runkernel.inc

linux内核

		mov fs,ax

;
; Copy command line.  Unfortunately, the kernel boot protocol requires
; the command line to exist in the 9xxxxh range even if the rest of the
; setup doesn't.
;
		cli				; In case of hooked interrupts
		test byte [LoadFlags],LOAD_HIGH
		jz need_high_cmdline
		cmp word [fs:su_version],0202h	; Support new cmdline protocol?
		jb need_high_cmdline
		; New cmdline protocol
		; Store 32-bit (flat) pointer to command line
		mov dword [fs:su_cmd_line_ptr],(real_mode_seg << 4) + cmd_line_here
		jmp short in_proper_place

need_high_cmdline:
;
; Copy command line up to 90000h
;
		mov ax,9000h			; Note AL <- 0
		mov es,ax
		mov si,cmd_line_here
		mov di,si
		mov [fs:kern_cmd_magic],word CMD_MAGIC ; Store magic
		mov [fs:kern_cmd_offset],di	; Store pointer

		mov cx,[CmdLineLen]
		cmp cx,255
		jna .len_ok
		mov cx,255			; Protocol < 0x202 has 255 as hard limit
.len_ok:
		fs rep movsb
		stosb				; Final null, note AL == 0 already

		push fs
		pop es

		test byte [LoadFlags],LOAD_HIGH
		jnz in_proper_place		; If high load, we're done

;
; Loading low; we can't assume it's safe to run in place.
;
; Copy real_mode stuff up to 90000h
;
		mov ax,9000h
		mov es,ax
		mov cx,[SetupSecs]
		inc cx				; Setup + boot sector
		shl cx,7			; Sectors -> dwords
		xor si,si
		xor di,di
		fs rep movsd			; Copy setup + boot sector
;
; Some kernels in the 1.2 ballpark but pre-bzImage have more than 4
; setup sectors, but the boot protocol had not yet been defined.  They
; rely on a signature to figure out if they need to copy stuff from
; the "protected mode" kernel area.  Unfortunately, we used that area
; as a transfer buffer, so it's going to find the signature there.
; Hence, zero the low 32K beyond the setup area.
;
		mov di,[SetupSecs]
		inc di				; Setup + boot sector
		mov cx,32768/512		; Sectors/32K
		sub cx,di			; Remaining sectors
		shl di,9			; Sectors -> bytes
		shl cx,7			; Sectors -> dwords
		xor eax,eax
		rep stosd			; Clear region
;
; Copy the kernel down to the "low" location
;
		mov ecx,[KernelSize]
		mov esi,100000h
		mov edi,10000h
		call bcopy

;
; Now everything is where it needs to be...
;
; When we get here, es points to the final segment, either
; 9000h or real_mode_seg
;
in_proper_place:

;
; If the default root device is set to FLOPPY (0000h), change to
; /dev/fd0 (0200h)
;
		cmp word [es:bs_rootdev],byte 0
		jne root_not_floppy
		mov word [es:bs_rootdev],0200h
root_not_floppy:

;
; Copy the disk table to high memory, then re-initialize the floppy
; controller
;
%if IS_SYSLINUX || IS_MDSLINUX
		lgs si,[cs:fdctab]
		mov di,linux_fdctab
		mov cx,6			; 12 bytes
		gs rep movsw
		mov [cs:fdctab],word linux_fdctab ; Save new floppy tab pos
		mov [cs:fdctab+2],es
%endif
;
; Linux wants the floppy motor shut off before starting the kernel,
; at least bootsect.S seems to imply so.
;
kill_motor:
		xor ax,ax
		xor dx,dx
		int 13h

;
; If we're debugging, wait for a keypress so we can read any debug messages
;
%ifdef debug
                xor ax,ax
                int 16h
%endif
;
; Set up segment registers and the Linux real-mode stack
; Note: es == the real mode segment
;
		cli
		mov bx,es
		mov ds,bx
		mov fs,bx
		mov gs,bx
		mov ss,bx
		mov sp,linux_stack
;
; We're done... now RUN THAT KERNEL!!!!
; Setup segment == real mode segment + 020h; we need to jump to offset
; zero in the real mode segment.
;
		add bx,020h
		push bx
		push word 0h
		retf

