int
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 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.
)
will fail if:
EFAULT
]