extlinux.asm

linux内核

; Truncate BP to MaxTransfer
;
maxtrans:
		cmp bp,[MaxTransfer]
		jna .ok
		mov bp,[MaxTransfer]
.ok:		ret

;
; Error message on failure
;
bailmsg:	db 'Boot error', 0Dh, 0Ah, 0

		; This fails if the boot sector overflows
		zb 1F8h-($-$$)

FirstSector	dd 0xDEADBEEF			; Location of sector 1
MaxTransfer	dw 0x007F			; Max transfer size
bootsignature	dw 0AA55h

;
; ===========================================================================
;  End of boot sector
; ===========================================================================
;  Start of LDLINUX.SYS
; ===========================================================================

ldlinux_sys:

syslinux_banner	db 0Dh, 0Ah
		db 'EXTLINUX '
		db version_str, ' ', date, ' ', 0
		db 0Dh, 0Ah, 1Ah	; EOF if we "type" this in DOS

		align 8, db 0
ldlinux_magic	dd LDLINUX_MAGIC
		dd LDLINUX_MAGIC^HEXDATE

;
; This area is patched by the installer.  It is found by looking for
; LDLINUX_MAGIC, plus 8 bytes.
;
patch_area:
LDLDwords	dw 0		; Total dwords starting at ldlinux_sys
LDLSectors	dw 0		; Number of sectors - (bootsec+this sec)
CheckSum	dd 0		; Checksum starting at ldlinux_sys
				; value = LDLINUX_MAGIC - [sum of dwords]
CurrentDir	dd 2		; "Current" directory inode number

; Space for up to 64 sectors, the theoretical maximum
SectorPtrs	times 64 dd 0

ldlinux_ent:
; 
; Note that some BIOSes are buggy and run 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.
;
		jmp 0:.next
.next:

;
; Tell the user we got this far
;
		mov si,syslinux_banner
		call writestr

;
; Tell the user if we're using EBIOS or CBIOS
;
print_bios:
		mov si,cbios_name
		cmp byte [getlinsec.jmp+1],(getlinsec_ebios-(getlinsec.jmp+2))
		jne .cbios
		mov si,ebios_name
.cbios:
		mov [BIOSName],si
		call writestr

		section .bss
%define	HAVE_BIOSNAME 1
BIOSName	resw 1

		section .text
;
; Now we read the rest of LDLINUX.SYS.	Don't bother loading the first
; sector again, though.
;
load_rest:
		mov si,SectorPtrs
		mov bx,7C00h+2*SECTOR_SIZE	; Where we start loading
		mov cx,[LDLSectors]

.get_chunk:
		jcxz .done
		xor bp,bp
		lodsd				; First sector of this chunk

		mov edx,eax

.make_chunk:
		inc bp
		dec cx
		jz .chunk_ready
		inc edx				; Next linear sector
		cmp [si],edx			; Does it match
		jnz .chunk_ready		; If not, this is it
		add si,4			; If so, add sector to chunk
		jmp short .make_chunk

.chunk_ready:
		call getlinsecsr
		shl bp,SECTOR_SHIFT
		add bx,bp
		jmp .get_chunk

.done:

;
; All loaded up, verify that we got what we needed.
; Note: the checksum field is embedded in the checksum region, so
; by the time we get to the end it should all cancel out.
;
verify_checksum:
		mov si,ldlinux_sys
		mov cx,[LDLDwords]
		mov edx,-LDLINUX_MAGIC
.checksum:
		lodsd
		add edx,eax
		loop .checksum

		and edx,edx			; Should be zero
		jz all_read			; We're cool, go for it!

;
; Uh-oh, something went bad...
;
		mov si,checksumerr_msg
		call writestr
		jmp kaboom

;
; -----------------------------------------------------------------------------
; Subroutines that have to be in the first sector
; -----------------------------------------------------------------------------

;
;
; writestr: write a null-terminated string to the console
;	    This assumes we're on page 0.  This is only used for early
;           messages, so it should be OK.
;
writestr:
.loop:		lodsb
		and al,al
                jz .return
		mov ah,0Eh		; Write to screen as TTY
		mov bx,0007h		; Attribute
		int 10h
		jmp short .loop
.return:	ret


; getlinsecsr: save registers, call getlinsec, restore registers
;
getlinsecsr:	pushad
		call getlinsec
		popad
		ret

;
; Checksum error message
;
checksumerr_msg	db ' Load error - ', 0	; Boot failed appended

