linux-kernel - Re: [PATCH bpf-next v3 11/14] tools build: Implement feature check for BPF atomics in Clang

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Date:   Thu, 3 Dec 2020 13:02:33 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Brendan Jackman <jackmanb@...gle.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        open list <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        "Frank Ch. Eigler" <fche@...hat.com>,
        Stephane Eranian <eranian@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Hebb <tommyhebb@...il.com>
Subject: Re: [PATCH bpf-next v3 11/14] tools build: Implement feature check
 for BPF atomics in Clang

On Thu, Dec 3, 2020 at 8:08 AM Brendan Jackman <jackmanb@...gle.com> wrote:
>
> Change-Id: Ia15bb76f7152fff2974e38242d7430ce2987a71e
>

See recent discussion on KP's patch set. There needs to be a commit
message, even if it's just a copy/paste of subject line. But see also
my other reply, I'm not sure it's worth it to do it this way for
selftests.

> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Quentin Monnet <quentin@...valent.com>
> Cc: "Frank Ch. Eigler" <fche@...hat.com>
> Cc: Stephane Eranian <eranian@...gle.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Thomas Hebb <tommyhebb@...il.com>
> Change-Id: Ie2c3832eaf050d627764071d1927c7546e7c4b4b
> Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
> ---
>  tools/build/feature/Makefile                 | 4 ++++
>  tools/build/feature/test-clang-bpf-atomics.c | 9 +++++++++
>  2 files changed, 13 insertions(+)
>  create mode 100644 tools/build/feature/test-clang-bpf-atomics.c
>
> diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
> index cdde783f3018..81370d7fa193 100644
> --- a/tools/build/feature/Makefile
> +++ b/tools/build/feature/Makefile
> @@ -70,6 +70,7 @@ FILES=                                          \
>           test-libaio.bin                       \
>           test-libzstd.bin                      \
>           test-clang-bpf-co-re.bin              \
> +         test-clang-bpf-atomics.bin            \
>           test-file-handle.bin                  \
>           test-libpfm4.bin
>
> @@ -331,6 +332,9 @@ $(OUTPUT)test-clang-bpf-co-re.bin:
>         $(CLANG) -S -g -target bpf -o - $(patsubst %.bin,%.c,$(@F)) |   \
>                 grep BTF_KIND_VAR
>
> +$(OUTPUT)test-clang-bpf-atomics.bin:
> +       $(CLANG) -S -g -target bpf -mcpu=v3 -Werror=implicit-function-declaration -o - $(patsubst %.bin,%.c,$(@F)) 2>&1
> +
>  $(OUTPUT)test-file-handle.bin:
>         $(BUILD)
>
> diff --git a/tools/build/feature/test-clang-bpf-atomics.c b/tools/build/feature/test-clang-bpf-atomics.c
> new file mode 100644
> index 000000000000..8b5fcdd4ba6f
> --- /dev/null
> +++ b/tools/build/feature/test-clang-bpf-atomics.c
> @@ -0,0 +1,9 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2020 Google
> +
> +int x = 0;
> +
> +int foo(void)
> +{
> +       return __sync_val_compare_and_swap(&x, 1, 2);
> +}
> --
> 2.29.2.454.gaff20da3a2-goog
>