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

[Jeff Law]

On 02/20/15 05:10, Jakub Jelinek wrote:
> 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.
Right.  If someone wants to take it up with the Austin group, that's 
fine. But until/unless the Austin group blesses, I don't think we should 
extend as a QoI matter.

jeff