.\"	$OpenBSD: i386_vm86.2,v 1.2 1996/10/08 01:20:07 michaels Exp $
.\"	$NetBSD: i386_vm86.2,v 1.1 1996/02/21 00:21:52 jtk Exp $
.\"
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by John Kohl.
.\"
.\" 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
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.\" 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.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"        This product includes software developed by the NetBSD 
.\"	  Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation nor the names of its 
.\"    contributors may be used to endorse or promote products derived 
.\"    from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 REGENTS OR CONTRIBUTORS BE
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\"
.\"     from: @(#)fork.2	6.5 (Berkeley) 3/10/91
.\"
.Dd February 20, 1996
.Dt I386_VM86 2
.Os
.Sh NAME
.Nm i386_vm86
.Nd set virtual 8086 processor registers and mode
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <signal.h>
.Fd #include <machine/segments.h>
.Fd #include <machine/sysarch.h>
.Fd #include <machine/vm86.h>
.Ft int
.Fn i386_vm86 "struct vm86_struct *vmcp"
.Sh DESCRIPTION
.Fn i386_vm86
will set the process into virtual 8086 mode using the registers and
selectors specified by the context pointed to by
.Ar vmcp .
The processor registers are set from 
.Ar vmcp->substr.regs ,
and the emulated processor type from 
.Ar vmcp->substr.ss_cpu_type .
.Pp
The kernel keeps a pointer to the context, and uses the tables stored at
.Ar vmcp->int_byuser
and
.Ar vmcp->int21_byuser
for fast virtual interrupt handling.  If the 
.Ar n th
bit is clear in the first of
these arrays, then the kernel may directly emulate the real-mode x86 INT
.Ar n
instruction handling.  If the
.Ar n
th bit is set, then the process is
delivered a signal when an INT instruction is executed.
.Pp
Since MS-DOS puts many DOS functions onto interrupt 21, it is handled
specially:  the
.Ar k
th bit in the
.Ar vmcp->int21_byuser
array is checked when INT
.Ar 21
is requested and the
.Ar ah
register is
.Ar k .
.Sh RETURN VALUES
This routine does not normally return: 32-bit mode will be restored by
the delivery of a signal to the process.  In case of an error in setting
the VM86 mode, a value of -1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn i386_vm86
will fail if:
.Bl -tag -width [EINVAL]
.It Bq Er EFAULT
The state at
.Ar vmcp
was not readable to the user process.
.Sh REFERENCES
i386 Microprocessor Programmer's Reference Manual, Intel