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biosboot.S revision 1.6 
      1 /*	$NetBSD: biosboot.S,v 1.6 2008/04/28 20:23:25 martin Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2003 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by David Laight.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <machine/asm.h>
     33 #include <sys/bootblock.h>
     34 
     35 /*
     36  * Code linked to 0x1000:0 and (usually) read from /boot by bootxx code
     37  *
     38  * On entry:
     39  * 	%dl			BIOS drive number
     40  *	%ebx			Sector number of netbsd partition
     41  *	%ds:%esi		Boot parameter block (patched by installboot)
     42  *	%cs			0x1000
     43  *	%ds, %es, %ss		All zero
     44  *	%sp			near 0xfffc
     45  */
     46 
     47 	.text
     48 	.code16
     49 ENTRY(boot_start)
     50 	jmp	boot_start_1
     51 	.balign	4
     52 ENTRY(boot_magic)
     53 	.long	X86_BOOT_MAGIC_2	/* checked for by bootxx code */
     54 ENTRY(boot_params)
     55 	.long	boot_start_1 - boot_params
     56 #include <boot_params.S>
     57 	. = boot_start + 0x80		/* space for patchable variables */
     58 boot_start_1:
     59 
     60 #if 0
     61 	/* Allow for boot_start not being %cs:0 */
     62 	call	2f
     63 2:	pop	%cx
     64 	sub	$2b, %cx		/* %ax is offset */
     65 	test	$0xf, %cx		/* check code seg aligned */
     66 	jz	3f
     67 	lret				/* not playing if not */
     68 3:	mov	%cs, %ax
     69 	shr	$4, %cx
     70 	add	%cx, %ax		/* segment staring at boot_start */
     71 	push	%ax
     72 	push	$4f
     73 	lret
     74 4:
     75 #endif
     76 
     77 	mov	%cs, %ax
     78 	mov	%ax, %es
     79 
     80 	/* Grab boot_params patched into bootxx by installboot */
     81 	cmpl	$X86_BOOT_MAGIC_1,-4(%si)	/* sanity check ptr */
     82 	jne	2f
     83 	mov	$boot_params, %di
     84 	movl	(%si),%ecx
     85 	cmp	$boot_start_1 - boot_params, %cx
     86 	jbe	1f
     87 	mov	$boot_start_1 - boot_params, %cx
     88 1:	cld
     89 	rep
     90 	movsb
     91 2:
     92 
     93 	mov	%ax, %ds
     94 	movl	$_end, %eax		/* top of bss */
     95 	shr	$4, %eax		/* as a segment */
     96 	add	$0x1001, %ax		/* and + 64k */
     97 	mov	%ax, %ss		/* for stack */
     98 	mov	$0xfffc, %sp		/* %sp at top of it */
     99 
    100 	call	gdt_fixup
    101 
    102 	calll	real_to_prot
    103 	.code32
    104 
    105 	movl	$_end, %ecx		/* zero bss */
    106 	movl	$__bss_start, %edi
    107 	subl	%edi, %ecx
    108 	shr	$2, %ecx		/* _end and __bss_start are aligned */
    109 	xor	%eax, %eax
    110 	rep
    111 	stosl
    112 
    113 	and	$0xff, %edx
    114 	push	%ebx			/* first sector of bios partition */
    115 	push	%edx			/* bios disk */
    116 	call	_C_LABEL(boot2)		/* C bootstrap code */
    117 	add	$8, %esp
    118 	call	prot_to_real
    119 	.code16
    120 
    121 boot_fail:
    122 	push	%ax
    123 	movw	$1f, %si
    124 	call	message
    125 	pop	%si
    126 	call	message
    127 	jmp	loopstop
    128 1:	.asciz	"Boot2 failed: "
    129 
    130 ENTRY(_rtt)
    131 	.code32
    132 	call	prot_to_real
    133 	.code16
    134 loopstop:
    135 	movb	0x86, %ah		/* delay for about a second */
    136 	movw	$16, %cx
    137 	int	$0x15
    138 	int	$0x18			/* might be a boot fail entry */
    139 1:	sti
    140 	hlt
    141 	jmp	1b
    142