From 4110cfca004249f99674747c5e12cc0bfd842762 Mon Sep 17 00:00:00 2001 From: Thomas Schmitt Date: Sat, 18 Oct 2008 11:30:11 +0000 Subject: [PATCH] Exposed function make_isohybrid_mbr() for discussion --- libisoburn/trunk/xorriso/make_isohybrid_mbr.c | 231 ++++++++++++++++++ 1 file changed, 231 insertions(+) create mode 100644 libisoburn/trunk/xorriso/make_isohybrid_mbr.c diff --git a/libisoburn/trunk/xorriso/make_isohybrid_mbr.c b/libisoburn/trunk/xorriso/make_isohybrid_mbr.c new file mode 100644 index 00000000..03185f2b --- /dev/null +++ b/libisoburn/trunk/xorriso/make_isohybrid_mbr.c @@ -0,0 +1,231 @@ + +#include +#include +#include +#include +#include +#include +#include +#include + +/* for gettimeofday() */ +#include + + +/* 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); +} + + +int main(int argc, char **argv) +{ + int ret, bin_lba= 10000, img_blocks= 100000; + char mbr[513]; + + /* setting up fly paper */ + mbr[511]= mbr[512]= 0x40; + + ret= make_isohybrid_mbr(bin_lba, &img_blocks, mbr, 0); + + /* looking for flies on paper */ + printf("aa,40 <-> %-2.2x,%-2.2x\n", + (unsigned int) ((unsigned char *) mbr)[511], + (unsigned int) ((unsigned char *) mbr)[512]); + + if(ret <= 0) + exit(1); + exit(0); +} + + +