Back out "exception_wrapper thrown variant via abi/runtime"

Summary: D26331579 (https://github.com/facebook/folly/commit/aa7f74aaf68ab0a7eb834f49a864c277dbe5fe09) was the offending diff that caused an insta crash on Messenger Android and Instagram Android. Backing out for now.

Reviewed By: JunqiWang

Differential Revision: D28308563

fbshipit-source-id: 87a547d9ba7cb3b33a4ddee9e273943f8379d990

folly/ExceptionWrapper-inl.h

@@ -127,6 +127,56 @@ inline std::exception const* exception_wrapper::as_exception_or_null_(
   return nullptr;
 }
 
+static_assert(
+    !kMicrosoftAbiVer || (kMicrosoftAbiVer >= 1900 && kMicrosoftAbiVer <= 2000),
+    "exception_wrapper is untested and possibly broken on your version of "
+    "MSVC");
+
+inline std::uintptr_t exception_wrapper::ExceptionPtr::as_int_(
+    std::exception_ptr const& ptr, std::exception const& e) noexcept {
+  if (!kMicrosoftAbiVer) {
+    return reinterpret_cast<std::uintptr_t>(&e);
+  } else {
+    // On Windows, as of MSVC2017, all thrown exceptions are copied to the stack
+    // first. Thus, we cannot depend on exception references associated with an
+    // exception_ptr to be live for the duration of the exception_ptr. We need
+    // to directly access the heap allocated memory inside the exception_ptr.
+    //
+    // std::exception_ptr is an opaque reinterpret_cast of
+    // std::shared_ptr<__ExceptionPtr>
+    // __ExceptionPtr is a non-virtual class with two members, a union and a
+    // bool. The union contains the now-undocumented EHExceptionRecord, which
+    // contains a struct which contains a void* which points to the heap
+    // allocated exception.
+    // We derive the offset to pExceptionObject via manual means.
+    FOLLY_PACK_PUSH
+    struct Win32ExceptionPtr {
+      char offset[8 + 4 * sizeof(void*)];
+      void* exceptionObject;
+    } FOLLY_PACK_ATTR;
+    FOLLY_PACK_POP
+
+    auto* win32ExceptionPtr =
+        reinterpret_cast<std::shared_ptr<Win32ExceptionPtr> const*>(&ptr)
+            ->get();
+    return reinterpret_cast<std::uintptr_t>(win32ExceptionPtr->exceptionObject);
+  }
+}
+inline std::uintptr_t exception_wrapper::ExceptionPtr::as_int_(
+    std::exception_ptr const&, AnyException e) noexcept {
+  return reinterpret_cast<std::uintptr_t>(e.typeinfo_) + 1;
+}
+inline bool exception_wrapper::ExceptionPtr::has_exception_() const {
+  return 0 == exception_or_type_ % 2;
+}
+inline std::exception const* exception_wrapper::ExceptionPtr::as_exception_()
+    const {
+  return reinterpret_cast<std::exception const*>(exception_or_type_);
+}
+inline std::type_info const* exception_wrapper::ExceptionPtr::as_type_() const {
+  return reinterpret_cast<std::type_info const*>(exception_or_type_ - 1);
+}
+
 inline void exception_wrapper::ExceptionPtr::copy_(
     exception_wrapper const* from, exception_wrapper* to) {
   ::new (static_cast<void*>(&to->eptr_)) ExceptionPtr(from->eptr_);
@@ -146,11 +196,14 @@ inline void exception_wrapper::ExceptionPtr::delete_(exception_wrapper* that) {
 }
 inline std::type_info const* exception_wrapper::ExceptionPtr::type_(
     exception_wrapper const* that) {
-  return exception_ptr_get_type(that->eptr_.ptr_);
+  if (auto e = get_exception_(that)) {
+    return &typeid(*e);
+  }
+  return that->eptr_.as_type_();
 }
 inline std::exception const* exception_wrapper::ExceptionPtr::get_exception_(
     exception_wrapper const* that) {
-  return exception_ptr_get_object<std::exception>(that->eptr_.ptr_);
+  return that->eptr_.has_exception_() ? that->eptr_.as_exception_() : nullptr;
 }
 inline exception_wrapper exception_wrapper::ExceptionPtr::get_exception_ptr_(
     exception_wrapper const* that) {
@@ -195,8 +248,8 @@ inline exception_wrapper exception_wrapper::InPlace<Ex>::get_exception_ptr_(
     exception_wrapper const* that) {
   try {
     throw_(that);
-  } catch (...) {
-    return exception_wrapper{std::current_exception()};
+  } catch (Ex const& ex) {
+    return exception_wrapper{std::current_exception(), ex};
   }
 }
 
