New function pointer APIs #123819

jgh07 · 2026-01-30T22:34:50Z

This implements #75348. It is not yet ready to be merged, but I'd appreciate a preliminary review before I tackle the remaining issues.

Type.MakeFunctionPointerSignatureType and Type.MakeModifiedSignatureType are implemented.
Type.MakeFunctionPointerType is not implemented yet. I am still debating wheter to include it in this PR.
EmitCalli is currently only implemented on ILGeneratorImpl. DynamicILGenerator is a wholly different code base, therefore I cannot make use of the helpers I added in Support function pointer types in System.Reflection.Emit #119935. I might have to reimplement parts of the logic I did for that PR.

…, ILGeneratorImpl.EmitCalli(Type)

dotnet-policy-service · 2026-01-30T22:35:57Z

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jgh07 · 2026-01-30T22:36:15Z

src/libraries/System.Private.CoreLib/src/System/Reflection/Emit/ILGenerator.cs

        public abstract void EmitCalli(OpCode opcode, CallingConvention unmanagedCallConv, Type? returnType, Type[]? parameterTypes);

+        /// <summary>
+        /// Puts a <see cref="OpCodes.Calli"/> instruction onto the Microsoft intermediate language (MSIL) stream,


I kept this description largely the same as the existing overloads. I think it might make more sense to update it though, since as far as I'm concerned the term MSIL was dropped in favor of CIL.

jgh07 · 2026-01-30T22:38:02Z

src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureType.cs

        public sealed override int GetHashCode() => base.GetHashCode();
 #endif
-        public sealed override Type UnderlyingSystemType => this;  // Equals(Type) depends on this.
+        public override Type UnderlyingSystemType => this;  // Equals(Type) depends on this.


This feels very wrong, and I hope there is a better way.
The comment is there for a reason, and it does indeed break Equals(Type) for SignatureModifiedType, but I honestly couldn't think of a better way to make the original, non-signature type available.

I cannot think of anything better.

jgh07 · 2026-01-30T22:40:25Z

src/libraries/System.Reflection.Emit/src/System/Reflection/Emit/SignatureHelper.cs

-            WriteSignatureForType(retTypeEncoder.Type(), returnType, module);
+            Type returnTypeToWrite = returnType;
+            if (returnTypeToWrite.IsSignatureType)
+                returnTypeToWrite = returnTypeToWrite.UnderlyingSystemType;


Not a no-op because of my override hack in SignatureModifiedType. I'd love to remove this in favor of a better solution.

Copilot

Pull request overview

This PR implements new function pointer APIs as proposed in issue #75348, enabling better support for function pointer types in IL generation and reflection scenarios.

Changes:

Adds Type.MakeFunctionPointerSignatureType and Type.MakeModifiedSignatureType static factory methods for creating signature types
Implements ILGenerator.EmitCalli(Type functionPointerType) overload in ILGeneratorImpl for modern function pointer calling conventions
Adds new internal SignatureFunctionPointerType and SignatureModifiedType classes to represent these signature types

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
System.Runtime.cs	Adds public API surface for new function pointer and modified signature type factory methods
Type.cs	Implements MakeFunctionPointerSignatureType and MakeModifiedSignatureType factory methods with XML documentation
SignatureFunctionPointerType.cs	New internal class representing function pointer signature types with support for calling conventions
SignatureModifiedType.cs	New internal class representing types with required/optional custom modifiers
SignatureType.cs	Changes UnderlyingSystemType from sealed to virtual to allow SignatureModifiedType to override it
ILGenerator.cs	Adds new EmitCalli overload accepting function pointer Type with XML documentation
ILGeneratorImpl.cs	Implements the new EmitCalli overload with stack tracking and signature token generation
SignatureHelper.cs	Makes WriteSignatureForFunctionPointerType internal and adds logic to unwrap SignatureTypes
ModuleBuilderImpl.cs	Adds GetFunctionPointerSignatureToken method to generate standalone signatures for calli instructions
DynamicILGenerator.cs	Adds stub TODO implementation for EmitCalli - not yet functional
System.Reflection.Emit.ILGeneration.cs	Adds public API surface for new EmitCalli overload
Strings.resx	Adds error message for invalid function pointer type arguments
System.Private.CoreLib.Shared.projitems	Adds new SignatureFunctionPointerType and SignatureModifiedType to project, plus unrelated whitespace fix
SignatureTypes.cs	Adds tests for the new MakeFunctionPointerSignatureType and MakeModifiedSignatureType methods
AssemblySaveILGeneratorTests.cs	Adds end-to-end test for EmitCalli with function pointer types
Utilities.cs	Adds ClassWithFunctionPointer test helper class

