linux-kernel - Re: [PATCH v4 27/31] kcov: test compiler capability in Kconfig and correct dependency

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Message-ID: <CAGXu5j+OAXpbc4qaKJfAaUNpPh3MsuFq6FWQ6iPky41ExuVUjA@mail.gmail.com>
Date:   Wed, 16 May 2018 23:33:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kbuild <linux-kbuild@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Ulf Magnusson <ulfalizer@...il.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Emese Revfy <re.emese@...il.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v4 27/31] kcov: test compiler capability in Kconfig and
 correct dependency

On Wed, May 16, 2018 at 11:17 PM, Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
> As Documentation/kbuild/kconfig-language.txt notes, 'select' should be
> be used with care - it forces a lower limit of another symbol, ignoring
> the dependency.  Currently, KCOV can select GCC_PLUGINS even if arch
> does not select HAVE_GCC_PLUGINS.  This could cause the unmet direct
> dependency.
>
> Now that Kconfig can test compiler capability, let's handle this in a
> more sophisticated way.
>
> There are two ways to enable KCOV; use the compiler that natively
> supports -fsanitize-coverage=trace-pc, or build the SANCOV plugin if
> the compiler has ability to build GCC plugins.  Hence, the correct
> dependency for KCOV is:
>
>   depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
>
> You do not need to build the SANCOV plugin if the compiler already
> supports -fsanitize-coverage=trace-pc.  Hence, the select should be:
>
>   select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
>
> With this, GCC_PLUGIN_SANCOV is selected only when necessary, so
> scripts/Makefile.gcc-plugins can be cleaner.
>
> I also cleaned up Kconfig and scripts/Makefile.kcov as well.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

-- 
Kees Cook
Pixel Security