Re: Process extensions

[Joel Sherrill <joel@oarcorp.com>]

On Fri, 27 Feb 1998, Zoltan Kocsi wrote:

> Just a question,
> 
> is it possible to attach additional process related information to a 
> process descriptor ?
> 
> I mean for example a pointer in the PCB which points to any user 
> defined data and which does not concern the kernel itself ?

RTEMS technically is only one process on each CPU with multiple
threads/tasks.  But the answer is yes.  The "extension manager" is
provided to do this.  It is used to implement the newlib C library
reentrancy and  stack overflow checking.

> What I'm looking for is a mechanism which I can use to add very low
> level features to the kernel (using the pre- and post-context switch
> extensions). I need to store extra information about the tasks and I
> don't want to do any sort of lookup at switch time. I don't want to
> touch the existing source either - I want the new stuff to be an optional
> module. I didn't find any formal way of doing that but I may have not
> looked hard enough.

The source for the manager providing this functinality is in
src/exec/sapi/src/extension.c

--joel