\input texinfo
@setfilename ld.info
@syncodeindex ky cp
-@c @include configdoc.texi
+@include configdoc.texi
+@c (configdoc.texi is generated by the Makefile)
@c @smallbook
-@c @cropmarks
@ifinfo
@format
@ifinfo
This file documents the GNU linker LD.
-Copyright (C) 1991, 1992, 1993 Free Software Foundation, Inc.
+Copyright (C) 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
@subtitle The GNU linker
@sp 1
@subtitle @code{ld} version 2
-@subtitle March 1993
+@subtitle January 1994
@author Steve Chamberlain and Roland Pesch
@author Cygnus Support
@page
\hfill Cygnus Support\par
\hfill steve\@cygnus.com, pesch\@cygnus.com\par
\hfill {\it Using LD, the GNU linker}\par
-\hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com), March 1993.\par
+\hfill Edited by Jeffrey Osier (jeffrey\@cygnus.com)\par
+\hfill and Roland Pesch (pesch\@cygnus.com)\par
}
\global\parindent=0pt % Steve likes it this way.
@end tex
@vskip 0pt plus 1filll
-Copyright @copyright{} 1991, 1992, 1993 Free Software Foundation, Inc.
+Copyright @copyright{} 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
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
@c FIXME! -relax only avail h8/300, i960. Conditionals screwed in examples.
@smallexample
-ld [-o @var{output} ] @var{objfile}@dots{}
+ld [ -o @var{output} ] @var{objfile}@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 ] [ -G @var{size} ] [ -i ]
- [ -l@var{ar} ] [ -L@var{searchdir} ] [ -M ] [ -Map @var{mapfile} ]
- [ -m @var{emulation} ] [ -N | -n ] [ -noinhibit-exec ]
- [ -oformat @var{output-format} ] [ -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] [-v] [ -X ] [-x ]
- [ -y@var{symbol} ]
+ [ -format @var{input-format} ] [ -g ] [ -G @var{size} ] [ -help ]
+ [ -i ] [ -l@var{archive} ] [ -L@var{searchdir} ] [ -M ]
+ [ -Map @var{mapfile} ] [ -m @var{emulation} ] [ -N | -n ]
+ [ -noinhibit-exec ] [ -oformat @var{output-format} ]
+ [ -R @var{filename} ] [ -relax ] [ -retain-symbols-file @var{filename} ]
+ [ -r | -Ur ] [ -S ] [ -s ] [ -sort-common ] [ -stats ]
+ [ -T @var{commandfile} ]
+ [ -Ttext @var{org} ] [ -Tdata @var{org} ]
+ [ -Tbss @var{org} ] [ -t ] [ -u @var{symbol}] [-V] [-v] [ -version ]
+ [ -warn-common ] [ -y @var{symbol} ] [ -X ] [-x ]
@end smallexample
This plethora of command-line options may seem intimidating, but in
an @var{objfile} argument may not be placed between an option 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 @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}.
+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}.
-Option arguments must either follow the option letter without intervening
+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{objfile}@dots{}
-The object files 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
@ifset I960
@cindex architectures
@kindex -A@var{arch}
@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{ld} 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.
-(You can list the available binary formats with @samp{objdump -i}.)
-@w{@samp{-format @var{input-format}}} has the same effect, as does the
-script command @code{TARGET}. @xref{BFD}.
+@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}.) @w{@samp{-format @var{input-format}}}
+has the same effect, as does the script command @code{TARGET}.
+@xref{BFD}.
You may want to use this option if you are linking files with an unusual
binary format. You can also use @samp{-b} to switch formats explicitly (when
@xref{Environment}.
@end ifset
You can also define the input
-format from a script, using the command @code{TARGET}; see @ref{Other
+format from a script, using the command @code{TARGET}; see @ref{Option
Commands}.
@end ifclear
compatibility with other linkers. They
assign space to common symbols even if a relocatable output file is
specified (with @samp{-r}). The script command
-@code{FORCE_COMMON_ALLOCATION} has the same effect. @xref{Other
+@code{FORCE_COMMON_ALLOCATION} has the same effect. @xref{Option
Commands}.
