[PATCH] selftests/powerpc: Fix prefixes in alignment_handler signal handler

[Jordan Niethe]

The signal handler in the alignment handler self test has the ability to
jump over the instruction that triggered the signal. It does this by
incrementing the PT_NIP in the user context by 4. If it were a prefixed
instruction this will mean that the suffix is then executed which is
incorrect. Instead check if the major opcode indicates a prefixed
instruction (e.g. it is 1) and if so increment PT_NIP by 8.

If ISA v3.1 is not available treat it as a word instruction even if the
major opcode is 1.

Fixes: 620a6473df36 ("selftests/powerpc: Add prefixed loads/stores to
alignment_handler test")
Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
---
 .../selftests/powerpc/alignment/alignment_handler.c   | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/powerpc/alignment/alignment_handler.c b/tools/testing/selftests/powerpc/alignment/alignment_handler.c
index 55ef15184057..c197ff828120 100644
--- a/tools/testing/selftests/powerpc/alignment/alignment_handler.c
+++ b/tools/testing/selftests/powerpc/alignment/alignment_handler.c
@@ -64,12 +64,14 @@ int bufsize;
 int debug;
 int testing;
 volatile int gotsig;
+bool haveprefixes;
 char *cipath = "/dev/fb0";
 long cioffset;
 
 void sighandler(int sig, siginfo_t *info, void *ctx)
 {
 	ucontext_t *ucp = ctx;
+	u32 inst;
 
 	if (!testing) {
 		signal(sig, SIG_DFL);
@@ -77,7 +79,12 @@ void sighandler(int sig, siginfo_t *info, void *ctx)
 	}
 	gotsig = sig;
 #ifdef __powerpc64__
-	ucp->uc_mcontext.gp_regs[PT_NIP] += 4;
+	if (haveprefixes) {
+		inst = *(u32 *)ucp->uc_mcontext.gp_regs[PT_NIP];
+		ucp->uc_mcontext.gp_regs[PT_NIP] += ((inst >> 26 == 1) ? 8 : 4);
+	} else {
+		ucp->uc_mcontext.gp_regs[PT_NIP] += 4;
+	}
 #else
 	ucp->uc_mcontext.uc_regs->gregs[PT_NIP] += 4;
 #endif
@@ -648,6 +655,8 @@ int main(int argc, char *argv[])
 		exit(1);
 	}
 
+	haveprefixes = have_hwcap2(PPC_FEATURE2_ARCH_3_1);
+
 	rc |= test_harness(test_alignment_handler_vsx_206,
 			   "test_alignment_handler_vsx_206");
 	rc |= test_harness(test_alignment_handler_vsx_207,
-- 
2.17.1