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

Florian Weimer fweimer@redhat.com
Fri Feb 20 11:06:00 GMT 2015

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;
  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.

Florian Weimer / Red Hat Product Security

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