Comments suppressed due to low confidence (1)

src/libraries/System.Reflection.Emit/src/System/Reflection/Emit/SignatureHelper.cs:6

This using directive appears to be unused. There are no references to System.IO types in this file. Consider removing it to keep the code clean.

using System.Reflection.Metadata;

Copilot · 2026-01-30T22:45:06Z

src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureFunctionPointerType.cs

+        public override Type[] GetFunctionPointerCallingConventions() => _callingConventions;
+        public override Type[] GetFunctionPointerParameterTypes() => _parameterTypes;


These methods return the internal arrays directly without cloning, which allows callers to mutate the internal state. This violates encapsulation and could lead to unexpected behavior. These methods should return clones of the arrays, similar to how SignatureConstructedGenericType.GenericTypeArguments clones the array before returning it.

Suggested change

public override Type[] GetFunctionPointerCallingConventions() => _callingConventions;

public override Type[] GetFunctionPointerParameterTypes() => _parameterTypes;

public override Type[] GetFunctionPointerCallingConventions() => (Type[])_callingConventions.Clone();

public override Type[] GetFunctionPointerParameterTypes() => (Type[])_parameterTypes.Clone();

Copilot · 2026-01-30T22:45:07Z

src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureModifiedType.cs

+        public override Type[] GetRequiredCustomModifiers() => _requiredCustomModifiers;
+        public override Type[] GetOptionalCustomModifiers() => _optionalCustomModifiers;


This method returns the internal arrays directly without cloning, which allows callers to mutate the internal state. This violates encapsulation and could lead to unexpected behavior. These methods should return clones of the arrays, similar to how SignatureConstructedGenericType.GenericTypeArguments clones the array before returning it.

Suggested change

public override Type[] GetRequiredCustomModifiers() => _requiredCustomModifiers;

public override Type[] GetOptionalCustomModifiers() => _optionalCustomModifiers;

public override Type[] GetRequiredCustomModifiers() => (Type[])_requiredCustomModifiers.Clone();

public override Type[] GetOptionalCustomModifiers() => (Type[])_optionalCustomModifiers.Clone();

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/DynamicILGenerator.cs

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

jkotas · 2026-01-31T04:47:43Z

src/libraries/System.Private.CoreLib/src/System/Type.cs

+        /// <returns>A <see cref="Type"/> object representing the constructed function pointer signature.</returns>
+        public static Type MakeFunctionPointerSignatureType(Type? returnType, Type[]? parameterTypes, bool isUnmanaged = false, Type[]? callingConventions = null)
+        {
+            returnType ??= typeof(void);


MakeFunctionPointerSignatureType is meant to work for System.Type from any reflection universe. I do not think we want to be substituting null with typeof(void). It would make it tied to runtime reflection universe.

We may want to make the returnType argument non-nullable to avoid this substitution.

I agree, I think that's sensible.

jgh07 added 2 commits January 30, 2026 21:21

Implement MakeFunctionPointerSignatureType, MakeModifiedSignatureType…

12c00b0

…, ILGeneratorImpl.EmitCalli(Type)

Override UnderlyingSystemType in SignatureModifiedType

d100b0f

Copilot AI review requested due to automatic review settings January 30, 2026 22:34

github-actions bot added the area-System.Reflection label Jan 30, 2026

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Copilot started reviewing on behalf of jgh07 January 30, 2026 22:35 View session

jgh07 commented Jan 30, 2026

View reviewed changes

Remove unused using

2fb7104

Copilot AI reviewed Jan 30, 2026

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Copilot AI mentioned this pull request Jan 31, 2026

[WIP] Implement remaining APIs for runtime issue 123819 jgh07/runtime#1

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jgh07 mentioned this pull request Jan 31, 2026

[API Proposal]: IL Emit support for FunctionPointer #75348

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		public override Type[] GetFunctionPointerCallingConventions() => _callingConventions;
		public override Type[] GetFunctionPointerParameterTypes() => _parameterTypes;

		public override Type[] GetRequiredCustomModifiers() => _requiredCustomModifiers;
		public override Type[] GetOptionalCustomModifiers() => _optionalCustomModifiers;

New function pointer APIs #123819

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