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/* $OpenBSD: srt0.S,v 1.1 2004/08/21 18:53:38 tom Exp $ */
/*
* Copyright (c) 1997 Michael Shalayeff
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
*/
#include <machine/asm.h>
#include <assym.h>
#define BOOTSTACK 0xfffc
.globl _C_LABEL(end)
.globl _C_LABEL(edata)
.globl _C_LABEL(boot)
.globl _C_LABEL(_rtt)
.globl _C_LABEL(bios_bootdev)
.globl _ASM_LABEL(pmm_init)
.globl Gdtr
.text
.code16
.globl _start
_start:
#ifdef DEBUG
movl $0xb80a0, %ebx
addr32 movl $0x07420742, (%ebx)
#endif
/* Clobbers %ax, maybe more */
#define putc(c) movb $c, %al; call Lchr
/*
* We operate as a no emulation boot image, as defined by the
* El Torito Bootable CD-ROM Format Specification v1.0. We use
* a load segment of 0x07C0 (physical load address of 0x7C00).
* Like the standard /boot, we are linked to run at 0x40120
* (load address 0x40000), so we relocate to there.
*
* From 0x7C00 to 0x40000 is 0x38400 (230400) bytes, so don't
* have to worry about an overlapping copy until cdboot is
* over 225 KB.
*
* Note that there are other reasons to be worried if
* sizeof(/boot) > 64 KB. So currently we copy a maximum of 64 KB.
*
* Our cdbr CD-ROM boot sector passes us the drive number to use
* in %dl.
*/
#define CDBOOTADDR 0x7c00 /* Address where BIOS loads up */
xorw %ax, %ax
movw %ax, %ss /* CPU disables interrupts till... */
movl $CDBOOTADDR-4, %esp /* after this instruction */
movw $(CDBOOTADDR >> 4), %ax
movw %ax, %ds
xorw %si, %si /* Where we're coming from */
movw $(LINKADDR >> 4), %ax
movw %ax, %es /* Set %es = 0x4000 */
xorw %di, %di /* Where we're going to */
movl $_C_LABEL(end), %ecx
subl $_C_LABEL(_start), %ecx /* How big are we? */
cld
rep; movsb /* Copy into place */
jmpl $(LINKADDR >> 4), $(relocated-_start) /* Now relocate */
relocated:
/*
* In 16-bit mode, we have segment registers == 0x4012, and
* offsets work from here, with offset(_start) == 0.
*
* In 32-bit mode, we have a flat memory model, where
* offset(_start) == 0x40120. This is how we're linked.
*
* Now transition to protected mode.
*
* First, initialise the global descriptor table.
*/
cli
push %cs
pop %ds
addr32 data32 lgdt (Gdtr - LINKADDR)
movl %cr0, %eax
orl $CR0_PE, %eax
data32 movl %eax, %cr0
data32 ljmp $8, $1f /* Seg sel 0x08 is flat 32-bit code */
1:
.code32
movl $0x10, %eax /* Seg sel 0x10 is flat 32-bit data */
mov %ax, %ds
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %ax, %ss
movl $BOOTSTACK, %esp
#ifdef DEBUG
movl $0xb8000, %ebx
movl $0x07420742, (%ebx)
#endif
movzbl %dl, %eax
orl $0x100, %eax /* Indicate that it's a cd device */
pushl %eax /* boot() takes this as a parameter */
/* Set up an interrupt descriptor table for protected mode. */
call _ASM_LABEL(pmm_init)
#ifdef DEBUG
movl $0xb80a4, %ebx
movl $0x07520752, (%ebx)
#endif
/* Zero .bss */
xorl %eax, %eax
movl $_C_LABEL(end), %ecx
subl $_C_LABEL(edata), %ecx
movl $_C_LABEL(edata), %edi
cld
rep; stosb
/* Set our program name ("CDBOOT", not "BOOT"). */
movl $cd_progname, %eax
movl %eax, progname
/* Put the boot device number into the globals that need it */
popl %eax /* Get this back from the stack */
pushl %eax /* boot() takes this as a parameter */
movl %eax, _C_LABEL(bios_bootdev)
movl %eax, _C_LABEL(bios_cddev)
/*
* Now call "main()".
*
* We run in flat 32-bit protected mode, with no address mapping.
*/
#ifdef DEBUG
movl $0xb8004, %ebx
movl $0x07410741, (%ebx)
#endif
call _C_LABEL(boot)
/* boot() should not return. If it does, reset computer. */
jmp _C_LABEL(_rtt)
ENTRY(debugchar)
pushl %ebx
movl 8(%esp), %ebx
addl %ebx, %ebx
addl $0xb8000, %ebx
xorl %eax, %eax
movb 12(%esp), %al
andl $0xfffffffe, %ebx
movb %al, (%ebx)
popl %ebx
ret
.code16
/*
* Display ASCIZ string at %si. Trashes %si.
*/
Lstr:
pushw %ax
cld
1:
lodsb /* %al = *%si++ */
testb %al, %al
jz 1f
call Lchr
jmp 1b
1: popw %ax
ret
/*
* Write out value in %ax in hex
*/
hex_word:
pushw %ax
mov %ah, %al
call hex_byte
popw %ax
/* fall thru */
/*
* Write out value in %al in hex
*/
hex_byte:
pushw %ax
shrb $4, %al
call hex_nibble
popw %ax
/* fall thru */
/* Write out nibble in %al */
hex_nibble:
and $0x0F, %al
add $'0', %al
cmpb $'9', %al
jbe Lchr
addb $'A'-'9'-1, %al
/* fall thru to Lchr */
/*
* Lchr: write the character in %al to console
*/
Lchr:
pushw %bx
movb $0x0e, %ah
xorw %bx, %bx
incw %bx /* movw $0x01, %bx */
int $0x10
popw %bx
ret
cd_progname:
.asciz "CDBOOT"
.end
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