🚀 go-pugleaf

In article <1992Aug20.092700.8373@wsl.ie> jja@wsl.ie (John J. Allen) writes:
>harris@garfield.catt.ncsu.edu (Michael Harris) writes:
>: Memory protection in OS/2 protects one process from another... not a process
>: from itself.
>
>OS/2 2.0 = Flat memory model
>OS/2 1.x = Segmented memory model.
>
>The segmented memory model had some advantages over the flat model. If I
>used DosAllocSeg() to create a 20k block and then ran off the end of
>it I'd get a segmentation violation as soon as I did that. (As in Win 3.x)
>
>So although the FLAT memory model simplifies programming it hampers
>debugging.

This is not entirely true. To make it similar, some programming would be
needed, however.

One could implement a malloc() and friends library which does not only
allocate memory in the usual manner but also two additional pages, one
before and one after some chunk of memory. These pages should then be
set up as "guard pages", this means, that any access to these pages
triggers an exception. A handler set up for this exception could then
write an entry to a log file and abort the program.

This method has the advantage over the 1.x segmented model that it is
not restricted to whole segments but it is still restricted to 4k
granularity (page size). Of course, it wastes memory too, but this
should not matter for a development cycle.

Note: I have not implemented such a library, but the memory management
API in OS/2 2.0 can be used to implement such a debugging aid, according
to the documentation.

Kai Uwe Rommel

/* Kai Uwe Rommel --- rommel@informatik.tu-muenchen.de */

DOS ... is still a real mode only non-reentrant interrupt
handler, and always will be.                -Russell Williams