isolinux.asm

Windows上的精简Linux系统

; -*- fundamental -*- (asm-mode sucks)
; $Id: isolinux.asm,v 1.95 2004/05/29 22:11:23 hpa Exp $
; ****************************************************************************
;
;  isolinux.asm
;
;  A program to boot Linux kernels off a CD-ROM using the El Torito
;  boot standard in "no emulation" mode, making the entire filesystem
;  available.  It is based on the SYSLINUX boot loader for MS-DOS
;  floppies.
;
;   Copyright (C) 1994-2004  H. Peter Anvin
;
;  This program is free software; you can redistribute it and/or modify
;  it under the terms of the GNU General Public License as published by
;  the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
;  USA; either version 2 of the License, or (at your option) any later
;  version; incorporated herein by reference.
; 
; ****************************************************************************

%define IS_ISOLINUX 1
%include "macros.inc"
%include "config.inc"
%include "kernel.inc"
%include "bios.inc"
%include "tracers.inc"

;
; Some semi-configurable constants... change on your own risk.
;
my_id		equ isolinux_id
FILENAME_MAX_LG2 equ 8			; log2(Max filename size Including final null)
FILENAME_MAX	equ (1 << FILENAME_MAX_LG2)
NULLFILE	equ 0			; Zero byte == null file name
retry_count	equ 6			; How patient are we with the BIOS?
%assign HIGHMEM_SLOP 128*1024		; Avoid this much memory near the top
MAX_OPEN_LG2	equ 6			; log2(Max number of open files)
MAX_OPEN	equ (1 << MAX_OPEN_LG2)
SECTORSIZE_LG2	equ 11			; 2048 bytes/sector (El Torito requirement)
SECTORSIZE	equ (1 << SECTORSIZE_LG2)

;
; This is what we need to do when idle
;
%macro	RESET_IDLE 0
	; Nothing
%endmacro
%macro	DO_IDLE 0
	; Nothing
%endmacro

;
; The following structure is used for "virtual kernels"; i.e. LILO-style
; option labels.  The options we permit here are `kernel' and `append
; Since there is no room in the bottom 64K for all of these, we
; stick them at vk_seg:0000 and copy them down before we need them.
;
; Note: this structure can be added to, but it must 
;
%define vk_power	6		; log2(max number of vkernels)
%define	max_vk		(1 << vk_power)	; Maximum number of vkernels
%define vk_shift	(16-vk_power)	; Number of bits to shift
%define vk_size		(1 << vk_shift)	; Size of a vkernel buffer

		struc vkernel
vk_vname:	resb FILENAME_MAX	; Virtual name **MUST BE FIRST!**
vk_rname:	resb FILENAME_MAX	; Real name
vk_appendlen:	resw 1
		alignb 4
vk_append:	resb max_cmd_len+1	; Command line
		alignb 4
vk_end:		equ $			; Should be <= vk_size
		endstruc

%ifndef DEPEND
%if (vk_end > vk_size) || (vk_size*max_vk > 65536)
%error "Too many vkernels defined, reduce vk_power"
%endif
%endif

;
; Segment assignments in the bottom 640K
; 0000h - main code/data segment (and BIOS segment)
;
real_mode_seg	equ 3000h
vk_seg          equ 2000h		; Virtual kernels
xfer_buf_seg	equ 1000h		; Bounce buffer for I/O to high mem
comboot_seg	equ real_mode_seg	; COMBOOT image loading zone

;
; File structure.  This holds the information for each currently open file.
;
		struc open_file_t
file_sector	resd 1			; Sector pointer (0 = structure free)
file_left	resd 1			; Number of sectors left
		endstruc

%ifndef DEPEND
%if (open_file_t_size & (open_file_t_size-1))
%error "open_file_t is not a power of 2"
%endif
%endif

; ---------------------------------------------------------------------------
;   BEGIN CODE
; ---------------------------------------------------------------------------

;
; Memory below this point is reserved for the BIOS and the MBR
;
 		absolute 1000h
trackbuf	resb 8192		; Track buffer goes here
trackbufsize	equ $-trackbuf
;		trackbuf ends at 3000h


;
; Constants for the xfer_buf_seg
;
; The xfer_buf_seg is also used to store message file buffers.  We
; need two trackbuffers (text and graphics), plus a work buffer
; for the graphics decompressor.
;
xbs_textbuf	equ 0			; Also hard-coded, do not change
xbs_vgabuf	equ trackbufsize
xbs_vgatmpbuf	equ 2*trackbufsize

		struc dir_t
dir_lba		resd 1			; Directory start (LBA)
dir_len		resd 1			; Length in bytes
dir_clust	resd 1			; Length in clusters
		endstruc

                absolute 5000h          ; Here we keep our BSS stuff
VKernelBuf:	resb vk_size		; "Current" vkernel
		alignb 4
AppendBuf       resb max_cmd_len+1	; append=
Ontimeout	resb max_cmd_len+1	; ontimeout
Onerror		resb max_cmd_len+1	; onerror
KbdMap		resb 256		; Keyboard map
FKeyName	resb 10*FILENAME_MAX	; File names for F-key help
NumBuf		resb 15			; Buffer to load number
NumBufEnd	resb 1			; Last byte in NumBuf
ISOFileName	resb 64			; ISO filename canonicalization buffer
ISOFileNameEnd	equ $
		alignb 32
KernelName      resb FILENAME_MAX       ; Mangled name for kernel
KernelCName     resb FILENAME_MAX	; Unmangled kernel name
InitRDCName     resb FILENAME_MAX       ; Unmangled initrd name
MNameBuf	resb FILENAME_MAX
InitRD		resb FILENAME_MAX
PartInfo	resb 16			; Partition table entry
E820Buf		resd 5			; INT 15:E820 data buffer
E820Mem		resd 1			; Memory detected by E820
E820Max		resd 1			; Is E820 memory capped?
HiLoadAddr      resd 1			; Address pointer for high load loop
HighMemSize	resd 1			; End of memory pointer (bytes)
RamdiskMax	resd 1			; Highest address for a ramdisk
KernelSize	resd 1			; Size of kernel (bytes)
SavedSSSP	resd 1			; Our SS:SP while running a COMBOOT image
PMESP		resd 1			; Protected-mode ESP
RootDir		resb dir_t_size		; Root directory
CurDir		resb dir_t_size		; Current directory
KernelClust	resd 1			; Kernel size in clusters
InitStack	resd 1			; Initial stack pointer (SS:SP)
FirstSecSum	resd 1			; Checksum of bytes 64-2048
ImageDwords	resd 1			; isolinux.bin size, dwords
FBytes		equ $			; Used by open/getc
FBytes1		resw 1
FBytes2		resw 1
FClust		resw 1			; Number of clusters in open/getc file
FNextClust	resw 1			; Pointer to next cluster in d:o
FPtr		resw 1			; Pointer to next char in buffer
CmdOptPtr       resw 1			; Pointer to first option on cmd line
KernelCNameLen  resw 1			; Length of unmangled kernel name
InitRDCNameLen  resw 1			; Length of unmangled initrd name
NextCharJump    resw 1			; Routine to interpret next print char
SetupSecs	resw 1			; Number of setup sectors
A20Test		resw 1			; Counter for testing status of A20
A20Type		resw 1			; A20 type
CmdLineLen	resw 1			; Length of command line including null
GraphXSize	resw 1			; Width of splash screen file
VGAPos		resw 1			; Pointer into VGA memory
VGACluster	resw 1			; Cluster pointer for VGA image file
VGAFilePtr	resw 1			; Pointer into VGAFileBuf
Com32SysSP	resw 1			; SP saved during COM32 syscall
ConfigFile	resw 1			; Socket for config file
PktTimeout	resw 1			; Timeout for current packet
KernelExtPtr	resw 1			; During search, final null pointer
LocalBootType	resw 1			; Local boot return code
ImageSectors	resw 1			; isolinux.bin size, sectors
DiskSys		resw 1			; Last INT 13h call
CursorDX        equ $
CursorCol       resb 1			; Cursor column for message file
CursorRow       resb 1			; Cursor row for message file
ScreenSize      equ $
VidCols         resb 1			; Columns on screen-1
VidRows         resb 1			; Rows on screen-1
BaudDivisor	resw 1			; Baud rate divisor
FlowControl	equ $
FlowOutput	resb 1			; Outputs to assert for serial flow
FlowInput	resb 1			; Input bits for serial flow
FlowIgnore	resb 1			; Ignore input unless these bits set
TextAttribute   resb 1			; Text attribute for message file
RetryCount      resb 1			; Used for disk access retries
KbdFlags	resb 1			; Check for keyboard escapes
LoadFlags	resb 1			; Loadflags from kernel
A20Tries	resb 1			; Times until giving up on A20
FuncFlag	resb 1			; == 1 if <Ctrl-F> pressed
DisplayMask	resb 1			; Display modes mask
ISOFlags	resb 1			; Flags for ISO directory search
DiskError	resb 1			; Error code for disk I/O
DriveNo		resb 1			; CD-ROM BIOS drive number
TextColorReg	resb 17			; VGA color registers for text mode
VGAFileBuf	resb FILENAME_MAX	; Unmangled VGA image name
VGAFileBufEnd	equ $
VGAFileMBuf	resb FILENAME_MAX	; Mangled VGA image name

		alignb open_file_t_size
Files		resb MAX_OPEN*open_file_t_size

		section .text
                org 7C00h
;;
;; Primary entry point.  Because BIOSes are buggy, we only load the first
;; CD-ROM sector (2K) of the file, so the number one priority is actually
;; loading the rest.
;;
bootsec		equ $

StackBuf	equ $-44

_start:		; Far jump makes sure we canonicalize the address
		cli
		jmp 0:_start1
		times 8-($-$$) nop		; Pad to file offset 8

		; This table gets filled in by mkisofs using the
		; -boot-info-table option
bi_pvd:		dd 0xdeadbeef			; LBA of primary volume descriptor
bi_file:	dd 0xdeadbeef			; LBA of boot file
bi_length:	dd 0xdeadbeef			; Length of boot file
bi_csum:	dd 0xdeadbeef			; Checksum of boot file
bi_reserved:	times 10 dd 0xdeadbeef		; Reserved

_start1:	mov [cs:InitStack],sp		; Save initial stack pointer
		mov [cs:InitStack+2],ss
		xor ax,ax
		mov ss,ax
		mov sp,StackBuf			; Set up stack
		mov ds,ax
		mov es,ax
		mov fs,ax
		mov gs,ax
		sti

		cld
		; Show signs of life
		mov si,syslinux_banner
		call writestr
%ifdef DEBUG_MESSAGES
		mov si,copyright_str
		call writestr
%endif

		;
		; Before modifying any memory, get the checksum of bytes
		; 64-2048
		;
initial_csum:	xor edi,edi
		mov si,_start1
		mov cx,(SECTORSIZE-64) >> 2
.loop:		lodsd
		add edi,eax
		loop .loop
		mov [FirstSecSum],edi

		; Set up boot file sizes
		mov eax,[bi_length]
		sub eax,SECTORSIZE-3
		shr eax,2			; bytes->dwords
		mov [ImageDwords],eax		; boot file dwords
		add eax,(2047 >> 2)
		shr eax,9			; dwords->sectors
		mov [ImageSectors],ax		; boot file sectors

		mov [DriveNo],dl
%ifdef DEBUG_MESSAGES
		mov si,startup_msg
		call writemsg
		mov al,dl
		call writehex2
		call crlf
%endif

		; Now figure out what we're actually doing
		; Note: use passed-in DL value rather than 7Fh because
		; at least some BIOSes will get the wrong value otherwise
		mov ax,4B01h			; Get disk emulation status
		mov dl,[DriveNo]
		mov si,spec_packet
		int 13h
		jc award_hack			; changed for BrokenAwardHack
		mov dl,[DriveNo]
		cmp [sp_drive],dl		; Should contain the drive number
		jne spec_query_failed

%ifdef DEBUG_MESSAGES
		mov si,spec_ok_msg
		call writemsg
		mov al,byte [sp_drive]
		call writehex2
		call crlf
%endif

found_drive:
		; Some BIOSes apparently have limitations on the size 
		; that may be loaded (despite the El Torito spec being very
		; clear on the fact that it must all be loaded.)  Therefore,
		; we load it ourselves, and *bleep* the BIOS.

