/* $OpenBSD: cdbr.S,v 1.3 2012/10/31 14:29:58 jsing Exp $ */ /* * Copyright (c) 2004 Tom Cosgrove <tom.cosgrove@arches-consulting.com> * Copyright (c) 2001 John Baldwin <jhb@FreeBSD.org> * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the author nor the names of any co-contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ .file "cdbr.S" /* #include <machine/asm.h> */ /* #include <assym.h> */ /* * This program is a CD boot sector, similar to the partition boot record * (pbr, also called biosboot) used by hard disks. It is implemented as a * "no-emulation" boot sector, as described in the "El Torito" Bootable * CD-ROM Format Specification. * * The function of this boot sector is to load and start the next-stage * cdboot program, which will load the kernel. * * The El Torito standard allows us to specify where we want to be loaded, * but for maximum compatibility we choose the default load address of * 0x07C00. * * Memory layout: * * 0x00000 -> 0x003FF real mode interrupt vector table * 0x00400 -> 0x00500 BIOS data segment * * 0x00000 -> 0x073FF our stack (grows down) (from 29k) * 0x07400 -> 0x07BFF we relocate to here (at 29k) * 0x07C00 -> 0x08400 BIOS loads us here (at 31k, for 2k) * 0x07C00 -> ... /cdboot * * The BIOS loads us at physical address 0x07C00. We then relocate to * 0x07400, seg:offset 0740:0000. We then load /cdboot at seg:offset * 07C0:0000. */ #define BOOTSEG 0x7c0 /* segment we're loaded to */ #define BOOTSECTSIZE 0x800 /* our size in bytes */ #define BOOTRELOCSEG 0x740 /* segment we relocate to */ #define BOOTSTACKOFF ((BOOTRELOCSEG << 4) - 4) /* starts here, grows down */ /* Constants for reading from the CD */ #define ERROR_TIMEOUT 0x80 /* BIOS timeout on read */ #define NUM_RETRIES 3 /* Num times to retry */ #define SECTOR_SIZE 0x800 /* size of a sector */ #define SECTOR_SHIFT 11 /* number of place to shift */ #define BUFFER_LEN 0x100 /* number of sectors in buffr */ #define MAX_READ 0x10000 /* max we can read at a time */ #define MAX_READ_PARAS MAX_READ >> 4 #define MAX_READ_SEC MAX_READ >> SECTOR_SHIFT #define MEM_READ_BUFFER 0x9000 /* buffer to read from CD */ #define MEM_VOLDESC MEM_READ_BUFFER /* volume descriptor */ #define MEM_DIR MEM_VOLDESC+SECTOR_SIZE /* Lookup buffer */ #define VOLDESC_LBA 0x10 /* LBA of vol descriptor */ #define VD_PRIMARY 1 /* Primary VD */ #define VD_END 255 /* VD Terminator */ #define VD_ROOTDIR 156 /* Offset of Root Dir Record */ #define DIR_LEN 0 /* Offset of Dir Rec length */ #define DIR_EA_LEN 1 /* Offset of EA length */ #define DIR_EXTENT 2 /* Offset of 64-bit LBA */ #define DIR_SIZE 10 /* Offset of 64-bit length */ #define DIR_NAMELEN 32 /* Offset of 8-bit name len */ #define DIR_NAME 33 /* Offset of dir name */ .text .code16 .globl start start: /* Set up stack */ xorw %ax, %ax movw %ax, %ss movw $BOOTSTACKOFF, %sp /* Relocate so we can load cdboot where we were */ movw $BOOTSEG, %ax movw %ax, %ds movw $BOOTRELOCSEG, %ax movw %ax, %es xorw %si, %si xorw %di, %di movw $BOOTSECTSIZE, %cx /* Bytes in cdbr, relocate it all */ cld rep movsb /* Jump to relocated self */ ljmp $BOOTRELOCSEG, $reloc reloc: /* * Set up %ds and %es: %ds is our data segment (= %cs), %es is * used to specify the segment address of the destination buffer * for cd reads. We initially have %es = %ds. */ movw %cs, %ax movw %ax, %ds movw %ax, %es movb %dl, drive /* Store the boot drive number */ movw $signon, %si /* Say "hi", and give boot drive */ call display_string movb drive, %al call hex_byte movw $crlf, %si call display_string /* * Load Volume Descriptor */ movl $VOLDESC_LBA, %eax /* Get the sector # for vol desc */ load_vd: pushl %eax movb $1, %dh /* One sector */ movw $MEM_VOLDESC, %bx /* Destination */ call read /* Read it in */ popl %eax cmpb $VD_PRIMARY, (%bx) /* Primary vol descriptor? */ je have_vd /* Yes */ inc %eax /* Try the next one */ cmpb $VD_END, (%bx) /* Is it the last one? */ jne load_vd /* No, so go try the next one */ movw $msg_novd, %si /* No pri vol descriptor */ jmp err_stop /* Panic */ have_vd: /* Have Primary VD */ /* * Look for the next-stage loader binary at pre-defined paths (loader_paths) */ movw $loader_paths, %si /* Point to start of array */ lookup_path: movw %si, loader /* remember the one we're looking for */ pushw %si /* Save file name pointer */ call lookup /* Try to find file */ popw %di /* Restore file name pointer */ jnc lookup_found /* Found this file */ xorb %al, %al /* Look for next */ movw $0xffff, %cx /* path name by */ repnz /* scanning for */ scasb /* nul char */ movw %di, %si /* Point %si at next path */ movb (%si), %al /* Get first char of next path */ orb %al, %al /* Is it double nul? */ jnz lookup_path /* No, try it */ movw $msg_failed, %si /* Failed message */ jmp err_stop /* Print it and halt */ lookup_found: /* Found a loader file */ /* * Load the binary into the buffer. Due to real mode addressing limitations * we have to read it in in 64k chunks. */ movl DIR_SIZE(%bx), %eax /* Read file length */ add $SECTOR_SIZE-1, %eax /* Convert length to sectors */ shr $SECTOR_SHIFT, %eax cmp $BUFFER_LEN, %eax jbe load_sizeok movw $msg_load2big, %si /* Error message */ jmp err_stop load_sizeok: movzbw %al, %cx /* Num sectors to read */ movl DIR_EXTENT(%bx), %eax /* Load extent */ xorl %edx, %edx movb DIR_EA_LEN(%bx), %dl addl %edx, %eax /* Skip extended */ /* Use %bx to hold the segment (para) number */ movw $BOOTSEG, %bx /* We put cdboot here too */ load_loop: movb %cl, %dh cmpb $MAX_READ_SEC, %cl /* Truncate to max read size */ jbe load_notrunc movb $MAX_READ_SEC, %dh load_notrunc: subb %dh, %cl /* Update count */ pushl %eax /* Save */ pushl %ebx /* Save */ movw %bx, %es /* %bx has the segment (para) number */ xorw %bx, %bx /* %es:0000 for destination */ call read /* Read it in */ popl %ebx /* Restore */ popl %eax /* Restore */ addl $MAX_READ_SEC, %eax /* Update LBA */ addw $MAX_READ_PARAS, %bx /* Update dest addr */ jcxz load_done /* Done? */ jmp load_loop /* Keep going */ load_done: /* Now we can start the loaded program */ movw loader, %cx /* Tell cdboot where it is */ /* (Older versions of cdbr have */ /* %cx == 0 from the jcxz load_done) */ movb drive, %dl /* Get the boot drive number */ ljmp $BOOTSEG, $0 /* Go run cdboot */ /* * Lookup the file in the path at [SI] from the root directory. * * Trashes: All but BX * Returns: CF = 0 (success), BX = pointer to record * CF = 1 (not found) */ lookup: movw $VD_ROOTDIR + MEM_VOLDESC, %bx /* Root directory record */ lookup_dir: lodsb /* Get first char of path */ cmpb $0, %al /* Are we done? */ je lookup_done /* Yes */ cmpb $'/', %al /* Skip path separator */ je lookup_dir decw %si /* Undo