libisofs/libisofs/make_isohybrid_mbr.c

199 lines
6.8 KiB
C

#include <ctype.h>
#include <stdint.h>
#include <sys/types.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
/* for gettimeofday() */
#include <sys/time.h>
/* This code stems from syslinux-3.72/utils/isohybrid, a perl script
under GPL which is Copyright 2002-2008 H. Peter Anvin.
Line numbers in comments refer to the lines of that script.
It has been analyzed and re-written in C language 2008 by Thomas Schmitt.
As soon as it is part of a libisofs test version, H. Peter Anvin will
be asked about his own copyright claims and/or license tolerance in
respect to this C code.
*/
/* A helper function. One could replace it by one or two macros. */
static int lsb_to_buf(char **wpt, int value, int bits, int flag)
{
int b;
for (b = 0; b < bits; b += 8)
*((unsigned char *) ((*wpt)++)) = (value >> b) & 0xff;
return (1);
}
/*
* Create a MBR for an isohybrid enabled ISOLINUX boot image.
*
* It is assumed that the caller has verified the readiness of the boot image
* by checking for 0xfb 0xc0 0x78 0x70 at bytes 0x40 to 0x43 of isolinux.bin.
*
* @param bin_lba The predicted LBA of isolinux.bin within the emerging ISO.
* @param img_blocks The predicted number of 2048 byte blocks in the ISO.
* It will get rounded up to full MBs and that many blocks
* must really be written as ISO 9660 image.
* @param mbr A buffer of at least 512 bytes to take the result which is
* to be written as the very beginning of the ISO.
* @param flag unused yet, submit 0
* @return <0 = fatal, 0 = failed , 1 = ok , 2 = ok with size warning
*/
int make_isohybrid_mbr(int bin_lba, int *img_blocks, char *mbr, int flag)
{
/* According to H. Peter Anvin this binary code stems from
syslinux-3.72/mbr/isohdpfx.S
*/
static int mbr_code_size = 271;
static unsigned char mbr_code[271] = { 0xfa, 0x31, 0xc0, 0x8e, 0xd8, 0x8e,
0xd0, 0xbc, 0x00, 0x7c, 0x89, 0xe6, 0x06, 0x57, 0x52, 0x8e, 0xc0,
0xfb, 0xfc, 0xbf, 0x00, 0x06, 0xb9, 0x00, 0x01, 0xf3, 0xa5, 0xea,
0x20, 0x06, 0x00, 0x00, 0x52, 0xb4, 0x41, 0xbb, 0xaa, 0x55, 0x31,
0xc9, 0x30, 0xf6, 0xf9, 0xcd, 0x13, 0x72, 0x14, 0x81, 0xfb, 0x55,
0xaa, 0x75, 0x0e, 0x83, 0xe1, 0x01, 0x74, 0x09, 0x66, 0xc7, 0x06,
0xb4, 0x06, 0xb4, 0x42, 0xeb, 0x15, 0x5a, 0x51, 0xb4, 0x08, 0xcd,
0x13, 0x83, 0xe1, 0x3f, 0x51, 0x0f, 0xb6, 0xc6,
0x40, 0x50, 0xf7, 0xe1, 0x52, 0x50, 0xbb, 0x00, 0x7c, 0xb9, 0x04,
0x00, 0x66, 0xa1, 0xb0, 0x07, 0xe8, 0x40, 0x00, 0x72, 0x74, 0x66,
0x40, 0x80, 0xc7, 0x02, 0xe2, 0xf4, 0x66, 0x81, 0x3e, 0x40, 0x7c,
0xfb, 0xc0, 0x78, 0x70, 0x75, 0x07, 0xfa, 0xbc, 0xf4, 0x7b, 0xe9,
0xc6, 0x75, 0xe8, 0x79, 0x00, 0x69, 0x73, 0x6f, 0x6c, 0x69, 0x6e,
0x75, 0x78, 0x2e, 0x62, 0x69, 0x6e, 0x20, 0x6d, 0x69, 0x73, 0x73,
0x69, 0x6e, 0x67, 0x20, 0x6f, 0x72, 0x20, 0x63, 0x6f, 0x72, 0x72,
0x75, 0x70, 0x74,
0x2e, 0x0d, 0x0a, 0x66, 0x60, 0x66, 0x31, 0xd2, 0x66, 0x52, 0x66,
0x50, 0x06, 0x53, 0x6a, 0x01, 0x6a, 0x10, 0x89, 0xe6, 0x66, 0xf7,
0x36, 0xf0, 0x7b, 0xc0, 0xe4, 0x06, 0x88, 0xe1, 0x88, 0xc5, 0x92,
