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2254 lines
76 KiB
Plaintext
2254 lines
76 KiB
Plaintext
\input texinfo
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@setfilename ld.info
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@syncodeindex ky cp
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@c @include configdoc.texi
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@c @smallbook
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@c @cropmarks
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@ifinfo
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@format
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START-INFO-DIR-ENTRY
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* Ld:: The GNU linker.
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END-INFO-DIR-ENTRY
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@end format
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@end ifinfo
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@ifinfo
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This file documents the GNU linker LD.
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Copyright (C) 1991, 1992, 1993 Free Software Foundation, Inc.
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Permission is granted to make and distribute verbatim copies of
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this manual provided the copyright notice and this permission notice
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are preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
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manual under the conditions for verbatim copying, provided also that
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the entire resulting derived work is distributed under the terms of a
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions.
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@ignore
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Permission is granted to process this file through Tex and print the
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results, provided the printed document carries copying permission
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notice identical to this one except for the removal of this paragraph
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(this paragraph not being relevant to the printed manual).
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@end ignore
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@end ifinfo
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@iftex
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@finalout
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@setchapternewpage odd
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@settitle Using LD, the GNU linker
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@titlepage
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@title Using ld
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@subtitle The GNU linker
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@sp 1
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@subtitle @code{ld} version 2
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@subtitle March 1993
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@author Steve Chamberlain and Roland Pesch
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@author Cygnus Support
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@page
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@tex
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{\parskip=0pt
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\hfill Cygnus Support\par
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\hfill steve\@cygnus.com, pesch\@cygnus.com\par
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\hfill {\it Using LD, the GNU linker}\par
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\hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com), March 1993.\par
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}
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\global\parindent=0pt % Steve likes it this way.
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@end tex
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@vskip 0pt plus 1filll
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Copyright @copyright{} 1991, 1992, 1993 Free Software Foundation, Inc.
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Permission is granted to make and distribute verbatim copies of
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this manual provided the copyright notice and this permission notice
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are preserved on all copies.
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Permission is granted to copy and distribute modified versions of this
|
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manual under the conditions for verbatim copying, provided also that
|
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the entire resulting derived work is distributed under the terms of a
|
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permission notice identical to this one.
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Permission is granted to copy and distribute translations of this manual
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into another language, under the above conditions for modified versions.
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@end titlepage
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@end iftex
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@c FIXME: Talk about importance of *order* of args, cmds to linker!
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@ifinfo
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@node Top
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@top Using ld
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This file documents the GNU linker ld.
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@menu
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* Overview:: Overview
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* Invocation:: Invocation
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* Commands:: Command Language
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@ifset GENERIC
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* Machine Dependent:: Machine Dependent Features
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@end ifset
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@ifclear GENERIC
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@ifset H8300
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* H8/300:: ld and the H8/300
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@end ifset
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@ifset I960
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* i960:: ld and the Intel 960 family
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@end ifset
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@end ifclear
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@ifclear SingleFormat
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* BFD:: BFD
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@end ifclear
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@c Following blank line required for remaining bug in makeinfo conds/menus
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* MRI:: MRI Compatible Script Files
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* Index:: Index
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@end menu
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@end ifinfo
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@node Overview
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@chapter Overview
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@cindex GNU linker
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@cindex what is this?
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@code{ld} combines a number of object and archive files, relocates
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their data and ties up symbol references. Usually the last step in
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compiling a program is to run @code{ld}.
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@code{ld} accepts Linker Command Language files written in
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a superset of AT&T's Link Editor Command Language syntax,
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to provide explicit and total control over the linking process.
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@ifclear SingleFormat
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This version of @code{ld} uses the general purpose BFD libraries
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to operate on object files. This allows @code{ld} to read, combine, and
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write object files in many different formats---for example, COFF or
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@code{a.out}. Different formats may be linked together to produce any
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available kind of object file. @xref{BFD} for a list of formats
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supported on various architectures.
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@end ifclear
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Aside from its flexibility, the GNU linker is more helpful than other
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linkers in providing diagnostic information. Many linkers abandon
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execution immediately upon encountering an error; whenever possible,
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@code{ld} continues executing, allowing you to identify other errors
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(or, in some cases, to get an output file in spite of the error).
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@node Invocation
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@chapter Invocation
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The GNU linker @code{ld} is meant to cover a broad range of situations,
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and to be as compatible as possible with other linkers. As a result,
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you have many choices to control its behavior.
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@ifset UsesEnvVars
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@menu
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* Options:: Command Line Options
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* Environment:: Environment Variables
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@end menu
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@node Options
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@section Command Line Options
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@end ifset
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@cindex command line
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@cindex options
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Here is a summary of the options you can use on the @code{ld} command
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line:
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@c FIXME! -relax only avail h8/300, i960. Conditionals screwed in examples.
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@smallexample
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ld [ -o @var{output} ] @var{objfile}@dots{}
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[ -A@var{architecture} ] [ -b @var{input-format} ] [ -Bstatic ]
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[ -c @var{MRI-commandfile} ] [ -d | -dc | -dp ]
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[ -defsym @var{symbol}=@var{expression} ]
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[ -e @var{entry} ] [ -F ] [ -F @var{format} ]
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[ -format @var{input-format} ] [ -g ] [ -G @var{size} ] [ --help ] [ -i ]
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[ -l@var{archive} ] [ -L@var{searchdir} ] [ -M ] [ -Map @var{mapfile} ]
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[ -m @var{emulation} ] [ -N | -n ] [ -noinhibit-exec ]
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[ -oformat @var{output-format} ] [ -R @var{filename} ] [ -relax ]
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[ -r | -Ur ] [ -S ] [ -s ] [ -sort-common ] [ -T @var{commandfile} ]
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[ -Ttext @var{org} ] [ -Tdata @var{org} ]
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[ -Tbss @var{org} ] [ -t ] [ -u @var{symbol}] [-V] [-v] [ --version ]
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[ -warn-common ] [ -y@var{symbol} ] [ -X ] [-x ]
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@end smallexample
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This plethora of command-line options may seem intimidating, but in
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actual practice few of them are used in any particular context.
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@cindex standard Unix system
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For instance, a frequent use of @code{ld} is to link standard Unix
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object files on a standard, supported Unix system. On such a system, to
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link a file @code{hello.o}:
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@example
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ld -o @var{output} /lib/crt0.o hello.o -lc
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@end example
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This tells @code{ld} to produce a file called @var{output} as the
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result of linking the file @code{/lib/crt0.o} with @code{hello.o} and
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the library @code{libc.a}, which will come from the standard search
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directories. (See the discussion of the @samp{-l} option below.)
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The command-line options to @code{ld} may be specified in any order, and
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may be repeated at will. Repeating most options with a
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different argument will either have no further effect, or override prior
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occurrences (those further to the left on the command line) of that
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option.
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@ifclear SingleFormat
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The exceptions---which may meaningfully be used more than once---are
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@samp{-A}, @samp{-b} (or its synonym @samp{-format}), @samp{-defsym},
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@samp{-L}, @samp{-l}, @samp{-R}, and @samp{-u}.
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@end ifclear
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@ifset SingleFormat
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The exceptions---which may meaningfully be used more than once---are
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@samp{-A}, @samp{-defsym}, @samp{-L}, @samp{-l}, @samp{-R}, and @samp{-u}.
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@end ifset
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@cindex object files
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The list of object files to be linked together, shown as @var{objfile}@dots{},
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may follow, precede, or be mixed in with command-line options, except that
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an @var{objfile} argument may not be placed between an option and
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its argument.
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Usually the linker is invoked with at least one object file, but other
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forms of binary input files can also be specified with @samp{-l},
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@samp{-R}, and the script command language. If @emph{no} binary input
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files at all are specified, the linker does not produce any output, and
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issues the message @samp{No input files}.
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Option arguments must either follow the option letter without intervening
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whitespace, or be given as separate arguments immediately following the
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option that requires them.
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@table @code
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@ifset I960
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@cindex architectures
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@kindex -A@var{arch}
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@item -A@var{architecture}
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In the current release of @code{ld}, this option is useful only for the
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Intel 960 family of architectures. In that @code{ld} configuration, the
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@var{architecture} argument identifies the particular architecture in
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the 960 family, enabling some safeguards and modifying the
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archive-library search path. @xref{i960,,@code{ld} and the Intel 960
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family}, for details.
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Future releases of @code{ld} may support similar functionality for
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other architecture families.
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@end ifset
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@ifclear SingleFormat
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@cindex binary input format
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@kindex -b @var{format}
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@cindex input format
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@item -b @var{input-format}
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@cindex input format
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Specify the binary format for input object files that follow this option
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on the command line. You don't usually need to specify this, as
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@code{ld} is configured to expect as a default input format the most
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usual format on each machine. @var{input-format} is a text string, the
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name of a particular format supported by the BFD libraries.
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(You can list the available binary formats with @samp{objdump -i}.)
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@w{@samp{-format @var{input-format}}} has the same effect, as does the
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script command @code{TARGET}. @xref{BFD}.
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You may want to use this option if you are linking files with an unusual
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binary format. You can also use @samp{-b} to switch formats explicitly (when
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linking object files of different formats), by including
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@samp{-b @var{input-format}} before each group of object files in a
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particular format.
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The default format is taken from the environment variable
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@code{GNUTARGET}.
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@ifset UsesEnvVars
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@xref{Environment}.
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@end ifset
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You can also define the input
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format from a script, using the command @code{TARGET}; see @ref{Option
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Commands}.
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@end ifclear
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@kindex -Bstatic
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@item -Bstatic
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Ignored. This option is accepted for command-line compatibility with
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the SunOS linker.
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@kindex -c @var{MRI-cmdfile}
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@cindex compatibility, MRI
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@item -c @var{MRI-commandfile}
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For compatibility with linkers produced by MRI, @code{ld} accepts script
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files written in an alternate, restricted command language, described in
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@ref{MRI,,MRI Compatible Script Files}. Introduce MRI script files with
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the option @samp{-c}; use the @samp{-T} option to run linker
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scripts written in the general-purpose @code{ld} scripting language.
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If @var{MRI-cmdfile} does not exist, @code{ld} looks for it in the directories
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specified by any @samp{-L} options.
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@cindex common allocation
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@kindex -d
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@item -d
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@kindex -dc
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@itemx -dc
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@kindex -dp
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@itemx -dp
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These three options are equivalent; multiple forms are supported for
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compatibility with other linkers. They
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assign space to common symbols even if a relocatable output file is
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specified (with @samp{-r}). The script command
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@code{FORCE_COMMON_ALLOCATION} has the same effect. @xref{Option
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Commands}.