;
; BIOS type string
;
cbios_name	db 'CBIOS', 0
ebios_name	db 'EBIOS', 0

;
; Debug routine
;
%ifdef debug
safedumpregs:
		cmp word [Debug_Magic],0D00Dh
		jnz nc_return
		jmp dumpregs
%endif

rl_checkpt	equ $				; Must be <= 8000h

rl_checkpt_off	equ ($-$$)
%ifndef DEPEND
%if rl_checkpt_off > 400h
%error "Sector 1 overflow"
%endif
%endif

; ----------------------------------------------------------------------------
;  End of code and data that have to be in the first sector
; ----------------------------------------------------------------------------

all_read:
;
; Let the user (and programmer!) know we got this far.  This used to be
; in Sector 1, but makes a lot more sense here.
;
		mov si,copyright_str
		call writestr

;
; Insane hack to expand the DOS superblock to dwords
;
expand_super:
		xor eax,eax
		mov si,superblock
		mov di,SuperInfo
		mov cx,superinfo_size
.loop:
		lodsw
		dec si
		stosd				; Store expanded word
		xor ah,ah
		stosd				; Store expanded byte
		loop .loop

;
; Load the real (ext2) superblock; 1024 bytes long at offset 1024
;
		mov bx,SuperBlock
		mov eax,1024 >> SECTOR_SHIFT
		mov bp,ax
		call getlinsec

;
; Compute some values...
;
		xor edx,edx
		inc edx

		; s_log_block_size = log2(blocksize) - 10
		mov cl,[SuperBlock+s_log_block_size]
		add cl,10
		mov [ClustByteShift],cl
		mov eax,edx
		shl eax,cl
		mov [ClustSize],eax

		sub cl,SECTOR_SHIFT
		mov [ClustShift],cl
		shr eax,SECTOR_SHIFT
		mov [SecPerClust],eax
		dec eax
		mov [ClustMask],eax

		add cl,SECTOR_SHIFT-2		; 4 bytes/pointer
		shl edx,cl
		mov [PtrsPerBlock1],edx
		shl edx,cl
		mov [PtrsPerBlock2],edx

;
; Common initialization code
;
%include "init.inc"
%include "cpuinit.inc"

;
; Initialize the metadata cache
;
		call initcache

;
; Now, everything is "up and running"... patch kaboom for more
; verbosity and using the full screen system
;
		; E9 = JMP NEAR
		mov dword [kaboom.patch],0e9h+((kaboom2-(kaboom.patch+3)) << 8)

;
; 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.  In fact, we may want to put them back if we're going
; to boot ELKS at some point.
;

;
; Load configuration file
;
load_config:
		mov di,ConfigName
		call open
		jz no_config_file

;
; Now we have the config file open.  Parse the config file and
; run the user interface.
;
%include "ui.inc"

;
; Linux kernel loading code is common.
;
%include "runkernel.inc"

;
; COMBOOT-loading code
;
%include "comboot.inc"
%include "com32.inc"
%include "cmdline.inc"

;
; Boot sector loading code
;
%include "bootsect.inc"


;
; getlinsec_ext: same as getlinsec, except load any sector from the zero
;		 block as all zeros; use to load any data derived
;		 from an ext2 block pointer, i.e. anything *except the
;		 superblock.*
;
getonesec_ext:
		mov bp,1

getlinsec_ext:
		cmp eax,[SecPerClust]
		jae getlinsec			; Nothing fancy

		; If we get here, at least part of what we want is in the
		; zero block.  Zero one sector at a time and loop.
		push eax
		push cx
		xchg di,bx
		xor eax,eax
		mov cx,SECTOR_SIZE >> 2
		rep stosd
		xchg di,bx
		pop cx
		pop eax
		inc eax
		dec bp
		jnz getlinsec_ext
		ret

;
; Abort loading code
;
%include "abort.inc"

