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

jgh07 · 2026-01-30T22:34:50Z

This implements #75348.

MakeFunctionPointerType is only implemented for CoreCLR, a Mono implementation will follow.

…, ILGeneratorImpl.EmitCalli(Type)

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

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

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

jkotas · 2026-02-22T00:37:07Z

I think the calling conventions specified via the explicit arg should always win. I do not think we should be smart about merging. We can throw an exception for now and see whether it causes issues in practices. We can replace the exception with merging later if it proves to be necessary. So something like:

If there are modopt calling conventions on the return type, they have to match the (non-built in subset of) calling conventions passed via the explicit arg. If they do not match, throw an exception.
If there are no modopt calling conventions on the return type and there are calling conventions passed in via the explicit arg, wrap the return type to inject the calling conventions as needed.

…test issues

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

Copilot

Pull request overview

Copilot reviewed 35 out of 35 changed files in this pull request and generated 3 comments.

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

src/libraries/System.Reflection.Emit/tests/Utilities.cs

Copilot · 2026-02-22T14:14:37Z

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

+        internal int GetFunctionPointerSignatureToken(Type functionPointerType)
+        {
+            BlobBuilder blobBuilder = new();
+            SignatureTypeEncoder encoder = new(blobBuilder);
+            MetadataSignatureHelper.WriteSignatureForFunctionPointerType(encoder, functionPointerType, this);
+
+            byte[] blob = blobBuilder.ToArray()[1..]; // Strip away ELEMENT_TYPE_FNPTR
+            return MetadataTokens.GetToken(_metadataBuilder.AddStandaloneSignature(_metadataBuilder.GetOrAddBlob(blob)));
+        }


GetFunctionPointerSignatureToken currently materializes the full blob to an array and then slices it ([1..]) to remove the leading ELEMENT_TYPE_FNPTR byte, which results in extra allocations (ToArray plus the slice copy). Consider emitting the standalone method signature blob without the ELEMENT_TYPE_FNPTR prefix in the first place (e.g., using a MethodSignatureEncoder / BlobEncoder directly, or writing into a second BlobBuilder starting at offset 1) to avoid the extra allocations when emitting many calli signatures.

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

Copilot

Pull request overview

Copilot reviewed 35 out of 35 changed files in this pull request and generated no new comments.

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

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

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

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

Copilot

Pull request overview

Copilot reviewed 36 out of 36 changed files in this pull request and generated 3 comments.

Copilot · 2026-02-23T16:46:17Z

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

+            foreach (Type callConv in callingConventions)
+                ArgumentNullException.ThrowIfNull(callConv, nameof(callingConventions));
+


MakeFunctionPointerSignatureType currently only null-checks the callingConventions array elements, but doesn’t validate that they are actually calling-convention marker types (e.g., System.Runtime.CompilerServices.CallConv*). As-is, callers can pass arbitrary types (or signature types) and get a Type whose GetFunctionPointerCallingConventions() returns values that cannot be meaningfully encoded/round-tripped as calling conventions. Consider validating each entry (e.g., FullName starts with CallingConventionTypePrefix, not HasElementType, not ContainsGenericParameters, and not IsSignatureType) and throwing ArgumentException for invalid entries.

Suggested change

foreach (Type callConv in callingConventions)

ArgumentNullException.ThrowIfNull(callConv, nameof(callingConventions));

foreach (Type callConv in callingConventions)

{

ArgumentNullException.ThrowIfNull(callConv, nameof(callingConventions));

if (callConv.HasElementType ||

callConv.ContainsGenericParameters ||

callConv.IsSignatureType ||

callConv.FullName is not string fullName ||

!fullName.StartsWith(CallingConventionTypePrefix, StringComparison.Ordinal))

{

throw new ArgumentException(

"Each calling convention type must be a non-generic, non-signature, non-element type whose full name starts with System.Runtime.CompilerServices.CallConv.",

nameof(callingConventions));

}

}

@jkotas Should we add this check after all? Since the modopt validation logic also assumes that the callingConventions elements adhere to this.

