NAME    [Toc]    [Back]

     i386_vm86 - set virtual 8086 processor registers and mode

LIBRARY    [Toc]    [Back]

     i386 Architecture Library (libi386, -li386)

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 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    [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]

     i386 Microprocessor Programmer's Reference Manual, Intel

BSD                            February 20, 1996                           BSD