config root man

/*-
 * Copyright (c) 1997 Jonathan Lemon
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD: release/9.1.0/sys/i386/i386/bioscall.s 103436 2002-09-17 01:49:00Z peter $
 */

/*
 * Functions for calling x86 BIOS functions from the BSD kernel
 */
	
#include <machine/asmacros.h>

#include "assym.s"

	.data
	ALIGN_DATA
bioscall_frame:		.long	0
bioscall_stack:		.long	0

	.text
/*
 * bios32(regs, offset, segment)
 *	struct bios_regs *regs;
 *	u_int offset;
 * 	u_short segment;
 */
ENTRY(bios32)
	pushl	%ebp
	movl	16(%esp),%ebp
	mov	%bp,bioscall_vector+4
	movl	12(%esp),%ebp
	movl	%ebp,bioscall_vector
	movl	8(%esp),%ebp
	pushl	%ebx
	pushl	%esi
	pushl	%edi
	movl	0(%ebp),%eax
	movl	4(%ebp),%ebx
	movl	8(%ebp),%ecx
	movl	12(%ebp),%edx
	movl	16(%ebp),%esi
	movl	20(%ebp),%edi
	pushl	%ebp
	lcall	*bioscall_vector
	popl	%ebp
	movl	%eax,0(%ebp)
	movl	%ebx,4(%ebp)
	movl	%ecx,8(%ebp)
	movl	%edx,12(%ebp)
	movl	%esi,16(%ebp)
	movl	%edi,20(%ebp)
	movl	$0,%eax			/* presume success */
	jnc	1f
	movl	$1,%eax			/* nope */
1:
	popl	%edi
	popl	%esi
	popl	%ebx
	popl	%ebp
	ret


/*
 * bios16_call(regs, stack)
 *	struct bios_regs *regs;
 *	char *stack;
 */
ENTRY(bios16_call)
	pushl	%ebp
	movl	%esp,%ebp
	addl	$4,%ebp			/* frame pointer */
	movl	%ebp,bioscall_frame	/* ... save it */
	pushl	%ebx
	pushl	%esi
	pushl	%edi
/*
 * the problem with a full 32-bit stack segment is that 16-bit code
 * tends to do a pushf, which only pushes %sp, not %esp.  This value
 * is then popped off (into %esp) which causes a page fault because 
 * it is the wrong address.
 *
 * the reverse problem happens for 16-bit stack addresses; the kernel
 * code attempts to get the address of something on the stack, and the
 * value returned is the address relative to %ss, not %ds.
 *
 * we fix this by installing a temporary stack at page 0, so the
 * addresses are always valid in both 32 bit and 16 bit modes.
 */
	movl	%esp,bioscall_stack	/* save current stack location */
	movl	8(%ebp),%esp		/* switch to page 0 stack */

	movl	4(%ebp),%ebp		/* regs */

	movl	0(%ebp),%eax
	movl	4(%ebp),%ebx
	movl	8(%ebp),%ecx
	movl	12(%ebp),%edx
	movl	16(%ebp),%esi
	movl	20(%ebp),%edi

	pushl	$BC32SEL
	leal	CNAME(bios16_jmp),%ebp
	andl	$PAGE_MASK,%ebp
	pushl	%ebp			/* reload %cs and */
	lret				/* ...continue below */
	.globl	CNAME(bios16_jmp)
CNAME(bios16_jmp):
	lcallw	*bioscall_vector	/* 16-bit call */

	jc	1f
	pushl	$0			/* success */
	jmp	2f
1:
	pushl	$1			/* failure */
2:
	movl	bioscall_frame,%ebp

	movl	4(%ebp),%ebp		/* regs */

	movl	%eax,0(%ebp)
	movl	%ebx,4(%ebp)
	movl	%ecx,8(%ebp)
	movl	%edx,12(%ebp)
	movl	%esi,16(%ebp)
	movl	%edi,20(%ebp)

	popl	%eax			/* recover return value */
	movl	bioscall_stack,%esp	/* return to normal stack */

	popl	%edi
	popl	%esi
	popl	%ebx
	popl	%ebp

	movl	(%esp),%ecx
	pushl	%ecx			/* return address */
	movl	$KCSEL,4(%esp)
	lret				/* reload %cs on the way out */