pxelinux.asm

Windows上的精简Linux系统

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

;
; pxenv
;
; This is the main PXENV+/!PXE entry point, using the PXENV+
; calling convention.  This is a separate local routine so
; we can hook special things from it if necessary.
;

pxenv:
.jump:		call 0:pxe_thunk		; Default to calling the thunk
		cld				; Make sure DF <- 0
		ret

; Must be after function def due to NASM bug
PXENVEntry	equ pxenv.jump+1

;
; pxe_thunk
;
; Convert from the PXENV+ calling convention (BX, ES, DI) to the !PXE
; calling convention (using the stack.)
;
; This is called as a far routine so that we can just stick it into
; the PXENVEntry variable.
;
pxe_thunk:	push es
		push di
		push bx
.jump:		call 0:0
		add sp,byte 6
		cmp ax,byte 1
		cmc				; Set CF unless ax == 0
		retf

; Must be after function def due to NASM bug
PXEEntry	equ pxe_thunk.jump+1

;
; getfssec: Get multiple clusters from a file, given the starting cluster.
;
;	In this case, get multiple blocks from a specific TCP connection.
;
;  On entry:
;	ES:BX	-> Buffer
;	SI	-> TFTP socket pointer
;	CX	-> 512-byte block count; 0FFFFh = until end of file
;  On exit:
;	SI	-> TFTP socket pointer (or 0 on EOF)
;	CF = 1	-> Hit EOF
;
getfssec:	push si
		push fs
		mov di,bx
		mov bx,si
		mov ax,pktbuf_seg
		mov fs,ax

		movzx ecx,cx
		shl ecx,TFTP_BLOCKSIZE_LG2	; Convert to bytes
		jz .hit_eof			; Nothing to do?
		
.need_more:
		push ecx

		movzx eax,word [bx+tftp_bytesleft]
		cmp ecx,eax
		jna .ok_size
		mov ecx,eax
		jcxz .need_packet		; No bytes available?
.ok_size:

		mov ax,cx			; EAX<31:16> == ECX<31:16> == 0
		mov si,[bx+tftp_dataptr]
		sub [bx+tftp_bytesleft],cx
		fs rep movsb			; Copy from packet buffer
		mov [bx+tftp_dataptr],si

		pop ecx
		sub ecx,eax
		jnz .need_more


.hit_eof:
		pop fs
		pop si

		; Is there anything left of this?
		mov eax,[si+tftp_filesize]
		sub eax,[si+tftp_filepos]
		jnz .bytes_left	; CF <- 0

		cmp [si+tftp_bytesleft],ax
		jnz .bytes_left	; CF <- 0

		; The socket is closed and the buffer drained
		; Close socket structure and re-init for next user
		call free_socket
		stc
.bytes_left:
		ret

;
; No data in buffer, check to see if we can get a packet...
;
.need_packet:
		pop ecx
		mov eax,[bx+tftp_filesize]
		cmp eax,[bx+tftp_filepos]
		je .hit_eof			; Already EOF'd; socket already closed

		pushad
		push es
		mov si,bx
		call get_packet
		pop es
		popad

		jmp .need_more

;
; Get a fresh packet; expects fs -> pktbuf_seg and ds:si -> socket structure
;
get_packet:
		mov ax,ds
		mov es,ax
	
.packet_loop:
		; Start by ACKing the previous packet; this should cause the
		; next packet to be sent.
		mov cx,PKT_RETRY
		mov word [PktTimeout],PKT_TIMEOUT

.send_ack:	push cx				; <D> Retry count

		mov ax,[si+tftp_lastpkt]
		call ack_packet			; Send ACK

		; We used to test the error code here, but sometimes
		; PXE would return negative status even though we really
		; did send the ACK.  Now, just treat a failed send as
		; a normally lost packet, and let it time out in due
		; course of events.

.send_ok:	; Now wait for packet.
		mov dx,[BIOS_timer]		; Get current time

		mov cx,[PktTimeout]
.wait_data:	push cx				; <E> Timeout
		push dx				; <F> Old time

		mov bx,[si+tftp_pktbuf]
		mov [pxe_udp_read_pkt.buffer],bx
		mov [pxe_udp_read_pkt.buffer+2],fs
		mov [pxe_udp_read_pkt.buffersize],word PKTBUF_SIZE
		mov eax,[si+tftp_remoteip]
		mov [pxe_udp_read_pkt.sip],eax
		mov eax,[MyIP]
		mov [pxe_udp_read_pkt.dip],eax
		mov ax,[si+tftp_remoteport]
		mov [pxe_udp_read_pkt.rport],ax
		mov ax,[si+tftp_localport]
		mov [pxe_udp_read_pkt.lport],ax
		mov di,pxe_udp_read_pkt
		mov bx,PXENV_UDP_READ
		push si				; <G>
		call pxenv
		pop si				; <G>
		and ax,ax
		jz .recv_ok

		; No packet, or receive failure
		mov dx,[BIOS_timer]
		pop ax				; <F> Old time
		pop cx				; <E> Timeout
		cmp ax,dx			; Same time -> don't advance timeout
		je .wait_data			; Same clock tick
		loop .wait_data			; Decrease timeout
		
		pop cx				; <D> Didn't get any, send another ACK
		shl word [PktTimeout],1		; Exponential backoff
		loop .send_ack
		jmp kaboom			; Forget it...

