Please amend me

src/core/signals.cpp

@@ -12,9 +12,81 @@
 #include <csignal>
 #ifdef ARCH_X86_64
 #include <Zydis/Formatter.h>
+#include <sys/ucontext.h>
 #endif
 #endif
 
+namespace {
+
+#ifdef _WIN32
+#define GET_XMM_POINTER(ctx, index, low, high) \
+    (void*)(&(ctx)->Xmm##index##.Low)
+#else
+#define GET_XMM_POINTER(ctx, index, low, high) \
+    (void*)(&(ctx)->uc_mcontext->fpregs._xmm[index].element[0])
+#endif
+
+#if defined(ARCH_X86_64)
+// We need to check, before patching, if there's enough space for a relative jump to the trampoline.
+// If there isn't, the instruction must be handled specially in the illegal instruction handler itself.
+bool shouldNotBePatched(void* code_address) {
+    ZydisDecodedInstruction instruction;
+    ZydisDecodedOperand operands[ZYDIS_MAX_OPERAND_COUNT];
+    const auto status = Common::Decoder::Instance().decodeInstruction(instruction, operands, code_address);
+    if (!ZYAN_SUCCESS(status)) {
+        LOG_ERROR(Core, "Failed to decode instruction at: {}", fmt::ptr(code_address));
+    }
+
+    if (instruction.length < 5) {
+        // not enough bytes for a relative jump for the trampoline
+        return true;
+    }
+
+    return false;
+}
+
+bool handleIllegalInstruction(void* code_address) {
+    ZydisDecodedInstruction instruction;
+    ZydisDecodedOperand operands[ZYDIS_MAX_OPERAND_COUNT];
+    const auto status = Common::Decoder::Instance().decodeInstruction(instruction, operands, code_address);
+
+    switch (instruction.mnemonic) {
+        case ZYDIS_MNEMONIC_EXTRQ: {
+            bool immediateForm = operands[1].type == ZYDIS_OPERAND_TYPE_IMMEDIATE &&
+                         operands[2].type == ZYDIS_OPERAND_TYPE_IMMEDIATE;
+            if (immediateForm) {
+                LOG_ERROR(Core, "EXTRQ immediate form should have been patched at code address: {}", fmt::ptr(code_address));
+            } else {
+                ASSERT_MSG(operands[0].type == ZYDIS_OPERAND_TYPE_REGISTER &&
+                           operands[1].type == ZYDIS_OPERAND_TYPE_REGISTER,
+                           "Unexpected operand types for EXTRQ instruction");
+                const auto dst = operands[0].reg.value;
+                const auto src = operands[1].reg.value;
+            }
+            break;
+        }
+        default: {
+            LOG_ERROR(Core, "Unhandled illegal instruction at code address {}: {}", fmt::ptr(code_address),
+                      ZydisMnemonicGetString(instruction.mnemonic));
+            return false;
+        }
+    }
+}
+#elif defined(ARCH_ARM64)
+// These functions shouldn't be needed for ARM as it will use a JIT so there's no need to patch instructions.
+// Returning false lets it go through with whatever handler is set up.
+bool shouldNotBePatched(void* code_address) {
+    return false;
+}
+
+bool handleIllegalInstruction(void* code_address) {
+    return false;
+}
+#else
+#error "Unsupported architecture"
+#endif
+} // namespace
+
 namespace Core {
 
 #if defined(_WIN32)
@@ -32,7 +104,11 @@ static LONG WINAPI SignalHandler(EXCEPTION_POINTERS* pExp) noexcept {
             pExp->ExceptionRecord->ExceptionInformation[0] == 1);
         break;
     case EXCEPTION_ILLEGAL_INSTRUCTION:
-        handled = signals->DispatchIllegalInstruction(code_address);
+        if (shouldNotBePatched(code_address)) {
+            handled = handleIllegalInstruction(code_address);
+        } else {
+            handled = signals->DispatchIllegalInstruction(code_address);
+        }
         break;
     default:
         break;
@@ -99,9 +175,16 @@ static void SignalHandler(int sig, siginfo_t* info, void* raw_context) {
         }
         break;
     case SIGILL:
-        if (!signals->DispatchIllegalInstruction(code_address)) {
-            UNREACHABLE_MSG("Unhandled illegal instruction at code address {}: {}",
-                            fmt::ptr(code_address), DisassembleInstruction(code_address));
+        if (shouldNotBePatched(code_address)) {
+            if (!handleIllegalInstruction(code_address)) {
+                UNREACHABLE_MSG("Unhandled illegal instruction at code address {}: {}",
+                                fmt::ptr(code_address), DisassembleInstruction(code_address));
+            }
+        } else {
+            if (!signals->DispatchIllegalInstruction(code_address)) {
+                UNREACHABLE_MSG("Unhandled illegal instruction at code address {}: {}",
+                                fmt::ptr(code_address), DisassembleInstruction(code_address));
+            }
         }
         break;
     default: