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|
; -----------------------------------------------------------------------
;
; Copyright 1994-2009 H. Peter Anvin - All Rights Reserved
; Copyright 2009 Intel Corporation; author: H. Peter Anvin
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
; Boston MA 02110-1301, USA; either version 2 of the License, or
; (at your option) any later version; incorporated herein by reference.
;
; -----------------------------------------------------------------------
;
; diskstart.inc
;
; Common early-bootstrap code for harddisk-based Syslinux derivatives.
;
; Expanded superblock
section .bss
alignb 8
SuperInfo resq 16 ; The first 16 bytes expanded 8 times
section .text
;
; Some of the things that have to be saved very early are saved
; "close" to the initial stack pointer offset, in order to
; reduce the code size...
;
StackBuf equ $-44-32 ; Start the stack here (grow down - 4K)
PartInfo equ StackBuf ; Saved partition table entry
FloppyTable equ PartInfo+16 ; Floppy info table (must follow PartInfo)
OrigFDCTabPtr equ StackBuf-8 ; The 2nd high dword on the stack
OrigESDI equ StackBuf-4 ; The high dword on the stack
;
; Primary entry point. Tempting as though it may be, we can't put the
; initial "cli" here; the jmp opcode in the first byte is part of the
; "magic number" (using the term very loosely) for the DOS superblock.
;
bootsec equ $
_start: jmp short start ; 2 bytes
nop ; 1 byte
;
; "Superblock" follows -- it's in the boot sector, so it's already
; loaded and ready for us
;
bsOemName db MY_NAME ; The SYS command sets this, so...
zb 8-($-bsOemName)
;
; These are the fields we actually care about. We end up expanding them
; all to dword size early in the code, so generate labels for both
; the expanded and unexpanded versions.
;
%macro superb 1
bx %+ %1 equ SuperInfo+($-superblock)*8+4
bs %+ %1 equ $
zb 1
%endmacro
%macro superw 1
bx %+ %1 equ SuperInfo+($-superblock)*8
bs %+ %1 equ $
zw 1
%endmacro
%macro superd 1
bx %+ %1 equ $ ; no expansion for dwords
bs %+ %1 equ $
zd 1
%endmacro
superblock equ $
superw BytesPerSec
superb SecPerClust
superw ResSectors
superb FATs
superw RootDirEnts
superw Sectors
superb Media
superw FATsecs
superw SecPerTrack
superw Heads
superinfo_size equ ($-superblock)-1 ; How much to expand
superd Hidden
superd HugeSectors
;
; This is as far as FAT12/16 and FAT32 are consistent
;
; FAT12/16 need 26 more bytes,
; FAT32 need 54 more bytes
;
superblock_len_fat16 equ $-superblock+26
superblock_len_fat32 equ $-superblock+54
zb 54 ; Maximum needed size
superblock_max equ $-superblock
SecPerClust equ bxSecPerClust
;
; Note we don't check the constraints above now; we did that at install
; time (we hope!)
;
start:
cli ; No interrupts yet, please
cld ; Copy upwards
;
; Set up the stack
;
xor ax,ax
mov ss,ax
mov sp,StackBuf ; Just below BSS
push es ; Save initial ES:DI -> $PnP pointer
push di
mov es,ax
;
; DS:SI may contain a partition table entry. Preserve it for us.
;
mov cx,8 ; Save partition info
mov di,PartInfo
rep movsw
mov ds,ax ; Now we can initialize DS...
;
; Now sautee the BIOS floppy info block to that it will support decent-
; size transfers; the floppy block is 11 bytes and is stored in the
; INT 1Eh vector (brilliant waste of resources, eh?)
;
; Of course, if BIOSes had been properly programmed, we wouldn't have
; had to waste precious space with this code.
;
mov bx,fdctab
lfs si,[bx] ; FS:SI -> original fdctab
push fs ; Save on stack in case we need to bail
push si
; Save the old fdctab even if hard disk so the stack layout
; is the same. The instructions above do not change the flags
mov [DriveNumber],dl ; Save drive number in DL
and dl,dl ; If floppy disk (00-7F), assume no
; partition table
js harddisk
floppy:
mov cl,6 ; 12 bytes (CX == 0)
; es:di -> FloppyTable already
; This should be safe to do now, interrupts are off...
mov [bx],di ; FloppyTable
mov [bx+2],ax ; Segment 0
fs rep movsw ; Faster to move words
mov cl,[bsSecPerTrack] ; Patch the sector count
mov [di-8],cl
; AX == 0 here
int 13h ; Some BIOSes need this
jmp short not_harddisk
;
; The drive number and possibly partition information was passed to us
; by the BIOS or previous boot loader (MBR). Current "best practice" is to
; trust that rather than what the superblock contains.
