os-version
@item --minor-os-version @var{value}
Sets the minor number of the "os version".  Defaults to 0.

@kindex --minor-subsystem-version
@item --minor-subsystem-version @var{value}
Sets the minor number of the "subsystem version".  Defaults to 0.

@cindex DEF files, creating
@cindex DLLs, creating
@kindex --output-def
@item --output-def @var{file}
The linker will create the file @var{file} which will contain a DEF
file corresponding to the DLL the linker is generating.  This DEF file
(which should be called @code{*.def}) may be used to create an import
library with @code{dlltool} or may be used as a reference to
automatically or implicitly exported symbols.

@kindex --section-alignment
@item --section-alignment
Sets the section alignment.  Sections in memory will always begin at
addresses which are a multiple of this number.  Defaults to 0x1000.

@cindex stack size
@kindex --stack
@item --stack @var{reserve}
@itemx --stack @var{reserve},@var{commit}
Specify the amount of memory to reserve (and optionally commit) to be
used as stack for this program.  The default is 32Mb reserved, 4K
committed.

@kindex --subsystem
@item --subsystem @var{which}
@itemx --subsystem @var{which}:@var{major}
@itemx --subsystem @var{which}:@var{major}.@var{minor}
Specifies the subsystem under which your program will execute.  The
legal values for @var{which} are @code{native}, @code{windows},
@code{console}, and @code{posix}.  You may optionally set the
subsystem version also.

@end table

@ifset UsesEnvVars
@node Environment
@section Environment Variables

You can change the behavior of @code{ld} with the environment variables
@code{GNUTARGET}, @code{LDEMULATION}, and @code{COLLECT_NO_DEMANGLE}.

@kindex GNUTARGET
@cindex default input format
@code{GNUTARGET} determines the input-file object format if you don't
use @samp{-b} (or its synonym @samp{--format}).  Its value should be one
of the BFD names for an input format (@pxref{BFD}).  If there is no
@code{GNUTARGET} in the environment, @code{ld} uses the natural format
of the target. If @code{GNUTARGET} is set to @code{default} then BFD
attempts to discover the input format by examining binary input files;
this method often succeeds, but there are potential ambiguities, since
there is no method of ensuring that the magic number used to specify
object-file formats is unique.  However, the configuration procedure for
BFD on each system places the conventional format for that system first
in the search-list, so ambiguities are resolved in favor of convention.

@kindex LDEMULATION
@cindex default emulation
@cindex emulation, default
@code{LDEMULATION} determines the default emulation if you don't use the
@samp{-m} option.  The emulation can affect various aspects of linker
behaviour, particularly the default linker script.  You can list the
available emulations with the @samp{--verbose} or @samp{-V} options.  If
the @samp{-m} option is not used, and the @code{LDEMULATION} environment
variable is not defined, the default emulation depends upon how the
linker was configured.
@end ifset

@kindex COLLECT_NO_DEMANGLE
@cindex demangling, default
Normally, the linker will default to demangling symbols.  However, if
@code{COLLECT_NO_DEMANGLE} is set in the environment, then it will
default to not demangling symbols.  This environment variable is used in
a similar fashion by the @code{gcc} linker wrapper program.  The default
may be overridden by the @samp{--demangle} and @samp{--no-demangle}
options.

@node Scripts
@chapter Linker Scripts

@cindex scripts
@cindex linker scripts
@cindex command files
Every link is controlled by a @dfn{linker script}.  This script is
written in the linker command language.

The main purpose of th