0xf6, 0x36, 0xf6, 0x7b, 0x88, 0xc6, 0x08, 0xe1, 0x41, 0xb8, 0x01,
0x02, 0x8a, 0x16, 0xfa, 0x7b, 0xcd, 0x13, 0x8d, 0x64, 0x10, 0x66,
0x61, 0xc3, 0xe8, 0x1e, 0x00, 0x4f, 0x70, 0x65, 0x72, 0x61, 0x74,
0x69, 0x6e, 0x67, 0x20, 0x73, 0x79, 0x73, 0x74, 0x65, 0x6d, 0x20,
0x6c, 0x6f, 0x61,
0x64, 0x20, 0x65, 0x72, 0x72, 0x6f, 0x72, 0x2e, 0x0d, 0x0a, 0x5e,
0xac, 0xb4, 0x0e, 0x8a, 0x3e, 0x62, 0x04, 0xb3, 0x07, 0xcd, 0x10,
0x3c, 0x0a, 0x75, 0xf1, 0xcd, 0x18, 0xf4, 0xeb, 0xfd };
static int h = 64, s = 32;
int i, warn_size = 0, id;
char *wpt;
off_t imgsize, cylsize, frac, padding, c, cc;
/* For generating a weak random number */
struct timeval tv;
struct timezone tz;
if (bin_lba < 0 || bin_lba >= (1 << 29))
return (0); /* 1 TB limit of signed 32 bit addressing of 512 byte blocks */
/*
84: Gets size of image in bytes.
89:
*/
imgsize = ((off_t) img_blocks) * (off_t) 2048;
/*
90: Computes $padding, size of padded image and number $c of
pseudo-cylinders ($h and $s are constants set in line 24).
102: $cc is $c curbed to 1024.
*/
cylsize = h * s * 512;
frac = imgsize % cylsize;
padding = (frac > 0 ? cylsize - frac : 0);
imgsize += padding;
*img_blocks = imgsize / (off_t) 2048;
c = imgsize / cylsize;
if (c > 1024) {
warn_size = 1;
cc = 1024;
} else
cc = c;
/*
107: Brings the hex-encoded bytes from the file __END__ into
113: the MBR buffer. (This function holds them in mbr_code[].)
*/
for (i = 0; i < mbr_code_size; i++)
mbr[i] = mbr_code[i];
/*
118: Pads up to 432
*/
for (i = mbr_code_size; i < 432; i++)
mbr[i] = 0;
/* From here on use write cursor wpt */
wpt = mbr + 432;
/*
120: Converts LBA of isolinux.bin to blocksize 512 and writes
to buffer. Appends 4 zero bytes.
*/
lsb_to_buf(&wpt, bin_lba * 4, 32, 0);
lsb_to_buf(&wpt, 0, 32, 0);
/*
121: I do not understand where $id should eventually come
from. An environment variable ?
125: Whatever, i use some 32-bit random value with no crypto strength.
*/
gettimeofday(&tv, &tz);
id = 0xffffffff & (tv.tv_sec ^ (tv.tv_usec * 2000));
/*
126: Adds 4 id bytes and 2 zero bytes.
*/
lsb_to_buf(&wpt, id, 32, 0);
lsb_to_buf(&wpt, 0, 16, 0);
/*
129: Composes 16 byte record from the parameters determined
147: so far. Appends it to buffer and add 48 zero bytes.
*/
/* There are 4 "partition slots". Only the first is non-zero here.
In the perl script, the fields are set in variables and then
written to buffer. I omit the variables.
*/
/* 0x80 */
lsb_to_buf(&wpt, 0x80, 8, 0);
/* bhead */
lsb_to_buf(&wpt, 0, 8, 0);
/* bsect */
lsb_to_buf(&wpt, 1, 8, 0);
/* bcyl */
lsb_to_buf(&wpt, 0, 8, 0);
/* fstype */
lsb_to_buf(&wpt, 0x83, 8, 0);
/* ehead */
lsb_to_buf(&wpt, h - 1, 8, 0);
/* esect */
lsb_to_buf(&wpt, s + (((cc - 1) & 0x300) >> 2), 8, 0);
/* ecyl */
lsb_to_buf(&wpt, (cc - 1) & 0xff, 8, 0);
/* 0 */
lsb_to_buf(&wpt, 0, 32, 0);
/* psize */
lsb_to_buf(&wpt, c * h * s, 32, 0);
/* Fill the other three slots with zeros */
for (i = 0; i < 3 * 4; i++)
lsb_to_buf(&wpt, 0, 32, 0);
/*
148: Appends bytes 0x55 , 0xAA.
*/
lsb_to_buf(&wpt, 0x55, 8, 0);
lsb_to_buf(&wpt, 0xaa, 8, 0);
return (1);
}