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I386_VM86(2) BSD/i386 System Calls Manual I386_VM86(2)
i386_vm86 -- set virtual 8086 processor registers and mode
i386 Architecture Library (libi386, -li386)
i386_vm86(struct vm86_struct *vmcp);
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 instruc-
tion 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
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.
i386 Microprocessor Programmer's Reference Manual, Intel
BSD February 20, 1996 BSD
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