win: Better setting of DI for register capture test

handler/win/crashy_test_program.cc

 // Copyright 2015 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 72 matching lines @@
   for (size_t i = 0; i < arraysize(kPageTypes); ++i) {
     void* result =
         VirtualAlloc(reinterpret_cast<void*>(reserve_as_int + (kPageSize * i)),
                      kPageSize,
                      MEM_COMMIT,
                      kPageTypes[i]);
     PCHECK(result) << "VirtualAlloc MEM_COMMIT " << i;
   }
 }
 
+DWORD WINAPI NullThreadProc(void* param) {
+  return 0;
+}
+
+// Creates a background thread, suspends it, and sets EDI/RDI to point at

[Mark Mentovai, 2016/01/10 04:46:29]

Creates a suspended background thread. Otherwise this sounds racy.

[scottmg, 2016/01/10 21:32:08]

Done.

+// g_test_memory so we can confirm it's available in the minidump.
+bool CreateThreadWithRegisterPointingToTestMemory() {
+  HANDLE thread = CreateThread(
+      nullptr, 0, &NullThreadProc, nullptr, CREATE_SUSPENDED, nullptr);
+  if (!thread) {
+    PLOG(ERROR) << "CreateThread";
+    return false;
+  }
+
+  CONTEXT context = {0};
+  context.ContextFlags = CONTEXT_INTEGER;
+  if (!GetThreadContext(thread, &context)) {
+    PLOG(ERROR) << "GetThreadContext";
+    return false;
+  }
+#if defined(ARCH_CPU_X86_64)
+  context.Rdi = reinterpret_cast<DWORD64>(g_test_memory);
+#elif defined(ARCH_CPU_X86)
+  context.Edi = reinterpret_cast<DWORD>(g_test_memory);
+#endif
+  if (!SetThreadContext(thread, &context)) {
+    PLOG(ERROR) << "SetThreadContext";
+    return false;
+  }
+
+  return true;
+}
+
 void SomeCrashyFunction() {
   // SetLastError and NTSTATUS so that we have something to view in !gle in
   // windbg. RtlNtStatusToDosError() stores STATUS_NO_SUCH_FILE into the
   // LastStatusError of the TEB as a side-effect, and we'll be setting
   // ERROR_FILE_NOT_FOUND for GetLastError().
   SetLastError(RtlNtStatusToDosError(STATUS_NO_SUCH_FILE));
 
-  // Set a register to point at some memory we can test to confirm it makes it
-  // into the minidump. We use __movsb as a way to set SI/DI without needing an
-  // external .asm file.
-  __movsb(g_test_memory, g_test_memory, 0);
-
   volatile int* foo = reinterpret_cast<volatile int*>(7);
   *foo = 42;
 }
 
 int CrashyMain(int argc, wchar_t* argv[]) {
   CrashpadClient client;
 
   if (argc == 2) {
     if (!client.SetHandlerIPCPipe(argv[1])) {
       LOG(ERROR) << "SetHandler";
@@ skipping 20 matching lines @@
     return EXIT_FAILURE;
   }
 
   AllocateMemoryOfVariousProtections();
 
   if (InitializeCriticalSectionWithDebugInfoIfPossible(
           &g_test_critical_section)) {
     EnterCriticalSection(&g_test_critical_section);
   }
 
+  if (!CreateThreadWithRegisterPointingToTestMemory())
+    return EXIT_FAILURE;
+
   SomeCrashyFunction();
 
   return EXIT_SUCCESS;
 }
 
 }  // namespace
 }  // namespace crashpad
 
 int wmain(int argc, wchar_t* argv[]) {
   return crashpad::CrashyMain(argc, argv);
 }