win: Capture some CRITICAL_SECTION debugging data

client/crashpad_client_win.cc

Index: client/crashpad_client_win.cc
diff --git a/client/crashpad_client_win.cc b/client/crashpad_client_win.cc
index 195916004198e2a517ff7b8fe30aa4f244552da9..7a1e547a4c8bfdbda64af09d36aee477e0b777ac 100644
--- a/client/crashpad_client_win.cc
+++ b/client/crashpad_client_win.cc
@@ -48,6 +48,13 @@ base::Lock* g_non_crash_dump_lock;
 // dump.
 crashpad::ExceptionInformation g_non_crash_exception_information;
 
+// A CRITICAL_SECTION initialized with
+// RTL_CRITICAL_SECTION_FLAG_FORCE_DEBUG_INFO to force it to be allocated with a
+// valid .DebugInfo field. The address of this critical section is given to the
+// handler. All critical sections with debug info are linked in a doubly-linked
+// list, so this allows the handler to capture all of them.
+CRITICAL_SECTION g_critical_section_with_debug_info;
+
 LONG WINAPI UnhandledExceptionHandler(EXCEPTION_POINTERS* exception_pointers) {
   // Tracks whether a thread has already entered UnhandledExceptionHandler.
   static base::subtle::AtomicWord have_crashed;
@@ -94,6 +101,18 @@ LONG WINAPI UnhandledExceptionHandler(EXCEPTION_POINTERS* exception_pointers) {
   return EXCEPTION_CONTINUE_SEARCH;
 }
 
+BOOL CrashpadInitializeCriticalSectionEx(
+    CRITICAL_SECTION* critical_section,
+    DWORD spin_count,
+    DWORD flags) {
+  static decltype(InitializeCriticalSectionEx)* initialize_critical_section_ex =
+      reinterpret_cast<decltype(InitializeCriticalSectionEx)*>(GetProcAddress(
+          LoadLibrary(L"kernel32.dll"), "InitializeCriticalSectionEx"));
+  if (!initialize_critical_section_ex)
+    return false;
+  return initialize_critical_section_ex(critical_section, spin_count, flags);
+}
+
 }  // namespace
 
 namespace crashpad {
@@ -118,6 +137,7 @@ bool CrashpadClient::SetHandler(const std::string& ipc_port) {
   DCHECK_EQ(g_signal_exception, INVALID_HANDLE_VALUE);
   DCHECK_EQ(g_signal_non_crash_dump, INVALID_HANDLE_VALUE);
   DCHECK_EQ(g_non_crash_dump_done, INVALID_HANDLE_VALUE);
+  DCHECK(!g_critical_section_with_debug_info.DebugInfo);
 
   ClientToServerMessage message;
   memset(&message, 0, sizeof(message));
@@ -129,6 +149,23 @@ bool CrashpadClient::SetHandler(const std::string& ipc_port) {
   message.registration.non_crash_exception_information =
       reinterpret_cast<WinVMAddress>(&g_non_crash_exception_information);
 
+  // We create this dummy CRITICAL_SECTION with the
+  // RTL_CRITICAL_SECTION_FLAG_FORCE_DEBUG_INFO flag set to have an entry point
+  // into the doubly-linked list of RTL_CRITICAL_SECTION_DEBUG objects. This
+  // allows us to walk the list at crash time to gather data for !locks. A
+  // debugger would instead inspect ntdll!RtlCriticalSectionList to get the head
+  // of the list. But that is not an exported symbol, so on an arbitrary client
+  // machine, we don't have a way of getting that pointer.
+  if (CrashpadInitializeCriticalSectionEx(
+          &g_critical_section_with_debug_info,
+          0,
+          RTL_CRITICAL_SECTION_FLAG_FORCE_DEBUG_INFO)) {
+    message.registration.critical_section_address =
+        reinterpret_cast<WinVMAddress>(&g_critical_section_with_debug_info);
+  } else {
+    PLOG(ERROR) << "InitializeCriticalSectionEx";
+  }
+
   ServerToClientMessage response = {0};
 
   if (!SendToCrashHandlerServer(