Re: CVS commit: src/common/lib/libc/string

[Alan Barrett <apb%cequrux.com@localhost>]

On Mon, 14 Apr 2014, Joerg Sonnenberger wrote:
> Modified Files:
>         src/common/lib/libc/string: bcopy.c
>
> Log Message:
> Using bcopy/memcpy with NULL arguments is valid as long as the size is
> also 0.

No, it's undefined behaviour.  C99 section 7.21.1:

   Unless explicitly stated otherwise in the description of a
   particular function in this subclause, pointer arguments on
   such a call shall still have valid values, as described in
   7.1.4.

and 7.1.4 says:

   If an argument to a function has an invalid value (such as ...
   a null pointer ...) ..., the behavior is undefined.

and 7.21.2.1 "The memcpy function" does not give any explicit 
permission for use of null pointers.

I don't object if the implementation wants to allow null pointers 
with zero size as an extension, but it should be clear that this 
is non-standard.

--apb (Alan Barrett)