@cindex symbols, from command line
Ignored. Some older linkers used this option throughout a compilation
toolchain for specifying object-file format for both input and output
object files. The mechanisms @code{ld} uses for this purpose (the
-@samp{-b} or @samp{-format} options for input files, the @code{TARGET}
-command in linker scripts for output files, the @code{GNUTARGET}
-environment variable) are more flexible, but @code{ld} accepts the
-@samp{-F} option for compatibility with scripts written to call the old
-linker.
+@samp{-b} or @samp{-format} options for input files, @samp{-oformat}
+option or the @code{TARGET} command in linker scripts for output files,
+the @code{GNUTARGET} environment variable) are more flexible, but
+@code{ld} accepts the @samp{-F} option for compatibility with scripts
+written to call the old linker.
@kindex -format
@item -format @var{input-format}
Set the maximum size of objects to be optimized using the GP register to
@var{size} under MIPS ECOFF. Ignored for other object file formats.
+@cindex help
+@cindex usage
+@kindex -help
+@item -help
+Print a summary of the command-line options on the standard output and exit.
+
@kindex -i
@cindex incremental link
@item -i
Perform an incremental link (same as option @samp{-r}).
@cindex archive files, from cmd line
-@kindex -l@var{ar}
+@kindex -l@var{archive}
@item -l@var{ar}
-Add archive file @var{ar} to the list of files to link. This
+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}
+path-list for occurrences of @code{lib@var{ar}.a} for every @var{archive}
specified.
@cindex search directory, from cmd line
@kindex -L@var{dir}
@item -L@var{searchdir}
+@itemx -L @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.
@itemx -m @var{emulation}
Emulate the @var{emulation} linker. You can list the available
emulations with the @samp{-V} option. The
-default is the system for which you configured @code{ld}.
+default depends on how your @code{ld} was configured.
@kindex -N
@cindex read/write from cmd line
not page-align the data segment. If the output format supports Unix
style magic numbers, mark the output as @code{OMAGIC}.
-@item -n
@kindex -n
@cindex read-only text
@kindex NMAGIC
+@item -n
Set the text segment to be read only, and mark the output as
@code{NMAGIC} if possible.
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.
+@ifclear SingleFormat
@kindex -oformat
@item -oformat @var{output-format}
-Specify the binary format for the output object file. You don't usually
-need to specify this, as @code{ld} is configured to produce as a default
-output format the most usual format on each machine.
-@var{output-format} is a text string, the name of a particular format
-supported by the BFD libraries. (You can list the available binary
-formats with @samp{objdump -i}.) The script command
-@code{OUTPUT_FORMAT} can also specify the output format, but this option
-overrides it. @xref{BFD}.
+@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
@item -R @var{filename}
@kindex -R @var{file}
@cindex symbol-only input
-On some platforms, this 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.
+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.
+@item -relax
+An option with machine dependent effects.
+@ifset GENERIC
+Currently this option is only supported on the H8/300 and the Intel 960.
+@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, use option performs global optimizations that
+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
+
+@item -retain-symbols-file @var{filename}
+@cindex retaining specified symbols
+@cindex stripping all but some symbols
+@cindex symbols, retaining selectively
+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}.
-@item -r
@cindex partial link
@cindex relocatable output
@kindex -r
+@item -r
Generate relocatable output---i.e., generate an output file that can in
turn serve as input to @code{ld}. This is often called @dfn{partial
linking}. As a side effect, in environments that support standard Unix
linking C++ programs, this option @emph{will not} resolve references to
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
+@item -S
Omit debugger symbol information (but not all symbols) from the output file.
-@item -s
@kindex -s
@cindex strip all symbols
+@item -s
Omit all symbol information from the output file.
-@item -Tbss @var{bssorg}
-@kindex -Tbss @var{bssorg}
-@itemx -Tdata @var{dataorg}
-@kindex -Tdata @var{dataorg}
-@itemx -Ttext @var{textorg}
-@kindex -Ttext @var{textorg}
+@item -sort-common
+Normally, when @code{ld} places the global common symbols in the
+appropriate output sections, it sorts them by size. First come all the
+one byte symbols, then all the two bytes, then all the four bytes, and
+then everything else. This is to prevent gaps between symbols due to
+alignment constraints. This option disables that sorting.
+
+@item -stats
+Compute and display statistics about the operation of the linker,
+such as execution time and memory usage.
+
+@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.
