memory stomping with runtime/valhalla/valuetypes/ValueOops.java

[Roland Westrelin]

I see the following crash when running a build of the current valhalla
repo:

# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007fe92853bec9, pid=27976, tid=27991
#
# JRE version: OpenJDK Runtime Environment (9.0) (fastdebug build 9-internal+0-2017-03-22-102420.rwestrel.valhalla)
# Java VM: OpenJDK 64-Bit Server VM (fastdebug 9-internal+0-2017-03-22-102420.rwestrel.valhalla, interpreted mode, compressed oops, concurrent mark sweep gc, linux-amd64)
# Problematic frame:
# V  [libjvm.so+0xfe6ec9]  verify_memory(void*)+0x99
#

V  [libjvm.so+0x12e2d1f]  VMError::report_and_die(int, char const*, char const*, __va_list_tag*, Thread*, unsigned char*, void*, void*, char const*, int, unsigned long)+0x15f
V  [libjvm.so+0x12e3a3a]  VMError::report_and_die(Thread*, char const*, int, char const*, char const*, __va_list_tag*)+0x4a
V  [libjvm.so+0x911b6e]  report_fatal(char const*, int, char const*, ...)+0xee
V  [libjvm.so+0xfe6f2d]  verify_memory(void*)+0xfd
V  [libjvm.so+0xfe8cbe]  os::free(void*)+0x4e
V  [libjvm.so+0x7fde82]  ClassLoaderData::~ClassLoaderData()+0xa2
V  [libjvm.so+0x80064c]  ClassLoaderDataGraph::purge()+0x6c
V  [libjvm.so+0xae3adc]  GenCollectedHeap::do_collection(bool, bool, unsigned long, bool, GenCollectedHeap::GenerationType)+0xaac
V  [libjvm.so+0xae3e6e]  GenCollectedHeap::do_full_collection(bool, GenCollectedHeap::GenerationType)+0x3e
V  [libjvm.so+0x12e4567]  VM_GenCollectFull::doit()+0xc7
V  [libjvm.so+0x1312770]  VM_Operation::evaluate()+0xb0
V  [libjvm.so+0x13101b0]  VMThread::evaluate_operation(VM_Operation*)+0x2e0
V  [libjvm.so+0x1310a83]  VMThread::loop()+0x4a3
V  [libjvm.so+0x1310cb3]  VMThread::run()+0xb3
V  [libjvm.so+0xffb60a]  java_start(Thread*)+0xea

That test is only run with -Xint. It fails approximately 1 in 20 runs of
the test.

Roland.