/*
 * This function will patch binary file
 */

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

static char buf[512];

static void
usage(void)
{
  printf("usage: binpatch [-h] <ofile> <ifile> <reloc> <off> <byte0> "
         "[<byte1> [<byte2> [<byte3>]]]\n");
  printf("this function patches binary file at specified offset with\n");
  printf("up to 4 bytes provided on command line \n");
  printf("-h       - prints this message\n\n");
  printf("<ofile>  - output file\n");
  printf("<ifile>  - input ifile\n");
  printf("<reloc>  - relocation address of image\n");
  printf("<off>    - offset of patch, offset in file is at off - reloc\n");
  printf("<byte0>  - byte 0 of patch\n");
  printf("<byte1>  - byte 1 of patch\n");
  printf("<byte2>  - byte 1 of patch\n");
  printf("<byte3>  - byte 1 of patch\n");
}

int
main(int argc, char **argv)
{
  int    c;
  FILE  *ofp, *ifp;
  char  *patch, *end;
  int    patchLen, tmp, i, off, cnt, patched, len, reloc;

  /* parse command line options */
  while ((c = getopt(argc, argv, "h")) >= 0) {
      switch (c) {
        case 'h':
          usage();
          return 0;
        default:
          usage();
          return 1;
        }
  }

  if(argc < 6) {
      usage();
      return 1;
  }

  /* Let us get offset in file */
  reloc = strtol(argv[3], &end, 0);
  if (end == argv[3] || reloc < 0) {
      fprintf(stderr, "bad reloc value %s\n", argv[3]);
      return 1;
  }

  off = strtol(argv[4], &end, 0);
  if (end == argv[4] || off < 0 || off < reloc) {
      fprintf(stderr, "bad offset value %s\n", argv[4]);
      return 1;
  }

  off -= reloc;

  /* Let us get patch  */
  patchLen = argc - 5;
  patch = calloc( patchLen, sizeof(char) );
  assert( patch );

  for (i=0; i<patchLen; i++) {
      tmp = strtol(argv[5+i], &end, 0);

      if (end == argv[4+i]) {
          fprintf(stderr, "bad byte value %s\n", argv[5+i]);
          free(patch);
          return 1;
      }
      if (tmp < 0 || tmp > 0xff) {
          fprintf(stderr, "not a byte value %s\n", argv[5+i]);
          free(patch);
          return 1;
      }
      patch[i] = (tmp & 0xff);
  }

  ifp = fopen(argv[2], "r");
  if (ifp == NULL) {
      fprintf(stderr, "unable to open file %s\n", argv[2]);
      free(patch);
      return 1;
  }

  ofp = fopen(argv[1], "w");
  if (ofp == NULL) {
      fprintf(stderr, "unable to open file %s\n", argv[1]);
      fclose(ifp);
      free(patch);
      return 1;
  }

  cnt     = 0;
  patched = 0;
  for(;;) {
      len = fread(buf, 1, sizeof(buf), ifp);

      if(len == 0) {
          break;
      }

      if (cnt <= off && (cnt + len) > off) {
          /* Perform patch */
          for(i=0; i<patchLen && (off+i)<(cnt+len); i++)
            {
              buf[off-cnt+i] = patch[i];
            }
          patched = 1;
      } else if(cnt > off && cnt < (off + patchLen)) {
          /* Perform patch */
          for(i=cnt-off; i<patchLen; i++) {
              buf[off-cnt+i] = patch[i];
          }
          patched = 1;
      }

      fwrite(buf, 1, len, ofp);

      cnt += len;
  }

  fclose(ifp);
  fclose(ofp);
  free(patch);

  if (!patched) {
      fprintf(stderr, "warning: offset is beyond input file length\n");
      fprintf(stderr, "         no patch is performed\n");
  }

  return 0;
}