[m-dev.] GCC 4.6, 4.7 and parallel grades

[Julien Fischer]

On Tue, Jul 2, 2013 at 9:09 PM, Paul Bone <paul at bone.id.au> wrote:

>
> A user reported to me a bug whereby a program (not even a parallel one) can
> crash (segfault) in a parallel low-level C grade.
>
> I've narrowed this down to GCC 4.6 and 4.7, (maybe later versions too), and
> the -freorder-functions optimisation that is enabled at -O2.  I think that
> calling a clusure is somehow involved - perhaps it's what is required to
> make the bug come to the surface.
>
> Does anyone know how these three things: -freorder-functions,
> parallelism/thread safty and closures may cause such a program.  In
> particular do we at any point rely on the order that functions appear in an
> executable's .text area?  This may just be an edge case that we havn't hit
> before with Mercury's use of non-local gotos.
>
> I've disassembled both object files (working and broken) for the same
> program and diffed them, there's no difference.  There is a difference in
> the disassembly of the _init.o file, the main function is placed in a new
> section named .text.startup.  I can't imagine how this could contribute to
> the problem.


What about in the object file for the runtime?  (Particularly, any contain
code
that deals with closures.)

Cheers,
Julien.
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