@itemx -T@var{commandfile}
@kindex -T @var{script}
@cindex script files
-Read link commands from the file
-@var{commandfile}. These commands completely override @code{ld}'s
-default link format (rather than adding to it); @var{commandfile} must
-specify everything necessary to describe the target format.
-@xref{Commands}.
-If @var{commandfile} does not exist, @code{ld} looks for it in the directories
-specified by any @samp{-L} options.
+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. @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.
-You may also include a script of link commands directly in the command
-line by bracketing it between @samp{@{} and @samp{@}}.
-
-@item -t
@kindex -t
@cindex verbose
@cindex input files, displaying
+@item -t
Print the names of the input files as @code{ld} processes them.
-@item -u @var{sym}
-@kindex -u @var{sym}
+@item -u @var{symbol}
+@kindex -u @var{symbol}
@cindex undefined symbol
-Force @var{sym} to be entered in the output file as an undefined symbol.
+Force @var{symbol} to be entered in the output file as an undefined symbol.
Doing this may, for example, trigger linking of additional modules from
standard libraries. @samp{-u} may be repeated with different option
arguments to enter additional undefined symbols.
@c Nice idea, but no such command: This option is equivalent
@c to the @code{EXTERN} linker command.
-@item -Ur
@kindex -Ur
@cindex constructors
+@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{will} resolve references to constructors, unlike @samp{-r}.
+@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.
-@item -V
@kindex -V
@cindex version
-Display the version number for @code{ld} and list the supported emulations.
-Print which input files can and can not be opened.
+@item -V
+Display the version number for @code{ld} and list the linker emulations
+supported. Display which input files can and cannot be opened.
-@item -v
@kindex -v
@cindex version
+@item -v
Display the version number for @code{ld}.
-Print which input files can and can not be opened.
-@item -X
+@item -version
+@kindex -version
+Display the version number for @code{ld} and exit.
+
+@item -warn-common
+@kindex -warn-comon
+@cindex warnings, on combining symbols
+@cindex combining symbols, warnings on
+Warn when a common symbol is combined with another common symbol or with
+a symbol definition. Unix linkers allow this somewhat sloppy practice,
+but linkers on some other operating systems do not. This option allows
+you to find potential problems from combining global symbols.
+Unfortunately, some C libraries use this practice, so you may get some
+warnings about symbols in the libraries as well as in your programs.
+
+There are three kinds of global symbols, illustrated here by C examples:
+
+@table @samp
+@item int i = 1;
+A definition, which goes in the initialized data section of the output
+file.
+
+@item extern int i;
+An undefined reference, which does not allocate space.
+There must be either a definition or a common symbol for the
+variable somewhere.
+
+@item int i;
+A common symbol. If there are only (one or more) common symbols for a
+variable, it goes in the uninitialized data area of the output file.
+The linker merges multiple common symbols for the same variable into a
+single symbol. If they are of different sizes, it picks the largest
+size. The linker turns a common symbol into a declaration, if there is
+a definition of the same variable.
+@end table
+
+The @samp{-warn-common} option can produce five kinds of warnings. Each
+warning consists of a pair of lines: the first describes the symbol just
+encountered, and the second describes the previous symbol encountered
+with the same name. One or both of the two symbols will be a common
+symbol.
+
+@enumerate
+@item
+Turning a common symbol into a reference, because there is already a
+definition for the symbol.
+@smallexample
+@var{file}(@var{section}): warning: common of `@var{symbol}'
+ overridden by definition
+@var{file}(@var{section}): warning: defined here
+@end smallexample
+
+@item
+Turning a common symbol into a reference, because a later definition for
+the symbol is encountered. This is the same as the previous case,
+except that the symbols are encountered in a different order.
+@smallexample
+@var{file}(@var{section}): warning: definition of `@var{symbol}'
+ overriding common
+@var{file}(@var{section}): warning: common is here
+@end smallexample
+
+@item
+Merging a common symbol with a previous same-sized common symbol.
+@smallexample
+@var{file}(@var{section}): warning: multiple common
+ of `@var{symbol}'
+@var{file}(@var{section}): warning: previous common is here
+@end smallexample
+
+@item
+Merging a common symbol with a previous larger common symbol.
