Exposed function make_isohybrid_mbr() for discussion
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#include <ctype.h>
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#include <stdint.h>
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#include <sys/types.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <string.h>
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#include <errno.h>
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/* for gettimeofday() */
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#include <sys/time.h>
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/* This code stems from syslinux-3.72/utils/isohybrid, a perl script
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under GPL which is Copyright 2002-2008 H. Peter Anvin.
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Line numbers in comments refer to the lines of that script.
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It has been analyzed and re-written in C language 2008 by Thomas Schmitt.
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As soon as it is part of a libisofs test version, H. Peter Anvin will
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be asked about his own copyright claims and/or license tolerance in
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respect to this C code.
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*/
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/* A helper function. One could replace it by one or two macros. */
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static int lsb_to_buf(char **wpt, int value, int bits, int flag)
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{
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int b;
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for(b= 0; b < bits; b+= 8)
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*((unsigned char *) ((*wpt)++))= (value >> b) & 0xff;
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return(1);
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}
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/* Create a MBR for an isohybrid enabled ISOLINUX boot image.
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It is assumed that the caller has verified the readiness of the boot image
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by checking for 0xfb 0xc0 0x78 0x70 at bytes 0x40 to 0x43 of isolinux.bin.
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@param bin_lba The predicted LBA of isolinux.bin within the emerging ISO.
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@param img_blocks The predicted number of 2048 byte blocks in the ISO.
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It will get rounded up to full MBs and that many blocks
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must really be written as ISO 9660 image.
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@param mbr A buffer of at least 512 bytes to take the result which is
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to be written as the very beginning of the ISO.
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@param flag unused yet, submit 0
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@return <0 = fatal, 0 = failed , 1 = ok , 2 = ok with size warning
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*/
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int make_isohybrid_mbr(int bin_lba, int *img_blocks, char *mbr, int flag)
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{
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/* According to H. Peter Anvin this binary code stems from
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syslinux-3.72/mbr/isohdpfx.S
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*/
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static int mbr_code_size= 271;
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static unsigned char mbr_code[271]= {
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0xfa, 0x31, 0xc0, 0x8e, 0xd8, 0x8e, 0xd0, 0xbc,
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0x00, 0x7c, 0x89, 0xe6, 0x06, 0x57, 0x52, 0x8e,
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0xc0, 0xfb, 0xfc, 0xbf, 0x00, 0x06, 0xb9, 0x00,
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0x01, 0xf3, 0xa5, 0xea, 0x20, 0x06, 0x00, 0x00,
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0x52, 0xb4, 0x41, 0xbb, 0xaa, 0x55, 0x31, 0xc9,
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0x30, 0xf6, 0xf9, 0xcd, 0x13, 0x72, 0x14, 0x81,
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0xfb, 0x55, 0xaa, 0x75, 0x0e, 0x83, 0xe1, 0x01,
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0x74, 0x09, 0x66, 0xc7, 0x06, 0xb4, 0x06, 0xb4,
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0x42, 0xeb, 0x15, 0x5a, 0x51, 0xb4, 0x08, 0xcd,
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0x13, 0x83, 0xe1, 0x3f, 0x51, 0x0f, 0xb6, 0xc6,
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0x40, 0x50, 0xf7, 0xe1, 0x52, 0x50, 0xbb, 0x00,
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0x7c, 0xb9, 0x04, 0x00, 0x66, 0xa1, 0xb0, 0x07,
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0xe8, 0x40, 0x00, 0x72, 0x74, 0x66, 0x40, 0x80,
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0xc7, 0x02, 0xe2, 0xf4, 0x66, 0x81, 0x3e, 0x40,
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0x7c, 0xfb, 0xc0, 0x78, 0x70, 0x75, 0x07, 0xfa,
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0xbc, 0xf4, 0x7b, 0xe9, 0xc6, 0x75, 0xe8, 0x79,
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0x00, 0x69, 0x73, 0x6f, 0x6c, 0x69, 0x6e, 0x75,
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0x78, 0x2e, 0x62, 0x69, 0x6e, 0x20, 0x6d, 0x69,
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0x73, 0x73, 0x69, 0x6e, 0x67, 0x20, 0x6f, 0x72,
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0x20, 0x63, 0x6f, 0x72, 0x72, 0x75, 0x70, 0x74,
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0x2e, 0x0d, 0x0a, 0x66, 0x60, 0x66, 0x31, 0xd2,
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0x66, 0x52, 0x66, 0x50, 0x06, 0x53, 0x6a, 0x01,
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0x6a, 0x10, 0x89, 0xe6, 0x66, 0xf7, 0x36, 0xf0,
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0x7b, 0xc0, 0xe4, 0x06, 0x88, 0xe1, 0x88, 0xc5,
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0x92, 0xf6, 0x36, 0xf6, 0x7b, 0x88, 0xc6, 0x08,
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0xe1, 0x41, 0xb8, 0x01, 0x02, 0x8a, 0x16, 0xfa,
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0x7b, 0xcd, 0x13, 0x8d, 0x64, 0x10, 0x66, 0x61,
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0xc3, 0xe8, 0x1e, 0x00, 0x4f, 0x70, 0x65, 0x72,
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0x61, 0x74, 0x69, 0x6e, 0x67, 0x20, 0x73, 0x79,
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0x73, 0x74, 0x65, 0x6d, 0x20, 0x6c, 0x6f, 0x61,
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0x64, 0x20, 0x65, 0x72, 0x72, 0x6f, 0x72, 0x2e,
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0x0d, 0x0a, 0x5e, 0xac, 0xb4, 0x0e, 0x8a, 0x3e,
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0x62, 0x04, 0xb3, 0x07, 0xcd, 0x10, 0x3c, 0x0a,
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0x75, 0xf1, 0xcd, 0x18, 0xf4, 0xeb, 0xfd
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};
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static int h= 64, s= 32;
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int i, warn_size= 0, id;
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char *wpt;
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off_t imgsize, cylsize, frac, padding, c, cc;
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/* For generating a weak random number */
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struct timeval tv;
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struct timezone tz;
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if(bin_lba < 0 || bin_lba >= (1 << 29))
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return(0); /* 1 TB limit of signed 32 bit addressing of 512 byte blocks */
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/*
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84: Gets size of image in bytes.
