src/tools/fixup_tos_boot_checksum/fixup_tos_boot_checksum.c

   1 #include <fcntl.h>
   2 #include <stdio.h>
   3 #include <stdint.h>
   4 #include <unistd.h>
   5
   6 uint8_t sector[512];
   7
   8 int main(int argc, char **argv)
   9 {
  10         int fd, i;
  11         uint16_t sum;
  12         uint8_t *p = sector;
  13         fd = open(argv[1], O_RDWR);
  14         if (fd < 0) {
  15                 return 1;
  16         }
  17         if (read(fd, sector, 512-2) < 512-2) {
  18                 perror("read");
  19                 return 1;
  20         }
  21         for (sum = 0, i = 0; i < (512-2)/2; i++) {
  22                 uint16_t v;
  23                 v = *p++ << 8;
  24                 v += *p++;
  25                 sum += v;
  26         }
  27         sum = 0x1234 - sum /*+ 1*/;
  28         //sum = 0xaa55;
  29         // big endian
  30         *p++ = (uint8_t)(sum >> 8);
  31         *p++ = (uint8_t)sum;
  32         //lseek(fd, 0LL, SEEK_SET);
  33         write(fd, &sector[512-2], 2);
  34         close(fd);
  35         return 0;
  36 }