/*
* Partly from:
* $FreeBSD: src/sys/boot/i386/pmbr/pmbr.s,v 1.2 2007/11/26 21:29:59 jhb Exp $
*
* Copyright (c) 2007 Yahoo!, Inc.
* All rights reserved.
* Written by: John Baldwin <jhb@FreeBSD.org>
*
* 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
* 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.
*
*
* Partly from:
* $FreeBSD: src/sys/boot/i386/mbr/mbr.s,v 1.7 2004/08/28 08:39:35 yar Exp $
*
* Copyright (c) 1999 Robert Nordier
* All rights reserved.
*
* Redistribution and use in source and binary forms are freely
* permitted provided that the above copyright notice and this
* paragraph and the following disclaimer are duplicated in all
* such forms.
*
* This software is provided "AS IS" and without any express or
* implied warranties, including, without limitation, the implied
* warranties of merchantability and fitness for a particular
* purpose.
*
*
* "Hybridisation" and modifications for booting Haiku by Andre' Braga
* (me@andrebraga.com), with valuable input from Jean-Loïc Charroud
* (jcharroud@free.fr). The modifications contained herein are released into
* the Public Domain.
*
*
* A 432 bytes MBR IPL (Initial Program Loader) that looks for the UUID of
* a Haiku Boot GUID partition and boots it, falling back to MBR partitions if
* said UUID isn't found or if the (primary) GPT is corrupted or non-existent.
* Its usefulness is in being a versatile, "universal" IPL that supports
* both partitioning styles, allowing it to be used transparently and even
* facilitating the conversion between partitioning styles, should the need
* for more partitions or volumes over 2TiB arise (for instance when cloning
* an older disk to a newer, more capacious one).
* It also paves the way for Haiku to create and support booting from
* multiple volumes larger than 2TiB, which we're in the very privileged
* position of enjoying efficiently in the near future due to BFS. Another use
* case is taking a disk from a Intel EFI machine, plugging it on a BIOS
* machine and boot just fine
* As mentioned, if there are valid partitions defined in the MBR, and the
* primary GPT becomes corrupt, it can fall back to loading the MBR partition
* with the active flag set, if one is defined.
* Currently there's no provision for falling back to the GPT copy that
* lives in the end of the disk, due to the 512 bytes constraint
* this is unlikely given that the code is packed tight. An alternative would be
* disabling support for booting from MBR using BIOS calls other than Int13h
* function 42h, "Extended Read From Disk" (i.e., LBA mode). It's unlikely that
* any machine that Haiku supports won't have this BIOS function, but having an
* "universal" IPL should be quite useful to, say, people using Haiku to
* rewrite a corrupt MBR on another disk using the excellent DiskProbe.
* The number of sectors loaded depends on the boot style. Booting from a
* MBR partition assumes that the Partition Boot Record is one sector long,
* whereas booting from a GPT partition assumes a partition exclusive for a
* system loader and will either copy its entirety into memory starting from
* address 0x7c00, or will copy up to circa 545KiB, whichever is smaller. Thus,
* it remains compatible with the FreeBSD gptloader and should work for loading
* Bootman from an exclusive Haiku boot manager partition as well.
* It should be easy to adjust the UUID signature as needed. It lives at
* offset 0x1a0 (416), leaving plenty of space before the 32-bit disk signature
* at offset 0x1b8 (440), so compatibility with Microsoft Windows and other OSs
* is maintained.
