ld.texinfo

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\input texinfo
@setfilename ld.info
@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
@c 2001 Free Software Foundation, Inc.
@syncodeindex ky cp
@include configdoc.texi
@c (configdoc.texi is generated by the Makefile)
@include ldver.texi

@c @smallbook

@ifinfo
@format
START-INFO-DIR-ENTRY
* Ld: (ld).                       The GNU linker.
END-INFO-DIR-ENTRY
@end format
@end ifinfo

@ifinfo
This file documents the @sc{gnu} linker LD version @value{VERSION}.

Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000 Free Software Foundation, Inc.

@ignore

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no Front-Cover Texts, and with no
Back-Cover Texts.  A copy of the license is included in the
section entitled "GNU Free Documentation License".

Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
@end ifinfo
@iftex
@finalout
@setchapternewpage odd
@settitle Using LD, the GNU linker
@titlepage
@title Using ld
@subtitle The GNU linker
@sp 1
@subtitle @code{ld} version 2
@subtitle Version @value{VERSION}
@author Steve Chamberlain
@author Ian Lance Taylor
@page

@tex
{\parskip=0pt
\hfill Red Hat Inc\par
\hfill nickc\@credhat.com, doc\@redhat.com\par
\hfill {\it Using LD, the GNU linker}\par
\hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
}
\global\parindent=0pt % Steve likes it this way.
@end tex

@vskip 0pt plus 1filll
Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000 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
      or any later version published by the Free Software Foundation;
      with no Invariant Sections, with no Front-Cover Texts, and with no
      Back-Cover Texts.  A copy of the license is included in the
      section entitled "GNU Free Documentation License".

@end titlepage
@end iftex
@c FIXME: Talk about importance of *order* of args, cmds to linker!

@ifinfo
@node Top
@top Using ld
This file documents the @sc{gnu} linker ld version @value{VERSION}.

This document is distributed under the terms of the GNU Free
Documentation License.  A copy of the license is included in the
section entitled "GNU Free Documentation License".

@menu
* Overview::                    Overview
* Invocation::                  Invocation
* Scripts::                     Linker Scripts
@ifset GENERIC
* Machine Dependent::           Machine Dependent Features
@end ifset
@ifclear GENERIC
@ifset H8300
* H8/300::                      ld and the H8/300
@end ifset
@ifset Hitachi
* Hitachi::                     ld and other Hitachi micros
@end ifset
@ifset I960
* i960::                        ld and the Intel 960 family
@end ifset
@ifset TICOFF
* TI COFF::                     ld and the TI COFF
@end ifset
@end ifclear
@ifclear SingleFormat
* BFD::                         BFD
@end ifclear
@c Following blank line required for remaining bug in makeinfo conds/menus

* Reporting Bugs::              Reporting Bugs
* MRI::                         MRI Compatible Script Files
* GNU Free Documentation License::  GNU Free Documentation License
* Index::                       Index
@end menu
@end ifinfo

@node Overview
@chapter Overview

@cindex @sc{gnu} linker
@cindex what is this?
@code{ld} combines a number of object and archive files, relocates
their data and ties up symbol references. Usually the last step in
compiling a program is to run @code{ld}.

@code{ld} accepts Linker Command Language files written in
a superset of AT&T's Link Editor Command Language syntax,
to provide explicit and total control over the linking process.

@ifclear SingleFormat
This version of @code{ld} uses the general purpose BFD libraries
to operate on object files. This allows @code{ld} to read, combine, and
write object files in many different formats---for example, COFF or
@code{a.out}.  Different formats may be linked together to produce any
available kind of object file.  @xref{BFD}, for more information.
@end ifclear

Aside from its flexibility, the @sc{gnu} linker is more helpful than other
linkers in providing diagnostic information.  Many linkers abandon
execution immediately upon encountering an error; whenever possible,
@code{ld} continues executing, allowing you to identify other errors
(or, in some cases, to get an output file in spite of the error).

@node Invocation
@chapter Invocation

The @sc{gnu} linker @code{ld} is meant to cover a broad range of situations,
and to be as compatible as possible with other linkers.  As a result,
you have many choices to control its behavior.

@ifset UsesEnvVars
@menu
* Options::                     Command Line Options
* Environment::                 Environment Variables
@end menu

@node Options
@section Command Line Options
@end ifset

@cindex command line
@cindex options
The linker supports a plethora of command-line options, but in actual
practice few of them are used in any particular context.
@cindex standard Unix system
For instance, a frequent use of @code{ld} is to link standard Unix
object files on a standard, supported Unix system.  On such a system, to
link a file @code{hello.o}:

@smallexample
ld -o @var{output} /lib/crt0.o hello.o -lc
@end smallexample

This tells @code{ld} to produce a file called @var{output} as the
result of linking the file @code{/lib/crt0.o} with @code{hello.o} and
the library @code{libc.a}, which will come from the standard search
directories.  (See the discussion of the @samp{-l} option below.)

Some of the command-line options to @code{ld} may be specified at any
point in the command line.  However, options which refer to files, such
as @samp{-l} or @samp{-T}, cause the file to be read at the point at
which the option appears in the command line, relative to the object
files and other file options.  Repeating non-file options with a
different argument will either have no further effect, or override prior
occurrences (those further to the left on the command line) of that
option.  Options which may be meaningfully specified more than once are
noted in the descriptions below.

