linux-kernel - Re: [PATCH 4/4] perf record: Handle argument change in sched

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Message-ID: <CAM9d7ciZcsTD7oK5JQA5PJ3gDHcN+Fzon=gVoPvyRb4yLzVF7w@mail.gmail.com>
Date:   Thu, 28 Apr 2022 16:58:02 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
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>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Song Liu <songliubraving@...com>, Hao Luo <haoluo@...gle.com>,
        bpf <bpf@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        Blake Jones <blakejones@...gle.com>
Subject: Re: [PATCH 4/4] perf record: Handle argument change in sched_switch

On Wed, Apr 27, 2022 at 12:26 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Wed, Apr 27, 2022 at 11:15 AM Namhyung Kim <namhyung@...nel.org> wrote:
> > Actually I tried something similar but it was with a variable (in bss)
> > so the verifier in an old kernel rejected it due to invalid arg access.
> >
> > I guess now the const makes the verifier ignore the branch as if
> > it's dead but the compiler still generates the code, right?
>
>
> yes, exactly

Then I'm curious how it'd work on newer kernels.
The verifier sees the false branch and detects type mismatch
for the second argument then it'd reject the program?

Thanks,
Namhyung