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@cindex symbols, from command line
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@kindex -defsym @var{symbol}=@var{exp}
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@item -defsym @var{symbol}=@var{expression}
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Create a global symbol in the output file, containing the absolute
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address given by @var{expression}. You may use this option as many
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times as necessary to define multiple symbols in the command line. A
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limited form of arithmetic is supported for the @var{expression} in this
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context: you may give a hexadecimal constant or the name of an existing
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symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
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constants or symbols. If you need more elaborate expressions, consider
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using the linker command language from a script (@pxref{Assignment, ,
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Assignment: Symbol Definitions}). @emph{Note:} there should be no
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white space between @var{symbol}, the equals sign (``@key{=}''), and
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@var{expression}.
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@cindex entry point, from command line
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@kindex -e @var{entry}
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@item -e @var{entry}
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Use @var{entry} as the explicit symbol for beginning execution of your
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program, rather than the default entry point. @xref{Entry Point}, for a
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discussion of defaults and other ways of specifying the
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entry point.
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@ifclear SingleFormat
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@kindex -F
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@item -F
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@itemx -F@var{format}
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Ignored. Some older linkers used this option throughout a compilation
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toolchain for specifying object-file format for both input and output
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object files. The mechanisms @code{ld} uses for this purpose (the
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@samp{-b} or @samp{-format} options for input files, @samp{-oformat}
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option or the @code{TARGET} command in linker scripts for output files,
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the @code{GNUTARGET} environment variable) are more flexible, but
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@code{ld} accepts the @samp{-F} option for compatibility with scripts
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written to call the old linker.
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@kindex -format
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@item -format @var{input-format}
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Synonym for @samp{-b @var{input-format}}.
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@end ifclear
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@kindex -g
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@item -g
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Ignored. Provided for compatibility with other tools.
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@kindex -G
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@cindex object size
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@item -G@var{value}
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@itemx -G @var{value}
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Set the maximum size of objects to be optimized using the GP register to
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@var{size} under MIPS ECOFF. Ignored for other object file formats.
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@item --help
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@kindex --help
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@cindex help
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@cindex usage
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Print a summary of the command-line options on the standard output and exit.
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This option and @samp{--version} begin with two dashes instead of one
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for compatibility with other GNU programs. The other options start with
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only one dash for compatibility with other linkers.
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@kindex -i
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@cindex incremental link
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@item -i
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Perform an incremental link (same as option @samp{-r}).
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|
@cindex archive files, from cmd line
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|
@kindex -l@var{archive}
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@item -l@var{ar}
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Add archive file @var{archive} to the list of files to link. This
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option may be used any number of times. @code{ld} will search its
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path-list for occurrences of @code{lib@var{ar}.a} for every @var{archive}
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specified.
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@cindex search directory, from cmd line
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@kindex -L@var{dir}
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@item -L@var{searchdir}
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@itemx -L @var{searchdir}
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|
Add path @var{searchdir} to the list of paths that @code{ld} will search
|
|
for archive libraries and @code{ld} control scripts. You may use this
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option any number of times.
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@ifset UsesEnvVars
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|
The default set of paths searched (without being specified with
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|
@samp{-L}) depends on which emulation mode @code{ld} is using, and in
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|
some cases also on how it was configured. @xref{Environment}.
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@end ifset
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|
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|
The paths can also be specified in a link script with the
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@code{SEARCH_DIR} command.
|
|
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|
@cindex link map
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|
@kindex -M
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|
@item -M
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|
Print (to the standard output) a link map---diagnostic information
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|
about where symbols are mapped by @code{ld}, and information on global
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|
common storage allocation.
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|
@cindex link map
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|
@kindex -Map
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@item -Map @var{mapfile}
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|
Print to the file @var{mapfile} a link map---diagnostic information
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|
about where symbols are mapped by @code{ld}, and information on global
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|
common storage allocation.
|
|
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@cindex emulation
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|
@kindex -m @var{emulation}
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@item -m@var{emulation}
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@itemx -m @var{emulation}
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|
Emulate the @var{emulation} linker. You can list the available
|
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emulations with the @samp{-V} option. The
|
|
default is the system for which you configured @code{ld}.
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|
@kindex -N
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|
@cindex read/write from cmd line
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|
@kindex OMAGIC
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|
@item -N
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|
Set the text and data sections to be readable and writable. Also, do
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|
not page-align the data segment. If the output format supports Unix
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|
style magic numbers, mark the output as @code{OMAGIC}.
|
|
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|
@item -n
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|
@kindex -n
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@cindex read-only text
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|
@kindex NMAGIC
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|
Set the text segment to be read only, and mark the output as
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|
@code{NMAGIC} if possible.
|
|
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|
@item -noinhibit-exec
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|
@cindex output file after errors
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|
@kindex -noinhibit-exec
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|
Retain the executable output file whenever it is still usable.
|
|
Normally, the linker will not produce an output file if it encounters
|
|
errors during the link process; it exits without writing an output file
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|
when it issues any error whatsoever.
|
|
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|
@item -o @var{output}
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|
@kindex -o @var{output}
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|
@cindex naming the output file
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|
Use @var{output} as the name for the program produced by @code{ld}; if this
|
|
option is not specified, the name @file{a.out} is used by default. The
|
|
script command @code{OUTPUT} can also specify the output file name.
|
|
|
|
@kindex -oformat
|
|
@item -oformat @var{output-format}
|
|
Specify the binary format for the output object file. You don't usually
|
|
need to specify this, as @code{ld} is configured to produce as a default
|
|
output format the most usual format on each machine.
|
|
@var{output-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}.) The script command
|
|
@code{OUTPUT_FORMAT} can also specify the output format, but this option
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|
overrides it. @xref{BFD}.
|
|
|
|
@item -R @var{filename}
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|
@kindex -R @var{file}
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|
@cindex symbol-only input
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|
Read symbol names and their addresses from @var{filename}, but do not
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|
relocate it or include it in the output. This allows your output file
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|
to refer symbolically to absolute locations of memory defined in other
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|
programs.
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|
@item -relax
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|
@kindex -relax
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|
@cindex synthesizing linker
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|
@cindex relaxing addressing modes
|
|
An option with machine dependent effects. Currently this option is only
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|
supported on the H8/300.
|
|
@ifset H8300
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|
@xref{H8/300,,@code{ld} and the H8/300}.
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|
@end ifset
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|
|
|
On some platforms, use option performs global optimizations that
|
|
become possible when the linker resolves addressing in the program, such
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|
as relaxing address modes and synthesizing new instructions in the
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|
output object file.
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|
|
|
On platforms where this is not supported, @samp{-relax} is accepted, but
|
|
ignored.
|
|
|
|
@item -r
|
|
@cindex partial link
|
|
@cindex relocatable output
|
|
@kindex -r
|
|
Generate relocatable output---i.e., generate an output file that can in
|
|
turn serve as input to @code{ld}. This is often called @dfn{partial
|
|
linking}. As a side effect, in environments that support standard Unix
|
|
magic numbers, this option also sets the output file's magic number to
|
|
@code{OMAGIC}.
|
|
@c ; see @code{-N}.
|
|
If this option is not specified, an absolute file is produced. When
|
|
linking C++ programs, this option @emph{will not} resolve references to
|
|
constructors; to do that, use @samp{-Ur}.
|
|
|
|
This option does the same thing as @samp{-i}.
|
|
|
|
@item -S
|
|
@kindex -S
|
|
@cindex strip debugger symbols
|
|
Omit debugger symbol information (but not all symbols) from the output file.
|
|
|
|
@item -s
|
|
@kindex -s
|
|
@cindex strip all symbols
|
|
Omit all symbol information from the output file.
|
|
|
|
@item -sort-common
|
|
Normally, when @code{ld} places the global common symbols in the
|
|
appropriate output sections, it sorts them by size. First come all the
|
|
one byte symbols, then all the two bytes, then all the four bytes, and
|
|
then everything else. This is to prevent gaps between symbols due to
|
|
alignment constraints. This option disables that sorting.
|
|
|
|
@item -Tbss @var{org}
|
|
@kindex -Tbss @var{org}
|
|
@itemx -Tdata @var{org}
|
|
@kindex -Tdata @var{org}
|
|
@itemx -Ttext @var{org}
|
|
@kindex -Ttext @var{org}
|
|
@cindex segment origins, cmd line
|
|
Use @var{org} as the starting address for---respectively---the
|
|
@code{bss}, @code{data}, or the @code{text} segment of the output file.
|
|
@var{org} must be a single hexadecimal integer;
|
|
for compatibility with other linkers, you may omit the leading
|
|
@samp{0x} usually associated with hexadecimal values.
|
|
|
|
@item -T @var{commandfile}
|
|
@itemx -T@var{commandfile}
|
|
@kindex -T @var{script}
|
|
@cindex script files
|
|
Read link commands from the file @var{commandfile}. These commands
|
|
completely override @code{ld}'s default link format (rather than adding
|
|
to it); @var{commandfile} must specify everything necessary to describe
|
|
the target format. @xref{Commands}. If @var{commandfile} does not
|
|
exist, @code{ld} looks for it in the directories specified by any
|
|
preceding @samp{-L} options. Multiple @samp{-T} options accumulate.
|
|
|
|
@item -t
|
|
@kindex -t
|
|
@cindex verbose
|
|
@cindex input files, displaying
|
|
Print the names of the input files as @code{ld} processes them.
|
|
|
|
@item -u @var{symbol}
|
|
@kindex -u @var{symbol}
|
|
@cindex undefined symbol
|
|
Force @var{symbol} to be entered in the output file as an undefined symbol.
|
|
Doing this may, for example, trigger linking of additional modules from
|
|
standard libraries. @samp{-u} may be repeated with different option
|
|
arguments to enter additional undefined symbols.
|
|
@c Nice idea, but no such command: This option is equivalent
|
|
@c to the @code{EXTERN} linker command.
|
|
|
|
@item -Ur
|
|
@kindex -Ur
|
|
@cindex constructors
|
|
For anything other than C++ programs, this option is equivalent to
|
|
@samp{-r}: it generates relocatable output---i.e., an output file that can in
|
|
turn serve as input to @code{ld}. When linking C++ programs, @samp{-Ur}
|
|
@emph{will} resolve references to constructors, unlike @samp{-r}.
|
|
It does not work to use @samp{-Ur} on files that were themselves linked
|
|
with @samp{-Ur}; once the constructor table has been built, it can not
|
|
be added to. Use @samp{-Ur} only for the last partial link, and
|
|
@samp{-r} for the others.
