[PATCH] arm_pmu: fix compiler warning in arm_pmu_device_probe

[PATCH] arm_pmu: fix compiler warning in arm_pmu_device_probe

[Chris Packham]

GCC warns

  arm_pmu_platform.c:234:5: error: 'err' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This is because we rely on the for_each_cpu loop in armpmu_request_irqs
to initialise err. The warning is a little bogus because we know if
there were 0 CPUs this code would not be running.

Initialise err to 0 to avoid the warning.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
---
This has been reported before in https://lkml.org/lkml/2018/3/5/508 I'm not
sure if it was dismmissed as "meh, gcc is wrong" or if it was just wainting for
someone with some round tuits.


 drivers/perf/arm_pmu_platform.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/perf/arm_pmu_platform.c b/drivers/perf/arm_pmu_platform.c
index 971ff336494a..96075cecb0ae 100644
--- a/drivers/perf/arm_pmu_platform.c
+++ b/drivers/perf/arm_pmu_platform.c
@@ -160,7 +160,7 @@ static int pmu_parse_irqs(struct arm_pmu *pmu)
 static int armpmu_request_irqs(struct arm_pmu *armpmu)
 {
 	struct pmu_hw_events __percpu *hw_events = armpmu->hw_events;
-	int cpu, err;
+	int cpu, err = 0;
 
 	for_each_cpu(cpu, &armpmu->supported_cpus) {
 		int irq = per_cpu(hw_events->irq, cpu);
-- 
2.18.0

[PATCH] arm_pmu: fix compiler warning in arm_pmu_device_probe

[Robin Murphy]

Hi Chris,

On 01/08/18 22:45, Chris Packham wrote:
> GCC warns
> 
>    arm_pmu_platform.c:234:5: error: 'err' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> This is because we rely on the for_each_cpu loop in armpmu_request_irqs
> to initialise err. The warning is a little bogus because we know if
> there were 0 CPUs this code would not be running.
> 
> Initialise err to 0 to avoid the warning.

Maybe initialising to something like -EINVAL would be more appropriate, 
just in case we did ever manage to get here with armpmu->supported_cpus 
unset?

Robin.

> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
> ---
> This has been reported before in https://lkml.org/lkml/2018/3/5/508 I'm not
> sure if it was dismmissed as "meh, gcc is wrong" or if it was just wainting for
> someone with some round tuits.
> 
> 
>   drivers/perf/arm_pmu_platform.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm_pmu_platform.c b/drivers/perf/arm_pmu_platform.c
> index 971ff336494a..96075cecb0ae 100644
> --- a/drivers/perf/arm_pmu_platform.c
> +++ b/drivers/perf/arm_pmu_platform.c
> @@ -160,7 +160,7 @@ static int pmu_parse_irqs(struct arm_pmu *pmu)
>   static int armpmu_request_irqs(struct arm_pmu *armpmu)
>   {
>   	struct pmu_hw_events __percpu *hw_events = armpmu->hw_events;
> -	int cpu, err;
> +	int cpu, err = 0;
>   
>   	for_each_cpu(cpu, &armpmu->supported_cpus) {
>   		int irq = per_cpu(hw_events->irq, cpu);
> 

[PATCH] arm_pmu: fix compiler warning in arm_pmu_device_probe

[Will Deacon]

On Thu, Aug 02, 2018 at 09:45:26AM +1200, Chris Packham wrote:
> GCC warns
> 
>   arm_pmu_platform.c:234:5: error: 'err' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> This is because we rely on the for_each_cpu loop in armpmu_request_irqs
> to initialise err. The warning is a little bogus because we know if
> there were 0 CPUs this code would not be running.
> 
> Initialise err to 0 to avoid the warning.
> 
> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
> ---
> This has been reported before in https://lkml.org/lkml/2018/3/5/508 I'm not
> sure if it was dismmissed as "meh, gcc is wrong" or if it was just wainting for
> someone with some round tuits.

Which version of GCC are you using? I don't see this warning locally.

Will

[PATCH] arm_pmu: fix compiler warning in arm_pmu_device_probe

[Chris Packham]

On 02/08/18 23:05, Will Deacon wrote:
> On Thu, Aug 02, 2018 at 09:45:26AM +1200, Chris Packham wrote:
>> GCC warns
>>
>>    arm_pmu_platform.c:234:5: error: 'err' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>
>> This is because we rely on the for_each_cpu loop in armpmu_request_irqs
>> to initialise err. The warning is a little bogus because we know if
>> there were 0 CPUs this code would not be running.
>>
>> Initialise err to 0 to avoid the warning.
>>
>> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
>> ---
>> This has been reported before in https://lkml.org/lkml/2018/3/5/508 I'm not
>> sure if it was dismmissed as "meh, gcc is wrong" or if it was just wainting for
>> someone with some round tuits.
> 
> Which version of GCC are you using? I don't see this warning locally.
> 

My local cross-compiler is

$ arm-softfloat-linux-gnueabi-gcc --version
arm-softfloat-linux-gnueabi-gcc (crosstool-NG crosstool-ng-1.22.0) 4.9.3

Old-ish but as far as I was aware still supported for building the kernel.

I've just tried 7.3.0 and 8.1.0 neither of which complain.

A quick look at the report linked to above seems they probably were 
using 4.6.3 and it still appears in current build reports

http://kisskb.ellerman.id.au/kisskb/buildresult/13455291/