;
; Would it be better to zero out bsHidden if we don't have a partition table?
;
; Note: di points to beyond the end of PartInfo
;
harddisk:
test byte [di-16],7Fh ; Sanity check: "active flag" should
jnz no_partition ; be 00 or 80
mov eax,[di-8] ; Partition offset (dword)
mov [bsHidden],eax
no_partition:
;
; Get disk drive parameters (don't trust the superblock.) Don't do this for
; floppy drives -- INT 13:08 on floppy drives will (may?) return info about
; what the *drive* supports, not about the *media*. Fortunately floppy disks
; tend to have a fixed, well-defined geometry which is stored in the superblock.
;
; DL == drive # still
mov ah,08h
int 13h
jc no_driveparm
and ah,ah
jnz no_driveparm
shr dx,8
inc dx ; Contains # of heads - 1
mov [bsHeads],dx
and cx,3fh
mov [bsSecPerTrack],cx
no_driveparm:
not_harddisk:
;
; Ready to enable interrupts, captain
;
sti
;
; Do we have EBIOS (EDD)?
;
eddcheck:
mov bx,55AAh
mov ah,41h ; EDD existence query
mov dl,[DriveNumber]
int 13h
jc .noedd
cmp bx,0AA55h
jne .noedd
test cl,1 ; Extended disk access functionality set
jz .noedd
;
; We have EDD support...
;
mov byte [getlinsec.jmp+1],(getlinsec_ebios-(getlinsec.jmp+2))
.noedd:
;
; Load the first sector of LDLINUX.SYS; this used to be all proper
; with parsing the superblock and root directory; it doesn't fit
; together with EBIOS support, unfortunately.
;
mov eax,[FirstSector] ; Sector start
mov bx,ldlinux_sys ; Where to load it
call getonesec
; Some modicum of integrity checking
cmp dword [ldlinux_magic+4],LDLINUX_MAGIC^HEXDATE
jne kaboom
; Go for it...
jmp ldlinux_ent
;
; getonesec: get one disk sector
;
getonesec:
mov bp,1 ; One sector
; Fall through
;
; getlinsec: load a sequence of BP floppy sector given by the linear sector
; number in EAX into the buffer at ES:BX. We try to optimize
; by loading up to a whole track at a time, but the user
; is responsible for not crossing a 64K boundary.
; (Yes, BP is weird for a count, but it was available...)
;
; On return, BX points to the first byte after the transferred
; block.
;
; This routine assumes CS == DS, and trashes most registers.
;
; Stylistic note: use "xchg" instead of "mov" when the source is a register
; that is dead from that point; this saves space. However, please keep
; the order to dst,src to keep things sane.
;
getlinsec:
add eax,[bsHidden] ; Add partition offset
xor edx,edx ; Zero-extend LBA (eventually allow 64 bits)
.jmp: jmp strict short getlinsec_cbios
;
; getlinsec_ebios:
;
; getlinsec implementation for EBIOS (EDD)
;
getlinsec_ebios:
.loop:
push bp ; Sectors left
.retry2:
call maxtrans ; Enforce maximum transfer size
movzx edi,bp ; Sectors we are about to read
mov cx,retry_count
.retry:
; Form DAPA on stack
push edx
push eax
push es
push bx
push di
push word 16
mov si,sp
pushad
mov dl,[DriveNumber]
push ds
push ss
pop ds ; DS <- SS
mov ah,42h ; Extended Read
int 13h
pop ds
popad
lea sp,[si+16] ; Remove DAPA
jc .error
pop bp
add eax,edi ; Advance sector pointer
sub bp,di ; Sectors left
shl di,SECTOR_SHIFT ; 512-byte sectors
add bx,di ; Advance buffer pointer
and bp,bp
jnz .loop
ret
.error:
; Some systems seem to get "stuck" in an error state when
; using EBIOS. Doesn't happen when using CBIOS, which is
; good, since some other systems get timeout failures
; waiting for the floppy disk to spin up.
pushad ; Try resetting the device
xor ax,ax
mov dl,[DriveNumber]
int 13h
popad
loop .retry ; CX-- and jump if not zero
;shr word [MaxTransfer],1 ; Reduce the transfer size
;jnz .retry2
; Total failure. Try falling back to CBIOS.
mov byte [getlinsec.jmp+1],(getlinsec_cbios-(getlinsec.jmp+2))
;mov byte [MaxTransfer],63 ; Max possibe CBIOS transfer
pop bp
; ... fall through ...
