Re: [Caml-list] segfault in simple program with 4.02 native

[Ashish Agarwal <agarwal1975@gmail.com>]

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>  First try a 'make test' from atdgen's source
...
The following tests failed:
ocaml internals
biniou correctness
json correctness
*** FAILURE ***

Thanks to everyone for all the replies. My type defs are small, so at least
I can easily bypass the issue by using Yojson directly.




On Fri, Sep 5, 2014 at 6:39 PM, Martin Jambon <martin.jambon@ens-lyon.org>
wrote:

> On 09/05/2014 03:18 PM, Richard W.M. Jones wrote:
>
>> On Fri, Sep 05, 2014 at 11:13:02PM +0100, Richard W.M. Jones wrote:
>>
>>> On Fri, Sep 05, 2014 at 06:06:55PM -0400, Ashish Agarwal wrote:
>>>
>>>> I increased the stack size to 65532, which is apparently the max
>>>> allowed on
>>>> a Mac, and it doesn't change the behavior.
>>>>
>>>
>>> Yup.  I was able to reproduce this on the non-core version, and indeed
>>> increasing the stack to unlimited on Linux does not help.
>>>
>>> The stack trace is simple:
>>>
>>> #0  0x00000000004543f4 in camlPervasives__output_string_1198 ()
>>> #1  0x0000000000472093 in camlCamlinternalFormat__output_acc_60624 ()
>>> #2  0x0000000000473a32 in camlPrintf__fun_1062 ()
>>> #3  0x000000000041e776 in camlApp__entry ()
>>> #4  0x000000000041c5f9 in caml_program ()
>>> #5  0x0000000000497f7e in caml_start_program ()
>>> #6  0x000000000049813d in __libc_csu_init ()
>>> #7  0x00007ffff7317d65 in __libc_start_main () from /lib64/libc.so.6
>>> #8  0x000000000041c2e9 in _start ()
>>>
>>> I'm just installing debuginfo so I can get more symbols ..
>>>
>>
>> .. although I guess the fact that the generated code in config_j.ml is
>> doing a lot of Obj.magic would be the first place to be suspicious.
>>
>> eg:
>>
>>      let (x : postgres) =
>>        {
>>          host = Obj.magic 0.0;
>> ...
>>
>> where the host field has declared type string.  Really?
>>
>
> That code is generated by atdgen. What happens is that we have to either
> create an empty record when starting to parse a list of unordered JSON
> fields, or use a bunch `let <field name> = ref None in` for each field and
> create the record in the end. While the latter approach is not much more
> work to implement, the resulting code was found to be significantly slower.
>
> The reason why it's using `Obj.magic 0.0` is that it worked in all cases
> (and has been for the past 4 years). Obtaining a well-formed constant value
> for any type is not trivial, so this what we have.
>
> It's very possible that it's now broken with OCaml 4.02. First try a 'make
> test' from atdgen's source directory (https://github.com/mjambon/atdgen)
> and see if it passes.
>
>
> Martin
>
>
>
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