\input texinfo
@setfilename ld.info
-@c $Id$
@syncodeindex ky cp
+@include configdoc.texi
+@c (configdoc.texi is generated by the Makefile)
+
@c @smallbook
-@c @cropmarks
@ifinfo
@format
START-INFO-DIR-ENTRY
-* Ld: (ld). The GNU linker.
+* Ld: (ld). The GNU linker.
END-INFO-DIR-ENTRY
@end format
@end ifinfo
@ifinfo
-This file documents the GNU linker GLD.
+This file documents the @sc{gnu} linker LD.
-Copyright (C) 1991, 1992 Free Software Foundation, Inc.
+Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 1998 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided also that
+the entire resulting derived work is distributed under the terms of a
+permission notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions.
+
@ignore
Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission
(this paragraph not being relevant to the printed manual).
@end ignore
-Permission is granted to copy and distribute modified versions of this
-manual under the conditions for verbatim copying, provided also that the
-section entitled ``GNU General Public License'' is included exactly as
-in the original, and provided that the entire resulting derived work is
-distributed under the terms of a permission notice identical to this
-one.
-
-Permission is granted to copy and distribute translations of this manual
-into another language, under the above conditions for modified versions,
-except that the section entitled ``GNU General Public License'' may be
-included in a translation approved by the author instead of in the
-original English.
@end ifinfo
@iftex
@finalout
@setchapternewpage odd
-@settitle GLD, the GNU linker
+@settitle Using LD, the GNU linker
@titlepage
-@title gld
+@title Using ld
@subtitle The GNU linker
@sp 1
-@subtitle Second Edition---@code{gld} version 2.0
-@subtitle January 1992
-@author Steve Chamberlain and Roland Pesch
+@subtitle @code{ld} version 2
+@subtitle January 1994
+@author Steve Chamberlain
@author Cygnus Support
@page
@tex
-\def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
-\xdef\manvers{\$Revision$} % For use in headers, footers too
{\parskip=0pt
\hfill Cygnus Support\par
-\hfill steve\@cygnus.com, pesch\@cygnus.com\par
-\hfill {\it GLD, the GNU linker}, \manvers\par
-\hfill \TeX{}info \texinfoversion\par
+\hfill steve\@cygnus.com, doc\@cygnus.com\par
+\hfill {\it Using LD, the GNU linker}\par
+\hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
}
\global\parindent=0pt % Steve likes it this way.
@end tex
@vskip 0pt plus 1filll
-Copyright @copyright{} 1991, 1992 Free Software Foundation, Inc.
+Copyright @copyright{} 1991, 92, 93, 94, 95, 96, 97, 1998 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@end iftex
@c FIXME: Talk about importance of *order* of args, cmds to linker!
-@node Top, Overview, (dir), (dir)
@ifinfo
-This file documents the GNU linker gld.
-@end ifinfo
+@node Top
+@top Using ld
+This file documents the @sc{gnu} linker ld.
@menu
* Overview:: Overview
* Invocation:: Invocation
* Commands:: Command Language
+@ifset GENERIC
* Machine Dependent:: Machine Dependent Features
+@end ifset
+@ifclear GENERIC
+@ifset H8300
+* H8/300:: ld and the H8/300
+@end ifset
+@ifset Hitachi
+* Hitachi:: ld and other Hitachi micros
+@end ifset
+@ifset I960
+* i960:: ld and the Intel 960 family
+@end ifset
+@end ifclear
+@ifclear SingleFormat
* BFD:: BFD
+@end ifclear
+@c Following blank line required for remaining bug in makeinfo conds/menus
+
+* Reporting Bugs:: Reporting Bugs
* MRI:: MRI Compatible Script Files
* Index:: Index
-
- --- The Detailed Node Listing ---
-
-Invocation
-
-* Options:: Command Line Options
-* Environment:: Environment Variables
-
-Command Language
-
-* Scripts:: Linker Scripts
-* Expressions:: Expressions
-* MEMORY:: MEMORY Command
-* SECTIONS:: SECTIONS Command
-* Entry Point:: The Entry Point
-* Other Commands:: Other Commands
-
-Expressions
-
-* Integers:: Integers
-* Symbols:: Symbol Names
-* Location Counter:: The Location Counter
-* Operators:: Operators
-* Evaluation:: Evaluation
-* Assignment:: Assignment: Defining Symbols
-* Built-ins:: Built-In Functions
-
-SECTIONS Command
-
-* Section Definition:: Section Definitions
-* Section Contents:: Section Contents
-* Section Options:: Optional Section Attributes
-
-Machine Dependent Features
-
-* H8/300:: @code{gld} and the H8/300
-* i960:: @code{gld} and the Intel 960 family
-* m68k:: @code{gld} and the Motorola 68000 family
-* m88k:: @code{gld} and the Motorola 880x0 family
-
-@code{gld} and the Intel 960 family
-
-* i960-arch:: Linking for a Specific i960 Architecture
-* i960-emulation:: Emulating Other i960 Linkers
-* i960-commands:: Command Language Extensions for i960
-
-BFD
-
-* BFD outline:: How it works: an outline of BFD
-* BFD information loss:: Information Loss
-* Mechanism:: Mechanism
@end menu
+@end ifinfo
-@node Overview, Invocation, Top, Top
+@node Overview
@chapter Overview
-@cindex GNU linker
+@cindex @sc{gnu} linker
@cindex what is this?
-@code{gld} combines a number of object and archive files, relocates
-their data and ties up symbol references. Often the last step in
-building a new compiled program to run is a call to @code{gld}.
+@code{ld} combines a number of object and archive files, relocates
+their data and ties up symbol references. Usually the last step in
+compiling a program is to run @code{ld}.
-@code{gld} accepts Linker Command Language files written in
+@code{ld} accepts Linker Command Language files written in
a superset of AT&T's Link Editor Command Language syntax,
to provide explicit and total control over the linking process.
-This version of @code{gld} uses the general purpose BFD libraries
-to operate on object files. This allows @code{gld} to read, combine, and
+@ifclear SingleFormat
+This version of @code{ld} uses the general purpose BFD libraries
+to operate on object files. This allows @code{ld} to read, combine, and
write object files in many different formats---for example, COFF or
@code{a.out}. Different formats may be linked together to produce any
-available kind of object file. @xref{BFD} for a list of formats
-supported on various architectures.
+available kind of object file. @xref{BFD}, for more information.
+@end ifclear
-Aside from its flexibility, the GNU linker is more helpful than other
+Aside from its flexibility, the @sc{gnu} linker is more helpful than other
linkers in providing diagnostic information. Many linkers abandon
execution immediately upon encountering an error; whenever possible,
-@code{gld} continues executing, allowing you to identify other errors
+@code{ld} continues executing, allowing you to identify other errors
(or, in some cases, to get an output file in spite of the error).
-@node Invocation, Commands, Overview, Top
+@node Invocation
@chapter Invocation
-The GNU linker @code{gld} is meant to cover a broad range of situations,
+The @sc{gnu} linker @code{ld} is meant to cover a broad range of situations,
and to be as compatible as possible with other linkers. As a result,
-you have many choices to control its behavior through the command line,
-and through environment variables.
+you have many choices to control its behavior.
+@ifset UsesEnvVars
@menu
* Options:: Command Line Options
* Environment:: Environment Variables
@end menu
-@node Options, Environment, Invocation, Invocation
+@node Options
@section Command Line Options
+@end ifset
@cindex command line
@cindex options
-Here is a sketch of the options you can use on the @code{gld} command
-line:
+The linker supports a plethora of command-line options, but in actual
+practice few of them are used in any particular context.
+@cindex standard Unix system
+For instance, a frequent use of @code{ld} is to link standard Unix
+object files on a standard, supported Unix system. On such a system, to
+link a file @code{hello.o}:
@smallexample
-gld [-o @var{output} ] @var{objfiles}@dots{}
- [ -A@var{architecture} ] [ -b @var{input-format} ] [ -Bstatic ]
- [ -c @var{MRI-commandfile} ] [ -d | -dc | -dp ]
- [ -defsym @var{symbol} = @var{expression} ]
- [ -e @var{entry} ] [ -F ] [ -F @var{format} ]
- [ -format @var{input-format} ] [ -g ] [ -i ]
- [ -l@var{ar} ] [ -L@var{searchdir} ] [ -M | -m ]
- [ -n ] [ -noinhibit-exec ] [ -R @var{filename} ] [ -relax ]
- [ -r | -Ur ] [ -S ] [ -s ] [ -T @var{commandfile} ]
- [ -Ttext @var{textorg} ] [ -Tdata @var{dataorg} ] [ -Tbss @var{bssorg} ]
- [ -t ] [ -u @var{sym}] [-v] [ -X ] [ -x ]
- [ @{ @var{script} @} ]
+ld -o @var{output} /lib/crt0.o hello.o -lc
@end smallexample
-This plethora of command-line options may seem intimidating, but in
-actual practice few of them are used in any particular context.
-@cindex standard Unix system
-For instance, a frequent use of @code{gld} is to link standard Unix
-object files on a standard, supported Unix system. On such a system, to
-link a file @code{hello.o}:
-@example
-$ gld -o output /lib/crt0.o hello.o -lc
-@end example
-This tells @code{gld} to produce a file called @code{output} as the
+This tells @code{ld} to produce a file called @var{output} as the
result of linking the file @code{/lib/crt0.o} with @code{hello.o} and
-the library @code{libc.a} which will come from the standard search
-directories.
+the library @code{libc.a}, which will come from the standard search
+directories. (See the discussion of the @samp{-l} option below.)
-The command-line options to @code{gld} may be specified in any order, and
-may be repeated at will. For the most part, repeating an option with a
-different argument will either have no further effect, or override prior
-occurrences (those further to the left on the command line) of an
-option.
-
-The exceptions---which may meaningfully be used more than once---are
-@code{-A}, @code{-b} (or its synonym @code{-format}), @code{-defsym},
-@code{-L}, @code{-l}, @code{-R}, and @code{-u}.
+The command-line options to @code{ld} may be specified in any order, and
+may be repeated at will. Repeating most options with a different
+argument will either have no further effect, or override prior
+occurrences (those further to the left on the command line) of that
+option. Options which may be meaningfully specified more than once are
+noted in the descriptions below.
@cindex object files
-The list of object files to be linked together, shown as @var{objfiles},
-may follow, precede, or be mixed in with command-line options; save that
-an @var{objfiles} argument may not be placed between an option flag and
-its argument.
-
-Usually the linker is invoked with at least one object file, but other
-forms of binary input files can also be specified with @code{-l},
-@code{-R}, and the script command language. If @emph{no} binary input
-files at all are specified, the linker does not produce any output, and
-issues the message @samp{No input files}.
-
-Option arguments must either follow the option letter without intervening
+Non-option arguments are objects files which are to be linked together.
+They may follow, precede, or be mixed in with command-line options,
+except that an object file argument may not be placed between an option
+and its argument.
+
+Usually the linker is invoked with at least one object file, but you can
+specify other forms of binary input files using @samp{-l}, @samp{-R},
+and the script command language. If @emph{no} binary input files at all
+are specified, the linker does not produce any output, and issues the
+message @samp{No input files}.
+
+If the linker can not recognize the format of an object file, it will
+assume that it is a linker script. A script specified in this way
+augments the main linker script used for the link (either the default
+linker script or the one specified by using @samp{-T}). This feature
+permits the linker to link against a file which appears to be an object
+or an archive, but actually merely defines some symbol values, or uses
+@code{INPUT} or @code{GROUP} to load other objects. Note that
+specifying a script in this way should only be used to augment the main
+linker script; if you want to use some command that logically can only
+appear once, such as the @code{SECTIONS} or @code{MEMORY} command, you
+must replace the default linker script using the @samp{-T} option.
+@xref{Commands}.
+
+For options whose names are a single letter,
+option arguments must either follow the option letter without intervening
whitespace, or be given as separate arguments immediately following the
option that requires them.
-@table @code
-@item @var{objfiles}@dots{}
-The object files @var{objfiles} to be linked.
+For options whose names are multiple letters, either one dash or two can
+precede the option name; for example, @samp{--oformat} and
+@samp{--oformat} are equivalent. Arguments to multiple-letter options
+must either be separated from the option name by an equals sign, or be
+given as separate arguments immediately following the option that
+requires them. For example, @samp{--oformat srec} and
+@samp{--oformat=srec} are equivalent. Unique abbreviations of the names
+of multiple-letter options are accepted.
+@table @code
+@kindex -a@var{keyword}
+@item -a@var{keyword}
+This option is supported for HP/UX compatibility. The @var{keyword}
+argument must be one of the strings @samp{archive}, @samp{shared}, or
+@samp{default}. @samp{-aarchive} is functionally equivalent to
+@samp{-Bstatic}, and the other two keywords are functionally equivalent
+to @samp{-Bdynamic}. This option may be used any number of times.
+
+@ifset I960
@cindex architectures
@kindex -A@var{arch}
@item -A@var{architecture}
-In the current release of @code{gld}, this option is useful only for the
-Intel 960 family of architectures. In that @code{gld} configuration, the
+@kindex --architecture=@var{arch}
+@itemx --architecture=@var{architecture}
+In the current release of @code{ld}, this option is useful only for the
+Intel 960 family of architectures. In that @code{ld} configuration, the
@var{architecture} argument identifies the particular architecture in
the 960 family, enabling some safeguards and modifying the
-archive-library search path. @xref{i960-arch,,,Linking for a Specific
-i960 Architecture}, for details.
+archive-library search path. @xref{i960,,@code{ld} and the Intel 960
+family}, for details.
-Future releases of @code{gld} may support similar functionality for
+Future releases of @code{ld} may support similar functionality for
other architecture families.
+@end ifset
+@ifclear SingleFormat
@cindex binary input format
@kindex -b @var{format}
+@kindex --format=@var{format}
@cindex input format
-@item -b @var{input-format}
@cindex input format
-Specify the binary format for input object files that follow this option
-on the command line. You don't usually need to specify this, as
-@code{gld} is configured to expect as a default input format the most
-usual format on each machine. @var{input-format} is a text string, the
-name of a particular format supported by the BFD libraries. @xref{BFD}.
-@code{-format @var{input-format}} has the same effect.@refill
+@item -b @var{input-format}
+@itemx --format=@var{input-format}
+@code{ld} may be configured to support more than one kind of object
+file. If your @code{ld} is configured this way, you can use the
+@samp{-b} option to specify the binary format for input object files
+that follow this option on the command line. Even when @code{ld} is
+configured to support alternative object formats, you don't usually need
+to specify this, as @code{ld} should be configured to expect as a
+default input format the most usual format on each machine.
+@var{input-format} is a text string, the name of a particular format
+supported by the BFD libraries. (You can list the available binary
+formats with @samp{objdump -i}.)
+@xref{BFD}.
You may want to use this option if you are linking files with an unusual
-binary format. You can also use @code{-b} to switch formats explicitly (when
+binary format. You can also use @samp{-b} to switch formats explicitly (when
linking object files of different formats), by including
-@code{-b @var{input-format}} before each group of object files in a
+@samp{-b @var{input-format}} before each group of object files in a
particular format.
The default format is taken from the environment variable
-@code{GNUTARGET}. @xref{Environment}. You can also define the input
-format from a script, using the command @code{TARGET}.
-
-@kindex -Bstatic
-@item -Bstatic
-This flag is accepted for command-line compatibility with the SunOS linker,
-but has no effect on @code{gld}.
+@code{GNUTARGET}.
+@ifset UsesEnvVars
+@xref{Environment}.
+@end ifset
+You can also define the input
+format from a script, using the command @code{TARGET}; see @ref{Option
+Commands}.
+@end ifclear
@kindex -c @var{MRI-cmdfile}
+@kindex --mri-script=@var{MRI-cmdfile}
@cindex compatibility, MRI
@item -c @var{MRI-commandfile}
+@itemx --mri-script=@var{MRI-commandfile}
For compatibility with linkers produced by MRI, @code{ld} accepts script
files written in an alternate, restricted command language, described in
-@ref{MRI,,MRI Compatible Script Files}. Introduce such script files
-with the option flag @samp{-c}.
-
-Use the @samp{-T} option to run linker scripts written in the general-purpose
-@code{ld} scripting language.
+@ref{MRI,,MRI Compatible Script Files}. Introduce MRI script files with
+the option @samp{-c}; use the @samp{-T} option to run linker
+scripts written in the general-purpose @code{ld} scripting language.
+If @var{MRI-cmdfile} does not exist, @code{ld} looks for it in the directories
+specified by any @samp{-L} options.
@cindex common allocation
@kindex -d
-@item -d
@kindex -dc
-@itemx -dc
@kindex -dp
+@item -d
+@itemx -dc
@itemx -dp
These three options are equivalent; multiple forms are supported for
-compatibility with other linkers. Use any of them to make @code{ld}
+compatibility with other linkers. They
assign space to common symbols even if a relocatable output file is
-specified (@code{-r}). The script command
-@code{FORCE_COMMON_ALLOCATION} has the same effect.
