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.
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+
115 * set the RBX_SERIAL bit in the howto byte.
117 orl $RB_SERIAL, (%bx) # enable serial console
119 #ifdef PROBE_KEYBOARD
121 * Look at the BIOS data area to see if we have an enhanced keyboard. If not,
122 * set the RBX_SERIAL bit in the howto byte.
124 testb $KEYBOARD_BIT, MEM_BIOS_KEYBOARD # keyboard present?
125 jnz keyb # yes, so skip
126 orl $RB_SERIAL, (%bx) # enable serial console
130 * Turn on the A20 address line
132 callw seta20 # Turn A20 on
134 * Relocate the loader and BTX using a very lazy protected mode
136 movw $relocate_msg, %si # Display the
137 callw putstr # relocation message
138 movl end+AOUT_ENTRY, %edi # %edi is the destination
139 movl $(end+AOUT_HEADER), %esi # %esi is
140 # the start of the text
142 movl end+AOUT_TEXT, %ecx # %ecx = length of the text
144 lgdt gdtdesc # setup our own gdt
145 cli # turn off interrupts
146 movl %cr0, %eax # Turn on
147 orb $0x1, %al # protected
148 movl %eax, %cr0 # mode
149 ljmp $SEL_SCODE,$pm_start # long jump to clear the
150 # instruction pre-fetch queue
152 pm_start: movw $SEL_SDATA, %ax # Initialize
153 movw %ax, %ds # %ds and
154 movw %ax, %es # %es to a flat selector
157 addl $(MEM_PAGE_SIZE - 1), %edi # pad %edi out to a new page
158 andl $~(MEM_PAGE_SIZE - 1), %edi # for the data segment
159 movl end+AOUT_DATA, %ecx # size of the data segment
162 movl end+AOUT_BSS, %ecx # size of the bss
163 xorl %eax, %eax # zero %eax
164 addb $3, %cl # round %ecx up to
165 shrl $2, %ecx # a multiple of 4
168 movl end+AOUT_ENTRY, %esi # %esi -> relocated loader
169 addl $MEM_BTX_OFFSET, %esi # %esi -> BTX in the loader
170 movl $MEM_BTX_ADDRESS, %edi # %edi -> where BTX needs to go
171 movzwl 0xa(%esi), %ecx # %ecx -> length of BTX
174 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM
176 pm_16: movw $SEL_RDATA, %ax # Initialize
177 movw %ax, %ds # %ds and
178 movw %ax, %es # %es to a real mode selector
179 movl %cr0, %eax # Turn off
180 andb $~0x1, %al # protected
181 movl %eax, %cr0 # mode
182 ljmp $0,$pm_end # Long jump to clear the
183 # instruction pre-fetch queue
184 pm_end: sti # Turn interrupts back on now
186 * Copy the BTX client to MEM_BTX_CLIENT
188 xorw %ax, %ax # zero %ax and set
189 movw %ax, %ds # %ds and %es
190 movw %ax, %es # to segment 0
191 movw $MEM_BTX_CLIENT, %di # Prepare to relocate
192 movw $btx_client, %si # the simple btx client
193 movw $(btx_client_end-btx_client), %cx # length of btx client
195 movsb # simple BTX client
197 * Copy the boot[12] args to where the BTX client can see them
199 movw $MEM_ARG, %si # where the args are at now
200 movw $MEM_ARG_BTX, %di # where the args are moving to
201 movw $(MEM_ARG_SIZE/4), %cx # size of the arguments in longs
205 * Save the entry point so the client can get to it later on
207 movl end+AOUT_ENTRY, %eax # load the entry point
208 stosl # add it to the end of the
211 * Now we just start up BTX and let it do the rest
213 movw $jump_message, %si # Display the
214 callw putstr # jump message
215 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point
218 * Display a null-terminated string
220 putstr: lodsb # load %al from %ds:(%si)
221 testb %al,%al # stop at null
222 jnz putc # if the char != null, output it
223 retw # return when null is hit
224 putc: movw $0x7,%bx # attribute for output
225 movb $0xe,%ah # BIOS: put_char
226 int $0x10 # call BIOS, print char in %al
227 jmp putstr # keep looping
230 * Enable A20. Put an upper limit on the amount of time we wait for the
231 * keyboard controller to get ready (65K x ISA access time). If
232 * we wait more than that amount, the hardware is probably
233 * legacy-free and simply doesn't have a keyboard controller.
234 * Thus, the A20 line is already enabled.
236 seta20: cli # Disable interrupts
238 seta20.1: inc %cx # Increment, overflow?
240 inb $0x64,%al # Get status
241 testb $0x2,%al # Busy?
243 movb $0xd1,%al # Command: Write
244 outb %al,$0x64 # output port
245 seta20.2: inb $0x64,%al # Get status
246 testb $0x2,%al # Busy?
248 movb $0xdf,%al # Enable
250 seta20.3: sti # Enable interrupts
254 * BTX client to start btxldr
257 btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi
260 movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push
262 push_arg: lodsl # Read argument
263 pushl %eax # Push it onto the stack
264 loop push_arg # Push all of the arguments
265 cld # In case anyone depends on this
266 pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of
268 pushl %eax # Emulate a near call
269 movl $0x1, %eax # 'exec' system call
270 int $INT_SYS # BTX system call
276 * Global descriptor table.
278 gdt: .word 0x0,0x0,0x0,0x0 # Null entry
279 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA
280 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA
281 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit)
282 .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit)
285 * Pseudo-descriptors.
287 gdtdesc: .word gdt.1-gdt-1 # Limit
290 welcome_msg: .asciz "PXE Loader 1.00\r\n\n"
291 bootinfo_msg: .asciz "Building the boot loader arguments\r\n"
292 relocate_msg: .asciz "Relocating the loader and the BTX\r\n"
293 jump_message: .asciz "Starting the BTX loader\r\n"