2 # Copyright (c) 2000 John Baldwin
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
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
16 # $FreeBSD: src/sys/boot/i386/pxeldr/pxeldr.s,v 1.1.2.5 2001/08/10 22:06:18 mp Exp $
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.
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
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
51 # Flags for kargs->bootflags
53 .set KARGS_FLAGS_PXE,0x2 # flag to indicate booting from
58 .set RB_SERIAL,0x1000 # serial console
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
69 .set INT_SYS,0x30 # BTX syscall interrupt
71 # Bit in MEM_BIOS_KEYBOARD that is set if an enhanced keyboard is present
73 .set KEYBOARD_BIT,0x10
75 # We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry
82 # BTX program loader for PXE network booting
84 start: 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
99 # Setup the arguments that the loader is expecting from boot[12]
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
108 rep # Clear the arguments
110 orb $KARGS_FLAGS_PXE, 0x8(%bx) # kargs->bootflags |=
112 popl 0xc(%bx) # kargs->pxeinfo = *PXENV+
113 ifdef(`PROBE_KEYBOARD',`
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
123 # Turn on the A20 address line
125 callw seta20 # Turn A20 on
127 # Relocate the loader and BTX using a very lazy protected mode
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
135 movl end+AOUT_TEXT, %ecx # %ecx = length of the text
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
145 pm_start: movw $SEL_SDATA, %ax # Initialize
146 movw %ax, %ds # %ds and
147 movw %ax, %es # %es to a flat selector
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
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
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
167 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM
169 pm_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
177 pm_end: sti # Turn interrupts back on now
179 # Copy the BTX client to MEM_BTX_CLIENT
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
188 movsb # simple BTX client
190 # Copy the boot[12] args to where the BTX client can see them
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
198 # Save the entry point so the client can get to it later on
200 movl end+AOUT_ENTRY, %eax # load the entry point
201 stosl # add it to the end of the
204 # Now we just start up BTX and let it do the rest
206 movw $jump_message, %si # Display the
207 callw putstr # jump message
208 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point
211 # Display a null-terminated string
213 putstr: 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
217 putc: 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
225 seta20: cli # Disable interrupts
226 seta20.1: inb $0x64,%al # Get status
227 testb $0x2,%al # Busy?
229 movb $0xd1,%al # Command: Write
230 outb %al,$0x64 # output port
231 seta20.2: inb $0x64,%al # Get status
232 testb $0x2,%al # Busy?
234 movb $0xdf,%al # Enable
236 sti # Enable interrupts
240 # BTX client to start btxldr
243 btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi
246 movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push
248 push_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
254 pushl %eax # Emulate a near call
255 movl $0x1, %eax # 'exec' system call
256 int $INT_SYS # BTX system call
262 # Global descriptor table.
264 gdt: .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)
271 # Pseudo-descriptors.
273 gdtdesc: .word gdt.1-gdt-1 # Limit
276 welcome_msg: .asciz "PXE Loader 1.00\r\n\n"
277 bootinfo_msg: .asciz "Building the boot loader arguments\r\n"
278 relocate_msg: .asciz "Relocating the loader and the BTX\r\n"
279 jump_message: .asciz "Starting the BTX loader\r\n"