[libunwind][AArch64] Fix _Unwind_ForcedUnwind via sigreturn.

[danielkiss]

Summary

When the sigreturn trampoline is found the unw_proc_info_t.end_ip need to be set to
indicate a stack frame is found.

[manojgupta]

Thanks, this also fixes one of the test failures we were seeing on AArch64 boards.

[cjdb]

Thanks!

[MaskRay]

libcxxabi/test/forced_unwind4.pass.cpp

13

This applies to glibc but not musl.

32

Use a condition variable to avoid the race?

[MaskRay]

LGTM.

libcxxabi/test/forced_unwind4.pass.cpp

46

delete braces

[rprichard]

libcxxabi/test/forced_unwind4.pass.cpp

13

Also: Bionic doesn't have pthread_cancel. Maybe this test will have to be disabled for Android/Bionic.

[danielkiss]

libcxxabi/test/forced_unwind4.pass.cpp

13

done. https://github.com/llvm/llvm-project/commit/6830ebb07eb9065dca0215e5ae6b22a24d35a745

[rprichard]

libcxxabi/test/forced_unwind4.pass.cpp

13

Thanks!

libcxxabi/test/forced_unwind4.pass.cpp

+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: linux && target={{aarch64-.+}}
+
+// pthread_cancel in case of glibc calls _Unwind_ForcedUnwind from a signal on
+// the child_thread. This test ensures sigretrun is handled correctly (see:
+// UnwindCursor<A, R>::setInfoForSigReturn).
+
+#include <chrono>
+#include <condition_variable>
+#include <pthread.h>
+#include <unistd.h>
+
+using namespace std::chrono_literals;
+
+std::condition_variable cv;
+std::mutex cv_m;
+bool thread_ready = false;
+
+static void* test(void* arg) {
+  (void)arg;
+  thread_ready = true;
+  cv.notify_all();
+
+  // This must be a pthread cancellation point.
+  while (1)
+    sleep(100);
+
+  return (void*)1;
+}
+
+int main() {
+  pthread_t child_thread;
+  std::unique_lock<std::mutex> lk(cv_m);
+  pthread_create(&child_thread, 0, test, (void*)0);
+
+  if (!cv.wait_for(lk, 100ms, [] { return thread_ready; }))
+    return -1;
+
+  pthread_cancel(child_thread);
+  pthread_join(child_thread, NULL);
+  return 0;
+}

libunwind/src/UnwindCursor.hpp

bool UnwindCursor<A, R>::setInfoForSigReturn(Registers_arm64 &) {
   //  - The PC is invalid and happens to point to unreadable or unmapped memory.
   //
   // [1] https://github.com/torvalds/linux/blob/master/arch/arm64/kernel/vdso/sigreturn.S
   const pint_t pc = static_cast<pint_t>(this->getReg(UNW_REG_IP));
   // Look for instructions: mov x8, #0x8b; svc #0x0
   if (_addressSpace.get32(pc) == 0xd2801168 &&
       _addressSpace.get32(pc + 4) == 0xd4000001) {
     _info = {};
+    _info.start_ip = pc;
+    _info.end_ip = pc + 4;
     _isSigReturn = true;
     return true;
   }
   return false;
 }
 
 template <typename A, typename R>
 int UnwindCursor<A, R>::stepThroughSigReturn(Registers_arm64 &) {