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I386_VM86(2) System Calls Manual (i386) I386_VM86(2)

i386_vm86set 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);

() 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.

Code using the () 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:

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

Intel, i386 Microprocessor Programmer's Reference Manual.

September 10, 2015 OpenBSD-6.3