NAME
i386_vm86 —
set virtual 8086 processor registers
and mode
SYNOPSIS
#include
<sys/types.h>
#include <signal.h>
#include <machine/segments.h>
#include <machine/sysarch.h>
#include <machine/vm86.h>
int
i386_vm86(struct
vm86_struct *vmcp);
DESCRIPTION
i386_vm86()
will set the process into virtual 8086 mode using the registers and
selectors specified by the context pointed to by vmcp.
The processor registers are set from
vmcp->substr.regs, and the emulated processor type
from vmcp->substr.ss_cpu_type.
The kernel keeps a pointer to the context, and uses the tables
stored at vmcp->int_byuser and
vmcp->int21_byuser for fast virtual interrupt
handling. If the nth bit is
clear in the first of these arrays, then the kernel may directly emulate the
real-mode x86 INT n instruction handling. If the
nth bit is set, then the
process is delivered a signal when an INT instruction is executed.
Since MS-DOS puts many DOS functions onto interrupt 21, it is
handled specially: the kth bit
in the vmcp->int21_byuser array is checked when INT
21 is requested and the ah
register is k.
Note:
Code using the
i386_vm86()
function must be compiled using -li386.
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 errno is set to indicate the error.
ERRORS
i386_vm86() will fail if:
- [
EFAULT] - The state at vmcp was not readable to the user process.
REFERENCES
Intel, i386 Microprocessor Programmer's Reference Manual.