From 8ab82522c5e3d633e51dc1f86429c814751ccda2 Mon Sep 17 00:00:00 2001
From: Jonathan Campbell <jonathan@castus.tv>
Date: Tue, 24 May 2022 11:33:35 -0700
Subject: [PATCH] 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      | 42 ++++++++++++++++++++++++++++++
 src/hardware/vga_pc98_gdc_draw.cpp |  3 +++
 2 files changed, 45 insertions(+)
 create mode 100644 include/cpu_io_is_forbidden.h

diff --git a/include/cpu_io_is_forbidden.h b/include/cpu_io_is_forbidden.h
new file mode 100644
index 000000000..63d871b16
--- /dev/null
+++ b/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. */
+
diff --git a/src/hardware/vga_pc98_gdc_draw.cpp b/src/hardware/vga_pc98_gdc_draw.cpp
index 54ab7d1a6..fc27c3d2f 100644
--- a/src/hardware/vga_pc98_gdc_draw.cpp
+++ b/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);