[test] Add basic _Unwind_ForcedUnwind + exception tests

[MaskRay]

Summary

Forced unwinding is like a foreign exception, which can be caught by catch (...) and rethrown.
If not rethrown, __cxa_end_cath will call _Unwind_DeleteException to destroy the object.

The behavior going through empty throw() and non-empty throw(int) is not
clear (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98785), so I do not add such
tests.

[MaskRay]

simplify

[MaskRay]

🙄

[ldionne]

Won't complain, you're adding tests. But can you please resolve the CI issues? This is breaking the tests under a few configurations. See https://buildkite.com/llvm-project/diff-checks/builds/26184.

[MaskRay]

Fix signature of _Unwind_Stop_Fn
Fix -Werror=shadow on GCC

[MaskRay]

Use a trait

[MaskRay]

UNSUPPORT c++03 because I use tuple_element

[MaskRay]

@ldionne PTAL.

https://buildkite.com/llvm-project/libcxx-ci/builds/1163 macosx 10.9 was flaky and failed for unrelated libc++ tests. Other configuration passed.

[ldionne]

Sorry about the flakiness, I'm working on fixing it.

[vvereschaka]

Hi @MaskRay,

these tests get failed on Windows to ARMv7 Linux cross builder with the following error:

C:/buildbot/as-builder-1/x-armv7l/llvm-project/libcxxabi/test/forced_unwind1.pass.cpp:37:42: error: typedef '_Unwind_Exception' cannot be referenced with a struct specifier

http://lab.llvm.org:8011/#/builders/60/builds/1855

[MaskRay]

In D95200#2538300, @vvereschaka wrote:

Hi @MaskRay,

these tests get failed on Windows to ARMv7 Linux cross builder with the following error:

C:/buildbot/as-builder-1/x-armv7l/llvm-project/libcxxabi/test/forced_unwind1.pass.cpp:37:42: error: typedef '_Unwind_Exception' cannot be referenced with a struct specifier

http://lab.llvm.org:8011/#/builders/60/builds/1855

The standard writes struct _Unwind_Exception *. This way it works in C as well. https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html

I am not sure libunwind's ARMEH implementation has working _Unwind_ForcedUnwind so looks like the best is to unsupport arm. How to do that?

[ikudrin]

In D95200#2538388, @MaskRay wrote:

I am not sure libunwind's ARMEH implementation has working _Unwind_ForcedUnwind so looks like the best is to unsupport arm. How to do that?

It looks like the function has not been implemented for Arm EHABI yet, see D89570.

There are a number of tests in the libcxxabi test suite that use #if !defined(_LIBCXXABI_ARM_EHABI) to do some adjustments or disable the test completely.

[MaskRay]

In D95200#2538493, @ikudrin wrote:

In D95200#2538388, @MaskRay wrote:

I am not sure libunwind's ARMEH implementation has working _Unwind_ForcedUnwind so looks like the best is to unsupport arm. How to do that?

It looks like the function has not been implemented for Arm EHABI yet, see D89570.

There are a number of tests in the libcxxabi test suite that use #if !defined(_LIBCXXABI_ARM_EHABI) to do some adjustments or disable the test completely.

In the absence of an ARMEH disabling directive, do this?

#ifdef _LIBCXXABI_ARM_EHABI
int main() {}
#else
...
#endif

[ikudrin]

Seems OK. Something similar is in exception_object_alignment.pass.cpp.

[vvereschaka]

@ikudrin thank you for your help.

[vvereschaka]

@MaskRay , ping

[MaskRay]

In D95200#2546067, @vvereschaka wrote:

@MaskRay , ping

Disabled in a4fa667dee6012e350bd405ee7a759a53738b279

[vvereschaka]

got it, thank you.

libcxxabi/test/forced_unwind1.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// _Unwind_ForcedUnwind raised exception can be caught by catch (...) and be
+// rethrown. If not rethrown, exception_cleanup will be called.
+
+// UNSUPPORTED: no-exceptions
+
+#include <stdlib.h>
+#include <string.h>
+#include <unwind.h>
+#include <tuple>
+
+static int bits = 0;
+
+struct C {
+  int bit;
+  C(int b) : bit(b) {}
+  ~C() { bits |= bit; }
+};
+
+template <typename T>
+struct Stop;
+
+template <typename R, typename... Args>
+struct Stop<R (*)(Args...)> {
+  // The third argument of _Unwind_Stop_Fn is uint64_t in Itanium C++ ABI/LLVM
+  // libunwind while _Unwind_Exception_Class in libgcc.
+  typedef typename std::tuple_element<2, std::tuple<Args...>>::type type;
+
+  static _Unwind_Reason_Code stop(int, _Unwind_Action actions, type,
+                                  struct _Unwind_Exception*,
+                                  struct _Unwind_Context*, void*) {
+    if (actions & _UA_END_OF_STACK)
+      abort();
+    return _URC_NO_REASON;
+  }
+};
+
+static void cleanup(_Unwind_Reason_Code, struct _Unwind_Exception* exc) {
+  bits |= 8;
+  delete exc;
+}
+
+static void forced_unwind() {
+  _Unwind_Exception* exc = new _Unwind_Exception;
+  exc->exception_class = 0;
+  exc->exception_cleanup = cleanup;
+  _Unwind_ForcedUnwind(exc, Stop<_Unwind_Stop_Fn>::stop, 0);
+  abort();
+}
+
+static void test() {
+  try {
+    C four(4);
+    try {
+      C one(1);
+      forced_unwind();
+    } catch (...) {
+      bits |= 2;
+      throw;
+    }
+  } catch (int) {
+  } catch (...) {
+    // __cxa_end_catch calls cleanup.
+  }
+}
+
+int main() {
+  test();
+  return bits != 15;
+}

libcxxabi/test/forced_unwind2.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Forced unwinding causes std::terminate when going through noexcept.
+
+// UNSUPPORTED: no-exceptions, c++03
+
+#include <exception>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unwind.h>
+#include <tuple>
+
+template <typename T>
+struct Stop;
+
+template <typename R, typename... Args>
+struct Stop<R (*)(Args...)> {
+  // The third argument of _Unwind_Stop_Fn is uint64_t in Itanium C++ ABI/LLVM
+  // libunwind while _Unwind_Exception_Class in libgcc.
+  typedef typename std::tuple_element<2, std::tuple<Args...>>::type type;
+
+  static _Unwind_Reason_Code stop(int, _Unwind_Action actions, type,
+                                  struct _Unwind_Exception*,
+                                  struct _Unwind_Context*, void*) {
+    if (actions & _UA_END_OF_STACK)
+      abort();
+    return _URC_NO_REASON;
+  }
+};
+
+static void forced_unwind() {
+  _Unwind_Exception* exc = new _Unwind_Exception;
+  exc->exception_class = 0;
+  exc->exception_cleanup = 0;
+  _Unwind_ForcedUnwind(exc, Stop<_Unwind_Stop_Fn>::stop, 0);
+  abort();
+}
+
+static void test() noexcept { forced_unwind(); }
+
+static void terminate() { exit(0); }
+
+int main() {
+  std::set_terminate(terminate);
+  try {
+    test();
+  } catch (...) {
+  }
+  abort();
+}