Exactly. This is also highly problematic if you try to perform atomic operations against bare 64 bit integers on those systems, because the atomic instructions

Exactly. This is also highly problematic if you try to perform atomic operations against bare 64 bit integers on those systems, because the atomic instructions do require them to be 8 byte aligned. In C11 and later it’s not an issue, because _Atomic(int64_t)’s alignment may be stricter than int64_t. This was also an issue in Go, because it tries to use the same alignment rules as C to make cgo work. There they also solved it by adding dedicated atomic types. https://github.com/golang/go/discussions/47141 https://github.com/golang/go/discussions/47141