RFR: 8287637: Loom: Mismatched VirtualThread::state accessor

[Aleksey Shipilev]

Found this by reading the code, no test failure detected yet.

The field is defined as:


    // virtual thread state, accessed by VM
    private volatile int state;


The field is defined on VM side as:


  macro(_state_offset,                     k, "state",              int_signature,               false)


And yet, it is accessed as `short`:


u2 java_lang_VirtualThread::state(oop vthread) {
  return vthread->short_field_acquire(_state_offset);
}


I think this is just asking for trouble on different endianness: the partial `u2` read from `int` field can read the "higher" two bytes, not the "lower" two bytes.

Additional testing:
 - [x] Linux x86_64 fastdebug, `jdk_loom hotspot_loom`
 - [ ] Linux AArch64 fastdebug, `jdk_loom hotspot_loom`

-------------

Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/8967/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8967&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287637
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8967.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8967/head:pull/8967

PR: https://git.openjdk.java.net/jdk/pull/8967