NAME
i386_vm86 —
set virtual 8086 processor
registers and mode
LIBRARY
i386 Architecture Library (libi386, -li386)
SYNOPSIS
#include <sys/types.h>
#include <signal.h>
#include <machine/mcontext.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
n th 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
n
th 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
k th bit in the
vmcp->int21_byuser array is checked when INT
21 is requested and the
ah
register is
k.
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
i386 Microprocessor Programmer's Reference Manual, Intel