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89:
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*/
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imgsize= ((off_t) img_blocks) * (off_t) 2048;
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/*
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90: Computes $padding, size of padded image and number $c of
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pseudo-cylinders ($h and $s are constants set in line 24).
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102: $cc is $c curbed to 1024.
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*/
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cylsize= h * s * 512;
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frac= imgsize % cylsize;
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padding= (frac > 0 ? cylsize - frac : 0);
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imgsize+= padding;
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*img_blocks= imgsize / (off_t) 2048;
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c= imgsize / cylsize;
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if(c > 1024) {
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warn_size= 1;
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cc= 1024;
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} else
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cc= c;
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/*
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107: Brings the hex-encoded bytes from the file __END__ into
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113: the MBR buffer. (This function holds them in mbr_code[].)
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*/
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for(i= 0; i < mbr_code_size; i++)
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mbr[i]= mbr_code[i];
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/*
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118: Pads up to 432
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*/
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for(i= mbr_code_size; i < 432; i++)
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mbr[i]= 0;
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/* From here on use write cursor wpt */
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wpt= mbr + 432;
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/*
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120: Converts LBA of isolinux.bin to blocksize 512 and writes
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to buffer. Appends 4 zero bytes.
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*/
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lsb_to_buf(&wpt, bin_lba * 4, 32, 0);
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lsb_to_buf(&wpt, 0, 32, 0);
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/*
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121: I do not understand where $id should eventually come
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from. An environment variable ?
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125: Whatever, i use some 32-bit random value with no crypto strength.
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*/
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gettimeofday(&tv, &tz);
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id= 0xffffffff & (tv.tv_sec ^ (tv.tv_usec * 2000));
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/*
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126: Adds 4 id bytes and 2 zero bytes.
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*/
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lsb_to_buf(&wpt, id, 32, 0);
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lsb_to_buf(&wpt, 0, 16, 0);
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/*
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129: Composes 16 byte record from the parameters determined
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147: so far. Appends it to buffer and add 48 zero bytes.
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*/
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/* There are 4 "partition slots". Only the first is non-zero here.
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In the perl script, the fields are set in variables and then
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written to buffer. I omit the variables.
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*/
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/* 0x80 */
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lsb_to_buf(&wpt, 0x80, 8, 0);
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/* bhead */
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lsb_to_buf(&wpt, 0, 8, 0);
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/* bsect */
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lsb_to_buf(&wpt, 1, 8, 0);
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/* bcyl */
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lsb_to_buf(&wpt, 0, 8, 0);
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/* fstype */
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lsb_to_buf(&wpt, 0x83, 8, 0);
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/* ehead */
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lsb_to_buf(&wpt, h - 1, 8, 0);
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/* esect */
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lsb_to_buf(&wpt, s + (((cc - 1) & 0x300) >> 2), 8, 0);
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/* ecyl */
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lsb_to_buf(&wpt, (cc - 1) & 0xff, 8, 0);
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/* 0 */
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lsb_to_buf(&wpt, 0, 32, 0);
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/* psize */
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lsb_to_buf(&wpt, c * h * s, 32, 0);
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/* Fill the other three slots with zeros */
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for(i= 0; i < 3 * 4; i++)
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lsb_to_buf(&wpt,0, 32, 0);
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/*
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148: Appends bytes 0x55 , 0xAA.
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*/
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lsb_to_buf(&wpt, 0x55, 8, 0);
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lsb_to_buf(&wpt, 0xaa, 8, 0);
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return(1);
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}
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int main(int argc, char **argv)
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{
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int ret, bin_lba= 10000, img_blocks= 100000;
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char mbr[513];
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/* setting up fly paper */
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mbr[511]= mbr[512]= 0x40;
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ret= make_isohybrid_mbr(bin_lba, &img_blocks, mbr, 0);
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/* looking for flies on paper */
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printf("aa,40 <-> %-2.2x,%-2.2x\n",
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(unsigned int) ((unsigned char *) mbr)[511],
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(unsigned int) ((unsigned char *) mbr)[512]);
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if(ret <= 0)
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exit(1);
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exit(0);
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}
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