.recv_ok:	pop dx				; <F>
		pop cx				; <E>

		cmp word [pxe_udp_read_pkt.buffersize],byte 4
		jb .wait_data			; Bad size for a DATA packet

		mov bx,[si+tftp_pktbuf]
		cmp word [fs:bx],TFTP_DATA	; Not a data packet?
		jne .wait_data			; Then wait for something else

		mov ax,[si+tftp_lastpkt]
		xchg ah,al			; Host byte order
		inc ax				; Which packet are we waiting for?
		xchg ah,al			; Network byte order
		cmp [fs:bx+2],ax
		je .right_packet

		; Wrong packet, ACK the packet and then try again
		; This is presumably because the ACK got lost,
		; so the server just resent the previous packet
		mov ax,[fs:bx+2]
		call ack_packet
		jmp .send_ok			; Reset timeout

.right_packet:	; It's the packet we want.  We're also EOF if the size < blocksize

		pop cx				; <D> Don't need the retry count anymore

		mov [si+tftp_lastpkt],ax	; Update last packet number

		movzx ecx,word [pxe_udp_read_pkt.buffersize]
		sub cx,byte 4			; Skip TFTP header

		; If this is a zero-length block, don't mess with the pointers,
		; since we may have just set up the previous block that way
		jz .last_block

		; Set pointer to data block
		lea ax,[bx+4]			; Data past TFTP header
		mov [si+tftp_dataptr],ax

		add [si+tftp_filepos],ecx
		mov [si+tftp_bytesleft],cx

		cmp cx,[si+tftp_blksize]	; Is it a full block?
		jb .last_block			; If so, it's not EOF

		; If we had the exact right number of bytes, always get
		; one more packet to get the (zero-byte) EOF packet and
		; close the socket.
		mov eax,[si+tftp_filepos]
		cmp [si+tftp_filesize],eax
		je .packet_loop

		ret


.last_block:	; Last block - ACK packet immediately
		mov ax,[fs:bx+2]
		call ack_packet

		; Make sure we know we are at end of file
		mov eax,[si+tftp_filepos]
		mov [si+tftp_filesize],eax
	
		ret

;
; ack_packet:
;
; Send ACK packet.  This is a common operation and so is worth canning.
;
; Entry:
;	SI 	= TFTP block
;	AX 	= Packet # to ack (network byte order)
; Exit:
;	ZF = 0 -> Error
;	All registers preserved
;
; This function uses the pxe_udp_write_pkt but not the packet_buf.
;
ack_packet:
		pushad
		mov [ack_packet_buf+2],ax	; Packet number to ack
		mov ax,[si]
		mov [pxe_udp_write_pkt.lport],ax
		mov ax,[si+tftp_remoteport]
		mov [pxe_udp_write_pkt.rport],ax
		mov eax,[si+tftp_remoteip]
		mov [pxe_udp_write_pkt.sip],eax
		xor eax,[MyIP]
		and eax,[Netmask]
		jz .nogw
		mov eax,[Gateway]
.nogw:
		mov [pxe_udp_write_pkt.gip],eax
		mov [pxe_udp_write_pkt.buffer],word ack_packet_buf
		mov [pxe_udp_write_pkt.buffersize], word 4
		mov di,pxe_udp_write_pkt
		mov bx,PXENV_UDP_WRITE
		call pxenv
		cmp ax,byte 0			; ZF = 1 if write OK
		popad
		ret

;
; unload_pxe:
;
; This function unloads the PXE and UNDI stacks and unclaims
; the memory.
;
unload_pxe:
		test byte [KeepPXE],01h		; Should we keep PXE around?
		jnz reset_pxe

		push ds
		push es

		mov ax,cs
		mov ds,ax
		mov es,ax

		mov si,new_api_unload
		cmp byte [APIVer+1],2		; Major API version >= 2?
		jae .new_api
		mov si,old_api_unload
.new_api:
		
.call_loop:	xor ax,ax
		lodsb
		and ax,ax
		jz .call_done
		xchg bx,ax
		mov di,pxe_unload_stack_pkt
		push di
		xor ax,ax
		mov cx,pxe_unload_stack_pkt_len >> 1
		rep stosw
		pop di
		call pxenv
		jc .cant_free
		mov ax,word [pxe_unload_stack_pkt.status]
		cmp ax,PXENV_STATUS_SUCCESS
		jne .cant_free
		jmp .call_loop

