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Register JNI natives via blittable JniNativeMethod #1474

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5bf02a7
[Java.Interop] Register JNI natives via blittable JniNativeMethod
simonrozsival Jun 12, 2026
2a87d46
Preserve JNI exception propagation in blittable RegisterNatives
simonrozsival Jun 12, 2026
3882658
Use stackalloc for native registration buffers
Copilot Jun 17, 2026
464419a
Add RequiresDynamicCode to native registration methods
Copilot Jun 17, 2026
fd98743
Apply suggestions from code review
simonrozsival Jun 18, 2026
00cb033
Guard ZeroFreeCoTaskMemUTF8 against IntPtr.Zero in RegisterNatives fi…
Copilot Jun 18, 2026
e2aa95c
Inline Marshal.GetFunctionPointerForDelegate call, remove unnecessary…
Copilot Jun 18, 2026
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66 changes: 57 additions & 9 deletions src/Java.Interop/Java.Interop/JniEnvironment.Types.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

using System;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Collections.Generic;
using System.Runtime.ExceptionServices;
using System.Runtime.InteropServices;
Expand Down Expand Up @@ -251,12 +252,14 @@ static string JavaClassToJniType (string value)
return value.Replace ('.', '/');
}

[RequiresDynamicCode ("Native method registration via JniNativeMethodRegistration[] requires dynamic code generation. Use the blittable RegisterNatives(JniObjectReference, ReadOnlySpan<JniNativeMethod>) overload with statically-compiled function pointers for Native AOT compatibility.")]
public static void RegisterNatives (JniObjectReference type, JniNativeMethodRegistration [] methods)
{
RegisterNatives (type, methods, methods == null ? 0 : methods.Length);
}

public static void RegisterNatives (JniObjectReference type, JniNativeMethodRegistration [] methods, int numMethods)
[RequiresDynamicCode ("Native method registration via JniNativeMethodRegistration[] requires dynamic code generation. Use the blittable RegisterNatives(JniObjectReference, ReadOnlySpan<JniNativeMethod>) overload with statically-compiled function pointers for Native AOT compatibility.")]
public static unsafe void RegisterNatives (JniObjectReference type, JniNativeMethodRegistration [] methods, int numMethods)
{
if ((numMethods < 0) ||
(numMethods > (methods?.Length ?? 0))) {
Expand All @@ -275,11 +278,43 @@ public static void RegisterNatives (JniObjectReference type, JniNativeMethodRegi
}
#endif // DEBUG

int r = _RegisterNatives (type, methods ?? Array.Empty<JniNativeMethodRegistration>(), numMethods);
if (numMethods == 0 || methods == null) {
return;
}

if (r != 0) {
throw new InvalidOperationException (
string.Format ("Could not register native methods for class '{0}'; JNIEnv::RegisterNatives() returned {1}.", GetJniTypeNameFromClass (type), r));
// Marshal the non-blittable JniNativeMethodRegistration[] into blittable JniNativeMethod
// values and dispatch to the blittable overload, instead of invoking the JNI
// `RegisterNatives` function pointer with a non-blittable managed-array parameter.
// The runtime marshalling stub synthesized for such a `delegate* unmanaged<>` call is
// miscompiled by crossgen2 under composite ReadyToRun + PGO: the JniNativeMethod `name`
// pointers end up referencing the managed `string` objects instead of marshalled UTF-8
// data, which corrupts the registered method names. See https://github.com/dotnet/android/issues/11633.
const int MaxStackAllocatedNativeMethods = 32;
bool useStackAllocatedBuffers = numMethods <= MaxStackAllocatedNativeMethods;
Span<JniNativeMethod> natives = useStackAllocatedBuffers
? stackalloc JniNativeMethod [numMethods]
: new JniNativeMethod [numMethods];
Span<IntPtr> unmanagedStrings = useStackAllocatedBuffers
? stackalloc IntPtr [numMethods * 2]
: new IntPtr [numMethods * 2];
unmanagedStrings.Clear ();
try {
for (int i = 0; i < numMethods; ++i) {
var m = methods [i];
IntPtr name = Marshal.StringToCoTaskMemUTF8 (m.Name);
unmanagedStrings [i * 2] = name;
IntPtr sig = Marshal.StringToCoTaskMemUTF8 (m.Signature);
unmanagedStrings [i * 2 + 1] = sig;
natives [i] = new JniNativeMethod ((byte*) name, (byte*) sig, Marshal.GetFunctionPointerForDelegate (m.Marshaler));

@github-actions github-actions Bot Jun 22, 2026

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🤖 💡 Error handling — Marshal.GetFunctionPointerForDelegate (m.Marshaler) throws ArgumentNullException when Marshaler is null, whereas the old _RegisterNatives path marshalled a null Delegate field to a null function pointer without throwing. The #if DEBUG block just above guards against m.Marshaler == null, so null is part of this method's existing input contract — this is a behavioral change. Either reject it explicitly with an actionable message that names the offending entry/index, or pass IntPtr.Zero when m.Marshaler is null. As written, the framework exception's parameter name (d) gives the caller no clue which registration was malformed.

