ldlinux.asm

linux内核

		mov cl,[ClustShift]
		mov dx,[gs:si+20]		; High cluster word
		shl edx,16
		mov dx,[gs:si+26]		; Low cluster word
		sub edx,2
		shl edx,cl
		add edx,[DataArea]
		mov [bx],edx			; Starting sector

		mov eax,[gs:si+28]		; File length again
		mov dx,[gs:si+30]		; 16-bitism, sigh
		mov si,bx
		and eax,eax			; ZF <- 0

		pop es
		pop gs
		pop cx
		pop bx
		ret

;
; writechr:	Write a single character in AL to the console without
;		mangling any registers; handle video pages correctly.
;
writechr:
		call write_serial	; write to serial port if needed
		pushfd
		test byte [cs:DisplayCon], 01h
		jz .nothing
		pushad
		mov ah,0Eh
		mov bl,07h		; attribute
		mov bh,[cs:BIOS_page]	; current page
		int 10h
		popad
.nothing:
		popfd
		ret

;
;
; kaboom2: once everything is loaded, replace the part of kaboom
;	   starting with "kaboom.patch" with this part

kaboom2:
		mov si,err_bootfailed
		call cwritestr
		call getchar
		call vgaclearmode
		int 19h			; And try once more to boot...
.norge:		jmp short .norge	; If int 19h returned; this is the end

;
; mangle_name: Mangle a DOS filename pointed to by DS:SI into a buffer pointed
;	       to by ES:DI; ends on encountering any whitespace
;

mangle_name:
		mov cx,11			; # of bytes to write
mn_loop:
		lodsb
		cmp al,' '			; If control or space, end
		jna mn_end
		cmp al,'.'			; Period -> space-fill
		je mn_is_period
		cmp al,'a'
		jb mn_not_lower
		cmp al,'z'
		ja mn_not_uslower
		sub al,020h
		jmp short mn_not_lower
mn_is_period:	mov al,' '			; We need to space-fill
mn_period_loop: cmp cx,3			; If <= 3 characters left
		jbe mn_loop			; Just ignore it
		stosb				; Otherwise, write a period
		loop mn_period_loop		; Dec CX and (always) jump
mn_not_uslower: cmp al,ucase_low
		jb mn_not_lower
		cmp al,ucase_high
		ja mn_not_lower
		mov bx,ucase_tab-ucase_low
                cs xlatb
mn_not_lower:	stosb
		loop mn_loop			; Don't continue if too long
mn_end:
		mov al,' '			; Space-fill name
		rep stosb			; Doesn't do anything if CX=0
		ret				; Done

;
; Upper-case table for extended characters; this is technically code page 865,
; but code page 437 users will probably not miss not being able to use the
; cent sign in kernel images too much :-)
;
; The table only covers the range 129 to 164; the rest we can deal with.
;
ucase_low	equ 129
ucase_high	equ 164
ucase_tab	db 154, 144, 'A', 142, 'A', 143, 128, 'EEEIII'
		db 142, 143, 144, 146, 146, 'O', 153, 'OUUY', 153, 154
		db 157, 156, 157, 158, 159, 'AIOU', 165

;
; unmangle_name: Does the opposite of mangle_name; converts a DOS-mangled
;                filename to the conventional representation.  This is needed
;                for the BOOT_IMAGE= parameter for the kernel.
;                NOTE: A 13-byte buffer is mandatory, even if the string is
;                known to be shorter.
;
;                DS:SI -> input mangled file name
;                ES:DI -> output buffer
;
;                On return, DI points to the first byte after the output name,
;                which is set to a null byte.
;
unmangle_name:
                push si                 ; Save pointer to original name
                mov cx,8
                mov bp,di
un_copy_body:   lodsb
                call lower_case
                stosb
                cmp al,' '
                jbe un_cb_space
                mov bp,di               ; Position of last nonblank+1
un_cb_space:    loop un_copy_body
                mov di,bp
                mov al,'.'              ; Don't save
                stosb
                mov cx,3
un_copy_ext:    lodsb
                call lower_case
                stosb
                cmp al,' '
                jbe un_ce_space
                mov bp,di
un_ce_space:    loop un_copy_ext
                mov di,bp
                mov byte [es:di], 0
                pop si
                ret

;
; lower_case: Lower case a character in AL
;
lower_case:
                cmp al,'A'
                jb lc_ret
                cmp al,'Z'
                ja lc_1
                or al,20h
                ret
lc_1:           cmp al,lcase_low
                jb lc_ret
                cmp al,lcase_high
                ja lc_ret
                push bx
                mov bx,lcase_tab-lcase_low
               	cs xlatb
                pop bx
lc_ret:         ret

