cpu_patches: Revert to ahead-of-time patching on Linux for now. (#949)

src/core/cpu_patches.cpp

@@ -658,26 +658,15 @@ static PatchModule* GetModule(const void* ptr) {
     return &(std::prev(upper_bound)->second);
 }
 
-static bool TryPatch(void* code_address) {
-    auto* code = static_cast<u8*>(code_address);
-    auto* module = GetModule(code);
-    if (module == nullptr) {
-        return false;
-    }
-
-    std::unique_lock lock{module->mutex};
-
-    // Return early if already patched, in case multiple threads signaled at the same time.
-    if (std::ranges::find(module->patched, code) != module->patched.end()) {
-        return true;
-    }
-
+/// Returns a boolean indicating whether the instruction was patched, and the offset to advance past
+/// whatever is at the current code pointer.
+static std::pair<bool, u64> TryPatch(u8* code, PatchModule* module) {
     ZydisDecodedInstruction instruction;
     ZydisDecodedOperand operands[ZYDIS_MAX_OPERAND_COUNT];
     const auto status =
         ZydisDecoderDecodeFull(&instr_decoder, code, module->end - code, &instruction, operands);
     if (!ZYAN_SUCCESS(status)) {
-        return false;
+        return std::make_pair(false, 1);
     }
 
     if (Patches.contains(instruction.mnemonic)) {
@@ -717,20 +706,52 @@ static bool TryPatch(void* code_address) {
                 module->patched.insert(code);
                 LOG_DEBUG(Core, "Patched instruction '{}' at: {}",
                           ZydisMnemonicGetString(instruction.mnemonic), fmt::ptr(code));
-                return true;
+                return std::make_pair(true, instruction.length);
             }
         }
     }
 
-    return false;
+    return std::make_pair(false, instruction.length);
+}
+
+static bool TryPatchJit(void* code_address) {
+    auto* code = static_cast<u8*>(code_address);
+    auto* module = GetModule(code);
+    if (module == nullptr) {
+        return false;
+    }
+
+    std::unique_lock lock{module->mutex};
+
+    // Return early if already patched, in case multiple threads signaled at the same time.
+    if (std::ranges::find(module->patched, code) != module->patched.end()) {
+        return true;
+    }
+
+    return TryPatch(code, module).first;
+}
+
+static void TryPatchAot(void* code_address, u64 code_size) {
+    auto* code = static_cast<u8*>(code_address);
+    auto* module = GetModule(code);
+    if (module == nullptr) {
+        return;
+    }
+
+    std::unique_lock lock{module->mutex};
+
+    const auto* end = code + code_size;
+    while (code < end) {
+        code += TryPatch(code, module).second;
+    }
 }
 
 static bool PatchesAccessViolationHandler(void* code_address, void* fault_address, bool is_write) {
-    return TryPatch(code_address);
+    return TryPatchJit(code_address);
 }
 
 static bool PatchesIllegalInstructionHandler(void* code_address) {
-    return TryPatch(code_address);
+    return TryPatchJit(code_address);
 }
 
 static void PatchesInit() {
@@ -757,17 +778,23 @@ void RegisterPatchModule(void* module_ptr, u64 module_size, void* trampoline_are
 }
 
 void PrePatchInstructions(u64 segment_addr, u64 segment_size) {
-#ifdef __APPLE__
+#if defined(__APPLE__)
     // HACK: For some reason patching in the signal handler at the start of a page does not work
     // under Rosetta 2. Patch any instructions at the start of a page ahead of time.
     if (!Patches.empty()) {
         auto* code_page = reinterpret_cast<u8*>(Common::AlignUp(segment_addr, 0x1000));
         const auto* end_page = code_page + Common::AlignUp(segment_size, 0x1000);
         while (code_page < end_page) {
-            TryPatch(code_page);
+            TryPatchJit(code_page);
             code_page += 0x1000;
         }
     }
+#elif !defined(_WIN32)
+    // Linux and others have an FS segment pointing to valid memory, so continue to do full
+    // ahead-of-time patching for now until a better solution is worked out.
+    if (!Patches.empty()) {
+        TryPatchAot(reinterpret_cast<void*>(segment_addr), segment_size);
+    }
 #endif
 }