x286emul(C)

x286emul -- emulate XENIX 80286

Syntax

x286emul [ arg ... ] prog286

Description

x286emul is an emulator that allows programs from XENIX System V/286 Release 2.3 or XENIX System V/286 Release 2.3.2 on the Intel 80286 to run on the Intel 80386 processor under UNIX System V Release 3.2 or later.

The UNIX system recognizes an attempt to exec(S) a 286 program, and automatically exec's the 286 emulator with the 286 program name as an additional argument. It is not necessary to specify the x286emul emulator on the command line. The 286 programs can be invoked using the same command format as on the XENIX System V/286.

x286emul reads the 286 program's text and data into memory and maps them through the LDT (via sysi86(S)) as 286 text and data segments. It also fills in the jam area, which is used by XENIX programs to do system calls and signal returns. x286emul starts the 286 program by jumping to its entry point.

When the 286 program attempts to do a system call, x286emul takes control. It does any conversions needed between the 286 system call and the equivalent 386 system call, and performs the 386 system call. The results are converted to the form the 286 program expects, and the 286 program is resumed.

The following are some of the differences between a program running on a 286 and a 286 program using x286emul on a 386:

Attempts to unlink or write on the 286 program will fail on the 286 with ETXTBSY. Under x286emul, they will not fail.
ptrace(S) is not supported under x286emul.
The 286 program must be readable for the emulator to read it.

Files

/bin/x286emul: the emulator must have this name and be in /bin if it is to be automatically invoked when exec is used on a 286 program