tools/firmware-utils/src/add_header.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * add_header.c - partially based on OpenWrt's motorola-bin.c
   4  *
   5  * Copyright (C) 2008 Imre Kaloz  <kaloz@openwrt.org>
   6  *                    Gabor Juhos <juhosg@openwrt.org>
   7  */
   8
   9 /*
  10  * The add_header utility used by various vendors preprends the buf
  11  * image with a header containing a CRC32 value which is generated for the
  12  * model id + reserved space for CRC32 + buf, then replaces the reserved
  13  * area with the actual CRC32. This replacement tool mimics this behavior.
  14  */
  15
  16 #include <stdio.h>
  17 #include <stdlib.h>
  18 #include <stddef.h>
  19 #include <unistd.h>
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <sys/mman.h>
  23 #include <string.h>
  24 #include <netinet/in.h>
  25 #include <inttypes.h>
  26
  27 #define BPB 8 /* bits/byte */
  28
  29 static uint32_t crc32[1<<BPB];
  30
  31 static void init_crc32()
  32 {
  33         const uint32_t poly = ntohl(0x2083b8ed);
  34         int n;
  35
  36         for (n = 0; n < 1<<BPB; n++) {
  37                 uint32_t crc = n;
  38                 int bit;
  39
  40                 for (bit = 0; bit < BPB; bit++)
  41                         crc = (crc & 1) ? (poly ^ (crc >> 1)) : (crc >> 1);
  42                 crc32[n] = crc;
  43         }
  44 }
  45
  46 static uint32_t crc32buf(unsigned char *buf, size_t len)
  47 {
  48         uint32_t crc = 0xFFFFFFFF;
  49
  50         for (; len; len--, buf++)
  51                 crc = crc32[(uint8_t)crc ^ *buf] ^ (crc >> BPB);
  52         return ~crc;
  53 }
  54
  55 struct header {
  56         char model[16];
  57         uint32_t crc;
  58 };
  59
  60 static void usage(const char *) __attribute__ (( __noreturn__ ));
  61
  62 static void usage(const char *mess)
  63 {
  64         fprintf(stderr, "Error: %s\n", mess);
  65         fprintf(stderr, "Usage: add_header model_id input_file output_file\n");
  66         fprintf(stderr, "\n");
  67         exit(1);
  68 }
  69
  70 int main(int argc, char **argv)
  71 {
  72         off_t len;                      // of original buf
  73         off_t buflen;                   // of the output file
  74         int fd;
  75         void *input_file;               // pointer to the input file (mmmapped)
  76         struct header header;
  77         unsigned char *buf;     // pointer to prefix + copy of original buf
  78
  79         // verify parameters
  80
  81         if (argc != 4)
  82                 usage("wrong number of arguments");
  83
  84         // mmap input_file
  85         if ((fd = open(argv[2], O_RDONLY))  < 0
  86         || (len = lseek(fd, 0, SEEK_END)) < 0
  87         || (input_file = mmap(0, len, PROT_READ, MAP_SHARED, fd, 0)) == (void *) (-1)
  88         || close(fd) < 0)
  89         {
  90                 fprintf(stderr, "Error loading file %s: %s\n", argv[2], strerror(errno));
  91                 exit(1);
  92         }
  93
  94         buflen = len + sizeof(header);
  95
  96         init_crc32();
  97
  98         // copy model name into header
  99         strncpy(header.model, argv[1], sizeof(header.model));
 100         header.crc = 0;
 101
 102         // create a firmware image in memory and copy the input_file to it
 103         buf = malloc(buflen);
 104         memcpy(buf, &header, sizeof(header));
 105         memcpy(&buf[sizeof(header)], input_file, len);
 106
 107         // CRC of temporary header + buf
 108         header.crc = htonl(crc32buf(buf, buflen));
 109
 110         memcpy(buf, &header, sizeof(header));
 111
 112         // write the buf
 113         if ((fd = open(argv[3], O_CREAT|O_WRONLY|O_TRUNC,0644)) < 0
 114         || write(fd, buf, buflen) != buflen
 115         || close(fd) < 0)
 116         {
 117                 fprintf(stderr, "Error storing file %s: %s\n", argv[3], strerror(errno));
 118                 exit(2);
 119         }
 120
 121         free(buf);
 122
 123         munmap(input_file,len);
 124
 125         return 0;
 126 }