handler/mac: Log a warning when an exception message has a suspicious

util/test/mac/mach_multiprocess.cc

Index: util/test/mac/mach_multiprocess.cc
diff --git a/util/test/mac/mach_multiprocess.cc b/util/test/mac/mach_multiprocess.cc
index 9660ee0e4aa4d45aaa4bb389d160719a6216a69b..f968cf37a9c8cdd183ba015699f40802f665af43 100644
--- a/util/test/mac/mach_multiprocess.cc
+++ b/util/test/mac/mach_multiprocess.cc
@@ -28,6 +28,7 @@
 #include "gtest/gtest.h"
 #include "util/file/file_io.h"
 #include "util/mach/mach_extensions.h"
+#include "util/mach/mach_message.h"
 #include "util/misc/scoped_forbid_return.h"
 #include "util/test/errors.h"
 #include "util/test/mac/mach_errors.h"
@@ -40,7 +41,10 @@ struct SendHelloMessage : public mach_msg_base_t {
 };
 
 struct ReceiveHelloMessage : public SendHelloMessage {
-  mach_msg_audit_trailer_t audit_trailer;
+  union {
+    mach_msg_trailer_t trailer;
+    mach_msg_audit_trailer_t audit_trailer;
+  };
 };
 
 }  // namespace
@@ -186,6 +190,8 @@ void MachMultiprocess::MultiprocessParent() {
   EXPECT_EQ(getgid(), audit_rgid);
   ASSERT_EQ(ChildPID(), audit_pid);
 
+  ASSERT_EQ(ChildPID(), AuditPIDFromMachMessageTrailer(&message.trailer));
+
   auditinfo_addr_t audit_info;
   int rv = getaudit_addr(&audit_info, sizeof(audit_info));
   ASSERT_EQ(0, rv) << ErrnoMessage("getaudit_addr");