[jdk21u-dev] RFR: 8334890: Missing unconditional cross modifying fence in nmethod entry barriers

[Boris Ulasevich]

The change adds an unconditional memory barrier to guarantee the instruction fetcher observes the correct updated immediate.

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

Commit messages:
 - Backport c0604fb823d9f3b2e347a9857b11606b223ad8ec

Changes: https://git.openjdk.org/jdk21u-dev/pull/1131/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8334890
  Stats: 18 lines in 1 file changed: 1 ins; 14 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1131.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1131/head:pull/1131

PR: https://git.openjdk.org/jdk21u-dev/pull/1131