[ubsan] Disable signal handling on Android.

[eugenis]

Summary

See rationale in the comments.

[eugenis]

add one more reason

[srhines]

Thanks so much for helping us figure this out. Hopefully we can find a better way to actually allow for signal interception, but this at least gets us back to a working build.

compiler-rt/lib/ubsan/ubsan_signals_standalone.cc

 //=-- ubsan_signals_standalone.cc
 //------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // Installs signal handlers and related interceptors for UBSan standalone.
 //
 //===----------------------------------------------------------------------===//
 
 #include "ubsan_platform.h"
+#include "sanitizer_common/sanitizer_platform.h"
 #if CAN_SANITIZE_UB
 #include "interception/interception.h"
 #include "sanitizer_common/sanitizer_stacktrace.h"
 #include "ubsan_diag.h"
 #include "ubsan_init.h"
 
+// Interception of signals breaks too many things on Android.
+// * It requires that ubsan is the first dependency of the main executable for
+// the interceptors to work correctly. This complicates deployment, as it
+// prevents us from enabling ubsan on random platform modules independently.
+// * For this to work with ART VM, ubsan signal handler has to be set after the
+// debuggerd handler, but before the ART handler.
+// * Interceptors don't work at all when ubsan runtime is loaded late, ex. when
+// it is part of an APK that does not use wrap.sh method.
+#if SANITIZER_FUCHSIA || SANITIZER_ANDROID
+
+namespace __ubsan {
+void InitializeDeadlySignals() {}
+}
+
+#else
+
 #define COMMON_INTERCEPT_FUNCTION(name) INTERCEPT_FUNCTION(name)
 #include "sanitizer_common/sanitizer_signal_interceptors.inc"
 
 namespace __ubsan {
 
-#if SANITIZER_FUCHSIA
-void InitializeDeadlySignals() {}
-#else
 static void OnStackUnwind(const SignalContext &sig, const void *,
                           BufferedStackTrace *stack) {
   GetStackTrace(stack, kStackTraceMax, sig.pc, sig.bp, sig.context,
                 common_flags()->fast_unwind_on_fatal);
 }
 
 static void UBsanOnDeadlySignal(int signo, void *siginfo, void *context) {
   HandleDeadlySignal(siginfo, context, GetTid(), &OnStackUnwind, nullptr);
 }
 
 static bool is_initialized = false;
 
 void InitializeDeadlySignals() {
   if (is_initialized)
     return;
   is_initialized = true;
   InitializeSignalInterceptors();
   InstallDeadlySignalHandlers(&UBsanOnDeadlySignal);
 }
-#endif
 
 } // namespace __ubsan
 
+#endif
+
 #endif // CAN_SANITIZE_UB