But aren't you reading off the end of the buffer in your memcpy(&w...)? Say with an empty input string whose start address is aligned to sizeof(size_t) bytes?
I just passed in the string length since the caller had that info, otherwise you'd scan the whole string again looking for the zero terminator.
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.