Some reusable routines may be compiled into a library, see the documentation
for the assembler and linkage editor (which are in <installdir>/share/sdcc/doc)
for how to create a .lib library file. Libraries created in this manner can be included in
the command line. Make sure you include the -L <library-path> option
to tell the linker where to look for these files if they are not in
the current directory. Here is an example, assuming you have the source
file foomain.c and a library foolib.lib in the directory
mylib (if that is not the same as your current project):
sdcc foomain.c foolib.lib -L mylib
Note here that mylib must be an absolute path name.
The most efficient way to use libraries is to keep separate modules
in separate source files. The lib file now should name all the modules.rel files. For an example see the standard library file libsdcc.lib
in the directory <installdir>/share/lib/small.