Xen devel - Aug 2009 - [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx)

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 at gmail.com>
Cc: Jeremy Fitzhardinge <jeremy at xensource.com>
Cc: Chris Wright <chrisw at sous-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;
 
 	cpuid_leaf1_edx_mask  		~((1 << X86_FEATURE_MCE)  |  /* disable MCE */
-- 
1.6.3.3

On 08/25/09 14:00, Jiri Slaby 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 at gmail.com>
> Cc: Jeremy Fitzhardinge <jeremy at xensource.com>
> Cc: Chris Wright <chrisw at sous-sol.org>
>   
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge at citrix.com>
> ---
>  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;
>  
>  	cpuid_leaf1_edx_mask >  		~((1 << X86_FEATURE_MCE)  |  /*
disable MCE */
>

* Jiri Slaby <jirislaby at gmail.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 at gmail.com>
> Cc: Jeremy Fitzhardinge <jeremy at xensource.com>
> Cc: Chris Wright <chrisw at sous-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