-
-@cindex symbols, from command line
-@kindex -defsym @var{symbol}=@var{exp}
-@item -defsym @var{symbol} = @var{expression}
-Create a global symbol in the output file, containing the absolute
-address given by @var{expression}. You may use this option as many
-times as necessary to define multiple symbols in the command line. A
-limited form of arithmetic is supported for the @var{expression} in this
-context: you may give a hexadecimal constant or the name of an existing
-symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
-constants or symbols. If you need more elaborate expressions, consider
-using the linker command language from a script.
+specified (with @samp{-r}). The script command
+@code{FORCE_COMMON_ALLOCATION} has the same effect. @xref{Option
+Commands}.
@cindex entry point, from command line
@kindex -e @var{entry}
+@kindex --entry=@var{entry}
@item -e @var{entry}
+@itemx --entry=@var{entry}
Use @var{entry} as the explicit symbol for beginning execution of your
program, rather than the default entry point. @xref{Entry Point}, for a
discussion of defaults and other ways of specifying the
entry point.
-@ignore
-@cindex fill, from command line
-@kindex -f @var{fill}
-@c -f in older GNU linker, not in new
-@item -f @var{fill}
-Sets the default fill pattern for ``holes'' in the output file to
-the lowest two bytes of the expression specified. Holes are created
-when you advance the location counter (@xref{Location Counter}), or when
-there is a gap between explicitly specified section addresses
-(@xref{Section Options}).
-@end ignore
+@cindex dynamic symbol table
+@kindex -E
+@kindex --export-dynamic
+@item -E
+@itemx --export-dynamic
+When creating a dynamically linked executable, add all symbols to the
+dynamic symbol table. The dynamic symbol table is the set of symbols
+which are visible from dynamic objects at run time.
+
+If you do not use this option, the dynamic symbol table will normally
+contain only those symbols which are referenced by some dynamic object
+mentioned in the link.
+
+If you use @code{dlopen} to load a dynamic object which needs to refer
+back to the symbols defined by the program, rather than some other
+dynamic object, then you will probably need to use this option when
+linking the program itself.
+
+@kindex -f
+@kindex --auxiliary
+@item -f
+@itemx --auxiliary @var{name}
+When creating an ELF shared object, set the internal DT_AUXILIARY field
+to the specified name. This tells the dynamic linker that the symbol
+table of the shared object should be used as an auxiliary filter on the
+symbol table of the shared object @var{name}.
+
+If you later link a program against this filter object, then, when you
+run the program, the dynamic linker will see the DT_AUXILIARY field. If
+the dynamic linker resolves any symbols from the filter object, it will
+first check whether there is a definition in the shared object
+@var{name}. If there is one, it will be used instead of the definition
+in the filter object. The shared object @var{name} need not exist.
+Thus the shared object @var{name} may be used to provide an alternative
+implementation of certain functions, perhaps for debugging or for
+machine specific performance.
+
+This option may be specified more than once. The DT_AUXILIARY entries
+will be created in the order in which they appear on the command line.
@kindex -F
-@item -F
-@itemx -F@var{format}
-Some older linkers used this option throughout a compilation toolchain
-for specifying object-file format for both input and output object
-files. @code{gld}'s mechanisms (the @code{-b} or @code{-format} options
-for input files, the @code{TARGET} command in linker scripts for output
-files, the @code{GNUTARGET} environment variable) are more flexible, but
-but it accepts (and ignores) the @code{-F} option flag for compatibility
-with scripts written to call the old linker.
-
-@kindex -format
-@item -format @var{input-format}
-Synonym for @code{-b} @var{input-format}.
+@kindex --filter
+@item -F @var{name}
+@itemx --filter @var{name}
+When creating an ELF shared object, set the internal DT_FILTER field to
+the specified name. This tells the dynamic linker that the symbol table
+of the shared object which is being created should be used as a filter
+on the symbol table of the shared object @var{name}.
+
+If you later link a program against this filter object, then, when you
+run the program, the dynamic linker will see the DT_FILTER field. The
+dynamic linker will resolve symbols according to the symbol table of the
+filter object as usual, but it will actually link to the definitions
+found in the shared object @var{name}. Thus the filter object can be
+used to select a subset of the symbols provided by the object
+@var{name}.
+
+Some older linkers used the @code{-F} option throughout a compilation
+toolchain for specifying object-file format for both input and output
+object files. The @sc{gnu} linker uses other mechanisms for this
+purpose: the @code{-b}, @code{--format}, @code{--oformat} options, the
+@code{TARGET} command in linker scripts, and the @code{GNUTARGET}
+environment variable. The @sc{gnu} linker will ignore the @code{-F}
+option when not creating an ELF shared object.
+
+@kindex --force-exe-suffix
+@item --force-exe-suffix
+Make sure that an output file has a .exe suffix.
+
+If a successfully built fully linked output file does not have a
+@code{.exe} or @code{.dll} suffix, this option forces the linker to copy
+the output file to one of the same name with a @code{.exe} suffix. This
+option is useful when using unmodified Unix makefiles on a Microsoft
+Windows host, since some versions of Windows won't run an image unless
+it ends in a @code{.exe} suffix.
@kindex -g
@item -g
-Accepted, but ignored; provided for compatibility with other tools.
+Ignored. Provided for compatibility with other tools.
+
+@kindex -G
+@kindex --gpsize
+@cindex object size
+@item -G@var{value}
+@itemx --gpsize=@var{value}
+Set the maximum size of objects to be optimized using the GP register to
+@var{size}. This is only meaningful for object file formats such as
+MIPS ECOFF which supports putting large and small objects into different
+sections. This is ignored for other object file formats.
+
+@cindex runtime library name
+@kindex -h@var{name}
+@kindex -soname=@var{name}
+@item -h@var{name}
+@itemx -soname=@var{name}
+When creating an ELF shared object, set the internal DT_SONAME field to
+the specified name. When an executable is linked with a shared object
+which has a DT_SONAME field, then when the executable is run the dynamic
+linker will attempt to load the shared object specified by the DT_SONAME
+field rather than the using the file name given to the linker.
@kindex -i
@cindex incremental link
@item -i
-Perform an incremental link (same as option @code{-r}).
+Perform an incremental link (same as option @samp{-r}).
@cindex archive files, from cmd line
-@kindex -l@var{ar}
-@item -l@var{ar}
-Add an archive file @var{ar} to the list of files to link. This
+@kindex -l@var{archive}
+@kindex --library=@var{archive}
+@item -l@var{archive}
+@itemx --library=@var{archive}
+Add archive file @var{archive} to the list of files to link. This
option may be used any number of times. @code{ld} will search its
-path-list for occurrences of @code{lib@var{ar}.a} for every @var{ar}
-specified.
+path-list for occurrences of @code{lib@var{archive}.a} for every
+@var{archive} specified.
+
+On systems which support shared libraries, @code{ld} may also search for
+libraries with extensions other than @code{.a}. Specifically, on ELF
+and SunOS systems, @code{ld} will search a directory for a library with
+an extension of @code{.so} before searching for one with an extension of
+@code{.a}. By convention, a @code{.so} extension indicates a shared
+library.
+
+The linker will search an archive only once, at the location where it is
+specified on the command line. If the archive defines a symbol which
+was undefined in some object which appeared before the archive on the
+command line, the linker will include the appropriate file(s) from the
+archive. However, an undefined symbol in an object appearing later on
+the command line will not cause the linker to search the archive again.
+
+See the @code{-(} option for a way to force the linker to search
+archives multiple times.
+
+You may list the same archive multiple times on the command line.
+
+@ifset GENERIC
+This type of archive searching is standard for Unix linkers. However,
+if you are using @code{ld} on AIX, note that it is different from the
+behaviour of the AIX linker.
+@end ifset
@cindex search directory, from cmd line
@kindex -L@var{dir}
+@kindex --library-path=@var{dir}
@item -L@var{searchdir}
-This command adds path @var{searchdir} to the list of paths that
-@code{gld} will search for archive libraries. You may use this option
-any number of times.
-
+@itemx --library-path=@var{searchdir}
+Add path @var{searchdir} to the list of paths that @code{ld} will search
+for archive libraries and @code{ld} control scripts. You may use this
+option any number of times. The directories are searched in the order
+in which they are specified on the command line. Directories specified
+on the command line are searched before the default directories. All
+@code{-L} options apply to all @code{-l} options, regardless of the
+order in which the options appear.
+
+@ifset UsesEnvVars
The default set of paths searched (without being specified with
-@code{-L}) depends on what emulation mode @code{gld} is using, and in
-some cases also on how it was configured. @xref{Environment}. The
-paths can also be specified in a link script with the @code{SEARCH_DIR}
-command.
+@samp{-L}) depends on which emulation mode @code{ld} is using, and in
+some cases also on how it was configured. @xref{Environment}.
+@end ifset
+
+The paths can also be specified in a link script with the
+@code{SEARCH_DIR} command. Directories specified this way are searched
+at the point in which the linker script appears in the command line.
+
+@cindex emulation
+@kindex -m @var{emulation}
+@item -m@var{emulation}
+Emulate the @var{emulation} linker. You can list the available
+emulations with the @samp{--verbose} or @samp{-V} options.
+
+If the @samp{-m} option is not used, the emulation is taken from the
+@code{LDEMULATION} environment variable, if that is defined.
+
+Otherwise, the default emulation depends upon how the linker was
+configured.
@cindex link map
@kindex -M
-@item -M
-@kindex -m
-@itemx -m
-Print (to the standard output file) a link map---diagnostic information
-about where symbols are mapped by @code{ld}, and information on global
-common storage allocation.
-
-@ignore
-@c -N in older GNU linker, not in new
-@kindex -N
-@cindex read/write from cmd line
-@kindex OMAGIC
-@item -N
-specifies readable and writable @code{text} and @code{data} sections. If
-the output format supports Unix style magic numbers, the output is
-marked as @code{OMAGIC}.
-@end ignore
+@kindex --print-map
+@item -M
+@itemx --print-map
+Print (to the standard output) a link map---diagnostic information about
+where symbols are mapped by @code{ld}, and information on global common
+storage allocation.
-@item -n
@kindex -n
@cindex read-only text
-@kindex NMAGIC
-sets the text segment to be read only, and @code{NMAGIC} is written
-if possible.
+@cindex NMAGIC
+@kindex --nmagic
+@item -n
+@itemx --nmagic
+Set the text segment to be read only, and mark the output as
+@code{NMAGIC} if possible.
-@item -noinhibit-exec
-@cindex output file after errors
-@kindex -noinhibit-exec
-Normally, the linker will not produce an output file if it encounters
-errors during the link process. With this flag, you can specify that
-you wish the output file retained even after non-fatal errors.
+@kindex -N
+@kindex --omagic
+@cindex read/write from cmd line
+@cindex OMAGIC
+@item -N
+@itemx --omagic
+Set the text and data sections to be readable and writable. Also, do
+not page-align the data segment. If the output format supports Unix
+style magic numbers, mark the output as @code{OMAGIC}.
-@item -o @var{output}
@kindex -o @var{output}
+@kindex --output=@var{output}
@cindex naming the output file
-@var{output} is a name for the program produced by @code{ld}; if this
-option is not specified, the name @samp{a.out} is used by default. The
+@item -o @var{output}
+@itemx --output=@var{output}
+Use @var{output} as the name for the program produced by @code{ld}; if this
+option is not specified, the name @file{a.out} is used by default. The
script command @code{OUTPUT} can also specify the output file name.
-@item -R @var{filename}
-@kindex -R @var{file}
-@cindex symbol-only input
-Read symbol names and their addresses from @var{filename}, but do not
-relocate it or include it in the output. This allows your output file
-to refer symbolically to absolute locations of memory defined in other
-programs.
-
-@item -relax
-@kindex -relax
-@cindex synthesizing linker
-@cindex relaxing addressing modes
-An option with machine dependent effects. Currently this option is only
-supported on the H8/300; see @ref{H8/300,,@code{gld} and the H8/300}.
-
-On some platforms, use this option to perform global optimizations that
-become possible when the linker resolves addressing in your 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
-has no effect.
-
-@item -r
@cindex partial link
@cindex relocatable output
@kindex -r
-Generates relocatable output---i.e., generate an output file that can in
-turn serve as input to @code{gld}. This is often called @dfn{partial
+@kindex --relocateable
+@item -r
+@itemx --relocateable
+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; @code{-Ur} is an alternative. @refill
+constructors; to do that, use @samp{-Ur}.
-This option does the same as @code{-i}.
+This option does the same thing as @samp{-i}.
-@item -S
-@kindex -S
-@cindex strip debugger symbols
-Omits debugger symbol information (but not all symbols) from the output file.
+@kindex -R @var{file}
+@kindex --just-symbols=@var{file}
+@cindex symbol-only input
+@item -R @var{filename}
+@itemx --just-symbols=@var{filename}
+Read symbol names and their addresses from @var{filename}, but do not
+relocate it or include it in the output. This allows your output file
+to refer symbolically to absolute locations of memory defined in other
+programs. You may use this option more than once.
+
+For compatibility with other ELF linkers, if the @code{-R} option is
+followed by a directory name, rather than a file name, it is treated as
+the @code{-rpath} option.
-@item -s
@kindex -s
+@kindex --strip-all
@cindex strip all symbols
-Omits all symbol information from the output file.
-
-@item @{ @var{script} @}
-@kindex @{ @var{script} @}
-@cindex scripts on command line
-You can, if you wish, include a script of linker commands directly in
-the command line instead of referring to it via an input file. When the
-character @samp{@{} occurs on the command line, the linker switches to
-interpreting the command language until the end of the list of commands
-is reached---flagged with a closing brace @samp{@}}. Other command-line
-options will not be recognized while parsing the script.
-@xref{Commands} for a description of the command language.
-
-@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{textorg} must be a hexadecimal integer.
-
-@item -T @var{commandfile}
-@itemx -T@var{commandfile}
-@kindex -T @var{script}
-@cindex script files
-Directs @code{gld} to read link commands from the file
-@var{commandfile}. These commands will completely override @code{gld}'s
-default link format (rather than adding to it); @var{commandfile} must
-specify everything necessary to describe the target format.
-@xref{Commands}.
+@item -s
+@itemx --strip-all
+Omit all symbol information from the output file.
-You may also include a script of link commands directly in the command
-line by bracketing it between @samp{@{} and @samp{@}} characters.
+@kindex -S
+@kindex --strip-debug
+@cindex strip debugger symbols
+@item -S
+@itemx --strip-debug
+Omit debugger symbol information (but not all symbols) from the output file.
-@item -t
@kindex -t
-@cindex verbose
+@kindex --trace
@cindex input files, displaying
-Prints names of input files as @code{ld} processes them.
+@item -t
+@itemx --trace
+Print the names of the input files as @code{ld} processes them.
-@item -u @var{sym}
-@kindex -u @var{sym}
+@kindex -T @var{script}
+@kindex --script=@var{script}
+@cindex script files
+@item -T @var{commandfile}
+@itemx --script=@var{commandfile}
+Read link commands from the file @var{commandfile}. These commands
+replace @code{ld}'s default link script (rather than adding to it), so
+@var{commandfile} must specify everything necessary to describe the
+target format. You must use this option if you want to use a command
+which can only appear once in a linker script, such as the
+@code{SECTIONS} or @code{MEMORY} command. @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.
+
+@kindex -u @var{symbol}
+@kindex --undefined=@var{symbol}
@cindex undefined symbol
-Forces @var{sym} to be entered in the output file as an undefined symbol.
-This may, for example, trigger linking of additional modules from
-standard libraries. @code{-u} may be repeated with different option
+@item -u @var{symbol}
+@itemx --undefined=@var{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
-@code{-r}: it generates relocatable output---i.e., an output file that can in
-turn serve as input to @code{gld}. When linking C++ programs, @code{-Ur}
-@emph{will} resolve references to constructors, unlike @code{-r}.
-
-@item -v
@kindex -v
+@kindex -V
+@kindex --version
@cindex version
-Display the version number for @code{gld}.
+@item -v
+@itemx --version
+@itemx -V
+Display the version number for @code{ld}. The @code{-V} option also
+lists the supported emulations.
+
+@kindex -x
+@kindex --discard-all
+@cindex deleting local symbols
+@item -x
+@itemx --discard-all
+Delete all local symbols.
-@item -X
@kindex -X
+@kindex --discard-locals
@cindex local symbols, deleting
@cindex L, deleting symbols beginning
-If @code{-s} or @code{-S} is also specified, delete only local symbols
-beginning with @samp{L}.
+@item -X
+@itemx --discard-locals
+Delete all temporary local symbols. For most targets, this is all local
+symbols whose names begin with @samp{L}.