+@smallexample
+@var{file}(@var{section}): warning: common of `@var{symbol}'
+ overridden by larger common
+@var{file}(@var{section}): warning: larger common is here
+@end smallexample
+
+@item
+Merging a common symbol with a previous smaller common symbol. This is
+the same as the previous case, except that the symbols are
+encountered in a different order.
+@smallexample
+@var{file}(@var{section}): warning: common of `@var{symbol}'
+ overriding smaller common
+@var{file}(@var{section}): warning: smaller common is here
+@end smallexample
+@end enumerate
+
@kindex -X
@cindex local symbols, deleting
@cindex L, deleting symbols beginning
+@item -X
If @samp{-s} or @samp{-S} is also specified, delete only local symbols
beginning with @samp{L}.
-@item -x
@kindex -x
@cindex deleting local symbols
+@item -x
If @samp{-s} or @samp{-S} is also specified, delete all local symbols,
not just those beginning with @samp{L}.
-@item -y@var{symbol}
-@kindex -y@var{symbol}
+@item -y @var{symbol}
+@kindex -y @var{symbol}
@cindex symbol tracing
Print the name of each linked file in which @var{symbol} appears. This
option may be given any number of times. On many systems it is necessary
use @samp{-b} (or its synonym @samp{-format}). Its value should be one
of the BFD names for an input format (@pxref{BFD}). If there is no
@code{GNUTARGET} in the environment, @code{ld} uses the natural format
-of the host. If @code{GNUTARGET} is set to @code{default} then BFD attempts to discover the
+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
@item
file formats
@item
-output file format
+output file layout
@item
addresses of sections
@item
You may supply a command file (also known as a link script) to the
linker either explicitly through the @samp{-T} option, or implicitly as
an ordinary file. If the linker opens a file which it cannot recognize
-as a supported object or archive format, it tries to interpret the file
-as a command file.
-
-You can also include a script directly on the @code{ld} command line,
-delimited by the characters @samp{@{} and @samp{@}}.
+as a supported object or archive format, it reports an error.
@menu
* Scripts:: Linker Scripts
* MEMORY:: MEMORY Command
* SECTIONS:: SECTIONS Command
* Entry Point:: The Entry Point
-* Other Commands:: Other Commands
+* Option Commands:: Option Commands
@end menu
@node Scripts
* Operators:: Operators
* Evaluation:: Evaluation
* Assignment:: Assignment: Defining Symbols
-* Built-ins:: Built-In Functions
+* Arithmetic Functions:: Built-In Functions
@end menu
@node Integers
@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
"with a space" = "also with a space" + 10;
@end example
+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
@subsection The Location Counter
@kindex .
@example
SECTIONS
@{
- output :
- @{
- file1(.text)
- . = . + 1000;
- file2(.text)
- . += 1000;
- file3(.text)
- @} = 0x1234;
+ output :
+ @{
+ file1(.text)
+ . = . + 1000;
+ file2(.text)
+ . += 1000;
+ file3(.text)
+ @} = 0x1234;
@}
@end example
@noindent
loaded. The notation @samp{= 0x1234} specifies what data to write in
the gaps (@pxref{Section Options}).
+@iftex
+@vfill
+@end iftex
+
+@need 5000
@node Operators
@subsection Operators
@cindex Operators for arithmetic
When a linker expression is evaluated and assigned to a variable, it is
given either an absolute or a relocatable type. An absolute expression
type is one in which the symbol contains the value that it will have in
-the output file, a relocatable expression type is one in which the
+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
is the last byte of an output section named @code{.data}:
@example
SECTIONS@{ @dots{}
-.data :
- @{
- *(.data)
- _edata = ABSOLUTE(.) ;
- @}
+ .data :
+ @{
+ *(.data)
+ _edata = ABSOLUTE(.) ;
+ @}
@dots{} @}
@end example
then an error results. For example, a script like the following
@example
SECTIONS @{ @dots{}
- text 9+this_isnt_constant :
- @{ @dots{}
- @}
+ text 9+this_isnt_constant :
+ @{ @dots{}
+ @}
@dots{} @}
@end example
@kindex Non constant expression
will cause the error message ``@code{Non constant expression for initial
address}''.
