From: Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v5 13/15] Compiler Attributes: enable -Wstringop-truncation
 on W=1 (gcc >= 8)
Date: Thu, 20 Sep 2018 12:52:57 -0700
Message-ID: <CAGXu5jKZYEK7Asy4KwtfVVxHLFbpeqpWWEOM-60h7h4gj3JZrw@mail.gmail.com>
References: <20180920172301.21868-1-miguel.ojeda.sandonis@gmail.com> <20180920172301.21868-14-miguel.ojeda.sandonis@gmail.com>
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Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Olof Johansson <olof@lxom.net>,
        Konstantin Ryabitsev <konstantin@linuxfoundation.org>,
        "David S . Miller" <davem@davemloft.net>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Paul Lawrence <paullawrence@google.com>,
        Sandipan Das <sandipan@linux.vnet.ibm.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Will Deacon <will.deacon@arm.com>,
        P
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20180920172301.21868-14-miguel.ojeda.sandonis@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Thu, Sep 20, 2018 at 10:22 AM, Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
> Commit 217c3e019675 ("disable stringop truncation warnings for now")
> disabled -Wstringop-truncation since it was too noisy.
>
> Having __nonstring available allows us to let GCC know that a string
> is not meant to be NUL-terminated, which helps suppressing some
> -Wstringop-truncation warnings.
>
> Note that using __nonstring actually triggers other warnings
> (-Wstringop-overflow, which is on by default) which may be real
> problems. Therefore, cleaning up -Wstringop-truncation warnings
> also buys us the ability to uncover further potential problems.
>
> To encourage the use of __nonstring, we put the warning back at W=1.
> In the future, if we end up with a fairly warning-free tree,
> we might want to enable it by default.
>
> Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

Yessss. :)

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

-Kees

> ---
>  scripts/Makefile.extrawarn | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 8d5357053f86..b8f36f5f43f2 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -29,6 +29,7 @@ warning-1 += $(call cc-option, -Wmissing-include-dirs)
>  warning-1 += $(call cc-option, -Wunused-but-set-variable)
>  warning-1 += $(call cc-option, -Wunused-const-variable)
>  warning-1 += $(call cc-option, -Wpacked-not-aligned)
> +warning-1 += $(call cc-option, -Wstringop-truncation)
>  warning-1 += $(call cc-disable-warning, missing-field-initializers)
>  warning-1 += $(call cc-disable-warning, sign-compare)
>
> --
> 2.17.1
>



-- 
Kees Cook
Pixel Security