Mitigate VMMethod::validatedId() crash

[zhengyu123]

What does this PR do?:
Mitigate VMMethod::validatedId() crash with 1.60.4

Motivation:
Avoid invalid jmethodId crashes JVM.

Additional Notes:
Early mitigation did not cover following check:
*(VMMethod**)method_id == this

Loading from invalid method_id results new crash.

How to test the change?:

• CI tests

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-13947

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:	Tue Apr 7 20:04:29 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	stackWalker.cpp	walkVM	848	37

[dd-octo-sts]

CI Test Results

Run: #24101747062 | Commit: 5d1cf62 | Duration: 21m 25s (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: 2026-04-07 20:39:43 UTC