RFR(xxs): 8167650: NMT should check for invalid MEMFLAGS.

[David Holmes]

In the interests of fairness I should also point out this is technically 
an enhancement not a bug fix.

David

On 13/10/2016 8:08 PM, David Holmes wrote:
> Hi Thomas,
>
> On 13/10/2016 3:49 PM, Thomas Stüfe wrote:
>> Hi all,
>>
>> may I have plase a review for this tiny change? It just adds some
>> assert to
>> NMT.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8167650
>> webrev:
>> http://cr.openjdk.java.net/~stuefe/webrevs/8167650-NMT-should-check_
>> MEMFLAGS/webrev.00/webrev/
>>
>> We had an ugly memory overwrite caused by this - ultimately our fault,
>> because we fed an invalid memory flag to NMT - but it was difficult to
>> find. An assert would have saved some time.
>
> I'm a little perplexed with asserting that something of MEMFLAGS type
> must be an actual MEMFLAGS value - it implies the caller is coercing
> plain int to MEMFLAGS, and I don't have much sympathy if they mess that
> up. Can't help wondering if there is some clever C++ trick to flag bad
> conversions at compile-time?
>
> The function that takes the index should validate the index, so that is
> fine.
>
> Which one were you actually passing the bad value to? :)
>
> This isn't a strong objection just musing if we can do better. And as
> the hs repos are still closed, and likely to remain so till early next
> week, we have some slack time :)
>
> Cheers,
> David
>
>> Thank you!
>>
>> Thomas
>>