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

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Message-Id: <20190822155611.a1a6e26db99ba0876ba9c8bd@linux-foundation.org>
Date:   Thu, 22 Aug 2019 15:56:11 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     20190819234111.9019-8-keescook@...omium.org
Cc:     Kees Cook <keescook@...omium.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        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

On Tue, 20 Aug 2019 09:47:55 -0700 Kees Cook <keescook@...omium.org> wrote:

> Reply-To: 20190819234111.9019-8-keescook@...omium.org

Really?

> Subject: [PATCH v2 7/7] bug: Move WARN_ON() "cut here" into exception handler

It's strange to receive a standalone [7/7] patch.

> 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 ;)

> 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>