[fault-injection] Profiler::recordSample() stack walk is unprotected

[zhengyu123]

What does this PR do?:

Motivation:

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 security review (run the dd:platform-security-review
  skill, or file a request via the PSEC review form).
  bewaire also runs automatically on every PR.
• This PR doesn't touch any of that.
• JIRA: PROF-15447

Unsure? Have a question? Request a review!

[Copilot]

Pull request overview

This PR hardens the native profiler’s initialization and stack-walking paths against startup-ordering issues (Agent_OnLoad) and fault/crash scenarios during sampling, and adds a regression test to prevent reintroducing the initialization regression.

Changes:

• Add setjmp/longjmp crash protection around Profiler::recordSample()’s stack unwind to avoid unrecoverable faults during metadata reads.
• Ensure HotSpot VMStructs initialization happens early enough for the -agentpath: (Agent_OnLoad) path by calling VM::ready() from VM::initProfilerBridge(), and add debug test logging for the decision points.
• Add a Java regression test that launches a child JVM with -agentpath: and asserts the DebugNonSafepoints flag lookup path is taken (not the CompiledMethodLoad workaround).

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
ddprof-test/src/test/java/com/datadoghq/profiler/JVMAccessTest.java	Adds regression test covering Agent_OnLoad initialization ordering and VM flag detection.
ddprof-lib/src/main/java/com/datadoghq/profiler/LibraryLoader.java	Exposes a package-visible library-path resolver for tests to supply a real -agentpath: without loading in-process.
ddprof-lib/src/main/cpp/vmEntry.h	Reworks _libjvm handling to a CodeCache* with an accessor using acquire semantics.
ddprof-lib/src/main/cpp/vmEntry.cpp	Makes VM::ready() idempotently initialize VMStructs once; calls ready() from initProfilerBridge() for Agent_OnLoad; adds test logs.
ddprof-lib/src/main/cpp/profiler.cpp	Wraps native+Java stack walking in recordSample() with crash protection and records an error frame on recovery; switches debug-symbol query to VM::libjvm().
ddprof-lib/src/main/cpp/hotspot/vmStructs.inline.h	Adds safe offset-load helpers and uses SafeAccess for VMFlag name reads; introduces fault-injection point for offset access.
ddprof-lib/src/main/cpp/hotspot/vmStructs.h	Moves offset accessors to inline definitions and adds a safe-load template; updates VMFlag::name() signature.
ddprof-lib/src/main/cpp/hotspot/vmStructs.cpp	Avoids repeated unsafe dereferences by caching VMFlag::name() into a local before strcmp.
ddprof-lib/src/main/cpp/hotspot/hotspotSupport.cpp	Adds a null-check for scope.method() and renames the recovered-longjmp counter to be stackwalk-generic.
ddprof-lib/src/main/cpp/flightRecorder.cpp	Switches debug-symbol setting emission to use VM::libjvm().
ddprof-lib/src/main/cpp/counters.h	Renames WALKVM_LONGJMP_RECOVERED to STACKWALK_LONGJMP_RECOVERED.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[dd-octo-sts]

CI Test Results

Run: #30093470859 | Commit: 7feb697 | Duration: 15m 21s (longest job)

❌ 7 of 32 test jobs failed

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

Failed Tests

glibc-aarch64/debug / 8-j9

Job: View logs

No detailed failure information available. Check the job logs.

glibc-aarch64/debug / 11-j9

Job: View logs

No detailed failure information available. Check the job logs.

glibc-aarch64/debug / 17-j9

Job: View logs

No detailed failure information available. Check the job logs.

glibc-amd64/debug / 8-j9

Job: View logs

No detailed failure information available. Check the job logs.

glibc-amd64/debug / 11-j9

Job: View logs

No detailed failure information available. Check the job logs.

glibc-amd64/debug / 8-ibm

Job: View logs

No detailed failure information available. Check the job logs.

glibc-amd64/debug / 17-j9

Job: View logs

No detailed failure information available. Check the job logs.

