Re: [PATCH bpf-next] bpf: fix compilation warning of selftests

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jianlin Lv <Jianlin.Lv@arm.com>
Cc: bpf <bpf@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Yonghong Song <yhs@fb.com>,
	Song.Zhu@arm.com, open list <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: fix compilation warning of selftests
Date: Fri, 31 Jul 2020 10:39:59 -0700	[thread overview]
Message-ID: <CAEf4BzY9Kc=Q664Yas+YY=2os_sjx9_RVwdQOwW_-=tkPAe8BA@mail.gmail.com> (raw)
In-Reply-To: <20200731061600.18344-1-Jianlin.Lv@arm.com>

On Thu, Jul 30, 2020 at 11:18 PM Jianlin Lv <Jianlin.Lv@arm.com> wrote:
>
> Clang compiler version: 12.0.0
> The following warning appears during the selftests/bpf compilation:
>
> prog_tests/send_signal.c:51:3: warning: ignoring return value of ‘write’,
> declared with attribute warn_unused_result [-Wunused-result]
>    51 |   write(pipe_c2p[1], buf, 1);
>       |   ^~~~~~~~~~~~~~~~~~~~~~~~~~
> prog_tests/send_signal.c:54:3: warning: ignoring return value of ‘read’,
> declared with attribute warn_unused_result [-Wunused-result]
>    54 |   read(pipe_p2c[0], buf, 1);
>       |   ^~~~~~~~~~~~~~~~~~~~~~~~~
> ......
>
> prog_tests/stacktrace_build_id_nmi.c:13:2: warning: ignoring return value
> of ‘fscanf’,declared with attribute warn_unused_result [-Wunused-resul]
>    13 |  fscanf(f, "%llu", &sample_freq);
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> test_tcpnotify_user.c:133:2: warning:ignoring return value of ‘system’,
> declared with attribute warn_unused_result [-Wunused-result]
>   133 |  system(test_script);
>       |  ^~~~~~~~~~~~~~~~~~~
> test_tcpnotify_user.c:138:2: warning:ignoring return value of ‘system’,
> declared with attribute warn_unused_result [-Wunused-result]
>   138 |  system(test_script);
>       |  ^~~~~~~~~~~~~~~~~~~
> test_tcpnotify_user.c:143:2: warning:ignoring return value of ‘system’,
> declared with attribute warn_unused_result [-Wunused-result]
>   143 |  system(test_script);
>       |  ^~~~~~~~~~~~~~~~~~~
>
> Add code that fix compilation warning about ignoring return value and
> handles any errors; Check return value of library`s API make the code
> more secure.
>
> Signed-off-by: Jianlin Lv <Jianlin.Lv@arm.com>
> ---
>  .../selftests/bpf/prog_tests/send_signal.c    | 37 ++++++++++++++-----
>  .../bpf/prog_tests/stacktrace_build_id_nmi.c  |  3 +-
>  .../selftests/bpf/test_tcpnotify_user.c       | 15 ++++++--
>  3 files changed, 41 insertions(+), 14 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/send_signal.c b/tools/testing/selftests/bpf/prog_tests/send_signal.c
> index 504abb7bfb95..7a5272e4e810 100644
> --- a/tools/testing/selftests/bpf/prog_tests/send_signal.c
> +++ b/tools/testing/selftests/bpf/prog_tests/send_signal.c
> @@ -48,22 +48,31 @@ static void test_send_signal_common(struct perf_event_attr *attr,
>                 close(pipe_p2c[1]); /* close write */
>
>                 /* notify parent signal handler is installed */
> -               write(pipe_c2p[1], buf, 1);
> +               if (CHECK_FAIL(write(pipe_c2p[1], buf, 1) != 1)) {
> +                       perror("Child: write pipe error");
> +                       goto close_out;
> +               }

Please don't use CHECK_FAIL. Using CHECK is better for many reasons,
but it will also be shorter here (while still recording failure):

CHECK(write(pipe_c2p[1], buf, 1) != 1, "pipe_write", "err %d\n", -errno);

>
>                 /* make sure parent enabled bpf program to send_signal */
> -               read(pipe_p2c[0], buf, 1);
> +               if (CHECK_FAIL(read(pipe_p2c[0], buf, 1) != 1)) {
> +                       perror("Child: read pipe error");
> +                       goto close_out;
> +               }
>

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