Re: [Caml-list] segmentation fault

[Josh Berdine <josh@berdine.net>]

On Mon, Jun 19 2017, Julia Lawall wrote:

> On Mon, 19 Jun 2017, David MENTRÉ wrote:
>
>> Hello Julia,
>>
>> Le 2017-06-18 à 21:41, Julia Lawall a écrit :
>> > Over several
>> > runs on two different laptops, the backtraces have nothing obvious in
>> > common.  The bytecode version does not seem to stack overflow.  Adding
>> > Gc.print_stat() at a periodic quiescent point in the execution did not
>> > show a memory leak.
>>
>> A similar issue related to random crash in native code version was asked
>> by Alexey Egorov on this list 9 days ago. Daniel Bünzli advised to him
>> to frequently call Gc.full_major () to have a crash closer to the real
>> issue.
>
> OK, I will try this.

Are you using Windows? I have only experienced segfaults from stack overflow on Windows.

>> In the case of Alexey, it was a non tail-recursive call that triggered a
>> stack overflow and that is not detected in OCaml native code. Apparently
>> this kind of issue is fixed in next to come OCaml 4.06.0.
>
> Why would something like this not be deterministic?  In my case, it can
> happen after seconds or after tens of minutes.

This sounds like an interaction with the GC to me.

>> Of course, your issue might be entirely different. But frequently
>> calling Gc.full_major () seems a sensible starting point to me.
>>
>> Otherwise you have the usual suspects: are you using C bidings? Threads?
>
> There are no threads.  The software may use C bindings.  I don't think
> they are involved in the failing execution, but I'm not 100% sure.

I have found running under valgrind to be helpful in this sort of situation, though it is slow and some valid code can trigger many warnings.

Cheers, Josh