runkernel.inc

Windows上的精简Linux系统

                call abort_check

		pop ecx				; Number of bytes in the initial portion
		pop si				; Restore file handle/cluster pointer
		mov eax,[KernelSize]
		sub eax,8000h			; Amount of kernel not yet loaded
		jbe high_load_done		; Zero left (tiny kernel)

		call load_high			; Copy the file

high_load_done:
                mov ax,real_mode_seg		; Set to real mode seg
                mov es,ax

                mov si,dot_msg
                call cwritestr

;
; Now see if we have an initial RAMdisk; if so, do requisite computation
; We know we have a new kernel; the old_kernel code already will have objected
; if we tried to load initrd using an old kernel
;
load_initrd:
                test byte [initrd_flag],1
                jz nk_noinitrd
                push es                         ; ES->real_mode_seg
                push ds
                pop es                          ; We need ES==DS
                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
                pop es
		jz initrd_notthere
		mov [es:su_ramdisklen1],ax	; Ram disk length
		mov [es:su_ramdisklen2],dx
		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
                xor dx,dx			; Round down to 64K boundary
		sub edx,[es:su_ramdisklen]	; Subtract size of ramdisk
                xor dx,dx			; Round down to 64K boundary
                mov [es:su_ramdiskat],edx	; Load address
		call loadinitrd			; Load initial ramdisk
		jmp short initrd_end

initrd_notthere:
                mov si,err_noinitrd
                call cwritestr
                mov si,InitRDCName
                call cwritestr
                mov si,crlf_msg
                jmp abort_load

no_high_mem:    mov si,err_nohighmem		; Error routine
                jmp abort_load

initrd_end:
nk_noinitrd:
;
; Abandon hope, ye that enter here!  We do no longer permit aborts.
;
                call abort_check        	; Last chance!!

		mov si,ready_msg
		call cwritestr

		call vgaclearmode		; We can't trust ourselves after this

		UNLOAD_PREP			; Module-specific hook

;
; Now, if we were supposed to load "low", copy the kernel down to 10000h
; and the real mode stuff to 90000h.  We assume that all bzImage kernels are
; capable of starting their setup from a different address.
;
		mov ax,real_mode_seg
		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
		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]
		add cx,byte 3
		shr cx,2			; Convert to dwords
		fs rep movsd

		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:
                test byte [initrd_flag],1	; Old kernel can't have initrd
                jz 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

;
; Load RAM disk into high memory
;
; Need to be set:
;	su_ramdiskat	- Where in memory to load
;	su_ramdisklen	- Size of file
;	SI		- initrd filehandle/cluster pointer
;
loadinitrd:
                push es                         ; Save ES on entry
		mov ax,real_mode_seg
                mov es,ax
                mov edi,[es:su_ramdiskat]	; 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

		mov eax,[es:su_ramdisklen]
		call load_high			; Load the file

		call crlf
                pop es                          ; Restore original ES
                ret