Summary: Total: 32 | Passed: 25 | Failed: 7

---

Updated: 2026-07-24 13:04:32 UTC

[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

[dd-octo-sts]

Benchmark Results (commit 86238c0)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/126639928 Commit: 86238c07f4f96c4d60956bc59cd8bbb07196a7c9

⚠️ Significant outliers

• 🔴 fj-kmeans (JDK 21): runtime +4.3% (2650→2763 ms)

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10301 ms (21 iters)	✅ 10332 ms (21 iters)	≈ +0.3% (±11.6%)	— / —
akka-uct	25	✅ 8814 ms (24 iters)	✅ 8767 ms (24 iters)	≈ -0.5% (±10.1%)	— / —
finagle-chirper	21	✅ 5965 ms (33 iters)	✅ 5977 ms (33 iters)	≈ +0.2% (±25.4%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5497 ms (36 iters)	✅ 5398 ms (36 iters)	≈ -1.8% (±24%)	⚠️ W:4 / ⚠️ W:3
fj-kmeans	21	✅ 2650 ms (71 iters)	✅ 2763 ms (68 iters)	🔴 +4.3%	— / —
fj-kmeans	25	✅ 2827 ms (66 iters)	✅ 2812 ms (66 iters)	≈ -0.5% (±2.6%)	— / —
future-genetic	21	✅ 2048 ms (90 iters)	✅ 2071 ms (89 iters)	≈ +1.1% (±2.6%)	— / —
future-genetic	25	✅ 2098 ms (89 iters)	✅ 2128 ms (87 iters)	≈ +1.4% (±2.5%)	— / —
naive-bayes	21	✅ 1266 ms (135 iters)	✅ 1237 ms (139 iters)	≈ -2.3% (±31.9%)	— / —
naive-bayes	25	✅ 1018 ms (168 iters)	✅ 1008 ms (170 iters)	≈ -1% (±31.3%)	— / —
reactors	21	✅ 16486 ms (15 iters)	✅ 16402 ms (15 iters)	≈ -0.5% (±7.8%)	— / —
reactors	25	✅ 18983 ms (15 iters)	✅ 18298 ms (15 iters)	≈ -3.6% (±4.1%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	2 / 2	2062 / 1958	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	1 / 2	2047 / 2212	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	4 / 2	7979 / 8465	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	2 / ✅	8174 / 8614	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	4 / 3	1292 / 1267	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	2 / 1	1254 / 1267	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	✅ / ✅	2964 / 2905	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	3 / 4	2947 / 2881	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	4 / ✅	3535 / 3561	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	2 / 1	3499 / 3501	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	✅ / 3	1704 / 1657	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	✅ / 3	1993 / 1778	✅ / ✅	✅ / ✅

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

[dd-octo-sts]

Benchmark Results (commit 490b055)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/126673593 Commit: 490b0557b9d16f598c0d6426e84de29eefac6b67

⚠️ Significant outliers

• 🟢 fj-kmeans (JDK 21): runtime -3.9% (2768→2659 ms)
• 🔴 future-genetic (JDK 21): runtime +3.2% (2049→2115 ms)
• 🔴 future-genetic (JDK 25): runtime +2.9% (2049→2109 ms)

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10354 ms (21 iters)	✅ 10192 ms (21 iters)	≈ -1.6% (±11.2%)	— / —
akka-uct	25	✅ 8881 ms (24 iters)	✅ 8835 ms (24 iters)	≈ -0.5% (±9.9%)	— / —
finagle-chirper	21	✅ 6005 ms (33 iters)	✅ 5958 ms (33 iters)	≈ -0.8% (±24.7%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5462 ms (36 iters)	✅ 5459 ms (36 iters)	≈ -0.1% (±24.2%)	⚠️ W:3 / ⚠️ W:3
fj-kmeans	21	✅ 2768 ms (68 iters)	✅ 2659 ms (70 iters)	🟢 -3.9%	— / —
fj-kmeans	25	✅ 2827 ms (66 iters)	✅ 2842 ms (66 iters)	≈ +0.5% (±2.6%)	— / —
future-genetic	21	✅ 2049 ms (91 iters)	✅ 2115 ms (87 iters)	🔴 +3.2%	— / —
future-genetic	25	✅ 2049 ms (90 iters)	✅ 2109 ms (88 iters)	🔴 +2.9%	— / —
naive-bayes	21	✅ 1263 ms (136 iters)	✅ 1255 ms (136 iters)	≈ -0.6% (±32.5%)	— / —
naive-bayes	25	✅ 1019 ms (168 iters)	✅ 1019 ms (168 iters)	≈ 0% (±31.7%)	— / —
reactors	21	✅ 16762 ms (15 iters)	✅ 17039 ms (15 iters)	≈ +1.7% (±7.9%)	— / —
reactors	25	✅ 18327 ms (15 iters)	✅ 18649 ms (15 iters)	≈ +1.8% (±5.2%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	3 / 3	1960 / 2024	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	3 / 1	2257 / 2267	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	4 / 4	8586 / 8261	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	1 / 2	8451 / 8698	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	✅ / 1	1282 / 1249	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	4 / 1	1305 / 1277	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	✅ / 2	3012 / 2866	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	3 / 2	2771 / 2856	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	3 / 8	3585 / 3500	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	2 / 1	3525 / 3516	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	1 / 1	1752 / 1584	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	3 / ✅	1862 / 1859	✅ / ✅	✅ / ✅

