feat: native signal handler strategy on Android by jpnurmi · Pull Request #4676 · getsentry/sentry-dotnet

jpnurmi · 2025-10-27T11:47:43Z

Experimental opt-in Android-only solution for:

Prevent Native/Cocoa SDKs from capturing errors that also get captured by .NET #3954

According to our newly introduced Android integration tests, CHAIN_AT_START works on android-arm64 and android-x64 in both Release and Debug configurations, but we'd like to validate the fix further in real-world conditions. To that end, we're making it opt-in initially so customers can try it on more devices, platforms, and configurations before considering it as the new default.

Note

Depends on:

github-actions · 2025-10-27T11:48:20Z

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📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

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codecov · 2025-10-27T12:03:59Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.99%. Comparing base (3e2eae9) to head (02f59c1).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4676      +/-   ##
==========================================
- Coverage   74.00%   73.99%   -0.02%     
==========================================
  Files         499      499              
  Lines       18066    18067       +1     
  Branches     3518     3519       +1     
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- Misses       3837     3839       +2     
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jpnurmi · 2025-11-04T11:24:38Z

@jamescrosswell This is marked as a draft because it's still waiting for dependencies, but we could already kick off the review process if you have time. :)

Do you have a preferred approach for exposing this as an opt-in API? The current proposal mirrors the sentry-native enum.

#if ANDROID
    options.Native.SignalHandlerStrategy = Sentry.Android.SignalHandlerStrategy.ChainAtStart;
#endif

With only two values, a simple boolean flag could also work for the time being, but I'm unsure if potential Android Tombstone support could change things in the future.

jpnurmi · 2026-01-26T11:38:56Z

Update: I'll get back to this after #4750 to make sure this works with .NET 10

github-actions · 2026-02-07T09:16:21Z

Semver Impact of This PR

⚪ None (no version bump detected)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

Features ✨

feat: native signal handler strategy on Android by jpnurmi in #4676

Fixes 🐛

fix: CaptureFeedback now supports multiple attachments correctly by bitsandfoxes in #5077

Dependencies ⬆️

Deps

chore(deps): update Native SDK to v0.13.4 by github-actions in #5081
chore(deps): update Java SDK to v8.37.1 by github-actions in #5071
chore(deps): update CLI to v3.3.4 by github-actions in #5068
chore(deps): update Java SDK to v8.37.0 by github-actions in #5069
chore(deps): update Cocoa SDK to v9.8.0 by github-actions in #5044
chore(deps): update Java SDK to v8.36.0 by github-actions in #5036
chore(deps): update epitaph to 0.1.1 by github-actions in #5036

Other

ci: fix workflows that always fail for fork PRs by jamescrosswell in #5065

_{🤖 This preview updates automatically when you update the PR.}

jpnurmi · 2026-02-09T13:35:08Z

While the signal handler strategy fixes the redundant SIGSEGV vs. NullReferenceException issue, the native exception test case breaks with .NET 10 on Android X86_64. 😢 All tests pass locally in an ARM64 Android emulator.

jpnurmi · 2026-02-10T12:38:01Z

Claude confidently claims the issue was fixed by:

[Mono]: Fix stackwalk callbacks calling mono_jit_info_get_method in async signal safe mode. dotnet/runtime#123346

The fix was backported to release/10.0. We can give it a try later with the next .NET 10 release.

Investigation: .NET 10 x86_64 native crash test failure

Traced the root cause via strace on the Android emulator.

What happens

When sentry-native defers to Mono's signal handler (CHAIN_AT_START), Mono's mono_handle_native_crash walks the managed stack. On .NET 10, this walk uses the MONO_UNWIND_SIGNAL_SAFE flag (added in d34ef7e), which causes AOT method JIT info to be loaded in async-safe mode with ji->async = TRUE. The stack walk callback print_stack_frame_signal_safe was not updated to check !ji->async before calling mono_jit_info_get_method(), which hits:

Assertion at jit-info.c:918, condition !ji->async not met

The assertion triggers abort(), and since mono_handle_native_crash already reset SIGABRT to SIG_DFL, the process is killed immediately — before control returns to sentry-native.

