New function pointer APIs by jgh07 · Pull Request #123819 · dotnet/runtime

jgh07 · 2026-01-30T22:34:50Z

This implements #75348.

The APIs from the proposal are all implemented now, but there are still some rough edges and design considerations needing to be discussed.

…, ILGeneratorImpl.EmitCalli(Type)

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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.

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

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;

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

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

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

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

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

src/coreclr/System.Private.CoreLib/src/System/RuntimeHandles.cs

src/coreclr/vm/runtimehandles.cpp

Copilot

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 7 comments.

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

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

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

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

src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs

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

…ointerSignatureType

Copilot

Pull request overview

Copilot reviewed 24 out of 24 changed files in this pull request and generated 3 comments.

src/libraries/System.Reflection.Emit.ILGeneration/tests/ILGenerator/Emit4Tests.cs

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

src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Reflection/SignatureTypes.cs

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

jgh07 · 2026-02-02T19:09:28Z

Since all methods from the API proposal are implemented now, I am removing the "Draft" marking.

About the suggestion of changing MakeFunctionPointerSignatureType to take a non-nullable Type for the return type, is that an acceptable deviation from the approved API shape or does it need to go through the review board again?

Copilot

Pull request overview

Copilot reviewed 25 out of 25 changed files in this pull request and generated 1 comment.

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

jkotas · 2026-02-02T19:25:44Z

About the suggestion of changing MakeFunctionPointerSignatureType to take a non-nullable Type for the return type, is that an acceptable deviation from the approved API shape

I think it is acceptable deviation.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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jkotas · 2026-02-02T20:06:55Z

src/libraries/System.Reflection.Emit.ILGeneration/tests/ILGenerator/Emit4Tests.cs

+                returnType,
+                parameterTypes: [typeof(string)],
+                isUnmanaged: true,
+                callingConventions: [typeof(CallConvCdecl)]));


CallConvCdecl and CallConvStdcall are encoded in same way. It would be more interesting to test one of the calling conventions with more complicated encoding, ,like CallConvCdecl + CallConvMemberFunction

Updating the test immediately caused it to fail – good catch.

I pushed a commit that provides the underlying infrastructure to deal with modopt-encoded calling conventions. For now the test still fails (for a different reason), I will investigate further tomorrow.

This should work now as of 5208c79.

I had to dig pretty deep to fix it, further complicated by the fact that unlike ELEMENT_TYPE_INTENRAL, ELEMENT_TYPE_CMOD_INTERNAL is not documented anywhere and is not even part of the CorElementType enum. I assume it is just a private CoreCLR implementation detail.

…ssue-75348

Copilot

Pull request overview

Copilot reviewed 25 out of 25 changed files in this pull request and generated 7 comments.

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

Copilot · 2026-02-06T19:58:22Z

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

+        public override Type UnderlyingSystemType => _unmodifiedType;
+        public override Type[] GetRequiredCustomModifiers() => (Type[])_requiredCustomModifiers.Clone();
+        public override Type[] GetOptionalCustomModifiers() => (Type[])_optionalCustomModifiers.Clone();
+
+        public override bool IsTypeDefinition => _unmodifiedType.IsTypeDefinition;


SignatureModifiedType overrides UnderlyingSystemType to the unmodified type, but it doesn't override Equals/GetHashCode. Since Type.Equals(Type) and Type.GetHashCode() are based on UnderlyingSystemType, this makes a SignatureModifiedType compare equal (and hash equal) to the unmodified type, which is very surprising for signature types. Consider overriding Equals/GetHashCode to preserve reference-based identity (like other SignatureType implementations), even if UnderlyingSystemType must point at the unmodified type for encoding.

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

Copilot · 2026-02-06T19:58:23Z

...raries/System.Reflection.Emit/tests/PersistedAssemblyBuilder/AssemblySaveILGeneratorTests.cs

+            il.Emit(OpCodes.Call, typeof(ClassWithFunctionPointer).GetMethod("Init"));
+            il.Emit(OpCodes.Ldc_I4_2);
+            il.Emit(OpCodes.Ldc_I4_3);
+            il.Emit(OpCodes.Ldsfld, typeof(ClassWithFunctionPointer).GetField("Method"));
+            il.EmitCalli(Type.MakeFunctionPointerSignatureType(typeof(int), [typeof(int), typeof(int)]));


These reflection lookups can return null (e.g., if names change), which would make the test fail with a NullReferenceException instead of a clear assertion failure. Consider using null-forgiving operators or Assert/ThrowHelper checks to ensure GetMethod/GetField results are non-null before emitting IL.

src/libraries/System.Runtime/ref/System.Runtime.cs

src/libraries/System.Reflection.Emit.ILGeneration/ref/System.Reflection.Emit.ILGeneration.cs

Copilot

Pull request overview

Copilot reviewed 25 out of 25 changed files in this pull request and generated 1 comment.

