Re: [Caml-list] memory corruption using C stub

[David Allsopp <dra-news@metastack.com>]

On 11 Jun 2017, at 12:54, Alexey Egorov <alex.only.d@gmail.com> wrote:
> 
> OCaml side is a complex server-side application; unfortunately, it's
> closed-source and when I'm trying to minimize OCaml side too it stops
> crashing...

Ah well! Are there other packages you are using which themselves have C stubs? If minimising the OCaml application is also eliminating the problem, then it could be that it's just the allocations in your (correct) C stub which are revealing the crash elsewhere. Unfortunately, incorrect C stub can include OCaml unix functions...

Spattering Gc.full_major on the OCaml can help try to find corruptions earlier - have you tried that too?

> I'm using fdopen's opam repository
> (https://github.com/fdopen/opam-repository-mingw) with compiler's
> versions from 4.03 to 4.05-beta3.

I presume you're seeing the crash from all versions? Are you able to do a 4.02.3 test, or is that impractical?


David


> 2017-06-11 16:45 GMT+05:00 David Allsopp <dra-news@metastack.com>:
>>> On 11 Jun 2017, at 12:38, Alexey Egorov <alex.only.d@gmail.com> wrote:
>>> 
>>> OK, I'm minimized this function as much as possible and it's still
>>> crashing - https://pastebin.com/MZ0Qkh9B
>>> Now I'm thinking that is compiler's bug on windows...
>> 
>> Are you able to post the OCaml side of your minimised code? Which port of OCaml are you using?
>> 
>> 
>> David
>> 
>> 
>>> 2017-06-10 20:33 GMT+05:00 Alexey Egorov <alex.only.d@gmail.com>:
>>>> Hello,
>>>> 
>>>> I have an OCaml application with some C code which (I believe) is the
>>>> reason of some random crashes.
>>>> 
>>>> Here is the code - https://pastebin.com/FVtLphZu
>>>> This function reads file at given offset, divides data into chunks and
>>>> compute checksums and compression ratio:
>>>> external compute_data_props
>>>>   : string -> int -> int -> int -> (int * int * float) list =
>>>> "compute_data_props"
>>>> 
>>>> The problem is, after some calls to this stub, application is crashing
>>>> at random places in OCaml code.
>>>> I can't figure out what's going wrong, but replacing this stub with
>>>> dummy function (which does nothing but returns some predefined list)
>>>> eliminates the problem.
>>>> 
>>>> What can we do to debug it? We are using OCaml 4.04.1 and Windows 10,
>>>> and there is no other C stubs in our codebase.
>>>> 
>>>> Thanks!
>>> 
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