|
|
|
|
@item -V
|
|
@kindex -V
|
|
@cindex version
|
|
Display the version number for @code{ld} and list the supported emulations.
|
|
Display which input files can and can not be opened.
|
|
|
|
@item -v
|
|
@kindex -v
|
|
@cindex version
|
|
Display the version number for @code{ld}.
|
|
|
|
@item --version
|
|
@kindex --version
|
|
Display the version number for @code{ld} and exit.
|
|
|
|
@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,
|
|
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
|
|
warnings about symbols in the libraries as well as in your programs.
|
|
|
|
There are three kinds of global symbols, illustrated here by C examples:
|
|
|
|
@table @samp
|
|
@item int i = 1;
|
|
A definition, which goes in the initialized data section of the output
|
|
file.
|
|
|
|
@item extern int i;
|
|
An undefined reference, which does not allocate space.
|
|
There must be either a definition or a common symbol for the
|
|
variable somewhere.
|
|
|
|
@item int i;
|
|
A common symbol. If there are only (one or more) common symbols for a
|
|
variable, it goes in the uninitialized data area of the output file.
|
|
The linker merges multiple common symbols for the same variable into a
|
|
single symbol. If they are of different sizes, it picks the largest
|
|
size. The linker turns a common symbol into a declaration, if there is
|
|
a definition of the same variable.
|
|
@end table
|
|
|
|
The @samp{-warn-common} option can produce five kinds of warnings. Each
|
|
warning consists of a pair of lines: the first describes the symbol just
|
|
encountered, and the second describes the previous symbol encountered
|
|
with the same name. One or both of the two symbols will be a common
|
|
symbol.
|
|
|
|
@enumerate
|
|
@item
|
|
Turning a common symbol into a reference, because there is already a
|
|
definition for the symbol.
|
|
@smallexample
|
|
@var{file}(@var{section}): warning: common of `@var{symbol}' overridden by definition
|
|
@var{file}(@var{section}): warning: defined here
|
|
@end smallexample
|
|
|
|
@item
|
|
Turning a common symbol into a reference, because a later definition for
|
|
the symbol is encountered. This is the same as the previous case,
|
|
except that the symbols are encountered in a different order.
|
|
@smallexample
|
|
@var{file}(@var{section}): warning: definition of `@var{symbol}' overriding common
|
|
@var{file}(@var{section}): warning: common is here
|
|
@end smallexample
|
|
|
|
@item
|
|
Merging a common symbol with a previous same-sized common symbol.
|
|
@smallexample
|
|
@var{file}(@var{section}): warning: multiple common of `@var{symbol}'
|
|
@var{file}(@var{section}): warning: previous common is here
|
|
@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
|
|
|
|
@item -X
|
|
@kindex -X
|
|
@cindex local symbols, deleting
|
|
@cindex L, deleting symbols beginning
|
|
If @samp{-s} or @samp{-S} is also specified, delete only local symbols
|
|
beginning with @samp{L}.
|
|
|
|
@item -x
|
|
@kindex -x
|
|
@cindex deleting local symbols
|
|
If @samp{-s} or @samp{-S} is also specified, delete all local symbols,
|
|
not just those beginning with @samp{L}.
|
|
|
|
@item -y@var{symbol}
|
|
@kindex -y@var{symbol}
|
|
@cindex symbol tracing
|
|
Print the name of each linked file in which @var{symbol} appears. This
|
|
option may be given any number of times. On many systems it is necessary
|
|
to prepend an underscore.
|
|
|
|
This option is useful when you have an undefined symbol in your link but
|
|
don't know where the reference is coming from.
|
|
@end table
|
|
|
|
@ifset UsesEnvVars
|
|
@node Environment
|
|
@section Environment Variables
|
|
|
|
You can change the behavior of @code{ld} with the environment
|
|
variable @code{GNUTARGET}.
|
|
|
|
@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 host. 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.
|
|
@end ifset
|
|
|
|
@node Commands
|
|
@chapter Command Language
|
|
|
|
@cindex command files
|
|
The command language provides explicit control over the link process,
|
|
allowing complete specification of the mapping between the linker's
|
|
input files and its output. It controls:
|
|
@itemize @bullet
|
|
@item
|
|
input files
|
|
@item
|
|
file formats
|
|
@item
|
|
output file layout
|
|
@item
|
|
addresses of sections
|
|
@item
|
|
placement of common blocks
|
|
@end itemize
|
|
|
|
You may supply a command file (also known as a link script) to the
|
|
linker either explicitly through the @samp{-T} option, or implicitly as
|
|
an ordinary file. If the linker opens a file which it cannot recognize
|
|
as a supported object or archive format, it reports an error.
|
|
|
|
@menu
|
|
* Scripts:: Linker Scripts
|
|
* Expressions:: Expressions
|
|
* MEMORY:: MEMORY Command
|
|
* SECTIONS:: SECTIONS Command
|
|
* Entry Point:: The Entry Point
|
|
* Option Commands:: Option Commands
|
|
@end menu
|
|
|
|
@node Scripts
|
|
@section Linker Scripts
|
|
The @code{ld} command language is a collection of statements; some are
|
|
simple keywords setting a particular option, some are used to select and
|
|
group input files or name output files; and two statement
|
|
types have a fundamental and pervasive impact on the linking process.
|
|
|
|
@cindex fundamental script commands
|
|
@cindex commands, fundamental
|
|
@cindex output file layout
|
|
@cindex layout of output file
|
|
The most fundamental command of the @code{ld} command language is the
|
|
@code{SECTIONS} command (@pxref{SECTIONS}). Every meaningful command
|
|
script must have a @code{SECTIONS} command: it specifies a
|
|
``picture'' of the output file's layout, in varying degrees of detail.
|
|
No other command is required in all cases.
|
|
|
|
The @code{MEMORY} command complements @code{SECTIONS} by describing the
|
|
available memory in the target architecture. This command is optional;
|
|
if you don't use a @code{MEMORY} command, @code{ld} assumes sufficient
|
|
memory is available in a contiguous block for all output.
|
|
@xref{MEMORY}.
|
|
|
|
@cindex comments
|
|
You may include comments in linker scripts just as in C: delimited
|
|
by @samp{/*} and @samp{*/}. As in C, comments are syntactically
|
|
equivalent to whitespace.
|
|
|
|
@node Expressions
|
|
@section Expressions
|
|
@cindex expression syntax
|
|
@cindex arithmetic
|
|
Many useful commands involve arithmetic expressions. The syntax for
|
|
expressions in the command language is identical to that of C
|
|
expressions, with the following features:
|
|
@itemize @bullet
|
|
@item
|
|
All expressions evaluated as integers and
|
|
are of ``long'' or ``unsigned long'' type.
|
|
@item
|
|
All constants are integers.
|
|
@item
|
|
All of the C arithmetic operators are provided.
|
|
@item
|
|
You may reference, define, and create global variables.
|
|
@item
|
|
You may call special purpose built-in functions.
|
|
@end itemize
|
|
|
|
@menu
|
|
* Integers:: Integers
|
|
* Symbols:: Symbol Names
|
|
* Location Counter:: The Location Counter
|
|
* Operators:: Operators
|
|
* Evaluation:: Evaluation
|
|
* Assignment:: Assignment: Defining Symbols
|
|
* Arithmetic Functions:: Built-In Functions
|
|
@end menu
|
|
|
|
@node Integers
|
|
@subsection Integers
|
|
@cindex integer notation
|
|
@cindex octal integers
|
|
An octal integer is @samp{0} followed by zero or more of the octal
|
|
digits (@samp{01234567}).
|
|
@example
|
|
_as_octal = 0157255;
|
|
@end example
|
|
|
|
@cindex decimal integers
|
|
A decimal integer starts with a non-zero digit followed by zero or
|
|
more digits (@samp{0123456789}).
|
|
@example
|
|
_as_decimal = 57005;
|
|
@end example
|
|
|
|
@cindex hexadecimal integers
|
|
@kindex 0x
|
|
A hexadecimal integer is @samp{0x} or @samp{0X} followed by one or
|
|
more hexadecimal digits chosen from @samp{0123456789abcdefABCDEF}.
|
|
@example
|
|
_as_hex = 0xdead;
|
|
@end example
|
|
|
|
@cindex negative integers
|
|
To write a negative integer, use
|
|
the prefix operator @samp{-}; @pxref{Operators}.
|
|
@example
|
|
_as_neg = -57005;
|
|
@end example
|
|
|
|
@cindex scaled integers
|
|
@cindex K and M integer suffixes
|
|
@cindex M and K integer suffixes
|
|
@cindex suffixes for integers
|
|
@cindex integer suffixes
|
|
Additionally the suffixes @code{K} and @code{M} may be used to scale a
|
|
constant by
|
|
@c TEXI2ROFF-KILL
|
|
@ifinfo
|
|
@c END TEXI2ROFF-KILL
|
|
@code{1024} or @code{1024*1024}
|
|
@c TEXI2ROFF-KILL
|
|
@end ifinfo
|
|
@tex
|
|
${\rm 1024}$ or ${\rm 1024}^2$
|
|
@end tex
|
|
@c END TEXI2ROFF-KILL
|
|
respectively. For example, the following all refer to the same quantity:
|
|
|
|
@example
|
|
_fourk_1 = 4K;
|
|
_fourk_2 = 4096;
|
|
_fourk_3 = 0x1000;
|
|
@end example
|
|
|
|
@node Symbols
|
|
@subsection Symbol Names
|
|
@cindex symbol names
|
|
@cindex names
|
|
@cindex quoted symbol names
|
|
@kindex "
|
|
Unless quoted, symbol names start with a letter, underscore, point or
|
|
hyphen and may include any letters, underscores, digits, points,
|
|
and minus signs. Unquoted symbol names must not conflict with any
|
|
keywords. You can specify a symbol which contains odd characters or has
|
|
the same name as a keyword, by surrounding the symbol name in double quotes:
|
|
@example
|
|
"SECTION" = 9;
|
|
"with a space" = "also with a space" + 10;
|
|
@end example
|
|
|
|
@node Location Counter
|
|
@subsection The Location Counter
|
|
@kindex .
|
|
@cindex dot
|
|
@cindex location counter
|
|
@cindex current output location
|
|
The special linker variable @dfn{dot} @samp{.} always contains the
|
|
current output location counter. Since the @code{.} always refers to
|
|
a location in an output section, it must always appear in an
|
|
expression within a @code{SECTIONS} command. The @code{.} symbol
|
|
may appear anywhere that an ordinary symbol is allowed in an
|
|
expression, but its assignments have a side effect. Assigning a value
|
|
to the @code{.} symbol will cause the location counter to be moved.
