Refactor stackwalker

[zhengyu123]

What does this PR do?:
This is the second part of code refactoring that builds better abstraction among different JVM implementations. This PR focuses on stack walker components.

• jvmSupport to encapsulate different JVM specific implementation details (hotspot/HotspotSupport, j9/J9Support and zing/ZingSupport)
• Moved Hotspot specific stack walkers (walkVMs) into HotspotSupport
• Moved hotspot specific JIT'ed code cache management to newly created hotspot/jitCodeCache.h/cpp
• Renamed J9Ext.h/cpp to J9Support.h/cpp to be consistent with others
• Removed unused files jvm.h/cpp
• Moved shared frame creation code to new frames.h

Motivation:
This is the second part of efforts to build abstraction among different JVM implements, so that one implementation specific code does not inadvertently pollute unsupported JVMs. This PR focus on stack walker.

Additional Notes:

How to test the change?:

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.
• JIRA: PROF-13889

Unsure? Have a question? Request a review!

[dd-octo-sts]

Scan-Build Report

User:	runner@runnervm727z3
Working Directory:	/home/runner/work/java-profiler/java-profiler/ddprof-lib/src/test/make
Command Line:	make -j4 all
Clang Version:	Ubuntu clang version 18.1.3 (1ubuntu1)
Date:	Wed Apr 8 15:35:53 2026

Bug Summary

Bug Type	Quantity	Display?
All Bugs	1
Logic error
Stack address stored into global variable	1

Reports

Bug Group	Bug Type ▾	File	Function/Method	Line	Path Length
Logic error	Stack address stored into global variable	hotspotSupport.cpp	walkVM	700	37

[dd-octo-sts]

CI Test Results

Run: #24143940840 | Commit: 10db83e | Duration: 27m 54s (longest job)

✅ All 32 test jobs passed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
8	-	✅	-	-
8-ibm	-	✅	-	-
8-j9	✅	✅	-	-
8-librca	-	-	✅	✅
8-orcl	-	✅	-	-
11	-	✅	-	-
11-j9	✅	✅	-	-
11-librca	-	-	✅	✅
17	✅	✅	-	-
17-graal	✅	✅	-	-
17-j9	✅	✅	-	-
17-librca	-	-	✅	✅
21	✅	✅	-	-
21-graal	✅	✅	-	-
21-librca	-	-	✅	✅
25	✅	✅	-	-
25-graal	✅	✅	-	-
25-librca	-	-	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 32 | Passed: 32 | Failed: 0

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Updated: 2026-04-08 16:11:51 UTC

[jbachorik]

🤖 Review generated by Claude Sonnet (AI assistant) on behalf of @jbachorik . All findings verified against the current state of the PR.

---

Summary: The refactoring is mostly mechanical code movement and generally clean. There are 2 correctness bugs introduced during the extraction, plus 4 dead-code leftovers. Findings below, roughly by severity.

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Additionally (line not in diff context):

profiler.h lines 114–117 + constructor init: _stubs_lock, _runtime_stubs, _call_stub_begin, _call_stub_end are still declared in Profiler and initialised in its constructor, but every usage was removed from profiler.cpp in this PR — all stub routing moved to JitCodeCache. These four fields are now dead weight. The alignment comment on line 63 (// _class_map_lock, _locks[], and _stubs_lock) should also be updated once _stubs_lock is removed.

[jbachorik]

🤖 Second review pass (ivoanjo lens) by Claude Sonnet on behalf of @jbachorik. All findings verified against the current state of the PR.

Six additional findings: 3 dead-code items, 1 mode inconsistency, 1 doc drift, 1 minor atomics issue.