[Mac] In base::mac::CxxPersonalityRoutine, delegate back to __gxx_personality_v0.

This fixes a hypothetical issue where returning _URC_END_OF_STACK in phase two
of exception processing could confuse libunwind. If this personality routine
is called in phase two, it will now delegate back to the normal C++ personality
routine. See https://crbug.com/576941#c62 for details.

BUG=576941
R=mark@chromium.org

Review-Url: https://codereview.chromium.org/2119553002
Cr-Commit-Position: refs/heads/master@{#403235}

base/mac/call_with_eh_frame.cc

@@ -12,27 +12,43 @@
 namespace base {
 namespace mac {
 
+#if defined(OS_IOS)
+// No iOS assembly implementation exists, so just call the block directly.
+void CallWithEHFrame(void (^block)(void)) {
+  block();
+}
+#else  // OS_MACOSX
+extern "C" _Unwind_Reason_Code __gxx_personality_v0(int,
+                                                    _Unwind_Action,
+                                                    uint64_t,
+                                                    struct _Unwind_Exception*,
+                                                    struct _Unwind_Context*);
+
 _Unwind_Reason_Code CxxPersonalityRoutine(
     int version,
     _Unwind_Action actions,
-    uint64_t exceptionClass,
-    struct _Unwind_Exception* exceptionObject,
+    uint64_t exception_class,
+    struct _Unwind_Exception* exception_object,
     struct _Unwind_Context* context) {
-  // Tell libunwind that this is the end of the stack. When it encounters the
-  // CallWithEHFrame, it will stop searching for an exception handler. The
-  // result is that no exception handler has been found higher on the stack,
-  // and any that are lower on the stack (e.g. in CFRunLoopRunSpecific), will
-  // now be skipped. Since this is reporting the end of the stack, and no
-  // exception handler will have been found, std::terminate() will be called.
-  return _URC_END_OF_STACK;
-}
+  // Unwinding is a two-phase process: phase one searches for an exception
+  // handler, and phase two performs cleanup. For phase one, this custom
+  // personality will terminate the search. For phase two, this should delegate
+  // back to the standard personality routine.
 
-#if defined(OS_IOS)
-// No iOS assembly implementation exists, so just call the block directly.
-void CallWithEHFrame(void (^block)(void)) {
-  block();
+  if ((actions & _UA_SEARCH_PHASE) != 0) {
+    // Tell libunwind that this is the end of the stack. When it encounters the
+    // CallWithEHFrame, it will stop searching for an exception handler. The
+    // result is that no exception handler has been found higher on the stack,
+    // and any that are lower on the stack (e.g. in CFRunLoopRunSpecific), will
+    // now be skipped. Since this is reporting the end of the stack, and no
+    // exception handler will have been found, std::terminate() will be called.
+    return _URC_END_OF_STACK;
+  }
+
+  return __gxx_personality_v0(version, actions, exception_class,
+                              exception_object, context);
 }
-#endif
+#endif  // defined(OS_IOS)
 
 }  // namespace mac
 }  // namespace base