linux-kernel - Re: [PATCH -tip] x86: kvm/paging_tmpl.h intialize the variable before using it

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Message-ID: <20090525060531.GA16990@elte.hu>
Date:	Mon, 25 May 2009 08:05:31 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] x86: kvm/paging_tmpl.h intialize the variable
	before using it


* Avi Kivity <avi@...hat.com> wrote:

> Jaswinder Singh Rajput wrote:
>> May be in some cases paging64_fetch() and paging32_fetch() will return sptep
>> without initialization.
>>
>> Also fixes compilation warning:
>>   CC      arch/x86/kernel/io_delay.o
>>  arch/x86/kvm/paging_tmpl.h: In function ‘paging64_fetch’:
>>  arch/x86/kvm/paging_tmpl.h:279: warning: ‘sptep’ may be used uninitialized in this function
>>  arch/x86/kvm/paging_tmpl.h: In function ‘paging32_fetch’:
>>  arch/x86/kvm/paging_tmpl.h:279: warning: ‘sptep’ may be used uninitialized in this function
>>
>> Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@...il.com>
>> ---
>>  arch/x86/kvm/paging_tmpl.h |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
>> index 6bd7020..99cb10d 100644
>> --- a/arch/x86/kvm/paging_tmpl.h
>> +++ b/arch/x86/kvm/paging_tmpl.h
>> @@ -276,7 +276,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
>>  {
>>  	unsigned access = gw->pt_access;
>>  	struct kvm_mmu_page *shadow_page;
>> -	u64 spte, *sptep;
>> +	u64 spte, *sptep = NULL;
>>  	int direct;
>>  	gfn_t table_gfn;
>>  	int r;
>>   
>
> It's a false alarm.  Isn't there a macro to shut up the warning?

there's uninitialized_var(), but that will shut up the warning and 
any _correct_ future warning - so it's dangerous. Initialize it to 
NULL and be done with it? We dont want stray warnings in the kernel.

	Ingo
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