[PATCH] selftests/powerpc: Fix wild_bctr test to work on BE

The selftest I recently added to test branching to an out-of-bounds
NIP doesn't work on big endian. It does fail but not in the right way.
That is it SEGVs trying to load from the opd at BAD_NIP, but it never
gets as far as branching to BAD_NIP.

To fix it we need to create an opd which is reachable but which holds
the bad address.

Fixes: b7683fc66eba ("selftests/powerpc: Add a test of wild bctr")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 tools/testing/selftests/powerpc/mm/wild_bctr.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/powerpc/mm/wild_bctr.c b/tools/testing/selftests/powerpc/mm/wild_bctr.c
index 1b0e9e9a2ddc..dda314bb59dd 100644
--- a/tools/testing/selftests/powerpc/mm/wild_bctr.c
+++ b/tools/testing/selftests/powerpc/mm/wild_bctr.c

@@ -105,6 +105,20 @@ static void dump_regs(void)
 	}
 }
 
+#ifdef __BIG_ENDIAN__
+struct opd {
+	unsigned long ip;
+	unsigned long toc;
+	unsigned long env;
+};
+static struct opd bad_opd = {
+	.ip = BAD_NIP,
+};
+#define BAD_FUNC (&bad_opd)
+#else
+#define BAD_FUNC BAD_NIP
+#endif
+
 int test_wild_bctr(void)
 {
 	int (*func_ptr)(void);

@@ -133,7 +147,7 @@ int test_wild_bctr(void)
 
 		poison_regs();
 
-		func_ptr = (int (*)(void))BAD_NIP;
+		func_ptr = (int (*)(void))BAD_FUNC;
 		func_ptr();
 
 		FAIL_IF(1); /* we didn't segv? */

-- 
2.17.2

Hi!

On Wed, Nov 07, 2018 at 09:17:23PM +1100, Michael Ellerman wrote:

The selftest I recently added to test branching to an out-of-bounds
NIP doesn't work on big endian. It does fail but not in the right way.
That is it SEGVs trying to load from the opd at BAD_NIP, but it never
gets as far as branching to BAD_NIP.

To fix it we need to create an opd which is reachable but which holds
the bad address.

+#ifdef __BIG_ENDIAN__

Maybe you should test for _CALL_AIXDESC instead?  It is more directly
what you want to know, and it even works correctly in all cases ;-)


Segher