A simple, practically zero cost fallback crash handler for Crashpad handler process.

components/crash/content/app/fallback_crash_handler_launcher_win.h

Index: components/crash/content/app/fallback_crash_handler_launcher_win.h
diff --git a/components/crash/content/app/fallback_crash_handler_launcher_win.h b/components/crash/content/app/fallback_crash_handler_launcher_win.h
new file mode 100644
index 0000000000000000000000000000000000000000..cb63351109398095a87616598d1b0c3b51539452
--- /dev/null
+++ b/components/crash/content/app/fallback_crash_handler_launcher_win.h
@@ -0,0 +1,68 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.

[scottmg, 2017/01/06 18:29:04]

2017 :)

[Sigurður Ásgeirsson, 2017/01/06 20:59:10]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_CRASH_CONTENT_APP_FALLBACK_CRASH_HANDLER_LAUNCHER_WIN_H_
+#define COMPONENTS_CRASH_CONTENT_APP_FALLBACK_CRASH_HANDLER_LAUNCHER_WIN_H_
+
+#include "base/command_line.h"
+#include "base/files/file_path.h"
+#include "base/macros.h"
+#include "base/win/scoped_handle.h"
+#include "base/win/startup_information.h"
+
+#include <windows.h>

[scottmg, 2017/01/06 18:29:04]

This goes before " includes.

[Sigurður Ásgeirsson, 2017/01/06 20:59:10]

Done.

+
+namespace crash_reporter {
+
+// This class is a last-ditch crash handler for the Crashpad handler process.
+// It prepares and stores a command line, ready for dispatching when
+// an exception occurs. Everything needed to call CreateProcess is pre-allocated
+// to minimize the odds of re-faulting due to e.g. tripping over the same issue
+// that caused the initial crash.
+// This is still very much best-effort, as doing anything at all inside a
+// process that's crashed is always going to be iffy^2.
+// Only one instance of this class can exist at a time.

[scottmg, 2017/01/06 18:29:04]

"Only one instance" should be confirmed somewhere if important, at least with a
DCHECK.

[Sigurður Ásgeirsson, 2017/01/06 20:59:10]

Ah, that's redundant. Initially I had wanted to make this class register the
UEF, but that made it really hard to test.

+class FallbackCrashHandlerLauncher {
+ public:
+  FallbackCrashHandlerLauncher();
+  ~FallbackCrashHandlerLauncher();
+
+  // Initialize
+  bool Initialize(const base::CommandLine& program,
+                  const base::FilePath& crashpad_database);
+
+  // Launch the pre-computed command line for the fallback error handler.
+  // The expectation is that this function will never return, as the fallback
+  // error handler should terminate it with the exception code as the process
+  // exit code. The return value from this function is therefore academic in
+  // the normal case.
+  // However, for completeness, this function returns one of:
+  // - The error from CreateProcess if it fails to launch the fallback handler.
+  // - The error from waiting on the fallback crash handler process if it
+  //   fails to wait for that process to exit.
+  // - The exit code from the fallback crash handler process.
+  // - The error encountered in retrieving the crash handler process' exit code.
+  DWORD LaunchAndWaitForHandler(EXCEPTION_POINTERS* pointers);
+
+ private:
+  // A copy of the actual exception pointers made at time of exception.
+  EXCEPTION_POINTERS exception_pointers_;
+
+  // The precomputed startup info and command line for launching the fallback
+  // handler.
+  base::win::StartupInformation startup_info_;
+  // Stores the pre-cooked command line, with an allottment of zeros at the back

[scottmg, 2017/01/06 18:29:04]

allotment

[Sigurður Ásgeirsson, 2017/01/06 20:59:10]

Done.

+  // sufficient for writing in the thread id, just before launch.
+  std::vector<wchar_t> cmd_line_;
+
+  // An inheritable handle to our own process, the raw handle is necessary
+  // for pre-computing the startup info.
+  base::win::ScopedHandle self_process_handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(FallbackCrashHandlerLauncher);
+};
+
+}  // namespace crash_reporter
+
+#endif  // COMPONENTS_CRASH_CONTENT_APP_FALLBACK_CRASH_HANDLER_LAUNCHER_WIN_H_