-@node Built-ins
-@subsection Built-In Functions
+@node Arithmetic Functions
+@subsection Arithmetic Functions
@cindex functions in expression language
The command language includes a number of built-in
functions for use in link script expressions.
values:
@example
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
@code{0x8000} boundary after the input sections:
@example
SECTIONS@{ @dots{}
- .data ALIGN(0x2000): @{
- *(.data)
- variable = ALIGN(0x8000);
- @}
+ .data ALIGN(0x2000): @{
+ *(.data)
+ variable = ALIGN(0x8000);
+ @}
@dots{} @}
@end example
@noindent
to set a global symbol @code{begin} to the first location in the
@code{.text} section---but if a symbol called @code{begin} already
existed, its value is preserved:
+
@smallexample
SECTIONS@{ @dots{}
- .text : @{
- begin = DEFINED(begin) ? begin : . ;
- @dots{}
- @}
+ .text : @{
+ begin = DEFINED(begin) ? begin : . ;
+ @dots{}
+ @}
@dots{} @}
@end smallexample
@c What does it return if the section hasn't been allocated? 0?
@example
SECTIONS@{ @dots{}
- .output @{
- .start = . ;
- @dots{}
- .end = . ;
- @}
- symbol_1 = .end - .start ;
- symbol_2 = SIZEOF(.output);
+ .output @{
+ .start = . ;
+ @dots{}
+ .end = . ;
+ @}
+ symbol_1 = .end - .start ;
+ symbol_2 = SIZEOF(.output);
@dots{} @}
@end example
@end table
@node MEMORY
-@section MEMORY Command
+@section Memory Layout
@kindex MEMORY
@cindex regions of memory
@cindex discontinuous memory
available regions, but does move the requested sections into the correct
regions and issue errors when the regions become too full.
-The 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
MEMORY
- @{
- @var{name} (@var{attr}) : ORIGIN = @var{origin}, LENGTH = @var{len}
- @dots{}
- @}
+ @{
+ @var{name} (@var{attr}) : ORIGIN = @var{origin}, LENGTH = @var{len}
+ @dots{}
+ @}
@end example
@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, file names or section
names. Use distinct names to specify multiple regions.
-@item (@var{attr})
+
@cindex memory region attributes
+@item (@var{attr})
is an optional list of attributes, permitted for compatibility with the
AT&T linker but not used by @code{ld} beyond checking that the
attribute list is valid. Valid attribute lists must be made up of the
characters ``@code{LIRWX}''. If you omit the attribute list, you may
omit the parentheses around it as well.
-@item @var{origin}
+
@kindex ORIGIN =
@kindex o =
@kindex org =
+@item @var{origin}
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}.
-@item @var{len}
+abbreviated to @code{org} or @code{o} (but not, for example, @samp{ORG}).
+
@kindex LENGTH =
@kindex len =
@kindex l =
+@item @var{len}
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
@example
MEMORY
- @{
- rom : ORIGIN = 0, LENGTH = 256K
- ram : org = 0x40000000, l = 4M
- @}
+ @{
+ rom : ORIGIN = 0, LENGTH = 256K
+ ram : org = 0x40000000, l = 4M
+ @}
@end example
Once you have defined a region of memory named @var{mem}, you can direct
big for the region, the linker will issue an error message.
@node SECTIONS
-@section SECTIONS Command
+@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 @pxref{Assignment}. They are permitted here as well for
+your convenience in reading the script, so that symbols and the entry
+point can be defined at meaningful points in your output-file layout.
-When no @code{SECTIONS} command is 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
@end menu
@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. Most of
these specifications are optional; the simplest form of a section
definition is
@example
SECTIONS @{ @dots{}
-@var{secname} : @{
- @var{contents}
- @}
+ @var{secname} : @{
+ @var{contents}
+ @}
@dots{} @}
@end example
@cindex naming output sections
@noindent
@var{secname} is the name of the output section, and @var{contents} a
specification of what goes there---for example, a list of input files or
-sections of input files. As you might assume, the whitespace shown is
-optional. You do need the colon @samp{:} and the braces @samp{@{@}},
-however.
+sections of input files (@pxref{Section Placement}). As you might
+assume, the whitespace shown is optional. You do need the colon
+@samp{:} and the braces @samp{@{@}}, however.
@var{secname} must meet the constraints of your output format. In
formats which only support a limited number of sections, such as
@code{.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
+sequence of characters, but any name which does not conform to the standard
@code{ld} symbol name syntax must be quoted.