Fix

Already merged upstream:

[Mono]: Fix stackwalk callbacks calling mono_jit_info_get_method in async signal safe mode. dotnet/runtime#123346 (f49873c) — adds !ji->async check to print_stack_frame_signal_safe and mono_find_jit_info
Backported to release/10.0 as [release/10.0] [Mono]: Fix stackwalk callbacks calling mono_jit_info_get_method in async signal safe mode. dotnet/runtime#123792 (cdc557a) on Feb 6, 2026
Related issue: Critical SIGABRT crash in .NET 10 Android (ARM64) – Assertion jit-info.c:918 (!ji->async) dotnet/runtime#122797

jpnurmi · 2026-02-11T06:32:26Z

SDK 10.0.103 ships with runtime 10.0.3, which was built 12 days before the fix was merged. The fix is in the release/10.0 branch but hasn't shipped in a servicing release yet. It will likely be in runtime 10.0.4.

Runtime pack: Microsoft.NETCore.App.Runtime.Mono.android-x64 10.0.3
Built from: commit c2435c3e0f46de784341ac3ed62863ce77e117b4 in the dotnet VMR
Package dates: January 25, 2026
Fix merged: February 6, 2026 (commit cdc557af23d)

Confirmed with strace — the crash sequence is identical to before:

07:17:43.198063  at <unknown> <0xffffffff>
07:17:43.198083  at Sentry.SentrySdk:NativeCrash <0x000d8>
07:17:43.198099  at Sentry.SentrySdk:CauseCrash <0x00a0a>
07:17:43.198145  * Assertion at jit-info.c:918, condition `!ji->async' not met
07:17:43.198800  FORTIFY: pthread_mutex_lock called on a destroyed mutex

jpnurmi · 2026-02-11T07:03:43Z

I confirmed with a locally built libmonosgen-2.0.so that dotnet/runtime#123346 fixes the issue.

I used the 10.0.3 baseline of dotnet/runtime, cherry-picked the fix, built (./build.sh mono -os android -arch x64 -c Release), and copied over /usr/share/dotnet/packs/Microsoft.NETCore.App.Runtime.Mono.android-x64/10.0.3/runtimes/android-x64/native/libmonosgen-2.0.so.

02-11 07:58:07.845  5437  5437 I DOTNET  :   Debug: Triggering a deliberate exception because SentrySdk.CauseCrash(CrashType.Native) was called
02-11 07:58:07.845  5437  5437 D app_process64:   Debug: Triggering a deliberate exception because SentrySdk.CauseCrash(CrashType.Native) was called
02-11 07:58:07.846  5437  5437 I sentry-native: entering signal handler
02-11 07:58:07.846  5437  5437 D sentry-native: defer to runtime signal handler at start
02-11 07:58:07.846  5437  5437 F libc    : Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0 in tid 5437 (egrationtestapp), pid 5437 (egrationtestapp)
02-11 07:58:08.031  5475  5475 F DEBUG   : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
02-11 07:58:08.031  5475  5475 F DEBUG   : Build fingerprint: 'google/sdk_gphone64_x86_64/emu64xa:16/BE2A.250530.026.F3/13894323:userdebug/dev-keys'
02-11 07:58:08.031  5475  5475 F DEBUG   : Revision: '0'
02-11 07:58:08.031  5475  5475 F DEBUG   : ABI: 'x86_64'
02-11 07:58:08.031  5475  5475 F DEBUG   : Timestamp: 2026-02-11 07:58:07.902802417+0100
02-11 07:58:08.031  5475  5475 F DEBUG   : Process uptime: 2s
02-11 07:58:08.031  5475  5475 F DEBUG   : Cmdline: io.sentry.dotnet.maui.device.integrationtestapp
02-11 07:58:08.031  5475  5475 F DEBUG   : pid: 5437, tid: 5437, name: egrationtestapp  >>> io.sentry.dotnet.maui.device.integrationtestapp <<<
02-11 07:58:08.031  5475  5475 F DEBUG   : uid: 10246
02-11 07:58:08.031  5475  5475 F DEBUG   : signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0000000000000000
02-11 07:58:08.031  5475  5475 F DEBUG   : Cause: null pointer dereference
02-11 07:58:08.031  5475  5475 F DEBUG   :     rax 0000000000000000  rbx 000079c99f938298  rcx 000079ca67c9d010  rdx 0000000000000200
02-11 07:58:08.031  5475  5475 F DEBUG   :     r8  0000000000000002  r9  00007ffdbd520910  r10 0000000000000005  r11 000079c918eb6eb0
02-11 07:58:08.031  5475  5475 F DEBUG   :     r12 000079c9f8856a88  r13 000079ca67c9d020  r14 000079c909c8a5b0  r15 000079cba7cb20d0
02-11 07:58:08.031  5475  5475 F DEBUG   :     rdi 000079cba7cb20d0  rsi 0000000000000006
02-11 07:58:08.031  5475  5475 F DEBUG   :     rbp 000079c99f938298  rsp 00007ffdbd5208d8  rip 000079c909c8a5be
02-11 07:58:08.031  5475  5475 F DEBUG   : 2 total frames
02-11 07:58:08.031  5475  5475 F DEBUG   : backtrace:
02-11 07:58:08.031  5475  5475 F DEBUG   :       #00 pc 00000000000005be  /data/app/~~RnBcgBqVyUx2MEIc7xRDiA==/io.sentry.dotnet.maui.device.integrationtestapp-hriVX4xDjbd5AhYJnurtoA==/lib/x86_64/libsentrysupplemental.so (crash+14) (BuildId: 852925ef6da49aeb59a096644bd533ff2fce55dc)
02-11 07:58:08.031  5475  5475 F DEBUG   :       #01 pc 00000000000e47a8  <anonymous:405af000>
02-11 07:58:08.044  5437  5437 D sentry-native: return from runtime signal handler, we handle the signal
02-11 07:58:08.047   716   740 I ActivityManager: Showing crash dialog for package io.sentry.dotnet.maui.device.integrationtestapp u0
02-11 07:58:08.053  5437  5437 D sentry-native: captured backtrace from ucontext with 2 frames
02-11 07:58:08.053  5437  5437 D sentry-native: captured backtrace with 2 frames
02-11 07:58:08.053  5437  5437 D sentry-native: merging global scope into event
02-11 07:58:08.053  5437  5437 D sentry-native: trying to read modules from /proc/self/maps
02-11 07:58:08.077  5437  5437 D sentry-native: read 445 modules from /proc/self/maps
02-11 07:58:08.077  5437  5437 D sentry-native: sending envelope
02-11 07:58:08.078  5437  5437 I sentry-native: crash has been captured