|
|
@cindex holes
|
|
This may be used to create holes in the output section. The location
|
|
counter may never be moved backwards.
|
|
@example
|
|
SECTIONS
|
|
@{
|
|
output :
|
|
@{
|
|
file1(.text)
|
|
. = . + 1000;
|
|
file2(.text)
|
|
. += 1000;
|
|
file3(.text)
|
|
@} = 0x1234;
|
|
@}
|
|
@end example
|
|
@noindent
|
|
In the previous example, @code{file1} is located at the beginning of the
|
|
output section, then there is a 1000 byte gap. Then @code{file2}
|
|
appears, also with a 1000 byte gap following before @code{file3} is
|
|
loaded. The notation @samp{= 0x1234} specifies what data to write in
|
|
the gaps (@pxref{Section Options}).
|
|
|
|
@node Operators
|
|
@subsection Operators
|
|
@cindex Operators for arithmetic
|
|
@cindex arithmetic operators
|
|
@cindex precedence in expressions
|
|
The linker recognizes the standard C set of arithmetic operators, with
|
|
the standard bindings and precedence levels:
|
|
@c TEXI2ROFF-KILL
|
|
@ifinfo
|
|
@c END TEXI2ROFF-KILL
|
|
@example
|
|
precedence associativity Operators Notes
|
|
(highest)
|
|
1 left ! - ~ (1)
|
|
2 left * / %
|
|
3 left + -
|
|
4 left >> <<
|
|
5 left == != > < <= >=
|
|
6 left &
|
|
7 left |
|
|
8 left &&
|
|
9 left ||
|
|
10 right ? :
|
|
11 right &= += -= *= /= (2)
|
|
(lowest)
|
|
@end example
|
|
Notes:
|
|
(1) Prefix operators
|
|
(2) @xref{Assignment}
|
|
@c TEXI2ROFF-KILL
|
|
@end ifinfo
|
|
@tex
|
|
\vskip \baselineskip
|
|
%"lispnarrowing" is the extra indent used generally for @example
|
|
\hskip\lispnarrowing\vbox{\offinterlineskip
|
|
\hrule
|
|
\halign
|
|
{\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ #\ \hfil&\vrule#&\strut\hfil\ {\tt #}\ \hfil&\vrule#\cr
|
|
height2pt&\omit&&\omit&&\omit&\cr
|
|
&Precedence&& Associativity &&{\rm Operators}&\cr
|
|
height2pt&\omit&&\omit&&\omit&\cr
|
|
\noalign{\hrule}
|
|
height2pt&\omit&&\omit&&\omit&\cr
|
|
&highest&&&&&\cr
|
|
% '176 is tilde, '~' in tt font
|
|
&1&&left&&\qquad- \char'176\ !\qquad\dag&\cr
|
|
&2&&left&&* / \%&\cr
|
|
&3&&left&&+ -&\cr
|
|
&4&&left&&>> <<&\cr
|
|
&5&&left&&== != > < <= >=&\cr
|
|
&6&&left&&\&&\cr
|
|
&7&&left&&|&\cr
|
|
&8&&left&&{\&\&}&\cr
|
|
&9&&left&&||&\cr
|
|
&10&&right&&? :&\cr
|
|
&11&&right&&\qquad\&= += -= *= /=\qquad\ddag&\cr
|
|
&lowest&&&&&\cr
|
|
height2pt&\omit&&\omit&&\omit&\cr}
|
|
\hrule}
|
|
@end tex
|
|
@iftex
|
|
{
|
|
@obeylines@parskip=0pt@parindent=0pt
|
|
@dag@quad Prefix operators.
|
|
@ddag@quad @xref{Assignment}.
|
|
}
|
|
@end iftex
|
|
@c END TEXI2ROFF-KILL
|
|
|
|
@node Evaluation
|
|
@subsection Evaluation
|
|
|
|
@cindex lazy evaluation
|
|
@cindex expression evaluation order
|
|
The linker uses ``lazy evaluation'' for expressions; it only calculates
|
|
an expression when absolutely necessary. The linker needs the value of
|
|
the start address, and the lengths of memory regions, in order to do any
|
|
linking at all; these values are computed as soon as possible when the
|
|
linker reads in the command file. However, other values (such as symbol
|
|
values) are not known or needed until after storage allocation. Such
|
|
values are evaluated later, when other information (such as the sizes of
|
|
output sections) is available for use in the symbol assignment
|
|
expression.
|
|
|
|
@node Assignment
|
|
@subsection Assignment: Defining Symbols
|
|
@cindex assignment in scripts
|
|
@cindex symbol definition, scripts
|
|
@cindex variables, defining
|
|
You may create global symbols, and assign values (addresses) to global
|
|
symbols, using any of the C assignment operators:
|
|
|
|
@table @code
|
|
@item @var{symbol} = @var{expression} ;
|
|
@itemx @var{symbol} &= @var{expression} ;
|
|
@itemx @var{symbol} += @var{expression} ;
|
|
@itemx @var{symbol} -= @var{expression} ;
|
|
@itemx @var{symbol} *= @var{expression} ;
|
|
@itemx @var{symbol} /= @var{expression} ;
|
|
@end table
|
|
|
|
Two things distinguish assignment from other operators in @code{ld}
|
|
expressions.
|
|
@itemize @bullet
|
|
@item
|
|
Assignment may only be used at the root of an expression;
|
|
@samp{a=b+3;} is allowed, but @samp{a+b=3;} is an error.
|
|
|
|
@kindex ;
|
|
@cindex semicolon
|
|
@item
|
|
You must place a trailing semicolon (``@key{;}'') at the end of an
|
|
assignment statement.
|
|
@end itemize
|
|
|
|
Assignment statements may appear:
|
|
@itemize @bullet
|
|
@item
|
|
as commands in their own right in an @code{ld} script; or
|
|
@item
|
|
as independent statements within a @code{SECTIONS} command; or
|
|
@item
|
|
as part of the contents of a section definition in a
|
|
@code{SECTIONS} command.
|
|
@end itemize
|
|
|
|
The first two cases are equivalent in effect---both define a symbol with
|
|
an absolute address. The last case defines a symbol whose address is
|
|
relative to a particular section (@pxref{SECTIONS}).
|
|
|
|
@cindex absolute and relocatable symbols
|
|
@cindex relocatable and absolute symbols
|
|
@cindex symbols, relocatable and absolute
|
|
When a linker expression is evaluated and assigned to a variable, it is
|
|
given either an absolute or a relocatable type. An absolute expression
|
|
type is one in which the symbol contains the value that it will have in
|
|
the output file; a relocatable expression type is one in which the
|
|
value is expressed as a fixed offset from the base of a section.
|
|
|
|
The type of the expression is controlled by its position in the script
|
|
file. A symbol assigned within a section definition is created relative
|
|
to the base of the section; a symbol assigned in any other place is
|
|
created as an absolute symbol. Since a symbol created within a
|
|
section definition is relative to the base of the section, it
|
|
will remain relocatable if relocatable output is requested. A symbol
|
|
may be created with an absolute value even when assigned to within a
|
|
section definition by using the absolute assignment function
|
|
@code{ABSOLUTE}. For example, to create an absolute symbol whose address
|
|
is the last byte of an output section named @code{.data}:
|
|
@example
|
|
SECTIONS@{ @dots{}
|
|
.data :
|
|
@{
|
|
*(.data)
|
|
_edata = ABSOLUTE(.) ;
|
|
@}
|
|
@dots{} @}
|
|
@end example
|
|
|
|
The linker tries to put off the evaluation of an assignment until all
|
|
the terms in the source expression are known (@pxref{Evaluation}). For
|
|
instance, the sizes of sections cannot be known until after allocation,
|
|
so assignments dependent upon these are not performed until after
|
|
allocation. Some expressions, such as those depending upon the location
|
|
counter @dfn{dot}, @samp{.} must be evaluated during allocation. If the
|
|
result of an expression is required, but the value is not available,
|
|
then an error results. For example, a script like the following
|
|
@example
|
|
SECTIONS @{ @dots{}
|
|
text 9+this_isnt_constant :
|
|
@{ @dots{}
|
|
@}
|
|
@dots{} @}
|
|
@end example
|
|
@kindex Non constant expression
|
|
@noindent
|
|
will cause the error message ``@code{Non constant expression for initial
|
|
address}''.
|
|
|
|
@node Arithmetic Functions
|
|
@subsection Arithmetic Functions
|
|
@cindex functions in expression language
|
|
The command language includes a number of built-in
|
|
functions for use in link script expressions.
|
|
@table @code
|
|
@item ABSOLUTE(@var{exp})
|
|
@kindex ABSOLUTE(@var{exp})
|
|
@cindex expression, absolute
|
|
Return the absolute (non-relocatable, as opposed to non-negative) value
|
|
of the expression @var{exp}. Primarily useful to assign an absolute
|
|
value to a symbol within a section definition, where symbol values are
|
|
normally section-relative.
|
|
|
|
@item ADDR(@var{section})
|
|
@kindex ADDR(@var{section})
|
|
@cindex section address
|
|
Return the absolute address of the named @var{section}. Your script must
|
|
previously have defined the location of that section. In the following
|
|
example, @code{symbol_1} and @code{symbol_2} are assigned identical
|
|
values:
|
|
@example
|
|
SECTIONS@{ @dots{}
|
|
.output1 :
|
|
@{
|
|
start_of_output_1 = ABSOLUTE(.);
|
|
@dots{}
|
|
@}
|
|
.output :
|
|
@{
|
|
symbol_1 = ADDR(.output1);
|
|
symbol_2 = start_of_output_1;
|
|
@}
|
|
@dots{} @}
|
|
@end example
|
|
|
|
@item ALIGN(@var{exp})
|
|
@kindex ALIGN(@var{exp})
|
|
@cindex rounding up location counter
|
|
Return the result of the current location counter (@code{.}) aligned to
|
|
the next @var{exp} boundary. @var{exp} must be an expression whose
|
|
value is a power of two. This is equivalent to
|
|
@example
|
|
(. + @var{exp} - 1) & ~(@var{exp} - 1)
|
|
@end example
|
|
|
|
@code{ALIGN} doesn't change the value of the location counter---it just
|
|
does arithmetic on it. As an example, to align the output @code{.data}
|
|
section to the next @code{0x2000} byte boundary after the preceding
|
|
section and to set a variable within the section to the next
|
|
@code{0x8000} boundary after the input sections:
|
|
@example
|
|
SECTIONS@{ @dots{}
|
|
.data ALIGN(0x2000): @{
|
|
*(.data)
|
|
variable = ALIGN(0x8000);
|
|
@}
|
|
@dots{} @}
|
|
@end example
|
|
@noindent
|
|
The first use of @code{ALIGN} in this example specifies the location of
|
|
a section because it is used as the optional @var{start} attribute of a
|
|
section definition (@pxref{Section Options}). The second use simply
|
|
defines the value of a variable.