+
+@kindex -y @var{symbol}
+@kindex --trace-symbol=@var{symbol}
+@cindex symbol tracing
+@item -y @var{symbol}
+@itemx --trace-symbol=@var{symbol}
+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.
+
+@kindex -Y @var{path}
+@item -Y @var{path}
+Add @var{path} to the default library search path. This option exists
+for Solaris compatibility.
+
+@kindex -z @var{keyword}
+@item -z @var{keyword}
+This option is ignored for Solaris compatibility.
+
+@kindex -(
+@cindex groups of archives
+@item -( @var{archives} -)
+@itemx --start-group @var{archives} --end-group
+The @var{archives} should be a list of archive files. They may be
+either explicit file names, or @samp{-l} options.
+
+The specified archives are searched repeatedly until no new undefined
+references are created. Normally, an archive is searched only once in
+the order that it is specified on the command line. If a symbol in that
+archive is needed to resolve an undefined symbol referred to by an
+object in an archive that appears later on the command line, the linker
+would not be able to resolve that reference. By grouping the archives,
+they all be searched repeatedly until all possible references are
+resolved.
+
+Using this option has a significant performance cost. It is best to use
+it only when there are unavoidable circular references between two or
+more archives.
+
+@kindex -assert @var{keyword}
+@item -assert @var{keyword}
+This option is ignored for SunOS compatibility.
+
+@kindex -Bdynamic
+@kindex -dy
+@kindex -call_shared
+@item -Bdynamic
+@itemx -dy
+@itemx -call_shared
+Link against dynamic libraries. This is only meaningful on platforms
+for which shared libraries are supported. This option is normally the
+default on such platforms. The different variants of this option are
+for compatibility with various systems. You may use this option
+multiple times on the command line: it affects library searching for
+@code{-l} options which follow it.
-@item -x
-@kindex -x
-@cindex deleting local symbols
-If @code{-s} or @code{-S} is also specified, delete all local symbols,
-not just those beginning with @samp{L}.
+@kindex -Bstatic
+@kindex -dn
+@kindex -non_shared
+@kindex -static
+@item -Bstatic
+@itemx -dn
+@itemx -non_shared
+@itemx -static
+Do not link against shared libraries. This is only meaningful on
+platforms for which shared libraries are supported. The different
+variants of this option are for compatibility with various systems. You
+may use this option multiple times on the command line: it affects
+library searching for @code{-l} options which follow it.
+
+@kindex -Bsymbolic
+@item -Bsymbolic
+When creating a shared library, bind references to global symbols to the
+definition within the shared library, if any. Normally, it is possible
+for a program linked against a shared library to override the definition
+within the shared library. This option is only meaningful on ELF
+platforms which support shared libraries.
+
+@cindex cross reference table
+@kindex --cref
+@item --cref
+Output a cross reference table. If a linker map file is being
+generated, the cross reference table is printed to the map file.
+Otherwise, it is printed on the standard output.
+
+The format of the table is intentionally simple, so that it may be
+easily processed by a script if necessary. The symbols are printed out,
+sorted by name. For each symbol, a list of file names is given. If the
+symbol is defined, the first file listed is the location of the
+definition. The remaining files contain references to the symbol.
-@ignore
-@c -z in older GNU linker, not in new
-@item -z
-@kindex -z
-@cindex read-only text
-Specifies a read-only, demand pageable, and shared @code{text} segment.
-If the output format supports Unix-style magic numbers, @code{-z} also
-marks the output as @code{ZMAGIC}, the default.
+@cindex symbols, from command line
+@kindex --defsym @var{symbol}=@var{exp}
+@item --defsym @var{symbol}=@var{expression}
+Create a global symbol in the output file, containing the absolute
+address given by @var{expression}. You may use this option as many
+times as necessary to define multiple symbols in the command line. A
+limited form of arithmetic is supported for the @var{expression} in this
+context: you may give a hexadecimal constant or the name of an existing
+symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
+constants or symbols. If you need more elaborate expressions, consider
+using the linker command language from a script (@pxref{Assignment, ,
+Assignment: Symbol Definitions}). @emph{Note:} there should be no
+white space between @var{symbol}, the equals sign (``@key{=}''), and
+@var{expression}.
+
+@cindex dynamic linker, from command line
+@kindex --dynamic-linker @var{file}
+@item --dynamic-linker @var{file}
+Set the name of the dynamic linker. This is only meaningful when
+generating dynamically linked ELF executables. The default dynamic
+linker is normally correct; don't use this unless you know what you are
+doing.
+
+@cindex big-endian objects
+@cindex endianness
+@kindex -EB
+@item -EB
+Link big-endian objects. This affects the default output format.
+
+@cindex little-endian objects
+@kindex -EL
+@item -EL
+Link little-endian objects. This affects the default output format.
+
+@cindex MIPS embedded PIC code
+@kindex --embedded-relocs
+@item --embedded-relocs
+This option is only meaningful when linking MIPS embedded PIC code,
+generated by the -membedded-pic option to the @sc{gnu} compiler and
+assembler. It causes the linker to create a table which may be used at
+runtime to relocate any data which was statically initialized to pointer
+values. See the code in testsuite/ld-empic for details.
+
+@cindex help
+@cindex usage
+@kindex --help
+@item --help
+Print a summary of the command-line options on the standard output and exit.
+
+@cindex link map
+@kindex -Map
+@item -Map @var{mapfile}
+Print to the file @var{mapfile} a link map---diagnostic information
+about where symbols are mapped by @code{ld}, and information on global
+common storage allocation.
-@c why was following here?. Is it useful to say '-z -r' for
-@c instance, or is this just a ref to other ways of setting
-@c magic no?
-Specifying a relocatable output file (@code{-r}) will also set the magic
-number to @code{OMAGIC}.
+@cindex memory usage
+@kindex --no-keep-memory
+@item --no-keep-memory
+@code{ld} normally optimizes for speed over memory usage by caching the
+symbol tables of input files in memory. This option tells @code{ld} to
+instead optimize for memory usage, by rereading the symbol tables as
+necessary. This may be required if @code{ld} runs out of memory space
+while linking a large executable.
+
+@kindex --no-warn-mismatch
+@item --no-warn-mismatch
+Normally @code{ld} will give an error if you try to link together input
+files that are mismatched for some reason, perhaps because they have
+been compiled for different processors or for different endiannesses.
+This option tells @code{ld} that it should silently permit such possible
+errors. This option should only be used with care, in cases when you
+have taken some special action that ensures that the linker errors are
+inappropriate.
+
+@kindex --no-whole-archive
+@item --no-whole-archive
+Turn off the effect of the @code{--whole-archive} option for subsequent
+archive files.
-See description of @code{-N}.
-@end ignore
+@cindex output file after errors
+@kindex --noinhibit-exec
+@item --noinhibit-exec
+Retain the executable output file whenever it is still usable.
+Normally, the linker will not produce an output file if it encounters
+errors during the link process; it exits without writing an output file
+when it issues any error whatsoever.
+
+@ifclear SingleFormat
+@kindex --oformat
+@item --oformat @var{output-format}
+@code{ld} may be configured to support more than one kind of object
+file. If your @code{ld} is configured this way, you can use the
+@samp{--oformat} option to specify the binary format for the output
+object file. Even when @code{ld} is configured to support alternative
+object formats, you don't usually need to specify this, as @code{ld}
+should be configured to produce as a default output format the most
+usual format on each machine. @var{output-format} is a text string, the
+name of a particular format supported by the BFD libraries. (You can
+list the available binary formats with @samp{objdump -i}.) The script
+command @code{OUTPUT_FORMAT} can also specify the output format, but
+this option overrides it. @xref{BFD}.
+@end ifclear
+
+@kindex -qmagic
+@item -qmagic
+This option is ignored for Linux compatibility.
+
+@kindex -Qy
+@item -Qy
+This option is ignored for SVR4 compatibility.
+
+@kindex --relax
+@cindex synthesizing linker
+@cindex relaxing addressing modes
+@item --relax
+An option with machine dependent effects.
+@ifset GENERIC
+This option is only supported on a few targets.
+@end ifset
+@ifset H8300
+@xref{H8/300,,@code{ld} and the H8/300}.
+@end ifset
+@ifset I960
+@xref{i960,, @code{ld} and the Intel 960 family}.
+@end ifset
+
+On some platforms, the @samp{--relax} 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.
+
+@ifset GENERIC
+On platforms where this is not supported, @samp{--relax} is accepted,
+but ignored.
+@end ifset
+
+@cindex retaining specified symbols
+@cindex stripping all but some symbols
+@cindex symbols, retaining selectively
+@item --retain-symbols-file @var{filename}
+Retain @emph{only} the symbols listed in the file @var{filename},
+discarding all others. @var{filename} is simply a flat file, with one
+symbol name per line. This option is especially useful in environments
+@ifset GENERIC
+(such as VxWorks)
+@end ifset
+where a large global symbol table is accumulated gradually, to conserve
+run-time memory.
+
+@samp{--retain-symbols-file} does @emph{not} discard undefined symbols,
+or symbols needed for relocations.
+
+You may only specify @samp{--retain-symbols-file} once in the command
+line. It overrides @samp{-s} and @samp{-S}.
+
+@ifset GENERIC
+@item -rpath @var{dir}
+@cindex runtime library search path
+@kindex -rpath
+Add a directory to the runtime library search path. This is used when
+linking an ELF executable with shared objects. All @code{-rpath}
+arguments are concatenated and passed to the runtime linker, which uses
+them to locate shared objects at runtime. The @code{-rpath} option is
+also used when locating shared objects which are needed by shared
+objects explicitly included in the link; see the description of the
+@code{-rpath-link} option. If @code{-rpath} is not used when linking an
+ELF executable, the contents of the environment variable
+@code{LD_RUN_PATH} will be used if it is defined.
+
+The @code{-rpath} option may also be used on SunOS. By default, on
+SunOS, the linker will form a runtime search patch out of all the
+@code{-L} options it is given. If a @code{-rpath} option is used, the
+runtime search path will be formed exclusively using the @code{-rpath}
+options, ignoring the @code{-L} options. This can be useful when using
+gcc, which adds many @code{-L} options which may be on NFS mounted
+filesystems.
+
+For compatibility with other ELF linkers, if the @code{-R} option is
+followed by a directory name, rather than a file name, it is treated as
+the @code{-rpath} option.
+@end ifset
+
+@ifset GENERIC
+@cindex link-time runtime library search path
+@kindex -rpath-link
+@item -rpath-link @var{DIR}
+When using ELF or SunOS, one shared library may require another. This
+happens when an @code{ld -shared} link includes a shared library as one
+of the input files.
+
+When the linker encounters such a dependency when doing a non-shared,
+non-relocateable link, it will automatically try to locate the required
+shared library and include it in the link, if it is not included
+explicitly. In such a case, the @code{-rpath-link} option
+specifies the first set of directories to search. The
+@code{-rpath-link} option may specify a sequence of directory names
+either by specifying a list of names separated by colons, or by
+appearing multiple times.
+
+The linker uses the following search paths to locate required shared
+libraries.
+@enumerate
+@item
+Any directories specified by @code{-rpath-link} options.
+@item
+Any directories specified by @code{-rpath} options. The difference
+between @code{-rpath} and @code{-rpath-link} is that directories
+specified by @code{-rpath} options are included in the executable and
+used at runtime, whereas the @code{-rpath-link} option is only effective
+at link time.
+@item
+On an ELF system, if the @code{-rpath} and @code{rpath-link} options
+were not used, search the contents of the environment variable
+@code{LD_RUN_PATH}.
+@item
+On SunOS, if the @code{-rpath} option was not used, search any
+directories specified using @code{-L} options.
+@item
+For a native linker, the contents of the environment variable
+@code{LD_LIBRARY_PATH}.
+@item
+The default directories, normally @file{/lib} and @file{/usr/lib}.
+@end enumerate
+
+If the required shared library is not found, the linker will issue a
+warning and continue with the link.
+@end ifset
+
+@kindex -shared
+@kindex -Bshareable
+@item -shared
+@itemx -Bshareable
+@cindex shared libraries
+Create a shared library. This is currently only supported on ELF, XCOFF
+and SunOS platforms. On SunOS, the linker will automatically create a
+shared library if the @code{-e} option is not used and there are
+undefined symbols in the link.
+
+@item --sort-common
+@kindex --sort-common
+This option tells @code{ld} to sort the common symbols by size when it
+places them in the appropriate output sections. 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.
+
+@kindex --split-by-file
+@item --split-by-file
+Similar to @code{--split-by-reloc} but creates a new output section for
+each input file.
+
+@kindex --split-by-reloc
+@item --split-by-reloc @var{count}
+Trys to creates extra sections in the output file so that no single
+output section in the file contains more than @var{count} relocations.
+This is useful when generating huge relocatable for downloading into
+certain real time kernels with the COFF object file format; since COFF
+cannot represent more than 65535 relocations in a single section. Note
+that this will fail to work with object file formats which do not
+support arbitrary sections. The linker will not split up individual
+input sections for redistribution, so if a single input section contains
+more than @var{count} relocations one output section will contain that
+many relocations.
+
+@kindex --stats
+@item --stats
+Compute and display statistics about the operation of the linker, such
+as execution time and memory usage.
+
+@kindex --traditional-format
+@cindex traditional format
+@item --traditional-format
+For some targets, the output of @code{ld} is different in some ways from
+the output of some existing linker. This switch requests @code{ld} to
+use the traditional format instead.
+
+@cindex dbx
+For example, on SunOS, @code{ld} combines duplicate entries in the
+symbol string table. This can reduce the size of an output file with
+full debugging information by over 30 percent. Unfortunately, the SunOS
+@code{dbx} program can not read the resulting program (@code{gdb} has no
+trouble). The @samp{--traditional-format} switch tells @code{ld} to not
+combine duplicate entries.
+
+@kindex -Tbss @var{org}
+@kindex -Tdata @var{org}
+@kindex -Ttext @var{org}
+@cindex segment origins, cmd line
+@item -Tbss @var{org}
+@itemx -Tdata @var{org}
+@itemx -Ttext @var{org}
+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.
+
+@kindex -Ur
+@cindex constructors
+@item -Ur
+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{does} 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 cannot
+be added to. Use @samp{-Ur} only for the last partial link, and
+@samp{-r} for the others.
+
+@kindex --verbose
+@cindex verbose
+@item --verbose
+Display the version number for @code{ld} and list the linker emulations
+supported. Display which input files can and cannot be opened. Display
+the linker script if using a default builtin script.
+
+@kindex --version-script=@var{version-scriptfile}
+@cindex version script, symbol versions
+@itemx --version-script=@var{version-scriptfile}
+Specify the name of a version script to the linker. This is typically
+used when creating shared libraries to specify additional information
+about the version heirarchy for the library being created. This option
+is only meaningful on ELF platforms which support shared libraries.
+@xref{Version Script}.
+
+@kindex --warn-comon
+@cindex warnings, on combining symbols
+@cindex combining symbols, warnings on
+@item --warn-common
+Warn when a common symbol is combined with another common symbol or with
+a symbol definition. Unix linkers allow this somewhat sloppy practice,
+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
+
+@kindex --warn-constructors
+@item --warn-constructors
+Warn if any global constructors are used. This is only useful for a few
+object file formats. For formats like COFF or ELF, the linker can not
+detect the use of global constructors.
+
+@kindex --warn-multiple-gp
+@item --warn-multiple-gp
+Warn if multiple global pointer values are required in the output file.
+This is only meaningful for certain processors, such as the Alpha.
+Specifically, some processors put large-valued constants in a special
+section. A special register (the global pointer) points into the middle
+of this section, so that constants can be loaded efficiently via a
+base-register relative addressing mode. Since the offset in
+base-register relative mode is fixed and relatively small (e.g., 16
+bits), this limits the maximum size of the constant pool. Thus, in
+large programs, it is often necessary to use multiple global pointer
+values in order to be able to address all possible constants. This
+option causes a warning to be issued whenever this case occurs.
+
+@kindex --warn-once
+@cindex warnings, on undefined symbols
+@cindex undefined symbols, warnings on
+@item --warn-once
+Only warn once for each undefined symbol, rather than once per module
+which refers to it.
+
+@kindex --warn-section-align
+@cindex warnings, on section alignment
+@cindex section alignment, warnings on
+@item --warn-section-align
+Warn if the address of an output section is changed because of
+alignment. Typically, the alignment will be set by an input section.
+The address will only be changed if it not explicitly specified; that
+is, if the @code{SECTIONS} command does not specify a start address for
+the section (@pxref{SECTIONS}).
+
+@kindex --whole-archive
+@cindex including an entire archive
+@item --whole-archive
+For each archive mentioned on the command line after the
+@code{--whole-archive} option, include every object file in the archive
+in the link, rather than searching the archive for the required object
+files. This is normally used to turn an archive file into a shared
+library, forcing every object to be included in the resulting shared
+library. This option may be used more than once.