@cindex object files
Non-option arguments are object files or archives which are to be linked
together.  They may follow, precede, or be mixed in with command-line
options, except that an object file argument may not be placed between
an option and its argument.

Usually the linker is invoked with at least one object file, but you can
specify other forms of binary input files using @samp{-l}, @samp{-R},
and the script command language.  If @emph{no} binary input files at all
are specified, the linker does not produce any output, and issues the
message @samp{No input files}.

If the linker can not recognize the format of an object file, it will
assume that it is a linker script.  A script specified in this way
augments the main linker script used for the link (either the default
linker script or the one specified by using @samp{-T}).  This feature
permits the linker to link against a file which appears to be an object
or an archive, but actually merely defines some symbol values, or uses
@code{INPUT} or @code{GROUP} to load other objects.  Note that
specifying a script in this way should only be used to augment the main
linker script; if you want to use some command that logically can only
appear once, such as the @code{SECTIONS} or @code{MEMORY} command, you
must replace the default linker script using the @samp{-T} option.
@xref{Scripts}.

For options whose names are a single letter,
option arguments must either follow the option letter without intervening
whitespace, or be given as separate arguments immediately following the
option that requires them.

For options whose names are multiple letters, either one dash or two can
precede the option name; for example, @samp{-trace-symbol} and
@samp{--trace-symbol} are equivalent.  Note - there is one exception to
this rule.  Multiple letter options that start with a lower case 'o' can
only be preceeded by two dashes.  This is to reduce confusion with the
@samp{-o} option.  So for example @samp{-omagic} sets the output file
name to @samp{magic} whereas @samp{--omagic} sets the NMAGIC flag on the
output.

Arguments to multiple-letter options must either be separated from the
option name by an equals sign, or be given as separate arguments
immediately following the option that requires them.  For example,
@samp{--trace-symbol foo} and @samp{--trace-symbol=foo} are equivalent.
Unique abbreviations of the names of multiple-letter options are
accepted.

Note - if the linker is being invoked indirectly, via a compiler driver
(eg @samp{gcc}) then all the linker command line options should be
prefixed by @samp{-Wl,} (or whatever is appropriate for the particular
compiler driver) like this:

@smallexample
  gcc -Wl,--startgroup foo.o bar.o -Wl,--endgroup
@end smallexample

This is important, because otherwise the compiler driver program may
silently drop the linker options, resulting in a bad link.

Here is a table of the generic command line switches accepted by the GNU
linker:

@table @code
@kindex -a@var{keyword}
@item -a@var{keyword}
This option is supported for HP/UX compatibility.  The @var{keyword}
argument must be one of the strings @samp{archive}, @samp{shared}, or
@samp{default}.  @samp{-aarchive} is functionally equivalent to
@samp{-Bstatic}, and the other two keywords are functionally equivalent
to @samp{-Bdynamic}.  This option may be used any number of times.

@ifset I960
@cindex architectures
@kindex -A@var{arch}
@item -A@var{architecture}
@kindex --architecture=@var{arch}
@itemx --architecture=@var{architecture}
In the current release of @code{ld}, this option is useful only for the
Intel 960 family of architectures.  In that @code{ld} configuration, the
@var{architecture} argument identifies the particular architecture in
the 960 family, enabling some safeguards and modifying the
archive-library search path.  @xref{i960,,@code{ld} and the Intel 960
family}, for details.

Future releases of @code{ld} may support similar functionality for
other architecture families.
@end ifset

@ifclear SingleFormat
@cindex binary input format
@kindex -b @var{format}
@kindex --format=@var{format}
@cindex input format
@cindex input format
@item -b @var{input-format}
@itemx --format=@var{input-format}
@code{ld} may be configured to support more than one kind of object
file.  If your @code{ld} is configured this way, you can use the
@samp{-b} option to specify the binary format for input object files
that follow this option on the command line.  Even when @code{ld} is
configured to support alternative object formats, you don't usually need
to specify this, as @code{ld} should be configured to expect as a
default input format the most usual format on each machine.
@var{input-format} is a text string, the name of a particular format
supported by the BFD libraries.  (You can list the available binary
formats with @samp{objdump -i}.)
@xref{BFD}.

You may want to use this option if you are linking files with an unusual
binary format.  You can also use @samp{-b} to switch formats explicitly (when
linking object files of different formats), by including
@samp{-b @var{input-format}} before each group of object files in a
particular format.

The default format is taken from the environment variable
@code{GNUTARGET}.
@ifset UsesEnvVars
@xref{Environment}.
@end ifset
You can also define the input format from a script, using the command
@code{TARGET}; see @ref{Format Commands}.
@end ifclear

@kindex -c @var{MRI-cmdfile}
@kindex --mri-script=@var{MRI-cmdfile}
@cindex compatibility, MRI
@item -c @var{MRI-commandfile}
@itemx --mri-script=@var{MRI-commandfile}
For compatibility with linkers produced by MRI, @code{ld} accepts script
files written in an alternate, restricted command language, described in
@ref{MRI,,MRI Compatible Script Files}.  Introduce MRI script files with
the option @samp{-c}; use the @samp{-T} option to run linker
scripts written in the general-purpose @code{ld} scripting language.
If @var{MRI-cmdfile} does not exist, @code{ld} looks for it in the directories
specified by any @samp{-L} options.

@cindex common allocation
@kindex -d
@kindex -dc
@kindex -dp