February 20, 1996 I386_VM86 2 i386

### NAME

i386_vm86 - set virtual 8086 processor registers and mode

### LIBRARY

i386 Architecture Library (libi386, -li386)

### SYNOPSIS

```int` i386_vm86(```struct vm86_struct *vmcp`)

### DESCRIPTION

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 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.

### RETURN VALUES

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.

### ERRORS

i386_vm86(``) will fail if:

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

### REFERENCES

i386 Microprocessor Programmer's Reference Manual, Intel