@xref{Symbols, , Symbol Names}.
-@node Section Contents
-@subsection Section Contents
+@node Section Placement
+@subsection Section Placement
+
@cindex contents of a section
-In a section definition, you can specify the contents of an output section by
-listing particular object 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.
+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
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:
+current section definition. If the file name has already been mentioned
+in another section definition, with an explicit section name list, then
+only those sections which have not yet been allocated are used.
+
+To specify a list of particular files by name:
@example
.data : @{ afile.o bfile.o cfile.o @}
@end example
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.
-
+@kindex @var{filename}(@var{section})
+@cindex files and sections, section defn
@item @var{filename}( @var{section} )
@itemx @var{filename}( @var{section}, @var{section}, @dots{} )
@itemx @var{filename}( @var{section} @var{section} @dots{} )
-@kindex @var{filename}(@var{section})
-@cindex files and sections, section defn
You can name one or more sections from your input files, for
insertion in the current output section. If you wish to specify a list
of input-file sections inside the parentheses, you may separate the
section names by either commas or whitespace.
-@item * (@var{section})
-@itemx * (@var{section}, @var{section}, @dots{})
-@itemx * (@var{section} @var{section} @dots{}
@cindex input sections to output section
@kindex *(@var{section})
+@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{ld} command
line: use @samp{*} instead of a particular file name before the
parenthesized input-file section list.
+If you have already explicitly included some files by name, @samp{*}
+refers to all @emph{remaining} files---those whose places in the output
+file have not yet been defined.
+
For example, to copy sections @code{1} through @code{4} from an Oasys file
into the @code{.text} section of an @code{a.out} file, and sections @code{13}
and @code{14} into the @code{.data} section:
@example
SECTIONS @{
- .text :@{
- *("1" "2" "3" "4")
- @}
-
- .data :@{
- *("13" "14")
- @}
+ .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.
-
-@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
uninitialized data from all input files (so far as it is not yet
three consecutive sections, named @code{.text}, @code{.data}, and
@code{.bss}, taking the input for each from the correspondingly named
sections of all the input files:
+
@example
SECTIONS @{
.text : @{ *(.text) @}
@example
SECTIONS @{
- outputa 0x10000 :
- @{
- all.o
- foo.o (.input1)
- @}
- outputb :
- @{
- foo.o (.input2)
- foo1.o (.input1)
- @}
- outputc :
- @{
- *(.input1)
- *(.input2)
- @}
+ outputa 0x10000 :
+ @{
+ all.o
+ foo.o (.input1)
+ @}
+ outputb :
+ @{
+ foo.o (.input2)
+ foo1.o (.input1)
+ @}
+ outputc :
+ @{
+ *(.input1)
+ *(.input2)
+ @}
@}
@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.
+@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
+@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 the input file. For instance, with @code{a.out}
+data written from that input file. For instance, with @code{a.out}
files it is conventional to have a symbol for each input file. You can
accomplish this by defining the output @code{.text} section as follows:
@example
SECTIONS @{
- .text 0x2020 :
- @{
- CREATE_OBJECT_SYMBOLS
- *(.text)
- _etext = ALIGN(0x2000);
- @}
- @dots{}
+ .text 0x2020 :
+ @{
+ CREATE_OBJECT_SYMBOLS
+ *(.text)
+ _etext = ALIGN(0x2000);
+ @}
+ @dots{}
@}
@end example
-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
@end example
@noindent
-@samp{ld -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
00000000 A __DYNAMIC
00002068 t d.o
@end example
-@item @var{symbol} = @var{expression} ;
@kindex @var{symbol} = @var{expression} ;
-@itemx @var{symbol} @var{f}= @var{expression} ;
@kindex @var{symbol} @var{f}= @var{expression} ;
+@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
SECTIONS @{
abs = 14 ;
@dots{}
@}
@end example
+
@c FIXME: Try above example!
@noindent
@code{abs} and @code{rel} do not have the same value; @code{rel} has the
same value as @code{abs2}.
-@item BYTE(@var{expression})
@kindex BYTE(@var{expression})
-@itemx SHORT(@var{expression})
@kindex SHORT(@var{expression})
-@itemx LONG(@var{expression})
@kindex LONG(@var{expression})
+@kindex QUAD(@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.
