arch/x86/lib/linux_start.S

/*
 * Copyright (C) 2009 Juergen Beisert, Pengutronix
 *
 * Mostly stolen from the GRUB2 project
 *  Copyright (C) 1999,2000,2001,2002,2003,2004,2005,2006,2007,2008  Free Software Foundation, Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
 *
 * This program 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
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 * MA 02111-1307 USA
 *
 */

/**
 * @file
 * @brief Start the Linux real mode setup code
 *
 * Note: These functions are running in flat and real mode. Due to some
 * other restrictions these routines must running from an address
 * space below 0x10000
 */

/*
 *   void bios_start_linux(unsigned segment)
 *
 */
#ifndef DOXYGEN_SHOULD_SKIP_THIS

	.section .boot.text.bios_start_linux, "ax"
	.code32
	.globl bios_start_linux
	.type bios_start_linux, @function

	.extern prot_to_real

bios_start_linux:
	/* 'prot_to_real' eats our eax content */
	movl %eax, %ebx
	addl $0x20, %eax
	movw %ax, setup_seg

	call prot_to_real

	.code16

	cli
	/* all segment registers are using the same segment */
	movw %bx, %ss
	movw %bx, %ds
	movw %bx, %es
	movw %bx, %fs
	movw %bx, %gs

	/* stack for the setup code (end of heap) */
	movw $0x9000, %sp

	/* do an 'ljmp' and never return */
	.byte	0xea
	.word	0
setup_seg:
	.word	0

	.code32

#endif