How to debug segmentation fault?

Question

It works when, in the loop, I set every element to 0 or to entry_count-1. It works when I set it up so that entry_count is small, and I write it by hand instead of by loop (

Answer 1

After a few days of experimentation, I figured out what was really going on.

For some reason the machine segfaults on unaligned access. That is, the integers I was writing were not being written to memory boundaries that were multiples of four bytes. Before the loop I computed the offset and shifted the array up that much:

int offset = (4 - (uintptr_t)(memory) % 4) % 4;
memory += offset;

After doing this everything behaved as expected again.