[tsan] Fix sigaction interceptor after D107186

Set SA_SIGINFO only if we set sighandler, or we can set the flag, and
return it as 'old' without actual sigaction set.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D108616

Author: vitalybuka

compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp

@@ -2459,9 +2459,11 @@ int sigaction_impl(int sig, const __sanitizer_sigaction *act,
 #endif
     internal_memcpy(&newact, act, sizeof(newact));
     internal_sigfillset(&newact.sa_mask);
-    newact.sa_flags |= SA_SIGINFO;
-    if ((uptr)act->handler != sig_ign && (uptr)act->handler != sig_dfl)
+    if ((act->sa_flags & SA_SIGINFO) ||
+        ((uptr)act->handler != sig_ign && (uptr)act->handler != sig_dfl)) {
+      newact.sa_flags |= SA_SIGINFO;
       newact.sigaction = sighandler;
+    }
     ReleaseStore(thr, pc, (uptr)&sigactions[sig]);
     act = &newact;
   }

compiler-rt/test/sanitizer_common/TestCases/Posix/replace_sigaction.cpp

@@ -0,0 +1,66 @@
+// RUN: %clangxx -std=c++11 -O0 -g %s -o %t && %run %t
+
+#include <assert.h>
+#include <signal.h>
+#include <unistd.h>
+
+static bool sahandler_done;
+static bool sasigaction_done;
+
+static void sahandler(int) { sahandler_done = true; }
+
+static void sasigaction(int, siginfo_t *, void *) { sasigaction_done = true; }
+
+template <typename T> void install(T *handler, struct sigaction *prev) {
+  bool siginfo = handler == (T *)&sasigaction;
+  struct sigaction act = {};
+  if (siginfo) {
+    act.sa_flags = SA_SIGINFO;
+    act.sa_sigaction = (decltype(act.sa_sigaction))handler;
+  } else {
+    act.sa_handler = (decltype(act.sa_handler))handler;
+  }
+  int ret = sigaction(SIGHUP, &act, prev);
+  assert(ret == 0);
+
+  if (handler == (T *)&sahandler) {
+    sahandler_done = false;
+    raise(SIGHUP);
+    assert(sahandler_done);
+  }
+
+  if (handler == (T *)&sasigaction) {
+    sasigaction_done = false;
+    raise(SIGHUP);
+    assert(sasigaction_done);
+  }
+}
+
+template <typename T1, typename T2> void test(T1 *from, T2 *to) {
+  install(from, nullptr);
+  struct sigaction prev = {};
+  install(to, &prev);
+
+  bool siginfo_from = (from == (T1 *)&sasigaction);
+  if (siginfo_from) {
+    assert(prev.sa_flags & SA_SIGINFO);
+    assert(prev.sa_sigaction == (decltype(prev.sa_sigaction))from);
+  } else {
+    assert((prev.sa_flags & SA_SIGINFO) == 0);
+    assert(prev.sa_handler == (decltype(prev.sa_handler))from);
+  }
+}
+
+template <typename T> void testAll(T *to) {
+  test(&sahandler, to);
+  test(&sasigaction, to);
+  test(SIG_IGN, to);
+  test(SIG_DFL, to);
+}
+
+int main(void) {
+  testAll(&sahandler);
+  testAll(&sasigaction);
+  testAll(SIG_IGN);
+  testAll(SIG_DFL);
+}