Re: [PATCH 2/5] powerpc: Fix vDSO clock_getres()

[Vincenzo Frascino <vincenzo.frascino@arm.com>]

On 02/04/2019 07:14, Christophe Leroy wrote:
> 
> 
> On 04/01/2019 11:51 AM, Vincenzo Frascino wrote:
>> clock_getres in the vDSO library has to preserve the same behaviour
>> of posix_get_hrtimer_res().
>>
>> In particular, posix_get_hrtimer_res() does:
>>      sec = 0;
>>      ns = hrtimer_resolution;
>> and hrtimer_resolution depends on the enablement of the high
>> resolution timers that can happen either at compile or at run time.
>>
>> Fix the powerpc vdso implementation of clock_getres keeping a copy of
>> hrtimer_resolution in vdso data and using that directly.
>>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> Cc: Paul Mackerras <paulus@samba.org>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>> ---
>>   arch/powerpc/include/asm/vdso_datapage.h  |  2 ++
>>   arch/powerpc/kernel/asm-offsets.c         |  2 +-
>>   arch/powerpc/kernel/time.c                |  1 +
>>   arch/powerpc/kernel/vdso32/gettimeofday.S | 22 +++++++++++++++-------
>>   arch/powerpc/kernel/vdso64/gettimeofday.S | 22 +++++++++++++++-------
>>   5 files changed, 34 insertions(+), 15 deletions(-)
>>
> 
> [...]
> 
>> diff --git a/arch/powerpc/kernel/vdso32/gettimeofday.S b/arch/powerpc/kernel/vdso32/gettimeofday.S
>> index 1e0bc5955a40..b21630079496 100644
>> --- a/arch/powerpc/kernel/vdso32/gettimeofday.S
>> +++ b/arch/powerpc/kernel/vdso32/gettimeofday.S
>> @@ -160,14 +160,21 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
>>   	cror	cr0*4+eq,cr0*4+eq,cr1*4+eq
>>   	bne	cr0,99f
>>   
>> -	li	r3,0
>> -	cmpli	cr0,r4,0
>> +	mflr	r12
>> +  .cfi_register lr,r12
>> +	mr	r11,r4
>> +	bl	__get_datapage@local
>> +	lwz	r5,CLOCK_REALTIME_RES(r3)
>> +	li	r4,0
>> +	cmplwi	r11,0		/* check if res is NULL */
>> +	beq	1f
>> +
>> +	stw	r4,TSPC32_TV_SEC(r11)
>> +	stw	r5,TSPC32_TV_NSEC(r11)
>> +
>> +1:	mtlr	r12
>>   	crclr	cr0*4+so
>> -	beqlr
>> -	lis	r5,CLOCK_REALTIME_RES@h
>> -	ori	r5,r5,CLOCK_REALTIME_RES@l
>> -	stw	r3,TSPC32_TV_SEC(r4)
>> -	stw	r5,TSPC32_TV_NSEC(r4)
>> +	li	r3,0
>>   	blr
> 
> The above can be done simpler, see below
> 
> @@ -160,12 +160,15 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
>   	cror	cr0*4+eq,cr0*4+eq,cr1*4+eq
>   	bne	cr0,99f
> 
> +	mflr	r12
> +  .cfi_register lr,r12
> +	bl	__get_datapage@local
> +	lwz	r5,CLOCK_REALTIME_RES(r3)
> +	mtlr	r12
>   	li	r3,0
>   	cmpli	cr0,r4,0
>   	crclr	cr0*4+so
>   	beqlr
> -	lis	r5,CLOCK_REALTIME_RES@h
> -	ori	r5,r5,CLOCK_REALTIME_RES@l
>   	stw	r3,TSPC32_TV_SEC(r4)
>   	stw	r5,TSPC32_TV_NSEC(r4)
>   	blr
> 

Thank you for this, I will update my code accordingly before posting v2.

> Christophe
> 
>>   
>>   	/*
>> @@ -175,6 +182,7 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
>>   	 */
>>   99:
>>   	li	r0,__NR_clock_getres
>> +  .cfi_restore lr
>>   	sc
>>   	blr
>>     .cfi_endproc
>> diff --git a/arch/powerpc/kernel/vdso64/gettimeofday.S b/arch/powerpc/kernel/vdso64/gettimeofday.S
>> index a4ed9edfd5f0..a7e49bddd475 100644
>> --- a/arch/powerpc/kernel/vdso64/gettimeofday.S
>> +++ b/arch/powerpc/kernel/vdso64/gettimeofday.S
>> @@ -190,14 +190,21 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
>>   	cror	cr0*4+eq,cr0*4+eq,cr1*4+eq
>>   	bne	cr0,99f
>>   
>> -	li	r3,0
>> -	cmpldi	cr0,r4,0
>> +	mflr	r12
>> +  .cfi_register lr,r12
>> +	mr	r11, r4
>> +	bl	V_LOCAL_FUNC(__get_datapage)
>> +	lwz	r5,CLOCK_REALTIME_RES(r3)
>> +	li	r4,0
>> +	cmpldi	r11,0		/* check if res is NULL */
>> +	beq	1f
>> +
>> +	std	r4,TSPC64_TV_SEC(r11)
>> +	std	r5,TSPC64_TV_NSEC(r11)
>> +
>> +1:	mtlr	r12
>>   	crclr	cr0*4+so
>> -	beqlr
>> -	lis	r5,CLOCK_REALTIME_RES@h
>> -	ori	r5,r5,CLOCK_REALTIME_RES@l
>> -	std	r3,TSPC64_TV_SEC(r4)
>> -	std	r5,TSPC64_TV_NSEC(r4)
>> +	li	r3,0
>>   	blr
> 
> The same type of simplification applies here too.
> 
> Christophe
> 
> 
>>   
>>   	/*
>> @@ -205,6 +212,7 @@ V_FUNCTION_BEGIN(__kernel_clock_getres)
>>   	 */
>>   99:
>>   	li	r0,__NR_clock_getres
>> +  .cfi_restore lr
>>   	sc
>>   	blr
>>     .cfi_endproc
>>

-- 
Regards,
Vincenzo