lodsb side effect */ call find_file /* Lookup first path item */ jnc lookup_dir /* Try next component */ ret lookup_done: movw $msg_loading, %si /* Success message - say which file */ call display_string mov loader, %si call display_string mov $crlf, %si call display_string clc /* Clear carry */ ret /* * Lookup file at [SI] in directory whose record is at [BX]. * * Trashes: All but returns * Returns: CF = 0 (success), BX = pointer to record, SI = next path item * CF = 1 (not found), SI = preserved */ find_file: mov DIR_EXTENT(%bx), %eax /* Load extent */ xor %edx, %edx mov DIR_EA_LEN(%bx), %dl add %edx, %eax /* Skip extended attributes */ mov %eax, rec_lba /* Save LBA */ mov DIR_SIZE(%bx), %eax /* Save size */ mov %eax, rec_size xor %cl, %cl /* Zero length */ push %si /* Save */ ff_namelen: inc %cl /* Update length */ lodsb /* Read char */ cmp $0, %al /* Nul? */ je ff_namedone /* Yes */ cmp $'/', %al /* Path separator? */ jnz ff_namelen /* No, keep going */ ff_namedone: dec %cl /* Adjust length and save */ mov %cl, name_len pop %si /* Restore */ ff_load: mov rec_lba, %eax /* Load LBA */ mov $MEM_DIR, %ebx /* Address buffer */ mov $1, %dh /* One sector */ call read /* Read directory block */ incl rec_lba /* Update LBA to next block */ ff_scan: mov %ebx, %edx /* Check for EOF */ sub $MEM_DIR, %edx cmp %edx, rec_size ja ff_scan_1 stc /* EOF reached */ ret ff_scan_1: cmpb $0, DIR_LEN(%bx) /* Last record in block? */ je ff_nextblock push %si /* Save */ movzbw DIR_NAMELEN(%bx), %si /* Find end of string */ ff_checkver: cmpb $'0', DIR_NAME-1(%bx,%si) /* Less than '0'? */ jb ff_checkver_1 cmpb $'9', DIR_NAME-1(%bx,%si) /* Greater than '9'? */ ja ff_checkver_1 dec %si /* Next char */ jnz ff_checkver jmp ff_checklen /* All numbers in name, so */ /* no version */ ff_checkver_1: movzbw DIR_NAMELEN(%bx), %cx cmp %cx, %si /* Did we find any digits? */ je ff_checkdot /* No */ cmpb $';', DIR_NAME-1(%bx,%si) /* Check for semicolon */ jne ff_checkver_2 dec %si /* Skip semicolon */ mov %si, %cx mov %cl, DIR_NAMELEN(%bx) /* Adjust length */ jmp ff_checkdot ff_checkver_2: mov %cx, %si /* Restore %si to end of string */ ff_checkdot: cmpb $'.', DIR_NAME-1(%bx,%si) /* Trailing dot? */ jne ff_checklen /* No */ decb DIR_NAMELEN(%bx) /* Adjust length */ ff_checklen: pop %si /* Restore */ movzbw name_len, %cx /* Load length of name */ cmp %cl, DIR_NAMELEN(%bx) /* Does length match? */ je ff_checkname /* Yes, check name */ ff_nextrec: add DIR_LEN(%bx), %bl /* Next record */ adc $0, %bh jmp ff_scan ff_nextblock: subl $SECTOR_SIZE, rec_size /* Adjust size */ jnc ff_load /* If subtract ok, keep going */ ret /* End of file, so not found */ ff_checkname: lea DIR_NAME(%bx), %di /* Address name in record */ push %si /* Save */ repe cmpsb /* Compare name */ jcxz ff_match /* We have a winner! */ pop %si /* Restore */ jmp ff_nextrec /* Keep looking */ ff_match: add $2, %sp /* Discard saved %si */ clc /* Clear carry */ ret /* * Load DH sectors starting at LBA %eax into address %es:%bx. * * Preserves %bx, %cx, %dx, %si, %es * Trashes %eax */ read: pushw %si /* Save */ pushw %cx /* Save since some BIOSs trash */ movl %eax, edd_lba /* LBA to read from */ movw %es, %ax /* Get the segment */ movw %ax, edd_addr + 2 /* and store */ movw %bx, edd_addr /* Store offset too */ read_retry: call twiddle /* Entertain the user */ pushw %dx /* Save */ movw $edd_packet, %si /* Address Packet */ movb %dh, edd_len /* Set length */ movb drive, %dl /* BIOS Device */ movb $0x42, %ah /* BIOS: Extended Read */ int $0x13 /* Call BIOS */ popw %dx /* Restore */ jc read_fail /* Worked? */ popw %cx /* Restore */ popw %si ret /* Return */ read_fail: cmpb $ERROR_TIMEOUT, %ah /* Timeout? */ je read_retry /* Yes, Retry */ read_error: pushw %ax /* Save error */ movw $msg_badread, %si /* "Read error: 0x" */ call display_string popw %ax /* Retrieve error code */ movb %ah, %al /* Into %al */ call hex_byte /* Display error code */ jmp stay_stopped /* ... then hang */ /* * Display the ASCIZ error message in %esi then halt */ err_stop: call display_string stay_stopped: sti /* Ensure Ctl-Alt-Del will work */ hlt /* (don't require power cycle) */ jmp stay_stopped /* (Just to make sure) */ /* * Output the "twiddle" */ twiddle: push %ax /* Save */ push %bx /* Save */ mov twiddle_index, %al /* Load index */ mov twiddle_chars, %bx /* Address table */ inc %al /* Next */ and $3, %al /* char */ mov %al, twiddle_index /* Save index for next call */ xlat /* Get char */ call display_char /* Output it */ mov $8, %al /* Backspace */ call display_char /* Output it */ pop %bx /* Restore */ pop %ax /* Restore */ ret /* * Display the ASCIZ string pointed to by %si. * * Destroys %si, possibly others. */ display_string: pushw %ax cld 1: lodsb /* %al = *%si++ */ testb %al, %al jz 1f call display_char jmp 1b /* * Write out value in %eax in hex */ hex_long: pushl %eax shrl $16, %eax call hex_word popl %eax /* fall thru */ /* * Write out value in %ax in hex */ hex_word: pushw %ax mov %ah, %al call hex_byte popw %ax /* fall thru */ /* * Write out value in %al in hex */ hex_byte: pushw %ax shrb $4, %al call hex_nibble popw %ax /* fall thru */ /* Write out nibble in %al */ hex_nibble: and $0x0F, %al add $'0', %al cmpb $'9', %al jbe display_char addb $'A'-'9'-1, %al /* fall thru to display_char */ /* * Display the character in %al */ display_char: pushw %ax pushw %bx movb $0x0e, %ah movw $1, %bx int $0x10 popw %bx 1: popw %ax ret /* * Data */ drive: .byte 0 /* Given to us by the BIOS */ signon: .asciz "CD-ROM: " crlf: .asciz "\r\n" msg_load2big: .asciz "File too big" msg_badread: .asciz "Read error: 0x" msg_novd: .asciz "No Primary Volume Descriptor" msg_loading: .asciz "Loading " /* State for searching dir */ rec_lba: .long 0x0 /* LBA (adjusted for EA) */ rec_size: .long 0x0 /* File size */ name_len: .byte 0x0 /* Length of current name */ twiddle_index: .byte 0x0 twiddle_chars: .ascii "|/-\\" /* Packet for LBA (CD) read */ edd_packet: .byte 0x10 /* Length */ .byte 0 /* Reserved */ edd_len: .byte 0x0 /* Num to read */ .byte 0 /* Reserved */ edd_addr: .word 0x0, 0x0 /* Seg:Off */ edd_lba: .quad 0x0 /* LBA */ /* The data from here must be last in the file, only followed by 0x00 bytes */ loader: .word 0 /* The path we end up using */ msg_failed: .ascii "Can't find " /* This string runs into... */ /* loader_paths is a list of ASCIZ strings followed by a term NUL byte */ loader_paths: .asciz "/cdboot" .asciz "/CDBOOT" .ascii "/", OSREV, "/", MACH, "/cdboot" .byte 0 /* NUL-term line above */ .ascii "/", OSREV, "/", MACH_U, "/CDBOOT" .byte 0 /* NUL-term line above */ .byte 0 /* Terminate the list */ . = BOOTSECTSIZE .end
