fix: don't disable profiler on Alpine/musl over missing libgcc_s.so.1 by jbachorik · Pull Request #720 · DataDog/java-profiler

jbachorik · 2026-08-06T09:55:50Z

What does this PR do?:
checkState() was failing profiler startup on any host missing libgcc_s.so.1, including musl/Alpine — but that failure mode (glibc's pthread_exit/pthread_cancel aborting via __libc_fatal when its private lazy dlopen of libgcc_s fails) is glibc-specific. musl never takes that code path, so a missing libgcc_s.so.1 there was never actually dangerous. The check now only treats prewarmUnwinder() failure as fatal off musl (!prewarmUnwinder() && !OS::isMusl()), so Alpine/musl hosts without libgcc_s.so.1 start normally.

Also rewrote the prewarmUnwinder() comment, which had drifted to attribute the eager load to only one of the two lazy-load issues it actually closes (J9's DWARF-unwinder signal-context dlopen, and the glibc pthread_exit path above) — it now documents both, and why only one of them gates fatality.

Motivation:
Distroless/hardened/Alpine images commonly ship without libgcc_s.so.1. The overly broad check meant the profiler refused to start on those musl hosts even though nothing there was actually at risk.

Additional Notes:
Also fixes faultInjection_ut.cpp's CheckStateSurfacesInjectedPrewarmUnwinderFailure test, which assumed an injected prewarmUnwinder() failure always surfaces as "Missing libgcc_s.so.1" — no longer true on musl. Latent until now since -PenableFaultInjection isn't wired into CI yet, but fixed ahead of that.

How to test the change?:

Updated faultInjection_ut.cpp to assert the correct behavior on both glibc and musl.
No behavior change on glibc hosts (still fails fast on missing libgcc_s.so.1); musl now starts normally instead of refusing to start.

For Datadog employees:

If this PR touches code that signs or publishes builds or packages, or handles
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JIRA: PROF-15664

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prewarmUnwinder() closes two separate lazy-load issues (J9 signal-context dlopen and glibc's pthread_exit __libc_dlopen abort) that share a fix but not a failure mode; only the glibc one should fail profiler startup. Fault-injection test updated to match. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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dd-octo-sts · 2026-08-06T09:59:01Z

Scan-Build Report

User:	runner@runnervmvrwv9
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:	Thu Aug 6 12:37:11 2026

Bug Summary

Logic error
Bug Type	Quantity	Display?
All Bugs	1
Dereference of null pointer	1

Reports

Bug Group	Bug Type ▾	File	Function/Method	Line	Path Length
Logic error	Dereference of null pointer	profiler.h	findLibraryByAddress	517	13

dd-octo-sts · 2026-08-06T10:13:17Z

CI Test Results

Run:#31102054098 | Commit:1dd43a5 | Duration: 14m 0s (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

Updated: 2026-08-06 12:52:56 UTC

dd-octo-sts · 2026-08-06T11:13:55Z

✅ All 40 integration tests passed

📊 Dashboard · 👷 Pipeline · 📦 3054c057

jbachorik · 2026-08-06T11:14:50Z

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dd-octo-sts · 2026-08-06T11:25:08Z

Benchmark Results (commit `a69976b`)

Pipeline: https://gitlab.ddbuild.io/DataDog/apm-reliability/benchmarking-platform/-/pipelines/129368968 Commit: a69976b22f74135954e5c473bd31ef3c3363ed69

✅ Within expected boundaries

No significant runtime deltas (all within run-to-run noise) and no internal-counter outliers.

Runtime details (per benchmark × JDK)

Benchmark	JDK	Latest	Dev	Δ (dev vs latest)	Issues L/D
akka-uct	21	✅ 10154 ms (21 iters)	✅ 10241 ms (21 iters)	≈ +0.9% (±10.6%)	— / —
akka-uct	25	✅ 8932 ms (24 iters)	✅ 8893 ms (24 iters)	≈ -0.4% (±9.4%)	— / —
finagle-chirper	21	✅ 5968 ms (33 iters)	✅ 5938 ms (33 iters)	≈ -0.5% (±25.2%)	⚠️ W:3 / ⚠️ W:3
finagle-chirper	25	✅ 5460 ms (36 iters)	✅ 5378 ms (36 iters)	≈ -1.5% (±23.2%)	⚠️ W:3 / ⚠️ W:3
fj-kmeans	21	✅ 2815 ms (66 iters)	✅ 2818 ms (66 iters)	≈ +0.1% (±2.5%)	— / —
fj-kmeans	25	✅ 2773 ms (67 iters)	✅ 2825 ms (66 iters)	≈ +1.9% (±2.6%)	— / —
future-genetic	21	✅ 2111 ms (88 iters)	✅ 2104 ms (88 iters)	≈ -0.3% (±2.6%)	— / —
future-genetic	25	✅ 1938 ms (96 iters)	✅ 1961 ms (94 iters)	≈ +1.2% (±2.6%)	— / —
naive-bayes	21	✅ 1266 ms (135 iters)	✅ 1246 ms (137 iters)	≈ -1.6% (±32.5%)	— / —
naive-bayes	25	✅ 1012 ms (169 iters)	✅ 1006 ms (170 iters)	≈ -0.6% (±31.2%)	— / —
reactors	21	✅ 16292 ms (15 iters)	✅ 15680 ms (15 iters)	≈ -3.8% (±8.4%)	— / —
reactors	25	✅ 18456 ms (15 iters)	✅ 18517 ms (15 iters)	≈ +0.3% (±5.1%)	— / —

