RFR(S): 8069124 - runtime/NMT/MallocSiteHashOverflow.java failing in nightlies

[David Holmes]

Hi Christian,

On 25/02/2015 12:57 PM, Christian Tornqvist wrote:
> Hi everyone,
>
>
>
> Please review this small fix for an issue with NMT.

The use of long in this function looks wrong, particularly as 
sizeof(long) might equal sizeof(int) and long is signed but now 
_hash_value is unsigned:

  72 // Hash code. Any better algorithm?
   73 unsigned int NativeCallStack::hash() const {
   74   long hash_val = _hash_value;
   75   if (hash_val == 0) {
   76     long pc;
   77     int  index;
   78     for (index = 0; index < NMT_TrackingStackDepth; index ++) {
   79       pc = (long)_stack[index];
   80       if (pc == 0) break;
   81       hash_val += pc;
   82     }
   83
   84     NativeCallStack* p = const_cast<NativeCallStack*>(this);
   85     p->_hash_value = (unsigned int)(hash_val & 0xFFFFFFFF);
   86   }
   87   return _hash_value;
   88 }

Even with the original code the use of long seems wrong.

David


>
>
> The failure was caused by reading random memory from the uninitialized
> _hash_value, when this value happened to be 0x80000000, hash_to_index()
> failed to negate the value and ended up with an index of -16:
>
>
>
> #  Internal Error
> (C:\\jprt\\T\\P1\\130630.ctornqvi\\s\\hotspot\\src\\share\\vm\\services\\mal
> locSiteTable.cpp:139), pid=5680, tid=4928
>
> #  assert(index >= 0) failed: Negative index -16
>
>
>
> Reproduced the issue and verified the fix using a debugger. Ran vm.quick and
> hotspot/test/:hotspot_jprt tests on Linux i586/x64 and Windows i586/x64 with
> -XX:NativeMemoryTracking=detail
>
>
>
> Webrev:
>
> http://cr.openjdk.java.net/~ctornqvi/webrev/8069124/webrev.00/
>
>
>
> Bug:
>
> https://bugs.openjdk.java.net/browse/JDK-8069124
>
>
>
> Thanks,
>
> Christian
>
>
>