I guess we can add it. It is easier to relax the validation after the fact if it proves to be problematic.

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

src/libraries/System.Reflection.Emit/tests/Utilities.cs

…ssue-75348

Copilot

Pull request overview

Copilot reviewed 36 out of 36 changed files in this pull request and generated 2 comments.

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

jkotas · 2026-02-24T20:18:33Z

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

+                    else if (callConvInModOpts)
+                    {
+                        if (callConvIndex != callingConventions.Length)
+                            throw new ArgumentException(SR.FunctionPointer_CallingConventionsUnbalanced, nameof(returnType));
+
+                        callConvsFinished = true;
+                    }


Suggested change

else if (callConvInModOpts)

{

if (callConvIndex != callingConventions.Length)

throw new ArgumentException(SR.FunctionPointer_CallingConventionsUnbalanced, nameof(returnType));

callConvsFinished = true;

}

I think it is ok to allow calling conventions to be interleaved with other modopts.

I think we can use callConvIndex != 0 instead of callConvInModOpts, and delete callConvInModOpts if you implement this suggestion.

jkotas · 2026-02-24T20:21:29Z

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

+                        if (callConvsFinished)
+                            throw new ArgumentException(SR.FunctionPointer_CallingConventionsUnbalanced, nameof(returnType));
+
+                        callConvInModOpts = true;
+
+                        if (builtInCallConv && IsBuiltInCallingConvention(typeName))
+                            throw new ArgumentException(SR.FunctionPointer_CallingConventionsUnbalanced, nameof(returnType));


Suggested change

if (callConvsFinished)

throw new ArgumentException(SR.FunctionPointer_CallingConventionsUnbalanced, nameof(returnType));

callConvInModOpts = true;

if (builtInCallConv && IsBuiltInCallingConvention(typeName))

throw new ArgumentException(SR.FunctionPointer_CallingConventionsUnbalanced, nameof(returnType));

if (builtInCallConv)

throw new ArgumentException(SR.FunctionPointer_CallingConventionsUnbalanced, nameof(returnType));

I do not think we need to re-check the typeName here. If we have a built-in callconv, we cannot have any callconvs in modopts.

jgh07 added 2 commits January 30, 2026 21:21

Implement MakeFunctionPointerSignatureType, MakeModifiedSignatureType…

12c00b0

…, ILGeneratorImpl.EmitCalli(Type)

Override UnderlyingSystemType in SignatureModifiedType

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

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

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Remove unused using

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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

Open

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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

Open

Clone arrays; Remove unbounded stackalloc

6334ac3

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Add more checks, defensive clones

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

Implement DynamicILGenerator.EmitCalli; Fix issues with MakeFunctionP…

646c698

…ointerSignatureType

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Clone before null checks

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jgh07 added 2 commits February 22, 2026 12:28

Validate that calling conventions and return type modopts match; Fix …

1975e84

…test issues

Fix bug introduced in dotnet#123925

20c325c

jgh07 mentioned this pull request Feb 22, 2026

[release/10.0] PersistedAssemblyBuilder: Fix encoding of custom modifiers. (#123925) #124537

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jgh07 mentioned this pull request Feb 22, 2026

Fix regression introduced in #123925 #124724

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Fix custom modifiers in WriteSignatureForFunctionPointerType

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Require callconvs in modopts to have same order as callingConventions

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Simplify validation logic

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Update changes from main

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Small enhancements

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jgh07 added 3 commits February 23, 2026 18:09

Remove unused using

aa53f93

Remove unused using

67293c1

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

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…ssue-75348

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build-analysis bot mentioned this pull request Feb 23, 2026

[wasm] OpenQA.Selenium.WebDriverTimeoutException: timeout: Timed out receiving message from renderer #117486

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		foreach (Type callConv in callingConventions)
		ArgumentNullException.ThrowIfNull(callConv, nameof(callingConventions));

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