From 68e5a0aa475e865561242a2ca32304fcd5c5c79c Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Mon, 11 Dec 2023 22:05:55 -0800
Subject: [PATCH] GB: Fix applying a patch that changes the cartridge mapper
 (fixes #3077)

---
 CHANGES     | 1 +
 src/gb/gb.c | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/CHANGES b/CHANGES
index 036378226..0e732633f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -13,6 +13,7 @@ Emulation fixes:
  - GBA BIOS: Fix clobbering registers with word-sized CpuSet
  - GBA SIO: Fix normal mode SI/SO semantics (fixes mgba.io/i/2925)
 Other fixes:
+ - GB: Fix applying a patch that changes the cartridge mapper (fixes mgba.io/i/3077)
  - GBA Savedata: Fix crash when resizing flash save games for RTC data
  - mGUI: Fix cases where an older save state screenshot would be shown (fixes mgba.io/i/2183)
  - Qt: Re-enable sync for multiplayer windows that aren't connected (fixes mgba.io/i/2974)
diff --git a/src/gb/gb.c b/src/gb/gb.c
index 4cbff7e4f..6c1c265dc 100644
--- a/src/gb/gb.c
+++ b/src/gb/gb.c
@@ -455,6 +455,9 @@ void GBApplyPatch(struct GB* gb, struct Patch* patch) {
 	if (patchedSize > GB_SIZE_CART_MAX) {
 		patchedSize = GB_SIZE_CART_MAX;
 	}
+
+	const struct GBCartridge* cart = (const struct GBCartridge*) &gb->memory.rom[0x100];
+	uint8_t type = cart->type;
 	void* newRom = anonymousMemoryMap(GB_SIZE_CART_MAX);
 	if (!patch->applyPatch(patch, gb->memory.rom, gb->pristineRomSize, newRom, patchedSize)) {
 		mappedMemoryFree(newRom, GB_SIZE_CART_MAX);
@@ -473,6 +476,12 @@ void GBApplyPatch(struct GB* gb, struct Patch* patch) {
 	}
 	gb->memory.rom = newRom;
 	gb->memory.romSize = patchedSize;
+
+	cart = (const struct GBCartridge*) &gb->memory.rom[0x100];
+	if (cart->type != type) {
+		gb->memory.mbcType = GB_MBC_AUTODETECT;
+		GBMBCInit(gb);
+	}
 	gb->romCrc32 = doCrc32(gb->memory.rom, gb->memory.romSize);
 	gb->cpu->memory.setActiveRegion(gb->cpu, gb->cpu->pc);
 }