+@item BYTE(@var{expression})
+@itemx SHORT(@var{expression})
+@itemx LONG(@var{expression})
+@itemx QUAD(@var{expression})
+By including one of these four statements in a section definition, you
+can explicitly place one, two, four, or eight bytes (respectively) at
+the current address of that section. @code{QUAD} is only supported when
+using a 64 bit host or target.
@ifclear SingleFormat
Multiple-byte quantities are represented in whatever byte order is
@kindex FILL(@var{expression})
@cindex holes, filling
@cindex unspecified memory
-Specifies the ``fill pattern'' for the current section. Any otherwise
+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
@smallexample
SECTIONS @{
@dots{}
-@var{secname} @var{start} BLOCK(@var{align}) (NOLOAD) : @{ @var{contents} @} =@var{fill} >@var{region}
+@var{secname} @var{start} BLOCK(@var{align}) (NOLOAD) : AT ( @var{ldadr} )
+ @{ @var{contents} @} =@var{fill} >@var{region}
@dots{}
@}
@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{(NOLOAD)} @code{=@var{fill}}, and @code{>@var{region}}---are all
-optional.
+Definition}, and @pxref{Section Placement} for details on
+@var{contents}. The remaining elements---@var{start},
+@code{BLOCK(@var{align)}}, @code{(NOLOAD)}, @code{AT ( @var{ldadr} )},
+@code{=@var{fill}}, and @code{>@var{region}}---are all optional.
@table @code
-@item @var{start}
@cindex start address, section
@cindex section start
@cindex section address
+@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
SECTIONS @{
- @dots{}
- output 0x40000000: @{
- @dots{}
- @}
- @dots{}
+ @dots{}
+ output 0x40000000: @{
+ @dots{}
+ @}
+ @dots{}
@}
@end example
-@item BLOCK(@var{align})
@kindex BLOCK(@var{align})
@cindex section alignment
@cindex aligning sections
+@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 (NOLOAD)
@kindex NOLOAD
@cindex prevent unnecessary loading
+@cindex loading, preventing
+@item (NOLOAD)
Use @samp{(NOLOAD)} to prevent a section from being loaded into memory
each time it is accessed. For example, in the script sample below, the
@code{ROM} segment is addressed at memory location @samp{0} and does not
need to be loaded into each object file:
+
@example
SECTIONS @{
- ROM 0 (NOLOAD) : @{ @dots{} @}
- @dots{}
+ ROM 0 (NOLOAD) : @{ @dots{} @}
+ @dots{}
@}
@end example
-@item =@var{fill}
+@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
+SECTIONS
+ @{
+ .text 0x1000 : @{ *(.text) _etext = . ; @}
+ .mdata 0x2000 :
+ AT ( ADDR(.text) + SIZEOF ( .text ) )
+ @{ _data = . ; *(.data); _edata = . ; @}
+ .bss 0x3000 :
+ @{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;@}
+@}
+@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
+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 smallexample
+
@kindex =@var{fill}
@cindex section fill pattern
@cindex fill pattern, entire section
-Including
-@code{=@var{fill}} in a section definition specifies the initial fill
-value for that section.
-You may use any expression to specify @var{fill}.
-Any unallocated holes in the current output
-section when written to the output file will be filled with the two
-least significant bytes of the value, repeated as necessary. You can
-also change the fill value with a @code{FILL} statement in the
-@var{contents} of a section definition.
+@item =@var{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.
-@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}.
@item
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
assignment statement: if no symbol @code{start} is defined within your
input files, you can simply define it, assigning it an appropriate
value---
+
@example
start = 0x2020;
@end example
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
-@section Other Commands
+@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
+This command ties up C++ style constructor and destructor records. The
+details of the constructor representation vary from one object format to
+another, but usually lists of constructors and destructors appear as
+special sections. The @code{CONSTRUCTORS} command specifies where the
+linker is to place the data from these sections, relative to the rest of
+the linked output. Constructor data is marked by the symbol
+@w{@code{__CTOR_LIST__}} at the start, and @w{@code{__CTOR_LIST_END}} at
+the end; destructor data is bracketed similarly, between
+@w{@code{__DTOR_LIST__}} and @w{@code{__DTOR_LIST_END}}. (The compiler
+must arrange to actually run this code; GNU C++ calls constructors from
+a subroutine @code{__main}, which it inserts automatically into the
+startup code for @code{main}, and destructors from @code{_exit}.)
