[sanitizer] Don't intercept signal and sigaction on Fuchsia

[phosek]

Summary

Fuchsia doesn't support signals, so don't use interceptors for signal or sigaction.

[mcgrathr]

What effect does this have?
Nothing built for Fuchsia ought to be using sanitizer_signal_interceptors.inc or HandleDeadlySignal in the first place.

[phosek]

This is used from ubsan_signals_standalone.cc. Alternative would be to exclude it from UBSan's CMakeLists.txt when compiling for Fuchsia and avoid the invocation of InitializeDeadlySignals() on Fuchsia in ubsan_init_standalone.cc.

[phosek]

The effect this will have is none, because InstallDeadlySignalHandlers which is supposed to install signal handles doesn't do anything on Fuchsia, see sanitizer_fuchsia.cc. Without the empty definition of HandleDeadlySignal, the build is broken because there's an undefined reference to it in UBsanOnDeadlySignal in ubsan_signals_standalone.cc.

[mcgrathr]

I wonder why my builds have never had an undefined symbol HandleDeadlySignal.

The norm in the sanitizer code for the most part is to #if out whole files rather than conditionalizing it in cmake.

Since we don't have or need a ubsan_fuchsia.cc, I'd just selectively #if out most of uban_signals_standalone.cc so that InitializeDeadSignals is a no-op for SANITIZER_FUCHSIA.

[phosek]

Done. This is a new code hence why you haven't hit it in the past.

[vitalybuka]

lib/ubsan/ubsan_signals_standalone.cc

27

Could you please either create _fuchsia.cc file or
consolidate code into single #if

e.g.:

#if SANITIZER_FUCHSIA 

void InitializeDeadlySignals() {}

#else

static void OnStackUnwind(const SignalContext &sig, const void *,
                          BufferedStackTrace *stack) {
...
}

static void UBsanOnDeadlySignal(int signo, void *siginfo, void *context) {
...
}
static bool is_initialized = false;

void InitializeDeadlySignals() {
  if (is_initialized)
    return;
  is_initialized = true;
  InitializeSignalInterceptors();
  InstallDeadlySignalHandlers(&UBsanOnDeadlySignal);
}

#endif

lib/sanitizer_common/sanitizer_platform_interceptors.h

 #define SANITIZER_INTERCEPT_PVALLOC \
   (!SI_FREEBSD && !SI_MAC && !SI_NETBSD && SI_NOT_FUCHSIA)
 #define SANITIZER_INTERCEPT_CFREE \
   (!SI_FREEBSD && !SI_MAC && !SI_NETBSD && SI_NOT_FUCHSIA)
 #define SANITIZER_INTERCEPT_ALIGNED_ALLOC (!SI_MAC)
 #define SANITIZER_INTERCEPT_MALLOC_USABLE_SIZE (!SI_MAC)
 #define SANITIZER_INTERCEPT_MCHECK_MPROBE SI_LINUX_NOT_ANDROID
 #define SANITIZER_INTERCEPT_WCSCAT SI_POSIX
-#define SANITIZER_INTERCEPT_SIGNAL_AND_SIGACTION (!SI_WINDOWS)
+#define SANITIZER_INTERCEPT_SIGNAL_AND_SIGACTION (!SI_WINDOWS && SI_NOT_FUCHSIA)
 #define SANITIZER_INTERCEPT_BSD_SIGNAL SI_ANDROID
 
 #endif  // #ifndef SANITIZER_PLATFORM_INTERCEPTORS_H

lib/ubsan/ubsan_signals_standalone.cc

 #include "ubsan_diag.h"
 #include "ubsan_init.h"
 
 #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) {
   GetStackTraceWithPcBpAndContext(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 // CAN_SANITIZE_UB