Rule: Include actionable details in exceptions

}
RegisterNatives (type, natives);
// Keep the Marshaler delegates alive at least until JNI has consumed the function pointers.
GC.KeepAlive (methods);
} finally {
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for (int i = 0; i < unmanagedStrings.Length; ++i) {
if (unmanagedStrings [i] != IntPtr.Zero)
Marshal.ZeroFreeCoTaskMemUTF8 (unmanagedStrings [i]);
}
}
}

Expand All @@ -290,7 +325,11 @@ public static void RegisterNatives (JniObjectReference type, JniNativeMethodRegi
/// </summary>
public static unsafe void RegisterNatives (JniObjectReference type, ReadOnlySpan<JniNativeMethod> methods)
{
if (!type.IsValid)
throw new ArgumentException ("Handle must be valid.", nameof (type));

IntPtr env = JniEnvironment.EnvironmentPointer;
int r;
fixed (JniNativeMethod* methodsPtr = methods) {
#if FEATURE_JNIENVIRONMENT_JI_FUNCTION_POINTERS
var registerNatives = (delegate* unmanaged<IntPtr, IntPtr, JniNativeMethod*, int, int>)
Expand All @@ -299,10 +338,19 @@ public static unsafe void RegisterNatives (JniObjectReference type, ReadOnlySpan
var registerNatives = (delegate* unmanaged<IntPtr, IntPtr, JniNativeMethod*, int, int>)
JniEnvironment.CurrentInfo.Invoker.env.RegisterNatives;
#endif
int r = registerNatives (env, type.Handle, methodsPtr, methods.Length);
if (r != 0) {
throw new InvalidOperationException ($"Could not register native methods for class '{GetJniTypeNameFromClass (type)}'; JNIEnv::RegisterNatives() returned {r}.");
}
r = registerNatives (env, type.Handle, methodsPtr, methods.Length);
}

// Surface (and clear) any pending Java exception raised by JNI::RegisterNatives()
// — e.g. NoSuchMethodError — before falling back to the return-code check, matching
// the behavior of the prior JniNativeMethodRegistration[] registration path. Leaving a pending
// exception in the JNIEnv would make subsequent JNI calls fail or abort.
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var thrown = JniEnvironment.GetExceptionForLastThrowable ();
if (thrown != null)
ExceptionDispatchInfo.Capture (thrown).Throw ();

if (r != 0) {
throw new InvalidOperationException ($"Could not register native methods for class '{GetJniTypeNameFromClass (type)}'; JNIEnv::RegisterNatives() returned {r}.");
}
}

Expand Down
1 change: 1 addition & 0 deletions src/Java.Interop/Java.Interop/JniType.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,7 @@ public bool IsInstanceOfType (JniObjectReference value)
JniNativeMethodRegistration[]? methods;
#pragma warning restore 0414

[RequiresDynamicCode ("Native method registration via JniNativeMethodRegistration[] requires dynamic code generation. Use the blittable RegisterNatives(JniObjectReference, ReadOnlySpan<JniNativeMethod>) overload with statically-compiled function pointers for Native AOT compatibility.")]
public void RegisterNativeMethods (params JniNativeMethodRegistration[] methods)
{
AssertValid ();
Expand Down
1 change: 1 addition & 0 deletions src/Java.Interop/Java.Interop/ManagedPeer.cs
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Expand Up @@ -23,6 +23,7 @@ namespace Java.Interop {

static readonly JniPeerMembers _members = new JniPeerMembers (JniTypeName, typeof (ManagedPeer));

[UnconditionalSuppressMessage ("AOT", "IL3050", Justification = "ManagedPeer is not compatible with Native AOT; it's only used by reflection-based JniRuntime.JniValueManager implementations.")]
static ManagedPeer ()
{
_members.JniPeerType.RegisterNativeMethods (
Expand Down
3 changes: 3 additions & 0 deletions tests/Java.Interop-Tests/Java.Interop/JniTypeTest.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
using System;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.InteropServices;

using Java.Interop;
Expand Down Expand Up @@ -42,6 +43,7 @@ public void Ctor_ThrowsIfTypeNotFound ()
}

[Test]
[UnconditionalSuppressMessage ("AOT", "IL3050", Justification = "Test exercises non-AOT-compatible JniType.RegisterNativeMethods API.")]
public unsafe void Dispose_Exceptions ()
{
var t = new JniType ("java/lang/Object");
Expand Down Expand Up @@ -175,6 +177,7 @@ public void RegisterWithRuntime ()
}

[Test]
[UnconditionalSuppressMessage ("AOT", "IL3050", Justification = "Test exercises non-AOT-compatible JniType.RegisterNativeMethods API.")]

@github-actions github-actions Bot Jun 22, 2026

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🤖 ⚠️ Testing — This PR fixes a method-name corruption bug in the JniNativeMethodRegistration[] registration path, but nothing exercises the reworked marshalling loop directly. RegisterNativeMethods () here calls the params overload with zero methods, so it returns at the new numMethods == 0 guard before any marshalling runs; and RegisterNativeMethods_JniNativeMethod tests the already-correct blittable ReadOnlySpan<JniNativeMethod> overload, not the array path. Please add a regression test that registers a method through JniType.RegisterNativeMethods (new JniNativeMethodRegistration ("add", "(II)I", ...)) and then invokes it from Java (mirroring RegisterNativeMethods_JniNativeMethod), so a future regression in the UTF-8 name marshalling is caught. Covering the > 32-method heap branch would be a bonus.

Rule: Bug fixes need regression tests

public void RegisterNativeMethods ()
{
using (var TestType_class = new JniType ("net/dot/jni/test/CallNonvirtualBase")) {
Expand Down