RFR: 8374744: Enable dumping of APX EGPRs (R16–R31) in JVM fatal error logs

Thu Jan 8 23:21:08 UTC 2026

The goal of this PR is to add support for printing the values of APX extended general-purpose registers (EGPRs, R16-R31) in hs_err_pid* crash logs on x86 platforms with APX support. The implementation detects APX support at runtime and attempts to dump the additional registers when available, improving post-mortem debugging capabilities.

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Commit messages:
 - dump EGPRs only when UseAPX is enabled; also add nullptr reference check for apx state
 - 8374744: Enable dumping of APX EGPRs (R16–R31) in JVM fatal error logs

Changes: https://git.openjdk.org/jdk/pull/29098/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29098&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374744
  Stats: 139 lines in 3 files changed: 117 ins; 1 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/29098.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29098/head:pull/29098

PR: https://git.openjdk.org/jdk/pull/29098