A tool to fix wrong byte order GBA EEPROM saves as created by some emulators.

gbaEepromSaveFix.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>



// Compile with "gcc -std=c17 -O2 -fstrict-aliasing -ffunction-sections -Wall -Wl,--gc-sections gbaEepromSaveFix.c -o gbaEepromSaveFix"
int main(int argc, char *argv[])
{
	int res = 0;
	FILE *f = fopen(argv[1], "rb+");
	if(f != NULL)
	{
		do
		{
			fseek(f, 0, SEEK_END);
			const size_t fSize = ftell(f);
			// Minimum 32 because of the unrolled byteswap loop below.
			// The last check is a power of 2 check.
			if(fSize == 0 || fSize < 32 || (fSize & (fSize - 1)) != 0)
			{
				fputs("Broken save file or incorrect size!\n", stderr);
				res = 2;
				break;
			}
			fseek(f, 0, SEEK_SET);

			uint64_t *buf = (uint64_t*)malloc(fSize);
			if(buf == NULL)
			{
				fputs("Out of memory.\n", stderr);
				res = 3;
				break;
			}

			if(fread(buf, 1, fSize, f) != fSize)
			{
				fputs("Failed to read file.\n", stderr);
				res = 4;
				free(buf);
				break;
			}

			for(size_t i = 0; i < fSize / 8; i += 4)
			{
				buf[i + 0] = __builtin_bswap64(buf[i + 0]);
				buf[i + 1] = __builtin_bswap64(buf[i + 1]);
				buf[i + 2] = __builtin_bswap64(buf[i + 2]);
				buf[i + 3] = __builtin_bswap64(buf[i + 3]);
			}

			fseek(f, 0, SEEK_SET);
			if(fwrite(buf, 1, fSize, f) != fSize)
			{
				fputs("Failed to write to file.\n", stderr);
				res = 5;
			}

			free(buf);
		} while(0);

		fclose(f);
	}
	else
	{
		fputs("Failed to open save file.\n", stderr);
		res = 1;
	}

	if(res == 0) puts("Done.");

	return res;
}

To compile on macOS: clang -std=c17 -O2 -fstrict-aliasing -ffunction-sections -Wall gbaEepromSaveFix.c -o gbaEepromSaveFix (the -Wl,--gc-sections part is removed)

Ah, thanks. Didn't know this is broken on OSX.

This doesn't work for me on Kirby & The Amazing Mirror. I tried using this to convert from open_agb_firm to emulator, and all save slots in the save file appear as 0% complete. Is there something I'm missing? I ran this on Windows 11 via WSL, compiled with the supplied gcc command.

Hmm, weird. I tried importing the save file from open_agb_firm directly into VisualBoyAdvance, and after giving me a "Cannot open file" error, it actually read it and converted the save. Not sure how that worked, but it did. I transfered that new save to Lemuroid and it worked there too. Again, very strange.

I'll just use that to transfer my save to and from open_agb_firm for now.

Is it even an EEPROM save? They usually have a size of either 512 bytes or 8 KiB.

It's 32KB.

Then it's a SRAM save and doesn't need conversion.

Oh, okay. That explains it. I'm sorry for wasting your time.