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

[Martin Jambon <martin.jambon@ens-lyon.org>]

On Fri 05 Sep 2014 04:39:54 PM PDT, Ashish Agarwal wrote:
> >  First try a 'make test' from atdgen's source
> ...
> The following tests failed:
> ocaml internals
> biniou correctness
> json correctness
> *** FAILURE ***

The "ocaml internals" test fails on this:

type internals1 = { int1 : bool }

...

  let f () = { int1 = Obj.magic false } in
  assert (f () != f ());

So don't use atdgen 1.3.1 or below with ocaml 4.02.0 or above.


No promise as when this will be fixed. Follow the activity on github if 
you're interested in following or contributing.


> 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 <mailto: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 <http://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
>     <https://github.com/mjambon/atdgen>) and see if it passes.
>
>
>     Martin
>
>
>
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