netdev - Re: [PATCH bpf-next 1/9] selftests/bpf: prevent headers to be compiled as C code

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Date:   Fri, 26 Jul 2019 14:42:23 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Stanislav Fomichev <sdf@...ichev.me>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 1/9] selftests/bpf: prevent headers to be
 compiled as C code

On Fri, Jul 26, 2019 at 2:21 PM Stanislav Fomichev <sdf@...ichev.me> wrote:
>
> On 07/26, Andrii Nakryiko wrote:
> > Apprently listing header as a normal dependency for a binary output
> > makes it go through compilation as if it was C code. This currently
> > works without a problem, but in subsequent commits causes problems for
> > differently generated test.h for test_progs. Marking those headers as
> > order-only dependency solves the issue.
> Are you sure it will not result in a situation where
> test_progs/test_maps is not regenerated if tests.h is updated.
>
> If I read the following doc correctly, order deps make sense for
> directories only:
> https://www.gnu.org/software/make/manual/html_node/Prerequisite-Types.html
>
> Can you maybe double check it with:
> * make
> * add new prog_tests/test_something.c
> * make
> to see if the binary is regenerated with test_something.c?

Yeah, tested that, it triggers test_progs rebuild.

Ordering is still preserved, because test.h is dependency of
test_progs.c, which is dependency of test_progs binary, so that's why
it works.

As to why .h file is compiled as C file, I have no idea and ideally
that should be fixed somehow.

I also started with just removing header as dependency completely
(because it's indirect dependency of test_progs.c), but that broke the
build logic. Dunno, too much magic... This works, tested many-many
times, so I was satisfied enough :)

>
> Maybe fix the problem of header compilation by having '#ifndef
> DECLARE_TEST #define DECLARE_TEST() #endif' in tests.h instead?

That's ugly, I'd like to avoid doing that.

>
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> >  tools/testing/selftests/bpf/Makefile | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > index 11c9c62c3362..bb66cc4a7f34 100644
> > --- a/tools/testing/selftests/bpf/Makefile
> > +++ b/tools/testing/selftests/bpf/Makefile
> > @@ -235,7 +235,7 @@ PROG_TESTS_H := $(PROG_TESTS_DIR)/tests.h
> >  PROG_TESTS_FILES := $(wildcard prog_tests/*.c)
> >  test_progs.c: $(PROG_TESTS_H)
> >  $(OUTPUT)/test_progs: CFLAGS += $(TEST_PROGS_CFLAGS)
> > -$(OUTPUT)/test_progs: test_progs.c $(PROG_TESTS_H) $(PROG_TESTS_FILES)
> > +$(OUTPUT)/test_progs: test_progs.c $(PROG_TESTS_FILES) | $(PROG_TESTS_H)
> >  $(PROG_TESTS_H): $(PROG_TESTS_FILES) | $(PROG_TESTS_DIR)
> >       $(shell ( cd prog_tests/; \
> >                 echo '/* Generated header, do not edit */'; \
> > @@ -256,7 +256,7 @@ MAP_TESTS_H := $(MAP_TESTS_DIR)/tests.h
> >  MAP_TESTS_FILES := $(wildcard map_tests/*.c)
> >  test_maps.c: $(MAP_TESTS_H)
> >  $(OUTPUT)/test_maps: CFLAGS += $(TEST_MAPS_CFLAGS)
> > -$(OUTPUT)/test_maps: test_maps.c $(MAP_TESTS_H) $(MAP_TESTS_FILES)
> > +$(OUTPUT)/test_maps: test_maps.c $(MAP_TESTS_FILES) | $(MAP_TESTS_H)
> >  $(MAP_TESTS_H): $(MAP_TESTS_FILES) | $(MAP_TESTS_DIR)
> >       $(shell ( cd map_tests/; \
> >                 echo '/* Generated header, do not edit */'; \
> > @@ -277,7 +277,7 @@ VERIFIER_TESTS_H := $(VERIFIER_TESTS_DIR)/tests.h
> >  VERIFIER_TEST_FILES := $(wildcard verifier/*.c)
> >  test_verifier.c: $(VERIFIER_TESTS_H)
> >  $(OUTPUT)/test_verifier: CFLAGS += $(TEST_VERIFIER_CFLAGS)
> > -$(OUTPUT)/test_verifier: test_verifier.c $(VERIFIER_TESTS_H)
> > +$(OUTPUT)/test_verifier: test_verifier.c | $(VERIFIER_TEST_FILES) $(VERIFIER_TESTS_H)
> >  $(VERIFIER_TESTS_H): $(VERIFIER_TEST_FILES) | $(VERIFIER_TESTS_DIR)
> >       $(shell ( cd verifier/; \
> >                 echo '/* Generated header, do not edit */'; \
> > --
> > 2.17.1
> >