From bdbe02b043d624dc3e0de9f8d0bb79b9b26a1c17 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Fri, 26 Nov 2021 13:54:28 +0200
Subject: [PATCH] Add a safe memory read API

---
 Cocoa/Document.m         |  2 +-
 Core/debugger.c          |  4 ++--
 Core/gb.h                |  1 +
 Core/memory.c            | 14 +++++++++++++-
 Core/memory.h            |  1 +
 Core/sm83_disassembler.c |  1 +
 6 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/Cocoa/Document.m b/Cocoa/Document.m
index 39f0852..fafdefc 100644
--- a/Cocoa/Document.m
+++ b/Cocoa/Document.m
@@ -1335,7 +1335,7 @@ static unsigned *multiplication_table_for_frequency(unsigned frequency)
 - (uint8_t) readMemory:(uint16_t)addr
 {
     while (!GB_is_inited(&gb));
-    return GB_read_memory(&gb, addr);
+    return GB_safe_read_memory(&gb, addr);
 }
 
 - (void) writeMemory:(uint16_t)addr value:(uint8_t)value
diff --git a/Core/debugger.c b/Core/debugger.c
index 5547721..b8d88d7 100644
--- a/Core/debugger.c
+++ b/Core/debugger.c
@@ -1451,7 +1451,7 @@ static bool examine(GB_gameboy_t *gb, char *arguments, char *modifiers, const de
             while (count) {
                 GB_log(gb, "%02x:%04x: ", addr.bank, addr.value);
                 for (unsigned i = 0; i < 16 && count; i++) {
-                    GB_log(gb, "%02x ", GB_read_memory(gb, addr.value + i));
+                    GB_log(gb, "%02x ", GB_safe_read_memory(gb, addr.value + i));
                     count--;
                 }
                 addr.value += 16;
@@ -1464,7 +1464,7 @@ static bool examine(GB_gameboy_t *gb, char *arguments, char *modifiers, const de
             while (count) {
                 GB_log(gb, "%04x: ", addr.value);
                 for (unsigned i = 0; i < 16 && count; i++) {
-                    GB_log(gb, "%02x ", GB_read_memory(gb, addr.value + i));
+                    GB_log(gb, "%02x ", GB_safe_read_memory(gb, addr.value + i));
                     count--;
                 }
                 addr.value += 16;
diff --git a/Core/gb.h b/Core/gb.h
index 0d3846a..d7d988d 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -742,6 +742,7 @@ struct GB_gameboy_internal_s {
         /* Temporary state */
         bool wx_just_changed;
         bool tile_sel_glitch;
+        bool disable_oam_corruption; // For safe memory reads
                
         GB_gbs_header_t gbs_header;
    );
diff --git a/Core/memory.c b/Core/memory.c
index 4e6665e..f428f05 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -444,7 +444,7 @@ static uint8_t read_high_memory(GB_gameboy_t *gb, uint16_t addr)
         }
         
         if (gb->oam_read_blocked) {
-            if (!GB_is_cgb(gb)) {
+            if (!GB_is_cgb(gb) && !gb->disable_oam_corruption) {
                 if (addr < 0xFEA0) {
                     uint16_t *oam = (uint16_t *)gb->oam;
                     if (gb->accessed_oam_row == 0) {
@@ -702,6 +702,18 @@ uint8_t GB_read_memory(GB_gameboy_t *gb, uint16_t addr)
     return data;
 }
 
+uint8_t GB_safe_read_memory(GB_gameboy_t *gb, uint16_t addr)
+{
+    gb->disable_oam_corruption = true;
+    uint8_t data = read_map[addr >> 12](gb, addr);
+    gb->disable_oam_corruption = false;
+    GB_apply_cheat(gb, addr, &data);
+    if (gb->read_memory_callback) {
+        data = gb->read_memory_callback(gb, addr, data);
+    }
+    return data;
+}
+
 static void write_mbc(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
 {
     switch (gb->cartridge_type->mbc_type) {
diff --git a/Core/memory.h b/Core/memory.h
index 0b7a43c..f351339 100644
--- a/Core/memory.h
+++ b/Core/memory.h
@@ -7,6 +7,7 @@ typedef uint8_t (*GB_read_memory_callback_t)(GB_gameboy_t *gb, uint16_t addr, ui
 void GB_set_read_memory_callback(GB_gameboy_t *gb, GB_read_memory_callback_t callback);
 
 uint8_t GB_read_memory(GB_gameboy_t *gb, uint16_t addr);
+uint8_t GB_safe_read_memory(GB_gameboy_t *gb, uint16_t addr); // Without side effects
 void GB_write_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value);
 #ifdef GB_INTERNAL
 internal void GB_dma_run(GB_gameboy_t *gb);
diff --git a/Core/sm83_disassembler.c b/Core/sm83_disassembler.c
index 894c766..f85bfc2 100644
--- a/Core/sm83_disassembler.c
+++ b/Core/sm83_disassembler.c
@@ -2,6 +2,7 @@
 #include <stdbool.h>
 #include "gb.h"
 
+#define GB_read_memory GB_safe_read_memory
 
 typedef void opcode_t(GB_gameboy_t *gb, uint8_t opcode, uint16_t *pc);