This is just a note in case this problem comes up again. I believe I've already resolved it.
Earlier versions of GCC appear to generate optimizations that result in invalid memory access patterns when working with mmapped files on AMD64: https://stackoverflow.com/a/47512025/238609.
I discovered that this could be resolved by updating GCC to 8.2.0. This was a pretty unsatisfying resolution, but at least I was able to work through the problem.
This is just a note in case this problem comes up again. I believe I've already resolved it.
Earlier versions of GCC appear to generate optimizations that result in invalid memory access patterns when working with mmapped files on AMD64: https://stackoverflow.com/a/47512025/238609.
I discovered that this could be resolved by updating GCC to 8.2.0. This was a pretty unsatisfying resolution, but at least I was able to work through the problem.