Linux/FaultSafeUserMemAccess: Break out fault safe handler

This is going to get used by gdbserver soon for ensuring memory accesses
are fault safe, because it tries to read outside of correct memory
bounds at times.

Source/Tools/LinuxEmulation/LinuxSyscalls/SignalDelegator.cpp

@@ -578,18 +578,8 @@ void SignalDelegator::HandleGuestSignal(FEX::HLE::ThreadStateObject* ThreadObjec
         ERROR_AND_DIE_FMT("X86 shouldn't hit this InterruptFaultPage");
 #endif
       }
-    } else if (Signal == SIGSEGV && (SigInfo.si_code == SEGV_MAPERR || SigInfo.si_code == SEGV_ACCERR) &&
-               FaultSafeUserMemAccess::IsFaultLocation(ArchHelpers::Context::GetPc(UContext))) {
-      // If you want to emulate EFAULT behaviour then enable this if-statement.
-      // Do this once we find an application that depends on this.
-      if constexpr (false) {
-        // Return from the subroutine, returning EFAULT.
-        ArchHelpers::Context::SetArmReg(UContext, 0, EFAULT);
-        ArchHelpers::Context::SetPc(UContext, ArchHelpers::Context::GetArmReg(UContext, 30));
-        return;
-      } else {
-        ERROR_AND_DIE_FMT("Received invalid data to syscall. Crashing now!");
-      }
+    } else if (FaultSafeUserMemAccess::TryHandleSafeFault(Signal, SigInfo, UContext)) {
+      ERROR_AND_DIE_FMT("Received invalid data to syscall. Crashing now!");
     } else {
       if (IsAsyncSignal(&SigInfo, Signal) && MustDeferSignal) {
         // If the signal is asynchronous (as determined by si_code) and FEX is in a state of needing

Source/Tools/LinuxEmulation/LinuxSyscalls/Syscalls.h

@@ -12,6 +12,7 @@ desc: Glue logic, STRACE magic
 #include "LinuxSyscalls/LinuxAllocator.h"
 #include "LinuxSyscalls/ThreadManager.h"
 #include "LinuxSyscalls/Seccomp/SeccompEmulator.h"
+#include "ArchHelpers/MContext.h"
 
 #include <FEXCore/Config/Config.h>
 #include <FEXCore/Core/Thunks.h>
@@ -674,6 +675,18 @@ namespace FaultSafeUserMemAccess {
   }
 #endif
   bool IsFaultLocation(uint64_t PC);
+
+  static inline bool TryHandleSafeFault(int Signal, siginfo_t const &SigInfo, void *UContext) {
+  if (Signal == SIGSEGV && (SigInfo.si_code == SEGV_MAPERR || SigInfo.si_code == SEGV_ACCERR) &&
+      FaultSafeUserMemAccess::IsFaultLocation(ArchHelpers::Context::GetPc(UContext))) {
+      // Return from the subroutine, returning EFAULT.
+      ArchHelpers::Context::SetArmReg(UContext, 0, EFAULT);
+      ArchHelpers::Context::SetPc(UContext, ArchHelpers::Context::GetArmReg(UContext, 30));
+      return true;
+    }
+
+    return false;
+  }
 } // namespace FaultSafeUserMemAccess
 
 } // namespace FEX::HLE