commit 26d83ba7abcbfa725794c144411214d16f64b75a
author Peter Collingbourne <pcc@google.com> Fri Jun 04 14:35:13 2021 -0700
committer Peter Collingbourne <pcc@google.com> Tue Jun 08 16:03:41 2021 -0700
tree 8195cbabb3da6b6bfb4c59072b5e9fc47ceb120b
parent 921b3a4642c2d24e7580ae542ff10e0319a2453d

Disable return PAC in __pthread_start.

This function doesn't return, but it does appear in stack traces. Avoid
using return PAC in this function because we may end up resetting IA,
which may confuse unwinders due to mismatching keys.

Bug: 189808795
Change-Id: I953da9078acd1d43eb7a47fb11f75caa0099fa12

libc/bionic/pthread_create.cpp

diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index 46d9e86..121b26f 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -331,6 +331,11 @@
 extern "C" int __rt_sigprocmask(int, const sigset64_t*, sigset64_t*, size_t);
 
 __attribute__((no_sanitize("hwaddress")))
+#ifdef __aarch64__
+// This function doesn't return, but it does appear in stack traces. Avoid using return PAC in this
+// function because we may end up resetting IA, which may confuse unwinders due to mismatching keys.
+__attribute__((target("branch-protection=bti")))
+#endif
 static int __pthread_start(void* arg) {
   pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg);
 

tests/stack_unwinding_test.cpp

diff --git a/tests/stack_unwinding_test.cpp b/tests/stack_unwinding_test.cpp
index 0ff6f30..2f891a6 100644
--- a/tests/stack_unwinding_test.cpp
+++ b/tests/stack_unwinding_test.cpp
@@ -66,13 +66,28 @@
   return count;
 }
 
-TEST(stack_unwinding, easy) {
+static void UnwindTest() {
   int count = 0;
   _Unwind_Backtrace(FrameCounter, &count);
   int deeper_count = unwind_one_frame_deeper();
   ASSERT_EQ(count + 1, deeper_count);
 }
 
+TEST(stack_unwinding, easy) {
+  UnwindTest();
+}
+
+TEST(stack_unwinding, thread) {
+  pthread_t thread;
+  ASSERT_EQ(0, pthread_create(&thread, nullptr, [](void*) -> void* {
+    UnwindTest();
+    return nullptr;
+  }, nullptr));
+  void *retval;
+  ASSERT_EQ(0, pthread_join(thread, &retval));
+  EXPECT_EQ(nullptr, retval);
+}
+
 struct UnwindData {
   volatile bool signal_handler_complete = false;
   int expected_frame_count = 0;
@@ -98,7 +113,7 @@
   EXPECT_EQ(unwind_data.handler_frame_count + 1, unwind_data.handler_one_deeper_frame_count);
 }
 
-static void noinline UnwindTest() {
+static void noinline SignalUnwindTest() {
   g_unwind_data = {};
 
   _Unwind_Backtrace(FrameCounter, &g_unwind_data.expected_frame_count);
@@ -114,12 +129,12 @@
 TEST(stack_unwinding, unwind_through_signal_frame) {
   ScopedSignalHandler ssh(SIGUSR1, UnwindSignalHandler);
 
-  UnwindTest();
+  SignalUnwindTest();
 }
 
 // On LP32, the SA_SIGINFO flag gets you __restore_rt instead of __restore.
 TEST(stack_unwinding, unwind_through_signal_frame_SA_SIGINFO) {
   ScopedSignalHandler ssh(SIGUSR1, UnwindSignalHandler, SA_SIGINFO);
 
-  UnwindTest();
+  SignalUnwindTest();
 }