[Mac] Redo NSException handling, and generate better stacks for C++ exceptions.

base/mac/call_with_eh_frame.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/mac/call_with_eh_frame.h"
+
+#include <unwind.h>
+
+#include "build/build_config.h"
+
+namespace base {
+namespace mac {
+
+_Unwind_Reason_Code CxxPersonalityRoutine(
+    int version,
+    _Unwind_Action actions,
+    uint64_t exceptionClass,
+    struct _Unwind_Exception* exceptionObject,
+    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;
+}
+
+#if defined(OS_IOS)
+// No iOS assembly implementation exists, so just call the block directly.
+void CallWithEHFrame(void (^block)(void)) {
+  block();
+}
+#endif
+
+}  // namespace mac
+}  // namespace base