+
+@kindex --wrap
+@item --wrap @var{symbol}
+Use a wrapper function for @var{symbol}. Any undefined reference to
+@var{symbol} will be resolved to @code{__wrap_@var{symbol}}. Any
+undefined reference to @code{__real_@var{symbol}} will be resolved to
+@var{symbol}.
+
+This can be used to provide a wrapper for a system function. The
+wrapper function should be called @code{__wrap_@var{symbol}}. If it
+wishes to call the system function, it should call
+@code{__real_@var{symbol}}.
+
+Here is a trivial example:
+
+@smallexample
+void *
+__wrap_malloc (int c)
+@{
+ printf ("malloc called with %ld\n", c);
+ return __real_malloc (c);
+@}
+@end smallexample
+
+If you link other code with this file using @code{--wrap malloc}, then
+all calls to @code{malloc} will call the function @code{__wrap_malloc}
+instead. The call to @code{__real_malloc} in @code{__wrap_malloc} will
+call the real @code{malloc} function.
+
+You may wish to provide a @code{__real_malloc} function as well, so that
+links without the @code{--wrap} option will succeed. If you do this,
+you should not put the definition of @code{__real_malloc} in the same
+file as @code{__wrap_malloc}; if you do, the assembler may resolve the
+call before the linker has a chance to wrap it to @code{malloc}.
@end table
-@node Environment, , Options, Invocation
+@ifset UsesEnvVars
+@node Environment
@section Environment Variables
-You can change the behavior of @code{gld} with two environment
-variables: @code{GNUTARGET} and @code{LDEMULATION}. Depending on the
-setting of the latter, other environment variables may be used as well.
+You can change the behavior of @code{ld} with the environment variables
+@code{GNUTARGET} and @code{LDEMULATION}.
@kindex GNUTARGET
@cindex default input format
@code{GNUTARGET} determines the input-file object format if you don't
-use @code{-b} (or its synonym @code{-format}). Its value should be one
+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{gld} 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 flag 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.
+@code{GNUTARGET} in the environment, @code{ld} uses the natural format
+of the target. If @code{GNUTARGET} is set to @code{default} then BFD
+attempts to discover the input format by examining binary input files;
+this method often succeeds, but there are potential ambiguities, since
+there is no method of ensuring that the magic number used to specify
+object-file formats is unique. However, the configuration procedure for
+BFD on each system places the conventional format for that system first
+in the search-list, so ambiguities are resolved in favor of convention.
@kindex LDEMULATION
-@cindex emulation
-@cindex environment vars
-@code{LDEMULATION} controls some aspects of @code{gld}'s dominant
-personality. Although @code{gld} is flexible enough to permit its use
-in many contexts regardless of configuration, you can use this variable
-to make it act more like one or another older linker by default.
-
-@cindex defaults
-@cindex library paths, default
-In particular, the value of @code{LDEMULATION} controls what default
-linker script is used (thereby controlling the default input and output
-formats; @pxref{BFD}); what default paths are searched for
-archive libraries; and in some cases whether additional linker script
-commands are available.
-
-Here is the current set of emulations available:
-@table @code
-
-@item LDEMULATION=gld
-@kindex gld
-@cindex emulating old GNU linker
-Emulate the older GNU linker. When this emulation is selected, the
-default library search paths are
-@example
-/lib
-/usr/lib
-/usr/local/lib/lib
-@end example
-@noindent
-The default output format is set to @code{a.out-generic-big}, and the
-default machine is the system's configured BFD default.
-
-@item LDEMULATION=gld68k
-@kindex gld68k
-@cindex m68k
-A variant of the @code{gld} emulation; only differs in specifically
-setting the default BFD machine as @code{m68k}.
-
-@item LDEMULATION=gld960
-@itemx LDEMULATION=lnk960
-Emulate older linkers for the i960 family; see @ref{i960,,@code{gld} and
-the Intel 960 family}, for details.
-
-@item LDEMULATION=gldm88kbcs
-Configure the linker for the Motorola 88K family.
-@xref{m88k,,@code{gld} and the Motorola 880x0 family}, for details.
-
-@item LDEMULATION=vanilla
-@kindex vanilla
-@cindex emulation, disabling
-@cindex disabling emulation
-This is the least specific setting for @code{gld}. You can set
-@code{LDEMULATION=vanilla} to disable emulation of other linkers. This
-setting makes @code{gld} take the default machine from the BFD
-configuration on your system; @code{a.out-generic-big} is the default
-target. No other defaults are specified.
-@end table
-
-@node Commands, Machine Dependent, Invocation, Top
+@cindex default emulation
+@cindex emulation, default
+@code{LDEMULATION} determines the default emulation if you don't use the
+@samp{-m} option. The emulation can affect various aspects of linker
+behaviour, particularly the default linker script. You can list the
+available emulations with the @samp{--verbose} or @samp{-V} options. If
+the @samp{-m} option is not used, and the @code{LDEMULATION} environment
+variable is not defined, the default emulation depends upon how the
+linker was configured.
+@end ifset
+
+@node Commands
@chapter Command Language
@cindex command files
-The command language allows explicit control over the link process,
+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. This includes:
+input files and its output. It controls:
@itemize @bullet
@item
input files
@item
file formats
@item
-output file format
+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 @code{-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 tries to interpret the file
-as a command file.
+You may supply a command file (also known as a linker script) to the
+linker either explicitly through the @samp{-T} option, or implicitly as
+an ordinary file. Normally you should use the @samp{-T} option. An
+implicit linker script should only be used when you want to augment,
+rather than replace, the default linker script; typically an implicit
+linker script would consist only of @code{INPUT} or @code{GROUP}
+commands.
-You can also include a script directly on the @code{gld} command line,
-delimited by the characters @samp{@{} and @samp{@}}.
+If the linker opens a file which it cannot recognize as a supported
+object or archive format, nor as a linker script, it reports an error.
@menu
* Scripts:: Linker Scripts
* Expressions:: Expressions
* MEMORY:: MEMORY Command
* SECTIONS:: SECTIONS Command
+* PHDRS:: PHDRS Command
* Entry Point:: The Entry Point
-* Other Commands:: Other Commands
+* Version Script:: Version Script
+* Option Commands:: Option Commands
@end menu
-@node Scripts, Expressions, Commands, Commands
+@node Scripts
@section Linker Scripts
-The @code{gld} command language is a collection of statements; some are
-simple keywords setting a particular flag, some are used to select and
-group input files or name output files; and two particular statement
+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{gld} command language is the
+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.
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{gld} assumes sufficient
+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}.
by @samp{/*} and @samp{*/}. As in C, comments are syntactically
equivalent to whitespace.
-@node Expressions, MEMORY, Scripts, Commands
+@node Expressions
@section Expressions
@cindex expression syntax
@cindex arithmetic
* Operators:: Operators
* Evaluation:: Evaluation
* Assignment:: Assignment: Defining Symbols
-* Built-ins:: Built-In Functions
+* Arithmetic Functions:: Built-In Functions
+* Semicolons:: Semicolon Usage
@end menu
-@node Integers, Symbols, Expressions, Expressions
+@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
+@smallexample
_as_octal = 0157255;
-@end example
+@end smallexample
@cindex decimal integers
A decimal integer starts with a non-zero digit followed by zero or
more digits (@samp{0123456789}).
-@example
+@smallexample
_as_decimal = 57005;
-@end example
+@end smallexample
@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
+@smallexample
_as_hex = 0xdead;
-@end example
+@end smallexample
@cindex negative integers
-Decimal integers have the usual values. To write a negative integer, use
-the prefix operator @samp{-}; @pxref{Operators}.
-@example
+To write a negative integer, use
+the prefix operator @samp{-} (@pxref{Operators}).
+@smallexample
_as_neg = -57005;
-@end example
+@end smallexample
@cindex scaled integers
@cindex K and M integer suffixes
${\rm 1024}$ or ${\rm 1024}^2$
@end tex
@c END TEXI2ROFF-KILL
-respectively. For example, the following all refer to the same quantity:@refill
+respectively. For example, the following all refer to the same quantity:
-@example
+@smallexample
_fourk_1 = 4K;
_fourk_2 = 4096;
_fourk_3 = 0x1000;
-@end example
+@end smallexample
-@node Symbols, Location Counter, Integers, Expressions
+@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
+Unless quoted, symbol names start with a letter, underscore, or point
+and may include any letters, underscores, digits, points,
+and hyphens. 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
+@smallexample
"SECTION" = 9;
"with a space" = "also with a space" + 10;
-@end example
+@end smallexample
+
+Since symbols can contain many non-alphabetic characters, it is safest
+to delimit symbols with spaces. For example, @samp{A-B} is one symbol,
+whereas @samp{A - B} is an expression involving subtraction.
-@node Location Counter, Operators, Symbols, Expressions
+@node Location Counter
@subsection The Location Counter
@kindex .
@cindex dot
@cindex holes
This may be used to create holes in the output section. The location
counter may never be moved backwards.
-@example
+@smallexample
SECTIONS
@{
- output :
- @{
- file1(.text)
- . = . + 1000;
- file2(.text)
- . += 1000;
- file3(.text)
- @} = 0x1234;
+ output :
+ @{
+ file1(.text)
+ . = . + 1000;
+ file2(.text)
+ . += 1000;
+ file3(.text)
+ @} = 0x1234;
@}
-@end example
+@end smallexample
@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}
loaded. The notation @samp{= 0x1234} specifies what data to write in
the gaps (@pxref{Section Options}).
-@node Operators, Evaluation, Location Counter, Expressions
+@iftex
+@vfill
+@end iftex
+
+@need 2000
+@node Operators
@subsection Operators
@cindex Operators for arithmetic
@cindex arithmetic operators
@c TEXI2ROFF-KILL
@ifinfo
@c END TEXI2ROFF-KILL
-@example
+@smallexample
precedence associativity Operators Notes
(highest)
1 left ! - ~ (1)
10 right ? :
11 right &= += -= *= /= (2)
(lowest)
-@end example
+@end smallexample
Notes:
(1) Prefix operators
-(2) @xref{Assignment}
+(2) @xref{Assignment}.
@c TEXI2ROFF-KILL
@end ifinfo
@tex
\vskip \baselineskip
-%"lispnarrowing" is the extra indent used generally for @example
+%"lispnarrowing" is the extra indent used generally for smallexample
\hskip\lispnarrowing\vbox{\offinterlineskip
\hrule
\halign
@end iftex
@c END TEXI2ROFF-KILL
-@node Evaluation, Assignment, Operators, Expressions
+@node Evaluation
@subsection Evaluation
@cindex lazy evaluation
output sections) is available for use in the symbol assignment
expression.
-@node Assignment, Built-ins, Evaluation, Expressions
+@node Assignment
@subsection Assignment: Defining Symbols
@cindex assignment in scripts
@cindex symbol definition, scripts
@itemx @var{symbol} /= @var{expression} ;
@end table
-Two things distinguish assignment from other operators in @code{gld}
+Two things distinguish assignment from other operators in @code{ld}
expressions.
@itemize @bullet
@item
@kindex ;
@cindex semicolon
@item
-A trailing semicolon is required at the end of an assignment
-statement.
+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 a @code{gld} script; or
+as commands in their own right in an @code{ld} script; or
@item
as independent statements within a @code{SECTIONS} command; or
@item
@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
+an absolute address. The last case defines a symbol whose address is
relative to a particular section (@pxref{SECTIONS}).
@cindex absolute and relocatable symbols
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 relocateable expression type is one in which the
+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
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
+@smallexample
SECTIONS@{ @dots{}
-.data :
- @{
- *(.data)
- _edata = ABSOLUTE(.) ;
- @}
+ .data :
+ @{
+ *(.data)
+ _edata = ABSOLUTE(.) ;
+ @}
@dots{} @}
-@end example
+@end smallexample
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,
+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
+@smallexample
SECTIONS @{ @dots{}
- text 9+this_isnt_constant:
- @{ @dots{}
- @}
+ text 9+this_isnt_constant :
+ @{ @dots{}
+ @}
@dots{} @}
-@end example
+@end smallexample
@kindex Non constant expression
@noindent
will cause the error message ``@code{Non constant expression for initial
-address}''.
-
-@node Built-ins, , Assignment, Expressions
-@subsection Built-In Functions
+address}''.
+
+@cindex provide
+In some cases, it is desirable for a linker script to define a symbol
+only if it is referenced, and only if it is not defined by any object
+included in the link. For example, traditional linkers defined the
+symbol @samp{etext}. However, ANSI C requires that the user be able to
+use @samp{etext} as a function name without encountering an error.
+The @code{PROVIDE} keyword may be used to define a symbol, such as
+@samp{etext}, only if it is referenced but not defined. The syntax is
+@code{PROVIDE(@var{symbol} = @var{expression})}.
+
+@node Arithmetic Functions
+@subsection Arithmetic Functions
@cindex functions in expression language
-The command language includes a number of special purpose built-in
+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
-returns the absolute 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 ABSOLUTE(@var{exp})
+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
-returns the absolute address of the named @var{section}. Your script must
+@item ADDR(@var{section})
+Return the absolute address of the named @var{section}. Your script must
previously have defined the location of that section. In the following
-example the @code{symbol_1} and @code{symbol_2} are assigned identical
+example, @code{symbol_1} and @code{symbol_2} are assigned identical
values:
-@example
+@smallexample
+@group
SECTIONS@{ @dots{}
- .output1:
- @{
- start_of_output_1 = ABSOLUTE(.);
- @dots{}
- @}
- .output:
- @{
- symbol_1 = ADDR(.output1);
- symbol_2 = start_of_output_1;
- @}
+ .output1 :
+ @{
+ start_of_output_1 = ABSOLUTE(.);
+ @dots{}
+ @}
+ .output :
+ @{
+ symbol_1 = ADDR(.output1);
+ symbol_2 = start_of_output_1;
+ @}
@dots{} @}
-@end example
+@end group
+@end smallexample
+
+@kindex LOADADDR(@var{section})
+@cindex section load address
+@item LOADADDR(@var{section})
+Return the absolute load address of the named @var{section}. This is
+normally the same as @code{ADDR}, but it may be different if the
+@code{AT} keyword is used in the section definition (@pxref{Section
+Options}).
-@item ALIGN(@var{exp})
@kindex ALIGN(@var{exp})
@cindex rounding up location counter
-returns the result of the current location counter (@code{.}) aligned to
+@item ALIGN(@var{exp})
+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
+@smallexample
+(. + @var{exp} - 1) & ~(@var{exp} - 1)
+@end smallexample
@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
+@smallexample
+@group
SECTIONS@{ @dots{}
- .data ALIGN(0x2000): @{
- *(.data)
- variable = ALIGN(0x8000);
- @}
+ .data ALIGN(0x2000): @{
+ *(.data)
+ variable = ALIGN(0x8000);
+ @}
@dots{} @}
-@end example
+@end group
+@end smallexample
@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
The built-in @code{NEXT} is closely related to @code{ALIGN}.
-@item DEFINED(@var{symbol})
@kindex DEFINED(@var{symbol})
@cindex symbol defaults
-Returns @code{1} if @var{symbol} is in the linker global symbol table and is
-defined, otherwise it returns @code{0}. You can use this to provide default
-values for symbols. For example, this command-file fragment shows how
+@item DEFINED(@var{symbol})
+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
+@group
SECTIONS@{ @dots{}
- .text: @{
- begin = DEFINED(begin) ? begin : . ;
- @dots{}
- @}
+ .text : @{
+ begin = DEFINED(begin) ? begin : . ;
+ @dots{}
+ @}
@dots{} @}
+@end group
@end smallexample
-@item NEXT(@var{exp})
@kindex NEXT(@var{exp})
@cindex unallocated address, next
-Returns the next unallocated address that is a multiple of @var{exp}.
-This command is closely related to @code{ALIGN(@var{exp})}; unless you
+@item NEXT(@var{exp})
+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 commands are equivalent.
+output file, the two functions are equivalent.
-@item SIZEOF(@var{section})
@kindex SIZEOF(@var{section})
@cindex section size
-returns the size in bytes of the named @var{section}, if the section has
-been allocated. In the following example the @code{symbol_1} and
+@item SIZEOF(@var{section})
+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:
-@example
+@c What does it return if the section hasn't been allocated? 0?
+@smallexample
+@group
SECTIONS@{ @dots{}
- .output @{
- .start = . ;
- @dots{}
- .end = .;
- @}
- symbol_1 = .end - .start;
- symbol_2 = SIZEOF(.output);
+ .output @{
+ .start = . ;
+ @dots{}
+ .end = . ;
+ @}
+ symbol_1 = .end - .start ;
+ symbol_2 = SIZEOF(.output);
@dots{} @}
+@end group
+@end smallexample
-@end example
-
-@item SIZEOF_HEADERS
@kindex SIZEOF_HEADERS
@cindex header size
-@itemx sizeof_headers
@kindex sizeof_headers
-the size in bytes of the output file's headers. You can use this number
+@item SIZEOF_HEADERS
+@itemx 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.