;
; getlinsec_cbios:
;
; getlinsec implementation for legacy CBIOS
;
getlinsec_cbios:
.loop:
push edx
push eax
push bp
push bx
movzx esi,word [bsSecPerTrack]
movzx edi,word [bsHeads]
;
; Dividing by sectors to get (track,sector): we may have
; up to 2^18 tracks, so we need to use 32-bit arithmetric.
;
div esi
xor cx,cx
xchg cx,dx ; CX <- sector index (0-based)
; EDX <- 0
; eax = track #
div edi ; Convert track to head/cyl
; We should test this, but it doesn't fit...
; cmp eax,1023
; ja .error
;
; Now we have AX = cyl, DX = head, CX = sector (0-based),
; BP = sectors to transfer, SI = bsSecPerTrack,
; ES:BX = data target
;
call maxtrans ; Enforce maximum transfer size
; Must not cross track boundaries, so BP <= SI-CX
sub si,cx
cmp bp,si
jna .bp_ok
mov bp,si
.bp_ok:
shl ah,6 ; Because IBM was STOOPID
; and thought 8 bits were enough
; then thought 10 bits were enough...
inc cx ; Sector numbers are 1-based, sigh
or cl,ah
mov ch,al
mov dh,dl
mov dl,[DriveNumber]
xchg ax,bp ; Sector to transfer count
mov ah,02h ; Read sectors
mov bp,retry_count
.retry:
pushad
int 13h
popad
jc .error
.resume:
movzx ecx,al ; ECX <- sectors transferred
shl ax,SECTOR_SHIFT ; Convert sectors in AL to bytes in AX
pop bx
add bx,ax
pop bp
pop eax
pop edx
add eax,ecx
sub bp,cx
jnz .loop
ret
.error:
dec bp
jnz .retry
xchg ax,bp ; Sectors transferred <- 0
shr word [MaxTransfer],1
jnz .resume
; Fall through to disk_error
;
; kaboom: write a message and bail out.
;
disk_error:
kaboom:
xor si,si
mov ss,si
mov sp,StackBuf-4 ; Reset stack
mov ds,si ; Reset data segment
pop dword [fdctab] ; Restore FDC table
.patch: ; When we have full code, intercept here
mov si,bailmsg
; Write error message, this assumes screen page 0
.loop: lodsb
and al,al
jz .done
mov ah,0Eh ; Write to screen as TTY
mov bx,0007h ; Attribute
int 10h
jmp short .loop
.done:
cbw ; AH <- 0
.again: int 16h ; Wait for keypress
; NB: replaced by int 18h if
; chosen at install time..
int 19h ; And try once more to boot...
.norge: jmp short .norge ; If int 19h returned; this is the end
;
; Truncate BP to MaxTransfer
;
maxtrans:
cmp bp,[MaxTransfer]
jna .ok
mov bp,[MaxTransfer]
.ok: ret
;
; Error message on failure
;
bailmsg: db 'Boot error', 0Dh, 0Ah, 0
; This fails if the boot sector overflows
zb 1F8h-($-$$)
FirstSector dd 0xDEADBEEF ; Location of sector 1
MaxTransfer dw 0x007F ; Max transfer size
; This field will be filled in 0xAA55 by the installer, but we abuse it
; to house a pointer to the INT 16h instruction at
; kaboom.again, which gets patched to INT 18h in RAID mode.
bootsignature dw kaboom.again-bootsec
;
; ===========================================================================
; End of boot sector
; ===========================================================================
; Start of LDLINUX.SYS
; ===========================================================================
ldlinux_sys:
syslinux_banner db 0Dh, 0Ah
db MY_NAME, ' ', VERSION_STR, ' ', DATE_STR, ' ', 0
db 0Dh, 0Ah, 1Ah ; EOF if we "type" this in DOS
alignz 8
ldlinux_magic dd LDLINUX_MAGIC
dd LDLINUX_MAGIC^HEXDATE
;
; This area is patched by the installer. It is found by looking for
; LDLINUX_MAGIC, plus 8 bytes.
