ldlinux.asm

这是Linux环境下的bootsyslinux-1.31版本

; say how to check for a 186/188, so I *hope* it falls out as a 8086
; or 286 in this test.
;
; Also, provide an escape route in case it doesn't work.
;
check_escapes:
		mov ah,02h			; Check keyboard flags
		int 16h
		mov [KbdFlags],al		; Save for boot prompt check
		test al,04h			; Ctrl->skip 386 check
		jnz skip_checks
test_8086:
		pushf				; Get flags
		pop ax
		and ax,0FFFh			; Clear top 4 bits
		push ax				; Load into FLAGS
		popf
		pushf				; And load back
		pop ax
		and ax,0F000h			; Get top 4 bits
		cmp ax,0F000h			; If set -> 8086/8088
		je not_386
test_286:
		pushf				; Get flags
		pop ax
		or ax,0F000h			; Set top 4 bits
		push ax
		popf
		pushf
		pop ax
		and ax,0F000h			; Get top 4 bits
		jnz is_386			; If not clear -> 386
not_386:
		mov si,err_not386
		call writestr
		jmp kaboom
is_386:
		.386				; Now we know it's a 386
;
; Now check that there is at least 608K of low (DOS) memory
; (608K = 9800h segments)
;
		int 12h
		cmp ax,608
		jae enough_ram
		mov si,err_noram
		call writestr
		jmp kaboom
enough_ram:
skip_checks:
;
; Initialization that does not need to go into the any of the pre-load
; areas
;
                mov al,[BIOS_vidrows]
                and al,al
                jnz vidrows_is_ok
                mov al,25                       ; No vidrows in BIOS, assume 25
vidrows_is_ok:  mov [VidRows],al
                mov ah,0fh
                int 10h                         ; Read video state
                mov [TextPage],bh
                dec ah                          ; Store count-1 (same as rows)
                mov [VidCols],ah
;
; Now we're all set to start with our *real* business.	First load the
; configuration file (if any) and parse it.
;
; In previous versions I avoided using 32-bit registers because of a
; rumour some BIOSes clobbered the upper half of 32-bit registers at
; random.  I figure, though, that if there are any of those still left
; they probably won't be trying to install Linux on them...
;
; The code is still ripe with 16-bitisms, though.  Not worth the hassle
; to take'm out.
;
		mov si,linuxauto_cmd		; Default command: "linux auto"
		mov di,default_cmd
                mov cx,linuxauto_len
		rep movsb
;
; Load configuration file
;
		mov di,syslinux_cfg
		call open
		jz near no_config_file
parse_config:
		call getkeyword
                jc near end_config_file		; Config file loaded
		cmp ax,'de'			; DEfault
		je pc_default
		cmp ax,'ap'			; APpend
		je pc_append
		cmp ax,'ti'			; TImeout
		je near pc_timeout
		cmp ax,'pr'			; PRompt
		je near pc_prompt
		cmp ax,'di'			; DIsplay
		je near pc_display
		cmp ax,'la'			; LAbel
		je near pc_label
		cmp ax,'ke'			; KErnel
		je pc_kernel
                cmp ax,'im'                     ; IMplicit
                je near pc_implicit
		cmp al,'f'			; F-key
		jne parse_config
		jmp pc_fkey
pc_default:	mov di,default_cmd		; "default" command
		call getline
		mov si,auto_cmd			; add "auto"+null
                mov cx,auto_len
		rep movsb
		jmp short parse_config
pc_append:      cmp word [VKernelCtr],byte 0	; "append" command
		ja pc_append_vk