.call_done:
%if USE_PXE_PROVIDED_STACK
		; We need to switch to our local stack here...
		pusha
		pushf
		push gs

		mov si,sp
		mov ax,ss
		mov gs,ax
		sub ax,[BaseStack+4]		; Are we using the base stack
		je .is_base_stack		; (as opposed to the COMBOOT stack)?

		lgs si,[SavedSSSP]		; COMBOOT stack
.is_base_stack:

		mov cx,[InitStack]
		mov di,StackBuf
		mov [BaseStack],di
		mov [BaseStack+4],es
		sub cx,si
		sub di,cx
		mov [SavedSSSP],di		; New SP
		mov [SavedSSSP+2],es
		gs rep movsb

		and ax,ax			; Remember which stack
		jne .combootstack

		; Update the base stack pointer since it's in use
		lss sp,[SavedSSSP]
		
.combootstack:
		pop gs
		popf
		popa
%endif
		mov bx,0FF00h

		mov dx,[RealBaseMem]
		cmp dx,[BIOS_fbm]		; Sanity check
		jna .cant_free
		inc bx

		; Check that PXE actually unhooked the INT 1Ah chain
		movzx eax,word [4*0x1a]
		movzx ecx,word [4*0x1a+2]
		shl ecx,4
		add eax,ecx
		shr eax,10
		cmp ax,dx			; Not in range
		jae .ok
		cmp ax,[BIOS_fbm]
		jae .cant_free
		; inc bx

.ok:
		mov [BIOS_fbm],dx
.pop_ret:
		pop es
		pop ds
		ret
		
.cant_free:
		mov si,cant_free_msg
		call writestr
		push ax
		xchg bx,ax
		call writehex4
		mov al,'-'
		call writechr
		pop ax
		call writehex4
		mov al,'-'
		call writechr
		mov eax,[4*0x1a]
		call writehex8
		call crlf
		jmp .pop_ret

		; We want to keep PXE around, but still we should reset
		; it to the standard bootup configuration
reset_pxe:
		push es
		push cs
		pop es
		mov bx,PXENV_UDP_CLOSE
		mov di,pxe_udp_close_pkt
		call pxenv
		pop es
		ret

;
; gendotquad
;
; Take an IP address (in network byte order) in EAX and
; output a dotted quad string to ES:DI.
; DI points to terminal null at end of string on exit.
;
; CX is destroyed.
;
gendotquad:
		push eax
		mov cx,4
.genchar:
		push eax
		cmp al,10		; < 10?
		jb .lt10		; If so, skip first 2 digits

		cmp al,100		; < 100
		jb .lt100		; If so, skip first digit

		aam 100
		; Now AH = 100-digit; AL = remainder
		add ah,'0'
		mov [es:di],ah
		inc di

.lt100:
		aam 10
		; Now AH = 10-digit; AL = remainder
		add ah,'0'
		mov [es:di],ah		
		inc di

.lt10:
		add al,'0'
		stosb
		mov al,'.'
		stosb
		pop eax
		ror eax,8	; Move next char into LSB
		loop .genchar
		dec di
		mov [es:di], byte 0
		pop eax
		ret

;
; parse_dhcp
;
; Parse a DHCP packet.  This includes dealing with "overloaded"
; option fields (see RFC 2132, section 9.3)
;
; This should fill in the following global variables, if the
; information is present:
;
; MyIP		- client IP address
; ServerIP	- boot server IP address
; Netmask	- network mask
; Gateway	- default gateway router IP
; UseGW		- zero if ServerIP local, otherwise Gateway
; BootFile	- boot file name
;
; This assumes the DHCP packet is in "trackbuf" and the length
; of the packet in in CX on entry.
;

parse_dhcp:
		mov byte [OverLoad],0		; Assume no overload
		mov eax, [trackbuf+bootp.yip]
		and eax, eax
		jz .noyip
		cmp al,224			; Class D or higher -> bad
		jae .noyip
		mov [MyIP], eax
.noyip:
		mov eax, [trackbuf+bootp.sip]
		and eax, eax
		jz .nosip
		cmp al,224			; Class D or higher -> bad
		jae .nosip
		mov [ServerIP], eax
.nosip:
		sub cx, bootp.options
		jbe .nooptions
		mov si, trackbuf+bootp.option_magic
		lodsd
		cmp eax, BOOTP_OPTION_MAGIC
		jne .nooptions
		call parse_dhcp_options
.nooptions:
		mov si, trackbuf+bootp.bootfile
		test byte [OverLoad],1
		jz .nofileoverload
		mov cx,128
		call parse_dhcp_options
		jmp short .parsed_file
.nofileoverload:
		cmp byte [si], 0
		jz .parsed_file			; No bootfile name
		mov di,BootFile
		mov cx,32
		rep movsd
		xor al,al
		stosb				; Null-terminate
.parsed_file:
		mov si, trackbuf+bootp.sname