Re: [Chicken-hackers] [PATCH] Fix for extremely obscure error in lolevel-tests

[Mario Domenech Goulart]

On Wed, 16 Apr 2014 15:50:18 +0200 Peter Bex <address@hidden> wrote:

> Mario discovered an obscure problem that we initially dismissed as a
> GCC bug:
> http://paste.call-cc.org/paste?id=fa2e0e8658c19ba639ae587128e6e1b1c58c6dd5
>
> We discovered that this was a bug in CHICKEN after all, probably another
> incarnation of this one: http://bugs.call-cc.org/ticket/916
>
> Felix found out that the reason it's failing is because the lolevel-tests
> call object-evict and then object-release on an object which is bound to
> a global variable ev-tstvec.  This global variable points to *freed memory*
> after object-release has been called.  Then, when a GC happens that memory
> gets pulled into the new heap, and the data there seems to get
> reinterpreted on the next GC.  This wreaks havoc with the tests, but only
> if the stars are aligned just so that malloc returns memory in this
> fashion and the stack size is just so, etc etc.  That's why it only
> happens on some Linuxen with some versions of GCC.
>
> This is a fundamental problem with object-release; there is currently no
> way to ensure there are no local variables still holding references to
> the freed memory.  Because this has been broken since the beginning and
> because changing this would probably involve a small overhaul of the GC,
> I think it's best to apply the attached patch by Felix which at least
> suppresses the problematic behaviour of the test, and go ahead with
> making a release candidate.  This should then be fixed by 4.10.0
> (or 5.0.0?).

The patch has been pushed to master and prerelease.  Thanks a lot.

Best wishes.
Mario
-- 
http://parenteses.org/mario