linux-kernel - Re: [PATCH v2] perf tools: Get a perf cgroup more portably in BPF

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Message-ID: <CA+khW7gQPqoBSi5bSQXFdnkVyjMpu4A=vzFXRLvWDjZww0brEA@mail.gmail.com>
Date:   Thu, 22 Sep 2022 12:35:58 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Song Liu <songliubraving@...com>,
        bpf@...r.kernel.org
Subject: Re: [PATCH v2] perf tools: Get a perf cgroup more portably in BPF

On Wed, Sep 21, 2022 at 9:40 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> The perf_event_cgrp_id can be different on other configurations.
> To be more portable as CO-RE, it needs to get the cgroup subsys id
> using the bpf_core_enum_value() helper.
>

I remember using bpf_core_enum_value requires a compiler built-in. So
the build will fail on old compiler such as clang-11. See [1]. Maybe
we should surround it with #if
__has_builtin(__builtin_preserve_enum_value) to be sure.

[1]  https://www.spinics.net/lists/bpf/msg30859.html

> Suggested-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
[...]