Cleanup: hide undefined behavior from the compiler better.

Submitting this on behalf of Paul Pluzhnikov.

R=mark@chromium.org

Review URL: https://breakpad.appspot.com/6674002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1342 4c0a9323-5329-0410-9bdc-e9ce6186880e

1 files changed, 18 insertions, 4 deletions

diff --git a/src/client/linux/handler/exception_handler_unittest.cc b/src/client/linux/handler/exception_handler_unittest.cc
index 976f9f41..fc81f61f 100644
--- a/src/client/linux/handler/exception_handler_unittest.cc
+++ b/src/client/linux/handler/exception_handler_unittest.cc
@@ -193,6 +193,20 @@ static bool DoneCallback(const MinidumpDescriptor& descriptor,
 
 #ifndef ADDRESS_SANITIZER
 
+// This is a replacement for "*reinterpret_cast<volatile int*>(NULL) = 0;"
+// It is needed because GCC is allowed to assume that the program will
+// not execute any undefined behavior (UB) operation. Further, when GCC
+// observes that UB statement is reached, it can assume that all statements
+// leading to the UB one are never executed either, and can completely
+// optimize them out. In the case of ExceptionHandlerTest::ExternalDumper,
+// GCC-4.9 optimized out the entire set up of ExceptionHandler, causing
+// test failure.
+volatile int *p_null;  // external linkage, so GCC can't tell that it
+                       // remains NULL. Volatile just for a good measure.
+static void DoNullPointerDereference() {
+  *p_null = 1;
+}
+
 void ChildCrash(bool use_fd) {
   AutoTempDir temp_dir;
   int fds[2] = {0};
@@ -219,7 +233,7 @@ void ChildCrash(bool use_fd) {
                                            true, -1));
       }
       // Crash with the exception handler in scope.
-      *reinterpret_cast<volatile int*>(NULL) = 0;
+      DoNullPointerDereference();
     }
   }
   if (!use_fd)
@@ -295,7 +309,7 @@ static void CrashWithCallbacks(ExceptionHandler::FilterCallback filter,
   ExceptionHandler handler(
       MinidumpDescriptor(path), filter, done, NULL, true, -1);
   // Crash with the exception handler in scope.
-  *reinterpret_cast<volatile int*>(NULL) = 0;
+  DoNullPointerDereference();
 }
 
 TEST(ExceptionHandlerTest, RedeliveryOnFilterCallbackFalse) {
@@ -386,7 +400,7 @@ TEST(ExceptionHandlerTest, RedeliveryOnBadSignalHandlerFlag) {
               reinterpret_cast<void*>(SIG_ERR));
 
     // Crash with the exception handler in scope.
-    *reinterpret_cast<volatile int*>(NULL) = 0;
+    DoNullPointerDereference();
   }
   // SIGKILL means Breakpad's signal handler didn't crash.
   ASSERT_NO_FATAL_FAILURE(WaitForProcessToTerminate(child, SIGKILL));
@@ -922,7 +936,7 @@ TEST(ExceptionHandlerTest, ExternalDumper) {
     ExceptionHandler handler(MinidumpDescriptor("/tmp1"), NULL, NULL,
                              reinterpret_cast<void*>(fds[1]), true, -1);
     handler.set_crash_handler(CrashHandler);
-    *reinterpret_cast<volatile int*>(NULL) = 0;
+    DoNullPointerDereference();
   }
   close(fds[1]);
   struct msghdr msg = {0};