linux-kernel - Re: [PATCH 1/1] XEN: enlighten, use uninitialized

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Date:	Wed, 26 Aug 2009 10:27:15 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jiri Slaby <jirislaby@...il.com>, jeremy@...source.com,
	chrisw@...s-sol.org, virtualization@...ts.osdl.org,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx)

On 08/25/2009 11:09 PM, Ingo Molnar wrote:
>>
>> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
>> index e90540a..5ab75e2 100644
>> --- a/arch/x86/xen/enlighten.c
>> +++ b/arch/x86/xen/enlighten.c
>> @@ -202,7 +202,7 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
>>  
>>  static __init void xen_init_cpuid_mask(void)
>>  {
>> -	unsigned int ax, bx, cx, dx;
>> +	unsigned int ax, bx, uninitialized_var(cx), dx;
> 
> Please dont use uninitialized_var(), it's an unreliable facility: if 
> this variable ever grows a real used-without-initialization bug in 
> the future, the compiler warning is turned off permanently. It's 
> rare but might happen. We are better off with initializing it to 
> zero.
> 

I hadn't seen this thread, but I pushed a patch to x86/urgent to do
exactly that while I was committing the Xen crash patch last night.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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