Hi — I’m trying to structure a Makefile for a situation where a target depends on inputs that are in a subdirectory, which can be rebuilt by recursive make.
The specific case is a top-level Makefile which builds a binary, which links with static libraries built in a subdirectory. The top-level Makefile doesn’t have visibility into the inputs to the libraries, so it needs to invoke the recursive make always. The problem I’m having is that Make’s decision as to whether or not to rebuild the binary seems to depend on whether the files are old *before* the subdirectory make is invoked, not afterwards. Thus, if an input to a library changes, I have to invoke make twice in order to get my binary rebuilt. Here is my top-level Makefile: all: bin bin_libs = lib/libfoo.a lib/libbar.a lib/libbaz.a bin: bin.o $(bin_libs) $(CC) -o $@ $^ $(bin_libs) : | build-bin-libs .PHONY: build-bin-libs build-bin-libs: $(MAKE) -C lib $(notdir $(bin_libs)) clean: rm -f bin *.o $(MAKE) -C lib clean And here is lib/Makefile: all: libfoo.a libbar.a libbaz.a libquux.a ARFLAGS = cru %.o: %.c $(CC) $(CFLAGS) -c $< -o $@ lib%.a: %.o rm -f $@ $(AR) $(ARFLAGS) $@ $^ clean: rm -f *.o *.a (Obviously this is a simplification of my real build environment.) When I do an initial build, everything’s fine: $ make cc -c -o bin.o bin.c make -C lib libfoo.a libbar.a libbaz.a make[1]: Entering directory `/home/jonathan/Cvs/scratch/Make-Recursive-Test/lib' cc -c foo.c -o foo.o rm -f libfoo.a ar cru libfoo.a foo.o cc -c bar.c -o bar.o rm -f libbar.a ar cru libbar.a bar.o cc -c baz.c -o baz.o rm -f libbaz.a ar cru libbaz.a baz.o rm baz.o foo.o bar.o make[1]: Leaving directory `/home/jonathan/Cvs/scratch/Make-Recursive-Test/lib' cc -o bin bin.o lib/libfoo.a lib/libbar.a lib/libbaz.a However, a change that causes one of the libraries to be rebuilt doesn’t cause bin to be rebuilt, so I have to invoke make twice. $ touch lib/foo.c $ make make -C lib libfoo.a libbar.a libbaz.a make[1]: Entering directory `/home/jonathan/Cvs/scratch/Make-Recursive-Test/lib' cc -c foo.c -o foo.o rm -f libfoo.a ar cru libfoo.a foo.o make[1]: `libbar.a' is up to date. make[1]: `libbaz.a' is up to date. rm foo.o make[1]: Leaving directory `/home/jonathan/Cvs/scratch/Make-Recursive-Test/lib' $ make make -C lib libfoo.a libbar.a libbaz.a make[1]: Entering directory `/home/jonathan/Cvs/scratch/Make-Recursive-Test/lib' make[1]: `libfoo.a' is up to date. make[1]: `libbar.a' is up to date. make[1]: `libbaz.a' is up to date. make[1]: Leaving directory `/home/jonathan/Cvs/scratch/Make-Recursive-Test/lib' cc -o bin bin.o lib/libfoo.a lib/libbar.a lib/libbaz.a What can I do about this? What’s the best (most idiomatic) way to structure my makefile such that it does what I want — always rebuild both the relevant library and the binary whenever one of the inputs to a library changes? Note that I don’t just want to do a ‘make all’ in lib — I want it to only build the libraries needed by bin, not (in the example) lib/libquux.a. (In our actual development environment, some irrelevant libraries may be temporarily broken by other developers, or just take a long time to build.) I’m using GNU Make 3.81, on Ubuntu 14.04, if that’s relevant. Thank you for any help! — Jonathan Lennox _______________________________________________ Help-make mailing list Help-make@gnu.org https://lists.gnu.org/mailman/listinfo/help-make
