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/* chain.S - LILO boot chainer */
/* Copyright 1992-1998 Werner Almesberger. See file COPYING for details. */
#define LILO_ASM
#include "lilo.h"
.text
.globl _main
.org 0
_main: jmp start
.org 6
.ascii "LILO"
.word STAGE_CHAIN
.word VERSION
offset: .word 0
drive: .byte 0
.byte 0 ! head, always zero
hint: .word drvmap ! pointer to drive map
ptable: .blkw 0x20 ! partition table to preload
start: cli ! set SS:SP to 0:7C00
xor ax,ax
mov ss,ax
mov ax,#0x7c00
mov sp,ax
sti
mov ax,#SETUPSEG ! move boot sector to default location
mov ds,ax
xor ax,ax
mov es,ax
mov cx,#256
mtmp = SETUPSECS-1 ! broken math ...
mov si,#mtmp*512
mov di,#BOOTSEG*16
rep
movsw
#ifdef DOS_D
dos4: seg es
mov byte ptr BOOTSEG*16+0x24,#0x81
#endif
mov cx,#0x20 ! move partition table
mov si,#ptable
mov di,#PART_TABLE
rep
movsw
! mess with the partition table
#if defined(LCF_REWRITE_TABLE) || defined(LCF_READONLY)
mov si,#prtmap ! get partition table change rules
prtclp: lodsw ! bios == 0 indicates end
or al,al
jz pmend ! at end -> quit
cmp al,cache ! already in cache ?
je incache ! yes -> no loading required
push ax ! save table data
call flush ! flush the cache
pop ax
push ax
mov cache,al ! remember drive in cache
cmp al,drive ! boot drive ?
jne noc ! no -> load into scratch area
xor ax,ax ! load at 0000:0600
mov bx,#PARTS_LOAD
jmp loadit
noc: mov ax,ds
mov bx,#PARTS_SCR ! scratch area
loadit: mov es,ax ! set up pointers and remember them
mov ces,ax
mov cbx,bx
mov ax,#0x201 ! load partition table, one sector
mov dx,cache ! drive from cache (DH = 0)
mov cx,#1
int 0x13 ! load it
jc wrfail ! error -> abort
pop ax ! get BIOS and offset
incache:les bx,cbx ! load pointer
add bx,#PART_TABLE_OFFSET ! move to partition table
add bl,ah ! offset is always in [0x1be,0x1fd]
lodsw ! see what we need to do
seg es ! match ?
cmp byte ptr (bx),al
jne nocng ! no -> do not change
seg es ! change
mov byte ptr (bx),ah
mov byte ptr dirty,#1 ! mark as dirty
nocng: br prtclp ! next one
flush: test byte ptr dirty,#1 ! dirty ?
jz noflush ! no -> do not write
mov ax,#0x301 ! write one sector
mov dx,cache ! get the drive
or dl,dl ! nothing cached ?
jz noflush ! no -> do not flush
les bx,cbx ! reload pointer
int 0x13 ! write ...
jc wrfail ! argl
noflush:ret
pmend: call flush ! flush table
br nopp ! and proceed
wrfail: mov si,#failmsg ! complain
call say
mov ax,#FIRSTSEG ! try to restart LILO
jmpi #GO,FIRSTSEG
cache: .byte 0 ! drive, 0 means not cached
.byte 0 ! head, always 0
cbx: .blkw 1
ces: .blkw 1
dirty: .byte 0
#endif
nopp:
mov ax,drvmap ! need to install mapper ?
or ax,ax
jz noimap ! no -> go on
call swap13
noimap:
mov si,offset ! DS:SI and ES:SI point to the partition
add si,#PART_TABLE
mov dx,drive ! initialize DX (drive and head)
xor ax,ax ! set DS and ES to zero
#ifdef XXX
mov ax,ds
mov es,ax
mov si,#lilosig
mov bx,#cmd
mov dl,#0xfe
#else
mov ds,ax
mov es,ax
#endif
mov bp,#0 ! might help some boot problems
mov ax,#0xaa55 ! boot signature (just in case ...)
jmpi #BOOTSEG*16,0 ! start boot sector
#ifdef XXX
lilosig:.ascii "LILO"
cmd: .ascii "98"
.byte 0
#endif
#if defined(LCF_REWRITE_TABLE)
! Display a NUL-terminated string on the console
say: lodsb ! get byte
or al,al ! NUL ?
jz aret ! yes -> done
mov ah,#14 ! display, tty-style
xor bh,bh
int 0x10
jmp say ! next one
aret: ret ! done
failmsg:.ascii "Rewrite error."
.byte 13,10,0
#endif
swap13: seg es ! allocate 1 kB
dec word ptr [0x413]
int 0x12 ! get start segment
mov cl,#6
shl ax,cl
cli ! disable interrupts
xor bx,bx ! zero a few registers
mov di,bx
seg es ! change offset
xchg bx,[0x4c]
mov old13of,bx
mov bx,ax ! change segment
seg es
xchg bx,[0x4e]
mov old13sg,bx
mov es,ax ! move drive swapper
mov si,#new13
mov cx,#new13end-new13
rep
movsb
sti ! enable interrupts
ret ! done
new13: push ax ! save AX (contains function code in AH)
push bp ! need BP to mess with stack
mov bp,sp
! Stack layout:
!
! +8 INT flags
! +6 INT CS
! +4 INT IP
! +2 AX
! BP+0 BP
pushf ! push flags (to act like interrupt)
push si
mov si,#drvmap-new13
mapfl: seg cs ! get next entry
lodsw
or ax,ax ! at end ?
jz nomap ! yes -> do not map
cmp dl,al ! match ?
jne mapfl ! no -> continue
mov dl,ah ! map drive
nomap: pop si ! restore SI
mov 8(bp),ax ! overwrite old flags (to remember mapping)
mov ax,2(bp) ! restore AX
mov bp,(bp) ! restore BP
.byte 0x9a ! CALL FAR
old13of:.word 0
old13sg:.word 0
push bp ! save BP again
mov bp,sp
! New stack layout:
!
! +10 mapping (was flags)
! +8 INT CS
! +6 INT IP
! +4 AX
! +2 obsolete BP
! BP+0 BP
xchg ax,4(bp) ! save AX and get command
pushf ! fix driver number, if necessary
cmp ah,#8 ! do not fix
je done13
cmp ah,#0x15 ! do not fix
je done13
mov ax,10(bp) ! no mapping ?
or ax,ax
jz done13
mov dl,al ! fix mapping
done13: mov ax,4(bp) ! restore AX
pop 10(bp) ! restore flags
pop bp ! get BP
add sp,#4 ! fix SP
iret ! done
drvmap: .blkw DRVMAP_SIZE+1
new13end:
#if defined(LCF_REWRITE_TABLE)
prtmap: .blkw PRTMAP_SIZE*2+1 ! only first word of last entry is read
#endif
theend:
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