extlinux.asm

linux内核

		add sp,4		; Drop directory inode

		cmp cx,T_IFREG
		je .file
		cmp cx,T_IFLNK
		je .symlink

		; Otherwise, something bad...
.err:
		call close
.err_noclose:
		xor eax,eax
		xor si,si
		cwd			; DX <- 0

.done:
		and eax,eax		; Set/clear ZF
		pop bp
		pop cx
		pop bx
		ret

		;
		; It's a file.
		;
.file:
		cmp byte [di],0		; End of path?
		je .done		; If so, done
		jmp .err		; Otherwise, error

		;
		; It's a directory.
		;
.directory:
		pop dword [ThisDir]	; Remember what directory we're searching

		cmp byte [di],0		; More path?
		je .err			; If not, bad
		
.skipslash:				; Skip redundant slashes
		cmp byte [di],'/'
		jne .readdir
		inc di
		jmp .skipslash

.readdir:
		mov bx,trackbuf
		push bx
		mov cx,[SecPerClust]
		call getfssec
		pop bx
		pushf			; Save EOF flag
		push si			; Save filesystem pointer
.getent:
		cmp dword [bx+d_inode],0
		je .endblock
		
		push di
		movzx cx,byte [bx+d_name_len]
		lea si,[bx+d_name]
		repe cmpsb
		je .maybe
.nope:
		pop di

		add bx,[bx+d_rec_len]
		jmp .getent

.endblock:
		pop si
		popf
		jnc .readdir		; There is more
		jmp .err		; Otherwise badness...

.maybe:
		mov eax,[bx+d_inode]
		
		; Does this match the end of the requested filename?
		cmp byte [di],0
		je .finish
		cmp byte [di],'/'
		jne .nope

		; We found something; now we need to open the file
.finish:
		pop bx			; Adjust stack (di)
		pop si
		call close		; Close directory
		pop bx			; Adjust stack (flags)
		jmp .open

		;
		; It's a symlink.  We have to determine if it's a fast symlink
		; (data stored in the inode) or not (data stored as a regular
		; file.)  Either which way, we start from the directory
		; which we just visited if relative, or from the root directory
		; if absolute, and append any remaining part of the path.
		;
.symlink:
		dec byte [SymlinkCtr]
		jz .err			; Too many symlink references

		cmp eax,SYMLINK_SECTORS*SECTOR_SIZE
		jae .err		; Symlink too long

		; Computation for fast symlink, as defined by ext2/3 spec
		xor ecx,ecx
		cmp [ThisInode+i_file_acl],ecx
		setne cl		; ECX <- i_file_acl ? 1 : 0
		cmp [ThisInode+i_blocks],ecx
		jne .slow_symlink

		; It's a fast symlink
.fast_symlink:
		call close		; We've got all we need
		mov si,ThisInode+i_block

		push di
		mov di,SymlinkTmpBuf
		mov ecx,eax
		rep movsb
		pop si

.symlink_finish:
		cmp byte [si],0
		je .no_slash
		mov al,'/'
		stosb
.no_slash:
		mov bp,SymlinkTmpBufEnd
		call strecpy
		jc .err_noclose		; Buffer overflow

		; Now copy it to the "real" buffer; we need to have
		; two buffers so we avoid overwriting the tail on the
		; next copy
		mov si,SymlinkTmpBuf
		mov di,SymlinkBuf
		push di
		call strcpy
		pop di
		mov eax,[ThisDir]	; Resume searching previous directory
		jmp .begin_path

.slow_symlink:
		mov bx,SymlinkTmpBuf
		mov cx,SYMLINK_SECTORS
		call getfssec
		; The EOF closed the file

		mov si,di		; SI = filename tail
		mov di,SymlinkTmpBuf
		add di,ax		; AX = file length
		jmp .symlink_finish


		section .bss
		alignb	4
SymlinkBuf	resb	SYMLINK_SECTORS*SECTOR_SIZE+64
SymlinkTmpBuf	 equ	trackbuf
SymlinkTmpBufEnd equ	trackbuf+SYMLINK_SECTORS*SECTOR_SIZE+64
ThisDir		resd	1
SymlinkCtr	resb	1

		section .text
;
; mangle_name: Mangle a filename pointed to by DS:SI into a buffer pointed
;	       to by ES:DI; ends on encountering any whitespace.
;
;	       This verifies that a filename is < FILENAME_MAX characters,
;	       doesn't contain whitespace, zero-pads the output buffer,
;	       and removes redundant slashes,
;	       so "repe cmpsb" can do a compare, and the
;	       path-searching routine gets a bit of an easier job.
;
;	       FIX: we may want to support \-escapes here (and this would
;	       be the place.)
;	       
mangle_name:
		push bx
		xor ax,ax
		mov cx,FILENAME_MAX-1
		mov bx,di

.mn_loop:
		lodsb
		cmp al,' '			; If control or space, end
		jna .mn_end
		cmp al,ah			; Repeated slash?
		je .mn_skip
		xor ah,ah
		cmp al,'/'
		jne .mn_ok
		mov ah,al
.mn_ok		stosb
.mn_skip:	loop .mn_loop
.mn_end:
		cmp bx,di			; At the beginning of the buffer?
		jbe .mn_zero
		cmp byte [di-1],'/'		; Terminal slash?
		jne .mn_zero
.mn_kill:	dec di				; If so, remove it
		inc cx
		jmp short .mn_end
.mn_zero:
		inc cx				; At least one null byte
		xor ax,ax			; Zero-fill name
		rep stosb
		pop bx
		ret				; Done

