Re: Obscure crashes due to gcc 4.9 -O2 => -fisolate-erroneous-paths-dereference

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Feb 20, 2015 at 12:06:28PM +0100, Florian Weimer wrote:
> On 02/19/2015 09:56 PM, Sandra Loosemore wrote:
> > Hmmmm,  Passing the additional option in user code would be one thing,
> > but what about library code?  E.g., using memcpy (either explicitly or
> > implicitly for a structure copy)?
> 
> The memcpy problem isn't restricted to embedded architectures.
> 
>   size_t size;
>   const unsigned char *source;
>   std::vector<char> vec;
>   …
>   vec.resize(size);
>   memcpy(vec.data(), source, size);
> 
> std::vector<T>::data() can return a null pointer if the vector is empty,
> which means that this code is invalid for empty inputs.
> 
> I think the C standard is wrong here.  We should extend it, as a QoI
> matter, and support null pointers for variable-length inputs and outputs
> if the size is 0.  But I suspect this is still a minority view.

I disagree.  If you want a function that will have that different property,
don't call it memcpy.

	Jakub