* [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx)
@ 2009-08-25 21:00 Jiri Slaby
2009-08-25 22:29 ` Jeremy Fitzhardinge
2009-08-26 6:09 ` Ingo Molnar
0 siblings, 2 replies; 4+ messages in thread
From: Jiri Slaby @ 2009-08-25 21:00 UTC (permalink / raw)
To: jeremy; +Cc: chrisw, virtualization, xen-devel, linux-kernel, Jiri Slaby
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@gmail.com>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@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
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx)
2009-08-25 21:00 [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx) Jiri Slaby
@ 2009-08-25 22:29 ` Jeremy Fitzhardinge
2009-08-26 6:09 ` Ingo Molnar
1 sibling, 0 replies; 4+ messages in thread
From: Jeremy Fitzhardinge @ 2009-08-25 22:29 UTC (permalink / raw)
To: Jiri Slaby
Cc: xen-devel, jeremy, the arch/x86 maintainers, linux-kernel, chrisw,
virtualization, Ingo Molnar
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@gmail.com>
> Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
> Cc: Chris Wright <chrisw@sous-sol.org>
>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@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 */
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx)
2009-08-25 21:00 [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx) Jiri Slaby
2009-08-25 22:29 ` Jeremy Fitzhardinge
@ 2009-08-26 6:09 ` Ingo Molnar
2009-08-26 17:27 ` H. Peter Anvin
1 sibling, 1 reply; 4+ messages in thread
From: Ingo Molnar @ 2009-08-26 6:09 UTC (permalink / raw)
To: Jiri Slaby; +Cc: jeremy, chrisw, virtualization, xen-devel, linux-kernel
* Jiri Slaby <jirislaby@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@gmail.com>
> Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
> Cc: Chris Wright <chrisw@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
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx)
2009-08-26 6:09 ` Ingo Molnar
@ 2009-08-26 17:27 ` H. Peter Anvin
0 siblings, 0 replies; 4+ messages in thread
From: H. Peter Anvin @ 2009-08-26 17:27 UTC (permalink / raw)
To: Ingo Molnar
Cc: xen-devel, Jiri Slaby, linux-kernel, chrisw, virtualization,
jeremy
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.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2009-08-25 21:00 [PATCH 1/1] XEN: enlighten, use uninitialized_var(cx) Jiri Slaby
2009-08-25 22:29 ` Jeremy Fitzhardinge
2009-08-26 6:09 ` Ingo Molnar
2009-08-26 17:27 ` H. Peter Anvin
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