Re: [Caml-list] a bad value detector

[Chet Murthy <murthy.chet@gmail.com>]

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If I remember correctly, a company once started with Boehm's conservative
GC, and by doing things somewhat like you suggest, built a
memory-leak-detector product.  So you're not alone in going down this sort
of path.

On Wed, May 2, 2018 at 9:19 AM, Frederic Perriot <fperriot@gmail.com> wrote:

> 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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