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7f9ae73e76
ld.texinfo: (a) fix INPUT cmd description (b) fix bad formatting in FSF
style (warning examples) (c) add some index entries on warnings
2267 lines
76 KiB
Plaintext
2267 lines
76 KiB
Plaintext
\input texinfo
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@setfilename ld.info
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@syncodeindex ky cp
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@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 you can
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specify other forms of binary input files using @samp{-l}, @samp{-R},
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and the script command language. If @emph{no} binary input files at all
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are specified, the linker does not produce any output, and issues the
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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
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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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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
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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.
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|
Normally, the linker will not produce an output file if it encounters
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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
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|
option is not specified, the name @file{a.out} is used by default. The
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script command @code{OUTPUT} can also specify the output file name.
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|
|
|
@ifclear SingleFormat
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|
@kindex -oformat
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|
@item -oformat @var{output-format}
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|
Specify the binary format for the output object file. You don't usually
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|
need to specify this, as @code{ld} is configured to produce as a default
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|
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
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|
@code{OUTPUT_FORMAT} can also specify the output format, but this option
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|
overrides it. @xref{BFD}.
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|
@end ifclear
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|
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|
@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
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|
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
|
|
as relaxing address modes and synthesizing new instructions in the
|
|
output object file.
|
|
|
|
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
|
|
@kindex -warn-comon
|
|
@cindex warnings, on combining symbols
|
|
@cindex combining symbols, warnings on
|
|
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.
|
|
Specify the full name for each @var{file}, including @samp{.a} if
|
|
required.
|
|
|
|
@code{ld} searches for each @var{file} through the archive-library
|
|
search path, just as for files you specify on the command line.
|
|
See the description of @samp{-L} in @ref{Options,,Command Line
|
|
Options}.
|
|
|
|
@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 @raisesections/@lowersections, but there seems to be a conflict
|
|
@c between those and node-defaulting.
|
|
@ifset H8300
|
|
@ifclear GENERIC
|
|
@raisesections
|
|
@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
|
|
@lowersections
|
|
@end ifclear
|
|
@end ifset
|
|
|
|
@ifset I960
|
|
@ifclear GENERIC
|
|
@raisesections
|
|
@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
|
|
@lowersections
|
|
@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
|
|
BFD header file version 0.18
|
|
a.out-i386
|
|
(header big endian, data big endian)
|
|
m68k:68020
|
|
a29k
|
|
sparc
|
|
i386
|
|
a.out-sunos-big
|
|
(header big endian, data big endian)
|
|
m68k:68020
|
|
a29k
|
|
sparc
|
|
i386
|
|
b.out.big
|
|
(header big endian, data little endian)
|
|
i960:core
|
|
b.out.little
|
|
(header little endian, data little endian)
|
|
i960:core
|
|
coff-a29k-big
|
|
(header big endian, data big endian)
|
|
a29k
|
|
coff-h8300
|
|
(header big endian, data big endian)
|
|
H8/300
|
|
coff-i386
|
|
(header little endian, data little endian)
|
|
i386
|
|
coff-Intel-big
|
|
(header big endian, data little endian)
|
|
i960:core
|
|
coff-Intel-little
|
|
(header little endian, data little endian)
|
|
i960:core
|
|
coff-m68k
|
|
(header big endian, data big endian)
|
|
m68k:68020
|
|
coff-m88kbcs
|
|
(header big endian, data big endian)
|
|
m88k:88100
|
|
ecoff-bigmips
|
|
(header big endian, data big endian)
|
|
mips
|
|
ecoff-littlemips
|
|
(header little endian, data little endian)
|
|
mips
|
|
elf-big
|
|
(header big endian, data big endian)
|
|
m68k:68020
|
|
vax
|
|
i960:core
|
|
a29k
|
|
sparc
|
|
mips
|
|
i386
|
|
m88k:88100
|
|
H8/300
|
|
rs6000:6000
|
|
elf-little
|
|
(header little endian, data little endian)
|
|
m68k:68020
|
|
vax
|
|
i960:core
|
|
a29k
|
|
sparc
|
|
mips
|
|
i386
|
|
m88k:88100
|
|
H8/300
|
|
rs6000:6000
|
|
ieee
|
|
(header big endian, data big endian)
|
|
m68k:68020
|
|
vax
|
|
i960:core
|
|
a29k
|
|
sparc
|
|
mips
|
|
i386
|
|
m88k:88100
|
|
H8/300
|
|
rs6000:6000
|
|
srec
|
|
(header big endian, data big endian)
|
|
m68k:68020
|
|
vax
|
|
i960:core
|
|
a29k
|
|
sparc
|
|
mips
|
|
i386
|
|
m88k:88100
|
|
H8/300
|
|
rs6000:6000
|
|
@end example
|
|
|
|
@cindex BFD requirements
|
|
@cindex requirements for BFD
|
|
As with most implementations, BFD is a compromise between
|
|
several conflicting requirements. The major factor influencing
|
|
BFD design was efficiency: any time used converting between
|
|
formats is time which would not have been spent had BFD not
|
|
been involved. This is partly offset by abstraction payback; since
|
|
BFD simplifies applications and back ends, more time and care
|
|
may be spent optimizing algorithms for a greater speed.
|
|
|
|
One minor artifact of the BFD solution which you should bear in
|
|
mind is the potential for information loss. There are two places where
|
|
useful information can be lost using the BFD mechanism: during
|
|
conversion and during output. @xref{BFD information loss}.
|
|
|
|
@menu
|
|
* BFD outline:: How it works: an outline of BFD
|
|
@end menu
|
|
|
|
@node BFD outline
|
|
@section How it works: an outline of BFD
|
|
@cindex opening object files
|
|
@include bfdsumm.texi
|
|
@end ifclear
|
|
|
|
@node MRI
|
|
@appendix MRI Compatible Script Files
|
|
@cindex MRI compatibility
|
|
To aid users making the transition to @sc{gnu} @code{ld} from the MRI
|
|
linker, @code{ld} can use MRI compatible linker scripts as an
|
|
alternative to the more general-purpose linker scripting language
|
|
described in @ref{Commands,,Command Language}. MRI compatible linker
|
|
scripts have a much simpler command set than the scripting language
|
|
otherwise used with @code{ld}. @sc{gnu} @code{ld} supports the most
|
|
commonly used MRI linker commands; these commands are described here.
|
|
|
|
In general, MRI scripts aren't of much use with the @code{a.out} object
|
|
file format, since it only has three sections and MRI scripts lack some
|
|
features to make use of them.
|
|
|
|
You can specify a file containing an MRI-compatible script using the
|
|
@samp{-c} command-line option.
|
|
|
|
Each command in an MRI-compatible script occupies its own line; each
|
|
command line starts with the keyword that identifies the command (though
|
|
blank lines are also allowed for punctuation). If a line of an
|
|
MRI-compatible script begins with an unrecognized keyword, @code{ld}
|
|
issues a warning message, but continues processing the script.
|
|
|
|
Lines beginning with @samp{*} are comments.
|
|
|
|
You can write these commands using all upper-case letters, or all
|
|
lower case; for example, @samp{chip} is the same as @samp{CHIP}.
|
|
The following list shows only the upper-case form of each command.
|
|
|
|
@table @code
|
|
@item ABSOLUTE @var{secname}
|
|
@item ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
|
|
@cindex @code{ABSOLUTE} (MRI)
|
|
Normally, @code{ld} includes in the output file all sections from all
|
|
the input files. However, in an MRI-compatible script, you can use the
|
|
@code{ABSOLUTE} command to restrict the sections that will be present in
|
|
your output program. If the @code{ABSOLUTE} command is used at all in a
|
|
script, then only the sections named explicitly in @code{ABSOLUTE}
|
|
commands will appear in the linker output. You can still use other
|
|
input sections (whatever you select on the command line, or using
|
|
@code{LOAD}) to resolve addresses in the output file.
|
|
|
|
@item ALIAS @var{out-secname}, @var{in-secname}
|
|
@cindex @code{ALIAS} (MRI)
|
|
Use this command to place the data from input section @var{in-secname}
|
|
in a section called @var{out-secname} in the linker output file.
|
|
|
|
@var{in-secname} may be an integer.
|
|
|
|
@item BASE @var{expression}
|
|
@cindex @code{BASE} (MRI)
|
|
Use the value of @var{expression} as the lowest address (other than
|
|
absolute addresses) in the output file.