|
|
|
|
The built-in @code{NEXT} is closely related to @code{ALIGN}.
|
|
|
|
@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 default
|
|
values for symbols. For example, the following command-file fragment shows how
|
|
to set a global symbol @code{begin} to the first location in the
|
|
@code{.text} section---but if a symbol called @code{begin} already
|
|
existed, its value is preserved:
|
|
@smallexample
|
|
SECTIONS@{ @dots{}
|
|
.text : @{
|
|
begin = DEFINED(begin) ? begin : . ;
|
|
@dots{}
|
|
@}
|
|
@dots{} @}
|
|
@end smallexample
|
|
|
|
@item NEXT(@var{exp})
|
|
@kindex NEXT(@var{exp})
|
|
@cindex unallocated address, next
|
|
Return the next unallocated address that is a multiple of @var{exp}.
|
|
This function is closely related to @code{ALIGN(@var{exp})}; unless you
|
|
use the @code{MEMORY} command to define discontinuous memory for the
|
|
output file, the two functions are equivalent.
|
|
|
|
@item SIZEOF(@var{section})
|
|
@kindex SIZEOF(@var{section})
|
|
@cindex section size
|
|
Return the size in bytes of the named @var{section}, if that section has
|
|
been allocated. In the following example, @code{symbol_1} and
|
|
@code{symbol_2} are assigned identical values:
|
|
@c What does it return if the section hasn't been allocated? 0?
|
|
@example
|
|
SECTIONS@{ @dots{}
|
|
.output @{
|
|
.start = . ;
|
|
@dots{}
|
|
.end = . ;
|
|
@}
|
|
symbol_1 = .end - .start ;
|
|
symbol_2 = SIZEOF(.output);
|
|
@dots{} @}
|
|
|
|
@end example
|
|
|
|
@item SIZEOF_HEADERS
|
|
@kindex SIZEOF_HEADERS
|
|
@cindex header size
|
|
@itemx sizeof_headers
|
|
@kindex sizeof_headers
|
|
Return the size in bytes of the output file's headers. You can use this number
|
|
as the start address of the first section, if you choose, to facilitate
|
|
paging.
|
|
|
|
@end table
|
|
|
|
@node MEMORY
|
|
@section Memory Layout
|
|
@kindex MEMORY
|
|
@cindex regions of memory
|
|
@cindex discontinuous memory
|
|
@cindex allocating memory
|
|
The linker's default configuration permits allocation of all available memory.
|
|
You can override this configuration by using the @code{MEMORY} command. The
|
|
@code{MEMORY} command describes the location and size of blocks of
|
|
memory in the target. By using it carefully, you can describe which
|
|
memory regions may be used by the linker, and which memory regions it
|
|
must avoid. The linker does not shuffle sections to fit into the
|
|
available regions, but does move the requested sections into the correct
|
|
regions and issue errors when the regions become too full.
|
|
|
|
A command file may contain at most one use of the @code{MEMORY}
|
|
command; however, you can define as many blocks of memory within it as
|
|
you wish. The syntax is:
|
|
|
|
@example
|
|
MEMORY
|
|
@{
|
|
@var{name} (@var{attr}) : ORIGIN = @var{origin}, LENGTH = @var{len}
|
|
@dots{}
|
|
@}
|
|
@end example
|
|
@table @code
|
|
@item @var{name}
|
|
@cindex naming memory regions
|
|
is a name used internally by the linker to refer to the region. Any
|
|
symbol name may be used. The region names are stored in a separate
|
|
name space, and will not conflict with symbols, file names or section
|
|
names. Use distinct names to specify multiple regions.
|
|
@item (@var{attr})
|
|
@cindex memory region attributes
|
|
is an optional list of attributes, permitted for compatibility with the
|
|
AT&T linker but not used by @code{ld} beyond checking that the
|
|
attribute list is valid. Valid attribute lists must be made up of the
|
|
characters ``@code{LIRWX}''. If you omit the attribute list, you may
|
|
omit the parentheses around it as well.
|
|
@item @var{origin}
|
|
@kindex ORIGIN =
|
|
@kindex o =
|
|
@kindex org =
|
|
is the start address of the region in physical memory. It is
|
|
an expression that must evaluate to a constant before
|
|
memory allocation is performed. The keyword @code{ORIGIN} may be
|
|
abbreviated to @code{org} or @code{o} (but not, for example, @samp{ORG}).
|
|
@item @var{len}
|
|
@kindex LENGTH =
|
|
@kindex len =
|
|
@kindex l =
|
|
is the size in bytes of the region (an expression).
|
|
The keyword @code{LENGTH} may be abbreviated to @code{len} or @code{l}.
|
|
@end table
|
|
|
|
For example, to specify that memory has two regions available for
|
|
allocation---one starting at 0 for 256 kilobytes, and the other
|
|
starting at @code{0x40000000} for four megabytes:
|
|
|
|
@example
|
|
MEMORY
|
|
@{
|
|
rom : ORIGIN = 0, LENGTH = 256K
|
|
ram : org = 0x40000000, l = 4M
|
|
@}
|
|
@end example
|
|
|
|
Once you have defined a region of memory named @var{mem}, you can direct
|
|
specific output sections there by using a command ending in
|
|
@samp{>@var{mem}} within the @code{SECTIONS} command (@pxref{Section
|
|
Options}). If the combined output sections directed to a region are too
|
|
big for the region, the linker will issue an error message.
|
|
|
|
@node SECTIONS
|
|
@section Specifying Output Sections
|
|
@kindex SECTIONS
|
|
The @code{SECTIONS} command controls exactly where input sections are
|
|
placed into output sections, their order in the output file, and to
|
|
which output sections they are allocated.
|
|
|
|
You may use at most one @code{SECTIONS} command in a script file,
|
|
but you can have as many statements within it as you wish. Statements
|
|
within the @code{SECTIONS} command can do one of three things:
|
|
@itemize @bullet
|
|
@item
|
|
define the entry point;
|
|
@item
|
|
assign a value to a symbol;
|
|
@item
|
|
describe the placement of a named output section, and which input
|
|
sections go into it.
|
|
@end itemize
|
|
|
|
The first two operations---defining the entry point and defining
|
|
symbols---can also be done outside the @code{SECTIONS} command:
|
|
@pxref{Entry Point}, and @pxref{Assignment}. They are permitted here as
|
|
well for your convenience in reading the script, so that symbols and the
|
|
entry point can be defined at meaningful points in your output-file
|
|
layout.
|
|
|
|
When no @code{SECTIONS} command is given, the linker places each input
|
|
section into an identically named output section in the order that the
|
|
sections are first encountered in the input files. If all input sections
|
|
are present in the first file, for example, the order of sections in the
|
|
output file will match the order in the first input file.
|
|
|
|
@menu
|
|
* Section Definition:: Section Definitions
|
|
* Section Placement:: Section Placement
|
|
* Section Data Expressions:: Section Data Expressions
|
|
* Section Options:: Optional Section Attributes
|
|
@end menu
|
|
|
|
@node Section Definition
|
|
@subsection Section Definitions
|
|
@cindex section definition
|
|
The most frequently used statement in the @code{SECTIONS} command is
|
|
the @dfn{section definition}, which specifies the
|
|
properties of an output section: its location, alignment, contents,
|
|
fill pattern, and target memory region. Most of
|
|
these specifications are optional; the simplest form of a section
|
|
definition is
|
|
@example
|
|
SECTIONS @{ @dots{}
|
|
@var{secname} : @{
|
|
@var{contents}
|
|
@}
|
|
@dots{} @}
|
|
@end example
|
|
@cindex naming output sections
|
|
@noindent
|
|
@var{secname} is the name of the output section, and @var{contents} a
|
|
specification of what goes there---for example, a list of input files or
|
|
sections of input files (@pxref{Section Placement}). As you might
|
|
assume, the whitespace shown is optional. You do need the colon
|
|
@samp{:} and the braces @samp{@{@}}, however.
|
|
|
|
@var{secname} must meet the constraints of your output format. In
|
|
formats which only support a limited number of sections, such as
|
|
@code{a.out}, the name must be one of the names supported by the format
|
|
(@code{a.out}, for example, allows only @code{.text}, @code{.data} or
|
|
@code{.bss}). If the output format supports any number of sections, but
|
|
with numbers and not names (as is the case for Oasys), the name should be
|
|
supplied as a quoted numeric string. A section name may consist of any
|
|
sequence of characters, but any name which does not conform to the standard
|
|
@code{ld} symbol name syntax must be quoted.
|
|
@xref{Symbols, , Symbol Names}.
|
|
|
|
@node Section Placement
|
|
@subsection Section Placement
|
|
@cindex contents of a section
|
|
In a section definition, you can specify the contents of an output section by
|
|
listing particular input files, by listing particular input-file
|
|
sections, or by a combination of the two. You can also place arbitrary
|
|
data in the section, and define symbols relative to the beginning of the
|
|
section.
|
|
|
|
The @var{contents} of a section definition may include any of the
|
|
following kinds of statement. You can include as many of these as you
|
|
like in a single section definition, separated from one another by
|
|
whitespace.
|
|
|
|
@table @code
|
|
@item @var{filename}
|
|
@kindex @var{filename}
|
|
@cindex input files, section defn
|
|
@cindex files, including in output sections
|
|
You may simply name a particular input file to be placed in the current
|
|
output section; @emph{all} sections from that file are placed in the
|
|
current section definition. If the file name has already been mentioned
|
|
in another section definition, with an explicit section name list, then
|
|
only those sections which have not yet been allocated are used.
|
|
|
|
To specify a list of particular files by name:
|
|
@example
|
|
.data : @{ afile.o bfile.o cfile.o @}
|
|
@end example
|
|
@noindent
|
|
The example also illustrates that multiple statements can be included in
|
|
the contents of a section definition, since each file name is a separate
|
|
statement.
|
|
|
|
@item @var{filename}( @var{section} )
|
|
@itemx @var{filename}( @var{section}, @var{section}, @dots{} )
|
|
@itemx @var{filename}( @var{section} @var{section} @dots{} )
|
|
@kindex @var{filename}(@var{section})
|
|
@cindex files and sections, section defn
|
|
You can name one or more sections from your input files, for
|
|
insertion in the current output section. If you wish to specify a list
|
|
of input-file sections inside the parentheses, you may separate the
|
|
section names by either commas or whitespace.
|
|
|
|
@item * (@var{section})
|
|
@itemx * (@var{section}, @var{section}, @dots{})
|
|
@itemx * (@var{section} @var{section} @dots{})
|
|
@cindex input sections to output section
|
|
@kindex *(@var{section})
|
|
Instead of explicitly naming particular input files in a link control
|
|
script, you can refer to @emph{all} files from the @code{ld} command
|
|
line: use @samp{*} instead of a particular file name before the
|
|
parenthesized input-file section list.
|
|
|
|
If you have already explicitly included some files by name, @samp{*}
|
|
refers to all @emph{remaining} files---those whose places in the output
|
|
file have not yet been defined.
|
|
|
|
For example, to copy sections @code{1} through @code{4} from an Oasys file
|
|
into the @code{.text} section of an @code{a.out} file, and sections @code{13}
|
|
and @code{14} into the @code{.data} section:
|
|
@example
|
|
SECTIONS @{
|
|
.text :@{
|
|
*("1" "2" "3" "4")
|
|
@}
|
|
|
|
.data :@{
|
|
*("13" "14")
|
|
@}
|
|
@}
|
|
@end example
|
|
|
|
@samp{[ @var{section} @dots{} ]} used to be accepted as an alternate way
|
|
to specify named sections from all unallocated input files. Because
|
|
some operating systems (VMS) allow brackets in file names, that notation
|
|
is no longer supported.
|
|
|
|
@item @var{filename}@code{( COMMON )}
|
|
@itemx *( COMMON )
|
|
@kindex *( COMMON )
|
|
@cindex uninitialized data
|
|
@cindex commons in output
|
|
Specify where in your output file to place uninitialized data
|
|
with this notation. @code{*(COMMON)} by itself refers to all
|
|
uninitialized data from all input files (so far as it is not yet
|
|
allocated); @var{filename}@code{(COMMON)} refers to uninitialized data
|
|
from a particular file. Both are special cases of the general
|
|
mechanisms for specifying where to place input-file sections:
|
|
@code{ld} permits you to refer to uninitialized data as if it
|
|
were in an input-file section named @code{COMMON}, regardless of the
|
|
input file's format.
|
|
@end table
|
|
|
|
For example, the following command script arranges the output file into
|
|
three consecutive sections, named @code{.text}, @code{.data}, and
|
|
@code{.bss}, taking the input for each from the correspondingly named
|
|
sections of all the input files:
|
|
@example
|
|
SECTIONS @{
|
|
.text : @{ *(.text) @}
|
|
.data : @{ *(.data) @}
|
|
.bss : @{ *(.bss) *(COMMON) @}
|
|
@}
|
|
@end example
|
|
|
|
The following example reads all of the sections from file @code{all.o}
|
|
and places them at the start of output section @code{outputa} which
|
|
starts at location @code{0x10000}. All of section @code{.input1} from
|
|
file @code{foo.o} follows immediately, in the same output section. All
|
|
of section @code{.input2} from @code{foo.o} goes into output section
|
|
@code{outputb}, followed by section @code{.input1} from @code{foo1.o}.
|
|
All of the remaining @code{.input1} and @code{.input2} sections from any
|
|
files are written to output section @code{outputc}.
|
|
|
|
@example
|
|
SECTIONS @{
|
|
outputa 0x10000 :
|
|
@{
|
|
all.o
|
|
foo.o (.input1)
|
|
@}
|
|
outputb :
|
|
@{
|
|
foo.o (.input2)
|
|
foo1.o (.input1)
|
|
@}
|
|
outputc :
|
|
@{
|
|
*(.input1)
|
|
*(.input2)
|
|
@}
|
|
@}
|
|
@end example
|
|
|
|
@node Section Data Expressions
|
|
@subsection Section Data Expressions
|
|
@cindex expressions in a section
|
|
The foregoing statements
|
|
arrange, in your output file, data originating from your input files.
|
|
You can also place data directly in an output section from the link
|
|
command script. Most of these additional statements involve
|
|
expressions; @pxref{Expressions}. Although these statements are shown
|
|
separately here for ease of presentation, no such segregation is needed
|
|
within a section definition in the @code{SECTIONS} command; you can
|
|
intermix them freely with any of the statements we've just described.
|
|
|
|
@table @code
|
|
@item CREATE_OBJECT_SYMBOLS
|
|
@kindex CREATE_OBJECT_SYMBOLS
|
|
@cindex input filename symbols
|
|
@cindex filename symbols
|
|
Create a symbol for each input file
|
|
in the current section, set to the address of the first byte of
|
|
data written from that input file. For instance, with @code{a.out}
|
|
files it is conventional to have a symbol for each input file. You can
|
|
accomplish this by defining the output @code{.text} section as follows:
|
|
@example
|
|
SECTIONS @{
|
|
.text 0x2020 :
|
|
@{
|
|
CREATE_OBJECT_SYMBOLS
|
|
*(.text)
|
|
_etext = ALIGN(0x2000);
|
|
@}
|
|
@dots{}
|
|
@}
|
|
@end example
|
|
|
|
If @code{sample.ld} is a file containing this script, and @code{a.o},
|
|
@code{b.o}, @code{c.o}, and @code{d.o} are four input files with
|
|
contents like the following---
|
|
@example
|
|
/* a.c */
|
|
|
|
afunction() @{ @}
|
|
int adata=1;
|
|
int abss;
|
|
@end example
|
|
|
|
@noindent
|
|
@samp{ld -M -T sample.ld a.o b.o c.o d.o} would create a map like this,
|
|
containing symbols matching the object file names:
|
|
@example
|
|
00000000 A __DYNAMIC
|
|
00004020 B _abss
|
|
00004000 D _adata
|
|
00002020 T _afunction
|
|
00004024 B _bbss
|
|
00004008 D _bdata
|
|
00002038 T _bfunction
|
|
00004028 B _cbss
|
|
00004010 D _cdata
|
|
00002050 T _cfunction
|
|
0000402c B _dbss
|
|
00004018 D _ddata
|
|
00002068 T _dfunction
|
|
00004020 D _edata
|
|
00004030 B _end
|
|
00004000 T _etext
|
|
00002020 t a.o
|
|
00002038 t b.o
|
|
00002050 t c.o
|
|
00002068 t d.o
|
|
@end example
|
|
|
|
@item @var{symbol} = @var{expression} ;
|
|
@kindex @var{symbol} = @var{expression} ;
|
|
@itemx @var{symbol} @var{f}= @var{expression} ;
|
|
@kindex @var{symbol} @var{f}= @var{expression} ;
|
|
@var{symbol} is any symbol name (@pxref{Symbols}). ``@var{f}=''
|
|
refers to any of the operators @code{&= += -= *= /=} which combine
|
|
arithmetic and assignment.
|
|
|
|
@cindex assignment, in section defn
|
|
When you assign a value to a symbol within a particular section
|
|
definition, the value is relative to the beginning of the section
|
|
(@pxref{Assignment}). If you write
|
|
@example
|
|
SECTIONS @{
|
|
abs = 14 ;
|
|
@dots{}
|
|
.data : @{ @dots{} rel = 14 ; @dots{} @}
|
|
abs2 = 14 + ADDR(.data);
|
|
@dots{}
|
|
@}
|
|
@end example
|
|
@c FIXME: Try above example!
|
|
@noindent
|
|
@code{abs} and @code{rel} do not have the same value; @code{rel} has the
|
|
same value as @code{abs2}.
|
|
|
|
@item BYTE(@var{expression})
|
|
@kindex BYTE(@var{expression})
|
|
@itemx SHORT(@var{expression})
|
|
@kindex SHORT(@var{expression})
|
|
@itemx LONG(@var{expression})
|
|
@kindex LONG(@var{expression})
|
|
@cindex direct output
|
|
By including one of these three statements in a section definition, you
|
|
can explicitly place one, two, or four bytes (respectively) at the
|
|
current address of that section.
|
|
|
|
@ifclear SingleFormat
|
|
Multiple-byte quantities are represented in whatever byte order is
|
|
appropriate for the output file format (@pxref{BFD}).
|
|
@end ifclear
|
|
|
|
@item FILL(@var{expression})
|
|
@kindex FILL(@var{expression})
|
|
@cindex holes, filling
|
|
@cindex unspecified memory
|
|
Specify the ``fill pattern'' for the current section. Any otherwise
|
|
unspecified regions of memory within the section (for example, regions
|
|
you skip over by assigning a new value to the location counter @samp{.})
|
|
are filled with the two least significant bytes from the
|
|
@var{expression} argument. A @code{FILL} statement covers memory
|
|
locations @emph{after} the point it occurs in the section definition; by
|
|
including more than one @code{FILL} statement, you can have different
|
|
fill patterns in different parts of an output section.
|
|
@end table
|
|
|
|
@node Section Options
|
|
@subsection Optional Section Attributes
|
|
@cindex section defn, full syntax
|
|
Here is the full syntax of a section definition, including all the
|
|
optional portions:
|
|
|
|
@smallexample
|
|
SECTIONS @{
|
|
@dots{}
|
|
@var{secname} @var{start} BLOCK(@var{align}) (NOLOAD) : @{ @var{contents} @} =@var{fill} >@var{region}
|
|
@dots{}
|
|
@}
|
|
@end smallexample
|
|
|
|
@var{secname} and @var{contents} are required. @xref{Section
|
|
Definition}, and @pxref{Section Placement} for details on @var{contents}.
|
|
The remaining elements---@var{start}, @code{BLOCK(@var{align)}},
|
|
@code{(NOLOAD)} @code{=@var{fill}}, and @code{>@var{region}}---are all
|
|
optional.
|
|
|
|
@table @code
|
|
@item @var{start}
|
|
@cindex start address, section
|
|
@cindex section start
|
|
@cindex section address
|
|
You can force the output section to be loaded at a specified address by
|
|
specifying @var{start} immediately following the section name.
|
|
@var{start} can be represented as any expression. The following
|
|
example generates section @var{output} at location
|
|
@code{0x40000000}:
|
|
@example
|
|
SECTIONS @{
|
|
@dots{}
|
|
output 0x40000000: @{
|
|
@dots{}
|
|
@}
|
|
@dots{}
|
|
@}
|
|
@end example
|
|
|
|
@item BLOCK(@var{align})
|
|
@kindex BLOCK(@var{align})
|
|
@cindex section alignment
|
|
@cindex aligning sections
|
|
You can include @code{BLOCK()} specification to advance
|
|
the location counter @code{.} prior to the beginning of the section, so
|
|
that the section will begin at the specified alignment. @var{align} is
|
|
an expression.
