RFR: 8247691: [aarch64] Incorrect handling of VM exceptions in C1 deopt stub/traps

[Patric Hedlin]

The immediate issue that causes the error symptom is due to the procedure link register (LR) not being preserved across
the actual call to the "patching" function (in code generated from '_generate_patching()_'), invoked as part of the C1
deoptimization traps.

However, this update addresses a larger issue with the current implementation.

Since the Aarch64 implementation does not adopt patching but deoptimization to support load-mirror et.al., the
"patching" stub-code does not need to support the exception protocol otherwise necessary when a VM transition might be
needed in the actual patching function. The deoptimization is compulsory and the transition to the interpreter will
cater for proper interaction with the VM.

The proposed solution is thus:
1. The version of '_patch_code()_' used with **DEOPTIMIZE_WHEN_PATCHING** should no be modelled as a **JRT_ENTRY**. The
"patching" functions will not transfer control to VM (for up-call or otherwise). 2. The patch-stub code does not need
to handle the VM exception protocol (code can be removed). 3. The patch-stub code need only to support deoptimization
and re-execute (it's a fatal error otherwise). 4. The patch-stub code does not need to utilise any instruction stream
synchronisation barrier as no patching/modifying of the instruction stream is done (including indirectly through a VM
transition).

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

Commit messages:
 - No need to synchronize the instruction stream when not patching.
 - Terminating in the no-deopt case.
 - 8247691: Crash in test/hotspot/jtreg/runtime/Thread/StopAtExit.java

Changes: https://git.openjdk.java.net/jdk/pull/344/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=344&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8247691
  Stats: 94 lines in 3 files changed: 15 ins; 60 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/344.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/344/head:pull/344

PR: https://git.openjdk.java.net/jdk/pull/344