pxeldr.S revision 81367 
1#
2# Copyright (c) 2000 John Baldwin
3# All rights reserved.
4#
5# Redistribution and use in source and binary forms are freely
6# permitted provided that the above copyright notice and this
7# paragraph and the following disclaimer are duplicated in all
8# such forms.
9#
10# This software is provided "AS IS" and without any express or
11# implied warranties, including, without limitation, the implied
12# warranties of merchantability and fitness for a particular
13# purpose.
14#
15
16# $FreeBSD: head/sys/boot/i386/pxeldr/pxeldr.S 81367 2001-08-09 20:47:58Z mp $
17
18#
19# This simple program is a preloader for the normal boot3 loader.  It is simply
20# prepended to the beginning of a fully built and btxld'd loader.  It then
21# copies the loader to the address boot2 normally loads it, emulates the
22# boot[12] environment (protected mode, a bootinfo struct, etc.), and then jumps
23# to the start of btxldr to start the boot process.  This method allows a stock
24# /boot/loader to be booted over the network via PXE w/o having to write a
25# separate PXE-aware client just to load the loader.
26#
27
28#
29# Memory locations.
30#
31		.set MEM_PAGE_SIZE,0x1000	# memory page size, 4k
32		.set MEM_ARG,0x900		# Arguments at start
33		.set MEM_ARG_BTX,0xa100		# Where we move them to so the
34						#  BTX client can see them
35		.set MEM_ARG_SIZE,0x18		# Size of the arguments
36		.set MEM_BTX_ADDRESS,0x9000	# where BTX lives
37		.set MEM_BTX_ENTRY,0x9010	# where BTX starts to execute
38		.set MEM_BTX_OFFSET,MEM_PAGE_SIZE # offset of BTX in the loader
39		.set MEM_BTX_CLIENT,0xa000	# where BTX clients live
40		.set MEM_BIOS_KEYBOARD,0x496	# BDA byte with keyboard bit
41#
42# a.out header fields
43#
44		.set AOUT_TEXT,0x04		# text segment size
45		.set AOUT_DATA,0x08		# data segment size
46		.set AOUT_BSS,0x0c		# zero'd BSS size
47		.set AOUT_SYMBOLS,0x10		# symbol table
48		.set AOUT_ENTRY,0x14		# entry point
49		.set AOUT_HEADER,MEM_PAGE_SIZE	# size of the a.out header
50#
51# Flags for kargs->bootflags
52#
53		.set KARGS_FLAGS_PXE,0x2	# flag to indicate booting from
54						#  PXE loader
55#
56# Boot howto bits
57#
58		.set RB_SERIAL,0x1000		# serial console
59#
60# Segment selectors.
61#
62		.set SEL_SDATA,0x8		# Supervisor data
63		.set SEL_RDATA,0x10		# Real mode data
64		.set SEL_SCODE,0x18		# PM-32 code
65		.set SEL_SCODE16,0x20		# PM-16 code
66#
67# BTX constants
68#
69		.set INT_SYS,0x30		# BTX syscall interrupt
70#
71# Bit in MEM_BIOS_KEYBOARD that is set if an enhanced keyboard is present
72#
73		.set KEYBOARD_BIT,0x10
74#
75# We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry
76# point)
77#
78		.code16
79		.globl start
80		.org 0x0, 0x0
81#
82# BTX program loader for PXE network booting
83#
84start:		cld				# string ops inc
85		xorw %ax, %ax			# zero %ax
86		movw %ax, %ss			# setup the
87		movw $start, %sp		#  stack
88		movw %es, %cx			# save PXENV+ segment
89		movw %ax, %ds			# setup the
90		movw %ax, %es			#  data segments
91		andl $0xffff, %ecx		# clear upper words
92		andl $0xffff, %ebx		#  of %ebx and %ecx
93		shll $4, %ecx			# calculate the offset of
94		addl %ebx, %ecx			#  the PXENV+ struct and
95		pushl %ecx			#  save it on the stack
96		movw $welcome_msg, %si		# %ds:(%si) -> welcome message
97		callw putstr			# display the welcome message
98#
99# Setup the arguments that the loader is expecting from boot[12]
100#
101		movw $bootinfo_msg, %si		# %ds:(%si) -> boot args message
102		callw putstr			# display the message
103		movw $MEM_ARG, %bx		# %ds:(%bx) -> boot args
104		movw %bx, %di			# %es:(%di) -> boot args
105		xorl %eax, %eax			# zero %eax
106		movw $(MEM_ARG_SIZE/4), %cx	# Size of arguments in 32-bit
107						#  dwords
108		rep				# Clear the arguments
109		stosl				#  to zero
110		orb $KARGS_FLAGS_PXE, 0x8(%bx)	# kargs->bootflags |=
111						#  KARGS_FLAGS_PXE
112		popl 0xc(%bx)			# kargs->pxeinfo = *PXENV+
113ifdef(`PROBE_KEYBOARD',`
114#
115# Look at the BIOS data area to see if we have an enhanced keyboard.  If not,
116# set the RBX_SERIAL bit in the howto byte.
