From 34647ffdca68da94f4fb5b51df4a8dc43758ad77 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Tue, 13 Jun 2017 21:14:20 -0700
Subject: [PATCH] GB: Trust ROM header for number of SRAM banks (fixes #726)

---
 CHANGES      | 1 +
 src/gb/mbc.c | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/CHANGES b/CHANGES
index d1fd75541..b1485c69b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -133,6 +133,7 @@ Misc:
  - Core: Move savestate creation time to extdata
  - Debugger: Add mDebuggerRunFrame convenience function
  - GBA Memory: Remove unused prefetch cruft
+ - GB: Trust ROM header for number of SRAM banks (fixes mgba.io/i/726)
 
 0.5.2: (2016-12-31)
 Bugfixes:
diff --git a/src/gb/mbc.c b/src/gb/mbc.c
index 544f01af8..a26edeac6 100644
--- a/src/gb/mbc.c
+++ b/src/gb/mbc.c
@@ -79,7 +79,11 @@ static bool _isMulticart(const uint8_t* mem) {
 
 void GBMBCSwitchSramBank(struct GB* gb, int bank) {
 	size_t bankStart = bank * GB_SIZE_EXTERNAL_RAM;
-	GBResizeSram(gb, (bank + 1) * GB_SIZE_EXTERNAL_RAM);
+	if (bankStart + GB_SIZE_EXTERNAL_RAM > gb->sramSize) {
+		mLOG(GB_MBC, GAME_ERROR, "Attempting to switch to an invalid RAM bank: %0X", bank);
+		bankStart &= (gb->sramSize - 1);
+		bank = bankStart / GB_SIZE_EXTERNAL_RAM;
+	}
 	gb->memory.sramBank = &gb->memory.sram[bankStart];
 	gb->memory.sramCurrentBank = bank;
 }