jamescrosswell · 2026-02-12T22:08:27Z

I used the 10.0.3 baseline of dotnet/runtime, cherry-picked the fix, built (./build.sh mono -os android -arch x64 -c Release), and copied over /usr/share/dotnet/packs/Microsoft.NETCore.App.Runtime.Mono.android-x64/10.0.3/runtimes/android-x64/native/libmonosgen-2.0.so.

Nice! So once 10.0.30 is released we could put together a fix. Would our SDK users also need to be building with 10.0.3 or is it sufficient for us to be building the Sentry SDK for .NET with it?

jpnurmi · 2026-02-13T08:25:08Z

Applying the fix when building Sentry alone is not sufficient. The fix must be present in the .NET runtime / Mono DLL that is packaged inside the application APK.

Unfortunately, the fix was not included in version 10.0.3, which was released a few days ago. We'll have to wait for 10.0.4, the next monthly servicing update.

jamescrosswell · 2026-03-15T22:50:20Z

Looks like 10.0.4 is finally out and even 10.0.5, which we have a PR to bump to here:

build(deps): bump dotnet-sdk from 10.0.102 to 10.0.201 #5029

That PR needs some debugging - @jpnurmi would you have the bandwidth to look at it or should @Flash0ver or I pick it up?

jpnurmi · 2026-03-16T08:32:37Z

Another issue has come up. 😓 While testing against 10.0.4, I discovered that the refactored inproc backend introduced in sentry-native 0.13 broke the CHAIN_AT_START signal chaining strategy. A fix is in progress:

fix(android): mask signal during CHAIN_AT_START to survive chained Mono handler re-raises sentry-native#1572

To prevent similar regressions going forward, we're also adding a .NET Android integration test to the Native SDK:

test: add Android emulator test for dotnet signal handling sentry-native#1574

jamescrosswell · 2026-03-17T00:39:52Z

Another issue has come up. 😓 While testing against 10.0.4, I discovered that the refactored inproc backend introduced in sentry-native 0.13 broke the CHAIN_AT_START signal chaining strategy.

Hm... what's your gut tell you about the robustness of the solution we're putting in place here? Is it something that's likely to work for long periods without us needing to pay attention to it or is it possibly fragile and going to be a time sink?

I mean, pretty much everything about MAUI seems fragile to some extent... is this going to be worse though?

jpnurmi · 2026-03-18T13:12:31Z

As AI would put it, "You're absolutely right to question that!"

Chaining signal handlers as we do with the "chain-at-start" strategy is not an officially supported use case and could potentially break in any future version of .NET or Android.