+@kindex MAX
+@item MAX(@var{exp1}, @var{exp2})
+Returns the maximum of @var{exp1} and @var{exp2}.
+
+@kindex MIN
+@item MIN(@var{exp1}, @var{exp2})
+Returns the minimum of @var{exp1} and @var{exp2}.
+
@end table
-@node MEMORY, SECTIONS, Expressions, Commands
-@section MEMORY Command
+@node Semicolons
+@subsection Semicolons
+
+Semicolons (``@key{;}'') are required in the following places. In all
+other places they can appear for aesthetic reasons but are otherwise ignored.
+
+@table @code
+@item Assignment
+Semicolons must appear at the end of assignment expressions.
+@xref{Assignment}
+
+@item PHDRS
+Semicolons must appear at the end of a @code{PHDRS} statement.
+@xref{PHDRS}
+@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 memory.
-You can override this by using the @code{MEMORY} command. The
+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
available regions, but does move the requested sections into the correct
regions and issue errors when the regions become too full.
-Command files may contain at most one use of the @code{MEMORY}
+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
+@smallexample
+@group
MEMORY
- @{
- @var{name} (@var{attr}): ORIGIN = @var{origin}, LENGTH = @var{len}
- @dots{}
- @}
-@end example
+ @{
+ @var{name} (@var{attr}) : ORIGIN = @var{origin}, LENGTH = @var{len}
+ @dots{}
+ @}
+@end group
+@end smallexample
@table @code
-@item @var{name}
@cindex naming memory regions
+@item @var{name}
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, filenames or section
+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{gld} 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{attr})
+is an optional list of attributes that specify whether to use a
+particular memory to place sections that are not listed in the linker
+script. Valid attribute lists must be made up of the characters
+``@code{ALIRWX}'' that match section attributes. If you omit the
+attribute list, you may omit the parentheses around it as well. The
+attributes currently supported are:
+
+@table @samp
+@item @code{Letter}
+@code{Section Attribute}
+
+@item @code{R}
+Read-only sections.
+
+@item @code{W}
+Read/write sections.
+
+@item @code{X}
+Sections containing executable code.
+
+@item @code{A}
+Allocated sections.
+
+@item @code{I}
+Initialized sections.
+
+@item @code{L}
+Same as @code{I}.
+
+@item @code{!}
+Invert the sense of any of the following attributes.
+@end table
+
+@kindex ORIGIN =
+@kindex o =
+@kindex org =
@item @var{origin}
-@kindex ORIGIN=
-@kindex o=
-@kindex org=
-is the start address of the region in physical memory. It is expressed as
-an expression, which must evaluate to a constant before
+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}.
+abbreviated to @code{org} or @code{o} (but not, for example, @samp{ORG}).
+
+@kindex LENGTH =
+@kindex len =
+@kindex l =
@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 @code{0} for 256 kilobytes, and the other
-starting at @code{0x40000000} for four megabytes:
+allocation---one starting at 0 for 256 kilobytes, and the other starting
+at @code{0x40000000} for four megabytes. The @code{rom} memory region
+will get all sections without an explicit memory register that are
+either read-only or contain code, while the @code{ram} memory region
+will get the sections.
-@example
+@smallexample
+@group
MEMORY
- @{
- rom : ORIGIN= 0, LENGTH = 256K
- ram : org= 0x40000000, l = 4M
- @}
-@end example
+ @{
+ rom (rx) : ORIGIN = 0, LENGTH = 256K
+ ram (!rx) : org = 0x40000000, l = 4M
+ @}
+@end group
+@end smallexample
Once you have defined a region of memory named @var{mem}, you can direct
specific output sections there by using a command ending in
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, Entry Point, MEMORY, Commands
-@section SECTIONS Command
+@node SECTIONS
+@section Specifying Output Sections
+
@kindex SECTIONS
The @code{SECTIONS} command controls exactly where input sections are
-placed into output sections, their order and to which output sections
-they are allocated.
+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 commands file,
+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 what input
-sections make it up.
+describe the placement of a named output section, and which input
+sections go into it.
@end itemize
-The first two possibilities---defining the entry point, and defining
-symbols---can also be done outside the @code{SECTIONS} command:
-@pxref{Entry Point}, @pxref{Assignment}. They are permitted here as
-well for your convenience in reading the script, so that symbols or the
-entry point can be defined at meaningful points in your output-file
-layout.
+You can also use the first two operations---defining the entry point and
+defining symbols---outside the @code{SECTIONS} command: @pxref{Entry
+Point}, and @ref{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 specified, the default action
-of the linker is to place 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.
+If you do not use a @code{SECTIONS} command, 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 Contents:: Section Contents
+* Section Placement:: Section Placement
+* Section Data Expressions:: Section Data Expressions
* Section Options:: Optional Section Attributes
+* Overlays:: Overlays
@end menu
-@node Section Definition, Section Contents, SECTIONS, SECTIONS
+@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 you can use to specify the
+the @dfn{section definition}, which specifies the
properties of an output section: its location, alignment, contents,
-fill pattern, and target memory region can all be specified. Most of
+fill pattern, and target memory region. Most of
these specifications are optional; the simplest form of a section
definition is
-@example
+@smallexample
SECTIONS @{ @dots{}
-@var{secname} : @{
- @var{contents}
- @}
+ @var{secname} : @{
+ @var{contents}
+ @}
@dots{} @}
-@end example
+@end smallexample
@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. As you might assume, the whitespace shown is
-optional; you do need the colon @samp{:} and the braces @samp{@{@}},
-however.
+specification of what goes there---for example, a list of input files or
+sections of input files (@pxref{Section Placement}). The whitespace
+around @var{secname} is required, so that the section name is
+unambiguous. The other 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{.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 characters, but any name which does not conform to the standard
-@code{gld} symbol name syntax must be quoted.
+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}.
+
+The special @var{secname} @samp{/DISCARD/} may be used to discard input
+sections. Any sections which are assigned to an output section named
+@samp{/DISCARD/} are not included in the final link output.
+
+The linker will not create output sections which do not have any
+contents. This is for convenience when referring to input sections that
+may or may not exist. For example,
+@smallexample
+.foo @{ *(.foo) @}
+@end smallexample
+will only create a @samp{.foo} section in the output file if there is a
+@samp{.foo} section in at least one input file.
+
+@node Section Placement
+@subsection Section Placement
-@node Section Contents, Section Options, Section Definition, SECTIONS
-@subsection Section Contents
@cindex contents of a section
-In a section definition, you can specify the contents of an output section by
-listing particular object files; by listing particular input-file
-sections; or a combination of the two. You can also place arbitrary
-data in the section, and define symbols relative to the beginning of the
-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.
+whitespace.
@table @code
-@item @var{filename}
@kindex @var{filename}
@cindex input files, section defn
@cindex files, including in output sections
+@item @var{filename}
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. To specify a list of particular files by
-name:
-@example
-.data: @{ afile.o bfile.o cfile.o @}
-@end example
+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:
+@smallexample
+.data : @{ afile.o bfile.o cfile.o @}
+@end smallexample
@noindent
The example also illustrates that multiple statements can be included in
-the contents of a section definition, since each filename is a separate
+the contents of a section definition, since each file name is a separate
statement.
-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.
-
-@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{filename}( @var{section} )
+@itemx @var{filename}( @var{section} , @var{section}, @dots{} )
+@itemx @var{filename}( @var{section} @var{section} @dots{} )
+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, separate the section names
+with 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})
+@item * (@var{section})
+@itemx * (@var{section}, @var{section}, @dots{})
+@itemx * (@var{section} @var{section} @dots{})
Instead of explicitly naming particular input files in a link control
-script, you can refer to @emph{all} files from the @code{gld} command
-line: use @samp{*} instead of a particular filename before the
+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.
-For example, to copy sections @code{1} through @code{4} from a Oasys file
+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
+@smallexample
+@group
SECTIONS @{
- .text :@{
- *("1" "2" "3" "4")
- @}
-
- .data :@{
- *("13" "14")
- @}
+ .text :@{
+ *("1" "2" "3" "4")
+ @}
+
+ .data :@{
+ *("13" "14")
+ @}
@}
-@end example
-
-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.
+@end group
+@end smallexample
-@item [ @var{section} ]
-@itemx [ @var{section}, @var{section}, @dots{} ]
-@itemx [ @var{section} @var{section} @dots{} ]
-@kindex [ @var{sections} ]
-This is an alternate notation to specify named sections from all
-unallocated input files; its effect is exactly the same as that of
-@samp{* (@var{section}@dots{})}
+@cindex @code{[@var{section}@dots{}]}, not supported
+@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
+@kindex *( COMMON )
+@item @var{filename}@code{( COMMON )}
+@itemx *( COMMON )
Specify where in your output file to place uninitialized data
-with this notation. @code{[COMMON]} by itself refers to all
+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{gld} permits you to refer to uninitialized data as if it
+@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
+In any place where you may use a specific file or section name, you may
+also use a wildcard pattern. The linker handles wildcards much as the
+Unix shell does. A @samp{*} character matches any number of characters.
+A @samp{?} character matches any single character. The sequence
+@samp{[@var{chars}]} will match a single instance of any of the
+@var{chars}; the @samp{-} character may be used to specify a range of
+characters, as in @samp{[a-z]} to match any lower case letter. A
+@samp{\} character may be used to quote the following character.
+
+When a file name is matched with a wildcard, the wildcard characters
+will not match a @samp{/} character (used to separate directory names on
+Unix). A pattern consisting of a single @samp{*} character is an
+exception; it will always match any file name. In a section name, the
+wildcard characters will match a @samp{/} character.
+
+Wildcards only match files which are explicitly specified on the command
+line. The linker does not search directories to expand wildcards.
+However, if you specify a simple file name---a name with no wildcard
+characters---in a linker script, and the file name is not also specified
+on the command line, the linker will attempt to open the file as though
+it appeared on the command line.
+
+In the following example, the 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
+
+@smallexample
+@group
SECTIONS @{
- .text: @{ *(.text) @}
- .data: @{ *(.data) @}
- .bss: @{ *(.bss) [COMMON] @}
+ .text : @{ *(.text) @}
+ .data : @{ *(.data) @}
+ .bss : @{ *(.bss) *(COMMON) @}
@}
-@end example
+@end group
+@end smallexample
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
All of the remaining @code{.input1} and @code{.input2} sections from any
files are written to output section @code{outputc}.
-@example
+@smallexample
+@group
+SECTIONS @{
+ outputa 0x10000 :
+ @{
+ all.o
+ foo.o (.input1)
+ @}
+ outputb :
+ @{
+ foo.o (.input2)
+ foo1.o (.input1)
+ @}
+ outputc :
+ @{
+ *(.input1)
+ *(.input2)
+ @}
+@}
+@end group
+@end smallexample
+
+This example shows how wildcard patterns might be used to partition
+files. All @code{.text} sections are placed in @code{.text}, and all
+@code{.bss} sections are placed in @code{.bss}. For all files beginning
+with an upper case character, the @code{.data} section is placed into
+@code{.DATA}; for all other files, the @code{.data} section is placed
+into @code{.data}.
+
+@smallexample
+@group
SECTIONS @{
- outputa 0x10000 :
- @{
- all.o
- foo.o (.input1)
- @}
- outputb :
- @{
- foo.o (.input2)
- foo1.o (.input1)
- @}
- outputc :
- @{
- *(.input1)
- *(.input2)
- @}
+ .text : @{ *(.text) @}
+ .DATA : @{ [A-Z]*(.data) @}
+ .data : @{ *(.data) @}
+ .bss : @{ *(.bss) @}
@}
-@end example
-
-There are still more kinds of statements permitted in the contents of
-output section definitions. The foregoing statements permitted you to
-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.
+@end group
+@end smallexample
+
+@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
-instructs the linker to create a symbol for each input file
-in the current section, set with the address of the first byte of
-data written from the input file. For instance, with @code{a.out}
+@kindex CREATE_OBJECT_SYMBOLS
+@item CREATE_OBJECT_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
+@smallexample
+@group
SECTIONS @{
- .text 0x2020 :
- @{
- CREATE_OBJECT_SYMBOLS
- *(.text)
- _etext = ALIGN(0x2000);
- @}
- @dots{}
+ .text 0x2020 :
+ @{
+ CREATE_OBJECT_SYMBOLS
+ *(.text)
+ _etext = ALIGN(0x2000);
+ @}
+ @dots{}
@}
-@end example
+@end group
+@end smallexample
-If @code{objsym} is a file containing this script, and @code{a.o},
+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
+@smallexample
+@group
/* a.c */
afunction() @{ @}
int adata=1;
int abss;
-@end example
+@end group
+@end smallexample
@noindent
-@samp{gld -M sample a.o b.o c.o d.o} would create a map like this,
+@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
+@smallexample
00000000 A __DYNAMIC
00004020 B _abss
00004000 D _adata
00002038 t b.o
00002050 t c.o
00002068 t d.o
-@end example
+@end smallexample
-@item @var{symbol} = @var{expression} ;
@kindex @var{symbol} = @var{expression} ;
-@itemx @var{symbol} @var{f}= @var{expression} ;
@kindex @var{symbol} @var{f}= @var{expression} ;
+@item @var{symbol} = @var{expression} ;
+@itemx @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.
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
+
+@smallexample
+@group
SECTIONS @{
abs = 14 ;
@dots{}
- .data: @{ @dots{} rel = 14 ; @dots{} @}
+ .data : @{ @dots{} rel = 14 ; @dots{} @}
abs2 = 14 + ADDR(.data);
@dots{}
@}
-@end example
+@end group
+@end smallexample
+
@c FIXME: Try above example!
@noindent
-@code{abs} and @var{rel} do not have the same value; @code{rel} has the
+@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})
+@kindex QUAD(@var{expression})
+@kindex SQUAD(@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. Multiple-byte quantities are
-represented in whatever byte order is appropriate for the output file
-format (@pxref{BFD}).
+@item BYTE(@var{expression})
+@itemx SHORT(@var{expression})
+@itemx LONG(@var{expression})
+@itemx QUAD(@var{expression})
+@itemx SQUAD(@var{expression})
+By including one of these four statements in a section definition, you
+can explicitly place one, two, four, eight unsigned, or eight signed
+bytes (respectively) at the current address of that section. When using
+a 64 bit host or target, @code{QUAD} and @code{SQUAD} are the same.
+When both host and target are 32 bits, @code{QUAD} uses an unsigned 32
+bit value, and @code{SQUAD} sign extends the value. Both will use the
+correct endianness when writing out the value.
+
+@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
-Specifies the ``fill pattern'' for the current section. Any otherwise
+@item FILL(@var{expression})
+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
fill patterns in different parts of an output section.
@end table
-@node Section Options, , Section Contents, SECTIONS
+@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:
-@example
+@smallexample
+@group
SECTIONS @{
@dots{}
-@var{secname} @var{start} BLOCK(@var{align}) : @{ @var{contents} @} =@var{fill} >@var{region}
+@var{secname} @var{start} BLOCK(@var{align}) (NOLOAD) : AT ( @var{ldadr} )
+ @{ @var{contents} @} >@var{region} :@var{phdr} =@var{fill}
@dots{}
@}
-@end example
+@end group
+@end smallexample
@var{secname} and @var{contents} are required. @xref{Section
-Definition}, and @pxref{Section Contents} for details on @var{contents}.
-The remaining elements---@var{start}, @code{BLOCK(@var{align)}},
-@code{=@var{fill}}, and @code{>@var{region}}---are all optional.
+Definition}, and @ref{Section Placement}, for details on
+@var{contents}. The remaining elements---@var{start},
+@code{BLOCK(@var{align)}}, @code{(NOLOAD)}, @code{AT ( @var{ldadr} )},
+@code{>@var{region}}, @code{:@var{phdr}}, and @code{=@var{fill}}---are
+all optional.
@table @code
-@item @var{start}
@cindex start address, section
@cindex section start
@cindex section address
+@item @var{start}
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
+
+@smallexample
+@group
SECTIONS @{
- @dots{}
- output 0x40000000: @{
- @dots{}
- @}
- @dots{}
+ @dots{}
+ output 0x40000000: @{
+ @dots{}
+ @}
+ @dots{}
@}
-@end example
+@end group
+@end smallexample
-@item BLOCK(@var{align})
@kindex BLOCK(@var{align})
@cindex section alignment
@cindex aligning sections
-You can include @code{BLOCK()} specification to advance the location of
+@item BLOCK(@var{align})
+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 =@var{fill}
-@kindex =@var{fill}
-@cindex section fill pattern
-@cindex fill pattern, entire section
-You may use any expression to specify @var{fill}. Including
-@code{=@var{fill}} in a section definition specifies the initial fill
-value for that section. 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.