;
patch_area:
LDLDwords dw 0 ; Total dwords starting at ldlinux_sys,
; not including ADVs
LDLSectors dw 0 ; Number of sectors - (bootsec+this sec)
; but including any ADVs
CheckSum dd 0 ; Checksum starting at ldlinux_sys
; value = LDLINUX_MAGIC - [sum of dwords]
%if IS_EXTLINUX
CurrentDir dd 2 ; "Current" directory inode number
%endif
; Space for up to 64 sectors, the theoretical maximum
SectorPtrs times 64 dd 0
ldlinux_ent:
;
; Note that some BIOSes are buggy and run the boot sector at 07C0:0000
; instead of 0000:7C00 and the like. We don't want to add anything
; more to the boot sector, so it is written to not assume a fixed
; value in CS, but we don't want to deal with that anymore from now
; on.
;
jmp 0:.next
.next:
sti ; In case of broken INT 13h BIOSes
;
; Tell the user we got this far
;
mov si,syslinux_banner
call writestr_early
;
; Tell the user if we're using EBIOS or CBIOS
;
print_bios:
mov si,cbios_name
cmp byte [getlinsec.jmp+1],(getlinsec_ebios-(getlinsec.jmp+2))
jne .cbios
mov si,ebios_name
.cbios:
mov [BIOSName],si
call writestr_early
section .bss
%define HAVE_BIOSNAME 1
BIOSName resw 1
section .text
;
; Now we read the rest of LDLINUX.SYS. Don't bother loading the first
; sector again, though.
;
load_rest:
mov si,SectorPtrs
mov bx,7C00h+2*SECTOR_SIZE ; Where we start loading
mov cx,[LDLSectors]
.get_chunk:
jcxz .done
xor bp,bp
lodsd ; First sector of this chunk
mov edx,eax
.make_chunk:
inc bp
dec cx
jz .chunk_ready
inc edx ; Next linear sector
cmp [si],edx ; Does it match
jnz .chunk_ready ; If not, this is it
add si,4 ; If so, add sector to chunk
jmp short .make_chunk
.chunk_ready:
call getlinsecsr
shl bp,SECTOR_SHIFT
add bx,bp
jmp .get_chunk
.done:
;
; All loaded up, verify that we got what we needed.
; Note: the checksum field is embedded in the checksum region, so
; by the time we get to the end it should all cancel out.
;
verify_checksum:
mov si,ldlinux_sys
mov cx,[LDLDwords]
mov edx,-LDLINUX_MAGIC
.checksum:
lodsd
add edx,eax
loop .checksum
and edx,edx ; Should be zero
jz all_read ; We're cool, go for it!
;
; Uh-oh, something went bad...
;
mov si,checksumerr_msg
call writestr_early
jmp kaboom
;
; -----------------------------------------------------------------------------
; Subroutines that have to be in the first sector
; -----------------------------------------------------------------------------
;
;
; writestr_early: write a null-terminated string to the console
; This assumes we're on page 0. This is only used for early
; messages, so it should be OK.
;
writestr_early:
pushad
.loop: lodsb
and al,al
jz .return
mov ah,0Eh ; Write to screen as TTY
mov bx,0007h ; Attribute
int 10h
jmp short .loop
.return: popad
ret
;
; getlinsecsr: save registers, call getlinsec, restore registers
; Save/restore the flags, too, especially IF.
;
getlinsecsr:
pushfd
pushad
call getlinsec
popad
popfd
ret
;
; Checksum error message
;
checksumerr_msg db ' Load error - ', 0 ; Boot failed appended
;
; BIOS type string
;
cbios_name db 'CBIOS', 0
ebios_name db 'EBIOS', 0
;
; Debug routine
;
%ifdef debug
safedumpregs:
cmp word [Debug_Magic],0D00Dh
jnz nc_return
jmp dumpregs
%endif
rl_checkpt equ $ ; Must be <= 8000h
rl_checkpt_off equ ($-$$)
%ifndef DEPEND
%if rl_checkpt_off > 400h
%error "Sector 1 overflow"
%endif
%endif
; ----------------------------------------------------------------------------
; End of code and data that have to be in the first sector
; ----------------------------------------------------------------------------
all_read:
;
; Let the user (and programmer!) know we got this far. This used to be
; in Sector 1, but makes a lot more sense here.
;
mov si,copyright_str
call writestr_early
;
; Insane hack to expand the DOS superblock to dwords
;
expand_super:
xor eax,eax
mov si,superblock
mov di,SuperInfo
mov cx,superinfo_size
.loop:
lodsw
dec si
stosd ; Store expanded word
xor ah,ah
stosd ; Store expanded byte
loop .loop
;
; Fall through to the mainline code...
;
section .text
|