I wrote:
> The attached revised patch contains a test case that demonstrably triggers
> the problem on gaur's host. Oddly, I do not get a crash either on a PPC
> Mac or a Raspberry Pi 3 running Raspbian. I'm not very sure why; I traced
> through things with gdb and it's definitely calling EA_flatten_into with
> an odd address and a non-flattened input. I guess both of those platforms
> have kernel handlers for misaligned accesses? But the Raspbian box ought
> to be nearly the same as chipmunk, which is where we saw the problem to
> begin with, so I'm a bit confused.
Ah: a bit of googling later, the mystery is solved. PPC does have support
for unaligned 32-bit accesses, which is as much as EA_flatten_into needs.
(It's 64-bit operations where you might have a problem.) My info was
also out of date about ARM: more recent processors, at least, can also
do unaligned 32-bit accesses. chipmunk either has a pretty old processor
or it is configured to disable unaligned access.
Apparently the only somewhat-modern architecture that is resolutely
unaligned-unfriendly is MIPS.
regards, tom lane
