Initial Commit of OhGodACsumFixer.

Author: OhGodAGirl

OhGodACsumFixer.c

@@ -0,0 +1,72 @@
+// Copyright (c) 2017 OhGodACompany - OhGodAGirl & OhGodAPet
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#define ATOM_CSUM_OFFSET		0x21
+
+int main(int argc, char **argv)
+{
+	FILE *VBIOSFile;
+	uint8_t *VBIOS, CSum = 0;
+	size_t VBIOSSize, BytesRead;
+	
+	if(argc != 2)
+	{
+		printf("Usage: %s <VBIOS file>\n", argv[0]);
+		return(1);
+	}
+	
+	VBIOSFile = fopen(argv[1], "rb+");
+	
+	if(!VBIOSFile)
+	{
+		printf("Cannot open VBIOS image %s (does it exist?)\n", argv[1]);
+		return(1);
+	}
+	
+	fseek(VBIOSFile, 0UL, SEEK_END);
+	VBIOSSize = ftell(VBIOSFile);
+	rewind(VBIOSFile);
+	
+	VBIOS = (uint8_t *)malloc(sizeof(uint8_t) * VBIOSSize);
+	
+	BytesRead = fread(VBIOS, sizeof(uint8_t), VBIOSSize, VBIOSFile);
+	
+	if(BytesRead != VBIOSSize)
+	{
+		printf("Could not read entire VBIOS image.\n");
+		fclose(VBIOSFile);
+		free(VBIOS);
+		return(1);
+	}
+		
+	for(int i = 0; i < (VBIOS[0x02] * 512); ++i) CSum += VBIOS[i];
+		
+	if(!CSum)
+	{
+		printf("Checksum already valid (0x%02X), nothing to fix.\n", VBIOS[ATOM_CSUM_OFFSET]);
+		fclose(VBIOSFile);
+		free(VBIOS);
+		return(0);
+	}
+	
+	printf("Checksum invalid, fixing...\n");
+		
+	VBIOS[ATOM_CSUM_OFFSET] -= CSum;
+	
+	fseek(VBIOSFile, ATOM_CSUM_OFFSET, SEEK_SET);
+	
+	if(fwrite(VBIOS + ATOM_CSUM_OFFSET, sizeof(uint8_t), 1, VBIOSFile) != 1)
+	{
+		printf("Error writing to VBIOS image.\n");
+		fclose(VBIOSFile);
+		free(VBIOS);
+		return(1);
+	}
+	
+	fclose(VBIOSFile);
+	free(VBIOS);
+	return(0);
+}