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	✅ / ✅	✅ / ✅	6 / 4	1925 / 1899	✅ / ✅	✅ / ✅
akka-uct	25	✅ / ✅	✅ / ✅	✅ / 2	2396 / 2160	✅ / ✅	✅ / ✅
finagle-chirper	21	✅ / ✅	✅ / ✅	4 / ✅	8463 / 8475	✅ / ✅	✅ / ✅
finagle-chirper	25	✅ / ✅	✅ / ✅	3 / 1	8470 / 8040	✅ / ✅	✅ / ✅
fj-kmeans	21	✅ / ✅	✅ / ✅	5 / 2	1251 / 1251	✅ / ✅	✅ / ✅
fj-kmeans	25	✅ / ✅	✅ / ✅	2 / 1	1262 / 1294	✅ / ✅	✅ / ✅
future-genetic	21	✅ / ✅	✅ / ✅	4 / ✅	3043 / 2950	✅ / ✅	✅ / ✅
future-genetic	25	✅ / ✅	✅ / ✅	✅ / ✅	2962 / 2987	✅ / ✅	✅ / ✅
naive-bayes	21	✅ / ✅	✅ / ✅	4 / 3	3495 / 3502	✅ / ✅	✅ / ✅
naive-bayes	25	✅ / ✅	✅ / ✅	4 / 1	3511 / 3497	✅ / ✅	✅ / ✅
reactors	21	✅ / ✅	✅ / ✅	2 / 1	1586 / 1586	✅ / ✅	✅ / ✅
reactors	25	✅ / ✅	✅ / ✅	1 / ✅	1780 / 1882	✅ / ✅	✅ / ✅

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…njected prewarm failures Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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…#720) (cherry picked from commit b220402)

…#720)

jbachorik added the AI label Aug 6, 2026

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CopilotAI reviewed Aug 6, 2026

jbachorik changed the title ~~fix: document libgcc_s prewarm landmines, gate fatality to glibc~~fix: don't disable profiler on Alpine/musl over missing libgcc_s.so.1Aug 6, 2026

jbachorik requested a review from zhengyu123 August 6, 2026 10:48

Merge branch 'main' into jb/libgcc_s
a69976b

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Comment threadddprof-lib/src/test/cpp/faultInjection_ut.cpp Outdated

jbachorik marked this pull request as ready for review August 6, 2026 11:41

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CopilotAI reviewed Aug 6, 2026

fix: use FAULTS_INJECTED counter delta, not error string, to detect i…
eee3295
…njected prewarm failures Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CopilotAI review requested due to automatic review settings August 6, 2026 11:59

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Merge branch 'main' into jb/libgcc_s
3054c05

CopilotAI review requested due to automatic review settings August 6, 2026 12:35

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Comment threadddprof-lib/src/main/cpp/profiler.cpp

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Comment threadddprof-lib/src/main/cpp/profiler.cpp

jbachorik merged commit b220402 into mainAug 6, 2026
109 checks passed

jbachorik deleted the jb/libgcc_s branch August 6, 2026 14:55

github-actionsBot added this to the 1.49.0 milestone Aug 6, 2026

jbachorik added a commit that referenced this pull request Aug 7, 2026
fix: don't disable profiler on Alpine/musl over missing libgcc_s.so.1 (…
05e5b81
…#720) (cherry picked from commit b220402)

jbachorik mentioned this pull request Aug 8, 2026
Bump java-profiler (ddprof) to 1.49.0 DataDog/dd-trace-java#12168
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zhengyu123 pushed a commit that referenced this pull request Aug 11, 2026
fix: don't disable profiler on Alpine/musl over missing libgcc_s.so.1 (…
1ec0a1a
…#720)

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Benchmark Results (commit a69976b)

✅ Within expected boundaries

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Benchmark Results (commit `a69976b`)