@@ -215,8 +268,8 @@ inline exception_wrapper
 exception_wrapper::SharedPtr::Impl<Ex>::get_exception_ptr_() const noexcept {
   try {
     throw_();
-  } catch (...) {
-    return exception_wrapper{std::current_exception()};
+  } catch (Ex& ex) {
+    return exception_wrapper{std::current_exception(), ex};
   }
 }
 inline void exception_wrapper::SharedPtr::copy_(
@@ -254,7 +307,7 @@ inline exception_wrapper exception_wrapper::SharedPtr::get_exception_ptr_(
 template <class Ex, typename... As>
 inline exception_wrapper::exception_wrapper(
     ThrownTag, in_place_type_t<Ex>, As&&... as)
-    : eptr_{std::make_exception_ptr(Ex(std::forward<As>(as)...))},
+    : eptr_{std::make_exception_ptr(Ex(std::forward<As>(as)...)), reinterpret_cast<std::uintptr_t>(std::addressof(typeid(Ex))) + 1u},
       vptr_(&ExceptionPtr::ops_) {}
 
 template <class Ex, typename... As>
@@ -302,17 +355,9 @@ inline exception_wrapper::~exception_wrapper() {
 
 template <class Ex>
 inline exception_wrapper::exception_wrapper(
-    std::exception_ptr const& ptr, Ex& ex) noexcept
-    : exception_wrapper{folly::copy(ptr), ex} {}
-
-template <class Ex>
-inline exception_wrapper::exception_wrapper(
-    std::exception_ptr&& ptr, Ex& ex) noexcept
-    : eptr_{std::move(ptr)}, vptr_(&ExceptionPtr::ops_) {
+    std::exception_ptr ptr, Ex& ex) noexcept
+    : eptr_{ptr, ExceptionPtr::as_int_(ptr, ex)}, vptr_(&ExceptionPtr::ops_) {
   assert(eptr_.ptr_);
-  (void)ex;
-  assert(exception_ptr_get_object<Ex>(eptr_.ptr_));
-  assert(exception_ptr_get_object<Ex>(eptr_.ptr_) == &ex || kIsWindows);
 }
 
 namespace exception_wrapper_detail {
@@ -412,6 +457,9 @@ inline std::exception_ptr exception_wrapper::to_exception_ptr() const noexcept {
 inline std::type_info const& exception_wrapper::none() noexcept {
   return typeid(void);
 }
+inline std::type_info const& exception_wrapper::unknown() noexcept {
+  return typeid(Unknown);
+}
 
 inline std::type_info const& exception_wrapper::type() const noexcept {
   return *vptr_->type_(this);
@@ -426,7 +474,9 @@ inline folly::fbstring exception_wrapper::what() const {
 
 inline folly::fbstring exception_wrapper::class_name() const {
   auto& ti = type();
-  return ti == none() ? "" : folly::demangle(ti);
+  return ti == none()   ? ""
+      : ti == unknown() ? "<unknown exception>"
+                        : folly::demangle(ti);
 }
 
 template <class Ex>

folly/ExceptionWrapper.cpp

@@ -37,6 +37,18 @@ exception_wrapper::VTable const exception_wrapper::ExceptionPtr::ops_{
 exception_wrapper::VTable const exception_wrapper::SharedPtr::ops_{
     copy_, move_, delete_, throw_, type_, get_exception_, get_exception_ptr_};
 