|
|
|
|
@item CHIP @var{expression}
|
|
@itemx CHIP @var{expression}, @var{expression}
|
|
@cindex @code{CHIP} (MRI)
|
|
This command does nothing; it is accepted only for compatibility.
|
|
|
|
@item END
|
|
@cindex @code{END} (MRI)
|
|
This command does nothing whatever; it's only accepted for compatibility.
|
|
|
|
@item FORMAT @var{output-format}
|
|
@cindex @code{FORMAT} (MRI)
|
|
Similar to the @code{OUTPUT_FORMAT} command in the more general linker
|
|
language, but restricted to one of these output formats:
|
|
@enumerate
|
|
@item
|
|
S-records, if @var{output-format} is @samp{S}
|
|
|
|
@item
|
|
IEEE, if @var{output-format} is @samp{IEEE}
|
|
|
|
@item
|
|
COFF (the @samp{coff-m68k} variant in BFD), if @var{output-format} is
|
|
@samp{COFF}
|
|
@end enumerate
|
|
|
|
@item LIST @var{anything}@dots{}
|
|
@cindex @code{LIST} (MRI)
|
|
Print (to the standard output file) a link map, as produced by the
|
|
@code{ld} command-line option @samp{-M}.
|
|
|
|
The keyword @code{LIST} may be followed by anything on the
|
|
same line, with no change in its effect.
|
|
|
|
@item LOAD @var{filename}
|
|
@item LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
|
|
@cindex @code{LOAD} (MRI)
|
|
Include one or more object file @var{filename} in the link; this has the
|
|
same effect as specifying @var{filename} directly on the @code{ld}
|
|
command line.
|
|
|
|
@item NAME @var{output-name}
|
|
@cindex @code{NAME} (MRI)
|
|
@var{output-name} is the name for the program produced by @code{ld}; the
|
|
MRI-compatible command @code{NAME} is equivalent to the command-line
|
|
option @samp{-o} or the general script language command @code{OUTPUT}.
|
|
|
|
@item ORDER @var{secname}, @var{secname}, @dots{} @var{secname}
|
|
@itemx ORDER @var{secname} @var{secname} @var{secname}
|
|
@cindex @code{ORDER} (MRI)
|
|
Normally, @code{ld} orders the sections in its output file in the
|
|
order in which they first appear in the input files. In an MRI-compatible
|
|
script, you can override this ordering with the @code{ORDER} command. The
|
|
sections you list with @code{ORDER} will appear first in your output
|
|
file, in the order specified.
|
|
|
|
@item PUBLIC @var{name}=@var{expression}
|
|
@itemx PUBLIC @var{name},@var{expression}
|
|
@itemx PUBLIC @var{name} @var{expression}
|
|
@cindex @code{PUBLIC} (MRI)
|
|
Supply a value (@var{expression}) for external symbol
|
|
@var{name} used in the linker input files.
|
|
|
|
@item SECT @var{secname}, @var{expression}
|
|
@itemx SECT @var{secname}=@var{expression}
|
|
@itemx SECT @var{secname} @var{expression}
|
|
@cindex @code{SECT} (MRI)
|
|
You can use any of these three forms of the @code{SECT} command to
|
|
specify the start address (@var{expression}) for section @var{secname}.
|
|
If you have more than one @code{SECT} statement for the same
|
|
@var{secname}, only the @emph{first} sets the start address.
|
|
@end table
|
|
|
|
|
|
@node Index
|
|
@unnumbered Index
|
|
|
|
@printindex cp
|
|
|
|
@tex
|
|
% I think something like @colophon should be in texinfo. In the
|
|
% meantime:
|
|
\long\def\colophon{\hbox to0pt{}\vfill
|
|
\centerline{The body of this manual is set in}
|
|
\centerline{\fontname\tenrm,}
|
|
\centerline{with headings in {\bf\fontname\tenbf}}
|
|
\centerline{and examples in {\tt\fontname\tentt}.}
|
|
\centerline{{\it\fontname\tenit\/} and}
|
|
\centerline{{\sl\fontname\tensl\/}}
|
|
\centerline{are used for emphasis.}\vfill}
|
|
\page\colophon
|
|
% Blame: pesch@cygnus.com, 28mar91.
|
|
@end tex
|
|
|
|
|
|
@contents
|
|
@bye
|
|
|
|
|