Using GCC dependency files causes Make to rebuild project completely every time

I've followed the instructions online to set up gcc (actually g++) to generate .d files for dependencies, and now my makefile looks something like this:

CPPFLAGS := ... -MMD -MP
...
OBJECTS := $(shell find *.cpp *.s | sed -e 's/\.cpp/\.o/' -e 's/\.s/\.o/')
all: setupdir $(OBJECTS) link image

And then at the end of the file:

-include $(pathsubst %.d,obj/%.d,$(OBJECTS:.o=.d))

The .d files ar开发者_运维百科e being correctly generated, and all show up in the obj directory. The problem is, now, even with the assembly files that don't have .d files generated for them the entire source tree is being rebuilt every time I run make. The project doesn't take long to compile, but still, how would one go about fixing it so that make runs correctly?

---

It's important to note that -M is not magic bullet for dependencies, in many cases you'll need to specify certain headers so things are re-built appropriately if they change. In fact, the most common problem with letting gcc handle dependencies is things not being re-built that should be (broadly depending on the version of GCC being used by whoever runs make).

That being said, I don't see anything blatantly wrong with what you're doing.

What I recommend doing is eliminating the shell tricks, since it's quite easy to specify exactly what you want. E.g.

foo_SOURCES = \
    src/foo.cpp \
    src/bar.cpp

foo_OBJECTS = $(foo_SOURCES:.cpp=.o)

foo_DEPS = $(foo_OBJECTS:.o=.d)

%.o : %.cpp
    $(CC) $(CFLAGS) ... $< -o $@
    $(CC) -M $< > $(@.o=.d)

# lots more rules and targets here

# and finally, at the bottom:

-include $(foo_DEPS)

This is off the top of my head in meta form, so check it to be sure. I believe your problem is actually the dependencies not being included, but I don't see anything obviously wrong with the way you are using pathsubst.

As people have noted in comments, running make with debug on may be helpful, but a good first step would be to specify your objects and dependencies without talking to the shell.

If you get that working, try just storing the results of your shell calls and echoing them to the screen. That's a lot less noisy than make's debug output.