linux-kernel - Re: [PATCH v2 7/7] bug: Move WARN_ON() "cut here" into exception handler

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Date:   Fri, 23 Aug 2019 16:26:59 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        20190819234111.9019-8-keescook@...omium.org
Cc:     Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Drew Davenport <ddavenport@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Feng Tang <feng.tang@...el.com>,
        Petr Mladek <pmladek@...e.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        YueHaibing <yuehaibing@...wei.com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/7] bug: Move WARN_ON() "cut here" into exception
 handler



Le 23/08/2019 à 00:56, Andrew Morton a écrit :
> On Tue, 20 Aug 2019 09:47:55 -0700 Kees Cook <keescook@...omium.org> wrote:
> 
>> Reply-To: 20190819234111.9019-8-keescook@...omium.org
> 
> Really?

That seems correct, that's the "[PATCH 7/7] bug: Move WARN_ON() "cut 
here" into exception handler" from the series at 
https://lkml.org/lkml/2019/8/19/1155


> 
>> Subject: [PATCH v2 7/7] bug: Move WARN_ON() "cut here" into exception handler
> 
> It's strange to receive a standalone [7/7] patch.

Iaw the Reply_To, I understand it as an update of the 7th patch of the 
series.

> 
>> Date:   Tue, 20 Aug 2019 09:47:55 -0700
>> Sender: linux-kernel-owner@...r.kernel.org
>>
>> The original clean up of "cut here" missed the WARN_ON() case (that
>> does not have a printk message), which was fixed recently by adding
>> an explicit printk of "cut here". This had the downside of adding a
>> printk() to every WARN_ON() caller, which reduces the utility of using
>> an instruction exception to streamline the resulting code. By making
>> this a new BUGFLAG, all of these can be removed and "cut here" can be
>> handled by the exception handler.
>>
>> This was very pronounced on PowerPC, but the effect can be seen on
>> x86 as well. The resulting text size of a defconfig build shows some
>> small savings from this patch:
>>
>>     text    data     bss     dec     hex filename
>> 19691167        5134320 1646664 26472151        193eed7 vmlinux.before
>> 19676362        5134260 1663048 26473670        193f4c6 vmlinux.after
>>
>> This change also opens the door for creating something like BUG_MSG(),
>> where a custom printk() before issuing BUG(), without confusing the "cut
>> here" line.
> 
> I can't get this to apply to anything, so I guess that [1/7]-[6/7]
> mattered ;)

On my side it applies cleanly on top of patch 1-6 of the series.

Christophe


> 
>> Reported-by: Christophe Leroy <christophe.leroy@....fr>
>> Fixes: Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
> 
> I'm seeing double.
> 
>> Signed-off-by: Kees Cook <keescook@...omium.org>