freebsd/sys/i386/boot/asm.S

/*
 * 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.
 *
 *	from: Mach, Revision 2.2  92/04/04  11:34:13  rpd
 *	$Id: asm.S,v 1.2 1993/10/16 19:11:27 rgrimes Exp $
 */


/*
  Copyright 1988, 1989, 1990, 1991, 1992 
   by Intel Corporation, Santa Clara, California.

                All Rights Reserved

Permission to use, copy, modify, and distribute this software and
its documentation for any purpose and without fee is hereby
granted, provided that the above copyright notice appears in all
copies and that both the copyright notice and this permission notice
appear in supporting documentation, and that the name of Intel
not be used in advertising or publicity pertaining to distribution
of the software without specific, written prior permission.

INTEL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
IN NO EVENT SHALL INTEL BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

	.file "asm.s"

#include "asm.h"


CR0_PE_ON	=	0x1
CR0_PE_OFF	=	0xfffffffe

.globl	_ouraddr
	.text

/*
#
# real_to_prot()
# 	transfer from real mode to protected mode.
*/

ENTRY(real_to_prot)
	# guarantee that interrupt is disabled when in prot mode
	cli

	# load the gdtr
	addr32
	data32
	lgdt	EXT(Gdtr)

	# set the PE bit of CR0
	mov	%cr0, %eax

	data32
	or	$CR0_PE_ON, %eax
	mov	%eax, %cr0 

	# make intrasegment jump to flush the processor pipeline and
	# reload CS register
	data32
	ljmp	$0x18, $xprot

xprot:
	# we are in USE32 mode now
	# set up the protected mode segment registers : DS, SS, ES
	mov	$0x20, %eax
	movw	%ax, %ds
	movw	%ax, %ss
	movw	%ax, %es

#ifdef BDE_DEBUGGER
	# load idtr so we can debug
	lidt	EXT(Idtr_prot)
#endif

	ret

/*
#
# prot_to_real()
# 	transfer from protected mode to real mode
# 
*/

ENTRY(prot_to_real)

	# set up a dummy stack frame for the second seg change.
	movl 	_ouraddr, %eax
	sarl	$4, %eax
	pushw	%ax
	movw	$xreal, %ax	# gas botches pushw $xreal - extra bytes 0, 0
	pushw	%ax		# decode to add %al, (%eax) (%al usually 0)

	# Change to use16 mode.
	ljmp	$0x28, $x16

x16:
	# clear the PE bit of CR0
	mov	%cr0, %eax
	data32
	and 	$CR0_PE_OFF, %eax
	mov	%eax, %cr0

	# make intersegment jmp to flush the processor pipeline
	# using the fake stack frame set up earlier
	# and reload CS register
	lret

xreal:
	# we are in real mode now
	# set up the real mode segment registers : DS, SS, ES
	movw	%cs, %ax
	movw	%ax, %ds
	movw	%ax, %ss
	movw	%ax, %es

#ifdef BDE_DEBUGGER
	# load idtr so we can debug
	addr32
	data32
	lidt	EXT(Idtr_real)
#endif

	data32
	ret

/*
#
# startprog(phyaddr)
#	start the program on protected mode where phyaddr is the entry point
#
*/

ENTRY(startprog)
	push	%ebp
	mov	%esp, %ebp

	# get things we need into registers
	movl	0x8(%ebp), %ecx		# entry offset 
	movl	0x0c(%ebp), %eax	# &argv

	# make a new stack at 0:0xa0000 (big segs)
	mov	$0x10, %ebx
	movw	%bx, %ss
	movl	$0xa0000, %ebx
	movl	%ebx, %esp
	
	# push some number of args onto the stack
	pushl	$0			# nominally a cyl offset in the boot.
	pushl	0x8(%eax)		# argv[2] = bootdev
	pushl	0x4(%eax)		# argv[1] = howto
	pushl	$0			# dummy 'return' address
	
	# push on our entry address
	mov	$0x08, %ebx		# segment
	pushl	%ebx
	pushl	%ecx

	# convert over the other data segs
	mov	$0x10, %ebx
	movw	%bx, %ds
	movw	%bx, %es

	# convert the PC (and code seg)
	lret
/*
#
# pbzero( dst, cnt)
#	where src is a virtual address and dst is a physical address
*/

ENTRY(pbzero)
	push	%ebp
	mov	%esp, %ebp
	push	%es
	push	%esi
	push	%edi
	push	%ecx

	cld

	# set %es to point at the flat segment
	mov	$0x10, %eax
	movw	%ax, %es

	mov	0x8(%ebp), %edi		# destination
	mov	0xc(%ebp), %ecx		# count
	mov	$0x0, %eax		# value

	rep
	stosb

	pop	%ecx
	pop	%edi
	pop	%esi
	pop	%es
	pop	%ebp

	ret
/*
#
# pcpy(src, dst, cnt)
#	where src is a virtual address and dst is a physical address
#
*/

ENTRY(pcpy)
	push	%ebp
	mov	%esp, %ebp
	push	%es
	push	%esi
	push	%edi
	push	%ecx

	cld

	# set %es to point at the flat segment
	mov	$0x10, %eax
	movw	%ax, %es

	mov	0x8(%ebp), %esi		# source
	mov	0xc(%ebp), %edi		# destination
	mov	0x10(%ebp), %ecx	# count

	rep
	movsb

	pop	%ecx
	pop	%edi
	pop	%esi
	pop	%es
	pop	%ebp

	ret