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

From: Christophe Leroy
Date: Fri Aug 23 2019 - 10:27:03 EST

Le 23/08/2019 Ã 00:56, Andrew Morton a ÃcritÂ:
On Tue, 20 Aug 2019 09:47:55 -0700 Kees Cook <keescook@xxxxxxxxxxxx> wrote:

Reply-To: 20190819234111.9019-8-keescook@xxxxxxxxxxxx


That seems correct, that's the "[PATCH 7/7] bug: Move WARN_ON() "cut here" into exception handler" from the series at

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@xxxxxxxxxxxxxxx

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.


Reported-by: Christophe Leroy <christophe.leroy@xxxxxx>
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@xxxxxxxxxxxx>