[nce] signal hanlder fixes for sigaction

Signed-off-by: lizzie <lizzie@eden-emu.dev>

src/common/signal_chain.cpp

@@ -10,27 +10,16 @@
 
 namespace Common {
 
+#ifdef __ANDROID__
 template <typename T>
 T* LookupLibcSymbol(const char* name) {
-#if defined(__BIONIC__)
     Common::DynamicLibrary provider("libc.so");
-    if (!provider.IsOpen()) {
-        UNREACHABLE_MSG("Failed to open libc!");
-    }
-#else
-    // For other operating environments, we assume the symbol is not overridden.
-    const char* base = nullptr;
-    Common::DynamicLibrary provider(base);
-#endif
-
+    ASSERT_MSG(provider.IsOpen(), "Failed to open libc!");
     void* sym = provider.GetSymbolAddress(name);
     if (sym == nullptr) {
         sym = dlsym(RTLD_DEFAULT, name);
     }
-    if (sym == nullptr) {
-        UNREACHABLE_MSG("Unable to find symbol {}!", name);
-    }
-
+    ASSERT_MSG(sym != nullptr, "Unable to find symbol {}!", name);
     return reinterpret_cast<T*>(sym);
 }
 
@@ -38,5 +27,10 @@ int SigAction(int signum, const struct sigaction* act, struct sigaction* oldact)
     static auto libc_sigaction = LookupLibcSymbol<decltype(sigaction)>("sigaction");
     return libc_sigaction(signum, act, oldact);
 }
+#else
+int SigAction(int signum, const struct sigaction* act, struct sigaction* oldact) {
+    return sigaction(signum, act, oldact);
+}
+#endif
 
 } // namespace Common

src/core/arm/nce/arm_nce.s

@@ -66,19 +66,20 @@ _ZN4Core6ArmNce37ReturnToRunCodeByExceptionLevelChangeEiPv:
 #endif
     /* This jumps to the signal handler, which will restore the entire context. */
     /* On entry, x0 = thread id, which is already in the right place. Even on macOS. */
-    /* Move tpidr to x9 so it is not trampled. */
-    mov     x9, x1
+    mov     x9, x1 /* Move tpidr to x9 so it is not trampled. */
     mov     x1, #(ReturnToRunCodeByExceptionLevelChangeSignal)
 #ifdef __APPLE__
     /* I can never be happy, why no tkill in mach kernel? Ugh ... */
     /* Signature: 328 AUE_PTHREADKILL ALL { int __pthread_kill(int thread_port, int sig); } */
     mov     x16, #(328)
+    svc     #0x80 /* Tail call the signal handler. */
+    brk     #0xF000 /* See: https://discourse.llvm.org/t/stepping-over-a-brk-instruction-on-arm64/69766/7 */
 #else
     /* Signature: int tgkill(pid_t tgid, pid_t tid, int sig); */
     mov     x8, #(__NR_tkill)
+    svc     #0 /* Tail call the signal handler. */
+    brk     #1000 /* Block execution from flowing here. */
 #endif
-    svc     #0              /* Tail call the signal handler. */
-    brk     #1000           /* Block execution from flowing here. */
 
 /* static void Core::ArmNce::ReturnToRunCodeByExceptionLevelChangeSignalHandler(int sig, void* info, void* raw_context) */
 #ifdef __APPLE__