/* APN ELF file Checksum generator
 * For hacking the Chrysler/Dodge/Jeep Alpine navigation systems.
 * Works with REC, RB1 and REJ units. May work with any Alpine system using ELF files for the firmware.

  Notes:
 Initial version 0.1 10/1/2006 - Vindes
 Tried to keep the code a simple as possible for platform and language portability.
 */
 
#include <stdio.h>
#include <stdlib.h>

main (argc, argv)
	int argc;
	char ** argv;
{
	FILE * apnfile;
	/* ELF header stuff - words and half words */
	unsigned int phdr_start, shdr_start;
	unsigned short ph_num, sh_size, sh_num;
	
	/* program header variables.  Program headers are 32 bytes each */
	unsigned int p_type; 	/* entry type */
	unsigned int p_offset; 	/* file offset - start of section in file */
	unsigned int p_vaddr; 	/* virtual address - where it goes in memory - ignore if 0 */
	unsigned int p_paddr; 	/* physical address - always zero for NAV */ 
	unsigned int p_filesz;	/* file size - size on disc */
	unsigned int p_memsz; 	/* memory size - size in memory, may be larger than on disc */
	unsigned int p_flags; 	/* entry flags */
	unsigned int p_align; 	/* memory/file alignment */
	
	/* misc variables */	
	unsigned int chksum_table_start, offset, size, checksum, addon, file_chksum;
	int section, wordcount, bytecount, shift;
	unsigned char *progsegment;
 	
	/* Take filename from first command line arg */
	apnfile = fopen (argv[1], "r");
	
	/* seek 28 bytes in to find offset for program headers and section headers */
	fseek (apnfile, 28, SEEK_SET);
	fread (&phdr_start, sizeof(phdr_start), 1, apnfile);
	fread (&shdr_start, sizeof(shdr_start), 1, apnfile);
	
	/* seek 44 bytes in for number of program headers, num sec. hdrs and size of sec hdrs */
	fseek (apnfile, 44, SEEK_SET);
	fread (&ph_num, sizeof(ph_num), 1, apnfile);
	fread (&sh_size, sizeof(sh_size), 1, apnfile);
	fread (&sh_num, sizeof(sh_num), 1, apnfile);
	
	/* Alpine special junk section is past end of section headers.  So add # headers * size of headers
	   to starting offset of section headers.  Checksum table is 76 bytes past that. */
	chksum_table_start = shdr_start + sh_size*sh_num + 76;

	/* Header for output table */
	printf ("Section\tChecksum\tFile says\n");
			
	/* Loop through program sections, generating checksums */
	for (section=0; section <= ph_num; section++)
	{
		/* Load program header for current section.  Each program header is 32 bytes */
		fseek (apnfile, phdr_start + section*32, SEEK_SET);
		fread (&p_type, 4, 1, apnfile);
		fread (&p_offset, 4, 1, apnfile);
		fread (&p_vaddr, 4, 1, apnfile);
		fread (&p_paddr, 4, 1, apnfile);
		fread (&p_filesz, 4, 1, apnfile);
		fread (&p_memsz, 4, 1, apnfile);
		fread (&p_flags, 4, 1, apnfile);
		
		/* seek to, and load segment into memory for checksum calculation - if it's a loadable segment */
		if ((p_vaddr > 0))
		{
			fseek (apnfile, p_offset, SEEK_SET); /* seek to location of segment */
			progsegment = malloc(p_filesz);  /* allocate bytes to read into */
			fread (progsegment, 1, p_filesz, apnfile); /* read into progsegment */
			checksum=0;
			
			/* Calculate the checksum of the segment */
			for (bytecount=0; bytecount < p_filesz; bytecount++)
			{
				shift = (bytecount&3)*8; /* doing it byte by byte, shifting each byte appropriately */
				addon = progsegment[bytecount];
				addon<<=shift;
				checksum=checksum + addon;
			}
			
			/* free up the space we allocated */
			free (progsegment);
			
			/* Load the checksum stored in the file */
			fseek (apnfile, chksum_table_start + section*4, SEEK_SET);
			fread (&file_chksum, 4, 1, apnfile);
			
			printf ("%2.2i\t0x%8.8x\t0x%8.8x\t", section, checksum, file_chksum);
			if (checksum == file_chksum) { printf("match\n"); } else { printf("DIFFERENT\n"); }
		}
	}
}