Quote from AMD64 System V ABI: "An array uses the same alignment as
its elements, except that a local or global array variable of length
at least 16 bytes or a C99 variable-length array variable always has
alignment of at least 16 bytes."

x86-64 psABI says that only the least significant 8 bits are
significant if RAX has a return value of a function returning bool.
Likewise, it looks like only the least significant 1 or 2 bytes
are guaranteed to have a correct value for char and short return
values, respectively.