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

[Andrew Haley]

On 02/20/2015 11:06 AM, 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.

Sure, but if that's a bug then it's a bug in the definition of
memcpy(), not in the definition of the properties of a null pointer.
If the size is zero then it really shouldn't matter if the destination
address is null.

Andrew.