[compiler-rt] Reapply "[sanitizer_common] AND signals in BlockSignals instead of deleting (#113443)" for non-Android Linux only (PR #115790)

[Thurston Dang via llvm-commits]

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@@ -164,33 +164,55 @@ void SetSigProcMask(__sanitizer_sigset_t *set, __sanitizer_sigset_t *oldset) {
   CHECK_EQ(0, internal_sigprocmask(SIG_SETMASK, set, oldset));
 }
 
+#  if SANITIZER_LINUX
+// Deletes the specified signal from newset, if it is not present in oldset
+// Equivalently: newset[signum] = newset[signum] & oldset[signum]
+static void KeepUnblocked(__sanitizer_sigset_t &newset,
+                          __sanitizer_sigset_t &oldset, int signum) {
+  // FIXME: Figure out why Android tests fail with internal_sigismember
+  // See also: comment in BlockSignals().
+  // In the meantime, we prefer to sometimes incorrectly unblock signals.
+  if (SANITIZER_ANDROID || !internal_sigismember(&oldset, signum))
+    internal_sigdelset(&newset, signum);
+}
+#  endif
+
 // Block asynchronous signals
 void BlockSignals(__sanitizer_sigset_t *oldset) {
-  __sanitizer_sigset_t set;
-  internal_sigfillset(&set);
+  __sanitizer_sigset_t currentset;
+#  if !SANITIZER_ANDROID
+  // FIXME: SetSigProcMask and pthread_sigmask cause mysterious failures
+  // See also: comment in KeepUnblocked().
+  // In the meantime, we prefer to sometimes incorrectly unblock signals.
+  SetSigProcMask(NULL, &currentset);
+#  endif
+
+  __sanitizer_sigset_t newset;
+  internal_sigfillset(&newset);
 #  if SANITIZER_LINUX && !SANITIZER_ANDROID
   // Glibc uses SIGSETXID signal during setuid call. If this signal is blocked
   // on any thread, setuid call hangs.
   // See test/sanitizer_common/TestCases/Linux/setuid.c.
-  internal_sigdelset(&set, 33);
+  KeepUnblocked(newset, currentset, 33);
 #  endif
 #  if SANITIZER_LINUX
   // Seccomp-BPF-sandboxed processes rely on SIGSYS to handle trapped syscalls.
   // If this signal is blocked, such calls cannot be handled and the process may
   // hang.
-  internal_sigdelset(&set, 31);
+  KeepUnblocked(newset, currentset, 31);
 
   // Don't block synchronous signals
-  internal_sigdelset(&set, SIGSEGV);
-  internal_sigdelset(&set, SIGBUS);
-  internal_sigdelset(&set, SIGILL);
-  internal_sigdelset(&set, SIGTRAP);
-  internal_sigdelset(&set, SIGABRT);
-  internal_sigdelset(&set, SIGFPE);
-  internal_sigdelset(&set, SIGPIPE);
+  // but also don't unblock signals that the user had deliberately blocked.
+  KeepUnblocked(newset, currentset, SIGSEGV);
+  KeepUnblocked(newset, currentset, SIGBUS);
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thurstond wrote:

Thanks for the confirmation! I will shortly update this patch to apply the pre-#98200 behavior for Android.

https://github.com/llvm/llvm-project/pull/115790