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

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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@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
---
  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

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




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