pxeldr.S revision 125693
1# 2# Copyright (c) 2000 John Baldwin 3# All rights reserved. 4# 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 8# such forms. 9# 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 13# purpose. 14# 15 16# $FreeBSD: head/sys/boot/i386/pxeldr/pxeldr.S 125693 2004-02-11 08:42:38Z ru $ 17 18# 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. 26# 27 28# 29# Memory locations. 30# 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 41# 42# a.out header fields 43# 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 50# 51# Flags for kargs->bootflags 52# 53 .set KARGS_FLAGS_PXE,0x2 # flag to indicate booting from 54 # PXE loader 55# 56# Boot howto bits 57# 58 .set RB_SERIAL,0x1000 # serial console 59# 60# Segment selectors. 61# 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 66# 67# BTX constants 68# 69 .set INT_SYS,0x30 # BTX syscall interrupt 70# 71# Bit in MEM_BIOS_KEYBOARD that is set if an enhanced keyboard is present 72# 73 .set KEYBOARD_BIT,0x10 74# 75# We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry 76# point) 77# 78 .code16 79 .globl start 80 .org 0x0, 0x0 81# 82# BTX program loader for PXE network booting 83# 84start: 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 98# 99# Setup the arguments that the loader is expecting from boot[12] 100# 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 107 # dwords 108 rep # Clear the arguments 109 stosl # to zero 110 orb $KARGS_FLAGS_PXE, 0x8(%bx) # kargs->bootflags |= 111 # KARGS_FLAGS_PXE 112 popl 0xc(%bx) # kargs->pxeinfo = *PXENV+ 113#ifdef ALWAYS_SERIAL 114# 115# set the RBX_SERIAL bit in the howto byte. 116 orl $RB_SERIAL, (%bx) # enable serial console 117#endif 118#ifdef PROBE_KEYBOARD 119# 120# Look at the BIOS data area to see if we have an enhanced keyboard. If not, 121# set the RBX_SERIAL bit in the howto byte. 122 testb $KEYBOARD_BIT, MEM_BIOS_KEYBOARD # keyboard present? 123 jnz keyb # yes, so skip 124 orl $RB_SERIAL, (%bx) # enable serial console 125keyb: 126#endif 127# 128# Turn on the A20 address line 129# 130 callw seta20 # Turn A20 on 131# 132# Relocate the loader and BTX using a very lazy protected mode 133# 134 movw $relocate_msg, %si # Display the 135 callw putstr # relocation message 136 movl end+AOUT_ENTRY, %edi # %edi is the destination 137 movl $(end+AOUT_HEADER), %esi # %esi is 138 # the start of the text 139 # segment 140 movl end+AOUT_TEXT, %ecx # %ecx = length of the text 141 # segment 142 lgdt gdtdesc # setup our own gdt 143 cli # turn off interrupts 144 movl %cr0, %eax # Turn on 145 orb $0x1, %al # protected 146 movl %eax, %cr0 # mode 147 ljmp $SEL_SCODE,$pm_start # long jump to clear the 148 # instruction pre-fetch queue 149 .code32 150pm_start: movw $SEL_SDATA, %ax # Initialize 151 movw %ax, %ds # %ds and 152 movw %ax, %es # %es to a flat selector 153 rep # Relocate the 154 movsb # text segment 155 addl $(MEM_PAGE_SIZE - 1), %edi # pad %edi out to a new page 156 andl $~(MEM_PAGE_SIZE - 1), %edi # for the data segment 157 movl end+AOUT_DATA, %ecx # size of the data segment 158 rep # Relocate the 159 movsb # data segment 160 movl end+AOUT_BSS, %ecx # size of the bss 161 xorl %eax, %eax # zero %eax 162 addb $3, %cl # round %ecx up to 163 shrl $2, %ecx # a multiple of 4 164 rep # zero the 165 stosl # bss 166 movl end+AOUT_ENTRY, %esi # %esi -> relocated loader 167 addl $MEM_BTX_OFFSET, %esi # %esi -> BTX in the loader 168 movl $MEM_BTX_ADDRESS, %edi # %edi -> where BTX needs to go 169 movzwl 0xa(%esi), %ecx # %ecx -> length of BTX 170 rep # Relocate 171 movsb # BTX 172 