Expose active exceptions stack in ExceptionStackTraceLib

Summary: It can be useful for diagnostics to print the stack traces of thrown exceptions that are not yet handled, for example if a fatal error happens during unwinding.

Reviewed By: philippv, luciang

Differential Revision: D19191089

fbshipit-source-id: dae8cc0a095570bfe7d6c4c7ef2b5dc08aa9f1f9

folly/experimental/exception_tracer/ExceptionStackTraceLib.cpp

@@ -30,13 +30,16 @@ namespace {
 // trace at all because in could be bogus
 FOLLY_TLS bool invalid;
 
-FOLLY_TLS StackTraceStack activeExceptions;
+FOLLY_TLS StackTraceStack uncaughtExceptions;
 FOLLY_TLS StackTraceStack caughtExceptions;
 
 } // namespace
 
-// This function is exported and may be found via dlsym(RTLD_NEXT, ...)
-extern "C" StackTraceStack* getExceptionStackTraceStack() {
+// These functions are exported and may be found via dlsym(RTLD_NEXT, ...)
+extern "C" StackTraceStack* getUncaughtExceptionStackTraceStack() {
+  return invalid ? nullptr : &uncaughtExceptions;
+}
+extern "C" StackTraceStack* getCaughtExceptionStackTraceStack() {
   return invalid ? nullptr : &caughtExceptions;
 }
 
@@ -45,8 +48,8 @@ namespace {
 void addActiveException() {
   // Capture stack trace
   if (!invalid) {
-    if (!activeExceptions.pushCurrent()) {
-      activeExceptions.clear();
+    if (!uncaughtExceptions.pushCurrent()) {
+      uncaughtExceptions.clear();
       caughtExceptions.clear();
       invalid = true;
     }
@@ -72,11 +75,11 @@ struct Initializer {
         });
 
     registerCxaBeginCatchCallback([](void*) noexcept {
-      moveTopException(activeExceptions, caughtExceptions);
+      moveTopException(uncaughtExceptions, caughtExceptions);
     });
 
     registerCxaRethrowCallback([]() noexcept {
-      moveTopException(caughtExceptions, activeExceptions);
+      moveTopException(caughtExceptions, uncaughtExceptions);
     });
 
     registerCxaEndCatchCallback([]() noexcept {
@@ -95,7 +98,7 @@ struct Initializer {
       // For Lua interop, we see the handlerCount = 0
       if ((top->handlerCount == 1) || (top->handlerCount == 0)) {
         if (!caughtExceptions.pop()) {
-          activeExceptions.clear();
+          uncaughtExceptions.clear();
           invalid = true;
         }
       }

folly/experimental/exception_tracer/ExceptionTracer.cpp

@@ -37,9 +37,10 @@ using namespace ::folly::symbolizer;
 using namespace __cxxabiv1;
 
 extern "C" {
-StackTraceStack* getExceptionStackTraceStack(void) __attribute__((__weak__));
-typedef StackTraceStack* (*GetExceptionStackTraceStackType)();
-GetExceptionStackTraceStackType getExceptionStackTraceStackFn;
+StackTraceStack* getCaughtExceptionStackTraceStack(void)
+    __attribute__((__weak__));
+typedef StackTraceStack* (*GetCaughtExceptionStackTraceStackType)();
+GetCaughtExceptionStackTraceStackType getCaughtExceptionStackTraceStackFn;
 }
 
 } // namespace
@@ -130,13 +131,14 @@ bool isAbiCppException(const __cxa_exception* exc) {
 std::vector<ExceptionInfo> getCurrentExceptions() {
   struct Once {
     Once() {
-      // See if linked in with us (getExceptionStackTraceStack is weak)
-      getExceptionStackTraceStackFn = getExceptionStackTraceStack;
+      // See if linked in with us (getCaughtExceptionStackTraceStack is weak)
+      getCaughtExceptionStackTraceStackFn = getCaughtExceptionStackTraceStack;
 
-      if (!getExceptionStackTraceStackFn) {
+      if (!getCaughtExceptionStackTraceStackFn) {
         // Nope, see if it's in a shared library
-        getExceptionStackTraceStackFn = (GetExceptionStackTraceStackType)dlsym(
-            RTLD_NEXT, "getExceptionStackTraceStack");
+        getCaughtExceptionStackTraceStackFn =
+            (GetCaughtExceptionStackTraceStackType)dlsym(
+                RTLD_NEXT, "getCaughtExceptionStackTraceStack");
       }
     }
   };
@@ -149,14 +151,14 @@ std::vector<ExceptionInfo> getCurrentExceptions() {
   }
 
   StackTraceStack* traceStack = nullptr;
-  if (!getExceptionStackTraceStackFn) {
+  if (!getCaughtExceptionStackTraceStackFn) {
     static bool logged = false;
     if (!logged) {
       LOG(WARNING)
           << "Exception tracer library not linked, stack traces not available";
       logged = true;
     }
-  } else if ((traceStack = getExceptionStackTraceStackFn()) == nullptr) {
+  } else if ((traceStack = getCaughtExceptionStackTraceStackFn()) == nullptr) {
     static bool logged = false;
     if (!logged) {
       LOG(WARNING)