+@kindex NOLOAD
+@cindex prevent unnecessary loading
+@cindex loading, preventing
+@item (NOLOAD)
+The @samp{(NOLOAD)} directive will mark a section to not be loaded at
+run time. The linker will process the section normally, but will mark
+it so that a program loader will not load it into memory. For example,
+in the script sample below, the @code{ROM} section is addressed at
+memory location @samp{0} and does not need to be loaded when the program
+is run. The contents of the @code{ROM} section will appear in the
+linker output file as usual.
+
+@smallexample
+@group
+SECTIONS @{
+ ROM 0 (NOLOAD) : @{ @dots{} @}
+ @dots{}
+@}
+@end group
+@end smallexample
+
+@kindex AT ( @var{ldadr} )
+@cindex specify load address
+@cindex load address, specifying
+@item AT ( @var{ldadr} )
+The expression @var{ldadr} that follows the @code{AT} keyword specifies
+the load address of the section. The default (if you do not use the
+@code{AT} keyword) is to make the load address the same as the
+relocation address. This feature is designed to make it easy to build a
+ROM image. For example, this @code{SECTIONS} definition creates two
+output sections: one called @samp{.text}, which starts at @code{0x1000},
+and one called @samp{.mdata}, which is loaded at the end of the
+@samp{.text} section even though its relocation address is
+@code{0x2000}. The symbol @code{_data} is defined with the value
+@code{0x2000}:
+
+@smallexample
+@group
+SECTIONS
+ @{
+ .text 0x1000 : @{ *(.text) _etext = . ; @}
+ .mdata 0x2000 :
+ AT ( ADDR(.text) + SIZEOF ( .text ) )
+ @{ _data = . ; *(.data); _edata = . ; @}
+ .bss 0x3000 :
+ @{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;@}
+@}
+@end group
+@end smallexample
+
+The run-time initialization code (for C programs, usually @code{crt0})
+for use with a ROM generated this way has to include something like
+the following, to copy the initialized data from the ROM image to its runtime
+address:
+
+@smallexample
+@group
+char *src = _etext;
+char *dst = _data;
+
+/* ROM has data at end of text; copy it. */
+while (dst < _edata) @{
+ *dst++ = *src++;
+@}
+
+/* Zero bss */
+for (dst = _bstart; dst< _bend; dst++)
+ *dst = 0;
+@end group
+@end smallexample
-@item >@var{region}
@kindex >@var{region}
@cindex section, assigning to memory region
@cindex memory regions and sections
+@item >@var{region}
Assign this section to a previously defined region of memory.
@xref{MEMORY}.
+@kindex :@var{phdr}
+@cindex section, assigning to program header
+@cindex program headers and sections
+@item :@var{phdr}
+Assign this section to a segment described by a program header.
+@xref{PHDRS}. If a section is assigned to one or more segments, then
+all subsequent allocated sections will be assigned to those segments as
+well, unless they use an explicitly @code{:@var{phdr}} modifier. To
+prevent a section from being assigned to a segment when it would
+normally default to one, use @code{:NONE}.
+
+@kindex =@var{fill}
+@cindex section fill pattern
+@cindex fill pattern, entire section
+@item =@var{fill}
+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.
+
+@end table
+
+@node Overlays
+@subsection Overlays
+@kindex OVERLAY
+@cindex overlays
+
+The @code{OVERLAY} command provides an easy way to describe sections
+which are to be loaded as part of a single memory image but are to be
+run at the same memory address. At run time, some sort of overlay
+manager will copy the overlaid sections in and out of the runtime memory
+address as required, perhaps by simply manipulating addressing bits.
+This approach can be useful, for example, when a certain region of
+memory is faster than another.
+
+The @code{OVERLAY} command is used within a @code{SECTIONS} command. It
+appears as follows:
+@smallexample
+@group
+ OVERLAY @var{start} : [ NOCROSSREFS ] AT ( @var{ldaddr} )
+ @{
+ @var{secname1} @{ @var{contents} @} :@var{phdr} =@var{fill}
+ @var{secname2} @{ @var{contents} @} :@var{phdr} =@var{fill}
+ @dots{}
+ @} >@var{region} :@var{phdr} =@var{fill}
+@end group
+@end smallexample
+
+Everything is optional except @code{OVERLAY} (a keyword), and each
+section must have a name (@var{secname1} and @var{secname2} above). The
+section definitions within the @code{OVERLAY} construct are identical to
+those within the general @code{SECTIONS} contruct (@pxref{SECTIONS}),
+except that no addresses and no memory regions may be defined for
+sections within an @code{OVERLAY}.
+
+The sections are all defined with the same starting address. The load
+addresses of the sections are arranged such that they are consecutive in
+memory starting at the load address used for the @code{OVERLAY} as a
+whole (as with normal section definitions, the load address is optional,
+and defaults to the start address; the start address is also optional,
+and defaults to @code{.}).
+
+If the @code{NOCROSSREFS} keyword is used, and there any references
+among the sections, the linker will report an error. Since the sections
+all run at the same address, it normally does not make sense for one
+section to refer directly to another. @xref{Option Commands,
+NOCROSSREFS}.
+
+For each section within the @code{OVERLAY}, the linker automatically
+defines two symbols. The symbol @code{__load_start_@var{secname}} is
+defined as the starting load address of the section. The symbol
+@code{__load_stop_@var{secname}} is defined as the final load address of
+the section. Any characters within @var{secname} which are not legal
+within C identifiers are removed. C (or assembler) code may use these
+symbols to move the overlaid sections around as necessary.
+
+At the end of the overlay, the value of @code{.} is set to the start
+address of the overlay plus the size of the largest section.
+
+Here is an example. Remember that this would appear inside a
+@code{SECTIONS} construct.
+
+@smallexample
+@group
+ OVERLAY 0x1000 : AT (0x4000)
+ @{
+ .text0 @{ o1/*.o(.text) @}
+ .text1 @{ o2/*.o(.text) @}
+ @}
+@end group
+@end smallexample
+
+This will define both @code{.text0} and @code{.text1} to start at
+address 0x1000. @code{.text0} will be loaded at address 0x4000, and
+@code{.text1} will be loaded immediately after @code{.text0}. The
+following symbols will be defined: @code{__load_start_text0},
+@code{__load_stop_text0}, @code{__load_start_text1},
+@code{__load_stop_text1}.
+
+C code to copy overlay @code{.text1} into the overlay area might look
+like the following.
+
+@smallexample
+@group
+ extern char __load_start_text1, __load_stop_text1;
+ memcpy ((char *) 0x1000, &__load_start_text1,
+ &__load_stop_text1 - &__load_start_text1);
+@end group
+@end smallexample
+
+Note that the @code{OVERLAY} command is just syntactic sugar, since
+everything it does can be done using the more basic commands. The above
+example could have been written identically as follows.
+
+@smallexample
+@group
+ .text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
+ __load_start_text0 = LOADADDR (.text0);
+ __load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0);
+ .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
+ __load_start_text1 = LOADADDR (.text1);
+ __load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1);
+ . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
+@end group
+@end smallexample
+
+@node PHDRS
+@section ELF Program Headers
+@kindex PHDRS
+@cindex program headers
+@cindex ELF program headers
+
+The ELF object file format uses @dfn{program headers}, which are read by
+the system loader and describe how the program should be loaded into
+memory. These program headers must be set correctly in order to run the
+program on a native ELF system. The linker will create reasonable
+program headers by default. However, in some cases, it is desirable to
+specify the program headers more precisely; the @code{PHDRS} command may
+be used for this purpose. When the @code{PHDRS} command is used, the
+linker will not generate any program headers itself.
+
+The @code{PHDRS} command is only meaningful when generating an ELF
+output file. It is ignored in other cases. This manual does not
+describe the details of how the system loader interprets program
+headers; for more information, see the ELF ABI. The program headers of
+an ELF file may be displayed using the @samp{-p} option of the
+@code{objdump} command.
+
+This is the syntax of the @code{PHDRS} command. The words @code{PHDRS},
+@code{FILEHDR}, @code{AT}, and @code{FLAGS} are keywords.
+
+@smallexample
+@group
+PHDRS
+@{
+ @var{name} @var{type} [ FILEHDR ] [ PHDRS ] [ AT ( @var{address} ) ]
+ [ FLAGS ( @var{flags} ) ] ;
+@}
+@end group
+@end smallexample
+
+The @var{name} is used only for reference in the @code{SECTIONS} command
+of the linker script. It does not get put into the output file.
+
+Certain program header types describe segments of memory which are
+loaded from the file by the system loader. In the linker script, the
+contents of these segments are specified by directing allocated output
+sections to be placed in the segment. To do this, the command
+describing the output section in the @code{SECTIONS} command should use
+@samp{:@var{name}}, where @var{name} is the name of the program header
+as it appears in the @code{PHDRS} command. @xref{Section Options}.
+
+It is normal for certain sections to appear in more than one segment.
+This merely implies that one segment of memory contains another. This
+is specified by repeating @samp{:@var{name}}, using it once for each
+program header in which the section is to appear.
+
+If a section is placed in one or more segments using @samp{:@var{name}},
+then all subsequent allocated sections which do not specify
+@samp{:@var{name}} are placed in the same segments. This is for
+convenience, since generally a whole set of contiguous sections will be
+placed in a single segment. To prevent a section from being assigned to
+a segment when it would normally default to one, use @code{:NONE}.
+
+The @code{FILEHDR} and @code{PHDRS} keywords which may appear after the
+program header type also indicate contents of the segment of memory.
+The @code{FILEHDR} keyword means that the segment should include the ELF
+file header. The @code{PHDRS} keyword means that the segment should
+include the ELF program headers themselves.
+
+The @var{type} may be one of the following. The numbers indicate the
+value of the keyword.
+
+@table @asis
+@item @code{PT_NULL} (0)
+Indicates an unused program header.
+
+@item @code{PT_LOAD} (1)
+Indicates that this program header describes a segment to be loaded from
+the file.
+
+@item @code{PT_DYNAMIC} (2)
+Indicates a segment where dynamic linking information can be found.
+
+@item @code{PT_INTERP} (3)
+Indicates a segment where the name of the program interpreter may be
+found.
+
+@item @code{PT_NOTE} (4)
+Indicates a segment holding note information.
+
+@item @code{PT_SHLIB} (5)
+A reserved program header type, defined but not specified by the ELF
+ABI.
+
+@item @code{PT_PHDR} (6)
+Indicates a segment where the program headers may be found.
+
+@item @var{expression}
+An expression giving the numeric type of the program header. This may
+be used for types not defined above.
@end table
-@node Entry Point, Other Commands, SECTIONS, Commands
+It is possible to specify that a segment should be loaded at a
+particular address in memory. This is done using an @code{AT}
+expression. This is identical to the @code{AT} command used in the
+@code{SECTIONS} command (@pxref{Section Options}). Using the @code{AT}
+command for a program header overrides any information in the
+@code{SECTIONS} command.
+
+Normally the segment flags are set based on the sections. The
+@code{FLAGS} keyword may be used to explicitly specify the segment
+flags. The value of @var{flags} must be an integer. It is used to
+set the @code{p_flags} field of the program header.
+
+Here is an example of the use of @code{PHDRS}. This shows a typical set
+of program headers used on a native ELF system.
+
+@example
+@group
+PHDRS
+@{
+ headers PT_PHDR PHDRS ;
+ interp PT_INTERP ;
+ text PT_LOAD FILEHDR PHDRS ;
+ data PT_LOAD ;
+ dynamic PT_DYNAMIC ;
+@}
+
+SECTIONS
+@{
+ . = SIZEOF_HEADERS;
+ .interp : @{ *(.interp) @} :text :interp
+ .text : @{ *(.text) @} :text
+ .rodata : @{ *(.rodata) @} /* defaults to :text */
+ @dots{}
+ . = . + 0x1000; /* move to a new page in memory */
+ .data : @{ *(.data) @} :data
+ .dynamic : @{ *(.dynamic) @} :data :dynamic
+ @dots{}
+@}
+@end group
+@end example
+
+@node Entry Point
@section The Entry Point
@kindex ENTRY(@var{symbol})
@cindex start of execution
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
+@smallexample
ENTRY(@var{symbol})
-@end example
+@end smallexample
Like symbol assignments, the @code{ENTRY} command may be placed either
as an independent command in the command file, or among the section
order of priority: methods higher in the list override methods lower down).
@itemize @bullet
@item
-the @code{-e} @var{entry} command-line option;
+the @samp{-e} @var{entry} command-line option;
@item
-the @code{ENTRY(@var{symbol}} command in a linker control script;
+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}.
assignment statement: if no symbol @code{start} is defined within your
input files, you can simply define it, assigning it an appropriate
value---
-@example
+
+@smallexample
start = 0x2020;
-@end example
+@end smallexample
@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 Other Commands, , Entry Point, Commands
-@section Other Commands
+@smallexample
+start = other_symbol ;
+@end smallexample
+
+@node Version Script
+@section Version Script
+@kindex VERSION @{script text@}
+@cindex symbol versions
+@cindex version script
+@cindex versions of symbols
+The linker command script includes a command specifically for
+specifying a version script, and is only meaningful for ELF platforms
+that support shared libraries. A version script can be
+build directly into the linker script that you are using, or you
+can supply the version script as just another input file to the linker
+at the time that you link. The command script syntax is:
+@smallexample
+VERSION @{ version script contents @}
+@end smallexample
+The version script can also be specified to the linker by means of the
+@samp{--version-script} linker command line option.
+Version scripts are only meaningful when creating shared libraries.
+
+The format of the version script itself is identical to that used by
+Sun's linker in Solaris 2.5. Versioning is done by defining a tree of
+version nodes with the names and interdependencies specified in the
+version script. The version script can specify which symbols are bound
+to which version nodes, and it can reduce a specified set of symbols to
+local scope so that they are not globally visible outside of the shared
+library.
+
+The easiest way to demonstrate the version script language is with a few
+examples.
+
+@smallexample
+VERS_1.1 @{
+ global:
+ foo1;
+ local:
+ old*;
+ original*;
+ new*;
+@};
+
+VERS_1.2 @{
+ foo2;
+@} VERS_1.1;
+
+VERS_2.0 @{
+ bar1; bar2;
+@} VERS_1.2;
+@end smallexample
+
+In this example, three version nodes are defined. @samp{VERS_1.1} is the
+first version node defined, and has no other dependencies. The symbol
+@samp{foo1} is bound to this version node, and a number of symbols
+that have appeared within various object files are reduced in scope to
+local so that they are not visible outside of the shared library.
+
+Next, the node @samp{VERS_1.2} is defined. It depends upon
+@samp{VERS_1.1}. The symbol @samp{foo2} is bound to this version node.
+
+Finally, the node @samp{VERS_2.0} is defined. It depends upon
+@samp{VERS_1.2}. The symbols @samp{bar1} and @samp{bar2} are bound to
+this version node.
+
+Symbols defined in the library which aren't specifically bound to a
+version node are effectively bound to an unspecified base version of the
+library. It is possible to bind all otherwise unspecified symbols to a
+given version node using @samp{global: *} somewhere in the version
+script.
+
+Lexically the names of the version nodes have no specific meaning other
+than what they might suggest to the person reading them. The @samp{2.0}
+version could just as well have appeared in between @samp{1.1} and
+@samp{1.2}. However, this would be a confusing way to write a version
+script.
+
+When you link an application against a shared library that has versioned
+symbols, the application itself knows which version of each symbol it requires,
+and it also knows which version nodes it needs from each shared library it is
+linked against. Thus at runtime, the dynamic loader can make a quick check to
+make sure that the libraries you have linked against do in fact supply all
+of the version nodes that the application will need to resolve all of the
+dynamic symbols. In this way it is possible for the dynamic linker to know
+with certainty that all external symbols that it needs will be resolvable
+without having to search for each symbol reference.
+
+The symbol versioning is in effect a much more sophisticated way of
+doing minor version checking that SunOS does. The fundamental problem
+that is being addressed here is that typically references to external
+functions are bound on an as-needed basis, and are not all bound when
+the application starts up. If a shared library is out of date, a
+required interface may be missing; when the application tries to use
+that interface, it may suddenly and unexpectedly fail. With symbol
+versioning, the user will get a warning when they start their program if
+the libraries being used with the application are too old.
+
+There are several GNU extensions to Sun's versioning approach. The
+first of these is the ability to bind a symbol to a version node in the
+source file where the symbol is defined instead of in the versioning
+script. This was done mainly to reduce the burden on the library
+maintainer. This can be done by putting something like:
+
+@smallexample
+__asm__(".symver original_foo,foo@@VERS_1.1");
+@end smallexample
+
+in the C source file. This renamed the function @samp{original_foo} to
+be an alias for @samp{foo} bound to the version node @samp{VERS_1.1}.
