[jdk25u] RFR: 8277444: Data race between JvmtiClassFileReconstituter::copy_bytecodes and class linking

Fri Sep 12 21:33:24 UTC 2025

A clean backport of https://bugs.openjdk.org/browse/JDK-8277444

This fixes a race condition that occurs when a class is simultaneously retransformed via the Instrumentation API and linked. This can lead to invalid bytecode which will cause a VerifyError. Even worse, if class verifying is turned off, which it is by default for java.* classes, this will cause the JVM to crash/segfault. 

The included test `test/jdk/java/lang/instrument/RetransformBigClassTest.java` fails before the patch and passes after

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Commit messages:
 - Backport 46ae1ee87152742082e6047d0556944d7ae4567d

Changes: https://git.openjdk.org/jdk25u/pull/197/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=197&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8277444
  Stats: 187 lines in 3 files changed: 186 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk25u/pull/197.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/197/head:pull/197

PR: https://git.openjdk.org/jdk25u/pull/197