*/
.set LOAD,0x7c00
.set EXEC,0x600
.set MAGIC,0xaa55
.set HANDSHAKE,0x55aa
.set SECSIZE,0x200
/* data offsets */
.set UUID,0x1a0
.set DISKSIG,0x1b8
.set PT_OFF,0x1be
.set GPTSTACK,EXEC+SECSIZE*4-8 /* Stack address */
.set LBABUF,GPTSTACK /* LBA address pointer buffer, */
/* 8 bytes long, after stack */
.set GPT_ADDR,LBABUF+8 /* GPT header address */
.set GPT_SIG,0 /* Signature offset from LBA 1 */
.set GPT_SIG_0,0x20494645 /* "EFI ", bswapped */
.set GPT_SIG_1,0x54524150 /* "PART", bswapped */
.set GPT_MYLBA,24 /* Offs of curr header copy addr */
.set GPT_PART_LBA,72 /* Offs of partitions start LBA */
.set GPT_NPART,80 /* Offs to number of partitions */
.set GPT_PART_SIZE,84 /* Offs to size of partition */
.set PART_ADDR,GPT_ADDR+SECSIZE /* GPT partition array addr. */
.set PART_TYPE,0
.set PART_START_LBA,32 /* Offs to 1st LBA on part entry */
.set PART_END_LBA,40 /* Offs to last LBA */
.set NHRDRV,0x475 /* Number of hard drives */
.globl start /* Entry point */
.code16
/*
* Setup the segment registers for flat addressing and setup the stack.
*/
start: cli /* Clear interrupts before relocation */
xorw %ax,%ax /* Zero */
movw %ax,%es /* Address */
movw %ax,%ds /* data */
movw %ax,%ss /* Set up */
movw $GPTSTACK,%sp /* stack */
std /* String ops set to decrement */
movw $LOAD,%si /* We'll clear working memory starting */
leaw -1(%si),%di /* from $LOAD-1 and stopping at EXEC. */
movw $(LOAD-EXEC-1),%cx /* In the end we have %si pointing */
rep stosb /* at LOAD and %di at EXEC. */
/*
* Relocate ourself to a lower address so that we have more room to load
* other sectors.
*/
reloc: cld /* String ops set to increment */
movw $SECSIZE,%cx /* Now we walk forward and relocate. */
rep movsb /* Tricky, but works great! */
/*
* Jump to the relocated code.
*/
jmp $0,$main /* Absolute address (far) jump */
/*
* Will land here
*/
main: sti /* Re-enable interrupts */
#ifdef VALIDATE_DRV
/*
* Validate drive number in %dl. Certain BIOSes might not like it.
*/
validate_drv:
cmpb $0x80,%dl /* Drive valid? (>= 0x80) */
jb validate_drv.1 /* No */
movb NHRDRV,%dh /* Calculate the highest */
addb $0x80,%dh /* drive number available */
cmpb %dh,%dl /* Within range? */
jb test_extensions /* Yes, proceed */
validate_drv.1:
movb $0x80,%dl /* Else, assume drive 0x80 */
#endif
/*
* Test if BIOS supports Int13h extensions. If so, will try GPT scheme first.
* Else, sets flag (%dh = 1) and goes straight to MBR code.
* (%dl still contains the drive number from BIOS bootstrap)
*/
test_extensions:
movb $0,%dh /* We'll test for EDD extensions. */
/* LBA read (Int13,42) uses only */
/* %dl to get drive number and if */
/* we must fall back to CHS read */
/* (Int13,02), %dh receives head */
/* number, so it's clear to use */
/* %dh to hold a "use CHS" flag */
movw $HANDSHAKE,%bx /* EDD extensions magic number */
movb $0x41,%ah /* BIOS: EDD extensions */
int $0x13 /* present? */
jc set_chs /* No, fall back to CHS read */
test_magic:
cmpw $MAGIC,%bx /* Magic ok? */
jne set_chs /* No, fall back to CHS read */
test_packet:
testb $0x1,%cl /* Packet mode present? */
jnz load_gpt_hdr /* Yes! */
set_chs:
movb $1,%dh /* read_chs overwrites this, and */
/* Int13,42 only uses %dl, so */
/* it's clear to use %dh as flag */
jmp try_mbr
/*
* If we reached here, drive is valid, LBA reads are available, will try GPT.
* Load the primary GPT header from LBA 1 and verify signature.
*/
load_gpt_hdr:
movw $GPT_ADDR,%bx
movw $LBABUF,%si /* Will load LBA sector 1 from disk */
movb $1,(%si) /* (64-bit value! Memory was zeroed so */
/* it's OK to write only the LSB) */
call read
cmpl $GPT_SIG_0,GPT_ADDR+GPT_SIG
jnz try_mbr /* If invalid GPT header */
cmpl $GPT_SIG_1,GPT_ADDR+GPT_SIG+4
jnz try_mbr /* Fluke :( Try MBR now */
/*
* GPT is valid. Load a partition table sector from disk and look for a
* partition matching the UUID found in boot_uuid.
