@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 @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} ] [ --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 ]
- [ -r | -Ur ] [ -S ] [ -s ] [ -sort-common ] [ -T @var{commandfile} ]
+ [ -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 ]
+ [ -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
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.
+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
@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
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.
-@item --help
-@kindex --help
@cindex help
@cindex usage
+@kindex -help
+@item -help
Print a summary of the command-line options on the standard output and exit.
-This option and @samp{--version} begin with two dashes instead of one
-for compatibility with other GNU programs. The other options start with
-only one dash for compatibility with other linkers.
@kindex -i
@cindex incremental link
@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.
@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}
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
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 -sort-common
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}
exist, @code{ld} looks for it in the directories specified by any
preceding @samp{-L} options. Multiple @samp{-T} options accumulate.
-@item -t
@kindex -t
@cindex verbose
@cindex input files, displaying
+@item -t
Print the names of the input files as @code{ld} processes them.
@item -u @var{symbol}
@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 can not
+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.
-Display 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}.
-@item --version
-@kindex --version
+@item -version
+@kindex -version
Display the version number for @code{ld} and exit.
@item -warn-common
@end smallexample
@end enumerate
-@item -X
@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
@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
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
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
@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} (but not, for example, @samp{ORG}).
-@item @var{len}
+
@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
@node SECTIONS
@section Specifying Output Sections
+
@kindex SECTIONS
The @code{SECTIONS} command controls exactly where input sections are
placed into output sections, their order in the output file, and to
You may use at most one @code{SECTIONS} command in a script file,
but you can have as many statements within it as you wish. Statements
within the @code{SECTIONS} command can do one of three things:
+
@itemize @bullet
@item
define the entry point;
+
@item
assign a value to a symbol;
+
@item
describe the placement of a named output section, and which input
sections go into it.
your convenience in reading the script, so that symbols and the entry
point can be defined at meaningful points in your output-file layout.
-When no @code{SECTIONS} command is given, the linker places each input
+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
definition is
@example
SECTIONS @{ @dots{}
-@var{secname} : @{
- @var{contents}
- @}
+ @var{secname} : @{
+ @var{contents}
+ @}
@dots{} @}
@end example
@cindex naming output sections
@node Section Placement
@subsection Section Placement
+
@cindex contents of a section
-In a section definition, you can specify the contents of an output section by
-listing particular input files, by listing particular input-file
-sections, or by a combination of the two. You can also place arbitrary
-data in the section, and define symbols relative to the beginning of the
-section.
+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. If the file name has already been mentioned
the contents of a section definition, since each file name is a separate
statement.
+@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.
+@cindex input sections to output section
+@kindex *(@var{section})
@item * (@var{section})
@itemx * (@var{section}, @var{section}, @dots{})
@itemx * (@var{section} @var{section} @dots{})
-@cindex input sections to output section
-@kindex *(@var{section})
Instead of explicitly naming particular input files in a link control
script, you can refer to @emph{all} files from the @code{ld} command
line: use @samp{*} instead of a particular file name before the
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
+@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
@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.
+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 that input file. For instance, with @code{a.out}
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
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})
-@itemx QUAD(@var{expression})
@kindex QUAD(@var{expression})
@cindex direct output
+@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
@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 Placement} for details on @var{contents}.
-The remaining elements---@var{start}, @code{BLOCK(@var{align)}},
-@code{(NOLOAD)} @code{=@var{fill}}, and @code{>@var{region}}---are all
-optional.
+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}.
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
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.
Specify the full name for each @var{file}, including @samp{.a} if
@item OUTPUT_FORMAT ( @var{bfdname} )
@kindex OUTPUT_FORMAT ( @var{bfdname} )
@cindex format, output file
-Specify a particular output format, with one of the names used by the
-BFD back-end routines (@pxref{BFD}). The effect is identical to the
-effect of the @samp{-oformat} command-line option.
-This selection will only affect
+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. 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
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
@lowersections
@end ifclear
@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
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 / binutils.git / blobdiff