section .text
org 7C00h
+;
+; 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 $
jmp short start ; 2 bytes
nop ; 1 byte
pop si
sd_nextentry: cmp byte [si],0 ; Directory high water mark
je kaboom
- mov di,ldlinux_sys
+ mov di,ldlinux_name
mov cx,11
push si
repe cmpsb
mul bx
add ax,[DataArea1]
adc dx,[DataArea2]
- mov bx,ldlinux_magic
- push bx
+ mov bx,ldlinux_sys
call getlinsec
mov si,bs_magic
- pop di
+ mov di,ldlinux_magic
mov cx,magic_len
repe cmpsb ; Make sure that the bootsector
jne kaboom ; matches LDLINUX.SYS
;
-; Some BIOSes are buggy and don't jump to 0000:7C00 but to an alias address.
-; We depend on CS == 0 later in the program, but in order to conserve space
-; we don't do this until here.
+; Done! Jump to the entry point!
+;
+ jmp ldlinux_ent
+
;
- jmp 0:ldlinux_ent
;
; writestr: write a null-terminated string to the console
;
; The "stupid patch area" gets replaced by the code
; mov bp,1 ; nop ... (BD 01 00 90 90...) when installing with
; the -s option.
-;
-; BUG ALERT: We can have up to 2^18 tracks (1024 cylinders*256 heads), but the
-; first divide only allows for 2^16-1.
-;
getlinsec:
mov si,[bsSecPerTrack]
- div si ; Convert linear to sector/track
- mov cx,dx ; Save sector
- xor dx,dx ; 32-bit track number
+ ;
+ ; Dividing by sectors to get (track,sector): we may have
+ ; up to 2^18 tracks, so we need to do this in two steps
+ ; to produce a 32-bit quotient.
+ ;
+ xchg di,ax ; DI <- LSW of LBA
+ xchg ax,dx
+ xor dx,dx ; DX:AX now == MSW of LBA
+ push dx
+ div si ; Obtain MSW of track #
+ xchg ax,di ; Save MSW of track, AX <- LSW of LBA
+ add ax,dx ; Add remainder from high word
+ pop dx ; DX <- 0, flags preserved!
+ adc dx,dx ; DX == 0, so DX <- CF ? 1 : 0
+ div si ; Obtain LSW of track #, remainder
+ xchg cx,dx ; CX <- Sector index (0-based)
+ xchg dx,di ; MSW of track #; DX:AX now == track #
div word [bsHeads] ; Convert track to head/cyl
;
; Now we have AX = cyl, DX = head, CX = sector (0-based),
gls_nonewcyl: sub cx,si ; First sector on new track
jmp short gls_nextchunk
-bailmsg db 'Boot failed!', 0Dh, 0Ah, 0
+bailmsg: db 'Boot failed', 0Dh, 0Ah, 0
-bs_checkpt equ $ ; Must be <= 1E3h
+bs_checkpt equ $ ; Must be <= 1EFh
- zb 1E3h-($-$$)
-bs_magic equ $ ; The following 32 bytes should
- ; match ldlinux_magic
-ldlinux_sys db 'LDLINUX SYS' ; Looks like this in the root dir
- db ' '
-bs_version db version_str
- db ' '
-bs_date db date
-magic_len equ $-bs_magic
+ zb 1EFh-($-$$)
+bs_magic equ $ ; From here to the magic_len equ
+ ; must match ldlinux_magic
+ldlinux_name: db 'LDLINUX SYS' ; Looks like this in the root dir
+ dd HEXDATE ; Hopefully unique between compiles
bootsignature dw 0AA55h
+magic_len equ $-bs_magic
;
; ===========================================================================
; ===========================================================================
; Start of LDLINUX.SYS
; ===========================================================================
-;
-; This "magic number" works well with the "type" command... the 0 we treat
-; as end of string, but is ignored by "type".
-;
-ldlinux_magic db 'LDLINUX'
-missing_dot db ' '
- db 'SYS ', version_str, ' ', date
-magic_eof db 0,
-crlf db 0Dh, 0Ah, 0, 01Ah
+
+ldlinux_sys:
+
+; The 1Ah is ^Z, which is an end-of-file marker if we "type" this file in DOS
+syslinux_banner db 0Dh, 0Ah, 'SYSLINUX ', version_str, ' ', date, 0
+ db 0Dh, 0Ah, 1Ah
+
+ldlinux_magic db 'LDLINUX SYS'
+ dd HEXDATE
+ dw 0AA55h
align 4
+
+;
+; Entry point. Note that some BIOSes are buggy and put 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.
+;
ldlinux_ent:
+ jmp 0:ldlinux_ent2
+ldlinux_ent2:
;
; Tell the user we got this far
;
- mov si,crlf
- call writestr
- mov byte [missing_dot],'.'
- mov si,ldlinux_magic
+ mov si,syslinux_banner
call writestr
;
; Remember, the boot sector loaded only the first cluster of LDLINUX.SYS.
call get_msg_file
jmp short fk_wrcmd
fk_nofile:
- mov si,crlf
+ mov si,crlf_msg
call writestr
fk_wrcmd:
mov si,boot_prompt
rep movsd
jmp short load_kernel
command_done:
- mov si,crlf
+ mov si,crlf_msg
call writestr
cmp di,command_line ; Did we just hit return?
je auto_boot
call writestr
pop si ; KernelCName
call writestr
- mov si,crlf
+ mov si,crlf_msg
jmp abort_load ; Ask user for clue
;
; bad_implicit: The user entered a nonvirtual kernel name, with "implicit 0"
mov si,offset cmd_line_here
call cwritestr
pop ds
- mov si,offset crlf
+ mov si,offset crlf_msg
call cwritestr
%endif
;
call writestr
mov si,InitRDCName
call writestr
- mov si,crlf
+ mov si,crlf_msg
jmp abort_load
no_high_mem: mov si,err_nohighmem ; Error routine
; Now we're as close to be done as we can be and still use our normal
; routines, print a CRLF to end the row of dots
;
- mov si,crlf
+ mov si,crlf_msg
call writestr
;
; If we're debugging, wait for a keypress so we can read any debug messages
push cs ; Set DS <- CS
pop ds
cld ; Clear direction flag
- mov si,offset crlf
+ mov si,offset crlf_msg
call writestr
mov bx,sp
add bx,byte 26
projects / platform / upstream / syslinux.git / commitdiff