                mov di,AppendBuf
		call getline
                sub di,AppendBuf
pc_app1:        mov [AppendLen],di
                jmp short parse_config
pc_append_vk:	mov di,VKernelBuf+vk_append	; "append" command (vkernel)
		call getline
		sub di,VKernelBuf+vk_append
                cmp di,byte 2
                jne pc_app2
                cmp byte [VKernelBuf+vk_append],'-'
                jne pc_app2
                mov di,0                        ; If "append -" -> null string
pc_app2:        mov [VKernelBuf+vk_appendlen],di
		jmp short parse_config_2	
pc_kernel:	cmp word [VKernelCtr],byte 0	; "kernel" command
		je near parse_config		; (vkernel only)
		mov di,trackbuf
		push di
		call getline
		pop si
		mov di,VKernelBuf+vk_rname
		call mangle_name
		jmp short parse_config_2
pc_timeout:	call getint			; "timeout" command
		jc parse_config_2
		mov ax,0D215h			; There are approx 1.D215h
		mul bx				; clock ticks per 1/10 s
		add bx,dx
		mov [KbdTimeOut],bx
		jmp short parse_config_2
pc_display:	mov di,trackbuf
		push di
		call getline			; Get filename to display
		pop si
		mov di,MNameBuf			; Mangled name buffer
		push di
		call mangle_name		; Mangle file name
		pop di
		call searchdir			; Search for file
		jz parse_config_2		; File not found?
		call get_msg_file		; Load and display file
parse_config_2: jmp parse_config
pc_prompt:	call getint			; "prompt" command
		jc parse_config_2
		mov [ForcePrompt],bx
		jmp short parse_config_2
pc_implicit:    call getint                     ; "implicit" command
                jc parse_config_2
                mov [AllowImplicit],bx
                jmp short parse_config_2
pc_fkey:	sub ah,'1'
		jnb pc_fkey1
		mov ah,9			; F10
pc_fkey1:	xor cx,cx
		mov cl,ah
		push cx
		mov ax,1
		shl ax,cl
		or [FKeyMap], ax			; Mark that we have this loaded
		mov di,trackbuf
		push di
		call getline			; Get filename to display
		pop si
		pop di
		shl di,4			; Multiply number by 16
		add di,FKeyName
		call mangle_name		; Mangle file name
		jmp short parse_config_2
pc_label:	call commit_vk			; Commit any current vkernel
		mov di,trackbuf			; Get virtual filename
		push di
		call getline
		pop si
		mov di,VKernelBuf+vk_vname
		call mangle_name		; Mangle virtual name
		inc word [VKernelCtr]		; One more vkernel
		mov si,VKernelBuf+vk_vname 	; By default, rname == vname
		mov di,VKernelBuf+vk_rname
		mov cx,11
		rep movsb
                mov si,AppendBuf         	; Default append==global append
                mov di,VKernelBuf+vk_append
                mov cx,[AppendLen]
                mov [VKernelBuf+vk_appendlen],cx
                rep movsb
		jmp short parse_config_2
;
; commit_vk: Store the current VKernelBuf into buffer segment
;
commit_vk:
		cmp word [VKernelCtr],byte 0
		je cvk_ret			; No VKernel = return
		cmp word [VKernelCtr],byte 16	; Above limit?
		ja cvk_overflow
		mov di,[VKernelCtr]
		dec di
		shl di,12			; 4K/buffer
		mov si,VKernelBuf
		mov cx,1024			; = 4K bytes
		push es
		push word vk_seg
		pop es
		rep movsd			; Copy to buffer segment
		pop es
cvk_ret:	ret
cvk_overflow:	mov word [VKernelCtr],16	; No more than 16, please
		ret

