On 14 April 2015 at 13:50, Dimitris Papastamos <s...@2f30.org> wrote: > dst and src are required to be valid objects even if n is 0, otherwise > this is undefined behaviour.
I looked this up in C11. Seems to be the case: > 7.24.2.1.2. The memcpy function copies n characters from the object > pointed to by s2 into the object pointed to by s1. > 6.2.6.1.2. Except for bit-fields, objects are composed of contiguous > sequences of one or more bytes, ... > 124) ... there are no pointers to or arrays of bit-field objects. An object pointed to by s1 or s2 is guaranteed to be at least 1 byte long, so memcpy is free to dereference the first byte of either, whether or not n > 0. I think it's a mistake that a libc actually go ahead and do this, but the C standard suggests that it is permitted, so we should certainly do the check. cls