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

ddprof-lib/src/main/cpp/vmEntry.cpp:581

• This header comment says the “VMStructs init below only ever runs once”, but VM::ready() is called from initLibrary(), initProfilerBridge(), and the VMInit callback, and there is no guard around VMStructs::init(lib)/VMStructs::ready(). Either add a guard, or adjust the comment so it doesn’t claim single execution.

// Run late initialization when JVM is ready. May be called more than once (from
// initProfilerBridge() directly, and later from the VMInit JVMTI callback, or from
// initLibrary() followed by a JNI-triggered attach) -- the VMStructs init below only
// ever runs once.

[dd-octo-sts]

Benchmark Results (commit 90fadfe)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/126772742 Commit: 90fadfeb11b854693bf84b6e7ef6421f463ae75e

⚠️ Significant outliers

• 🟢 future-genetic (JDK 25): runtime -3.2% (2077→2011 ms)

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10324 ms (21 iters)	✅ 10431 ms (21 iters)	≈ +1% (±11.8%)	— / —
akka-uct	25	✅ 8786 ms (24 iters)	✅ 8931 ms (24 iters)	≈ +1.7% (±9.9%)	— / —
finagle-chirper	21	✅ 6030 ms (33 iters)	✅ 6016 ms (33 iters)	≈ -0.2% (±26.1%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5449 ms (36 iters)	✅ 5448 ms (36 iters)	≈ -0% (±24.6%)	⚠️ W:3 / ⚠️ W:3
fj-kmeans	21	✅ 2751 ms (68 iters)	✅ 2683 ms (70 iters)	≈ -2.5% (±2.7%)	— / —
fj-kmeans	25	✅ 2842 ms (66 iters)	✅ 2814 ms (66 iters)	≈ -1% (±2.5%)	— / —
future-genetic	21	✅ 2076 ms (89 iters)	✅ 2101 ms (88 iters)	≈ +1.2% (±2.7%)	— / —
future-genetic	25	✅ 2077 ms (89 iters)	✅ 2011 ms (93 iters)	🟢 -3.2%	— / —
naive-bayes	21	✅ 1264 ms (135 iters)	✅ 1280 ms (133 iters)	≈ +1.3% (±32.7%)	— / —
naive-bayes	25	✅ 1006 ms (169 iters)	✅ 976 ms (174 iters)	≈ -3% (±31.7%)	— / —
reactors	21	✅ 16957 ms (15 iters)	✅ 16446 ms (15 iters)	≈ -3% (±6.6%)	— / —
reactors	25	✅ 18310 ms (15 iters)	✅ 18574 ms (15 iters)	≈ +1.4% (±5%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	3 / ✅	2007 / 1989	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	1 / 2	2249 / 2195	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	6 / 2	8633 / 8540	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	1 / ✅	8691 / 8542	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	3 / ✅	1270 / 1287	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	3 / 2	1281 / 1276	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	3 / 3	2939 / 2945	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	1 / ✅	2878 / 2858	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	✅ / 6	3515 / 3506	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	5 / 3	3447 / 3501	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	✅ / 1	1709 / 1603	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	1 / ✅	1936 / 1940	✅ / ✅	✅ / ✅

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

[dd-octo-sts]

Benchmark Results (commit e3556f8)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/126938656 Commit: e3556f88d7a8848f2e654fced724413663ee01f5