Furthermore, there's an endless combination of versions and targets/devices/emulators/architectures to cover, and we have quite big gaps in testing as we currently can't even test on ARM64 (#4660). If we still want to release this, it's best to start with an opt-in to gather feedback.

jamescrosswell · 2026-03-18T21:39:38Z

As AI would put it, "You're absolutely right to question that!"

🤣

If we still want to release this, it's best to start with an opt-in to gather feedback.

That sounds like a good approach... maybe we leave it opt in for a decent amount of time to see if it can survive major version bumps in the various different moving parts.

jpnurmi · 2026-03-26T12:17:08Z

~~Temporarily rebased on top of #5069.~~ Android jobs are green. Finally! 🎉

#5069 needs to be merged, and then this will be ready to go. Do the changes look otherwise good, btw?

jamescrosswell

Thanks @jpnurmi - the other dependencies are now merged so I think this is almost ready.

The changes themselves look fine functionally (pretty trivial - just wrapping an android SDK option). I made a few suggestions that might hopefully head off confusion for our SDK users though.

src/Sentry/Platforms/Android/NativeOptions.cs

…T runtimes Add a runtime version check that falls back to Default on .NET 10.0.0–10.0.3, which crash with ChainAtStart due to dotnet/runtime#123346. Also fix swapped runtime/SDK version numbers in XML docs. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…falling back Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Sentry/Platforms/Android/SentrySdk.cs

…tead of falling back" This reverts commit 9698020. Use warning + fallback to Default instead of throwing during initialization. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

jamescrosswell

LGTM assuming the iOS failure is just flaky tests.

Massive thank you for this @jpnurmi ❤️

This was referenced Oct 27, 2025

fix: AOT interop with managed .NET runtimes getsentry/sentry-native#1392

Merged

Prevent Native/Cocoa SDKs from capturing errors that also get captured by .NET #3954

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jpnurmi mentioned this pull request Nov 4, 2025

chore(deps): update Native SDK to v0.12.1 getsentry/sentry-java#4859

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Base automatically changed from version6 to main November 14, 2025 02:30

jpnurmi force-pushed the feat/android-signal-handler-strategy branch from af57caa to 4486918 Compare November 20, 2025 10:31

jpnurmi force-pushed the feat/android-signal-handler-strategy branch 2 times, most recently from 7a489eb to 543b3e3 Compare January 2, 2026 14:57

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jpnurmi force-pushed the feat/android-signal-handler-strategy branch from b64b284 to bda8f1b Compare February 11, 2026 06:00

jpnurmi force-pushed the feat/android-signal-handler-strategy branch 2 times, most recently from 862423a to 47248ba Compare March 11, 2026 10:09

jpnurmi mentioned this pull request Mar 11, 2026

fix(android): mask signal during CHAIN_AT_START to survive chained Mono handler re-raises getsentry/sentry-native#1572

Merged

jpnurmi force-pushed the feat/android-signal-handler-strategy branch from 47248ba to 448380a Compare March 26, 2026 11:19

feat: allow configuring native signal handler strategy on Android

13e3e29

jpnurmi force-pushed the feat/android-signal-handler-strategy branch from 448380a to 13e3e29 Compare March 27, 2026 06:37

jpnurmi removed the Blocked label Mar 27, 2026

Remove changelog entry

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jpnurmi marked this pull request as ready for review March 27, 2026 07:17

jpnurmi requested review from Flash0ver and jamescrosswell as code owners March 27, 2026 07:17

jamescrosswell reviewed Mar 30, 2026

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jpnurmi force-pushed the feat/android-signal-handler-strategy branch from 97c35d2 to 2a04f8f Compare March 30, 2026 20:01

jpnurmi and others added 4 commits March 30, 2026 22:30

docs: clarify SignalHandlerStrategy enum values

01849fc

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: throw on ChainAtStart with incompatible .NET runtime instead of …

9698020

…falling back Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs: clarify ChainAtStart requires Android 8.0 (API 26)

b2f595d

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

refactor: move SignalHandlerStrategy to NativeExperimentalOptions

08f3294

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

jamescrosswell reviewed Mar 30, 2026

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jpnurmi and others added 2 commits March 31, 2026 07:07

Revert "fix: throw on ChainAtStart with incompatible .NET runtime ins…

dcb7fc0

…tead of falling back" This reverts commit 9698020. Use warning + fallback to Default instead of throwing during initialization. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs: fix .NET SDK version numbers in SignalHandlerStrategy docs

02f59c1

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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