Support for exempting native libraries from JNI preload by grendello · Pull Request #10787 · dotnet/android

grendello · 2026-02-09T16:36:24Z

Fixes: #10617
Context: cba39dc

cba39dc introduced support for preloading of JNI native libraries at
application startup. However, it appears that in some scenarios this
behavior isn't desired.

This PR introduces a mechanism which allows exempting some or all (with
exception of the BCL libraries) libraries from the preload mechanism.

In order to not preload any JNI libraries it's now possible to set the
$(AndroidIgnoreAllJniPreload) MSBuild property to true.

It is also possible to exempt individual libraries from preload by
adding their name to the AndroidNativeLibraryNoJniPreload MSBuild
item group, for instance:

<ItemGroup>
  <AndroidNativeLibraryNoJniPreload Include="libMyLibrary.so" />
</ItemGroup>

jonathanpeppers · 2026-02-09T22:45:30Z

  <_AndroidStripNativeLibraries Condition=" '$(AndroidStripNativeLibraries)' != '' And '$(AndroidStripNativeLibraries)' == 'true' ">true</_AndroidStripNativeLibraries>
  <_AndroidStripNativeLibraries Condition=" '$(_AndroidStripNativeLibraries)' != 'true' ">false</_AndroidStripNativeLibraries>
+
+  <AndroidIgnoreAllJniPreload Condition=" '$(AndroidIgnoreAllJniPreload)' == '' ">false</AndroidIgnoreAllJniPreload>


How common do you think people would have to do this? Should it be a public, documented property?

Or is it an edge-case, and $(_AndroidIgnoreAllJniPreload) would be fine?

I don't know, to be honest. The original scenario it addresses appears to be quite unusual, but with the dependency hell that the AndroidX ecosystem is, who knows? I would make it a documented and supported property, just to be safe and not let people without easy choice.

Copilot

Pull request overview

Adds an opt-out mechanism for JNI native library preloading, including per-library exemptions and a global “ignore all” switch, with supporting build/test infrastructure and documentation updates.

Changes:

Introduces $(AndroidIgnoreAllJniPreload) and @(AndroidNativeLibraryNoJniPreload) integration into native application config generation.
Adds a small “test JNI library” build path to enable preload-related tests.
Expands test utilities and adds new tests validating JNI preload inclusion/exclusion behavior.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/native/native.targets	Adds targets to configure/build a test JNI library as part of runtime build.
src/native/common/test-jni-library/stub.cc	Adds minimal `JNI_OnLoad` stub for preload tests.
src/native/common/test-jni-library/CMakeLists.txt	Builds the test JNI shared library and outputs to test directory.
src/native/CMakePresets.json.in	Adds `XA_TEST_OUTPUT_DIR` to presets cache variables.
src/native/CMakeLists.txt	Wires `BUILD_TEST_JNI_LIBRARY` flow and requires `XA_TEST_OUTPUT_DIR`.
src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets	Defines new property and item groups; passes new item lists into generator task.
src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs	Adds helper to normalize native library names.
src/Xamarin.Android.Build.Tasks/Utilities/ApplicationConfigNativeAssemblyGeneratorCLR.cs	Implements ignore/always-preload resolution for JNI preload list generation (CoreCLR path).
src/Xamarin.Android.Build.Tasks/Utilities/ApplicationConfigNativeAssemblyGenerator.cs	Applies same JNI preload ignore logic (MonoVM path).
src/Xamarin.Android.Build.Tasks/Tasks/GenerateNativeApplicationConfigSources.cs	Adds task parameters for preload ignore/always-preload lists.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Android/AndroidItem.cs	Adds test project item wrapper for `AndroidNativeLibraryNoJniPreload`.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Android/AndroidBuildActions.cs	Adds build action constant for `AndroidNativeLibraryNoJniPreload`.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/EnvironmentHelper.cs	Extends parsing helpers to read JNI preload index data from generated native sources.
src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest3.cs	Adds tests validating JNI preload inclusion/exemption and deduplication.
build-tools/xaprepare/xaprepare/xaprepare.targets	Adds placeholder replacement for `TestOutputDirectory`.
build-tools/xaprepare/xaprepare/Steps/Step_GenerateFiles.cs	Plumbs `XA_TEST_OUTPUT_DIR` into generated CMake presets.
build-tools/xaprepare/xaprepare/Application/Properties.Defaults.cs.in	Adds default for `TestOutputDirectory`.
build-tools/xaprepare/xaprepare/Application/KnownProperties.cs	Adds `TestOutputDirectory` known property.
Documentation/docs-mobile/building-apps/build-properties.md	Documents `AndroidIgnoreAllJniPreload`.
Documentation/docs-mobile/building-apps/build-items.md	Documents `AndroidNativeLibraryNoJniPreload`.

Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>

MonoVM tests are weirdly broken (appconfig reads incorrectly, need to investigate)

jonathanpeppers

I think it's OK we can get this into main and see how it goes in .NET 11 previews.

Fixes: #10617 Context: cba39dc cba39dc introduced support for preloading of JNI native libraries at application startup. However, it appears that in some scenarios this behavior isn't desired. This PR introduces a mechanism which allows exempting some or all (with exception of the BCL libraries) libraries from the preload mechanism. In order to not preload any JNI libraries it's now possible to set the `$(AndroidIgnoreAllJniPreload)` MSBuild property to `true`. It is also possible to exempt individual libraries from preload by adding their name to the `AndroidNativeLibraryNoJniPreload` MSBuild item group, for instance: <ItemGroup> <AndroidNativeLibraryNoJniPreload Include="libMyLibrary.so" /> </ItemGroup>

…eload (#10879) Backport of: #10787 Fixes: #10617 Context: cba39dc cba39dc introduced support for preloading of JNI native libraries at application startup. However, it appears that in some scenarios this behavior isn't desired. This PR introduces a mechanism which allows exempting some or all (with exception of the BCL libraries) libraries from the preload mechanism. In order to not preload any JNI libraries it's now possible to set the `$(AndroidIgnoreAllJniPreload)` MSBuild property to `true`. It is also possible to exempt individual libraries from preload by adding their name to the `AndroidNativeLibraryNoJniPreload` MSBuild item group, for instance: <ItemGroup> <AndroidNativeLibraryNoJniPreload Include="libMyLibrary.so" /> </ItemGroup> Co-authored-by: Marek Habersack <grendel@twistedcode.net>

jonathanpeppers reviewed Feb 9, 2026

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grendello force-pushed the dev/grendel/jni-preload-exemption branch 4 times, most recently from d399967 to afa6525 Compare February 13, 2026 13:00

grendello force-pushed the dev/grendel/jni-preload-exemption branch 3 times, most recently from 6df6659 to 2d3b823 Compare February 18, 2026 15:52

grendello marked this pull request as ready for review February 18, 2026 15:52

grendello requested a review from simonrozsival as a code owner February 18, 2026 15:52

Copilot AI review requested due to automatic review settings February 18, 2026 15:52

Copilot AI reviewed Feb 18, 2026

View reviewed changes

grendello and others added 18 commits February 19, 2026 09:26

Basics

ac37252

Slightly broken, tbc tomorrow

fcd4b69

Update src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

4498b97

Co-authored-by: Jonathan Peppers <jonathan.peppers@microsoft.com>

Default config works (CLR only for now)

964df0f

Beginnings of unit tests

713e29a

Environment test helper progress

d4adec8

[clr] first basic test works

531e623

A tiny refactoring in prep for more tests

8eedb61

Fix after rebase

1366a74

New test + small refactoring

f9cd9b9

Update defaults checks

661de64

Add a native library for JNI preload tests, tbc

ecc47eb

Output the test JNI library to bin/Test${CONFIGURATION}/${RID}

7d7b9c2

New test (WIP) + small refactoring

2ced8cc

More tests + some cleanup

afca8d7

New tests + fix test .so path on CI

1d0941f

Yeah, that...

e82c7c7

Refactoring + MonoVM tests

48c1582

MonoVM tests are weirdly broken (appconfig reads incorrectly, need to investigate)

grendello added 5 commits February 19, 2026 09:26

Fix reading of the MonoVM application config

d40e938

MonoVM dso cache reader implemented

6429ca8

Mono tests work now

e0f3a6a

Docs

551c6ef

Address feedback

b597b5f

grendello force-pushed the dev/grendel/jni-preload-exemption branch from 2d3b823 to b597b5f Compare February 19, 2026 08:42

jonathanpeppers approved these changes Feb 23, 2026

View reviewed changes

grendello merged commit adaf1d2 into main Feb 24, 2026
6 checks passed

grendello deleted the dev/grendel/jni-preload-exemption branch February 24, 2026 09:06

This was referenced Feb 27, 2026

java.lang.ExceptionInInitializerError on dotnet 10 #10848

Open

MAUI10 Thin binding around Mapbox crash at runtime #10878

Open

This was referenced Mar 3, 2026

[release/10.0.1xx] Support for exempting native libraries from JNI preload #10879

Merged

.NET 10 Android: DexGuard-protected AAR fails to load encrypted classes (regression from .NET 9) #10615

Open

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Support for exempting native libraries from JNI preload#10787

Support for exempting native libraries from JNI preload#10787
grendello merged 23 commits intomainfrom
dev/grendel/jni-preload-exemption

grendello commented Feb 9, 2026 •

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Pull request overview

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grendello commented Feb 9, 2026 •

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