xpatch.c

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

int print_help_and_exit(const char *progname) {
	fprintf(stderr, "Usage: %s <options> <filename> [<bytes>]\n"
		"Options:\n"
		"	-b <base_addr>	Use <base_addr> as base (will be substracted from <addr>)\n"
		"	-r <addr>	Read first 16 bytes at <addr>\n"
		"	-w <addr>	Write <bytes> at <addr>\n",
	progname);
	exit(-1);
}

void *xmalloc(int size) {
	void *ret = malloc(size);
	if(!ret) {
		fprintf(stderr, "Couldn't malloc\n");
		exit(-1);
	}
	return(ret);
}

FILE *xfopen(const char *filename, const char *mode, unsigned int addr) {
	FILE *ret = fopen(filename, mode);
	if(!ret)
		perror("Couldn't open file");
	fseek(ret, addr, SEEK_SET);
	return(ret);
}

int act_read(const char *filename, unsigned int addr) {
	unsigned char buf[16];
	int i;
	FILE *file = xfopen(filename, "rb", addr);
	int bytes_read = fread(buf, 1, 16, file);
	fclose(file);

	for(i = 0; i < bytes_read; i++) {
		printf("%02x ", buf[i]);
	}

	printf("\n");
}

int act_write(const char *filename, unsigned int addr, char *buf, int length) {
	FILE *file = xfopen(filename, "rb+", addr);
	fwrite(buf, 1, length, file);
	fclose(file);
}

int main(int argc, char **argv) {
	#define ACT_READ (1 << 0)
	#define ACT_WRITE (1 << 1)
	#define CHECK_USAGE(x) if(!(x)) { print_help_and_exit(argv[0]); }
	unsigned int addr, base_addr = 0;
	char c, action = 0;
	int i;

	// Parsing <options> with getopt
	CHECK_USAGE(argc >= 1);
	while ((c = getopt (argc, argv, "b:r:w:")) != -1)	{
		switch (c) {
			case 'b':
				sscanf(optarg, "%x", &base_addr);
				break;
			case 'r':
				action |= ACT_READ;
				sscanf(optarg, "%x", &addr);
				break;
			case 'w':
				action |= ACT_WRITE;
				sscanf(optarg, "%x", &addr);
				break;
		}
	}

	// Taking trailing <filename>
	CHECK_USAGE(optind < argc);
	char *filename = argv[optind];
	optind++;

	// Taking trailing <bytes>
	int value;
	char *bytes = NULL;
	for(i = optind; i < argc; i++) {
		if(bytes == NULL)
			bytes = xmalloc(argc - optind);
		sscanf(argv[i], "%02x", &value);
		bytes[i-optind] = value;
	}

	// Executing an appropriate action
	switch(action) { 
		case ACT_READ:
			CHECK_USAGE(bytes == NULL);
			act_read(filename, addr - base_addr);
			break;
		case ACT_WRITE:
			CHECK_USAGE(bytes != NULL);
			act_write(filename, addr - base_addr, bytes, argc - optind);
			break;
		default:
			CHECK_USAGE(0);
	}

	free(bytes);
	exit(0);
}