How to merge two “ar” static libraries into one?

Question

I have 2 static Linux libraries, created by ar cr, libabc.a and libxyz.a.
I want to merge them into one static library libaz

Answer 1

Even better you perform partial linking on each library and them make an archive of the two resulting object files. That way it operates like shared libraries would

You do partial linking with

gcc -r --nostdlib

so either instead of making the intermediate archive or after reextracting it, run

gcc -r --nostdlib $CFLAGS $OBJECTS_A -o $LIBNAME_A.o
gcc -r --nostdlib $CFLAGS $OBJECTS_B -o $LIBNAME_B.o

then

ar -cr $LIBNAME_JOINED.a $LIBNAME_A.o $LIBNAME_B.o