linux-kernel - Re: [tip:perf/urgent] x86/oprofile: Fix uninitialized variable use in debug printk

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Message-ID: <20101025102738.GA26151@elte.hu>
Date:	Mon, 25 Oct 2010 12:27:38 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Richter <robert.richter@....com>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:perf/urgent] x86/oprofile: Fix uninitialized variable use
 in debug printk


* Robert Richter <robert.richter@....com> wrote:

> On 25.10.10 02:52:03, tip-bot for Ingo Molnar wrote:
> > Commit-ID:  2c78ffeca98fcd5a1dfd4a322438944506ed5e64
> > Gitweb:     http://git.kernel.org/tip/2c78ffeca98fcd5a1dfd4a322438944506ed5e64
> > Author:     Ingo Molnar <mingo@...e.hu>
> > AuthorDate: Mon, 25 Oct 2010 08:41:09 +0200
> > Committer:  Ingo Molnar <mingo@...e.hu>
> > CommitDate: Mon, 25 Oct 2010 08:46:20 +0200
> > 
> > x86/oprofile: Fix uninitialized variable use in debug printk
> > 
> > Stephen Rothwell reported this build warning:
> > 
> >   arch/x86/oprofile/op_model_amd.c: In function 'ibs_eilvt_valid':
> >   arch/x86/oprofile/op_model_amd.c:289: warning: 'offset' may be used uninitialized in this function
> > 
> > And correctly observed that indeed the variable is used uninitialized in
> > this function. The result of this bug can be a debug printk with a bogus
> > value.
> > 
> > Also fix a few more small details that made this function hard to read
> > and which probably contributed to the bug being introduced to begin with:
> > 
> >  - Use more symmetric error conditions
> > 
> >  - Remove the !0 obfuscation
> > 
> >  - Add newlines to the printk output
> > 
> >  - Remove bogus linebreaks in printk strings and elsewhere
> 
> Ingo, thanks for changing this, it all looks good to me, though we actually don't 
> have to print the offset as the valid bit is not set.

Yeah - thought of that, but didnt want to change behavior.

> For some reason I didn't catch the warning:
> 
> ...
>   LD      arch/x86/kernel/acpi/built-in.o
>   CC      arch/x86/oprofile/op_model_amd.o
>   CC      arch/x86/kernel/cpu/intel_cacheinfo.o
> ...
> 
> (using gcc (Gentoo 4.4.3-r2 p1.2) 4.4.3)
> 
> ... but it should warn.

Weird - should be very obvious for a compiler to see that.

	Ingo
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