From bc6a7e51e4787bad7ab32c8ac4634eb99c477922 Mon Sep 17 00:00:00 2001
From: Christopher Ferris <cferris@google.com>
Date: Fri, 18 Jan 2019 16:33:27 -0800
Subject: [PATCH] Fix flaky signal tests.

The signal tests that send a SIGUSR1 signal to a remote process, can
lead to a case where the code winds up in a location for which the
unwind information is not 100% accurate. This happens near the
end of the atomic functions which manipulate the stack right before
returning, but do not have separate cfi instructions for those last
few instructions.

Add a new test type for the from_context test that will wait explicitly
for the global g_finish and not piggy back on the remote test type.

Bug: 122902885

Test: Ran flaky tests 1000 times without failure on a taimen.
Change-Id: I7d0c9b016e3a3a2c0c0949cf74af11d7785a008c
---
 libunwindstack/tests/UnwindTest.cpp | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/libunwindstack/tests/UnwindTest.cpp b/libunwindstack/tests/UnwindTest.cpp
index a91bd9506..c747eabc6 100644
--- a/libunwindstack/tests/UnwindTest.cpp
+++ b/libunwindstack/tests/UnwindTest.cpp
@@ -47,6 +47,7 @@ namespace unwindstack {
 enum TestTypeEnum : uint8_t {
   TEST_TYPE_LOCAL_UNWINDER = 0,
   TEST_TYPE_LOCAL_UNWINDER_FROM_PID,
+  TEST_TYPE_LOCAL_WAIT_FOR_FINISH,
   TEST_TYPE_REMOTE,
   TEST_TYPE_REMOTE_WITH_INVALID_CALL,
 };
@@ -79,7 +80,10 @@ static void SignalHandler(int, siginfo_t*, void* sigcontext) {
 
 extern "C" void SignalInnerFunction() {
   g_signal_ready_for_remote = true;
-  while (!g_finish.load()) {
+  // Avoid any function calls because not every instruction will be
+  // unwindable.
+  // This method of looping is only used when testing a remote unwind.
+  while (true) {
   }
 }
 
@@ -134,6 +138,11 @@ static void VerifyUnwind(pid_t pid, Maps* maps, Regs* regs,
 // off. If this doesn't happen, then all of the calls will be optimized
 // away.
 extern "C" void InnerFunction(TestTypeEnum test_type) {
+  if (test_type == TEST_TYPE_LOCAL_WAIT_FOR_FINISH) {
+    while (!g_finish.load()) {
+    }
+    return;
+  }
   if (test_type == TEST_TYPE_REMOTE || test_type == TEST_TYPE_REMOTE_WITH_INVALID_CALL) {
     g_ready_for_remote = true;
     g_ready = true;
@@ -141,7 +150,10 @@ extern "C" void InnerFunction(TestTypeEnum test_type) {
       void (*crash_func)() = nullptr;
       crash_func();
     }
-    while (!g_finish.load()) {
+    // Avoid any function calls because not every instruction will be
+    // unwindable.
+    // This method of looping is only used when testing a remote unwind.
+    while (true) {
     }
     return;
   }
@@ -271,7 +283,7 @@ TEST_F(UnwindTest, from_context) {
   std::atomic_int tid(0);
   std::thread thread([&]() {
     tid = syscall(__NR_gettid);
-    OuterFunction(TEST_TYPE_REMOTE);
+    OuterFunction(TEST_TYPE_LOCAL_WAIT_FOR_FINISH);
   });
 
   struct sigaction act, oldact;