plugmem.c

一个用在mips体系结构中的操作系统

/*
 * Copyright (C) 1996-1998 by the Board of Trustees
 *    of Leland Stanford Junior University.
 * 
 * This file is part of the SimOS distribution. 
 * See LICENSE file for terms of the license. 
 *
 */

#include <stdio.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h> 
#include <fcntl.h>    

#define MAPADDR 0x60000000

int 
main(int argc, char **argv)
{
   char *fileName;
   int  fd;
   uint  offset;
   uint  oldValue;
   uint  newValue;
   void *mapAddr;
   void *plugAddr;

   if (argc != 5) {
      printf("Usage: %s file offset old_value new_value\n", argv[0]);
      exit();
   }

   fileName = (char *)argv[1];
   offset   = (uint)strtoul(argv[2], NULL, 16);
   oldValue = (uint)strtoul(argv[3], NULL, 16);
   newValue = (uint)strtoul(argv[4], NULL, 16);
   
   printf("Attempting to change offset %#x from %#x to %#x\n",
          offset, oldValue, newValue);
   
   if ((fd = open(fileName, O_RDWR)) == -1) {
      printf("Can't open file\n", fileName);
      perror("Opening");
      exit();
   }
   if ((mapAddr = mmap((void *)MAPADDR, 4096, PROT_READ|PROT_WRITE, 
                       MAP_SHARED, fd, offset&0xfffff000)) == (void *)-1) {
      
      printf("Problem mapping %s\n", fileName);
      perror("Mapping");
      exit();
   }
   plugAddr = (void *)((uint)mapAddr+(offset & 0x00000fff));
   printf("Current value at %#x is %#x\n", offset, *(int *)plugAddr);

   if (*(uint *)plugAddr != oldValue) {
      printf("This offset doesn't have the old value specified\n");
      exit();
   }

   *(uint *)(uint)plugAddr = (uint) newValue;
   printf("New value is %#x\n", *(uint *)plugAddr);
   close(fd);
   printf("You've successfully plugged, homeboy\n");
}