NetBSD/sys/arch/i386/boot/boot2.S

/*
 * Ported to boot 386BSD by Julian Elischer (julian@tfs.com) Sept 1992
 *
 * Mach Operating System
 * Copyright (c) 1992, 1991 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */

/*
 * HISTORY
 * $Log: boot2.S,v $
 * Revision 1.4  1993/11/10 16:08:19  cgd
 * add addr32, as noted on freebsd-hackers by bde himself.
 *
Revision 1.3  1993/07/13  21:51:36  mycroft
Fix addressing bug in bdb junk.

Revision 1.2  1993/07/11  12:02:22  andrew
Fixes from bde, including support for loading @ any MB boundary (e.g. a
kernel linked for 0xfe100000 will load at the 1MB mark) and read-ahead
buffering to speed booting from floppies.  Also works with aha174x
controllers in enhanced mode.

 *
 * 93/07/06  bde
 *	Delete LOADMSG define (not used).
 *
 * 93/06/29  bde
 *	Use EXT.
 *
 *	Initialize GDT and IDT pointers at boot time.
 *
 *	Convert (drive | head | junk) to drive arg for boot() (not strictly
 *	necessary - boot() only uses drive & 0x80).
 *
 * 93/06/28  bde
 *	Initialize top bits of %eax for setting _ouraddr.  start.s
 *	initialized them suitably, but this isn't documented, and the BIOS
 *	isn't documented to preserve them.
 *
 *	Use addr32 for setting _ouraddr.  Without this, there were extra bytes
 *	0, 0 after the store.  These decode as "add %al, (%bx,%si)" in 16-bit
 *	mode would clobber something (except %al is very likely to be 0 :-).
 *
 *	Clear the bss.  This may be unnecessary.  Some is already cleared in
 *	the disk image.
 *
 *	Loop if boot() returns.
 *
Revision 1.1  1993/03/21  18:08:33  cgd
after 0.2.2 "stable" patches applied

 * Revision 2.2  92/04/04  11:35:26  rpd
 * 	From 2.5
 * 	[92/03/30            rvb]
 * 
 * Revision 2.2  91/04/02  14:39:21  mbj
 * 	Put into rcs tree
 * 	[90/02/09            rvb]
 * 
 */

#include	"asm.h"

/* Conventional GDT indexes. */
#define BOOT_CS_INDEX		3
#define BOOT_CS16_INDEX		5
#define BOOT_DS_INDEX		4
#define DB_CS_INDEX		14
#define DB_CS16_INDEX		15
#define DB_DS_INDEX		16
#define GDT_INDEX		17

/* Vector numbers. */
#define BREAKPOINT_VECTOR	3
#define DEBUG_VECTOR		1

/*
 * boot2() -- second stage boot
 */

.globl EXT(ouraddr)

ENTRY(boot2)
	data32
	subl	%eax, %eax
	mov	%cs, %ax
	mov	%ax, %ds
	mov	%ax, %es
	data32
	shll	$4, %eax
	addr32
	data32
	movl	%eax, EXT(ouraddr)

	/* fix up GDT entries for bootstrap */
#define FIXUP(gdt_index) \
	addr32; \
	movl	%eax, EXT(Gdt)+(8*gdt_index)+2;	/* actually movw %ax */ \
	addr32; \
	movb	%bl, EXT(Gdt)+(8*gdt_index)+4

	data32
	shld	$16, %eax, %ebx
	FIXUP(BOOT_CS_INDEX)
	FIXUP(BOOT_CS16_INDEX)
	FIXUP(BOOT_DS_INDEX)

	/* fix up GDT entry for GDT, and GDT and IDT pointers */
	data32
	movl	%eax, %ecx
	data32
	addl	$ EXT(Gdt), %eax
	data32
	shld	$16, %eax, %ebx
	FIXUP(GDT_INDEX)
	addr32
	data32
	movl	%eax, EXT(Gdtr)+2
	data32
	addl	$ EXT(Idt), %ecx
	addr32
	data32
	movl	%ecx, EXT(Idtr_prot)+2

	/* %es = vector table segment for a while */
	push	%es
	data32
	subl	%eax, %eax
	mov	%ax, %es

	/* fix up GDT entries for bdb */
	data32
	movl	$4*DEBUG_VECTOR, %esi
	addr32
	movl	%es: 2(%esi), %eax	/* actually movw to %ax */
	data32
	shll	$4, %eax
	data32
	shld	$16, %eax, %ebx
	FIXUP(DB_CS_INDEX)
	FIXUP(DB_CS16_INDEX)
	FIXUP(DB_DS_INDEX)

	/* Fetch entry points of bdb's protected mode trap handlers.  These
	 * are stored at 2 before the corresponding entry points for real mode.
	 */
	data32
	subl	%ebx, %ebx
	addr32
	movl	%es: (%esi), %ebx	/* actually movw to %bx */
	data32
	subl	%ecx, %ecx
	addr32
	movl	%es: 4*(BREAKPOINT_VECTOR-DEBUG_VECTOR)(%esi), %ecx
					/* actually movw to %cx */

	/* %es = bdb segment for a while */
	data32
	shrl	$4, %eax
	mov	%ax, %es

	/* fix up IDT entries for bdb */
	addr32
	movl	%es: -2(%ebx), %eax	/* actually movw to %ax */
	addr32
	movl	%eax, EXT(Idt)+8*DEBUG_VECTOR	/* actually movw %ax */
	movl	%es: -2(%ecx), %eax	/* actually movw to %ax */
	addr32
	movl	%eax, EXT(Idt)+8*BREAKPOINT_VECTOR	/* actually movw %ax */

	/* finished with groping in real mode segments */
	pop	%es

	/* change to protected mode */
	data32
	call	EXT(real_to_prot)

	/* clear the bss */
	movl	$ EXT(edata), %edi	/* no EXT(_edata) - krufty ld */
	movl	$ EXT(end), %ecx	/* or EXT(_end) */
	subl	%edi, %ecx
	subb	%al, %al
	rep
	stosb

	movzbl	%dl, %edx	/* discard head (%dh) and random high bits */
	pushl	%edx
	call	EXT(boot)
oops:
	hlt
	jmp	oops

	.data
        .align 2
#if 0 /* XXX this would give losing "_ouraddr :".  Better declared in C */
EXT(ouraddr):
#else
_ouraddr:
#endif
        .long 0