added "code in RAM" execution check for F4SC, F6SC and F8SC (addresses #933)

src/emucore/Cart.hxx

@@ -254,6 +254,13 @@ class Cartridge : public Device
     */
     virtual uInt16 ramBankCount() const { return 0; }
 
+    /**
+      Query wether the current PC allows code execution.
+
+      @return  true, if code execution is allowed
+    */
+    virtual bool canExecute(uInt16 PC) const { return true; }
+
     /**
       Get the number of segments supported by the cartridge.
     */

src/emucore/CartEnhanced.hxx

@@ -99,6 +99,22 @@ class CartridgeEnhanced : public Cartridge
     */
     uInt16 ramBankCount() const override;
 
+    /**
+      Query wether the current PC allows code execution.
+
+      @return  true, if code execution is allowed
+    */
+    bool canExecute(uInt16 PC) const override {
+      return !(PC & 0x1000) || (PC & ROM_MASK) >= myRomOffset || executableCartRam();
+    }
+
+    /**
+      Query wether the cart RAM allows code execution.
+
+      @return  true, if code execution is allowed
+    */
+    virtual bool executableCartRam() const { return true; }
+
     /**
       Get the number of segments supported by the cartridge.
     */

src/emucore/CartF4SC.hxx

@@ -49,6 +49,13 @@ class CartridgeF4SC : public CartridgeF4
     ~CartridgeF4SC() override = default;
 
   public:
+    /**
+      Query wether the cart RAM allows code execution.
+
+      @return  true, if code execution is allowed
+    */
+    bool executableCartRam() const override { return false; }
+
     /**
       Get a descriptor for the device name (used in error checking).
 

src/emucore/CartF6SC.hxx

@@ -49,6 +49,13 @@ class CartridgeF6SC : public CartridgeF6
     ~CartridgeF6SC() override = default;
 
   public:
+    /**
+      Query wether the cart RAM allows code execution.
+
+      @return  true, if code execution is allowed
+    */
+    bool executableCartRam() const override { return false; }
+
     /**
       Get a descriptor for the device name (used in error checking).
 

src/emucore/CartF8SC.hxx

@@ -49,6 +49,13 @@ class CartridgeF8SC : public CartridgeF8
     ~CartridgeF8SC() override = default;
 
   public:
+    /**
+      Query wether the cart RAM allows code execution.
+
+      @return  true, if code execution is allowed
+    */
+    bool executableCartRam() const override { return false; }
+
     /**
       Get a descriptor for the device name (used in error checking).
 

src/emucore/M6502.cxx

@@ -339,6 +339,10 @@ inline void M6502::_execute(uInt64 cycles, DispatchResult& result)
         icycles = 0;
     #ifdef DEBUGGER_SUPPORT
         const uInt16 oldPC = PC;
+
+        // Only check for code in RAM execution if we have debugger support
+        if(!mySystem->cart().canExecute(PC))
+          FatalEmulationError::raise("cannot run code from cart RAM");
     #endif
 
         // Fetch instruction at the program counter