RFR: 8170812: Metaspace corruption caused by incorrect memory size for MethodCounters

[Andrew Haley]

If sizeof (MethodCounters) is not a multiple of wordSize, memory
allocator metadata is corrupted, causing the VM to become unstable and
eventually crash.

The fix is very simple:

diff -r 85b6ca9458ed src/share/vm/oops/methodCounters.hpp
--- a/src/share/vm/oops/methodCounters.hpp      Wed Mar 29 15:44:34 2017 +0000
+++ b/src/share/vm/oops/methodCounters.hpp      Wed Apr 05 15:42:18 2017 +0100
@@ -116,7 +116,7 @@

   AOT_ONLY(Method* method() const { return _method; })

-  static int size() { return sizeof(MethodCounters) / wordSize; }
+  static int size() { return align_size_up(sizeof(MethodCounters), wordSize) / wordSize; }

   bool is_klass() const { return false; }

This is very low risk because if the size is already a multiple of
wordSize, this patch will have no effect.  If the size is not a
multiple of wordSize, this patch will prevent an inevitable crash.

I've applied for a JDK9 fix request.  I'll need a sponsor.

Andrew.