117		testb $KEYBOARD_BIT, MEM_BIOS_KEYBOARD # keyboard present?
118		jnz keyb			# yes, so skip
119		orl $RB_SERIAL, (%bx)		# enable serial console
120keyb:
121')
122#
123# Turn on the A20 address line
124#
125		callw seta20			# Turn A20 on
126#
127# Relocate the loader and BTX using a very lazy protected mode
128#
129		movw $relocate_msg, %si		# Display the
130		callw putstr			#  relocation message
131		movl end+AOUT_ENTRY, %edi	# %edi is the destination
132		movl $(end+AOUT_HEADER), %esi	# %esi is
133						#  the start of the text
134						#  segment
135		movl end+AOUT_TEXT, %ecx	# %ecx = length of the text
136						#  segment
137		lgdt gdtdesc			# setup our own gdt
138		cli				# turn off interrupts
139		movl %cr0, %eax			# Turn on
140		orb $0x1, %al			#  protected
141		movl %eax, %cr0			#  mode
142		ljmp $SEL_SCODE,$pm_start	# long jump to clear the
143						#  instruction pre-fetch queue
144		.code32
145pm_start:	movw $SEL_SDATA, %ax		# Initialize
146		movw %ax, %ds			#  %ds and
147		movw %ax, %es			#  %es to a flat selector
148		rep				# Relocate the
149		movsb				#  text segment
150		addl $(MEM_PAGE_SIZE - 1), %edi	# pad %edi out to a new page
151		andl $~(MEM_PAGE_SIZE - 1), %edi #  for the data segment
152		movl end+AOUT_DATA, %ecx	# size of the data segment
153		rep				# Relocate the
154		movsb				#  data segment
155		movl end+AOUT_BSS, %ecx		# size of the bss
156		xorl %eax, %eax			# zero %eax
157		addb $3, %cl			# round %ecx up to
158		shrl $2, %ecx			#  a multiple of 4
159		rep				# zero the
160		stosl				#  bss
161		movl end+AOUT_ENTRY, %esi	# %esi -> relocated loader
162		addl $MEM_BTX_OFFSET, %esi	# %esi -> BTX in the loader
163		movl $MEM_BTX_ADDRESS, %edi	# %edi -> where BTX needs to go
164		movzwl 0xa(%esi), %ecx		# %ecx -> length of BTX
165		rep				# Relocate
166		movsb				#  BTX
167		ljmp $SEL_SCODE16,$pm_16	# Jump to 16-bit PM
168		.code16
169pm_16:		movw $SEL_RDATA, %ax		# Initialize
170		movw %ax, %ds			#  %ds and
171		movw %ax, %es			#  %es to a real mode selector
172		movl %cr0, %eax			# Turn off
173		andb $~0x1, %al			#  protected
174		movl %eax, %cr0			#  mode
175		ljmp $0,$pm_end			# Long jump to clear the
176						#  instruction pre-fetch queue
177pm_end:		sti				# Turn interrupts back on now
178#
179# Copy the BTX client to MEM_BTX_CLIENT
180#
181		xorw %ax, %ax			# zero %ax and set
182		movw %ax, %ds			#  %ds and %es
183		movw %ax, %es			#  to segment 0
184		movw $MEM_BTX_CLIENT, %di	# Prepare to relocate
185		movw $btx_client, %si		#  the simple btx client
186		movw $(btx_client_end-btx_client), %cx # length of btx client
187		rep				# Relocate the
188		movsb				#  simple BTX client
189#
190# Copy the boot[12] args to where the BTX client can see them
191#
192		movw $MEM_ARG, %si		# where the args are at now
