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