2 * Copyright (c) 2000 John Baldwin
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * This simple program is a preloader for the normal boot3 loader. It is simply
30 * prepended to the beginning of a fully built and btxld'd loader. It then
31 * copies the loader to the address boot2 normally loads it, emulates the
32 * boot[12] environment (protected mode, a bootinfo struct, etc.), and then jumps
33 * to the start of btxldr to start the boot process. This method allows a stock
34 * /boot/loader to be booted over the network via PXE w/o having to write a
35 * separate PXE-aware client just to load the loader.
38 #include <sys/reboot.h>
44 .set MEM_PAGE_SIZE,0x1000 # memory page size, 4k
45 .set MEM_ARG,0x900 # Arguments at start
46 .set MEM_ARG_BTX,0xa100 # Where we move them to so the
47 # BTX client can see them
48 .set MEM_ARG_SIZE,0x18 # Size of the arguments
49 .set MEM_BTX_ADDRESS,0x9000 # where BTX lives
50 .set MEM_BTX_ENTRY,0x9010 # where BTX starts to execute
51 .set MEM_BTX_OFFSET,MEM_PAGE_SIZE # offset of BTX in the loader
52 .set MEM_BTX_CLIENT,0xa000 # where BTX clients live
53 .set MEM_BIOS_KEYBOARD,0x496 # BDA byte with keyboard bit
57 .set AOUT_TEXT,0x04 # text segment size
58 .set AOUT_DATA,0x08 # data segment size
59 .set AOUT_BSS,0x0c # zero'd BSS size
60 .set AOUT_SYMBOLS,0x10 # symbol table
61 .set AOUT_ENTRY,0x14 # entry point
62 .set AOUT_HEADER,MEM_PAGE_SIZE # size of the a.out header
66 .set SEL_SDATA,0x8 # Supervisor data
67 .set SEL_RDATA,0x10 # Real mode data
68 .set SEL_SCODE,0x18 # PM-32 code
69 .set SEL_SCODE16,0x20 # PM-16 code
73 .set INT_SYS,0x30 # BTX syscall interrupt
75 * Bit in MEM_BIOS_KEYBOARD that is set if an enhanced keyboard is present
77 .set KEYBOARD_BIT,0x10
79 * We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry
86 * BTX program loader for PXE network booting
88 start: cld # string ops inc
89 xorw %ax, %ax # zero %ax
90 movw %ax, %ss # setup the
91 movw $start, %sp # stack
92 movw %es, %cx # save PXENV+ segment
93 movw %ax, %ds # setup the
94 movw %ax, %es # data segments
95 andl $0xffff, %ecx # clear upper words
96 andl $0xffff, %ebx # of %ebx and %ecx
97 shll $4, %ecx # calculate the offset of
98 addl %ebx, %ecx # the PXENV+ struct and
99 pushl %ecx # save it on the stack
100 movw $welcome_msg, %si # %ds:(%si) -> welcome message
101 callw putstr # display the welcome message
103 * Setup the arguments that the loader is expecting from boot[12]
105 movw $bootinfo_msg, %si # %ds:(%si) -> boot args message
106 callw putstr # display the message
107 movw $MEM_ARG, %bx # %ds:(%bx) -> boot args
108 movw %bx, %di # %es:(%di) -> boot args
109 xorl %eax, %eax # zero %eax
110 movw $(MEM_ARG_SIZE/4), %cx # Size of arguments in 32-bit
112 rep # Clear the arguments
114 orb $KARGS_FLAGS_PXE, 0x8(%bx) # kargs->bootflags |=
116 popl 0xc(%bx) # kargs->pxeinfo = *PXENV+
119 * set the RBX_SERIAL bit in the howto byte.
121 orl $RB_SERIAL, (%bx) # enable serial console
123 #ifdef PROBE_KEYBOARD
125 * Look at the BIOS data area to see if we have an enhanced keyboard. If not,
126 * set the RBX_DUAL and RBX_SERIAL bits in the howto byte.
128 testb $KEYBOARD_BIT, MEM_BIOS_KEYBOARD # keyboard present?