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

jkotas · 2026-02-06T22:32:22Z

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


            // Push the return value if there is one.
-            if (methodInfo.ReturnType != voidType)
+            if (methodInfo.ReturnType.UnderlyingSystemType != voidType)


Should we have a test for the case that this is fixing?

jkotas · 2026-02-06T22:55:38Z

src/libraries/System.Reflection.Emit.ILGeneration/ref/System.Reflection.Emit.ILGeneration.cs

        public abstract void EmitCall(System.Reflection.Emit.OpCode opcode, System.Reflection.MethodInfo methodInfo, System.Type[]? optionalParameterTypes);
        public abstract void EmitCalli(System.Reflection.Emit.OpCode opcode, System.Reflection.CallingConventions callingConvention, System.Type? returnType, System.Type[]? parameterTypes, System.Type[]? optionalParameterTypes);
        public abstract void EmitCalli(System.Reflection.Emit.OpCode opcode, System.Runtime.InteropServices.CallingConvention unmanagedCallConv, System.Type? returnType, System.Type[]? parameterTypes);
+        public virtual void EmitCalli(System.Type functionPointerType) { throw null; }


Suggested change

public virtual void EmitCalli(System.Type functionPointerType) { throw null; }

public virtual void EmitCalli(System.Type functionPointerType) { }

Nit - consistent formatting with the next line and with what the autogenerator for ref files generates.

jkotas · 2026-02-07T04:23:48Z

src/libraries/System.Reflection.Emit.ILGeneration/tests/ILGenerator/Emit4Tests.cs

+            il.Emit(OpCodes.Ret);
+
+            StringReverseCdecl del = new(StringReverse);
+            IntPtr funcPtr = Marshal.GetFunctionPointerForDelegate(del);


The calling convention of the function that this is going to call needs to match the calling convention of the calli. Delegate marshalling does not support more complicated signatures like that. This needs to use a method annotated with UnmanagedCallersOnly and the matching calling convention as the target.

Also, this should exercise a signature where typeof(CallConvCdecl), typeof(CallConvMemberFunction)]) makes a difference from the default calling conventions on some platforms at least. For example, something like this:

struct TwoLongs { long a, b; } [UnmanagedCallersOnly(CallConvs = new [] {typeof(CallConvCdecl), typeof(CallConvMemberFunction)})] TwoLongs MethodWithReturnBuffer(IntPtr pThis) => *(TwoLongs*)pThis;

jkotas · 2026-02-07T04:30:50Z

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

+                        throw new ArgumentException(SR.Argument_ArraysInvalid, nameof(requiredCustomModifiers));
+
+                    if (t.ContainsGenericParameters)
+                        throw new ArgumentException(SR.Argument_GenericsInvalid, nameof(requiredCustomModifiers));


Should this check for function pointers too?

jgh07 added 2 commits January 30, 2026 21:21

Implement MakeFunctionPointerSignatureType, MakeModifiedSignatureType…

12c00b0

…, ILGeneratorImpl.EmitCalli(Type)

Override UnderlyingSystemType in SignatureModifiedType

d100b0f

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Remove unused using

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[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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Implement RuntimeType.MakeFunctionPointerType

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This was referenced Feb 1, 2026

iOS.Device test WorkItemExecutions #122874

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XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796

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Clone arrays; Remove unbounded stackalloc

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Add more checks, defensive clones

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Implement DynamicILGenerator.EmitCalli; Fix issues with MakeFunctionP…

646c698

…ointerSignatureType

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Clone before null checks

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Add test cases for MakeFunctionPointerType

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src/libraries/System.Private.CoreLib/src/System/Reflection/SignatureFunctionPointerType.cs Outdated Show resolved Hide resolved

Implement ContainsGenericParameters property

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Copilot AI review requested due to automatic review settings February 2, 2026 19:32

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Merge branch 'main' into issue-75348

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jgh07 added 4 commits February 3, 2026 18:01

Make return type non-nullable in MakeFunctionPointerSignatureType

235a1eb

Merge branch 'issue-75348' of https://github.com/jgh07/runtime into i…

3e69ba5

…ssue-75348

Correctly handle modopt-encoded calling conventions on DynamicMethod

992f8ef

Encode custom modifiers on return type correctly for DynamicMethod

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Address review comments

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Throw if calling conventions are supplied for managed function pointers

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src/libraries/System.Reflection.Emit/src/System/Reflection/Emit/ILGeneratorImpl.cs Show resolved Hide resolved

Compute stack change based on unmodified return type

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	public virtual void EmitCalli(System.Type functionPointerType) { throw null; }
	public virtual void EmitCalli(System.Type functionPointerType) { }

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jgh07 commented Jan 30, 2026 •

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