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Protect methods called from signal handlers against partially initialized thread structures during GC worker thread creation. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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rkennke
approved these changes
Jan 21, 2026
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What does this PR do?:
Use SafeAccess for signal-handler memory reads in vmStructs.h to prevent crashes when reading from partially initialized thread structures during GC worker thread creation.
Motivation:
Fixes ASan heap-buffer-overflow errors in CI where the CTimer signal handler was delivering signals to newly created GC worker threads before their
VMThreadstructure was fully initialized. The TLS pointer returned a valid address but offset calculations resulted in reading memory before the allocated region ("72 bytes to the left").Additional Notes:
While doing this change I took a sweep on other signal-handler-accessible methods where
SafeAccessmakes sense:VMThread::state()- UsesSafeAccess::load32()VMThread::inDeopt()- UsesSafeAccess::loadPtr()JavaFrameAnchor::lastJavaSP()- UsesSafeAccess::loadPtr()JavaFrameAnchor::lastJavaFP()- UsesSafeAccess::loadPtr()JavaFrameAnchor::lastJavaPC()- UsesSafeAccess::loadPtr()JavaFrameAnchor::fromEntryFrame()- UsesSafeAccess::loadPtr()How to test the change?:
For Datadog employees:
credentials of any kind, I've requested a review from
@DataDog/security-design-and-guidance.🤖 Generated with Claude Code