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

[Renato Golin]

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