A32: Introduce PreCodeReadHook (#763)

* A32: Introduce PreCodeReadHook

* A32: Invert code read hook return value

src/dynarmic/frontend/A32/translate/translate_arm.cpp

@@ -30,6 +30,11 @@ IR::Block TranslateArm(LocationDescriptor descriptor, TranslateCallbacks* tcb, c
         const u32 arm_pc = visitor.ir.current_location.PC();
         u64 ticks_for_instruction = 1;
 
+        if (!tcb->PreCodeReadHook(false, arm_pc, visitor.ir)) {
+            should_continue = false;
+            break;
+        }
+
         if (const auto arm_instruction = tcb->MemoryReadCode(arm_pc)) {
             visitor.current_instruction_size = 4;
 

src/dynarmic/frontend/A32/translate/translate_callbacks.h

@@ -18,7 +18,13 @@ struct TranslateCallbacks {
     // Memory must be interpreted as little endian.
     virtual std::optional<std::uint32_t> MemoryReadCode(VAddr vaddr) = 0;
 
-    // Thus function is called before the instruction at pc is interpreted.
+    // This function is called before the instruction at pc is read.
+    // IR code can be emitted by the callee prior to instruction handling.
+    // By returning false the callee precludes the translation of the instruction;
+    // in such case the callee is responsible for setting the terminal.
+    virtual bool PreCodeReadHook(bool is_thumb, VAddr pc, A32::IREmitter& ir) = 0;
+
+    // This function is called before the instruction at pc is interpreted.
     // IR code can be emitted by the callee prior to translation of the instruction.
     virtual void PreCodeTranslationHook(bool is_thumb, VAddr pc, A32::IREmitter& ir) = 0;
 

src/dynarmic/frontend/A32/translate/translate_thumb.cpp

@@ -111,6 +111,11 @@ IR::Block TranslateThumb(LocationDescriptor descriptor, TranslateCallbacks* tcb,
         const u32 arm_pc = visitor.ir.current_location.PC();
         u64 ticks_for_instruction = 1;
 
+        if (!tcb->PreCodeReadHook(true, arm_pc, visitor.ir)) {
+            should_continue = false;
+            break;
+        }
+
         if (const auto maybe_instruction = ReadThumbInstruction(arm_pc, tcb)) {
             const auto [thumb_instruction, inst_size] = *maybe_instruction;
             const bool is_thumb_16 = inst_size == ThumbInstSize::Thumb16;

src/dynarmic/interface/A32/config.h

@@ -65,6 +65,12 @@ struct UserCallbacks : public TranslateCallbacks {
     // Memory must be interpreted as little endian.
     std::optional<std::uint32_t> MemoryReadCode(VAddr vaddr) override { return MemoryRead32(vaddr); }
 
+    // This function is called before the instruction at pc is read.
+    // IR code can be emitted by the callee prior to instruction handling.
+    // By returning true the callee precludes the translation of the instruction;
+    // in such case the callee is responsible for setting the terminal.
+    bool PreCodeReadHook(bool /*is_thumb*/, VAddr /*pc*/, A32::IREmitter& /*ir*/) override { return true; }
+
     // Thus function is called before the instruction at pc is interpreted.
     // IR code can be emitted by the callee prior to translation of the instruction.
     void PreCodeTranslationHook(bool /*is_thumb*/, VAddr /*pc*/, A32::IREmitter& /*ir*/) override {}