GBA: Fix some GBA ROM misdetection (fixes #978)

CHANGES

@@ -46,6 +46,7 @@ Bugfixes:
  - GBA Memory: Partially revert prefetch changes (fixes mgba.io/i/840)
  - PSP2: Fix issues causing poor audio
  - Wii: Fix screen tear when unpausing
+ - GBA: Fix some GBA ROM misdetection (fixes mgba.io/i/978)
 Misc:
  - GBA Timer: Use global cycles for timers
  - GBA: Extend oddly-sized ROMs to full address space (fixes mgba.io/i/722)

src/gba/gba.c

@@ -33,6 +33,9 @@ const uint32_t GBA_COMPONENT_MAGIC = 0x1000000;
 static const size_t GBA_ROM_MAGIC_OFFSET = 3;
 static const uint8_t GBA_ROM_MAGIC[] = { 0xEA };
 
+static const size_t GBA_ROM_MAGIC_OFFSET2 = 0xB2;
+static const uint8_t GBA_ROM_MAGIC2[] = { 0x96 };
+
 static const size_t GBA_MB_MAGIC_OFFSET = 0xC0;
 
 static void GBAInit(void* cpu, struct mCPUComponent* component);
@@ -543,17 +546,48 @@ bool GBAIsROM(struct VFile* vf) {
 	if (!vf) {
 		return false;
 	}
+
+	uint8_t signature[sizeof(GBA_ROM_MAGIC) + sizeof(GBA_ROM_MAGIC2)];
 	if (vf->seek(vf, GBA_ROM_MAGIC_OFFSET, SEEK_SET) < 0) {
 		return false;
 	}
-	uint8_t signature[sizeof(GBA_ROM_MAGIC)];
-	if (vf->read(vf, &signature, sizeof(signature)) != sizeof(signature)) {
+	if (vf->read(vf, &signature, sizeof(GBA_ROM_MAGIC)) != sizeof(GBA_ROM_MAGIC)) {
 		return false;
 	}
+	if (memcmp(signature, GBA_ROM_MAGIC, sizeof(GBA_ROM_MAGIC)) != 0) {
+		return false;
+	}
+
+	if (vf->seek(vf, GBA_ROM_MAGIC_OFFSET2, SEEK_SET) < 0) {
+		return false;
+	}
+	if (vf->read(vf, &signature, sizeof(GBA_ROM_MAGIC2)) != sizeof(GBA_ROM_MAGIC2)) {
+		return false;
+	}
+	if (memcmp(signature, GBA_ROM_MAGIC2, sizeof(GBA_ROM_MAGIC2)) != 0) {
+		// If the signature byte is missing then we must be using an unfixed ROM
+		uint32_t buffer[0x9C / sizeof(uint32_t)];
+		if (vf->seek(vf, 0x4, SEEK_SET) < 0) {
+			return false;
+		}
+		if (vf->read(vf, &buffer, sizeof(buffer)) != sizeof(buffer)) {
+			return false;
+		}
+		uint32_t bits = 0;
+		size_t i;
+		for (i = 0; i < sizeof(buffer) / sizeof(*buffer); ++i) {
+			bits |= buffer[i];
+		}
+		if (bits) {
+			return false;
+		}
+	}
+
+
 	if (GBAIsBIOS(vf)) {
 		return false;
 	}
-	return memcmp(signature, GBA_ROM_MAGIC, sizeof(signature)) == 0;
+	return true;
 }
 
 bool GBAIsMB(struct VFile* vf) {