[PATCH] selftests/powerpc: Fix TM resched DSCR test with some compilers

The tm-resched-dscr test has started failing sometimes, depending on
what compiler it's built with, eg:

  test: tm_resched_dscr
  Check DSCR TM context switch: tm-resched-dscr: tm-resched-dscr.c:76: test_body: Assertion `rv' failed.
  !! child died by signal 6

When it fails we see that the compiler doesn't initialise rv to 1 before
entering the inline asm block. Although that's counter intuitive, it
is allowed because we tell the compiler that the inline asm will write
to rv (using "=r"), meaning the original value is irrelevant.

Marking it as a read/write parameter would presumably work, but it seems
simpler to fix it by setting the initial value of rv in the inline asm.

Fixes: 96d016108640 ("powerpc: Correct DSCR during TM context switch")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 tools/testing/selftests/powerpc/tm/tm-resched-dscr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/powerpc/tm/tm-resched-dscr.c b/tools/testing/selftests/powerpc/tm/tm-resched-dscr.c
index d9c49f41515e..e79ccd6aada1 100644
--- a/tools/testing/selftests/powerpc/tm/tm-resched-dscr.c
+++ b/tools/testing/selftests/powerpc/tm/tm-resched-dscr.c

@@ -42,12 +42,12 @@ int test_body(void)
 	printf("Check DSCR TM context switch: ");
 	fflush(stdout);
 	for (;;) {
-		rv = 1;
 		asm __volatile__ (
 			/* set a known value into the DSCR */
 			"ld      3, %[dscr1];"
 			"mtspr   %[sprn_dscr], 3;"
 
+			"li      %[rv], 1;"
 			/* start and suspend a transaction */
 			"tbegin.;"
 			"beq     1f;"

-- 
2.7.4

On Fri, 2017-05-19 at 11:37 +1000, Michael Ellerman wrote:

The tm-resched-dscr test has started failing sometimes, depending on
what compiler it's built with, eg:
=20
=C2=A0 test: tm_resched_dscr
=C2=A0 Check DSCR TM context switch: tm-resched-dscr: tm-resched-dscr.c:7=

6:

test_body: Assertion `rv' failed.
=C2=A0 !! child died by signal 6
=20
When it fails we see that the compiler doesn't initialise rv to 1 before
entering the inline asm block. Although that's counter intuitive, it
is allowed because we tell the compiler that the inline asm will write
to rv (using "=3Dr"), meaning the original value is irrelevant.
=20
Marking it as a read/write parameter would presumably work, but it seems
simpler to fix it by setting the initial value of rv in the inline asm.
=20
Fixes: 96d016108640 ("powerpc: Correct DSCR during TM context switch")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Thanks.

Acked-by: Michael Neuling <redacted>

On Fri, 2017-05-19 at 01:37:45 UTC, Michael Ellerman wrote:

The tm-resched-dscr test has started failing sometimes, depending on
what compiler it's built with, eg:

  test: tm_resched_dscr
  Check DSCR TM context switch: tm-resched-dscr: tm-resched-dscr.c:76: test_body: Assertion `rv' failed.
  !! child died by signal 6

When it fails we see that the compiler doesn't initialise rv to 1 before
entering the inline asm block. Although that's counter intuitive, it
is allowed because we tell the compiler that the inline asm will write
to rv (using "=r"), meaning the original value is irrelevant.

Marking it as a read/write parameter would presumably work, but it seems
simpler to fix it by setting the initial value of rv in the inline asm.

Fixes: 96d016108640 ("powerpc: Correct DSCR during TM context switch")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Michael Neuling <redacted>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/fe06fe860250a4f01d0eaf70a2563b

cheers