129 jnz keyb # yes, so skip
130 orl $(RB_MULTIPLE | RB_SERIAL), (%bx) # enable serial console
134 * Turn on the A20 address line
136 callw seta20 # Turn A20 on
138 * Relocate the loader and BTX using a very lazy protected mode
140 movw $relocate_msg, %si # Display the
141 callw putstr # relocation message
142 movl end+AOUT_ENTRY, %edi # %edi is the destination
143 movl $(end+AOUT_HEADER), %esi # %esi is
144 # the start of the text
146 movl end+AOUT_TEXT, %ecx # %ecx = length of the text
148 lgdt gdtdesc # setup our own gdt
149 cli # turn off interrupts
150 movl %cr0, %eax # Turn on
151 orb $0x1, %al # protected
152 movl %eax, %cr0 # mode
153 ljmp $SEL_SCODE,$pm_start # long jump to clear the
154 # instruction pre-fetch queue
156 pm_start: movw $SEL_SDATA, %ax # Initialize
157 movw %ax, %ds # %ds and
158 movw %ax, %es # %es to a flat selector
161 addl $(MEM_PAGE_SIZE - 1), %edi # pad %edi out to a new page
162 andl $~(MEM_PAGE_SIZE - 1), %edi # for the data segment
163 movl end+AOUT_DATA, %ecx # size of the data segment
166 movl end+AOUT_BSS, %ecx # size of the bss
167 xorl %eax, %eax # zero %eax
168 addb $3, %cl # round %ecx up to
169 shrl $2, %ecx # a multiple of 4
172 movl end+AOUT_ENTRY, %esi # %esi -> relocated loader
173 addl $MEM_BTX_OFFSET, %esi # %esi -> BTX in the loader
174 movl $MEM_BTX_ADDRESS, %edi # %edi -> where BTX needs to go
175 movzwl 0xa(%esi), %ecx # %ecx -> length of BTX
178 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM
180 pm_16: movw $SEL_RDATA, %ax # Initialize
181 movw %ax, %ds # %ds and
182 movw %ax, %es # %es to a real mode selector
183 movl %cr0, %eax # Turn off
184 andb $~0x1, %al # protected
185 movl %eax, %cr0 # mode
186 ljmp $0,$pm_end # Long jump to clear the
187 # instruction pre-fetch queue
188 pm_end: sti # Turn interrupts back on now
190 * Copy the BTX client to MEM_BTX_CLIENT
192 xorw %ax, %ax # zero %ax and set
193 movw %ax, %ds # %ds and %es
194 movw %ax, %es # to segment 0
195 movw $MEM_BTX_CLIENT, %di # Prepare to relocate
196 movw $btx_client, %si # the simple btx client
197 movw $(btx_client_end-btx_client), %cx # length of btx client
199 movsb # simple BTX client
201 * Copy the boot[12] args to where the BTX client can see them
203 movw $MEM_ARG, %si # where the args are at now
204 movw $MEM_ARG_BTX, %di # where the args are moving to
205 movw $(MEM_ARG_SIZE/4), %cx # size of the arguments in longs
209 * Save the entry point so the client can get to it later on
211 movl end+AOUT_ENTRY, %eax # load the entry point
212 stosl # add it to the end of the
215 * Now we just start up BTX and let it do the rest
217 movw $jump_message, %si # Display the
218 callw putstr # jump message
219 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point
222 * Display a null-terminated string
224 putstr: lodsb # load %al from %ds:(%si)
225 testb %al,%al # stop at null
226 jnz putc # if the char != null, output it
227 retw # return when null is hit
228 putc: movw $0x7,%bx # attribute for output
229 movb $0xe,%ah # BIOS: put_char
230 int $0x10 # call BIOS, print char in %al
231 jmp putstr # keep looping
234 * Enable A20. Put an upper limit on the amount of time we wait for the
235 * keyboard controller to get ready (65K x ISA access time). If
236 * we wait more than that amount, the hardware is probably
237 * legacy-free and simply doesn't have a keyboard controller.
238 * Thus, the A20 line is already enabled.
240 seta20: cli # Disable interrupts
242 seta20.1: inc %cx # Increment, overflow?
244 inb $0x64,%al # Get status
245 testb $0x2,%al # Busy?
247 movb $0xd1,%al # Command: Write
248 outb %al,$0x64 # output port
249 seta20.2: inb $0x64,%al # Get status
250 testb $0x2,%al # Busy?
252 movb $0xdf,%al # Enable
254 seta20.3: sti # Enable interrupts
258 * BTX client to start btxldr
261 btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi
264 movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push
266 push_arg: lodsl # Read argument
267 pushl %eax # Push it onto the stack
268 loop push_arg # Push all of the arguments
269 cld # In case anyone depends on this
270 pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of
272 pushl %eax # Emulate a near call
273 movl $0x1, %eax # 'exec' system call
274 int $INT_SYS # BTX system call
280 * Global descriptor table.
282 gdt: .word 0x0,0x0,0x0,0x0 # Null entry
283 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA
284 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA
285 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit)
286 .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit)
289 * Pseudo-descriptors.
291 gdtdesc: .word gdt.1-gdt-1 # Limit
294 welcome_msg: .asciz "PXE Loader 1.00\r\n\n"
295 bootinfo_msg: .asciz "Building the boot loader arguments\r\n"
296 relocate_msg: .asciz "Relocating the loader and the BTX\r\n"
297 jump_message: .asciz "Starting the BTX loader\r\n"