[PATCH v1 4/4] selftests/powerpc/ptrace: Declare test temporary variables as volatile

[Benjamin Gray]

While the target is volatile, the temporary variables used to access the
target cast away the volatile. This is undefined behaviour, and a
compiler may optimise away/reorder these accesses, breaking the test.

This was observed with GCC 13.1.1, but it can be difficult to reproduce
because of the dependency on compiler behaviour.

Signed-off-by: Benjamin Gray <bgray at linux.ibm.com>
---
 .../selftests/powerpc/ptrace/ptrace-hwbreak.c | 24 +++++++++----------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c b/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c
index a16239277a6f..75d30d61ab0e 100644
--- a/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c
+++ b/tools/testing/selftests/powerpc/ptrace/ptrace-hwbreak.c
@@ -64,26 +64,26 @@ static bool dawr_present(struct ppc_debug_info *dbginfo)
 
 static void write_var(int len)
 {
-	__u8 *pcvar;
-	__u16 *psvar;
-	__u32 *pivar;
-	__u64 *plvar;
+	volatile __u8 *pcvar;
+	volatile __u16 *psvar;
+	volatile __u32 *pivar;
+	volatile __u64 *plvar;
 
 	switch (len) {
 	case 1:
-		pcvar = (__u8 *)&glvar;
+		pcvar = (volatile __u8 *)&glvar;
 		*pcvar = 0xff;
 		break;
 	case 2:
-		psvar = (__u16 *)&glvar;
+		psvar = (volatile __u16 *)&glvar;
 		*psvar = 0xffff;
 		break;
 	case 4:
-		pivar = (__u32 *)&glvar;
+		pivar = (volatile __u32 *)&glvar;
 		*pivar = 0xffffffff;
 		break;
 	case 8:
-		plvar = (__u64 *)&glvar;
+		plvar = (volatile __u64 *)&glvar;
 		*plvar = 0xffffffffffffffffLL;
 		break;
 	}
@@ -98,16 +98,16 @@ static void read_var(int len)
 
 	switch (len) {
 	case 1:
-		cvar = (__u8)glvar;
+		cvar = (volatile __u8)glvar;
 		break;
 	case 2:
-		svar = (__u16)glvar;
+		svar = (volatile __u16)glvar;
 		break;
 	case 4:
-		ivar = (__u32)glvar;
+		ivar = (volatile __u32)glvar;
 		break;
 	case 8:
-		lvar = (__u64)glvar;
+		lvar = (volatile __u64)glvar;
 		break;
 	}
 }
-- 
2.41.0