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/* * Copyright (c) 2000 John Baldwin * All rights reserved. * * Redistribution and use in source and binary forms are freely * permitted provided that the above copyright notice and this * paragraph and the following disclaimer are duplicated in all * such forms. * * This software is provided "AS IS" and without any express or * implied warranties, including, without limitation, the implied * warranties of merchantability and fitness for a particular * purpose. * * $FreeBSD: release/9.1.0/sys/boot/i386/pxeldr/pxeldr.S 237761 2012-06-29 10:10:16Z avg $ */ /* * This simple program is a preloader for the normal boot3 loader. It is simply * prepended to the beginning of a fully built and btxld'd loader. It then * copies the loader to the address boot2 normally loads it, emulates the * boot[12] environment (protected mode, a bootinfo struct, etc.), and then jumps * to the start of btxldr to start the boot process. This method allows a stock * /boot/loader to be booted over the network via PXE w/o having to write a * separate PXE-aware client just to load the loader. */ #include <sys/reboot.h> #include <bootargs.h> /* * Memory locations. */ .set MEM_PAGE_SIZE,0x1000 # memory page size, 4k .set MEM_ARG,0x900 # Arguments at start .set MEM_ARG_BTX,0xa100 # Where we move them to so the # BTX client can see them .set MEM_ARG_SIZE,0x18 # Size of the arguments .set MEM_BTX_ADDRESS,0x9000 # where BTX lives .set MEM_BTX_ENTRY,0x9010 # where BTX starts to execute .set MEM_BTX_OFFSET,MEM_PAGE_SIZE # offset of BTX in the loader .set MEM_BTX_CLIENT,0xa000 # where BTX clients live .set MEM_BIOS_KEYBOARD,0x496 # BDA byte with keyboard bit /* * a.out header fields */ .set AOUT_TEXT,0x04 # text segment size .set AOUT_DATA,0x08 # data segment size .set AOUT_BSS,0x0c # zero'd BSS size .set AOUT_SYMBOLS,0x10 # symbol table .set AOUT_ENTRY,0x14 # entry point .set AOUT_HEADER,MEM_PAGE_SIZE # size of the a.out header /* * Segment selectors. */ .set SEL_SDATA,0x8 # Supervisor data .set SEL_RDATA,0x10 # Real mode data .set SEL_SCODE,0x18 # PM-32 code .set SEL_SCODE16,0x20 # PM-16 code /* * BTX constants */ .set INT_SYS,0x30 # BTX syscall interrupt /* * Bit in MEM_BIOS_KEYBOARD that is set if an enhanced keyboard is present */ .set KEYBOARD_BIT,0x10 /* * We expect to be loaded by the BIOS at 0x7c00 (standard boot loader entry * point) */ .code16 .globl start .org 0x0, 0x0 /* * BTX program loader for PXE network booting */ start: cld # string ops inc xorw %ax, %ax # zero %ax movw %ax, %ss # setup the movw $start, %sp # stack movw %es, %cx # save PXENV+ segment movw %ax, %ds # setup the movw %ax, %es # data segments andl $0xffff, %ecx # clear upper words andl $0xffff, %ebx # of %ebx and %ecx shll $4, %ecx # calculate the offset of addl %ebx, %ecx # the PXENV+ struct and pushl %ecx # save it on the stack movw $welcome_msg, %si # %ds:(%si) -> welcome message callw putstr # display the welcome message /* * Setup the arguments that the loader is expecting from boot[12] */ movw $bootinfo_msg, %si # %ds:(%si) -> boot args message callw putstr # display the message movw $MEM_ARG, %bx # %ds:(%bx) -> boot args movw %bx, %di # %es:(%di) -> boot args xorl %eax, %eax # zero %eax movw $(MEM_ARG_SIZE/4), %cx # Size of arguments in 32-bit # dwords rep # Clear the arguments stosl # to zero orb $KARGS_FLAGS_PXE, 0x8(%bx) # kargs->bootflags |= # KARGS_FLAGS_PXE popl 0xc(%bx) # kargs->pxeinfo = *PXENV+ #ifdef ALWAYS_SERIAL /* * set the RBX_SERIAL bit in the howto byte. */ orl $RB_SERIAL, (%bx) # enable serial console #endif #ifdef PROBE_KEYBOARD /* * Look at the BIOS data area to see if we have an enhanced keyboard. If not, * set the RBX_DUAL and RBX_SERIAL bits in the howto byte. */ testb $KEYBOARD_BIT, MEM_BIOS_KEYBOARD # keyboard present? jnz keyb # yes, so skip orl $(RB_MULTIPLE | RB_SERIAL), (%bx) # enable serial console keyb: #endif /* * Turn on the A20 address line */ callw seta20 # Turn A20 on /* * Relocate the loader and BTX using a very lazy protected mode */ movw $relocate_msg, %si # Display the callw putstr # relocation message movl end+AOUT_ENTRY, %edi # %edi is the destination movl $(end+AOUT_HEADER), %esi # %esi is # the start of the text # segment movl end+AOUT_TEXT, %ecx # %ecx = length of the text # segment lgdt gdtdesc # setup our own gdt cli # turn off interrupts movl %cr0, %eax # Turn on orb $0x1, %al # protected movl %eax, %cr0 # mode ljmp $SEL_SCODE,$pm_start # long jump to clear the # instruction pre-fetch queue .code32 pm_start: movw $SEL_SDATA, %ax # Initialize movw %ax, %ds # %ds and movw %ax, %es # %es to a flat selector rep # Relocate the movsb # text segment addl $(MEM_PAGE_SIZE - 1), %edi # pad %edi out to a new page andl $~(MEM_PAGE_SIZE - 1), %edi # for the data segment movl end+AOUT_DATA, %ecx # size of the data segment rep # Relocate the movsb # data segment movl end+AOUT_BSS, %ecx # size of the bss xorl %eax, %eax # zero %eax addb $3, %cl # round %ecx up to shrl $2, %ecx # a multiple of 4 rep # zero the stosl # bss movl end+AOUT_ENTRY, %esi # %esi -> relocated loader addl $MEM_BTX_OFFSET, %esi # %esi -> BTX in the loader movl $MEM_BTX_ADDRESS, %edi # %edi -> where BTX needs to go movzwl 0xa(%esi), %ecx # %ecx -> length of BTX rep # Relocate movsb # BTX ljmp $SEL_SCODE16,$pm_16 # Jump to 16-bit PM .code16 pm_16: movw $SEL_RDATA, %ax # Initialize movw %ax, %ds # %ds and movw %ax, %es # %es to a real mode selector movl %cr0, %eax # Turn off andb $~0x1, %al # protected movl %eax, %cr0 # mode ljmp $0,$pm_end # Long jump to clear the # instruction pre-fetch queue pm_end: sti # Turn interrupts back on now /* * Copy the BTX client to MEM_BTX_CLIENT */ xorw %ax, %ax # zero %ax and set movw %ax, %ds # %ds and %es movw %ax, %es # to segment 0 movw $MEM_BTX_CLIENT, %di # Prepare to relocate movw $btx_client, %si # the simple btx client movw $(btx_client_end-btx_client), %cx # length of btx client rep # Relocate the movsb # simple BTX client /* * Copy the boot[12] args to where the BTX client can see them */ movw $MEM_ARG, %si # where the args are at now movw $MEM_ARG_BTX, %di # where the args are moving to movw $(MEM_ARG_SIZE/4), %cx # size of the arguments in longs rep # Relocate movsl # the words /* * Save the entry point so the client can get to it later on */ movl end+AOUT_ENTRY, %eax # load the entry point stosl # add it to the end of the # arguments /* * Now we just start up BTX and let it do the rest */ movw $jump_message, %si # Display the callw putstr # jump message ljmp $0,$MEM_BTX_ENTRY # Jump to the BTX entry point /* * Display a null-terminated string */ putstr: lodsb # load %al from %ds:(%si) testb %al,%al # stop at null jnz putc # if the char != null, output it retw # return when null is hit putc: movw $0x7,%bx # attribute for output movb $0xe,%ah # BIOS: put_char int $0x10 # call BIOS, print char in %al jmp putstr # keep looping /* * Enable A20. Put an upper limit on the amount of time we wait for the * keyboard controller to get ready (65K x ISA access time). If * we wait more than that amount, the hardware is probably * legacy-free and simply doesn't have a keyboard controller. * Thus, the A20 line is already enabled. */ seta20: cli # Disable interrupts xor %cx,%cx # Clear seta20.1: inc %cx # Increment, overflow? jz seta20.3 # Yes inb $0x64,%al # Get status testb $0x2,%al # Busy? jnz seta20.1 # Yes movb $0xd1,%al # Command: Write outb %al,$0x64 # output port seta20.2: inb $0x64,%al # Get status testb $0x2,%al # Busy? jnz seta20.2 # Yes movb $0xdf,%al # Enable outb %al,$0x60 # A20 seta20.3: sti # Enable interrupts retw # To caller /* * BTX client to start btxldr */ .code32 btx_client: movl $(MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE-4), %esi # %ds:(%esi) -> end # of boot[12] args movl $(MEM_ARG_SIZE/4), %ecx # Number of words to push std # Go backwards push_arg: lodsl # Read argument pushl %eax # Push it onto the stack loop push_arg # Push all of the arguments cld # In case anyone depends on this pushl MEM_ARG_BTX-MEM_BTX_CLIENT+MEM_ARG_SIZE # Entry point of # the loader pushl %eax # Emulate a near call movl $0x1, %eax # 'exec' system call int $INT_SYS # BTX system call btx_client_end: .code16 .p2align 4 /* * Global descriptor table. */ gdt: .word 0x0,0x0,0x0,0x0 # Null entry .word 0xffff,0x0,0x9200,0xcf # SEL_SDATA .word 0xffff,0x0,0x9200,0x0 # SEL_RDATA .word 0xffff,0x0,0x9a00,0xcf # SEL_SCODE (32-bit) .word 0xffff,0x0,0x9a00,0x8f # SEL_SCODE16 (16-bit) gdt.1: /* * Pseudo-descriptors. */ gdtdesc: .word gdt.1-gdt-1 # Limit .long gdt # Base welcome_msg: .asciz "PXE Loader 1.00\r\n\n" bootinfo_msg: .asciz "Building the boot loader arguments\r\n" relocate_msg: .asciz "Relocating the loader and the BTX\r\n" jump_message: .asciz "Starting the BTX loader\r\n" .p2align 4 end: