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3.4.4 Other Linker Script Commands

There are a few other linker scripts commands.

ASSERT(exp, message)
Ensure that exp is non-zero. If it is zero, then exit the linker with an error code, and print message.
EXTERN(symbol symbol ...)
Force 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. You may list several symbols for each EXTERN, and you may use EXTERN multiple times. This command has the same effect as the `-u' command-line option.
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').
This command has the same effect as the `--no-define-common' command-line option: to make ld omit the assignment of addresses to common symbols even for a non-relocatable output file.
NOCROSSREFS(section section ...)
This command may be used to tell ld to issue an error about any references among certain output sections.

In certain types of programs, particularly on embedded systems when using overlays, 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 output section names. If ld detects any cross references between the sections, it reports an error and returns a non-zero exit status. Note that the NOCROSSREFS command uses output section names, not input section names.

Specify a particular output machine architecture. The argument is one of the names used by the BFD library (see BFD). You can see the architecture of an object file by using the objdump program with the `-f' option.