[cfe-dev] Unstable ARM buldbots == Unaligned Clang?

[Sean Silva]

-fsanitize=undefined should catch and diagnose these sorts of alignment
issues IIRC.

-- Sean Silva

On Tue, Jun 16, 2015 at 1:59 PM, Renato Golin <renato.golin at linaro.org>
wrote:

> Hi Galina,
>
> I was wondering what's so unstable about the panda bots. In the past,
> I used to have them crashing down instead of failing to run a test,
> and your bots are pretty consistent at failing the same set of Clang
> tests.
>
> It's possible that this has nothing to do with the pandaboard, but to
> do with the other Clang problem that we are aware for a while now:
> Clang objects not always align well in memory, and occasionally break
> at run time on ARM.
>
> https://llvm.org/bugs/show_bug.cgi?id=22728
>
> http://lists.cs.uiuc.edu/pipermail/cfe-dev/2015-February/041493.html
>
> If this is the case, I think we need a bigger effort to fix this, as
> it seems wide-spread enough that my poor Clang skills won't cut. Also,
> this problem affects self-hosting on ARM every other month and
> disappear out of the blue. We really need to nail it once and for all.
>
> Reid,
>
> On the list you said instead of trying to get it right, we should just
> set alignment of 1 to all such objects. That won't work with some ARM
> instructions that force alignment if the structure happens to be
> somewhere in between. I believe this is what's causing it to crash on
> ARM and not on other self-hosting platforms.
>
> Do you have any other suggestion? Why is this code so complicated? Why
> not let the compiler calculate the size/alignment?
>
> cheers,
> --renato
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