⚠️ Significant outliers

• 🟢 future-genetic (JDK 25): runtime -3.1% (2111→2045 ms)

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10324 ms (21 iters)	✅ 10273 ms (21 iters)	≈ -0.5% (±11.3%)	— / —
akka-uct	25	✅ 8845 ms (24 iters)	✅ 8832 ms (24 iters)	≈ -0.1% (±9.8%)	— / —
finagle-chirper	21	✅ 6012 ms (33 iters)	✅ 5977 ms (33 iters)	≈ -0.6% (±25%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5418 ms (36 iters)	✅ 5432 ms (36 iters)	≈ +0.3% (±24.1%)	⚠️ W:3 / ⚠️ W:3
fj-kmeans	21	✅ 2733 ms (68 iters)	✅ 2729 ms (68 iters)	≈ -0.1% (±2.7%)	— / —
fj-kmeans	25	✅ 2835 ms (66 iters)	✅ 2829 ms (66 iters)	≈ -0.2% (±2.6%)	— / —
future-genetic	21	✅ 2062 ms (91 iters)	✅ 2041 ms (90 iters)	≈ -1% (±2.5%)	— / —
future-genetic	25	✅ 2111 ms (88 iters)	✅ 2045 ms (91 iters)	🟢 -3.1%	— / —
naive-bayes	21	✅ 1279 ms (134 iters)	✅ 1232 ms (138 iters)	≈ -3.7% (±32.3%)	— / —
naive-bayes	25	✅ 1007 ms (170 iters)	✅ 1012 ms (169 iters)	≈ +0.5% (±31.6%)	— / —
reactors	21	✅ 15868 ms (15 iters)	✅ 16735 ms (15 iters)	≈ +5.5% (±8.4%)	— / —
reactors	25	✅ 18780 ms (15 iters)	✅ 18600 ms (15 iters)	≈ -1% (±3.5%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	2 / 3	1966 / 2035	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	1 / ✅	2136 / 2349	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	1 / 3	8760 / 8482	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	4 / 1	8820 / 8102	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	✅ / 4	1241 / 1269	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	3 / 1	1258 / 1254	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	✅ / 1	2981 / 2900	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	2 / 1	2864 / 2926	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	4 / 3	3480 / 3499	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	11 / 4	3495 / 3518	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	4 / 2	1630 / 1779	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	✅ / 1	1969 / 1853	✅ / ✅	✅ / ✅

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (2)

ddprof-lib/src/test/cpp/faultInjection_ut.cpp:66

• fi_signal_wrapper calls Profiler::checkFault with the old one-argument signature, but Profiler::checkFault now requires (ProfiledThread*, siginfo_t*, void*). This will fail to compile and also prevents checkFault from inspecting the ucontext/siginfo when deciding whether to longjmp.

static void fi_signal_wrapper(int signo, siginfo_t* siginfo, void* context) {
  if (SafeAccess::handle_safefetch(signo, context)) {
    return;  // safefetch load recovered; PC already rewritten to _cont.
  }
  Profiler::checkFault(ProfiledThread::current());  // longjmp if protected
  // Not protected and not a safefetch fault — real crash.

ddprof-lib/src/main/cpp/profiler.cpp:1034

• Profiler::checkFault is using siginfo->si_addr to decide whether to longjmp and also asserts that profiler{min,max}_address are non-null. For unwind faults, si_addr is typically the bad dereferenced metadata pointer (not an address inside libjavaProfiler), so this will skip recovery and crash. It also makes gtests that call checkFault without having run setupSignalHandlers() hit the assert. Use the instruction PC from ucontext for the range check (or fall back to unconditional longjmp when the range isn’t initialized), and compare addresses as uintptr_t.

  const uintptr_t min = (uintptr_t)_profiler_min_address;
  const uintptr_t max = (uintptr_t)_profiler_max_address;

  // If the profiler address range is not initialized (e.g. unit tests), fall back

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (3)

ddprof-lib/src/test/cpp/faultInjection_ut.cpp:65

• Profiler::checkFault now requires siginfo_t* and ucontext, but the fault-injection signal wrapper calls it with a single argument. This will not compile, and it also prevents checkFault from reading the faulting PC from the provided ucontext for origin filtering.