+namespace {
+std::exception const* get_std_exception_(std::exception_ptr eptr) noexcept {
+  try {
+    std::rethrow_exception(eptr);
+  } catch (const std::exception& ex) {
+    return &ex;
+  } catch (...) {
+    return nullptr;
+  }
+}
+} // namespace
+
 exception_wrapper exception_wrapper::from_exception_ptr(
     std::exception_ptr const& ptr) noexcept {
   return from_exception_ptr(folly::copy(ptr));
@@ -44,16 +56,31 @@ exception_wrapper exception_wrapper::from_exception_ptr(
 
 exception_wrapper exception_wrapper::from_exception_ptr(
     std::exception_ptr&& ptr) noexcept {
-  return !ptr ? exception_wrapper() : exception_wrapper(std::move(ptr));
+  if (!ptr) {
+    return exception_wrapper();
+  }
+  try {
+    std::rethrow_exception(std::move(ptr));
+  } catch (std::exception& e) {
+    return exception_wrapper(std::current_exception(), e);
+  } catch (...) {
+    return exception_wrapper(std::current_exception());
+  }
 }
 
-exception_wrapper::exception_wrapper(std::exception_ptr const& ptr) noexcept
-    : exception_wrapper{folly::copy(ptr)} {}
-
-exception_wrapper::exception_wrapper(std::exception_ptr&& ptr) noexcept {
+exception_wrapper::exception_wrapper(std::exception_ptr ptr) noexcept
+    : exception_wrapper{} {
   if (ptr) {
-    ::new (&eptr_) ExceptionPtr{std::move(ptr)};
-    vptr_ = &ExceptionPtr::ops_;
+    if (auto e = get_std_exception_(ptr)) {
+      LOG(DFATAL)
+          << "Performance error: Please construct exception_wrapper with a "
+             "reference to the std::exception along with the "
+             "std::exception_ptr.";
+      *this = exception_wrapper{std::move(ptr), *e};
+    } else {
+      Unknown uk;
+      *this = exception_wrapper{ptr, uk};
+    }
   }
 }
 

folly/ExceptionWrapper.h

@@ -31,7 +31,6 @@
 #include <utility>
 
 #include <folly/CPortability.h>
-#include <folly/CppAttributes.h>
 #include <folly/Demangle.h>
 #include <folly/ExceptionString.h>
 #include <folly/FBString.h>
@@ -39,7 +38,6 @@
 #include <folly/Traits.h>
 #include <folly/Utility.h>
 #include <folly/lang/Assume.h>
-#include <folly/lang/Exception.h>
 
 #ifdef __GNUC__
 #pragma GCC diagnostic push
@@ -179,7 +177,10 @@ class exception_wrapper final {
   //  1. An small object stored in-situ.
   //  2. A larger object stored on the heap and referenced with a
   //     std::shared_ptr.
-  //  3. A std::exception_ptr.
+  //  3. A std::exception_ptr, together with either:
+  //       a. A pointer to the referenced std::exception object, or
+  //       b. A pointer to a std::type_info object for the referenced exception,
+  //          or for an unspecified type if the type is unknown.
   // This is accomplished with the help of a union and a pointer to a hand-
   // rolled virtual table. This virtual table contains pointers to functions
   // that know which field of the union is active and do the proper action.
@@ -211,6 +212,8 @@ class exception_wrapper final {
   using IsCatchAll =
       std::is_same<arg_type<std::decay_t<CatchFn>>, AnyException>;
 
+  struct Unknown {};
+
   // Sadly, with the gcc-4.9 platform, std::logic_error and std::runtime_error
   // do not fit here. They also don't have noexcept copy-ctors, so the internal
   // storage wouldn't be used anyway. For the gcc-5 platform, both logic_error
@@ -252,7 +255,19 @@ class exception_wrapper final {
 
   struct ExceptionPtr {
     std::exception_ptr ptr_;
-
+    std::uintptr_t exception_or_type_; // odd for type_info
+    static_assert(
+        1 < alignof(std::exception) && 1 < alignof(std::type_info),
+        "Surprise! std::exception and std::type_info don't have alignment "
+        "greater than one. as_int_ below will not work!");
+
+    static std::uintptr_t as_int_(
+        std::exception_ptr const& ptr, std::exception const& e) noexcept;
+    static std::uintptr_t as_int_(
+        std::exception_ptr const& ptr, AnyException e) noexcept;
+    bool has_exception_() const;
+    std::exception const* as_exception_() const;
+    std::type_info const* as_type_() const;
     static void copy_(exception_wrapper const* from, exception_wrapper* to);
     static void move_(exception_wrapper* from, exception_wrapper* to);
     static void delete_(exception_wrapper* that);
@@ -393,19 +408,19 @@ class exception_wrapper final {
 
   ~exception_wrapper();
 
