RFR (XXS): 8016474: Crash in sun.reflect.UnsafeObjectFieldAccessorImpl.get

[Christian Thalinger]

http://cr.openjdk.java.net/~twisti/8016474

8016474: Crash in sun.reflect.UnsafeObjectFieldAccessorImpl.get
Summary: C1's GetUnsafeObject G1 pre-barrier uses the wrong type to read the klass pointer.
Reviewed-by:

There is a bug in C1's GetUnsafeObject G1 pre-barrier code.  If UseCompressedKlassPointers is on we use T_OBJECT to read the klass pointer of the object.  If we also use a different object alignment like 16 or 32 (-XX:ObjectAlignmentInBytes=16) the klass pointer gets decoded with the wrong shift resulting in a wrong pointer and a crash.

The fix is to always use T_ADDRESS for klass pointer reads.

src/share/vm/c1/c1_LIRGenerator.cpp
test/compiler/unsafe/GetUnsafeObjectG1PreBarrier.java