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

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Message-ID: <20090826060925.GA6194@elte.hu>
Date:	Wed, 26 Aug 2009 08:09:25 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	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)


* Jiri Slaby <jirislaby@...il.com> wrote:

> To avoid a wrong compiler warning, use unitialized_var(cx) in
> xen_init_cpuid_mask.
> 
> cx needn't be initialized for cpuid when ax is 1.
> 
> Signed-off-by: Jiri Slaby <jirislaby@...il.com>
> Cc: Jeremy Fitzhardinge <jeremy@...source.com>
> Cc: Chris Wright <chrisw@...s-sol.org>
> ---
>  arch/x86/xen/enlighten.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> 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.

	Ingo
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