;
; 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:	call strcpy
		dec di				; Point to final null byte
		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


;
; linsector:	Convert a linear sector index in a file to a linear sector number
;	EAX	-> linear sector number
;	DS:SI	-> open_file_t
;
;		Returns next sector number in EAX; CF on EOF (not an error!)
;
linsector:
		push gs
		push ebx
		push esi
		push edi
		push ecx
		push edx
		push ebp

		push eax		; Save sector index
		mov cl,[ClustShift]
		shr eax,cl		; Convert to block number
		push eax
		mov eax,[si+file_in_sec]
		mov bx,si
		call getcachesector	; Get inode
		add si,[bx+file_in_off]	; Get *our* inode
		pop eax
		lea ebx,[i_block+4*eax]
		cmp eax,EXT2_NDIR_BLOCKS
		jb .direct
		mov ebx,i_block+4*EXT2_IND_BLOCK
		sub eax,EXT2_NDIR_BLOCKS
		mov ebp,[PtrsPerBlock1]
		cmp eax,ebp
		jb .ind1
		mov ebx,i_block+4*EXT2_DIND_BLOCK
		sub eax,ebp
		mov ebp,[PtrsPerBlock2]
		cmp eax,ebp
		jb .ind2
		mov ebx,i_block+4*EXT2_TIND_BLOCK
		sub eax,ebp

.ind3:
		; Triple indirect; eax contains the block no
		; with respect to the start of the tind area;
		; ebx contains the pointer to the tind block.
		xor edx,edx
		div dword [PtrsPerBlock2]
		; EAX = which dind block, EDX = pointer within dind block
		push ax
		shr eax,SECTOR_SHIFT-2
		mov ebp,[gs:si+bx]
		shl ebp,cl
		add eax,ebp
		call getcachesector
		pop bx
		and bx,(SECTOR_SIZE >> 2)-1
		shl bx,2
		mov eax,edx		; The ind2 code wants the remainder...

.ind2:
		; Double indirect; eax contains the block no
		; with respect to the start of the dind area;
		; ebx contains the pointer to the dind block.
		xor edx,edx
		div dword [PtrsPerBlock1]
		; EAX = which ind block, EDX = pointer within ind block
		push ax
		shr eax,SECTOR_SHIFT-2
		mov ebp,[gs:si+bx]
		shl ebp,cl
		add eax,ebp
		call getcachesector
		pop bx
		and bx,(SECTOR_SIZE >> 2)-1
		shl bx,2
		mov eax,edx		; The int1 code wants the remainder...

.ind1:
		; Single indirect; eax contains the block no
		; with respect to the start of the ind area;
		; ebx contains the pointer to the ind block.
		push ax
		shr eax,SECTOR_SHIFT-2
		mov ebp,[gs:si+bx]
		shl ebp,cl
		add eax,ebp
		call getcachesector
		pop bx
		and bx,(SECTOR_SIZE >> 2)-1
		shl bx,2

.direct:
		mov ebx,[gs:bx+si]	; Get the pointer

		pop eax			; Get the sector index again
		shl ebx,cl		; Convert block number to sector
		and eax,[ClustMask]	; Add offset within block
		add eax,ebx

		pop ebp
		pop edx
		pop ecx
		pop edi
		pop esi
		pop ebx
		pop gs
		ret

;
; 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 ebp
		push eax
		push edx
		push edi

		movzx ecx,cx
		cmp ecx,[si]			; Number of sectors left
		jbe .lenok
		mov cx,[si]
.lenok:
.getfragment:
		mov eax,[si+file_sector]	; Current start index
		mov edi,eax
		call linsector
		push eax			; Fragment start sector
		mov edx,eax
		xor ebp,ebp			; Fragment sector count
.getseccnt:
		inc bp
		dec cx
		jz .do_read
		xor eax,eax
		mov ax,es
		shl ax,4
		add ax,bx			; Now DI = 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...
		inc edi				; Sector index
		inc edx				; Linearly next sector
		mov eax,edi
		call linsector
		; jc .do_read
		cmp edx,eax
		je .getseccnt
.do_read:
		pop eax				; Linear start sector
		pushad
		call getlinsec_ext
		popad
		push bp
		shl bp,9
		add bx,bp			; Adjust buffer pointer
		pop bp
		add [si+file_sector],ebp	; Next sector index
		sub [si],ebp			; Sectors consumed
		jcxz .done
		jnz .getfragment
		; Fall through
.done:
		cmp dword [si],1		; Did we run out of file?
		; CF set if [SI] < 1, i.e. == 0
		pop edi
		pop edx
		pop eax
		pop ebp
		ret

; -----------------------------------------------------------------------------
;  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 "strecpy.inc"          ; strcpy with end pointer check
%include "cache.inc"

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

		section .data
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 extlinux.conf.', CR, LF, 0
err_noparm      db 'Missing parameter in extlinux.conf.', 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_bssimage	db 'BSS images not supported.', 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
ConfigName	db 'extlinux.conf',0		; Unmangled form

;
; 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).
;
		align 4, db 0
exten_table:	db '.cbt'		; COMBOOT (specific)
		db '.img'		; Disk image
		db '.bs', 0		; Boot sector
		db '.com'		; COMBOOT (same as DOS)
		db '.c32'		; 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