SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

We want to clear/memset the padding bytes, not just each member,
so using assignment or {} initialization is not an option.

To silence the warnings, cast the object pointer to u8* (which is not
undefined behavior) to make it explicit to the compiler that we want
to fill the object representation.

Migrates the software backend over to the fmt-capable logger.

Gets several constants out of global scope.