		mov eax,[bi_file]		; Address of code to load
		inc eax				; Don't reload bootstrap code
%ifdef DEBUG_MESSAGES
		mov si,offset_msg
		call writemsg
		call writehex8
		call crlf
%endif

		; Just in case some BIOSes have problems with
		; segment wraparound, use the normalized address
		mov bx,((7C00h+2048) >> 4)
		mov es,bx
		xor bx,bx
		mov bp,[ImageSectors]
%ifdef DEBUG_MESSAGES
		push ax
		mov si,size_msg
		call writemsg
		mov ax,bp
		call writehex4
		call crlf
		pop ax
%endif
		call getlinsec

		push ds
		pop es

%ifdef DEBUG_MESSAGES
		mov si,loaded_msg
		call writemsg
%endif

		; Verify the checksum on the loaded image.
verify_image:
		mov si,7C00h+2048
		mov bx,es
		mov ecx,[ImageDwords]
		mov edi,[FirstSecSum]		; First sector checksum
.loop		es lodsd
		add edi,eax
		dec ecx
		jz .done
		and si,si
		jnz .loop
		; SI wrapped around, advance ES
		add bx,1000h
		mov es,bx
		jmp short .loop
.done:		mov ax,ds
		mov es,ax
		cmp [bi_csum],edi
		je integrity_ok

		mov si,checkerr_msg
		call writemsg
		jmp kaboom

integrity_ok:
%ifdef DEBUG_MESSAGES
		mov si,allread_msg
		call writemsg
%endif
		jmp all_read			; Jump to main code

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Start of BrokenAwardHack --- 10-nov-2002           [e-mail]
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; There is a problem with certain versions of the AWARD BIOS ... 
;; the boot sector will be loaded and executed correctly, but, because the
;; int 13 vector points to the wrong code in the BIOS, every attempt to
;; load the spec packet will fail. We scan for the equivalent of
;;
;;	mov	ax,0201h
;;	mov	bx,7c00h
;;	mov	cx,0006h
;;	mov	dx,0180h
;;	pushf
;;	call	<direct far>
;;
;; and use <direct far> as the new vector for int 13. The code above is
;; used to load the boot code into ram, and there should be no reason
;; for anybody to change it now or in the future. There are no opcodes
;; that use encodings relativ to IP, so scanning is easy. If we find the
;; code above in the BIOS code we can be pretty sure to run on a machine
;; with an broken AWARD BIOS ... 
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
									     ;;
%ifdef DEBUG_MESSAGES							     ;;
									     ;;
award_notice	db	"Trying BrokenAwardHack first ...",CR,LF,0	     ;;
award_not_orig	db	"BAH: Original Int 13 vector   : ",0		     ;;
award_not_new	db	"BAH: Int 13 vector changed to : ",0		     ;;
award_not_succ	db	"BAH: SUCCESS",CR,LF,0				     ;;
award_not_fail	db	"BAH: FAILURE"					     ;;
award_not_crlf	db	CR,LF,0						     ;;
									     ;;
%endif									     ;;
									     ;;
award_oldint13	dd	0						     ;;
award_string	db	0b8h,1,2,0bbh,0,7ch,0b9h,6,0,0bah,80h,1,09ch,09ah    ;;
									     ;;
						;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
award_hack:	mov 	si,spec_err_msg		; Moved to this place from
		call 	writemsg		; spec_query_faild
						;
%ifdef DEBUG_MESSAGES				;
						;
		mov	si,award_notice		; display our plan
		call	writemsg		;
		mov	si,award_not_orig	; display original int 13
		call	writemsg		; vector
%endif						;
		mov	eax,[13h*4]		;
		mov	[award_oldint13],eax	;
						;
%ifdef DEBUG_MESSAGES				;
						;
		call	writehex8		;
		mov	si,award_not_crlf	; 
		call	writestr		;
%endif						;
		push	es			; save ES
		mov 	ax,0f000h		; ES = BIOS Seg
		mov 	es,ax			;
	    	cld				;
		xor 	di,di			; start at ES:DI = f000:0