[PATCH] powerpc: Mark variable `cpumsr` as unused

[PATCH] powerpc: Mark variable `cpumsr` as unused

[Mathieu Malaterre]

Add gcc attribute unused for `cpumsr` variable.

Fix warnings treated as errors with W=1:

  arch/powerpc/kernel/process.c:231:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]
  arch/powerpc/kernel/process.c:296:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]

Signed-off-by: Mathieu Malaterre <malat@debian.org>
---
 arch/powerpc/kernel/process.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 96f34730010f..b9f1a2408738 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -228,7 +228,7 @@ EXPORT_SYMBOL_GPL(flush_fp_to_thread);
 
 void enable_kernel_fp(void)
 {
-	unsigned long cpumsr;
+	unsigned long cpumsr __maybe_unused;
 
 	WARN_ON(preemptible());
 
@@ -293,7 +293,7 @@ EXPORT_SYMBOL(giveup_altivec);
 
 void enable_kernel_altivec(void)
 {
-	unsigned long cpumsr;
+	unsigned long cpumsr __maybe_unused;
 
 	WARN_ON(preemptible());
 
-- 
2.11.0

Re: [PATCH] powerpc: Mark variable `cpumsr` as unused

[Christophe Leroy]

On 11/07/2018 08:26 PM, Mathieu Malaterre wrote:
> Add gcc attribute unused for `cpumsr` variable.
> 
> Fix warnings treated as errors with W=1:
> 
>    arch/powerpc/kernel/process.c:231:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]
>    arch/powerpc/kernel/process.c:296:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]
> 
> Signed-off-by: Mathieu Malaterre <malat@debian.org>

I don't think this is the good way to fix that. This problem was 
introduced by commit 5c784c8414fb ("powerpc/tm: Remove 
msr_tm_active()"). That commit should be reverted and fixed.

That commit should have removed the macro and kept the inline function.

Christophe

> ---
>   arch/powerpc/kernel/process.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 96f34730010f..b9f1a2408738 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -228,7 +228,7 @@ EXPORT_SYMBOL_GPL(flush_fp_to_thread);
>   
>   void enable_kernel_fp(void)
>   {
> -	unsigned long cpumsr;
> +	unsigned long cpumsr __maybe_unused;
>   
>   	WARN_ON(preemptible());
>   
> @@ -293,7 +293,7 @@ EXPORT_SYMBOL(giveup_altivec);
>   
>   void enable_kernel_altivec(void)
>   {
> -	unsigned long cpumsr;
> +	unsigned long cpumsr __maybe_unused;
>   
>   	WARN_ON(preemptible());
>   
> 

Re: [PATCH] powerpc: Mark variable `cpumsr` as unused

[Mathieu Malaterre]

On Thu, Nov 8, 2018 at 7:09 AM Christophe Leroy <christophe.leroy@c-s.fr> wrote:
>
>
>
> On 11/07/2018 08:26 PM, Mathieu Malaterre wrote:
> > Add gcc attribute unused for `cpumsr` variable.
> >
> > Fix warnings treated as errors with W=1:
> >
> >    arch/powerpc/kernel/process.c:231:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]
> >    arch/powerpc/kernel/process.c:296:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]
> >
> > Signed-off-by: Mathieu Malaterre <malat@debian.org>
>
> I don't think this is the good way to fix that. This problem was
> introduced by commit 5c784c8414fb ("powerpc/tm: Remove
> msr_tm_active()"). That commit should be reverted and fixed.

I see, it makes sense.

> That commit should have removed the macro and kept the inline function.

Breno, what do you think ?

> Christophe
>
> > ---
> >   arch/powerpc/kernel/process.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> > index 96f34730010f..b9f1a2408738 100644
> > --- a/arch/powerpc/kernel/process.c
> > +++ b/arch/powerpc/kernel/process.c
> > @@ -228,7 +228,7 @@ EXPORT_SYMBOL_GPL(flush_fp_to_thread);
> >
> >   void enable_kernel_fp(void)
> >   {
> > -     unsigned long cpumsr;
> > +     unsigned long cpumsr __maybe_unused;
> >
> >       WARN_ON(preemptible());
> >
> > @@ -293,7 +293,7 @@ EXPORT_SYMBOL(giveup_altivec);
> >
> >   void enable_kernel_altivec(void)
> >   {
> > -     unsigned long cpumsr;
> > +     unsigned long cpumsr __maybe_unused;
> >
> >       WARN_ON(preemptible());
> >
> >

Re: [PATCH] powerpc: Mark variable `cpumsr` as unused

[Breno Leitao]

Hi Mathieu, Christophe

Thanks for spotting and fixing this bug.

On 11/08/2018 05:25 AM, Mathieu Malaterre wrote:
> On Thu, Nov 8, 2018 at 7:09 AM Christophe Leroy <christophe.leroy@c-s.fr> wrote:
>>
>>
>>
>> On 11/07/2018 08:26 PM, Mathieu Malaterre wrote:
>>> Add gcc attribute unused for `cpumsr` variable.
>>>
>>> Fix warnings treated as errors with W=1:
>>>
>>>    arch/powerpc/kernel/process.c:231:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]
>>>    arch/powerpc/kernel/process.c:296:16: error: variable ‘cpumsr’ set but not used [-Werror=unused-but-set-variable]
>>>
>>> Signed-off-by: Mathieu Malaterre <malat@debian.org>
>>
>> I don't think this is the good way to fix that. This problem was
>> introduced by commit 5c784c8414fb ("powerpc/tm: Remove
>> msr_tm_active()"). That commit should be reverted and fixed.
> 
> I see, it makes sense.
> 
>> That commit should have removed the macro and kept the inline function.
> 
> Breno, what do you think ?

Turning this macro into a function might cause the code to be more confused,
since all the other TM states bits are checked using a macro, for example:

 MSR_TM_SUSPENDED     Checks if the MSR has Suspended bits set
 MSR_TM_TRANSACTIONAL Checks if the MSR has the transactional bits set
 MSR_TM_RESV          Checks if the MSR has the TM reserved bits set	

That said, I understand that it makes sense to have an uniform way to check
for TM bits in MSR, thus having a MSR_TM_ACTIVE macro to check for the active
bits. Using a non-uniform function just to fix this warning seems to be an
overkill. Reverting the patch seems to bring back the old style, which is
having a macro and a function with the same name, where the function just
calls the macro.

Anyway, I think it might have other ways to fix warning, as I can think now:

 1) Avoid setting cpumsr if CONFIG_PPC_TRANSACTIONAL_MEM is not enabled

 2) If !CONFIG_PPC_TRANSACTIONAL_MEM, redefine MSR_TM_ACTIVE(x) to something
as (x & 0) instead of 0.

 3) Avoid double definition of MSR_TM_ACTIVE, i.e, have the same definition
independent of PPC_TRANSACTIONAL_MEM being set or not.

Anyway, I would like to try option 3), which is the hardest one to implement
and validate, but it seems to be the most correct option, once it checks for
a MSR bit configuration, and the caller should have the logic.