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM 173 .code16 174pm_16: movw $SEL_RDATA, %ax # Initialize 175 movw %ax, %ds # %ds and 176 movw %ax, %es # %es to a real mode selector 177 movl %cr0, %eax # Turn off 178 andb $~0x1, %al # protected 179 movl %eax, %cr0 # mode 180 ljmp $0,$pm_end # Long jump to clear the 181 # instruction pre-fetch queue 182pm_end: sti # Turn interrupts back on now 183# 184# Copy the BTX client to MEM_BTX_CLIENT 185# 186 xorw %ax, %ax # zero %ax and set 187 movw %ax, %ds # %ds and %es 188 movw %ax, %es # to segment 0 189 movw $MEM_BTX_CLIENT, %di # Prepare to relocate 190 movw $btx_client, %si # the simple btx client 191 movw $(btx_client_end-btx_client), %cx # length of btx client 192 rep # Relocate the 193 movsb # simple BTX client 194# 195# Copy the boot[12] args to where the BTX client can see them 196# 197 movw $MEM_ARG, %si # where the args are at now 198 movw $MEM_ARG_BTX, %di # where the args are moving to 199 movw $(MEM_ARG_SIZE/4), %cx # size of the arguments in longs 200 rep # Relocate 201 movsl # the words 202# 203# Save the entry point so the client can get to it later on 204# 205 movl end+AOUT_ENTRY, %eax # load the entry point 206 stosl # add it to the end of the 207 # arguments 208# 209# Now we just start up BTX and let it do the rest 210# 211 movw $jump_message, %si # Display the 212 callw putstr # jump message 213 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point 214 215# 216# Display a null-terminated string 217# 218putstr: lodsb # load %al from %ds:(%si) 219 testb %al,%al # stop at null 220 jnz putc # if the char != null, output it 221 retw # return when null is hit 222putc: movw $0x7,%bx # attribute for output 223 movb $0xe,%ah # BIOS: put_char 224 int $0x10 # call BIOS, print char in %al 225 jmp putstr # keep looping 226 227# 228# Enable A20 229# 230seta20: cli # Disable interrupts 231seta20.1: inb $0x64,%al # Get status 232 testb $0x2,%al # Busy? 233 jnz seta20.1 # Yes 234 movb $0xd1,%al # Command: Write 235 outb %al,$0x64 # output port 236seta20.2: inb $0x64,%al # Get status 237 testb $0x2,%al # Busy? 238 jnz seta20.2 # Yes 239 movb $0xdf,%al # Enable 240 outb %al,$0x60 # A20 241 sti # Enable interrupts 242 retw # To caller 243 244# 245# BTX client to start btxldr 246# 247 .code32 248btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi 249 # %ds:(%esi) -> end 250 # of boot[12] args 251 movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push 252 std # Go backwards 253push_arg: lodsl # Read argument 254 pushl %eax # Push it onto the stack 255 loop push_arg # Push all of the arguments 256 cld # In case anyone depends on this 257 pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of 258 # the loader 259 pushl %eax # Emulate a near call 260 movl $0x1, %eax # 'exec' system call 261 int $INT_SYS # BTX system call 262btx_client_end: 263 .code16 264 265 .p2align 4 266# 267# Global descriptor table. 268# 269gdt: .word 0x0,0x0,0x0,0x0 # Null entry 270 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA 271 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA 272 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit) 273 .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit) 274gdt.1: 275# 276# Pseudo-descriptors. 277# 278gdtdesc: .word gdt.1-gdt-1 # Limit 279 .long gdt # Base 280 281welcome_msg: .asciz "PXE Loader 1.00\r\n\n" 282bootinfo_msg: .asciz "Building the boot loader arguments\r\n" 283relocate_msg: .asciz "Relocating the loader and the BTX\r\n" 284jump_message: .asciz "Starting the BTX loader\r\n" 285 286 .p2align 4 287end: 288