;
; getfssec_edx: Get multiple sectors from a file
;
;	This routine makes sure the subtransfers do not cross a 64K boundary,
;	and will correct the situation if it does, UNLESS *sectors* cross
;	64K boundaries.
;
;	ES:BX	-> Buffer
;	EDX	-> Current sector number
;	CX	-> Sector count (0FFFFh = until end of file)
;                  Must not exceed the ES segment
;	Returns EDX=0, CF=1 on EOF (not necessarily error)
;	All arguments are advanced to reflect data read.
;
getfssec_edx:
		push ebp
		push eax
.getfragment:
		xor ebp,ebp			; Fragment sector count
		push edx			; Starting sector pointer
.getseccnt:
		inc bp
		dec cx
		jz .do_read
		xor eax,eax
		mov ax,es
		shl ax,4
		add ax,bx			; Now AX = how far into 64K block we are
		not ax				; Bytes left in 64K block
		inc eax
		shr eax,SECTOR_SHIFT		; Sectors left in 64K block
		cmp bp,ax
		jnb .do_read			; Unless there is at least 1 more sector room...
		mov eax,edx			; Current sector
		inc edx				; Predict it's the linearly next sector
		call nextsector
		jc .do_read
		cmp edx,eax			; Did it match?
		jz .getseccnt
.do_read:
		pop eax				; Starting sector pointer
		call getlinsecsr
		lea eax,[eax+ebp-1]		; This is the last sector actually read
		shl bp,9
		add bx,bp			; Adjust buffer pointer
		call nextsector
		jc .eof
		mov edx,eax
		and cx,cx
		jnz .getfragment
.done:
		pop eax
		pop ebp
		ret
.eof:
		xor edx,edx
		stc
		jmp .done

;
; getfssec: Get multiple sectors from a file
;
;	Same as above, except SI is a pointer to a open_file_t
;
;	ES:BX	-> Buffer
;	DS:SI	-> Pointer to open_file_t
;	CX	-> Sector count (0FFFFh = until end of file)
;                  Must not exceed the ES segment
;	Returns CF=1 on EOF (not necessarily error)
;	All arguments are advanced to reflect data read.
;
getfssec:
		push edx
		movzx edx,cx
		cmp edx,[si+4]
		jbe .sizeok
		mov edx,[si+4]
		mov cx,dx
.sizeok:
		sub [si+4],edx
		mov edx,[si]
		call getfssec_edx
		mov [si],edx
		pop edx
		ret

;
; nextcluster: Advance a cluster pointer in EDI to the next cluster
;	       pointed at in the FAT tables.  CF=0 on return if end of file.
;
nextcluster:
		jmp strict short nextcluster_fat28	; This gets patched

nextcluster_fat12:
		push eax
		push edx
		push bx
		push cx
		push si
		mov edx,edi
		shr edi,1
		pushf			; Save the shifted-out LSB (=CF)
		add edx,edi
		mov eax,edx
		shr eax,9
		call getfatsector
		mov bx,dx
		and bx,1FFh
		mov cl,[gs:si+bx]
		inc edx
		mov eax,edx
		shr eax,9
		call getfatsector
		mov bx,dx
		and bx,1FFh
		mov ch,[gs:si+bx]
		popf
		jnc .even
		shr cx,4
.even:		and cx,0FFFh
		movzx edi,cx
		cmp di,0FF0h
		pop si
		pop cx
		pop bx
		pop edx
		pop eax
		ret

;
; FAT16 decoding routine.
;
nextcluster_fat16:
		push eax
		push si
		push bx
		mov eax,edi
		shr eax,SECTOR_SHIFT-1
		call getfatsector
		mov bx,di
		add bx,bx
		and bx,1FEh
		movzx edi,word [gs:si+bx]
		cmp di,0FFF0h
		pop bx
		pop si
		pop eax
		ret
;
; FAT28 ("FAT32") decoding routine.
;
nextcluster_fat28:
		push eax
		push si
		push bx
		mov eax,edi
		shr eax,SECTOR_SHIFT-2
		call getfatsector
		mov bx,di
		add bx,bx
		add bx,bx
		and bx,1FCh
		mov edi,dword [gs:si+bx]
		and edi,0FFFFFFFh	; 28 bits only
		cmp edi,0FFFFFF0h
		pop bx
		pop si
		pop eax
		ret

;
; nextsector:	Given a sector in EAX on input, return the next sector
;	     	of the same filesystem object, which may be the root
;              	directory or a cluster chain.  Returns  EOF.
;
;	      	Assumes CS == DS.
;
nextsector:
		push edi
		push edx
		mov edx,[DataArea]
		mov edi,eax
		sub edi,edx
		jae .isdata

		; Root directory
		inc eax
		cmp eax,edx
		cmc
		jmp .done

.isdata:
		not edi
		test edi,[ClustMask]
		jz .endcluster

		; It's not the final sector in a cluster
		inc eax
		jmp .done

.endcluster:
		push gs			; nextcluster trashes gs
		push cx
		not edi
		mov cl,[ClustShift]
		shr edi,cl
		add edi,2

		; Now EDI contains the cluster number
		call nextcluster
		cmc
		jc .exit		; There isn't anything else...

