linux-kernel - Re: [PATCH] Introduced new tracing mode KCOV_MODE

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Date:   Mon, 22 Mar 2021 13:17:04 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Alexander Lochmann <info@...xander-lochmann.de>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Miguel Ojeda <ojeda@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Klychkov <andrew.a.klychkov@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        Maciej Grochowski <maciej.grochowski@...me>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Introduced new tracing mode KCOV_MODE_UNIQUE.

Hi Alexander,

On Sun, Mar 21, 2021 at 8:14 PM Alexander Lochmann
<info@...xander-lochmann.de> wrote:
>
> diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst
> index d2c4c27e1702..e105ffe6b6e3 100644
> --- a/Documentation/dev-tools/kcov.rst
> +++ b/Documentation/dev-tools/kcov.rst
> @@ -127,6 +127,86 @@ That is, a parent process opens /sys/kernel/debug/kcov, enables trace mode,
>  mmaps coverage buffer and then forks child processes in a loop. Child processes
>  only need to enable coverage (disable happens automatically on thread end).
>
> +If someone is interested in a set of executed PCs, and does not care about
> +execution order, he or she can advise KCOV to do so:

Please mention explicitly that KCOV_INIT_UNIQUE should be used for
that, i.e. readers of the example shouldn't need to read every line to
figure it out.

> +    #define KCOV_INIT_TRACE                    _IOR('c', 1, unsigned long)

Trace is not used in the example.

> +       /* KCOV was initialized, but recording of unique PCs hasn't been chosen yet. */
> +       KCOV_MODE_INIT_UNQIUE = 2,

Typo? It isn't used?

PS: not sure why I was Cc'd, but I hope that helps.

Cheers,
Miguel