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

[Michael Neuling]

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:
> 
>   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 at ellerman.id.au>

Thanks.

Acked-by: Michael Neuling <mikey at neuling.org>

> ---
>  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;"