+The @samp{local:} directive can be used to prevent the symbol
+@samp{original_foo} from being exported.
+
+The second GNU extension is to allow multiple versions of the same function
+to appear in a given shared library. In this way an incompatible change to
+an interface can take place without increasing the major version number of
+the shared library, while still allowing applications linked against the old
+interface to continue to function.
+
+This can only be accomplished by using multiple @samp{.symver}
+directives in the assembler. An example of this would be:
+
+@smallexample
+__asm__(".symver original_foo,foo@@");
+__asm__(".symver old_foo,foo@@VERS_1.1");
+__asm__(".symver old_foo1,foo@@VERS_1.2");
+__asm__(".symver new_foo,foo@@@@VERS_2.0");
+@end smallexample
+
+In this example, @samp{foo@@} represents the symbol @samp{foo} bound to the
+unspecified base version of the symbol. The source file that contains this
+example would define 4 C functions: @samp{original_foo}, @samp{old_foo},
+@samp{old_foo1}, and @samp{new_foo}.
+
+When you have multiple definitions of a given symbol, there needs to be
+some way to specify a default version to which external references to
+this symbol will be bound. This can be accomplished with the
+@samp{foo@@@@VERS_2.0} type of @samp{.symver} directive. Only one version of
+a symbol can be declared 'default' in this manner - otherwise you would
+effectively have multiple definitions of the same symbol.
+
+If you wish to bind a reference to a specific version of the symbol
+within the shared library, you can use the aliases of convenience
+(i.e. @samp{old_foo}), or you can use the @samp{.symver} directive to
+specifically bind to an external version of the function in question.
+
+@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 CONSTRUCTORS
+@cindex C++ constructors, arranging in link
+@cindex constructors, arranging in link
+@item CONSTRUCTORS
+When linking using the @code{a.out} object file format, the linker uses
+an unusual set construct to support C++ global constructors and
+destructors. When linking object file formats which do not support
+arbitrary sections, such as @code{ECOFF} and @code{XCOFF}, the linker
+will automatically recognize C++ global constructors and destructors by
+name. For these object file formats, the @code{CONSTRUCTORS} command
+tells the linker where this information should be placed. The
+@code{CONSTRUCTORS} command is ignored for other object file formats.
+
+The symbol @w{@code{__CTOR_LIST__}} marks the start of the global
+constructors, and the symbol @w{@code{__DTOR_LIST}} marks the end. The
+first word in the list is the number of entries, followed by the address
+of each constructor or destructor, followed by a zero word. The
+compiler must arrange to actually run the code. For these object file
+formats @sc{gnu} C++ calls constructors from a subroutine @code{__main};
+a call to @code{__main} is automatically inserted into the startup code
+for @code{main}. @sc{gnu} C++ runs destructors either by using
+@code{atexit}, or directly from the function @code{exit}.
+
+For object file formats such as @code{COFF} or @code{ELF} which support
+multiple sections, @sc{gnu} C++ will normally arrange to put the
+addresses of global constructors and destructors into the @code{.ctors}
+and @code{.dtors} sections. Placing the following sequence into your
+linker script will build the sort of table which the @sc{gnu} C++
+runtime code expects to see.
+
+@smallexample
+ __CTOR_LIST__ = .;
+ LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
+ *(.ctors)
+ LONG(0)
+ __CTOR_END__ = .;
+ __DTOR_LIST__ = .;
+ LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
+ *(.dtors)
+ LONG(0)
+ __DTOR_END__ = .;
+@end smallexample
+
+Normally the compiler and linker will handle these issues automatically,
+and you will not need to concern yourself with them. However, you may
+need to consider this if you are using C++ and writing your own linker
+scripts.
+
+@need 1000
@kindex FLOAT
-@itemx NOFLOAT
@kindex NOFLOAT
+@item FLOAT
+@itemx NOFLOAT
These keywords were used in some older linkers to request a particular
-math subroutine library. @code{gld} doesn't use the keywords, assuming
+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 @code{-d} command-line option:
+@item FORCE_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 (@code{-r}).
+output file is specified (@samp{-r}).
+
+@kindex INCLUDE @var{filename}
+@cindex including a linker script
+@item INCLUDE @var{filename}
+Include the linker script @var{filename} at this point. The file will
+be searched for in the current directory, and in any directory specified
+with the @code{-L} option. You can nest calls to @code{INCLUDE} up to
+10 levels deep.
-@item INPUT ( @var{file}, @var{file}, @dots{} )
@kindex INPUT ( @var{files} )
-@itemx INPUT ( @var{file} @var{file} @dots{} )
@cindex binary input files
+@item INPUT ( @var{file}, @var{file}, @dots{} )
+@itemx INPUT ( @var{file} @var{file} @dots{} )
Use this command to include binary input files in the link, without
-including them in a particular section definition. Files specified this
-way are treated identically to object files listed on the command line.
+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}.
+
+If you use @samp{-l@var{file}}, @code{ld} will transform the name to
+@code{lib@var{file}.a} as with the command line argument @samp{-l}.
+
+@kindex GROUP ( @var{files} )
+@cindex grouping input files
+@item GROUP ( @var{file}, @var{file}, @dots{} )
+@itemx GROUP ( @var{file} @var{file} @dots{} )
+This command is like @code{INPUT}, except that the named files should
+all be archives, and they are searched repeatedly until no new undefined
+references are created. See the description of @samp{-(} in
+@ref{Options,,Command Line Options}.
@ignore
-@item MAP ( @var{name} )
@kindex MAP ( @var{name} )
+@item 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
-Name the link output file @var{filename}. The effect of
-@code{OUTPUT(@var{filename})} is identical to the effect of
-@w{@code{-o @var{filename}}}, and whichever is encountered last 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}.
+@item OUTPUT ( @var{filename} )
+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}}}, which overrides it. You can use this
+command to supply a default output-file name other than @code{a.out}.
-@item OUTPUT_ARCH ( @var{bfdname} )
+@ifclear SingleFormat
@kindex OUTPUT_ARCH ( @var{bfdname} )
@cindex machine architecture, output
+@item OUTPUT_ARCH ( @var{bfdname} )
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. @refill
+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}). This selection will only affect
-the output file; the related command @code{TARGET} affects primarily
-input files.@refill
+@item OUTPUT_FORMAT ( @var{bfdname} )
+When @code{ld} is configured to support multiple object code formats,
+you can use this command to specify a particular output format.
+@var{bfdname} is 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 affects only 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{gld} looks for
+@item SEARCH_DIR ( @var{path} )
+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 @code{-L@var{path})} on the command line.
+effect as @samp{-L@var{path}} on the command line.
-@item STARTUP ( @var{filename} )
@kindex STARTUP ( @var{filename} )
@cindex first input file
+@item STARTUP ( @var{filename} )
Ensure that @var{filename} is the first input file used in the link
process.
-@item TARGET ( @var{format} )
+@ifclear SingleFormat
@cindex input file format
@kindex TARGET ( @var{format} )
-Change the input-file object code format (like the command-line option
-@code{-b} or its synonym @code{-format}). The argument @var{format} is
-one of the strings used by BFD to name binary formats. In the current
-@code{gld} implementation, 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{gld} output file.
-@xref{BFD}.@refill
+@item TARGET ( @var{format} )
+When @code{ld} is configured to support multiple object code formats,
+you can use this command to 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{gld} uses the value of
+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{gld} uses
+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
+
+@cindex cross references
+@kindex NOCROSSREFS ( @var{sections} )
+@item NOCROSSREFS ( @var{section} @var{section} @dots{} )
+This command may be used to tell @code{ld} to issue an error about any
+references among certain sections.
+
+In certain types of programs, particularly on embedded systems, when one
+section is loaded into memory, another section will not be. Any direct
+references between the two sections would be errors. For example, it
+would be an error if code in one section called a function defined in
+the other section.
+
+The @code{NOCROSSREFS} command takes a list of section names. If
+@code{ld} detects any cross references between the sections, it reports
+an error and returns a non-zero exit status. The @code{NOCROSSREFS}
+command uses output section names, defined in the @code{SECTIONS}
+command. It does not use the names of input sections.
@end table
-@node Machine Dependent, BFD, Commands, Top
+@ifset GENERIC
+@node Machine Dependent
@chapter Machine Dependent Features
@cindex machine dependencies
-@code{gld} has additional features on some platforms; the following
-sections describe them. Machines where @code{gld} has no additional
+@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{gld} and the H8/300
-* i960:: @code{gld} and the Intel 960 family
-* m68k:: @code{gld} and the Motorola 68000 family
-* m88k:: @code{gld} and the Motorola 880x0 family
+* H8/300:: @code{ld} and the H8/300
+* i960:: @code{ld} and the Intel 960 family
@end menu
+@end ifset
-@node H8/300, i960, Machine Dependent, Machine Dependent
-@section @code{gld} and the H8/300
+@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{gld} can perform these global optimizations when
-you specify the @samp{-relax} command-line option.
+For the H8/300, @code{ld} can perform these global optimizations when
+you specify the @samp{--relax} command-line option.
@table @emph
+@cindex relaxing on H8/300
@item relaxing address modes
-@cindex relaxing on i960
-@code{gld} finds all @code{jsr} and @code{jmp} instructions whose
+@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.
+@cindex synthesizing on H8/300
@item synthesizing instructions
-@cindex synthesizing on i960
@c FIXME: specifically mov.b, or any mov instructions really?
-@code{gld} finds all @code{mov.b} instructions which use the
+@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
-
-@node i960, m68k, H8/300, Machine Dependent
-@section @code{gld} and the Intel 960 family
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
+@ifclear GENERIC
+@ifset Hitachi
+@c This stuff is pointless to say unless you're especially concerned
+@c with Hitachi chips; don't enable it for generic case, please.
+@node Hitachi
+@chapter @code{ld} and other Hitachi chips
+
+@code{ld} also supports the H8/300H, the H8/500, and the Hitachi SH. No
+special features, commands, or command-line options are required for
+these chips.
+@end ifset
+@end ifclear
+
+@ifset I960
+@ifclear GENERIC
+@raisesections
+@end ifclear
+@node i960
+@section @code{ld} and the Intel 960 family
@cindex i960 support
-@menu
-* i960-arch:: Linking for a Specific i960 Architecture
-* i960-emulation:: Emulating Other i960 Linkers
-* i960-commands:: Command Language Extensions for i960
-@end menu
-@node i960-arch, i960-emulation, i960, i960
-@subsection Linking for a Specific i960 Architecture
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
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{gld} command line included @w{@samp{-ACA}} as
+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 @code{-L}) for a library with
+paths, and in any paths you specify with @samp{-L}) for a library with
the names
-@example
+
+@smallexample
+@group
try
libtry.a
tryca
libtryca.a
-@end example
+@end group
+@end smallexample
+
@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 @code{-A} more than once on a command line, since
+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{@code{-l}}
+use will add another pair of name variants to search for when @w{@samp{-l}}
specifies a library.
-@node i960-emulation, i960-commands, i960-arch, i960
-@subsection Emulating Other i960 Linkers
-You can set the @code{LDEMULATION} environment variable
-(@pxref{Environment,,Environment Variables}) to make
-@code{gld} more compatible with two older Intel 960 linkers:
-
-@table @code
-@item LDEMULATION=gld960
-@kindex gld960
-@kindex G960LIB
-@kindex G960BASE
-@cindex i960
-Emulate the Intel port of the older @code{gld} for the i960
-architectures. The default library search paths are taken from two
-other environment variables, @code{G960LIB} and @code{G960BASE}. The
-default architecture is @code{i960}. The default output format is set
-to @code{b.out.big}, and in fact the default output file name (if
-@code{-o} is not specified) is @code{b.out}, to reflect this variant
-format, for this emulation.
-
-@kindex GNU960
-This emulation can behave slightly differently depending on the setting
-of the @code{gld} compile-time switch @code{GNU960}. If @code{gld} is
-compiled with @code{GNU960} defined, then an additional environment
-variable---@code{GNUTARGET}---is available; its value, if available,
-specifies some other default output format than @code{b.out.big}.
-
-@item LDEMULATION=lnk960
-@kindex lnk960
-@cindex i960
-@cindex Architectures, i960 family
-Emulate the Intel linker @code{lnk960}. The default output format is
-@code{coff-Intel-big}. With this emulation, @code{gld}
-supports the additional script commands @code{HLL} and @code{SYSLIB} for
-specification of library archives. This is the only emulation with
-extensive support for the @code{-A} (architecture) command-line option.
-By default, the architecture @code{CORE} is assumed, but you can choose
-additional features from the i960 architecture family by using one of
-the following with @code{-A} (or by using the @code{OUTPUT_ARCH} command
-from a script):
-@example
-CORE
-KB
-SB
-MC
-XA
-CA
-KA
-SA
-@end example
-
-The default libraries are chosen with some attention to the architecture
-selected; the core library @file{cg} is always included, but the library
-@code{fpg} is also used if you've specified any of the architectures
-@code{KA}, @code{SA}, or @code{CA}.
-
-@kindex GNU960
-Like @code{gld960}, this emulation uses additional environment variables
-to set the default library search paths. Also like @code{gld960}, the
-behavior of this emulation is slightly different depending on whether
-@code{gld} itself was compiled with @code{GNU960} defined.
-
-@kindex G960BASE
-@kindex G960LIB
-@kindex I960BASE
-If your @code{gld} was compiled with @code{GNU960} defined, the default
-paths are taken from all three of @code{G960LIB}, @code{G960BASE}, and
-@code{I960BASE}. For the first two, paths you supply are automatically
-suffixed with @samp{/lib/libcoff}; for the last, your path is
-automatically suffixed with @samp{/lib}.
-
-If your @code{gld} was @emph{not} compiled with @code{GNU960} defined,
-the default paths are taken from @code{I960BASE}, and @code{G960BASE} is
-only consulted if @code{I960BASE} is undefined. In this case
-@code{G960LIB} is not used at all.
-@end table
-
-@node i960-commands, , i960-emulation, i960
-@subsection Command Language Extensions for i960
-
-@code{gld} understands the following additional commands when
-@code{LDEMULATION} is set to @samp{lnk960}:
-
-@table @code
-@item HLL ( @var{file}, @var{file}, @dots{} )
-@itemx HLL ( @var{file} @var{file} @dots{} )
-@itemx HLL ( )
-@kindex HLL ( @var{files} )
-Include ``high-level libraries'' or archives as input files in the link.
-Using @code{HLL(@var{file}} in a linker script is equivalent to
-including @code{-l}@var{file} on the command line.
-
-@cindex @code{lnk960} command @code{HLL}
-The @code{HLL} command is only supported when @code{gld} emulates
-@code{lnk960}, as specified by the @code{LDEMULATION} environment
-variable.
-
-@item SYSLIB ( @var{file}, @var{file}, @dots{} )
-@itemx SYSLIB ( @var{file} @var{file} @dots{} )
-@kindex SYSLIB ( @var{file}, @var{file}, @dots{} )
-Use the named @var{file}s as binary input files, searching for them in
-the same list of paths as archives.
-
-@cindex @code{lnk960} command @code{SYSLIB}
-The @code{SYSLIB} command is only supported when @code{gld} emulates
-@code{lnk960}, as specified by the @code{LDEMULATION} environment
-variable.
-
-@end table
-
-@node m68k, m88k, i960, Machine Dependent
-@section @code{gld} and the Motorola 680x0 family
-
-@cindex m68k support
-You can set the environment variable @code{LDEMULATION} to @samp{gld68k}
-for closer compatibility with the older GNU linker on Motorola 680x0
-platforms. This emulation is a variant of the @code{gld} emulation; it
-only differs in specifically setting the default BFD machine as
-@code{m68k}. @xref{Environment,,Environment Variables}.
-
-@node m88k, , m68k, Machine Dependent
-@section @code{gld} and the Motorola 880x0 family
-
-@cindex m88k support
-@kindex gldm88kbcs
-You can configure the linker to conform to the Motorola 88K BCS by
-setting the environment variable @code{LDEMULATION} to @samp{gldm88kbcs}.
-This sets the output format to @code{m88kbcs} and the architecture to
-@code{m88k}. Default library search paths are
-@example
-/lib
-/usr/lib
-/usr/local/lib
-@end example
-
-For other settings of @code{LDEMULATION}, consult
-@ref{Environment,,Environment Variables}.
-
-@node BFD, MRI, Machine Dependent, Top
+@cindex @code{--relax} on i960
+@cindex relaxing on i960
+@code{ld} supports the @samp{--relax} option for the i960 family. If
+you specify @samp{--relax}, @code{ld} finds all @code{balx} and
+@code{calx} instructions whose targets are within 24 bits, and turns
+them into 24-bit program-counter relative @code{bal} and @code{cal}
+instructions, respectively. @code{ld} also turns @code{cal}
+instructions into @code{bal} instructions when it determines that the
+target subroutine is a leaf routine (that is, the target subroutine does
+not itself call any subroutines).
