Date:   Tue, 16 Jul 2019 17:22:04 -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>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>,
        Kernel Team <kernel-team@...com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf 1/2] selftests/bpf: fix test_verifier/test_maps make dependencies

On Tue, Jul 16, 2019 at 5:15 PM Stanislav Fomichev <sdf@...ichev.me> wrote:
>
> On 07/16, Andrii Nakryiko wrote:
> > On Tue, Jul 16, 2019 at 3:57 PM Stanislav Fomichev <sdf@...ichev.me> wrote:
> > >
> > > On 07/16, Andrii Nakryiko wrote:
> > > > On Tue, Jul 16, 2019 at 12:55 PM Stanislav Fomichev <sdf@...ichev.me> wrote:
> > > > >
> > > > > On 07/16, Andrii Nakryiko wrote:
> > > > > > e46fc22e60a4 ("selftests/bpf: make directory prerequisites order-only")
> > > > > > exposed existing problem in Makefile for test_verifier and test_maps tests:
> > > > > > their dependency on auto-generated header file with a list of all tests wasn't
> > > > > > recorded explicitly. This patch fixes these issues.
> > > > > Why adding it explicitly fixes it? At least for test_verifier, we have
> > > > > the following rule:
> > > > >
> > > > >         test_verifier.c: $(VERIFIER_TESTS_H)
> > > > >
> > > > > And there should be implicit/builtin test_verifier -> test_verifier.c
> > > > > dependency rule.
> > > > >
> > > > > Same for maps, I guess:
> > > > >
> > > > >         $(OUTPUT)/test_maps: map_tests/*.c
> > > > >         test_maps.c: $(MAP_TESTS_H)
> > > > >
> > > > > So why is it not working as is? What I'm I missing?
> > > >
> > > > I don't know exactly why it's not working, but it's clearly because of
> > > > that. It's the only difference between how test_progs are set up,
> > > > which didn't break, and test_maps/test_verifier, which did.
> > > >
> > > > Feel free to figure it out through a maze of Makefiles why it didn't
> > > > work as expected, but this definitely fixed a breakage (at least for
> > > > me).
> > > Agreed on not wasting time. I took a brief look (with make -qp) and I
> > > don't have any clue.
> >
> > Oh, -qp is cool, noted :)
> >
> > >
> > > By default implicit matching doesn't work:
> > > # makefile (from 'Makefile', line 261)
> > > /linux/tools/testing/selftests/bpf/test_maps: CFLAGS += $(TEST_MAPS_CFLAGS)
> > > /linux/tools/testing/selftests/bpf/test_maps: map_tests/sk_storage_map.c /linux/tools/testing/selftests/bpf/test_stub.o /linux/tools/testing/selftests/bpf/libbpf.a
> > > #  Implicit rule search has not been done.
> > > #  File is an intermediate prerequisite.
> > > #  Modification time never checked.
> > > #  File has not been updated.
> > > # variable set hash-table stats:
> > > # Load=1/32=3%, Rehash=0, Collisions=0/2=0%
> > >
> > > If I comment out the following line:
> > > $(TEST_GEN_PROGS): $(OUTPUT)/test_stub.o $(BPFOBJ)
> > >
> > > Then it works:
> > > # makefile (from 'Makefile', line 261)
> > > /linux/tools/testing/selftests/bpf/test_maps: CFLAGS += $(TEST_MAPS_CFLAGS)
> > > /linux/tools/testing/selftests/bpf/test_maps: test_maps.c map_tests/sk_storage_map.c
> > > #  Implicit rule search has been done.
> > > #  Implicit/static pattern stem: 'test_maps'
> > > #  File is an intermediate prerequisite.
> > > #  File does not exist.
> > > #  File has not been updated.
> > > # variable set hash-table stats:
> > > # Load=1/32=3%, Rehash=0, Collisions=0/2=0%
> > > #  recipe to execute (from '../lib.mk', line 138):
> > >         $(LINK.c) $^ $(LDLIBS) -o $@
> > >
> > > It's because "File is an intermediate prerequisite.", but I
> > > don't see how it's is a intermediate prerequisite for anything...
> >
> > Well, it's "File is an intermediate prerequisite." in both cases, so I
> > don't know if that's it.
> > Makefiles is not my strong suit, honestly, and definitely not an area
> > of passion, so no idea
> >
> > >
> > >
> > > One other optional suggestion I have to your second patch: maybe drop all
> > > those dependencies on the directories altogether? Why not do the following
> > > instead, for example (same for test_progs/test_maps)?
> >
> > Some of those _TEST_DIR's are dependencies of multiple targets, so
> > you'd need to replicate that `mkdir -p $@` in multiple places, which
> > is annoying.
> Agreed, but one single "mkdir -p $@" might be better than having three
> lines that define XXX_TEST_DIR and then add a target that mkdir's it.
> Up to you, I can give it a try once your changes are in; the
> Makefile becomes hairier by the day, thx for cleaning it up a bit :-)
>
> > But I also don't think we need to worry about creating them, because
> > there is always at least one test (otherwise those tests are useless
> > anyways) in those directories, so we might as well just remove those
> > dependencies, I guess.
> We probably care about them for "make -C tools/selftests O=$PWD/xyz" case
> where OUTPUT would point to a fresh/clean directory.

Oh, yes, out-of-tree builds, forgot about that, so yeah, we need that.

>
> > TBH, those explicit dependencies are good to specify anyways, so I
> > think this fix is good. Second patch just makes the layout of
> > dependencies similar, so it's easier to spot differences like this
> > one.
> >
> > As usual, I'll let Alexei and Daniel decide which one to apply (or if
> > we need to take some other approach to fixing this).
> I agree, both of your changes look good. I was just trying to understand
> what's happening because I was assuming implicit rules to always kick
> in.
>
> > > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > > index 1296253b3422..c2d087ce6d4b 100644
> > > --- a/tools/testing/selftests/bpf/Makefile
> > > +++ b/tools/testing/selftests/bpf/Makefile
> > > @@ -277,12 +277,9 @@ VERIFIER_TESTS_H := $(OUTPUT)/verifier/tests.h
> > >  test_verifier.c: $(VERIFIER_TESTS_H)
> > >  $(OUTPUT)/test_verifier: CFLAGS += $(TEST_VERIFIER_CFLAGS)
> > >
> > > -VERIFIER_TESTS_DIR = $(OUTPUT)/verifier
> > > -$(VERIFIER_TESTS_DIR):
> > > -       mkdir -p $@
> > > -
> > >  VERIFIER_TEST_FILES := $(wildcard verifier/*.c)
> > > -$(OUTPUT)/verifier/tests.h: $(VERIFIER_TEST_FILES) | $(VERIFIER_TESTS_DIR)
> > > +$(OUTPUT)/verifier/tests.h: $(VERIFIER_TEST_FILES)
> > > +       mkdir -p $(dir $@)
> > >         $(shell ( cd verifier/; \
> > >                   echo '/* Generated header, do not edit */'; \
> > >                   echo '#ifdef FILL_ARRAY'; \

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