Porting Unix to the 386: A Practical Approach

William & Lynne Jolitz

Started open source UNIX.

Appeared in part as a 17 article magazine series in 1991-1992.

Documented the "how, what, why, who, when" of porting BSD to the 386.

Done while BSD was becoming "open source".

Porting Unix to the 386: A Practical Approach - intersegment return

intersegment return:

Processor Support -- i386.c

We initialized the processor with initial descriptor and page tables - one needs to run with the tables before activating memory/interrupt kernel functions.

System Call Handling

System calls were handled by a call gate, a 386 peculiar mechanism which allowed for ring crossing into supervisor mode using a special segment descriptor call. We simulated user mode to test prior to running in the kernel.