[POWERPC] Fix VDSO gettimeofday() when called with NULL struct timeval

Consider the prototype for gettimeofday():
int gettimofday(struct timeval *tv, struct timezone *tz);

Although it is valid to call with /either/ tv or tz being NULL, and
the C version of sys_gettimeofday() supports this, the current version
of gettimeofday() in the VDSO will SEGV if called with a NULL tv.

This adds a check for tv being NULL so that it doesn't SEGV.

Signed-off-by: Tony Breeds <[e-mail]>
Acked-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Paul Mackerras <[e-mail]>

arch/powerpc/kernel/vdso32/gettimeofday.S

···
 	mr	r11,r4			/* r11 saves tz */
 	bl	__get_datapage@local	/* get data page */
 	mr	r9, r3			/* datapage ptr in r9 */
+	cmplwi	r10,0			/* check if tv is NULL */
+	beq	3f
 	bl	__do_get_xsec@local	/* get xsec from tb & kernel */
 	bne-	2f			/* out of line -> do syscall */
 
···
 	mulhwu	r5,r5,r6
 	stw	r5,TVAL32_TV_USEC(r10)
 
-	cmpli	cr0,r11,0		/* check if tz is NULL */
+3:	cmplwi	r11,0			/* check if tz is NULL */
 	beq	1f
 	lwz	r4,CFG_TZ_MINUTEWEST(r9)/* fill tz */
 	lwz	r5,CFG_TZ_DSTTIME(r9)

arch/powerpc/kernel/vdso64/gettimeofday.S

···
-
-	/*
+/*
  * Userland implementation of gettimeofday() for 64 bits processes in a
  * ppc64 kernel for use in the vDSO
  *
···
 	mr	r11,r3			/* r11 holds tv */
 	mr	r10,r4			/* r10 holds tz */
 	bl	V_LOCAL_FUNC(__get_datapage)	/* get data page */
+	cmpldi	r10,0			/* check if tv is NULL */
+	beq	2f
 	bl	V_LOCAL_FUNC(__do_get_xsec)	/* get xsec from tb & kernel */
 	lis     r7,15			/* r7 = 1000000 = USEC_PER_SEC */
 	ori     r7,r7,16960
···
 					 * XSEC_PER_SEC
 					 */
 	rldicl  r0,r0,44,20
-	cmpldi	cr0,r10,0		/* check if tz is NULL */
 	std	r0,TVAL64_TV_USEC(r11)	/* store usec in tv */
+2:	cmpldi	r10,0			/* check if tz is NULL */
 	beq	1f
 	lwz	r4,CFG_TZ_MINUTEWEST(r3)/* fill tz */
 	lwz	r5,CFG_TZ_DSTTIME(r3)