		; New cluster number now in EDI
		sub edi,2
		shl edi,cl		; CF <- 0, unless something is very wrong
		lea eax,[edi+edx]
.exit:
		pop cx
		pop gs
.done:
		pop edx
		pop edi
		ret

;
; getfatsector: Check for a particular sector (in EAX) in the FAT cache,
;		and return a pointer in GS:SI, loading it if needed.
;
;		Assumes CS == DS.
;
getfatsector:
		add eax,[FAT]		; FAT starting address
		jmp getcachesector

; -----------------------------------------------------------------------------
;  Common modules
; -----------------------------------------------------------------------------

%include "getc.inc"		; getc et al
%include "conio.inc"		; Console I/O
%include "writestr.inc"		; String output
%include "parseconfig.inc"	; High-level config file handling
%include "parsecmd.inc"		; Low-level config file handling
%include "bcopy32.inc"		; 32-bit bcopy
%include "loadhigh.inc"		; Load a file into high memory
%include "font.inc"		; VGA font stuff
%include "graphics.inc"		; VGA graphics
%include "highmem.inc"		; High memory sizing
%include "strcpy.inc"           ; strcpy()
%include "cache.inc"		; Metadata disk cache

; -----------------------------------------------------------------------------
;  Begin data section
; -----------------------------------------------------------------------------

		section .data
;
; Lower-case table for codepage 865
;
lcase_low       equ 128
lcase_high      equ 165
lcase_tab       db 135, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138
                db 139, 140, 141, 132, 134, 130, 145, 145, 147, 148, 149
                db 150, 151, 152, 148, 129, 155, 156, 155, 158, 159, 160
                db 161, 162, 163, 164, 164

copyright_str   db ' Copyright (C) 1994-', year, ' H. Peter Anvin'
		db CR, LF, 0
boot_prompt	db 'boot: ', 0
wipe_char	db BS, ' ', BS, 0
err_notfound	db 'Could not find kernel image: ',0
err_notkernel	db CR, LF, 'Invalid or corrupt kernel image.', CR, LF, 0
err_noram	db 'It appears your computer has less than '
		asciidec dosram_k
		db 'K of low ("DOS")'
		db CR, LF
		db 'RAM.  Linux needs at least this amount to boot.  If you get'
		db CR, LF
		db 'this message in error, hold down the Ctrl key while'
		db CR, LF
		db 'booting, and I will take your word for it.', CR, LF, 0
err_badcfg      db 'Unknown keyword in syslinux.cfg.', CR, LF, 0
err_noparm      db 'Missing parameter in syslinux.cfg.', CR, LF, 0
err_noinitrd    db CR, LF, 'Could not find ramdisk image: ', 0
err_nohighmem   db 'Not enough memory to load specified kernel.', CR, LF, 0
err_highload    db CR, LF, 'Kernel transfer failure.', CR, LF, 0
err_oldkernel   db 'Cannot load a ramdisk with an old kernel image.'
                db CR, LF, 0
err_notdos	db ': attempted DOS system call', CR, LF, 0
err_comlarge	db 'COMBOOT image too large.', CR, LF, 0
err_a20		db CR, LF, 'A20 gate not responding!', CR, LF, 0
err_bootfailed	db CR, LF, 'Boot failed: please change disks and press '
		db 'a key to continue.', CR, LF, 0
ready_msg	db 'Ready.', CR, LF, 0
crlfloading_msg	db CR, LF
loading_msg     db 'Loading ', 0
dotdot_msg      db '.'
dot_msg         db '.', 0
aborted_msg	db ' aborted.'			; Fall through to crlf_msg!
crlf_msg	db CR, LF
null_msg	db 0
crff_msg	db CR, FF, 0
syslinux_cfg	db 'SYSLINUXCFG'		; Mangled form
ConfigName	db 'syslinux.cfg',0		; Unmangled form
%if IS_MDSLINUX
manifest	db 'MANIFEST   '
%endif
;
; Command line options we'd like to take a look at
;
; mem= and vga= are handled as normal 32-bit integer values
initrd_cmd	db 'initrd='
initrd_cmd_len	equ 7

;
; Config file keyword table
;
%include "keywords.inc"

;
; Extensions to search for (in *forward* order).
;
exten_table:	db 'CBT',0		; COMBOOT (specific)
		db 'BSS',0		; Boot Sector (add superblock)
		db 'BS ',0		; Boot Sector 
		db 'COM',0		; COMBOOT (same as DOS)
		db 'C32',0		; COM32
exten_table_end:
		dd 0, 0			; Need 8 null bytes here

;
; Misc initialized (data) variables
;
%ifdef debug				; This code for debugging only
debug_magic	dw 0D00Dh		; Debug code sentinel
%endif

		alignb 4, db 0
BufSafe		dw trackbufsize/SECTOR_SIZE	; Clusters we can load into trackbuf
BufSafeSec	dw trackbufsize/SECTOR_SIZE	; = how many sectors?
BufSafeBytes	dw trackbufsize		; = how many bytes?
EndOfGetCBuf	dw getcbuf+trackbufsize	; = getcbuf+BufSafeBytes
%ifndef DEPEND
%if ( trackbufsize % SECTOR_SIZE ) != 0
%error trackbufsize must be a multiple of SECTOR_SIZE
%endif
%endif