MirBSD manpage: i386_vm86(2)

I386_VM86(2)            BSD Programmer's Manual (i386)            I386_VM86(2)


     i386_vm86 - set virtual 8086 processor registers and mode


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

     i386_vm86(struct vm86_struct *vmcp);


     i386_vm86() will set the process into virtual 8086 mode using the regis-
     ters and selectors specified by the context pointed to by vmcp. The pro-
     cessor registers are set from vmcp->substr.regs, and the emulated proces-
     sor 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 han-
     dling. 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.


     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.


     i386_vm86() will fail if:

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


     Intel, i386 Microprocessor Programmer's Reference Manual.

MirBSD #10-current            February 20, 1996                              1

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