[LLVMdev] ubsan - active member check for unions

[Yury Gribov]

On 12/19/2014 01:14 AM, Nick Lewycky wrote:
> On 12/16/2014 02:43 AM, Yury Gribov wrote:
>> On 12/15/2014 10:24 PM, Ismail Pazarbasi wrote:
>>>      s.d = 42.0;
>>>      if (s.l > 100) // fire here
>>
>> Note that code like this is frequently used to convert integers to
>> floats so you'll get tons of false positives.
>
> True positives. The fix is to use memcpy instead.

Hm, I thought C aliasing rules explicitly allow changing types through 
unions. Anyway, the pattern is so widespread that IMHO most maintainers 
will find such errors useless.

-Y