;
; allocate_file: Allocate a file structure
;
;		If successful:
;		  ZF set
;		  BX = file pointer
;		In unsuccessful:
;		  ZF clear
;
allocate_file:
		TRACER 'a'
		push cx
		mov bx,Files
		mov cx,MAX_OPEN
.check:		cmp dword [bx], byte 0
		je .found
		add bx,open_file_t_size		; ZF = 0
		loop .check
		; ZF = 0 if we fell out of the loop
.found:		pop cx
		ret
;
; open_inode:
;	     Open a file indicated by an inode number in EAX
;
;	     NOTE: This file considers finding a zero-length file an
;	     error.  This is so we don't have to deal with that special
;	     case elsewhere in the program (most loops have the test
;	     at the end).
;
;	     If successful:
;		ZF clear
;		SI	    = file pointer
;		DX:AX = EAX = file length in bytes
;		ThisInode   = the first 128 bytes of the inode
;	     If unsuccessful
;		ZF set
;
;	     Assumes CS == DS == ES.
;
open_inode.allocate_failure:
		xor eax,eax
		pop bx
		pop di
		ret

open_inode:
		push di
		push bx
		call allocate_file
		jnz .allocate_failure

		push cx
		push gs
		; First, get the appropriate inode group and index
		dec eax				; There is no inode 0
		xor edx,edx
		mov [bx+file_sector],edx
		div dword [SuperBlock+s_inodes_per_group]
		; EAX = inode group; EDX = inode within group
		push edx

		; Now, we need the block group descriptor.
		; To get that, we first need the relevant descriptor block.
				
		shl eax, ext2_group_desc_lg2size ; Get byte offset in desc table
		xor edx,edx
		div dword [ClustSize]
		; eax = block #, edx = offset in block
		add eax,dword [SuperBlock+s_first_data_block]
		inc eax				; s_first_data_block+1
		mov cl,[ClustShift]
		shl eax,cl
		push edx
		shr edx,SECTOR_SHIFT
		add eax,edx
		pop edx
		and dx,SECTOR_SIZE-1
		call getcachesector		; Get the group descriptor
		add si,dx
		mov esi,[gs:si+bg_inode_table]	; Get inode table block #
		pop eax				; Get inode within group
		movzx edx, word [SuperBlock+s_inode_size]
		mul edx
		; edx:eax = byte offset in inode table
		div dword [ClustSize]
		; eax = block # versus inode table, edx = offset in block
		add eax,esi
		shl eax,cl			; Turn into sector
		push dx
		shr edx,SECTOR_SHIFT
		add eax,edx
		mov [bx+file_in_sec],eax
		pop dx
		and dx,SECTOR_SIZE-1
		mov [bx+file_in_off],dx

		call getcachesector
		add si,dx
		mov cx,EXT2_GOOD_OLD_INODE_SIZE >> 2
		mov di,ThisInode
		gs rep movsd

		mov ax,[ThisInode+i_mode]
		mov [bx+file_mode],ax
		mov eax,[ThisInode+i_size]
		push eax
		add eax,SECTOR_SIZE-1
		shr eax,SECTOR_SHIFT
		mov [bx+file_left],eax
		pop eax
		mov si,bx
		mov edx,eax
		shr edx,16			; 16-bitism, sigh
		and eax,eax			; ZF clear unless zero-length file
		pop gs
		pop cx
		pop bx
		pop di
		ret

		section .latebss
		alignb 4
ThisInode	resb EXT2_GOOD_OLD_INODE_SIZE	; The most recently opened inode

		section .text
;
; close:
;	     Deallocates a file structure (pointer in SI)
;	     Assumes CS == DS.
;
close:
		mov dword [si],0		; First dword == file_left
		ret

;
; searchdir:
;	     Search the root directory for a pre-mangled filename in DS:DI.
;
;	     NOTE: This file considers finding a zero-length file an
;	     error.  This is so we don't have to deal with that special
;	     case elsewhere in the program (most loops have the test
;	     at the end).
;
;	     If successful:
;		ZF clear
;		SI	    = file pointer
;		DX:AX = EAX = file length in bytes
;	     If unsuccessful
;		ZF set
;
;	     Assumes CS == DS == ES; *** IS THIS CORRECT ***?
;
searchdir:
		push bx
		push cx
		push bp
		mov byte [SymlinkCtr],MAX_SYMLINKS

		mov eax,[CurrentDir]
.begin_path:
.leadingslash:
		cmp byte [di],'/'	; Absolute filename?
		jne .gotdir
		mov eax,EXT2_ROOT_INO
		inc di			; Skip slash
		jmp .leadingslash
.gotdir:

		; At this point, EAX contains the directory inode,
		; and DS:DI contains a pathname tail.
.open:
		push eax		; Save directory inode

		call open_inode
		jz .done		; If error, done

		mov cx,[si+file_mode]
		shr cx,S_IFSHIFT	; Get file type

		cmp cx,T_IFDIR
		je .directory