i16_init_vm.s

基于组件方式开发操作系统的OSKIT源代码

/*
 * Copyright (c) 1994-1995, 1998, 1999 University of Utah and the Flux Group.
 * All rights reserved.
 * 
 * This file is part of the Flux OSKit.  The OSKit is free software, also known
 * as "open source;" you can redistribute it and/or modify it under the terms
 * of the GNU General Public License (GPL), version 2, as published by the Free
 * Software Foundation (FSF).  To explore alternate licensing terms, contact
 * the University of Utah at [e-mail] or [phone].
 * 
 * The OSKit is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GPL for more details.  You should have
 * received a copy of the GPL along with the OSKit; see the file COPYING.  If
 * not, write to the FSF, 59 Temple Place #330, Boston, MA 02111-1307, USA.
 */
#include <oskit/config.h>
#ifdef HAVE_CODE16

#include <oskit/x86/asm.h>

/*
 * This function is called by i16_crt0 (or the equivalent)
 * to set up our basic virtual memory layout variables
 * to settings appropriate when running in 16-bit real mode,
 * before calling i16_main().
 */

	.text
	.code16

ENTRY(i16_init_vm)
	pushl %eax

	/* Find our 16-bit code/data/everything segment.  */
	movw	%cs, %ax
ADDR32	movw	%ax, EXT(real_cs)
	movzwl	%ax, %eax

	/*
	 * Find out where the bottom of physical memory is.
	 * (We won't be able to directly use it for 32-bit accesses
	 * until we actually get into 32-bit mode.)
	 */
	sall	$4, %eax
	negl	%eax
ADDR32	movl	%eax, EXT(phys_mem_va)

	/*
	 * The base of linear memory is at the same place,
	 * at least until we turn paging on.
	 */
ADDR32	movl	%eax, EXT(linear_base_va)

	popl	%eax
#ifdef HAVE_CODE16GCC
	retl		/* NOTE: 32bit return */
#else
	ret
#endif

#endif /* HAVE_CODE16 */