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
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.
28 #include <sys/reboot.h>
34 .set MEM_PAGE_SIZE,0x1000 # memory page size, 4k
35 .set MEM_ARG,0x900 # Arguments at start
36 .set MEM_ARG_BTX,0xa100 # Where we move them to so the
37 # BTX client can see them
38 .set MEM_ARG_SIZE,0x18 # Size of the arguments
39 .set MEM_BTX_ADDRESS,0x9000 # where BTX lives
40 .set MEM_BTX_ENTRY,0x9010 # where BTX starts to execute
41 .set MEM_BTX_OFFSET,MEM_PAGE_SIZE # offset of BTX in the loader
42 .set MEM_BTX_CLIENT,0xa000 # where BTX clients live
43 .set MEM_BIOS_KEYBOARD,0x496 # BDA byte with keyboard bit
47 .set AOUT_TEXT,0x04 # text segment size
48 .set AOUT_DATA,0x08 # data segment size
49 .set AOUT_BSS,0x0c # zero'd BSS size
50 .set AOUT_SYMBOLS,0x10 # symbol table
51 .set AOUT_ENTRY,0x14 # entry point
52 .set AOUT_HEADER,MEM_PAGE_SIZE # size of the a.out header
56 .set SEL_SDATA,0x8 # Supervisor data
57 .set SEL_RDATA,0x10 # Real mode data
58 .set SEL_SCODE,0x18 # PM-32 code
59 .set SEL_SCODE16,0x20 # PM-16 code
63 .set INT_SYS,0x30 # BTX syscall interrupt
65 * Bit in MEM_BIOS_KEYBOARD that is set if an enhanced keyboard is present
67 .set KEYBOARD_BIT,0x10
69 * We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry
76 * BTX program loader for PXE network booting
78 start: cld # string ops inc
79 xorw %ax, %ax # zero %ax
80 movw %ax, %ss # setup the
81 movw $start, %sp # stack
82 movw %es, %cx # save PXENV+ segment
83 movw %ax, %ds # setup the
84 movw %ax, %es # data segments
85 andl $0xffff, %ecx # clear upper words
86 andl $0xffff, %ebx # of %ebx and %ecx
87 shll $4, %ecx # calculate the offset of
88 addl %ebx, %ecx # the PXENV+ struct and
89 pushl %ecx # save it on the stack
90 movw $welcome_msg, %si # %ds:(%si) -> welcome message
91 callw putstr # display the welcome message
93 * Setup the arguments that the loader is expecting from boot[12]
95 movw $bootinfo_msg, %si # %ds:(%si) -> boot args message
96 callw putstr # display the message
97 movw $MEM_ARG, %bx # %ds:(%bx) -> boot args
98 movw %bx, %di # %es:(%di) -> boot args
99 xorl %eax, %eax # zero %eax
100 movw $(MEM_ARG_SIZE/4), %cx # Size of arguments in 32-bit
102 rep # Clear the arguments
104 orb $KARGS_FLAGS_PXE, 0x8(%bx) # kargs->bootflags |=
106 popl 0xc(%bx) # kargs->pxeinfo = *PXENV+
109 * set the RBX_SERIAL bit in the howto byte.
111 orl $RB_SERIAL, (%bx) # enable serial console
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_DUAL and RBX_SERIAL bits in the howto byte.
118 testb $KEYBOARD_BIT, MEM_BIOS_KEYBOARD # keyboard present?
