diff options
Diffstat (limited to 'sys')
| -rw-r--r-- | sys/arch/i386/stand/mbr/mbr.S | 612 |
1 files changed, 412 insertions, 200 deletions
diff --git a/sys/arch/i386/stand/mbr/mbr.S b/sys/arch/i386/stand/mbr/mbr.S index 6829c7b47e9..4b9e8532fa7 100644 --- a/sys/arch/i386/stand/mbr/mbr.S +++ b/sys/arch/i386/stand/mbr/mbr.S @@ -1,7 +1,8 @@ -/* $OpenBSD: mbr.S,v 1.18 2003/06/03 20:22:12 mickey Exp $ */ +/* $OpenBSD: mbr.S,v 1.19 2004/01/05 00:08:23 tom Exp $ */ /* * Copyright (c) 1997 Michael Shalayeff and Tobias Weingartner + * Copyright (c) 2003 Tom Cosgrove <tom.cosgrove@arches-consulting.com> * All rights reserved. * * Redistribution and use in source and binary forms, with or without @@ -40,13 +41,36 @@ #include <machine/asm.h> #include <assym.h> -#define data32 .byte 0x66 -#define addr32 .byte 0x67 - -#define BOOTBIOS 0x7c0 /* segment where we are loaded */ -#define BOOTRELOC 0x7a0 /* segment where to relocate */ +/* + * Memory layout: + * + * 0x07C00 -> 0x07DFF BIOS loads us here (at 31k) + * 0x07E00 -> 0x17BFC our stack (to 95k) + * + * 0x07A00 -> 0x07BFF we relocate to here (at 30k5) + * + * 0x07C00 -> 0x07DFF we load PBR here (at 31k) + * + * The BIOS loads us at physical address 0x07C00. We use a long jmp to + * normalise our address to seg:offset 07C0:0000. We then relocate to + * 0x07A00, seg:offset 07A0:0000. + * + * We use a long jmp to normalise our address to seg:offset 07A0:0000 + * We set the stack to start at 07C0:FFFC (grows down on i386) + * We load the partition boot record (PBR) /boot at seg:offset 4000:0000 + */ +#define BOOTSEG 0x7c0 /* segment where we are loaded */ +#define BOOTRELOCSEG 0x7a0 /* segment where we relocate to */ +#define BOOTSTACKOFF 0xfffc /* stack starts here, grows down */ #define PARTSZ 16 /* each partition table entry is 16 bytes */ +#define CHAR_LBA_READ '.' +#define CHAR_CHS_READ ';' +#define CHAR_CHS_FORCE '!' +#define CHAR_SHIFT_SEEN 0x07 /* Use BEL */ + +#define MBR_FLAGS_FORCE_CHS 0x0001 + #ifdef DEBUG #define CHAR_S 'S' /* started */ #define CHAR_R 'R' /* relocated */ @@ -54,293 +78,482 @@ #define CHAR_B 'B' /* loading boot */ #define CHAR_G 'G' /* jumping to boot */ -#define DBGMSG(msg) \ - movb $msg, %al; \ - /* call Lchr */; \ - .byte 0xe8; \ - .word Lchr - . - 2 +#define DBGMSG(c) movb $c, %al; call Lchr #else /* !DEBUG */ -#define DBGMSG(msg) +#define DBGMSG(c) #endif /* !DEBUG */ -#define puts(s) \ - data32; \ - movl $s, %esi; \ - /* call Lmessage */; \ - .byte 0xe8; \ - .word Lmessage - . - 2 + +/* Clobbers %al - maybe more */ +#define putc(c) movb $c, %al; call Lchr + +/* Clobbers %esi - maybe more */ +#define puts(s) movw $s, %si; call Lmessage + .text + .code16 .globl start start: /* Adjust %cs to be right */ - data32 - ljmp $BOOTBIOS, $1f + ljmp $BOOTSEG, $1f 1: /* Set up stack */ - movl %cs, %eax - cli - mov %ax, %ss - data32 - movl $0xfffc, %esp - sti + movw %cs, %ax + + /* + * We don't need to disable and re-enable interrupts around the + * the load of ss and sp. + * + * From 80386 Programmer's Reference Manual: + * "A MOV into SS inhibits all interrupts until after the execution + * of the next instruction (which is presumably a MOV into eSP)" + * + * According to Hamarsoft's 86BUGS list (which is distributed with + * Ralph Brown's Interrupt List), some early 8086/88 processors + * failed to disable interrupts following a load into a segment + * register, but this was fixed with later steppings. + * + * Accordingly, this code will fail on very early 8086/88s, but + * nick@ will just have to live with it. Others will note that + * we require an 80386 (or compatible) or above processor, anyway. + */ + /* cli */ + movw %ax, %ss + movw $BOOTSTACKOFF, %sp + /* sti */ /* XXX not necessary; see above */ /* Set up data segment */ - mov %ax, %ds + movw %ax, %ds DBGMSG(CHAR_S) - /* Relocate 512 bytes so we can load PBS here */ - data32 - movl $BOOTRELOC, %eax - movl %eax, %es - data32 - xorl %esi, %esi - data32 - xorl %edi, %edi - data32 - movl $0x200, %ecx + /* + * On the PC architecture, the boot record (originally on a floppy + * disk) is loaded at 0000:7C00 (hex) and execution starts at the + * beginning. + * + * When hard disk support was added, a scheme to partition disks into + * four separate partitions was used, to allow multiple operating + * systems to be installed on the one disk. The boot sectors of the + * operating systems on each partition would of course expect to be + * loaded at 0000:7C00. + * + * The first sector of the hard disk is the master boot record (MBR). + * It is this which defines the partitions and says which one is + * bootable. Of course, the BIOS loads the MBR at 0000:7C00, the + * same location where the MBR needs to load the partition boot + * record (PBR, called biosboot in OpenBSD). + * + * Therefore, the MBR needs to relocate itself before loading the PBR. + * + * Make it so. + */ + movw $BOOTRELOCSEG, %ax + movw %ax, %es + xorw %si, %si + xorw %di, %di + movw $0x200, %cx /* Bytes in MBR, relocate it all */ cld rep movsb /* Jump to relocated self */ - data32 - ljmp $BOOTRELOC, $reloc + ljmp $BOOTRELOCSEG, $reloc reloc: DBGMSG(CHAR_R) /* Set up %es and %ds */ - pushl %ds - popl %es /* next boot is at the same place as we were loaded */ - pushl %cs - popl %ds /* and %ds is at the %cs */ + pushw %ds + popw %es /* next boot is at the same place as we were loaded */ + pushw %cs + popw %ds /* and %ds is at the %cs */ #ifdef SERIAL /* Initialize the serial port to 9600 baud, 8N1. - * Do we need to do this? Most things at this level - * do not know or care (on a PC) where the output is - * happening to go. I think if we are headless, - * /boot should figure (as it does now) that out. - * - * If there is a problem with this stage of the boot - * process, connect up a monitor and kbd, and see what - * is going on. Left here for the time being. - * - * --Toby. */ - xorl %eax, %eax + xorw %ax, %ax movb $0xe3, %ax - data32 - movl $SERIAL, %dx + movw $SERIAL, %dx int $0x14 #endif - /* bootstrap passes us drive number in %dl - * - * XXX - This is not always true. We currently - * check if %dl points to a HD, and if not we - * complain, and set it to point to the first - * HDD. Note, this is not 100% correct, since - * there is a possibility that you boot of of - * HD #2, and still get (%dl & 0x80) == 0x00, - * these type of systems will loose. I don't - * know of any like this, but I've come to the - * conclusion, that if it can exist, it will, - * someplace in the PC world. If anyone knows - * how to fix this, speak up! + /* + * If the SHIFT key is held down on entry, force CHS read + */ + + /* + * BIOS call "INT 0x16 Get Keyboard Shift Flags + * Call with %ah = 0x02 + * Return: + * %al = shift flags + * %ah - undefined by many BIOSes + */ + movb $0x02, %ah + int $0x16 + testb $0x3, %al /* Either shift key down? */ + jz no_shift + + putc(CHAR_SHIFT_SEEN) /* Signal that shift key was seen */ + + orb $MBR_FLAGS_FORCE_CHS, flags + +no_shift: + /* BIOS passes us drive number in %dl * - * Toby - Thu Jul 31 21:01:00 CDT 1997 + * XXX - This is not always true. We currently check if %dl + * points to a HD, and if not we complain, and set it to point + * to the first HDD. Note, this is not 100% correct, since + * there is a possibility that you boot of of HD #2, and still + * get (%dl & 0x80) == 0x00, these type of systems will lose. */ testb $0x80, %dl - jnz 1f + jnz drive_ok /* MBR on floppy or old BIOS - * Note: MBR (this code) should never - * be on a floppy. It does not belong - * there, so %dl should never be 0x00. + * Note: MBR (this code) should never be on a floppy. It does + * not belong there, so %dl should never be 0x00. * - * Here we simply complain (should we?), - * and then hardcode the boot drive to - * 0x80. + * Here we simply complain (should we?), and then hardcode the + * boot drive to 0x80. */ - puts(fdmbr) + puts(efdmbr) - /* If we are passed bogus data, set it to HD #1. - * We should load the value from a hard coded - * location in this sector. Maybe I'll write - * that next, since my machines seem to be one - * of the weird ones... + /* If we are passed bogus data, set it to HD #1 */ movb $0x80, %dl - /* Do we need to check our signature? The BIOS will - * check it for us, I doubt there is a need for us to - * do the same thing over again. If we fail here, - * something terrible is wrong. However, I doubt we - * can recover anyways. The message might be nice - * for the (l)user though. - */ -1: xor %bx, %bx - # cmpw $DOSMBR_SIGNATURE, (%bx) - .byte 0x81, 0xbf - .word signature - .word DOSMBR_SIGNATURE - je sigok - puts(esig) - - /* find the first active partition - * Note: this should be the only active - * partition. We currently don't check - * for that, but we really should. If - * and when I feel up to it, I'll add - * that code. +drive_ok: + /* Find the first active partition. + * Note: this should be the only active partition. We currently + * don't check for that. */ -sigok: - data32 - movl $pt, %esi - data32 - movl $NDOSPART, %ecx -1: + movw $pt, %si + + movw $NDOSPART, %cx +find_active: DBGMSG(CHAR_L) - # movb (%si), %al - .byte 0x8a, 0x44, 0x00 + movb (%si), %al + cmpb $DOSACTIVE, %al je found - data32 - addl $PARTSZ, %esi - loop 1b + + addw $PARTSZ, %si + loop find_active /* No bootable partition */ no_part: - puts(noboot) + movw $enoboot, %si + err_stop: + call Lmessage + +stay_stopped: cli hlt /* Just to make sure */ - jmp err_stop + jmp stay_stopped - /* Found bootable partition */ found: + /* + * Found bootable partition + */ + DBGMSG(CHAR_B) - pushl %eax - /* Save drive and partition */ - movl %edx, %eax - andl $0x0F, %eax - orl $0x30, %eax - #movb %al, adrive - .byte 0xA2 - .word adrive - - movl %ecx, %eax - decl %eax - xorl $0x03, %eax - andl $0x0F, %eax - orl $0x30, %eax - #movb %al, aprtn - .byte 0xA2 - .word aprtn - - popl %eax - /* Load values from active partition table entry */ - # movb 1(%si), %dh # head - .byte 0x8a, 0x74, 0x01 - # movw 2(%si), %cx # sect, cyl - .byte 0x8b, 0x4c, 0x02 - # movb 4(%si), %al # partition type - .byte 0x8a, 0x44, 0x04 + /* Store the drive number (from %dl) in decimal */ + movb %dl, %al + andb $0x0F, %al + addb $'0', %al + movb %al, drive_num -/* -# BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory -# Call with %ah = 0x2 -# %al = number of sectors -# %ch = cylinder -# %cl = sector -# %dh = head -# %dl = drive (0x80 for hard disk, 0x0 for floppy disk) -# %es:%bx = segment:offset of buffer -# Return: -# %al = 0x0 on success; err code on failure -*/ - data32 - movl $0x200 | 1, %eax /* number of blocks */ - xor %bx, %bx /* put it at %es:0 */ + /* + * Store the partition number, in decimal. + * + * We started with cx = 4; if found we want part '0' + * cx = 3; part '1' + * cx = 2; part '2' + * cx = 1; part '3' + * + * We'll come into this with no other values for cl. + */ + movb $'0'+4, %al + subb %cl, %al + movb %al, part_num + + /* + * Tell operator what partition we're trying to boot. + * + * Using drive X, partition Y + * - this used to be printed out after successfully loading the + * partition boot record; we now print it out before + */ + pushw %si + movw $info, %si + testb $MBR_FLAGS_FORCE_CHS, flags + jnz 1f + incw %si +1: + call Lmessage + popw %si + + /* + * Partition table entry format: + * + * 0x00 BYTE boot indicator (0x80 = active, 0x00 = inactive) + * 0x01 BYTE start head + * 0x02 WORD start cylinder, sector + * 0x04 BYTE system type (0xA6 = OpenBSD) + * 0x05 BYTE end head + * 0x06 WORD end cylinder, sector + * 0x08 LONG start LBA sector + * 0x0C LONG number of sectors in partition + * + * In the case of a partition that extends beyond the 8GB boundary, + * the LBA values will be correct, the CHS values will have their + * maximums (typically (C,H,S) = (1023,255,63)). + * + * %ds:%si points to the active partition table entry. + */ + + /* We will load the partition boot sector (biosboot) where we + * were originally loaded. We'll check to make sure something + * valid comes in. So that we don't find ourselves, zero out + * the signature at the end. + */ + movw $0, %es:signature(,1) + + /* + * Have we been instructed to ignore LBA? + */ + testb $MBR_FLAGS_FORCE_CHS, flags + jnz do_chs + + /* + * We will use the LBA sector number if we have LBA support, + * so find out. + */ + + /* + * BIOS call "INT 0x13 Extensions Installation Check" + * Call with %ah = 0x41 + * %bx = 0x55AA + * %dl = drive (0x80 for 1st hd, 0x81 for 2nd, etc) + * Return: + * carry set: failure + * %ah = error code (0x01, invalid func) + * carry clear: success + * %bx = 0xAA55 (must verify) + * %ah = major version of extensions + * %al (internal use) + * %cx = capabilities bitmap + * 0x0001 - extnd disk access funcs + * 0x0002 - rem. drive ctrl funcs + * 0x0004 - EDD functions with EBP + * %dx (extension version?) + */ + + movb %dl, (%si) /* Store drive here temporarily */ + /* (This call trashes %dl) */ + /* + * XXX This is actually the correct + * place to store this. The 0x80 + * value used to indicate the + * active partition is by intention + * the same as the BIOS drive value + * for the first hard disk (0x80). + * At one point, 0x81 would go here + * for the second hard disk; the + * 0x80 value is often used as a + * bit flag for testing, rather + * than an exact byte value. + */ + movw $0x55AA, %bx + movb $0x41, %ah int $0x13 - jnc 1f - puts(eread) + + movb (%si), %dl /* Get back drive number */ + + jc do_chs /* Did the command work? Jump if not */ + cmpw $0xAA55, %bx /* Check that bl, bh exchanged */ + jne do_chs /* If not, don't have EDD extensions */ + testb $0x01, %cl /* And do we have "read" available? */ + jz do_chs /* Again, use CHS if not */ + +do_lba: + /* + * BIOS call "INT 0x13 Extensions Extended Read" + * Call with %ah = 0x42 + * %dl = drive (0x80 for 1st hd, 0x81 for 2nd, etc) + * %ds:%si = segment:offset of command packet + * Return: + * carry set: failure + * %ah = error code (0x01, invalid func) + * command packet's sector count field set + * to the number of sectors successfully + * transferred + * carry clear: success + * %ah = 0 (success) + * Command Packet: + * 0x0000 BYTE packet size (0x10 or 0x18) + * 0x0001 BYTE reserved (should be 0) + * 0x0002 WORD sectors to transfer (max 127) + * 0x0004 DWORD seg:offset of transfer buffer + * 0x0008 QWORD starting sector number + */ + movb $CHAR_LBA_READ, %al + call Lchr + + /* Load LBA sector number from active partition table entry */ + movl 8(%si), %ecx + movl %ecx, lba_sector + + pushw %si /* We'll need %si later */ + + movb $0x42, %ah + movw $lba_command, %si + int $0x13 + + popw %si /* (get back %si) flags unchanged */ + + jnc booting_os /* If it worked, run the pbr we got */ + + /* + * LBA read failed, fall through to try CHS read + */ + +do_chs: + /* + * BIOS call "INT 0x13 Function 0x2" to read sectors from disk into + * memory + * Call with %ah = 0x2 + * %al = number of sectors + * %ch = cylinder & 0xFF + * %cl = sector (0-63) | rest of cylinder bits + * %dh = head + * %dl = drive (0x80 for hard disk) + * %es:%bx = segment:offset of buffer + * Return: + * carry set: failure + * %ah = err code + * %al = number of sectors transferred + * carry clear: success + * %al = 0x0 OR number of sectors transferred + * (depends on BIOS!) + * (according to Ralph Brown Int List) + */ + movb $CHAR_CHS_READ, %al + call Lchr + + /* Load values from active partition table entry */ + movb 1(%si), %dh /* head */ + movw 2(%si), %cx /* sect, cyl */ + movw $0x201, %ax /* function and number of blocks */ + xorw %bx, %bx /* put it at %es:0 */ + int $0x13 + jnc booting_os + +read_error: + movw $eread, %si jmp err_stop -1: +booting_os: + puts(crlf) DBGMSG(CHAR_G) - puts(info) - # jump to the new code (%ds:%si is at the right point) - data32 - ljmp $0, $BOOTBIOS << 4 + /* + * Make sure the pbr we loaded has a valid signature at the end. + * This also ensures that something did load where we were expecting + * it, as there's still a copy of our code there... + */ + cmpw $DOSMBR_SIGNATURE, %es:signature(,1) + jne missing_os + + /* jump to the new code (%ds:%si is at the right point) */ + ljmp $0, $BOOTSEG << 4 /* not reached */ +missing_os: + movw $enoos, %si + jmp err_stop + /* * Display string */ Lmessage: - pushl %eax + pushw %ax cld 1: - lodsb # load a byte into %al + lodsb /* %al = *%si++ */ testb %al, %al jz 1f - /* call Lchr */ - .byte 0xe8 - .word Lchr - . - 2 + call Lchr jmp 1b -# -# Lchr: write the error message in %ds:%si to console -# +/* + * Lchr: write the error message in %ds:%si to console + */ Lchr: - pushl %eax + pushw %ax -#ifndef SERIAL - pushl %ebx - movb $0x0e, %ah - xor %bx, %bx - inc %bx /* movw $0x01, %bx */ - int $0x10 - popl %ebx -#else - pushl %edx +#ifdef SERIAL + pushw %dx movb $0x01, %ah - data32 - movl SERIAL, %dx + movw SERIAL, %dx int $0x14 - popl %edx + popw %dx +#else + pushw %bx + movb $0x0e, %ah + movw $1, %bx + int $0x10 + popw %bx #endif -1: popl %eax +1: popw %ax ret +/* command packet for LBA read of boot sector */ +lba_command: + .byte 0x10 /* size of command packet */ + .byte 0x00 /* reserved */ + .word 0x0001 /* sectors to transfer, just 1 */ + .word 0 /* target buffer, offset */ + .word BOOTSEG /* target buffer, segment */ +lba_sector: + .long 0, 0 /* sector number */ + /* Info messages */ -info: .ascii "Using Drive: " -adrive: .byte 'X' - .ascii " Partition: " -aprtn: .byte 'Y' - .asciz "\r\n" +info: .ascii "!Using drive " +drive_num: + .byte 'X' + .ascii ", partition " +part_num: + .asciz "Y" /* Error messages */ -fdmbr: .asciz "MBR on floppy or old BIOS\r\n" -eread: .asciz "Read error\r\n" -noboot: .asciz "No active partition\r\n" -esig: .asciz "Invalid Signature\r\n" +efdmbr: .asciz "MBR on floppy or old BIOS\r\n" +eread: .asciz "\r\nRead error\r\n" +enoos: .asciz "No O/S\r\n" +enoboot: .ascii "No active partition" /* runs into crlf... */ +crlf: .asciz "\r\n" endofcode: nop -/* (MBR) NT registry offset */ +/* We're going to store a flags word here */ + + . = 0x1b4 +flags: + .word 0x0000 + .ascii "Ox" /* Indicate that the two bytes */ + /* before us are the flags word */ + +/* (MBR) NT disk signature offset */ . = 0x1b8 .space 4, 0 /* partition table */ /* flag, head, sec, cyl, type, ehead, esect, ecyl, start, len */ - . = DOSPARTOFF # starting address of partition table + . = DOSPARTOFF /* starting address of partition table */ pt: .byte 0x0,0,0,0,0,0,0,0 .long 0,0 @@ -355,4 +568,3 @@ pt: signature: .short DOSMBR_SIGNATURE . = 0x200 - |