*/
load_part:
movw $GPT_ADDR+GPT_PART_LBA,%si
movw $PART_ADDR,%bx
call read
scan:
movw %bx,%si /* Compare partition UUID */
movw $boot_uuid,%di /* with Haiku boot UUID */
movb $0x10,%cl /* (16 bytes) */
repe cmpsb
jnz next_part /* Didn't match, next partition */
/*
* We found a partition. Load it into RAM starting at 0x7c00.
*/
movw %bx,%di /* Save partition pointer in %di */
leaw PART_START_LBA(%di),%si
movw $LOAD/16,%bx
movw %bx,%es
xorw %bx,%bx
load_bootcode:
push %si /* Save %si */
call read
pop %si /* Restore */
movl PART_END_LBA(%di),%eax /* See if this was the last LBA */
cmpl (%si),%eax
jnz next_boot_lba
movl PART_END_LBA+4(%di),%eax
cmpl 4(%si),%eax
jnz next_boot_lba
jmp start_loader /* Jump to boot code */
next_boot_lba:
incl (%si) /* Next LBA */
adcl $0,4(%si)
mov %es,%ax /* Adjust segment for next */
addw $SECSIZE/16,%ax /* sector */
cmp $0x9000,%ax /* Don't load past 0x90000, */
jae start_loader /* 545k should be enough for */
mov %ax,%es /* any boot code. :) */
jmp load_bootcode
/*
* Move to the next partition. If we walk off the end of the sector, load
* the next sector.
*/
next_part:
decl GPT_ADDR+GPT_NPART /* Was this the last partition? */
jz try_mbr /* UUID boot signature not found */
movw GPT_ADDR+GPT_PART_SIZE,%ax
addw %ax,%bx /* Next partition */
cmpw $PART_ADDR+0x200,%bx /* Still in sector? */
jb scan
incl GPT_ADDR+GPT_PART_LBA /* Next sector */
adcl $0,GPT_ADDR+GPT_PART_LBA+4
jmp load_part
/*
* If loading boot sectors from a GPT partition fails, try booting a MBR part.
* Reset stack/segment. Could have been tainted by the GPT loading code.
*/
try_mbr:
xorw %ax,%ax /* Zero */
movw %ax,%es /* extra segment */
movw $LOAD,%sp /* Reset stack */
xorw %si,%si /* Will point to active partition */
movw $(EXEC+PT_OFF),%bx /* Point to partition table start */
movw $0x4,%cx /* Tested entries counter (4 total) */
read_mbr_entry:
cmpb %ch,(%bx) /* Null entry? (%ch just zeroed) */
je next_mbr_entry /* Yes */
jg err_part_table /* If 0x1..0x7f */
testw %si,%si /* Active already found? */
jnz err_part_table /* Yes */
movw %bx,%si /* Point to active */
next_mbr_entry:
addb $0x10,%bl /* Till */
loop read_mbr_entry /* done */
testw %si,%si /* Active found? */
jnz read_bootsect /* Yes, read OS loader */
try_diskless:
int $0x18 /* Else, BIOS: Diskless boot */
/*
* Ok, now that we have a valid drive and partition entry, load either CHS
* or LBA from the partition entry and read the boot sector from the partition.
*/
read_bootsect:
movw %sp,%bx /* Write addr. (%sp points to LOAD) */
pushw %si /* Points at active part. entry
/* save, else 'read' will trash it */
test_flag:
cmpb $1,%dh /* Test flag set by set_chs above */
jz read_chs /* CHS read if set */
read_lba:
addw $0x8,%si /* Start LBA of partition, 32-bit */
movw $LBABUF,%di /* So far either QWORD 1 or 0, so */
movsl /* more significant bytes are all 0 */
xchg %di,%si /* Copy to buffer and swap pointers */
subw $0x4,%si /* Adjust back to start of buffer */
call read
jmp finished_read /* Skip the CHS setup */
read_chs:
movb 0x1(%si),%dh /* Load head */
movw 0x2(%si),%cx /* Load cylinder:sector */
movb $2,%al /* Read two sectors */
movb $2,%ah /* BIOS: Read sectors from disk */
int $0x13 /* Call the BIOS */
finished_read:
jc err_reading /* If error */
/*
* Now that we've loaded the bootstrap, check for the 0xaa55 signature. If it
* is present, execute the bootstrap we just loaded.
