NetBSD/lib/libarch/i386/i386_vm86.2

.\"	$NetBSD: i386_vm86.2,v 1.6 1999/07/02 15:14:07 simonb Exp $
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.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by John Kohl.
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.\"     from: @(#)fork.2	6.5 (Berkeley) 3/10/91
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.Dd February 20, 1996
.Dt I386_VM86 2
.Os
.Sh NAME
.Nm i386_vm86
.Nd set virtual 8086 processor registers and mode
.Sh LIBRARY
.Lb libi386
.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.
.El
.Sh REFERENCES
i386 Microprocessor Programmer's Reference Manual, Intel