The link-editor accepts one or more support libraries provided by either the SGS_SUPPORT environment variable or with the link-editor's -S option. The environment variable consists of a colon separated list of support libraries.
$ SGS_SUPPORT=support.so.1:support.so.2 cc ...
The -S option specifies a single support library. Multiple -S options can be specified.
$ LD_OPTIONS="-Ssupport.so.1 -Ssupport.so.2" cc ...
A support library is a shared object. The link-editor opens each support library, in the order the libraries are specified, using dlopen(3C). If both the environment variable and -S option are encountered, then the support libraries specified with the environment variable are processed first. Each support library is then searched, using dlsym(3C), for any support interface routines. These support routines are then called at various stages of link-editing.
A support library must be consistent with the ELF class of the link-editor being invoked, either 32–bit or 64–bit. See 32–Bit Environments and 64–Bit Environments for more details.
As described in 32–Bit Environments and 64–Bit Environments, the 64–bit link-editor, ld(1), is capable of generating 32–bit objects. In addition, the 32–bit link-editor is capable of generating 64–bit objects. Each of these objects has an associated support interface defined.
The support interface for 64–bit objects is similar to the interface of 32–bit objects, but ends in a 64 suffix. For example ld_start() and ld_start64(). This convention allows both implementations of the support interface to reside in a single shared object of each class, 32–bit and 64–bit.
The SGS_SUPPORT environment variable can be specified with a _32 or _64 suffix, and the link-editor options -z ld32 and -z ld64 can be used to define -S option requirements. These definitions will only be interpreted, respectively, by the 32–bit or 64–bit class of the link-editor. This enables both classes of support library to be specified when the class of the link-editor might not be known.