2 * wndr3700.c - partially based on OpenWrt's add_header.c
4 * Copyright (C) 2009 Anael Orlinski <naouel@naouel.org>
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License,
8 * version 2 as published by the Free Software Foundation.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
21 * The add_header utility used by various vendors preprends the buf
22 * image with a header containing a CRC32 value which is generated for the
23 * model id + reserved space for CRC32 + buf, then replaces the reserved
24 * area with the actual CRC32. This replacement tool mimics this behavior.
35 #include <netinet/in.h>
38 #define BPB 8 /* bits/byte */
40 #define WNDR3700_MAGIC_LEN 4
42 static uint32_t crc32[1<<BPB];
43 static char *magic = "3700";
45 static void init_crc32()
47 const uint32_t poly = ntohl(0x2083b8ed);
50 for (n = 0; n < 1<<BPB; n++) {
54 for (bit = 0; bit < BPB; bit++)
55 crc = (crc & 1) ? (poly ^ (crc >> 1)) : (crc >> 1);
60 static uint32_t crc32buf(unsigned char *buf, size_t len)
62 uint32_t crc = 0xFFFFFFFF;
64 for (; len; len--, buf++)
65 crc = crc32[(uint8_t)crc ^ *buf] ^ (crc >> BPB);
70 unsigned char magic[WNDR3700_MAGIC_LEN];
72 unsigned char stuff[56];
75 static void usage(const char *) __attribute__ (( __noreturn__ ));
77 static void usage(const char *mess)
79 fprintf(stderr, "Error: %s\n", mess);
80 fprintf(stderr, "Usage: wndr3700 input_file output_file [magic]\n");
81 fprintf(stderr, "\n");
85 int main(int argc, char **argv)
87 off_t len; // of original buf
88 off_t buflen; // of the output file
90 void *input_file; // pointer to the input file (mmmapped)
92 unsigned char *buf; // pointer to prefix + copy of original buf
97 usage("wrong number of arguments");
102 if (strlen(magic) != WNDR3700_MAGIC_LEN) {
103 fprintf(stderr, "Invalid magic: '%s'\n", magic);
108 if ((fd = open(argv[1], O_RDONLY)) < 0
109 || (len = lseek(fd, 0, SEEK_END)) < 0
110 || (input_file = mmap(0, len, PROT_READ, MAP_SHARED, fd, 0)) == (void *) (-1)
113 fprintf(stderr, "Error loading file %s: %s\n", argv[1], strerror(errno));
122 memcpy(&header, input_file, sizeof(header));
124 memcpy(header.magic, magic, WNDR3700_MAGIC_LEN);
127 // create a firmware image in memory and copy the input_file to it
128 buf = malloc(buflen);
129 memcpy(buf, input_file, len);
131 // CRC of temporary header
132 header.crc = htonl(crc32buf((unsigned char*)&header, sizeof(header)));
134 memcpy(buf, &header, sizeof(header));
137 if ((fd = open(argv[2], O_CREAT|O_WRONLY|O_TRUNC,0644)) < 0
138 || write(fd, buf, buflen) != buflen
141 fprintf(stderr, "Error storing file %s: %s\n", argv[2], strerror(errno));
147 munmap(input_file,len);