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NAME

     i386_vm86 - control vm86-related functions

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/types.h>
     #include <machine/sysarch.h>
     #include <machine/vm86.h>

     int
     i386_vm86(int function, void *data);

DESCRIPTION

     The i386_vm86() system call is used to call various vm86 related
     functions.  The function argument can be one of the following values:

           VM86_INIT     This will initialize the kernel’s vm86 parameter area
                         for the process, and permit the process to make vm86
                         calls.  The data argument points to the following
                         structure:

                         struct vm86_init_args {
                                 int     debug;
                                 int     cpu_type;
                                 u_char  int_map[32];
                         };

                         The debug argument is used to turn on debugging code.
                         The cpu_type argument controls the type of CPU being
                         emulated, and is currently unimplemented.  The
                         int_map argument is a bitmap which determines whether
                         vm86 interrupts should be handled in vm86 mode, or
                         reflected back to the process.  If the Nth bit is
                         set, the interrupt will be reflected to the process,
                         otherwise it will be dispatched by the vm86 interrupt
                         table.

           VM86_INTCALL  This allows calls to be made to vm86 interrupt
                         handlers by the process.  It effectively simulates an
                         INT instruction.  data should point to the following
                         structure:

                         struct vm86_intcall_args {
                                 int     intnum;
                                 struct  vm86frame vmf;
                         };

                         intnum specifies the operand of INT for the simulated
                         call.  A value of 0x10, for example, would often be
                         used to call into the VGA BIOS.  vmf is used to
                         initialize CPU registers according to the calling
                         convention for the interrupt handler.

           VM86_GET_VME  This is used to retrieve the current state of the
                         Pentium(r) processor’s VME (Virtual-8086 Mode
                         Extensions) flag, which is bit 0 of CR4.  data should
                         be initialized to point to the following:

                         struct vm86_vme_args {
                                 int     state;                  /* status */
                         };

                         state will contain the state of the VME flag on
                         return.

     vm86 mode is entered by calling sigreturn(2) with the correct machine
     context for vm86, and with the PSL_VM bit set.  Control returns to the
     process upon delivery of a signal.

RETURN VALUES

     The i386_vm86() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS

     The i386_vm86() system call will fail if:

     [EINVAL]           The kernel does not have vm86 support, or an invalid
                        function was specified.

     [ENOMEM]           There is not enough memory to initialize the kernel
                        data structures.

AUTHORS

     This man page was written by Jonathan Lemon, and updated by Bruce M
     Simpson.