It turns out that ARMCC generates a call to malloc when you use a VLA. Was a bit of a suprrise when I used one in an ISR explicitly to AVOID malloc. Apparently

It turns out that ARMCC generates a call to malloc when you use a VLA. Was a bit of a suprrise when I used one in an ISR explicitly to AVOID malloc. Apparently the lack of a frame pointer on ARM means that tracking dynamically sized stack frames is a problem.