linux-kernel - Re: [PATCH] vsprintf: make %pV handling compatible with kasprintf()

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Message-Id: <4F55CFCD02000078000768ED@nat28.tlf.novell.com>
Date:	Tue, 06 Mar 2012 07:50:21 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Joe Perches" <joe@...ches.com>
Cc:	<akpm@...ux-foundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vsprintf: make %pV handling compatible with
 kasprintf()

>>> On 05.03.12 at 18:02, Joe Perches <joe@...ches.com> wrote:
> On Mon, 2012-03-05 at 16:49 +0000, Jan Beulich wrote:
>> kasprintf() (and potentially other functions that I didn't run across
>> so far) want to evaluate argument lists twice. Caring to do so for the
>> primary list is obviously their job, but they can't reasonably be
>> expected to check the format string for instances of %pV, which however
>> need special handling too: On architectures like x86-64 (as opposed to
>> e.g. ix86), using the same argument list twice doesn't produce the
>> expected results, as an internally managed cursor gets updated during
>> the first run.
>> 
>> Fix the problem by always acting on a copy of the original list when
>> handling %pV.
> 
> Wouldn't stable need this too?

Possibly, but I'm not certain - this is more of a latent bug that I ran
into with some not yet submitted Xen code. And I'm not sure
whether latent bugs qualify for stable...

Jan

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