It took a long time, could you understand why this bug happens.
On the iphone I get the same bug with ocaml-3.12?

On Wed, Nov 24, 2010 at 3:20 AM, <rixed@happyleptic.org> wrote:

> For some time now I'm after a bug hitting a program of mine when
> compiled on ARM with ocaml 3.12.0.
> I initially though my own C code was misbehaving but the program keep
> crashing, although not as early, if I comment out all calls to the C
> functions.
>
> The segfaults happen frequently during the GC, in oldify_one or
> oldify_mopup, but also in a few other places such as camlList__rev_append
> or caml__apply2 or any other places as well. In caml_oldify_one, for
> instance, the segfault always happen at the same location : the
> assertion that sz is not 0 (and of course when you read the code it's
> pretty clear that sz=0 correspond to the case "already forwarded" that's
> handled at the beginning of the function).
>
> The pattern, then, is that a register (usually r0, r2 or r5) is
> restored from the stack after a call to a function that might call the
> GC (or to a call to the GC itself), then dereferenced. It's obvious
> inspecting the stack with gdb that this very word was changed during the
> call and a value like 0, 3 or 1024 is read back into the register
> instead of an mlvalue.
>
> I didn't managed (yet) to reduce the size of the program to a small show
> case, and I am under the impression that all these components are
> required in order for the bug to happen 'fast enough' :
>
> - threads
> - floats
> - call to C function (greatly reduce the time to wait before the crash)
>
> I am also under the impression that the bug is affected by the new stack
> alignment requirement (because in one occurrence, calling or not a
> function that does nothing from within a function hit by the bug reduced
> drastically the probability of the bug, and the major difference I saw
> was that on one version of the function the stack size was 16 bytes and
> the other 24 bytes (16+4 apparently for the address of a "module"
> structure, aligned up to 24 bytes). I thus manually checked the
> generated framesets but they were allright as far as I understand them.
>
> Now I'm a little desperate since each recompile+test takes about 20
> minutes and the bug is so erratic ; so if someone here is familiar with
> ARM arch and in particular the difference between old and new ABI please
> suggest me what I should check, or any hint whatsoever. I'd be very much
> grateful as this consumes a lot of my spare time.
>
> Also, I'm compiling ocaml with gcc 4.2.1 - do you think it may be a
> problem with gcc not following the very same ABI ?
>
> Also I've run the testsuite but it did not reveal anything.
>
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