*/
popw %si /* Restore %si (active part entry) */
movb %dl,(%si) /* Patch part record with drive num */
cmpw $MAGIC,0x1fe(%bx) /* Bootable? */
jne err_noboot /* No, error out. */
/* Else, start loader */
start_loader:
xorw %ax,%ax
movw %ax,%es /* Reset %es to zero */
jmp $0,$LOAD /* Jump to boot code */
/* Auxiliary functions */
/*
* Load a sector (64-bit LBA at %si) from disk %dl into %es:%bx by creating
* a EDD packet on the stack and passing it to the BIOS. Trashes %ax and %si.
*/
read:
pushl 0x4(%si) /* Set the LBA */
pushl 0x0(%si) /* address */
pushw %es /* Set the address of */
pushw %bx /* the transfer buffer */
pushw $0x1 /* Read 1 sector */
pushw $0x10 /* Packet length */
movw %sp,%si /* Packet pointer */
movw $0x4200,%ax /* BIOS: LBA Read from disk */
int $0x13 /* Call the BIOS */
add $0x10,%sp /* Restore stack */
jc err_reading /* If error */
ret
/*
* Output an ASCIZ string pointed at by %si to the console via the BIOS.
*/
putstr.0:
movw $0x7,%bx /* Page:attribute */
movb $0xe,%ah /* BIOS: Display */
int $0x10 /* character */
putstr:
lodsb /* Get character */
testb %al,%al /* End of string? */
jnz putstr.0 /* No */
ret
/*
* Various error message entry points.
*/
err_part_table:
movw $msg_badtable,%si /* "Bad Part. Table!" */
call putstr
jmp halt
err_reading:
movw $msg_ioerror,%si /* "Read Error!" */
call putstr
jmp halt
err_noboot:
movw $msg_noloader,%si /* "No Sys Loader!" */
call putstr
/* fall-through to halt */
halt:
cli
hlt
jmp halt
/* Data section */
#ifdef VALIDATE_DRV
/* Messages must be shortened so the code fits 440 bytes */
msg_badtable: .asciz "BadPTbl!"
msg_ioerror: .asciz "IOErr!"
msg_noloader: .asciz "NoSysLdr!"
#else
msg_badtable: .asciz "Bad Part. Table!"
msg_ioerror: .asciz "Read Error!"
msg_noloader: .asciz "No Sys Loader!"
#endif
/* Boot partition UUID signature */
.org UUID,0x0 /* Zero-pad up to UUID offset */
boot_uuid:
.long 0x42465331 /* 'BFS1' (formally, UUID time-low) */
.word 0x3ba3 /* UUID time-mid */
.word 0x10f1 /* UUID time-high & version (v1) */
.byte 0x80 /* UUID DCE 1.1 variant */
.byte 0x2a /* '*' (formally, UUID clock-seq-low) */
.byte 0x48 /* 'H' */
.byte 0x61 /* 'a' */
.byte 0x69 /* 'i' */
.byte 0x6b /* 'k' */
.byte 0x75 /* 'u' */
.byte 0x21 /* '!' */
#ifndef MBR_CODE_ONLY
/* Disk signature */
.org DISKSIG,0x0 /* Zero-pad up to signature offset */
sig:
.long 0 /* OS Disk Signature */
.word 0 /* "Unknown" in PMBR */
/* Partition table */
.org PT_OFF,0x0 /* Won't pad, just documenting */
partbl:
.fill 0x10,0x4,0x0 /* Partition table */
.word MAGIC /* Magic number */
#endif
