Re: Segments

Terje Mathisen <terje.mathisen@tmsw.no> writes:

The best idea I have seen to help detect out of bounds accesses, is to
round all requested memory blocks up to the next 4K boundary and mark
the next page as unavailable, then return a skewed pointer back, so that
the end of the requested region coincides with the end of the (last)
allocated page.

I think I've mentioned this once before, but I did precisely this during my
time at Sequent, and the C library blew up.  Turned out the C string support
routines were pulling in cache line lengths at a time, and it was such a win
they didn't want to observe "strict" C string access rules.  I assume they
padded things such that no "real life" string could end up against a page
boundary abutted to an invalid page address, but since they weren't
interested in fixing it, I stopped worrying about it.

A kinder, gentler time.  I wonder if such things still lurk out there.

Andy Valencia
Home page: https://www.vsta.org/andy/
To contact me: https://www.vsta.org/contact/andy.html
Fediverse: @vandys@goto.vsta.org