119 jnz keyb # yes, so skip
120 orl $(RB_MULTIPLE | RB_SERIAL), (%bx) # enable serial console
124 * Turn on the A20 address line
126 callw seta20 # Turn A20 on
128 * Relocate the loader and BTX using a very lazy protected mode
130 movw $relocate_msg, %si # Display the
131 callw putstr # relocation message
132 movl end+AOUT_ENTRY, %edi # %edi is the destination
133 movl $(end+AOUT_HEADER), %esi # %esi is
134 # the start of the text
136 movl end+AOUT_TEXT, %ecx # %ecx = length of the text
138 lgdt gdtdesc # setup our own gdt
139 cli # turn off interrupts
140 movl %cr0, %eax # Turn on
141 orb $0x1, %al # protected
142 movl %eax, %cr0 # mode
143 ljmp $SEL_SCODE,$pm_start # long jump to clear the
144 # instruction pre-fetch queue
146 pm_start: movw $SEL_SDATA, %ax # Initialize
147 movw %ax, %ds # %ds and
148 movw %ax, %es # %es to a flat selector
151 addl $(MEM_PAGE_SIZE - 1), %edi # pad %edi out to a new page
152 andl $~(MEM_PAGE_SIZE - 1), %edi # for the data segment
153 movl end+AOUT_DATA, %ecx # size of the data segment
156 movl end+AOUT_BSS, %ecx # size of the bss
157 xorl %eax, %eax # zero %eax
158 addb $3, %cl # round %ecx up to
159 shrl $2, %ecx # a multiple of 4
162 movl end+AOUT_ENTRY, %esi # %esi -> relocated loader
163 addl $MEM_BTX_OFFSET, %esi # %esi -> BTX in the loader
164 movl $MEM_BTX_ADDRESS, %edi # %edi -> where BTX needs to go
165 movzwl 0xa(%esi), %ecx # %ecx -> length of BTX
168 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM
170 pm_16: movw $SEL_RDATA, %ax # Initialize
171 movw %ax, %ds # %ds and
172 movw %ax, %es # %es to a real mode selector
173 movl %cr0, %eax # Turn off
174 andb $~0x1, %al # protected
175 movl %eax, %cr0 # mode
176 ljmp $0,$pm_end # Long jump to clear the
177 # instruction pre-fetch queue
178 pm_end: sti # Turn interrupts back on now
180 * Copy the BTX client to MEM_BTX_CLIENT
182 xorw %ax, %ax # zero %ax and set
183 movw %ax, %ds # %ds and %es
184 movw %ax, %es # to segment 0
185 movw $MEM_BTX_CLIENT, %di # Prepare to relocate
186 movw $btx_client, %si # the simple btx client
187 movw $(btx_client_end-btx_client), %cx # length of btx client
189 movsb # simple BTX client
191 * Copy the boot[12] args to where the BTX client can see them
193 movw $MEM_ARG, %si # where the args are at now
194 movw $MEM_ARG_BTX, %di # where the args are moving to
195 movw $(MEM_ARG_SIZE/4), %cx # size of the arguments in longs
199 * Save the entry point so the client can get to it later on
201 movl end+AOUT_ENTRY, %eax # load the entry point
202 stosl # add it to the end of the
205 * Now we just start up BTX and let it do the rest
207 movw $jump_message, %si # Display the
208 callw putstr # jump message
209 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point
212 * Display a null-terminated string
214 putstr: lodsb # load %al from %ds:(%si)
215 testb %al,%al # stop at null
216 jnz putc # if the char != null, output it
217 retw # return when null is hit
218 putc: movw $0x7,%bx # attribute for output
219 movb $0xe,%ah # BIOS: put_char
220 int $0x10 # call BIOS, print char in %al
221 jmp putstr # keep looping
224 * Enable A20. Put an upper limit on the amount of time we wait for the
225 * keyboard controller to get ready (65K x ISA access time). If
226 * we wait more than that amount, the hardware is probably
227 * legacy-free and simply doesn't have a keyboard controller.
228 * Thus, the A20 line is already enabled.
230 seta20: cli # Disable interrupts
232 seta20.1: inc %cx # Increment, overflow?
234 inb $0x64,%al # Get status
235 testb $0x2,%al # Busy?
237 movb $0xd1,%al # Command: Write
238 outb %al,$0x64 # output port
239 seta20.2: inb $0x64,%al # Get status
240 testb $0x2,%al # Busy?
242 movb $0xdf,%al # Enable
244 seta20.3: sti # Enable interrupts
248 * BTX client to start btxldr
251 btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi
254 movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push
256 push_arg: lodsl # Read argument
257 pushl %eax # Push it onto the stack
258 loop push_arg # Push all of the arguments
259 cld # In case anyone depends on this
260 pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of
262 pushl %eax # Emulate a near call
263 movl $0x1, %eax # 'exec' system call
264 int $INT_SYS # BTX system call
270 * Global descriptor table.
272 gdt: .word 0x0,0x0,0x0,0x0 # Null entry
273 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA
274 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA
275 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit)
276 .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit)
279 * Pseudo-descriptors.
281 gdtdesc: .word gdt.1-gdt-1 # Limit
284 welcome_msg: .asciz "PXE Loader 1.00\r\n\n"
285 bootinfo_msg: .asciz "Building the boot loader arguments\r\n"
286 relocate_msg: .asciz "Relocating the loader and the BTX\r\n"
287 jump_message: .asciz "Starting the BTX loader\r\n"