|
|
|
|
@item (NOLOAD)
|
|
@kindex NOLOAD
|
|
@cindex prevent unnecessary loading
|
|
Use @samp{(NOLOAD)} to prevent a section from being loaded into memory
|
|
each time it is accessed. For example, in the script sample below, the
|
|
@code{ROM} segment is addressed at memory location @samp{0} and does not
|
|
need to be loaded into each object file:
|
|
@example
|
|
SECTIONS @{
|
|
ROM 0 (NOLOAD) : @{ @dots{} @}
|
|
@dots{}
|
|
@}
|
|
@end example
|
|
|
|
@item =@var{fill}
|
|
@kindex =@var{fill}
|
|
@cindex section fill pattern
|
|
@cindex fill pattern, entire section
|
|
Including
|
|
@code{=@var{fill}} in a section definition specifies the initial fill
|
|
value for that section.
|
|
You may use any expression to specify @var{fill}.
|
|
Any unallocated holes in the current output
|
|
section when written to the output file will be filled with the two
|
|
least significant bytes of the value, repeated as necessary. You can
|
|
also change the fill value with a @code{FILL} statement in the
|
|
@var{contents} of a section definition.
|
|
|
|
@item >@var{region}
|
|
@kindex >@var{region}
|
|
@cindex section, assigning to memory region
|
|
@cindex memory regions and sections
|
|
Assign this section to a previously defined region of memory.
|
|
@xref{MEMORY}.
|
|
|
|
@end table
|
|
|
|
@node Entry Point
|
|
@section The Entry Point
|
|
@kindex ENTRY(@var{symbol})
|
|
@cindex start of execution
|
|
@cindex first instruction
|
|
The linker command language includes a command specifically for
|
|
defining the first executable instruction in an output file (its
|
|
@dfn{entry point}). Its argument is a symbol name:
|
|
@example
|
|
ENTRY(@var{symbol})
|
|
@end example
|
|
|
|
Like symbol assignments, the @code{ENTRY} command may be placed either
|
|
as an independent command in the command file, or among the section
|
|
definitions within the @code{SECTIONS} command---whatever makes the most
|
|
sense for your layout.
|
|
|
|
@cindex entry point, defaults
|
|
@code{ENTRY} is only one of several ways of choosing the entry point.
|
|
You may indicate it in any of the following ways (shown in descending
|
|
order of priority: methods higher in the list override methods lower down).
|
|
@itemize @bullet
|
|
@item
|
|
the @samp{-e} @var{entry} command-line option;
|
|
@item
|
|
the @code{ENTRY(@var{symbol}} command in a linker control script;
|
|
@item
|
|
the value of the symbol @code{start}, if present;
|
|
@item
|
|
the value of the symbol @code{_main}, if present;
|
|
@item
|
|
the address of the first byte of the @code{.text} section, if present;
|
|
@item
|
|
The address @code{0}.
|
|
@end itemize
|
|
|
|
For example, you can use these rules to generate an entry point with an
|
|
assignment statement: if no symbol @code{start} is defined within your
|
|
input files, you can simply define it, assigning it an appropriate
|
|
value---
|
|
@example
|
|
start = 0x2020;
|
|
@end example
|
|
|
|
@noindent
|
|
The example shows an absolute address, but you can use any expression.
|
|
For example, if your input object files use some other symbol-name
|
|
convention for the entry point, you can just assign the value of
|
|
whatever symbol contains the start address to @code{start}:
|
|
@example
|
|
start = other_symbol ;
|
|
@end example
|
|
|
|
@node Option Commands
|
|
@section Option Commands
|
|
The command language includes a number of other commands that you can
|
|
use for specialized purposes. They are similar in purpose to
|
|
command-line options.
|
|
|
|
@table @code
|
|
@item FLOAT
|
|
@kindex FLOAT
|
|
@itemx NOFLOAT
|
|
@kindex NOFLOAT
|
|
These keywords were used in some older linkers to request a particular
|
|
math subroutine library. @code{ld} doesn't use the keywords, assuming
|
|
instead that any necessary subroutines are in libraries specified using
|
|
the general mechanisms for linking to archives; but to permit the use of
|
|
scripts that were written for the older linkers, the keywords
|
|
@code{FLOAT} and @code{NOFLOAT} are accepted and ignored.
|
|
|
|
@item FORCE_COMMON_ALLOCATION
|
|
@kindex FORCE_COMMON_ALLOCATION
|
|
@cindex common allocation
|
|
This command has the same effect as the @samp{-d} command-line option:
|
|
to make @code{ld} assign space to common symbols even if a relocatable
|
|
output file is specified (@samp{-r}).
|
|
|
|
@item INPUT ( @var{file}, @var{file}, @dots{} )
|
|
@kindex INPUT ( @var{files} )
|
|
@itemx INPUT ( @var{file} @var{file} @dots{} )
|
|
@cindex binary input files
|
|
Use this command to include binary input files in the link, without
|
|
including them in a particular section definition. Files specified this
|
|
way are treated identically to object files listed on the command line.
|
|
|
|
@ignore
|
|
@item MAP ( @var{name} )
|
|
@kindex MAP ( @var{name} )
|
|
@c MAP(...) appears to look for an F in the arg, ignoring all other
|
|
@c chars; if it finds one, it sets "map_option_f" to true. But nothing
|
|
@c checks map_option_f. Apparently a stub for the future...
|
|
@end ignore
|
|
|
|
@item OUTPUT ( @var{filename} )
|
|
@kindex OUTPUT ( @var{filename} )
|
|
@cindex naming the output file
|
|
Use this command to name the link output file @var{filename}. The
|
|
effect of @code{OUTPUT(@var{filename})} is identical to the effect of
|
|
@w{@samp{-o @var{filename}}}, and whichever is encountered last
|
|
(@samp{-T} or @samp{-o} will control the name actually used to name the
|
|
output file. In particular, you can use this command to supply a
|
|
default output-file name other than @code{a.out}.
|
|
|
|
@ifclear SingleFormat
|
|
@item OUTPUT_ARCH ( @var{bfdname} )
|
|
@kindex OUTPUT_ARCH ( @var{bfdname} )
|
|
@cindex machine architecture, output
|
|
Specify a particular output machine architecture, with one of the names
|
|
used by the BFD back-end routines (@pxref{BFD}). This command is often
|
|
unnecessary; the architecture is most often set implicitly by either the
|
|
system BFD configuration or as a side effect of the @code{OUTPUT_FORMAT}
|
|
command.
|
|
|
|
@item OUTPUT_FORMAT ( @var{bfdname} )
|
|
@kindex OUTPUT_FORMAT ( @var{bfdname} )
|
|
@cindex format, output file
|
|
Specify a particular output format, with one of the names used by the
|
|
BFD back-end routines (@pxref{BFD}). The effect is identical to the
|
|
effect of the @samp{-oformat} command-line option.
|
|
This selection will only affect
|
|
the output file; the related command @code{TARGET} affects primarily
|
|
input files.
|
|
@end ifclear
|
|
|
|
@item SEARCH_DIR ( @var{path} )
|
|
@kindex SEARCH_DIR ( @var{path} )
|
|
@cindex path for libraries
|
|
@cindex search path, libraries
|
|
Add @var{path} to the list of paths where @code{ld} looks for
|
|
archive libraries. @code{SEARCH_DIR(@var{path})} has the same
|
|
effect as @samp{-L@var{path}} on the command line.
|
|
|
|
@item STARTUP ( @var{filename} )
|
|
@kindex STARTUP ( @var{filename} )
|
|
@cindex first input file
|
|
Ensure that @var{filename} is the first input file used in the link
|
|
process.
|
|
|
|
@ifclear SingleFormat
|
|
@item TARGET ( @var{format} )
|
|
@cindex input file format
|
|
@kindex TARGET ( @var{format} )
|
|
Change the input-file object code format (like the command-line option
|
|
@samp{-b} or its synonym @samp{-format}). The argument @var{format} is
|
|
one of the strings used by BFD to name binary formats. If @code{TARGET}
|
|
is specified but @code{OUTPUT_FORMAT} is not, the last @code{TARGET}
|
|
argument is also used as the default format for the @code{ld} output
|
|
file. @xref{BFD}.
|
|
|
|
@kindex GNUTARGET
|
|
If you don't use the @code{TARGET} command, @code{ld} uses the value of
|
|
the environment variable @code{GNUTARGET}, if available, to select the
|
|
output file format. If that variable is also absent, @code{ld} uses
|
|
the default format configured for your machine in the BFD libraries.
|
|
@end ifclear
|
|
@end table
|
|
|
|
@ifset GENERIC
|
|
@node Machine Dependent
|
|
@chapter Machine Dependent Features
|
|
|
|
@cindex machine dependencies
|
|
@code{ld} has additional features on some platforms; the following
|
|
sections describe them. Machines where @code{ld} has no additional
|
|
functionality are not listed.
|
|
|
|
@menu
|
|
* H8/300:: @code{ld} and the H8/300
|
|
* i960:: @code{ld} and the Intel 960 family
|
|
@end menu
|
|
@end ifset
|
|
|
|
@c FIXME! This could use @up/@down, but there seems to be a conflict
|
|
@c between those and node-defaulting.
|
|
@ifset H8300
|
|
@ifclear GENERIC
|
|
@up
|
|
@end ifclear
|
|
@node H8/300
|
|
@section @code{ld} and the H8/300
|
|
|
|
@cindex H8/300 support
|
|
For the H8/300, @code{ld} can perform these global optimizations when
|
|
you specify the @samp{-relax} command-line option.
|
|
|
|
@table @emph
|
|
@item relaxing address modes
|
|
@cindex relaxing on H8/300
|
|
@code{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.
|
|
|
|
@item synthesizing instructions
|
|
@cindex synthesizing on H8/300
|
|
@c FIXME: specifically mov.b, or any mov instructions really?
|
|
@code{ld} finds all @code{mov.b} instructions which use the
|
|
sixteen-bit absolute address form, but refer to the top
|
|
page of memory, and changes them to use the eight-bit address form.
|
|
(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).
