Compiling and Linking a C Program with Assembly Language Routines

The makefile in the next example maintains a program with C source files linked with assembly language routines. There are two varieties of assembly source files: those that do not contain cpp preprocessor directives, and those that do.

By convention, assembly source files without preprocessor directives have the .s suffix. Assembly sources that require preprocessing have the .S suffix.

ASFLAGS passes options for as to the .s.o and .S.o implicit rules.

Assembly sources are assembled to form object files in a fashion similar to that used to compile C sources. The object files can then be linked into a C program. make has implicit rules for transforming .s and .S files into object files, so a target entry for a C program with assembly routines need only specify how to link the object files. You can use the familiar cc command to link object files produced by the assembler:

CFLAGS= -O 
ASFLAGS= -O 

.KEEP_STATE:

driver: c_driver.o s_routines.o S_routines.o 
        	cc -o driver c_driver.o s_routines.o
         S_routines.o

Note that the .S files are processed using the cc command, which invokes the C preprocessor cpp, and invokes the assembler.