11.4 Suffix Rules for Archive Files

You can write a special kind of suffix rule for dealing with archive files. See section 10.7 Old-Fashioned Suffix Rules, for a full explanation of suffix rules. Archive suffix rules are obsolete in GNU make, because pattern rules for archives are a more general mechanism (see section 11.2 Implicit Rule for Archive Member Targets). But they are retained for compatibility with other makes.

To write a suffix rule for archives, you simply write a suffix rule using the target suffix `.a' (the usual suffix for archive files). For example, here is the old-fashioned suffix rule to update a library archive from C source files:

.c.a: $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o $(AR) r $@ $*.o $(RM) $*.o

This works just as if you had written the pattern rule:

(%.o): %.c $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o $(AR) r $@ $*.o $(RM) $*.o

In fact, this is just what make does when it sees a suffix rule with `.a' as the target suffix. Any double-suffix rule `.x.a' is converted to a pattern rule with the target pattern `(%.o)' and a prerequisite pattern of `%.x'.

Since you might want to use `.a' as the suffix for some other kind of file, make also converts archive suffix rules to pattern rules in the normal way (see section 10.7 Old-Fashioned Suffix Rules). Thus a double-suffix rule `.x.a' produces two pattern rules: `(%.o): %.x' and `%.a: %.x'.