+
+@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{ld} doesn't use the keywords, assuming
instead that any necessary subroutines are in libraries specified using
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
+@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 (@samp{-r}).
-@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}.
@ignore
@item MAP ( @var{name} )
@cindex naming the output file
Use this command to name the link output file @var{filename}. The
effect of @code{OUTPUT(@var{filename})} is identical to the effect of
-@w{@samp{-o @var{filename}}}, and whichever is encountered last 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}.
+@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}.
@ifclear SingleFormat
@item OUTPUT_ARCH ( @var{bfdname} )
@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
+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 TARGET ( @var{format} )
@cindex input file format
@kindex TARGET ( @var{format} )
-Change the input-file object code format (like the command-line option
-@samp{-b} or its synonym @samp{-format}). The argument @var{format} is
-one of the strings used by BFD to name binary formats. In the current
-@code{ld} 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{ld} output file.
-@xref{BFD}.
+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{ld} uses the value of
@end menu
@end ifset
-@c FIXME! This could use @up/@down, but there seems to be a conflict
+@c FIXME! This could use @raisesections/@lowersections, but there seems to be a conflict
@c between those and node-defaulting.
@ifset H8300
@ifclear GENERIC
-@up
+@raisesections
@end ifclear
@node H8/300
@section @code{ld} and the H8/300
top page of memory).
@end table
@ifclear GENERIC
-@down
+@lowersections
@end ifclear
@end ifset
@ifset I960
@ifclear GENERIC
-@up
+@raisesections
@end ifclear
@node i960
@section @code{ld} and the Intel 960 family
the 960 architecture family allows combination of target architectures; each
use will add another pair of name variants to search for when @w{@samp{-l}}
specifies a library.
+
+@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
-@down
+@lowersections
@end ifclear
@end ifset
@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
@menu
* BFD outline:: How it works: an outline of BFD
-* BFD information loss:: Information Loss
-* Mechanism:: Mechanism
@end menu
@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 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
-@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 (e.g.,
-@code{a.out}) or has sections without names (e.g., 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 would 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,
-there is no information lost 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
-@section Mechanism
-The greatest potential for loss of information occurs when there is the least
-overlap between the information provided by the source format, that
-stored by the canonical format, and that needed by the
-destination format. A brief description of the canonical form may help
-you understand which kinds of data you can count on preserving across
-conversions.
-@cindex BFD canonical format
-@cindex internal object-file format
-
-@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 pagable bit and a write protected bit.
-Information like Unix magic numbers is not stored here---only the magic
-numbers' meaning, so a @code{ZMAGIC} file would have both the demand pagable
-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 options, 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 option 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. Doing this ensures that each symbol points to its containing
-section. Each symbol also has a varying amount of hidden
-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{ld} 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 by passing messages through the relocation type
-descriptor and the symbol pointer. Therefore, relocations can be performed
-on output data using a relocation method that is 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 finding out 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
+@include bfdsumm.texi
@end ifclear
@node 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
+@cindex @code{ABSOLUTE} (MRI)
@item ABSOLUTE @var{secname}
@item ABSOLUTE @var{secname}, @var{secname}, @dots{} @var{secname}
-@cindex @code{ABSOLUTE} (MRI)
Normally, @code{ld} includes in the output file all sections from all
the input files. However, in an MRI-compatible script, you can use the
@code{ABSOLUTE} command to restrict the sections that will be present in
input sections (whatever you select on the command line, or using
@code{LOAD}) to resolve addresses in the output file.
-@item ALIAS @var{out-secname}, @var{in-secname}
@cindex @code{ALIAS} (MRI)
+@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{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; 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{anything}@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 on the
same line, with no change in its effect.
+@cindex @code{LOAD} (MRI)
@item LOAD @var{filename}
@item LOAD @var{filename}, @var{filename}, @dots{} @var{filename}
-@cindex @code{LOAD} (MRI)
Include one or more object file @var{filename} in the link; this has the
same effect as specifying @var{filename} directly on the @code{ld}
command line.
-@item NAME @var{output-name}
@cindex @code{NAME} (MRI)
+@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 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)
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
projects / deliverable / binutils-gdb.git / blobdiff