Avoid optimizing out the access to the injected location by compiler

The "SRAR DCU" test case failed on a CLX-AP server. It's root caused
that the gcc v8.2.1 optimized out the access to the injected location.

Move the "total" from being a local variable to a global to avoid the
optimization by the compiler. Consequently, it can make sure the poisoned
data is consumed to trigger the machine check recovery process.

Before applying the patch:
  run : ./srar_recovery.sh -d
  log : The poisoned process can't be killed by kernel automatically. Test fails!

After applying the patch:
  run : ./srar_recovery.sh -d
  log : ./srar_recovery.sh: line 80: 11650 Broken pipe tail -f trigger --pid=$$
         11651 Bus error (core dumped) | victim $1 > log
         SRAR/DCU test passes!

Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/tools/victim/victim.c b/tools/victim/victim.c
index 31f868a..5aa8c1e 100644
--- a/tools/victim/victim.c
+++ b/tools/victim/victim.c
@@ -215,10 +215,19 @@ static int parse_addr_subopts(char *subopts, unsigned long long *virt,
 	return 0;
 }
 
+/*
+ * The "SRAR DCU" test case failed on a CLX-AP server. It's root caused
+ * that the gcc v8.2.1 optimized out the access to the injected location.
+ *
+ * If keep "total" as a local, even mark it "volatile", the gcc v8.2.1
+ * still optimizes out the memory access. Therefore, move the "total" from
+ * being a local variable to a global to avoid such optimization.
+ */
+long total;
+
 int main(int argc, char **argv)
 {
 	unsigned long long virt, phys;
-	long total;
 	char *buf;
 	int c, i;
 	int iflag = 0, dflag = 0;