;
; Load an older kernel.  Older kernels always have 4 setup sectors, can't have
; initrd, and are always loaded low.
;
old_kernel:
               	cmp word [InitRDPtr],0		; Old kernel can't have initrd
                je load_old_kernel
                mov si,err_oldkernel
                jmp abort_load
load_old_kernel:
		mov word [SetupSecs],4		; Always 4 setup sectors
		mov byte [LoadFlags],0		; Always low
		jmp read_kernel

;
; parse_load_initrd
;
; Parse an initrd= option and load the initrds.  Note that we load
; from the high end of memory first, so we parse this option from
; left to right.
;
parse_load_initrd:
		push es
		push ds
		mov ax,real_mode_seg
		mov ds,ax
		push cs
		pop es			; DS == real_mode_seg, ES == CS

		mov si,[cs:InitRDPtr]
.find_end:
		lodsb
		cmp al,' '
		ja .find_end
		; Now SI points to one character beyond the
		; byte that ended this option.

.get_chunk:
		dec si

		; DS:SI points to a termination byte

		xor ax,ax
		xchg al,[si]		; Zero-terminate
		push si			; Save ending byte address
		push ax			; Save ending byte

.find_start:
		dec si
		cmp si,[cs:InitRDPtr]
		je .got_start
		cmp byte [si],','
		jne .find_start

		; It's a comma byte
		inc si

.got_start:
		push si
		mov di,InitRD		; Target buffer for mangled name
		call mangle_name
		call loadinitrd
		pop si

		pop ax
		pop di
		mov [di],al		; Restore ending byte

		cmp si,[cs:InitRDPtr]
		ja .get_chunk

		pop ds
		pop es
		ret

;
; Load RAM disk into high memory
;
; Input:	InitRD		- set to the mangled name of the initrd
;
loadinitrd:
		push ds
		push es
		mov ax,cs			; CS == DS == ES
		mov ds,ax
		mov es,ax
                mov si,InitRD
                mov di,InitRDCName
                call unmangle_name              ; Create human-readable name
                sub di,InitRDCName
                mov [InitRDCNameLen],di
                mov di,InitRD
                call searchdir                  ; Look for it in directory
		jz .notthere

		mov cx,dx
		shl ecx,16
		mov cx,ax			; ECX <- ram disk length

		mov ax,real_mode_seg
		mov es,ax

		push ecx			; Bytes to load
		cmp dword [es:su_ramdisklen],0
		je .nopadding			; Don't pad the last initrd
		add ecx,4095
		and cx,0F000h
.nopadding:
		add [es:su_ramdisklen],ecx
		mov edx,[HighMemSize]		; End of memory
		dec edx
		mov eax,[RamdiskMax]		; Highest address allowed by kernel
		cmp edx,eax
		jna .memsize_ok
		mov edx,eax			; Adjust to fit inside limit
.memsize_ok:
		inc edx
                and dx,0F000h			; Round down to 4K boundary
		sub edx,ecx			; Subtract size of ramdisk
                and dx,0F000h			; Round down to 4K boundary
		cmp edx,[KernelEnd]		; Are we hitting the kernel image?
		jb no_high_mem

                mov [es:su_ramdiskat],edx	; Load address
		mov [RamdiskMax],edx		; Next initrd loaded here

                mov edi,edx			; initrd load address
		push si
		mov si,crlfloading_msg		; Write "Loading "
		call cwritestr
                mov si,InitRDCName		; Write ramdisk name
                call cwritestr
                mov si,dotdot_msg		; Write dots
                call cwritestr
		pop si

		pop eax				; Bytes to load
		mov dx,0FFFh			; Pad to page
		call load_high			; Load the file

		pop es
		pop ds
		jmp crlf			; Print carriage return and return

.notthere:
                mov si,err_noinitrd
                call cwritestr
                mov si,InitRDCName
                call cwritestr
                mov si,crlf_msg
                jmp abort_load

no_high_mem:    				; Error routine
		mov si,err_nohighmem
                jmp abort_load

                ret

		section .data
boot_image      db 'BOOT_IMAGE='
boot_image_len  equ $-boot_image

		section .bss
		alignb 4
RamdiskMax	resd 1			; Highest address for ramdisk
KernelSize	resd 1			; Size of kernel in bytes
KernelSects	resd 1			; Size of kernel in sectors
KernelEnd	resd 1			; Ending address of the kernel image
CmdLineLen	resw 1			; Length of command line including null
SetupSecs	resw 1			; Number of setup sectors
InitRDPtr	resw 1			; Pointer to initrd= option in command line
LoadFlags	resb 1			; Loadflags from kernel