193		movw $MEM_ARG_BTX, %di		# where the args are moving to
194		movw $(MEM_ARG_SIZE/4), %cx	# size of the arguments in longs
195		rep				# Relocate
196		movsl				#  the words
197#
198# Save the entry point so the client can get to it later on
199#
200		movl end+AOUT_ENTRY, %eax	# load the entry point
201		stosl				# add it to the end of the
202						#  arguments
203#
204# Now we just start up BTX and let it do the rest
205#
206		movw $jump_message, %si		# Display the
207		callw putstr			#  jump message
208		ljmp $0,$MEM_BTX_ENTRY		# Jump to the BTX entry point
209
210#
211# Display a null-terminated string
212#
213putstr:		lodsb				# load %al from %ds:(%si)
214		testb %al,%al			# stop at null
215		jnz putc			# if the char != null, output it
216		retw				# return when null is hit
217putc:		movw $0x7,%bx			# attribute for output
218		movb $0xe,%ah			# BIOS: put_char
219		int $0x10			# call BIOS, print char in %al
220		jmp putstr			# keep looping
221
222#
223# Enable A20
224#
225seta20: 	cli				# Disable interrupts
226seta20.1:	inb $0x64,%al			# Get status
227		testb $0x2,%al			# Busy?
228		jnz seta20.1			# Yes
229		movb $0xd1,%al			# Command: Write
230		outb %al,$0x64			#  output port
231seta20.2:	inb $0x64,%al			# Get status
232		testb $0x2,%al			# Busy?
233		jnz seta20.2			# Yes
234		movb $0xdf,%al			# Enable
235		outb %al,$0x60			#  A20
236		sti				# Enable interrupts
237		retw				# To caller
238
239#
240# BTX client to start btxldr
241#
242		.code32
243btx_client:	movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi
244						# %ds:(%esi) -> end
245						#  of boot[12] args
246		movl $(MEM_ARG_SIZE/4), %ecx	# Number of words to push
247		std				# Go backwards
248push_arg:	lodsl				# Read argument
249		pushl %eax			# Push it onto the stack
250		loop push_arg			# Push all of the arguments
251		cld				# In case anyone depends on this
252		pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of
253						#  the loader
254		pushl %eax			# Emulate a near call
255		movl $0x1, %eax			# 'exec' system call
256		int $INT_SYS			# BTX system call
257btx_client_end:
258		.code16
259
260		.p2align 4
261#
262# Global descriptor table.
263#
264gdt:		.word 0x0,0x0,0x0,0x0		# Null entry
265		.word 0xffff,0x0,0x9200,0xcf	# SEL_SDATA
266		.word 0xffff,0x0,0x9200,0x0	# SEL_RDATA
267		.word 0xffff,0x0,0x9a00,0xcf	# SEL_SCODE (32-bit)
268		.word 0xffff,0x0,0x9a00,0x8f	# SEL_SCODE16 (16-bit)
269gdt.1:
270#
271# Pseudo-descriptors.
272#
273gdtdesc:	.word gdt.1-gdt-1		# Limit
274		.long gdt			# Base
275
276welcome_msg:	.asciz	"PXE Loader 1.00\r\n\n"
277bootinfo_msg:	.asciz	"Building the boot loader arguments\r\n"
278relocate_msg:	.asciz	"Relocating the loader and the BTX\r\n"
279jump_message:	.asciz	"Starting the BTX loader\r\n"
280
281		.p2align 4
282end:
283