[orlp]

> But aren't you reading off the end of the buffer in your memcpy(&w...)?

If we go by the absolute strictest interpretation of the C standard my above implementation is UB.

But in practice, if p is word-aligned and is at least valid for 1 byte, then you will not pagefault for reading a whole word. In fact, this is how GCC/musl implement strlen itself.

> Say with an empty input string whose start address is aligned to sizeof(size_t) bytes?

Then the start address is valid (it must contain the null byte), and aligned to a word boundary, in which case I assume it is ok to also read a whole word there.