Adapt QTest::FatalSignalHandler() to support sa_sigaction when available

We don't currently have a use for the extra parameters, but Samuel
Mira's fix to ensure we don't miss fatal signals on Android needs to
be able to call the prior handler, which may need these parameters.

In the process, check returns from sigaction() and use its nullptr
semantics to query first when detecting whether to restore the default
when done, rather than setting and then restoring if it turns out
we've been replaced in the meantime.

Task-number: QTBUG-97652
Change-Id: If30a0db35946c3dceb409ae3f41aa437149472e6
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit fcecaf53f51d4da708a7ef5d05f56f7286d2139c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 23 insertions, 6 deletions

diff --git a/src/testlib/qtestcase.cpp b/src/testlib/qtestcase.cpp
index 1e5b8d225f..c22d6e0daa 100644
--- a/src/testlib/qtestcase.cpp
+++ b/src/testlib/qtestcase.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2021 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Copyright (C) 2016 Intel Corporation.
 ** Contact: https://www.qt.io/licensing/
 **
@@ -1684,7 +1684,12 @@ public:
 
         struct sigaction act;
         memset(&act, 0, sizeof(act));
+#  ifdef SA_SIGINFO
+        act.sa_flags |= SA_SIGINFO;
+        act.sa_sigaction = FatalSignalHandler::signal;
+#  else
         act.sa_handler = FatalSignalHandler::signal;
+#  endif
 
         // Remove the handler after it is invoked.
 #  if !defined(Q_OS_INTEGRITY)
@@ -1746,21 +1751,29 @@ public:
     ~FatalSignalHandler()
     {
 #if defined(Q_OS_UNIX) && !defined(Q_OS_WASM)
-        // Unregister any of our remaining signal handlers
+        // Restore the default signal handler in place of ours.
+        // If ours has been replaced, leave the replacement alone.
         struct sigaction act;
         memset(&act, 0, sizeof(act));
         act.sa_handler = SIG_DFL;
 
+        auto isOurs = [](const struct sigaction &old) {
+#  ifdef SA_SIGINFO
+            return (old.sa_flags & SA_SIGINFO) && old.sa_sigaction == FatalSignalHandler::signal;
+#  else
+            return old.sa_handler == FatalSignalHandler::signal;
+#  endif
+        };
         struct sigaction oldact;
 
         for (int i = 1; i < 32; ++i) {
             if (!sigismember(&handledSignals, i))
                 continue;
-            sigaction(i, &act, &oldact);
+            if (sigaction(i, nullptr, &oldact))
+                continue; // Failed to query present handler
 
-            // If someone overwrote it in the mean time, put it back
-            if (oldact.sa_handler != FatalSignalHandler::signal)
-                sigaction(i, &oldact, nullptr);
+            if (isOurs(oldact))
+                sigaction(i, &act, nullptr);
         }
 #endif
     }
@@ -1812,7 +1825,11 @@ private:
 #endif // defined(Q_OS_WIN)
 
 #if defined(Q_OS_UNIX) && !defined(Q_OS_WASM)
+#  ifdef SA_SIGINFO
+    static void signal(int signum, siginfo_t * /* info */, void * /* ucontext */)
+#  else
     static void signal(int signum)
+#endif
     {
         const int msecsFunctionTime = qRound(QTestLog::msecsFunctionTime());
         const int msecsTotalTime = qRound(QTestLog::msecsTotalTime());