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.
CONSTRUCTORS
When linking using the a.out object file format, the linker uses
an unusual set construct to support C++ global constructors and
destructors. When linking object file formats which do not support
arbitrary sections, such as ECOFF and XCOFF, the linker
will automatically recognize C++ global constructors and destructors by
name. For these object file formats, the CONSTRUCTORS command
tells the linker where this information should be placed. The
CONSTRUCTORS command is ignored for other object file formats.
The symbol __CTOR_LIST__ marks the start of the global
constructors, and the symbol __DTOR_LIST marks the end. The
first word in the list is the number of entries, followed by the address
of each constructor or destructor, followed by a zero word. The
compiler must arrange to actually run the code. For these object file
formats GNU C++ calls constructors from a subroutine __main;
a call to __main is automatically inserted into the startup code
for main. GNU C++ runs destructors either by using
atexit, or directly from the function exit.
For object file formats such as COFF or ELF which support
multiple sections, GNU C++ will normally arrange to put the
addresses of global constructors and destructors into the .ctors
and .dtors sections. Placing the following sequence into your
linker script will build the sort of table which the GNU C++
runtime code expects to see.
Normally the compiler and linker will handle these issues automatically,
and you will not need to concern yourself with them. However, you may
need to consider this if you are using C++ and writing your own linker
scripts.
FLOAT
NOFLOAT
These keywords were used in some older linkers to request a particular
math subroutine library. ld doesn't use the keywords, assuming
instead that any necessary subroutines are in libraries specified using
the general mechanisms for linking to archives; but to permit the use of
scripts that were written for the older linkers, the keywords
FLOAT and NOFLOAT are accepted and ignored.
FORCE_COMMON_ALLOCATION
This command has the same effect as the `-d' command-line option:
to make ld assign space to common symbols even if a relocatable
output file is specified (`-r').
INCLUDE filename
Include the linker script filename at this point. The file will
be searched for in the current directory, and in any directory specified
with the -L option. You can nest calls to INCLUDE up to
10 levels deep.
INPUT ( file, file, ... )
INPUT ( filefile ... )
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 file, including `.a' if
required.
ld searches for each file through the archive-library
search path, just as for files you specify on the command line.
See the description of `-L' in Command Line Options.
If you use `-lfile', ld will transform the name to
libfile.a as with the command line argument `-l'.
GROUP ( file, file, ... )
GROUP ( filefile ... )
This command is like INPUT, except that the named files should
all be archives, and they are searched repeatedly until no new undefined
references are created. See the description of `-(' in
Command Line Options.
OUTPUT ( filename )
Use this command to name the link output file filename. The
effect of OUTPUT(filename) is identical to the effect of
`-o filename', which overrides it. You can use this
command to supply a default output-file name other than a.out.
OUTPUT_ARCH ( bfdname )
Specify a particular output machine architecture, with one of the names
used by the BFD back-end routines (see section 5. BFD). This command is often
unnecessary; the architecture is most often set implicitly by either the
system BFD configuration or as a side effect of the OUTPUT_FORMAT
command.
OUTPUT_FORMAT ( bfdname )
When ld is configured to support multiple object code formats,
you can use this command to specify a particular output format.
bfdname is one of the names used by the BFD back-end routines
(see section 5. BFD). The effect is identical to the effect of the
`--oformat' command-line option. This selection affects only the
output file; the related command TARGET affects primarily input
files.
SEARCH_DIR ( path )
Add path to the list of paths where ld looks for
archive libraries. SEARCH_DIR(path) has the same
effect as `-Lpath' on the command line.
STARTUP ( filename )
Ensure that filename is the first input file used in the link
process.
TARGET ( format )
When 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 `-b' or its synonym `--format').
The argument format is one of the strings used by BFD to name
binary formats. If TARGET is specified but OUTPUT_FORMAT
is not, the last TARGET argument is also used as the default
format for the ld output file. See section 5. BFD.
If you don't use the TARGET command, ld uses the value of
the environment variable GNUTARGET, if available, to select the
output file format. If that variable is also absent, ld uses
the default format configured for your machine in the BFD libraries.
NOCROSSREFS ( sectionsection ... )
This command may be used to tell ld to issue an error about any
references among certain sections.
In certain types of programs, particularly on embedded systems, when one
section is loaded into memory, another section will not be. Any direct
references between the two sections would be errors. For example, it
would be an error if code in one section called a function defined in
the other section.
The NOCROSSREFS command takes a list of section names. If
ld detects any cross references between the sections, it reports
an error and returns a non-zero exit status. The NOCROSSREFS
command uses output section names, defined in the SECTIONS
command. It does not use the names of input sections.