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
+@ifclear SingleFormat
+@node BFD
@chapter BFD
@cindex back end
@cindex object file management
+@cindex object formats available
+@kindex objdump -i
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}
+it to the library. To conserve runtime memory, however, the linker and
+associated tools are usually configured to support only a subset of the
+object file formats available. 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
+list all the formats available for your configuration.
@cindex BFD requirements
@cindex requirements for BFD
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
+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
-* BFD information loss:: Information Loss
-* Mechanism:: Mechanism
@end menu
-@node BFD outline, BFD information loss, BFD, BFD
+@node BFD outline
@section How it works: an outline of BFD
@cindex opening object files
-When an object file is opened, BFD subroutines automatically
-determine the format of the input object file, and build a descriptor in
-memory with pointers to routines that will be used to access elements of
-the object file's data structures.
-
-As different information from the the object files is required
-BFD reads from different sections of the file and processes them.
-For example a very common operation for the linker is processing symbol
-tables. Each BFD back end provides a routine for converting
-between the object file's representation of symbols and an internal
-canonical format. When the linker asks for the symbol table of an object
-file, it calls through the memory pointer to the relevant BFD
-back end routine which reads and converts the table into a canonical
-form. The linker then operates upon the common form. When the link is
-finished and the linker writes the symbol table of the output file,
-another BFD back end routine is called which takes the newly
-created symbol table and converts it into the chosen output format.
-
-@node BFD information loss, Mechanism, BFD outline, BFD
-@section Information Loss
-@emph{Information can be lost during output.} The output formats
-supported by BFD do not provide identical facilities, and
-information which may be described in one form has nowhere to go in
-another format. One example of this is alignment information in
-@code{b.out}. There is nowhere in an @code{a.out} format file to store
-alignment information on the contained data, so when a file is linked
-from @code{b.out} and an @code{a.out} image is produced, alignment
-information will not propagate to the output file. (The linker will
-still use the alignment information internally, so the link is performed
-correctly).
-
-Another example is COFF section names. COFF files may contain an
-unlimited number of sections, each one with a textual section name. If
-the target of the link is a format which does not have many sections (eg
-@code{a.out}) or has sections without names (eg the Oasys format) the
-link cannot be done simply. You can circumvent this problem by
-describing the desired input-to-output section mapping with the command
-language.
-
-@emph{Information can be lost during canonicalization.} The BFD
-internal canonical form of the external formats is not exhaustive; there
-are structures in input formats for which there is no direct
-representation internally. This means that the BFD back ends
-cannot maintain all possible data richness through the transformation
-between external to internal and back to external formats.
-
-This limitation is only a problem when using the linker to read one
-format and write another. Each BFD back end is responsible for
-maintaining as much data as possible, and the internal BFD
-canonical form has structures which are opaque to the BFD core,
-and exported only to the back ends. When a file is read in one format,
-the canonical form is generated for BFD and the linker. At the
-same time, the back end saves away any information which may otherwise
-be lost. If the data is then written back in the same format, the back
-end routine will be able to use the canonical form provided by the
-BFD core as well as the information it prepared earlier. Since
-there is a great deal of commonality between back ends, this mechanism
-is very useful. There is no information lost for this reason when
-linking big endian COFF to little endian COFF, or from @code{a.out} to
-@code{b.out}. When a mixture of formats is linked, the information is
-only lost from the files whose format differs from the destination.
-
-@node Mechanism, , BFD information loss, BFD
-@section Mechanism
-The greatest potential for loss of information is when there is least
-overlap between the information provided by the source format, that
-stored by the canonical format, and the information needed by the
-destination format. A brief description of the canonical form may help
-you appreciate what kinds of data you can count on preserving across
-conversions.
-@cindex BFD canonical format
-@cindex internal object-file format
+@include bfdsumm.texi
+@end ifclear
-@table @emph
-@item files
-Information on target machine architecture, particular implementation
-and format type are stored on a per-file basis. Other information
-includes a demand pageable bit and a write protected bit. Note that
-information like Unix magic numbers is not stored here---only the magic
-numbers' meaning, so a @code{ZMAGIC} file would have both the demand pageable
-bit and the write protected text bit set.
-
-The byte order of the target is stored on a per-file basis, so that big-
-and little-endian object files may be linked with one another.
-
-@item sections
-Each section in the input file contains the name of the section, the
-original address in the object file, various flags, size and alignment
-information and pointers into other BFD data structures.
-
-@item symbols
-Each symbol contains a pointer to the object file which originally
-defined it, its name, its value, and various flag bits. When a
-BFD back end reads in a symbol table, the back end relocates all
-symbols to make them relative to the base of the section where they were
-defined. This ensures that each symbol points to its containing
-section. Each symbol also has a varying amount of hidden data to contain
-private data for the BFD back end. Since the symbol points to the
-original file, the private data format for that symbol is accessible.
-@code{gld} can operate on a collection of symbols of wildly different
-formats without problems.
-
-Normal global and simple local symbols are maintained on output, so an
-output file (no matter its format) will retain symbols pointing to
-functions and to global, static, and common variables. Some symbol
-information is not worth retaining; in @code{a.out} type information is
-stored in the symbol table as long symbol names. This information would
-be useless to most COFF debuggers and may be thrown away with
-appropriate command line switches. (The GNU debugger @code{gdb} does
-support @code{a.out} style debugging information in COFF).
-
-There is one word of type information within the symbol, so if the
-format supports symbol type information within symbols (for example COFF,
-IEEE, Oasys) and the type is simple enough to fit within one word
-(nearly everything but aggregates) the information will be preserved.
-
-@item relocation level
-Each canonical BFD relocation record contains a pointer to the symbol to
-relocate to, the offset of the data to relocate, the section the data
-is in and a pointer to a relocation type descriptor. Relocation is
-performed effectively by message passing through the relocation type
-descriptor and symbol pointer. It allows relocations to be performed
-on output data using a relocation method only available in one of the
-input formats. For instance, Oasys provides a byte relocation format.
-A relocation record requesting this relocation type would point
-indirectly to a routine to perform this, so the relocation may be
-performed on a byte being written to a COFF file, even though 68k COFF
-has no such relocation type.
-@c FIXME why specific reference to 68K above?
-
-@item line numbers
-Object formats can contain, for debugging purposes, some form of mapping
-between symbols, source line numbers, and addresses in the output file.
-These addresses have to be relocated along with the symbol information.
-Each symbol with an associated list of line number records points to the
-first record of the list. The head of a line number list consists of a
-pointer to the symbol, which allows divination of the address of the
-function whose line number is being described. The rest of the list is
-made up of pairs: offsets into the section and line numbers. Any format
-which can simply derive this information can pass it successfully
-between formats (COFF, IEEE and Oasys).
-@end table
+@node Reporting Bugs
+@chapter Reporting Bugs
+@cindex bugs in @code{ld}
+@cindex reporting bugs in @code{ld}
+
+Your bug reports play an essential role in making @code{ld} reliable.
+
+Reporting a bug may help you by bringing a solution to your problem, or
+it may not. But in any case the principal function of a bug report is
+to help the entire community by making the next version of @code{ld}
+work better. Bug reports are your contribution to the maintenance of
+@code{ld}.
-@node MRI, Index, BFD, Top
+In order for a bug report to serve its purpose, you must include the
+information that enables us to fix the bug.
+
+@menu
+* Bug Criteria:: Have you found a bug?
+* Bug Reporting:: How to report bugs
+@end menu
+
+@node Bug Criteria
+@section Have you found a bug?
+@cindex bug criteria
+
+If you are not sure whether you have found a bug, here are some guidelines:
+
+@itemize @bullet
+@cindex fatal signal
+@cindex linker crash
+@cindex crash of linker
+@item
+If the linker gets a fatal signal, for any input whatever, that is a
+@code{ld} bug. Reliable linkers never crash.
+
+@cindex error on valid input
+@item
+If @code{ld} produces an error message for valid input, that is a bug.
+
+@cindex invalid input
+@item
+If @code{ld} does not produce an error message for invalid input, that
+may be a bug. In the general case, the linker can not verify that
+object files are correct.
+
+@item
+If you are an experienced user of linkers, your suggestions for
+improvement of @code{ld} are welcome in any case.
+@end itemize
+
+@node Bug Reporting
+@section How to report bugs
+@cindex bug reports
+@cindex @code{ld} bugs, reporting
+
+A number of companies and individuals offer support for @sc{gnu}
+products. If you obtained @code{ld} from a support organization, we
+recommend you contact that organization first.
+
+You can find contact information for many support companies and
+individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
+distribution.
+
+In any event, we also recommend that you send bug reports for @code{ld}
+to @samp{bug-gnu-utils@@prep.ai.mit.edu}.
+
+The fundamental principle of reporting bugs usefully is this:
+@strong{report all the facts}. If you are not sure whether to state a
+fact or leave it out, state it!
+
+Often people omit facts because they think they know what causes the
+problem and assume that some details do not matter. Thus, you might
+assume that the name of a symbol you use in an example does not matter.
+Well, probably it does not, but one cannot be sure. Perhaps the bug is
+a stray memory reference which happens to fetch from the location where
+that name is stored in memory; perhaps, if the name were different, the
+contents of that location would fool the linker into doing the right
+thing despite the bug. Play it safe and give a specific, complete
+example. That is the easiest thing for you to do, and the most helpful.
+
+Keep in mind that the purpose of a bug report is to enable us to fix the bug if
+it is new to us. Therefore, always write your bug reports on the assumption
+that the bug has not been reported previously.
+
+Sometimes people give a few sketchy facts and ask, ``Does this ring a
+bell?'' Those bug reports are useless, and we urge everyone to
+@emph{refuse to respond to them} except to chide the sender to report
+bugs properly.
+
+To enable us to fix the bug, you should include all these things:
+
+@itemize @bullet
+@item
+The version of @code{ld}. @code{ld} announces it if you start it with
+the @samp{--version} argument.
+
+Without this, we will not know whether there is any point in looking for
+the bug in the current version of @code{ld}.
+
+@item
+Any patches you may have applied to the @code{ld} source, including any
+patches made to the @code{BFD} library.
+
+@item
+The type of machine you are using, and the operating system name and
+version number.
+
+@item
+What compiler (and its version) was used to compile @code{ld}---e.g.
+``@code{gcc-2.7}''.
+
+@item
+The command arguments you gave the linker to link your example and
+observe the bug. To guarantee you will not omit something important,
+list them all. A copy of the Makefile (or the output from make) is
+sufficient.
+
+If we were to try to guess the arguments, we would probably guess wrong
+and then we might not encounter the bug.
+
+@item
+A complete input file, or set of input files, that will reproduce the
+bug. It is generally most helpful to send the actual object files,
+uuencoded if necessary to get them through the mail system. Making them
+available for anonymous FTP is not as good, but may be the only
+reasonable choice for large object files.
+
+If the source files were assembled using @code{gas} or compiled using
+@code{gcc}, then it may be OK to send the source files rather than the
+object files. In this case, be sure to say exactly what version of
+@code{gas} or @code{gcc} was used to produce the object files. Also say
+how @code{gas} or @code{gcc} were configured.
+
+@item
+A description of what behavior you observe that you believe is
+incorrect. For example, ``It gets a fatal signal.''
+
+Of course, if the bug is that @code{ld} gets a fatal signal, then we
+will certainly notice it. But if the bug is incorrect output, we might
+not notice unless it is glaringly wrong. You might as well not give us
+a chance to make a mistake.
+
+Even if the problem you experience is a fatal signal, you should still
+say so explicitly. Suppose something strange is going on, such as, your
+copy of @code{ld} is out of synch, or you have encountered a bug in the
+C library on your system. (This has happened!) Your copy might crash
+and ours would not. If you told us to expect a crash, then when ours
+fails to crash, we would know that the bug was not happening for us. If
+you had not told us to expect a crash, then we would not be able to draw
+any conclusion from our observations.
+
+@item
+If you wish to suggest changes to the @code{ld} source, send us context
+diffs, as generated by @code{diff} with the @samp{-u}, @samp{-c}, or
+@samp{-p} option. Always send diffs from the old file to the new file.
+If you even discuss something in the @code{ld} source, refer to it by
+context, not by line number.
+
+The line numbers in our development sources will not match those in your
+sources. Your line numbers would convey no useful information to us.
+@end itemize
+
+Here are some things that are not necessary:
+
+@itemize @bullet
+@item
+A description of the envelope of the bug.
+
+Often people who encounter a bug spend a lot of time investigating
+which changes to the input file will make the bug go away and which
+changes will not affect it.
+
+This is often time consuming and not very useful, because the way we
+will find the bug is by running a single example under the debugger
+with breakpoints, not by pure deduction from a series of examples.
+We recommend that you save your time for something else.
+
+Of course, if you can find a simpler example to report @emph{instead}
+of the original one, that is a convenience for us. Errors in the
+output will be easier to spot, running under the debugger will take
+less time, and so on.
+
+However, simplification is not vital; if you do not want to do this,
+report the bug anyway and send us the entire test case you used.
+
+@item
+A patch for the bug.
+
+A patch for the bug does help us if it is a good one. But do not omit
+the necessary information, such as the test case, on the assumption that
+a patch is all we need. We might see problems with your patch and decide
+to fix the problem another way, or we might not understand it at all.
+
+Sometimes with a program as complicated as @code{ld} it is very hard to
+construct an example that will make the program follow a certain path
+through the code. If you do not send us the example, we will not be
+able to construct one, so we will not be able to verify that the bug is
+fixed.
+
+And if we cannot understand what bug you are trying to fix, or why your
+patch should be an improvement, we will not install it. A test case will
+help us to understand.
+
+@item
+A guess about what the bug is or what it depends on.
+
+Such guesses are usually wrong. Even we cannot guess right about such
+things without first using the debugger to find the facts.
+@end itemize
+
+@node MRI
@appendix MRI Compatible Script Files
@cindex MRI compatibility
To aid users making the transition to @sc{gnu} @code{ld} from the MRI
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.
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)
+@item ABSOLUTE @var{secname}
+@itemx ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
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
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
-{LOAD}) to resolve addresses in the output file.
+@code{LOAD}) to resolve addresses in the output file.
-@item ALIAS @var{out-secname}, @var{in-secname}
@cindex @code{ALIAS} (MRI)
+@item ALIAS @var{out-secname}, @var{in-secname}
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{ALIGN} (MRI)
+@item ALIGN @var{secname} = @var{expression}
+Align the section called @var{secname} to @var{expression}. The
+@var{expression} should be a power of two.
+
@cindex @code{BASE} (MRI)
+@item BASE @var{expression}
Use the value of @var{expression} as the lowest address (other than
absolute addresses) in the output file.
+@cindex @code{CHIP} (MRI)
@item CHIP @var{expression}
@itemx CHIP @var{expression}, @var{expression}
-@cindex @code{CHIP} (MRI)
-This command does nothing whatever; it's only accepted for compatibility.
+This command does nothing; it is accepted only for compatibility.
-@item END
@cindex @code{END} (MRI)
+@item END
This command does nothing whatever; it's only accepted for compatibility.
-@item FORMAT @var{output-format}
@cindex @code{FORMAT} (MRI)
+@item FORMAT @var{output-format}
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}
@samp{COFF}
@end enumerate
-@item LIST @var{@dots{}}
@cindex @code{LIST} (MRI)
+@item LIST @var{anything}@dots{}
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 whatsoever on the
-same line, with no change in its effect.)
+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)
+@item LOAD @var{filename}
+@itemx LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
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)
+@item NAME @var{output-name}
@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}.
+@cindex @code{ORDER} (MRI)
@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 whatever
-order they first appear in the input files. In an MRI-compatible
-script, you can override this with the @code{ORDER} command. The
+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.
+@cindex @code{PUBLIC} (MRI)
@item PUBLIC @var{name}=@var{expression}
@itemx PUBLIC @var{name},@var{expression}
@itemx PUBLIC @var{name} @var{expression}
-@cindex @code{PUBLIC} (MRI)
-This command supplies a value (@var{expression}) for an external symbol
+Supply a value (@var{expression}) for external symbol
@var{name} used in the linker input files.
+@cindex @code{SECT} (MRI)
@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, , MRI, Top
+@node Index
@unnumbered Index
@printindex cp
\centerline{{\sl\fontname\tensl\/}}
\centerline{are used for emphasis.}\vfill}
\page\colophon
-% Blame: pesch@cygnus.com, 28mar91.
+% Blame: doc@cygnus.com, 28mar91.
@end tex
projects / deliverable / binutils-gdb.git / blobdiff