NAME    [Toc]    [Back]

     i386_vm86 - set virtual 8086 processor registers and mode

SYNOPSIS    [Toc]    [Back]

     #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    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     i386_vm86() will fail if:

     [EFAULT]  The state at vmcp was not  readable  to  the  user
process.

REFERENCES    [Toc]    [Back]

     Intel, i386 Microprocessor Programmer's Reference Manual.

OpenBSD      3.6                        February     20,     1996