+  //! \pre `ptr` is empty, or it holds a reference to an exception that is not
+  //!     derived from `std::exception`.
   //! \post `!ptr || bool(*this)`
-  //! \post `hasThrownException() == bool(ptr)`
-  explicit exception_wrapper(std::exception_ptr const& ptr) noexcept;
-  explicit exception_wrapper(std::exception_ptr&& ptr) noexcept;
+  //! \post `hasThrownException() == true`
+  //! \post `type() == unknown()`
+  explicit exception_wrapper(std::exception_ptr ptr) noexcept;
 
   //! \pre `ptr` holds a reference to `ex`.
   //! \post `hasThrownException() == true`
   //! \post `bool(*this)`
   //! \post `type() == typeid(ex)`
   template <class Ex>
-  exception_wrapper(std::exception_ptr const& ptr, Ex& ex) noexcept;
-  template <class Ex>
-  exception_wrapper(std::exception_ptr&& ptr, Ex& ex) noexcept;
+  exception_wrapper(std::exception_ptr ptr, Ex& ex) noexcept;
 
   //! \pre `typeid(ex) == typeid(typename decay<Ex>::type)`
   //! \post `bool(*this)`
@@ -491,16 +506,23 @@ class exception_wrapper final {
   //! \return the `typeid` of an unspecified type used by
   //!     `exception_wrapper::type()` to denote an empty `exception_wrapper`.
   static std::type_info const& none() noexcept;
+  //! \return the `typeid` of an unspecified type used by
+  //!     `exception_wrapper::type()` to denote an `exception_wrapper` that
+  //!     holds an exception of unknown type.
+  static std::type_info const& unknown() noexcept;
 
   //! Returns the `typeid` of the wrapped exception object. If there is no
-  //!     wrapped exception object, returns `exception_wrapper::none()`.
+  //!     wrapped exception object, returns `exception_wrapper::none()`. If
+  //!     this instance wraps an exception of unknown type not derived from
+  //!     `std::exception`, returns `exception_wrapper::unknown()`.
   std::type_info const& type() const noexcept;
 
   //! \return If `get_exception() != nullptr`, `class_name() + ": " +
   //!     get_exception()->what()`; otherwise, `class_name()`.
   folly::fbstring what() const;
 
-  //! \return If `!*this`, the empty string; otherwise,
+  //! \return If `!*this`, the empty string; otherwise, if
+  //!     `type() == unknown()`, the string `"<unknown exception>"`; otherwise,
   //!     the result of `type().name()` after demangling.
   folly::fbstring class_name() const;
 
@@ -636,8 +658,8 @@ template <typename F, typename Ex, typename... Exs>
 inline exception_wrapper try_and_catch_(F&& f) {
   try {
     return try_and_catch_<F, Exs...>(std::forward<F>(f));
-  } catch (Ex&) {
-    return exception_wrapper(std::current_exception());
+  } catch (Ex& ex) {
+    return exception_wrapper(std::current_exception(), ex);
   }
 }
 } // namespace detail
@@ -687,6 +709,8 @@ exception_wrapper try_and_catch(F&& fn) noexcept {
   try {
     static_cast<F&&>(fn)();
     return exception_wrapper{};
+  } catch (std::exception const& ex) {
+    return exception_wrapper{std::current_exception(), ex};
   } catch (...) {
     return exception_wrapper{std::current_exception()};
   }

folly/test/ExceptionWrapperTest.cpp

@@ -239,13 +239,13 @@ TEST(ExceptionWrapper, get_or_make_exception_ptr_test) {
 
 TEST(ExceptionWrapper, from_exception_ptr_empty) {
   auto ep = std::exception_ptr();
-  auto ew = exception_wrapper{ep};
+  auto ew = exception_wrapper::from_exception_ptr(ep);
   EXPECT_FALSE(bool(ew));
 }
 
 TEST(ExceptionWrapper, from_exception_ptr_exn) {
   auto ep = std::make_exception_ptr(std::runtime_error("foo"));
-  auto ew = exception_wrapper{ep};
+  auto ew = exception_wrapper::from_exception_ptr(ep);
   EXPECT_TRUE(bool(ew));
   EXPECT_EQ(ep, folly::as_const(ew).to_exception_ptr());
   EXPECT_EQ(ep, ew.to_exception_ptr());
@@ -254,7 +254,7 @@ TEST(ExceptionWrapper, from_exception_ptr_exn) {
 
