netdev - Re: [PATCH bpf] selftests: bpf: fix makefile dependencies on libbpf

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Message-ID: <CAEf4Bza82pfB-DniE+Snb7nZLHXmPBmkgE7yj9qwkdYyOq_qXQ@mail.gmail.com>
Date:   Mon, 27 Sep 2021 21:53:57 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Benc <jbenc@...hat.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf] selftests: bpf: fix makefile dependencies on libbpf

On Mon, Sep 27, 2021 at 9:02 AM Jiri Benc <jbenc@...hat.com> wrote:
>
> When building bpf selftest with make -j, I'm randomly getting build failures
> such as this one:
>
> > In file included from progs/bpf_flow.c:19:
> > [...]/tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:11:10: fatal error: 'bpf_helper_defs.h' file not found
> > #include "bpf_helper_defs.h"
> >          ^~~~~~~~~~~~~~~~~~~
>
> The file that fails the build varies between runs but it's always in the
> progs/ subdir.
>
> The reason is a missing make dependency on libbpf for the .o files in
> progs/. There was a dependency before commit 3ac2e20fba07e but that commit
> removed it to prevent unneeded rebuilds. However, that only works if libbpf
> has been built already; the 'wildcard' prerequisite does not trigger when
> there's no bpf_helper_defs.h generated yet.
>
> Keep the libbpf as an order-only prerequisite to satisfy both goals. It is
> always built before the progs/ objects but it does not trigger unnecessary
> rebuilds by itself.
>
> Fixes: 3ac2e20fba07e ("selftests/bpf: BPF object files should depend only on libbpf headers")
> Signed-off-by: Jiri Benc <jbenc@...hat.com>
> ---
>  tools/testing/selftests/bpf/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 866531c08e4f..e7c42695dbbf 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -375,7 +375,8 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.o:                         \
>                      $(TRUNNER_BPF_PROGS_DIR)/%.c                       \
>                      $(TRUNNER_BPF_PROGS_DIR)/*.h                       \
>                      $$(INCLUDE_DIR)/vmlinux.h                          \
> -                    $(wildcard $(BPFDIR)/bpf_*.h) | $(TRUNNER_OUTPUT)
> +                    $(wildcard $(BPFDIR)/bpf_*.h) | $(TRUNNER_OUTPUT)  \
> +                    $$(BPFOBJ)


I've moved `| $(TRUNNER_OUTPUT)` into this new line so it's more
obvious that both are order-only prerequisites. Applied to bpf,
thanks.

>         $$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@,                      \
>                                           $(TRUNNER_BPF_CFLAGS))
>
> --
> 2.18.1
>