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 * $FreeBSD: head/sys/boot/i386/pxeldr/pxeldr.S 129240 2004-05-14 20:29:30Z ru $ |
16 */ 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 */ |
117 orl $RB_SERIAL, (%bx) # enable serial console |
118#endif 119#ifdef PROBE_KEYBOARD 120/* 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. 123 */ |
124 testb $KEYBOARD_BIT, MEM_BIOS_KEYBOARD # keyboard present? 125 jnz keyb # yes, so skip 126 orl $RB_SERIAL, (%bx) # enable serial console |
127keyb: 128#endif 129/* 130 * Turn on the A20 address line 131 */ |
132 callw seta20 # Turn A20 on |
133/* 134 * Relocate the loader and BTX using a very lazy protected mode 135 */ |
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 141 # segment 142 movl end+AOUT_TEXT, %ecx # %ecx = length of the text 143 # segment 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 |
151 .code32 |
152pm_start: movw $SEL_SDATA, %ax # Initialize 153 movw %ax, %ds # %ds and 154 movw %ax, %es # %es to a flat selector 155 rep # Relocate the 156 movsb # text segment 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 160 rep # Relocate the 161 movsb # 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 4 166 rep # zero the 167 stosl # bss 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 172 rep # Relocate 173 movsb # BTX 174 ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM |
175 .code16 |
176pm_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 184pm_end: sti # Turn interrupts back on now |
185/* 186 * Copy the BTX client to MEM_BTX_CLIENT 187 */ |
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 194 rep # Relocate the 195 movsb # simple BTX client |
196/* 197 * Copy the boot[12] args to where the BTX client can see them 198 */ |
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 202 rep # Relocate 203 movsl # the words |
204/* 205 * Save the entry point so the client can get to it later on 206 */ |
207 movl end+AOUT_ENTRY, %eax # load the entry point 208 stosl # add it to the end of the 209 # arguments |
210/* 211 * Now we just start up BTX and let it do the rest 212 */ |
213 movw $jump_message, %si # Display the 214 callw putstr # jump message 215 ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point |
216 217/* 218 * Display a null-terminated string 219 */ |
220putstr: 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 224putc: 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 |
228 229/* 230 * Enable A20 231 */ |
232seta20: cli # Disable interrupts 233seta20.1: inb $0x64,%al # Get status 234 testb $0x2,%al # Busy? 235 jnz seta20.1 # Yes 236 movb $0xd1,%al # Command: Write 237 outb %al,$0x64 # output port 238seta20.2: inb $0x64,%al # Get status 239 testb $0x2,%al # Busy? 240 jnz seta20.2 # Yes 241 movb $0xdf,%al # Enable 242 outb %al,$0x60 # A20 243 sti # Enable interrupts 244 retw # To caller |
245 246/* 247 * BTX client to start btxldr 248 */ 249 .code32 250btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi |
251 # %ds:(%esi) -> end 252 # of boot[12] args 253 movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push 254 std # Go backwards 255push_arg: lodsl # Read argument 256 pushl %eax # Push it onto the stack 257 loop push_arg # Push all of the arguments 258 cld # In case anyone depends on this 259 pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of 260 # the loader 261 pushl %eax # Emulate a near call 262 movl $0x1, %eax # 'exec' system call 263 int $INT_SYS # BTX system call |
264btx_client_end: 265 .code16 266 267 .p2align 4 268/* 269 * Global descriptor table. 270 */ |
271gdt: .word 0x0,0x0,0x0,0x0 # Null entry 272 .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA 273 .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA 274 .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit) 275 .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit) |
276gdt.1: 277/* 278 * Pseudo-descriptors. 279 */ |
280gdtdesc: .word gdt.1-gdt-1 # Limit 281 .long gdt # Base |
282 283welcome_msg: .asciz "PXE Loader 1.00\r\n\n" 284bootinfo_msg: .asciz "Building the boot loader arguments\r\n" 285relocate_msg: .asciz "Relocating the loader and the BTX\r\n" 286jump_message: .asciz "Starting the BTX loader\r\n" 287 288 .p2align 4 289end: |