|
|
@end table
|
|
@ifclear GENERIC
|
|
@down
|
|
@end ifclear
|
|
@end ifset
|
|
|
|
@ifset I960
|
|
@ifclear GENERIC
|
|
@up
|
|
@end ifclear
|
|
@node i960
|
|
@section @code{ld} and the Intel 960 family
|
|
|
|
@cindex i960 support
|
|
|
|
You can use the @samp{-A@var{architecture}} command line option to
|
|
specify one of the two-letter names identifying members of the 960
|
|
family; the option specifies the desired output target, and warns of any
|
|
incompatible instructions in the input files. It also modifies the
|
|
linker's search strategy for archive libraries, to support the use of
|
|
libraries specific to each particular architecture, by including in the
|
|
search loop names suffixed with the string identifying the architecture.
|
|
|
|
For example, if your @code{ld} command line included @w{@samp{-ACA}} as
|
|
well as @w{@samp{-ltry}}, the linker would look (in its built-in search
|
|
paths, and in any paths you specify with @samp{-L}) for a library with
|
|
the names
|
|
|
|
@example
|
|
try
|
|
libtry.a
|
|
tryca
|
|
libtryca.a
|
|
@end example
|
|
|
|
@noindent
|
|
The first two possibilities would be considered in any event; the last
|
|
two are due to the use of @w{@samp{-ACA}}.
|
|
|
|
You can meaningfully use @samp{-A} more than once on a command line, since
|
|
the 960 architecture family allows combination of target architectures; each
|
|
use will add another pair of name variants to search for when @w{@samp{-l}}
|
|
specifies a library.
|
|
@ifclear GENERIC
|
|
@down
|
|
@end ifclear
|
|
@end ifset
|
|
|
|
@ifclear SingleFormat
|
|
@node BFD
|
|
@chapter BFD
|
|
|
|
@cindex back end
|
|
@cindex object file management
|
|
The linker accesses object and archive files using the BFD libraries.
|
|
These libraries allow the linker to use the same routines to operate on
|
|
object files whatever the object file format. A different object file
|
|
format can be supported simply by creating a new BFD back end and adding
|
|
it to the library. You can use @code{objdump -i}
|
|
(@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}) to
|
|
list all the formats available for each architecture under BFD. This
|
|
was the list of formats, and of architectures supported for each format,
|
|
as of the time this manual was prepared:
|
|
@cindex formats available
|
|
@cindex architectures available
|
|
@example
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BFD header file version 0.18
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a.out-i386
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(header big endian, data big endian)
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m68k:68020
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a29k
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sparc
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i386
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a.out-sunos-big
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(header big endian, data big endian)
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m68k:68020
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a29k
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sparc
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i386
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b.out.big
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(header big endian, data little endian)
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i960:core
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b.out.little
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(header little endian, data little endian)
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i960:core
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coff-a29k-big
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(header big endian, data big endian)
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a29k
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coff-h8300
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(header big endian, data big endian)
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H8/300
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coff-i386
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(header little endian, data little endian)
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i386
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coff-Intel-big
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(header big endian, data little endian)
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i960:core
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coff-Intel-little
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(header little endian, data little endian)
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i960:core
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coff-m68k
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(header big endian, data big endian)
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m68k:68020
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coff-m88kbcs
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(header big endian, data big endian)
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m88k:88100
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ecoff-bigmips
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(header big endian, data big endian)
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mips
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ecoff-littlemips
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(header little endian, data little endian)
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mips
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elf-big
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(header big endian, data big endian)
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m68k:68020
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vax
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i960:core
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a29k
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sparc
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mips
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i386
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m88k:88100
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H8/300
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rs6000:6000
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elf-little
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(header little endian, data little endian)
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m68k:68020
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vax
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i960:core
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a29k
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sparc
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mips
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i386
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m88k:88100
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H8/300
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rs6000:6000
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ieee
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(header big endian, data big endian)
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m68k:68020
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vax
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i960:core
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a29k
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|
sparc
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|
mips
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i386
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m88k:88100
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H8/300
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rs6000:6000
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srec
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(header big endian, data big endian)
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m68k:68020
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vax
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i960:core
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a29k
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sparc
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mips
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i386
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m88k:88100
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H8/300
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rs6000:6000
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@end example
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@cindex BFD requirements
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@cindex requirements for BFD
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As with most implementations, BFD is a compromise between
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several conflicting requirements. The major factor influencing
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BFD design was efficiency: any time used converting between
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formats is time which would not have been spent had BFD not
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been involved. This is partly offset by abstraction payback; since
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BFD simplifies applications and back ends, more time and care
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may be spent optimizing algorithms for a greater speed.
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One minor artifact of the BFD solution which you should bear in
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mind is the potential for information loss. There are two places where
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useful information can be lost using the BFD mechanism: during
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conversion and during output. @xref{BFD information loss}.
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@menu
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* BFD outline:: How it works: an outline of BFD
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@end menu
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@node BFD outline
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@section How it works: an outline of BFD
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@cindex opening object files
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@include bfdsumm.texi
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@end ifclear
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@node MRI
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@appendix MRI Compatible Script Files
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@cindex MRI compatibility
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To aid users making the transition to @sc{gnu} @code{ld} from the MRI
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linker, @code{ld} can use MRI compatible linker scripts as an
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alternative to the more general-purpose linker scripting language
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described in @ref{Commands,,Command Language}. MRI compatible linker
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scripts have a much simpler command set than the scripting language
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otherwise used with @code{ld}. @sc{gnu} @code{ld} supports the most
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commonly used MRI linker commands; these commands are described here.
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In general, MRI scripts aren't of much use with the @code{a.out} object
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file format, since it only has three sections and MRI scripts lack some
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features to make use of them.
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You can specify a file containing an MRI-compatible script using the
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@samp{-c} command-line option.
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Each command in an MRI-compatible script occupies its own line; each
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command line starts with the keyword that identifies the command (though
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blank lines are also allowed for punctuation). If a line of an
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MRI-compatible script begins with an unrecognized keyword, @code{ld}
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issues a warning message, but continues processing the script.
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Lines beginning with @samp{*} are comments.
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You can write these commands using all upper-case letters, or all
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lower case; for example, @samp{chip} is the same as @samp{CHIP}.
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The following list shows only the upper-case form of each command.
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@table @code
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@item ABSOLUTE @var{secname}
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@item ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
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@cindex @code{ABSOLUTE} (MRI)
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Normally, @code{ld} includes in the output file all sections from all
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the input files. However, in an MRI-compatible script, you can use the
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@code{ABSOLUTE} command to restrict the sections that will be present in
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your output program. If the @code{ABSOLUTE} command is used at all in a
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script, then only the sections named explicitly in @code{ABSOLUTE}
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commands will appear in the linker output. You can still use other
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input sections (whatever you select on the command line, or using
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@code{LOAD}) to resolve addresses in the output file.
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@item ALIAS @var{out-secname}, @var{in-secname}
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@cindex @code{ALIAS} (MRI)
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Use this command to place the data from input section @var{in-secname}
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in a section called @var{out-secname} in the linker output file.
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@var{in-secname} may be an integer.
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@item BASE @var{expression}
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@cindex @code{BASE} (MRI)
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Use the value of @var{expression} as the lowest address (other than
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absolute addresses) in the output file.
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@item CHIP @var{expression}
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@itemx CHIP @var{expression}, @var{expression}
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@cindex @code{CHIP} (MRI)
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This command does nothing; it is accepted only for compatibility.
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@item END
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@cindex @code{END} (MRI)
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This command does nothing whatever; it's only accepted for compatibility.
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@item FORMAT @var{output-format}
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@cindex @code{FORMAT} (MRI)
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Similar to the @code{OUTPUT_FORMAT} command in the more general linker
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language, but restricted to one of these output formats:
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@enumerate
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@item
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S-records, if @var{output-format} is @samp{S}
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@item
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IEEE, if @var{output-format} is @samp{IEEE}
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@item
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COFF (the @samp{coff-m68k} variant in BFD), if @var{output-format} is
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@samp{COFF}
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@end enumerate
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@item LIST @var{anything}@dots{}
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@cindex @code{LIST} (MRI)
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Print (to the standard output file) a link map, as produced by the
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@code{ld} command-line option @samp{-M}.
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The keyword @code{LIST} may be followed by anything on the
|
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same line, with no change in its effect.
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@item LOAD @var{filename}
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@item LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
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@cindex @code{LOAD} (MRI)
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Include one or more object file @var{filename} in the link; this has the
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same effect as specifying @var{filename} directly on the @code{ld}
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command line.
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@item NAME @var{output-name}
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@cindex @code{NAME} (MRI)
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@var{output-name} is the name for the program produced by @code{ld}; the
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MRI-compatible command @code{NAME} is equivalent to the command-line
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option @samp{-o} or the general script language command @code{OUTPUT}.
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@item ORDER @var{secname}, @var{secname}, @dots{} @var{secname}
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@itemx ORDER @var{secname} @var{secname} @var{secname}
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@cindex @code{ORDER} (MRI)
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|
Normally, @code{ld} orders the sections in its output file in the
|
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order in which they first appear in the input files. In an MRI-compatible
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script, you can override this ordering with the @code{ORDER} command. The
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sections you list with @code{ORDER} will appear first in your output
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file, in the order specified.
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@item PUBLIC @var{name}=@var{expression}
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@itemx PUBLIC @var{name},@var{expression}
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@itemx PUBLIC @var{name} @var{expression}
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@cindex @code{PUBLIC} (MRI)
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Supply a value (@var{expression}) for external symbol
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@var{name} used in the linker input files.
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@item SECT @var{secname}, @var{expression}
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@itemx SECT @var{secname}=@var{expression}
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@itemx SECT @var{secname} @var{expression}
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@cindex @code{SECT} (MRI)
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You can use any of these three forms of the @code{SECT} command to
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specify the start address (@var{expression}) for section @var{secname}.
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If you have more than one @code{SECT} statement for the same
|
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@var{secname}, only the @emph{first} sets the start address.
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@end table
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|
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@node Index
|
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@unnumbered Index
|
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|
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@printindex cp
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|
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@tex
|
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% I think something like @colophon should be in texinfo. In the
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% meantime:
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\long\def\colophon{\hbox to0pt{}\vfill
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\centerline{The body of this manual is set in}
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\centerline{\fontname\tenrm,}
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\centerline{with headings in {\bf\fontname\tenbf}}
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\centerline{and examples in {\tt\fontname\tentt}.}
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\centerline{{\it\fontname\tenit\/} and}
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\centerline{{\sl\fontname\tensl\/}}
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\centerline{are used for emphasis.}\vfill}
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\page\colophon
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% Blame: pesch@cygnus.com, 28mar91.
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@end tex
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@contents
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@bye
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