Hello caml-list,
I'd like to propose a detector to help in the detection of incorrect C
bindings that do not follow the GC rules.
The idea is rather simple:
1. after a minor collection, mprotect the pages of the minor heap to
disallow reads and writes
2. install a SEGV handler to catch the ensuing faults
3. if the faulting address is above caml_young_ptr - Max_young_whsize,
unprotect the page and carry on
4. otherwise, the program has no business accessing a value in the
unallocated part of the minor heap, so let it crash
I've hacked up a prototype that protects a single page at
caml_young_start, and it catches the bug I mention in my other message
entitled "an implicit GC rule".
Such a change surely degrades performance, but maybe it would be
useful as a runtime option available through CAMLRUNPARAM, to detect
misbehaved C bindings.
Does it sound like a viable technique?
I'm curious to hear what you think.
thanks,
Frédéric Perriot
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