 TEST(ExceptionWrapper, from_exception_ptr_any) {
   auto ep = std::make_exception_ptr<int>(12);
-  auto ew = exception_wrapper{ep};
+  auto ew = exception_wrapper::from_exception_ptr(ep);
   EXPECT_TRUE(bool(ew));
   EXPECT_EQ(ep, folly::as_const(ew).to_exception_ptr());
   EXPECT_EQ(ep, ew.to_exception_ptr());
@@ -420,7 +420,7 @@ TEST(ExceptionWrapper, with_non_std_exception_test) {
 
 TEST(ExceptionWrapper, with_exception_ptr_any_nil_test) {
   auto ep = std::make_exception_ptr<int>(12);
-  auto ew = exception_wrapper(ep);
+  auto ew = exception_wrapper(ep); // concrete type is erased
   EXPECT_TRUE(bool(ew));
   EXPECT_EQ(nullptr, ew.get_exception());
   EXPECT_EQ(nullptr, ew.get_exception<std::exception>());
@@ -428,8 +428,9 @@ TEST(ExceptionWrapper, with_exception_ptr_any_nil_test) {
   EXPECT_EQ(12, *ew.get_exception<int>());
   EXPECT_EQ(ep, folly::as_const(ew).to_exception_ptr());
   EXPECT_EQ(ep, ew.to_exception_ptr());
-  EXPECT_EQ("int", ew.class_name());
-  EXPECT_EQ("int", ew.what());
+  EXPECT_EQ("<unknown exception>", ew.class_name()); // because concrete type is
+  // erased
+  EXPECT_EQ("<unknown exception>", ew.what());
   EXPECT_FALSE(ew.is_compatible_with<std::exception>());
   EXPECT_FALSE(ew.is_compatible_with<std::runtime_error>());
   EXPECT_TRUE(ew.is_compatible_with<int>());
@@ -538,16 +539,23 @@ TEST(ExceptionWrapper, implicitConstruction) {
 }
 
 namespace {
-struct BaseNonStdException {
-  virtual ~BaseNonStdException() {}
+struct BaseException {
+  virtual ~BaseException() {}
 };
-struct DerivedNonStdException : BaseNonStdException {};
+struct DerivedException : BaseException {};
+exception_wrapper testNonStdException() {
+  try {
+    throw DerivedException{};
+  } catch (const BaseException& e) {
+    return exception_wrapper{std::current_exception(), e};
+  }
+}
 } // namespace
 
 TEST(ExceptionWrapper, base_derived_non_std_exception_test) {
-  exception_wrapper ew{std::make_exception_ptr(DerivedNonStdException{})};
-  EXPECT_TRUE(ew.type() == typeid(DerivedNonStdException));
-  EXPECT_TRUE(ew.with_exception([](const DerivedNonStdException&) {}));
+  auto ew = testNonStdException();
+  EXPECT_TRUE(ew.type() == typeid(DerivedException));
+  EXPECT_TRUE(ew.with_exception([](const DerivedException&) {}));
 }
 
 namespace {
@@ -834,26 +842,26 @@ TEST(ExceptionWrapper, handle_non_std_exception_big) {
 }
 
 TEST(ExceptionWrapper, handle_non_std_exception_rethrow_base_derived) {
-  exception_wrapper ew{std::make_exception_ptr(DerivedNonStdException{})};
+  auto ew = testNonStdException();
   bool handled = false;
   EXPECT_THROW(
       ew.handle(
-          [&](const DerivedNonStdException& e) {
+          [&](const DerivedException& e) {
             handled = true;
             throw e;
           },
-          [](const BaseNonStdException&) { ADD_FAILURE(); }),
-      DerivedNonStdException);
+          [](const BaseException&) { ADD_FAILURE(); }),
+      DerivedException);
   EXPECT_TRUE(handled);
   handled = false;
   EXPECT_THROW(
       ew.handle(
-          [&](const DerivedNonStdException& e) {
+          [&](const DerivedException& e) {
             handled = true;
             throw e;
           },
           [](...) { ADD_FAILURE(); }),
-      DerivedNonStdException);
+      DerivedException);
   EXPECT_TRUE(handled);
 }