r_u.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <string.h>

static int usage()
{
    fprintf(stderr,"r [-b|-s] <address> [<value>]\n");
    return -1;
}

int r_main(int argc, char *argv[])
{
    int width = 4, set = 0, fd;
    unsigned addr, value, endaddr = 0;
    unsigned long mmap_start, mmap_size;
    void *page;
    char *end;

    if(argc < 2 || (argv[1][0] == '-' && argc < 3)) return usage();

    if(strcmp(argv[1], "-b") == 0) {
        width = 1;
        argc--;
        argv++;
    } else if(strcmp(argv[1], "-s") == 0) {
        width = 2;
        argc--;
        argv++;
    }

    addr = strtoul(argv[1], 0, 16);
    end = strchr(argv[1], '-');
    if(end) endaddr = strtoul(end + 1, 0, 16);
    if(!endaddr) endaddr = addr + width - 1;

    if(endaddr <= addr) {
        fprintf(stderr, "invalid end address\n");
        return -1;
    }

    if(argc > 2) {
        set = 1;
        value = strtoul(argv[2], 0, 16);
    }

    fd = open("/dev/mem", O_RDWR | O_SYNC);
    if(fd < 0) {
        fprintf(stderr,"cannot open /dev/mem\n");
        return -1;
    }

    mmap_start = addr;
    mmap_size = endaddr - mmap_start + 1;

    page = mmap(0, mmap_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, mmap_start);

    if(page == MAP_FAILED) {
        fprintf(stderr,"cannot mmap region\n");
        return -1;
    }

    while(addr <= endaddr) {
        switch(width){
			case 4: {
				unsigned int *x = (unsigned int *)(((char *)page) + (addr & 4095));
				if(set) *x = value;
				fprintf(stderr,"%08x: %08x\n", addr, *x);
				break;
			}
			case 2: {
				unsigned short int *x = (unsigned short int *)(((char *)page) + (addr & 4095));
				if(set) *x = value;
				fprintf(stderr,"%08x: %04x\n", addr, *x);
				break;
			}
			case 1: {
				unsigned char *x = (unsigned char*)(((char *)page) + (addr & 4095));
				if(set) *x = value;
				fprintf(stderr,"%08x: %02x\n", addr, *x);
				break;
			}
        }
        addr += width;
    }
    return 0;
}