Add include header that redefines common CPU memory I/O functions to make them invalid. This is intended for source files that emulate behavior on hardware outside the CPU and should never issue CPU memory I/O from that source file

include/cpu_io_is_forbidden.h

@@ -0,0 +1,42 @@
+
+#undef mem_readb
+#define mem_readb(x) THIS_IS_ILLEGAL_HERE
+
+#undef mem_writeb
+#define mem_writeb(x,b) THIS_IS_ILLEGAL_HERE
+
+#undef mem_readw
+#define mem_readw(x) THIS_IS_ILLEGAL_HERE
+
+#undef mem_writew
+#define mem_writew(x,b) THIS_IS_ILLEGAL_HERE
+
+#undef mem_readd
+#define mem_readd(x) THIS_IS_ILLEGAL_HERE
+
+#undef mem_writed
+#define mem_writed(x,b) THIS_IS_ILLEGAL_HERE
+
+#undef real_readb
+#define real_readb(x) THIS_IS_ILLEGAL_HERE
+
+#undef real_writeb
+#define real_writeb(x,b) THIS_IS_ILLEGAL_HERE
+
+#undef real_readw
+#define real_readw(x) THIS_IS_ILLEGAL_HERE
+
+#undef real_writew
+#define real_writew(x,b) THIS_IS_ILLEGAL_HERE
+
+#undef real_readd
+#define real_readd(x) THIS_IS_ILLEGAL_HERE
+
+#undef real_writed
+#define real_writed(x,b) THIS_IS_ILLEGAL_HERE
+
+/* NTS: phys_readb/phys_writeb are fine, because they
+ *      go directly to system memory. However unless
+ *      you're emulating a PCI device with bus mastering
+ *      enabled, you should not be using those either. */
+

src/hardware/vga_pc98_gdc_draw.cpp

@@ -9,6 +9,9 @@
 #include "pc98_gdc_const.h"
 #include <math.h>
 
+/* do not issue CPU-side I/O here -- this code emulates functions that the GDC itself carries out, not on the CPU */
+#include "cpu_io_is_forbidden.h"
+
 uint8_t pc98_gdc_vread(const uint32_t addr);
 void pc98_gdc_vwrite(const uint32_t addr,const uint8_t b);