static void fi_signal_wrapper(int signo, siginfo_t* siginfo, void* context) {
  if (SafeAccess::handle_safefetch(signo, context)) {
    return;  // safefetch load recovered; PC already rewritten to _cont.
  }
  Profiler::checkFault(ProfiledThread::current());  // longjmp if protected

ddprof-lib/src/main/cpp/vmEntry.cpp:581

• The comment says the VMStructs init path "only ever runs once", but VM::ready() is invoked from both initLibrary() and initProfilerBridge() and currently calls VMStructs::init() on every invocation. Either guard the init, or adjust the comment to match the actual behavior/assumptions.

// Run late initialization when JVM is ready. May be called more than once (from
// initProfilerBridge() directly, and later from the VMInit JVMTI callback, or from
// initLibrary() followed by a JNI-triggered attach) -- the VMStructs init below only
// ever runs once.

ddprof-lib/src/test/cpp/hotspot_crash_protection_ut.cpp:337

• The section header above still mentions HotspotSupport::checkFault(), but the test now calls Profiler::checkFault(). Updating the header/comment avoids confusion when navigating the crash-protection tests.

// ---------------------------------------------------------------------------

TEST(CheckFaultGuardTest, NullThreadIsNoop) {
    Profiler::checkFault(nullptr, nullptr, nullptr);  // must not crash

[dd-octo-sts]

Benchmark Results (commit b128b86)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/126984072 Commit: b128b866223759bb9f87498be379cc6aea69a833

⚠️ Significant outliers

• 🟢 fj-kmeans (JDK 21): runtime -2.6% (2821→2748 ms)

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10325 ms (21 iters)	✅ 10466 ms (21 iters)	≈ +1.4% (±11.3%)	— / —
akka-uct	25	✅ 8806 ms (24 iters)	✅ 8923 ms (24 iters)	≈ +1.3% (±10.6%)	— / —
finagle-chirper	21	✅ 5971 ms (33 iters)	✅ 6034 ms (33 iters)	≈ +1.1% (±25.3%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5453 ms (36 iters)	✅ 5488 ms (36 iters)	≈ +0.6% (±24.5%)	⚠️ W:3 / ⚠️ W:3
fj-kmeans	21	✅ 2821 ms (66 iters)	✅ 2748 ms (68 iters)	🟢 -2.6%	— / —
fj-kmeans	25	✅ 2839 ms (66 iters)	✅ 2827 ms (66 iters)	≈ -0.4% (±2.6%)	— / —
future-genetic	21	✅ 2119 ms (87 iters)	✅ 2100 ms (88 iters)	≈ -0.9% (±2.8%)	— / —
future-genetic	25	✅ 2056 ms (90 iters)	✅ 2093 ms (90 iters)	≈ +1.8% (±2.6%)	— / —
naive-bayes	21	✅ 1244 ms (137 iters)	✅ 1306 ms (131 iters)	≈ +5% (±33.3%)	— / —
naive-bayes	25	✅ 986 ms (173 iters)	✅ 1014 ms (169 iters)	≈ +2.8% (±32.1%)	— / —
reactors	21	✅ 16355 ms (15 iters)	✅ 16274 ms (15 iters)	≈ -0.5% (±8.8%)	— / —
reactors	25	✅ 18339 ms (15 iters)	✅ 18305 ms (15 iters)	≈ -0.2% (±4.7%)	— / —

Internal counter details (ddprof)

ddprof internal counters, latest / dev (✅ = 0, · = unavailable):

Benchmark	JDK	Dropped rec	Dropped jvmti	Dropped trace	Skipped WC	AGCT fail	Unwind fail
akka-uct	21	✅ / ✅	✅ / ✅	1 / ✅	1902 / 2042	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	3 / 1	2364 / 2260	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	3 / 4	8493 / 8807	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	1 / 1	8606 / 8299	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	1 / 3	1249 / 1270	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	2 / 1	1282 / 1292	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	2 / ✅	2947 / 2977	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	3 / ✅	2881 / 2914	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	2 / 5	3513 / 3471	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	4 / 4	3475 / 3473	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	✅ / 3	1664 / 1621	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	✅ / ✅	1825 / 1843	✅ / ✅	✅ / ✅