;
; End of configuration file
;
end_config_file:
		call commit_vk			; Commit any current vkernel
no_config_file:
;
; Check whether or not we are supposed to display the boot prompt.
;
check_for_key:
		cmp word [ForcePrompt],byte 0	; Force prompt?
		jnz enter_command
		test byte [KbdFlags],5Bh	; Caps, Scroll, Shift, Alt
		jz near auto_boot		; If neither, default boot

enter_command:
		mov si,boot_prompt
		call writestr

		mov di,command_line
;
; get the very first character -- we can either time
; out, or receive a character press at this time.  Some dorky BIOSes stuff
; a return in the buffer on bootup, so wipe the keyboard buffer first.
;
clear_buffer:	mov ah,1			; Check for pending char
		int 16h
		jz get_char_time
		xor ax,ax			; Get char
		int 16h
		jmp short clear_buffer
get_char_time:	mov cx,[KbdTimeOut]
		and cx,cx
		jz get_char			; Timeout == 0 -> no timeout
		inc cx				; The first loop will happen
						; immediately as we don't
						; know the appropriate DX value
time_loop:	push cx
tick_loop:	push dx
		mov ah,1			; Check for pending keystroke
		int 16h
		jnz get_char_pop
		xor ax,ax
		int 1Ah				; Get time "of day"
		pop ax
		cmp dx,ax			; Has the timer advanced?
		je tick_loop
		pop cx
		loop time_loop			; If so, decrement counter
		jmp command_done		; Timeout!
get_char_pop:	pop eax				; Clear the stack
get_char:	xor ax,ax			; Get char
		int 16h
		and al,al
		jz func_key
		cmp al,' '			; ASCII?
		jb not_ascii
		ja enter_char
		cmp di,command_line		; Space must not be first
		je get_char
enter_char:	cmp di,max_cmd_len+command_line ; Check there's space
		jnb get_char
		stosb				; Save it
		call writechr			; Echo to screen
		jmp short get_char
not_ascii:	cmp al,0Dh			; Enter
		je command_done
		cmp al,08h			; Backspace
		jne get_char
		cmp di,command_line		; Make sure there is anything
		je get_char			; to erase
		dec di				; Unstore one character
		mov si,wipe_char		; and erase it from the screen
		call writestr
		jmp short get_char
func_key:
		push di
		cmp ah,68			; F10
		ja get_char
		sub ah,59			; F1
		jb get_char
		mov cl,ah
		shr ax,4			; Convert to x16
		mov bx,1
		shl bx,cl
		and bx,[FKeyMap]
		jz get_char			; Undefined F-key
		mov di,ax
		add di,FKeyName
		call searchdir
		jz fk_nofile
		call get_msg_file
		jmp short fk_wrcmd
fk_nofile:
		mov si,crlf
		call writestr
fk_wrcmd:
		mov si,boot_prompt
		call writestr
		pop di				; Command line write pointer
		push di
		mov byte [di],0			; Null-terminate command line
		mov si,command_line
		call writestr			; Write command line so far
		pop di
		jmp short get_char
auto_boot:
		mov si,default_cmd
		mov di,command_line
		mov cx,(max_cmd_len+4) >> 2
		rep movsd
		jmp short load_kernel
command_done:
		mov si,crlf
		call writestr
		cmp di,command_line		; Did we just hit return?
		je auto_boot
		xor al,al			; Store a final null
		stosb

load_kernel:					; Load the kernel now
;
; First we need to mangle the kernel name the way DOS would...
;
		mov si,command_line
                mov di,KernelName
                push si
                push di
		call mangle_name
		pop di
                pop si
;
; Fast-forward to first option (we start over from the beginning, since
; mangle_name doesn't necessarily return a consistent ending state.)
;
clin_non_wsp:   lodsb
                cmp al,' '
                ja clin_non_wsp
clin_is_wsp:    and al,al
                jz clin_opt_ptr
                lodsb
                cmp al,' '
                jbe clin_is_wsp
clin_opt_ptr:   dec si                          ; Point to first nonblank
                mov [CmdOptPtr],si		; Save ptr to first option
;
; Now check if it is a "virtual kernel"
;
		mov cx,[VKernelCtr]
		push ds
		push word vk_seg
		pop ds
		cmp cx,byte 0
		je not_vk
		xor si,si			; Point to first vkernel
vk_check:	pusha
		mov cx,11
		repe cmpsb			; Is this it?
		je vk_found
		popa
		add si,4096			; 4K per vkernel structure
		loop vk_check
not_vk:		pop ds
;
; Not a "virtual kernel" - check that's OK and construct the command line
;
                cmp word [AllowImplicit],byte 0
                je bad_implicit
                push es
                push si
                push di
                mov di,real_mode_seg
                mov es,di
                mov si,AppendBuf
                mov di,cmd_line_here
                mov cx,[AppendLen]
                rep movsb
                mov [CmdLinePtr],di
                pop di
                pop si
                pop es
;
; Find the kernel on disk
;
get_kernel:     mov si,KernelName
                mov di,KernelCName
                call unmangle_name              ; Get human form
                sub di,KernelCName
                mov [KernelCNameLen],di
                mov di,KernelName        	; Search on disk
                call searchdir
                jnz kernel_good
bad_kernel:     mov si,err_notfound		; Complain about missing kernel
		call writestr
                mov si,KernelCName
                call writestr
                mov si,crlf
                jmp abort_load                  ; Ask user for clue
;
; bad_implicit: The user entered a nonvirtual kernel name, with "implicit 0"
;
bad_implicit:   mov si,KernelName		; For the error message
                mov di,KernelCName
                call unmangle_name
                jmp short bad_kernel
;
; vk_found: We *are* using a "virtual kernel"
;
vk_found:	popa
		push di
		mov di,VKernelBuf
		mov cx,vk_size >> 2
		rep movsd
		push es				; Restore old DS
		pop ds
		push es
		push word real_mode_seg
		pop es
		mov di,cmd_line_here
		mov si,VKernelBuf+vk_append
		mov cx,[VKernelBuf+vk_appendlen]
		rep movsb