1 files changed, 82 insertions, 48 deletions

diff --git a/lib/Support/CrashRecoveryContext.cpp b/lib/Support/CrashRecoveryContext.cpp
index 98865f5e065e..bd38dd88201f 100644
--- a/lib/Support/CrashRecoveryContext.cpp
+++ b/lib/Support/CrashRecoveryContext.cpp
@@ -78,6 +78,9 @@ static bool gCrashRecoveryEnabled = false;
 static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContext>>
        tlIsRecoveringFromCrash;
 
+static void installExceptionOrSignalHandlers();
+static void uninstallExceptionOrSignalHandlers();
+
 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}
 
 CrashRecoveryContext::~CrashRecoveryContext() {
@@ -113,6 +116,23 @@ CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
   return CRCI->CRC;
 }
 
+void CrashRecoveryContext::Enable() {
+  sys::ScopedLock L(*gCrashRecoveryContextMutex);
+  // FIXME: Shouldn't this be a refcount or something?
+  if (gCrashRecoveryEnabled)
+    return;
+  gCrashRecoveryEnabled = true;
+  installExceptionOrSignalHandlers();
+}
+
+void CrashRecoveryContext::Disable() {
+  sys::ScopedLock L(*gCrashRecoveryContextMutex);
+  if (!gCrashRecoveryEnabled)
+    return;
+  gCrashRecoveryEnabled = false;
+  uninstallExceptionOrSignalHandlers();
+}
+
 void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
 {
   if (!cleanup)
@@ -140,30 +160,70 @@ CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) {
   delete cleanup;
 }
 
-#ifdef LLVM_ON_WIN32
+#if defined(_MSC_VER)
+// If _MSC_VER is defined, we must have SEH. Use it if it's available. It's way
+// better than VEH. Vectored exception handling catches all exceptions happening
+// on the thread with installed exception handlers, so it can interfere with
+// internal exception handling of other libraries on that thread. SEH works
+// exactly as you would expect normal exception handling to work: it only
+// catches exceptions if they would bubble out from the stack frame with __try /
+// __except.
 
-#include "Windows/WindowsSupport.h"
+static void installExceptionOrSignalHandlers() {}
+static void uninstallExceptionOrSignalHandlers() {}
 
-// On Windows, we can make use of vectored exception handling to
-// catch most crashing situations.  Note that this does mean
-// we will be alerted of exceptions *before* structured exception
-// handling has the opportunity to catch it.  But that isn't likely
-// to cause problems because nowhere in the project is SEH being
-// used.
+bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
+  if (!gCrashRecoveryEnabled) {
+    Fn();
+    return true;
+  }
+
+  bool Result = true;
+  __try {
+    Fn();
+  } __except (1) { // Catch any exception.
+    Result = false;
+  }
+  return Result;
+}
+
+#else // !_MSC_VER
+
+#if defined(LLVM_ON_WIN32)
+// This is a non-MSVC compiler, probably mingw gcc or clang without
+// -fms-extensions. Use vectored exception handling (VEH).
+//
+// On Windows, we can make use of vectored exception handling to catch most
+// crashing situations.  Note that this does mean we will be alerted of
+// exceptions *before* structured exception handling has the opportunity to
+// catch it. Unfortunately, this causes problems in practice with other code
+// running on threads with LLVM crash recovery contexts, so we would like to
+// eventually move away from VEH.
 //
-// Vectored exception handling is built on top of SEH, and so it
-// works on a per-thread basis.
+// Vectored works on a per-thread basis, which is an advantage over
+// SetUnhandledExceptionFilter. SetUnhandledExceptionFilter also doesn't have
+// any native support for chaining exception handlers, but VEH allows more than
+// one.
 //
 // The vectored exception handler functionality was added in Windows
 // XP, so if support for older versions of Windows is required,
 // it will have to be added.
-//
-// If we want to support as far back as Win2k, we could use the
-// SetUnhandledExceptionFilter API, but there's a risk of that
-// being entirely overwritten (it's not a chain).
+
+#include "Windows/WindowsSupport.h"
 
 static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
 {
+  // DBG_PRINTEXCEPTION_WIDE_C is not properly defined on all supported
+  // compilers and platforms, so we define it manually.
+  constexpr ULONG DbgPrintExceptionWideC = 0x4001000AL;
+  switch (ExceptionInfo->ExceptionRecord->ExceptionCode)
+  {
+  case DBG_PRINTEXCEPTION_C:
+  case DbgPrintExceptionWideC:
+  case 0x406D1388:  // set debugger thread name
+    return EXCEPTION_CONTINUE_EXECUTION;
+  }
+
   // Lookup the current thread local recovery object.
   const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
 
@@ -192,14 +252,7 @@ static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
 // non-NULL, valid VEH handles, or NULL.
 static sys::ThreadLocal<const void> sCurrentExceptionHandle;
 
-void CrashRecoveryContext::Enable() {
-  sys::ScopedLock L(*gCrashRecoveryContextMutex);
-
-  if (gCrashRecoveryEnabled)
-    return;
-
-  gCrashRecoveryEnabled = true;
-
+static void installExceptionOrSignalHandlers() {
   // We can set up vectored exception handling now.  We will install our
   // handler as the front of the list, though there's no assurances that
   // it will remain at the front (another call could install itself before
@@ -208,14 +261,7 @@ void CrashRecoveryContext::Enable() {
   sCurrentExceptionHandle.set(handle);
 }
 
-void CrashRecoveryContext::Disable() {
-  sys::ScopedLock L(*gCrashRecoveryContextMutex);
-
-  if (!gCrashRecoveryEnabled)
-    return;
-
-  gCrashRecoveryEnabled = false;
-
+static void uninstallExceptionOrSignalHandlers() {
   PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
   if (currentHandle) {
     // Now we can remove the vectored exception handler from the chain
@@ -226,7 +272,7 @@ void CrashRecoveryContext::Disable() {
   }
 }
 
-#else
+#else // !LLVM_ON_WIN32
 
 // Generic POSIX implementation.
 //
@@ -278,14 +324,7 @@ static void CrashRecoverySignalHandler(int Signal) {
     const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
 }
 
-void CrashRecoveryContext::Enable() {
-  sys::ScopedLock L(*gCrashRecoveryContextMutex);
-
-  if (gCrashRecoveryEnabled)
-    return;
-
-  gCrashRecoveryEnabled = true;
-
+static void installExceptionOrSignalHandlers() {
   // Setup the signal handler.
   struct sigaction Handler;
   Handler.sa_handler = CrashRecoverySignalHandler;
@@ -297,20 +336,13 @@ void CrashRecoveryContext::Enable() {
   }
 }
 
-void CrashRecoveryContext::Disable() {
-  sys::ScopedLock L(*gCrashRecoveryContextMutex);
-
-  if (!gCrashRecoveryEnabled)
-    return;
-
-  gCrashRecoveryEnabled = false;
-
+static void uninstallExceptionOrSignalHandlers() {
   // Restore the previous signal handlers.
   for (unsigned i = 0; i != NumSignals; ++i)
     sigaction(Signals[i], &PrevActions[i], nullptr);
 }
 
-#endif
+#endif // !LLVM_ON_WIN32
 
 bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
   // If crash recovery is disabled, do nothing.
@@ -328,6 +360,8 @@ bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
   return true;
 }
 
+#endif // !_MSC_VER
+
 void CrashRecoveryContext::HandleCrash() {
   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
   assert(CRCI && "Crash recovery context never initialized!");