Class `Vector3` field assignation overwrites the next field's contents when using LLVM AOT

[rolfbjarne]

From @jeromelaban on Wed, 18 Dec 2024 15:09:40 GMT

Apple platform

iOS, macOS, Mac Catalyst, tvOS

Framework version

net9.0-*

Affected platform version

9.0.101

Description

When a class contains two consecutive Vector3 fields, setting the value for the first will modify the first inner field (X) of the second field.

Steps to Reproduce

Add the following code to an app, then run, the error message should not happen:

public partial class MyTestClass
{
    private Vector3 _offset;
    private Vector3 _scale = new Vector3(1, 1, 1);

    internal static void RunTest()
    {
		var v1 = new MyTestClass();
		System.Console.WriteLine($"Scale: {v1.Scale} Offset: {v1.Offset} Scale: {v1.Scale}");

		var v2 = new MyTestClass() { Offset = new(1.1f, 1.1f, 5.0f) };
		System.Console.WriteLine($"Scale: {v2.Scale} Offset: {v2.Offset} Scale: {v2.Scale}");

		if(v2.Scale != new Vector3(1, 1, 1))
                {
			System.Console.WriteLine("Error: Scale is not 1, 1, 1");
                }
    }

    public Vector3 Offset
    {
        get => _offset;
        set
        {
            System.Console.WriteLine($"Before Offset: {Offset} Scale: {Scale}");

            _offset = value;

            System.Console.WriteLine($"After Offset: {Offset} Scale: {Scale}");
        }
    }

    public Vector3 Scale => _scale;
}

Repro project: 21825-iosllvmissue.zip

Did you find any workaround?

Adding a field of another type in between seems to works around the issue.

Relevant logs

No response

Copied from original issue dotnet/macios#21825

[rolfbjarne]

From @rolfbjarne on Wed, 18 Dec 2024 19:00:24 GMT

I can reproduce this in the iOS simulator, by building like this:

dotnet build /p:Configuration=Release -f net9.0-ios

Output:

Scale: <1, 1, 1> Offset: <0, 0, 0> Scale: <1, 1, 1>
Before Offset: <0, 0, 0> Scale: <1, 1, 1>
After Offset: <1.1, 1.1, 5> Scale: <0, 1, 1>
Scale: <0, 1, 1> Offset: <1.1, 1.1, 5> Scale: <0, 1, 1>
Error: Scale is not 1, 1, 1

Moving to dotnet/runtime, since this looks like a codegen issue.

[jeromelaban]

As an update, I also tried to use my own simple version of Vector3, the issue does not happen.

[dotnet-policy-service]

Tagging subscribers to this area: @steveisok, @vitek-karas
See info in area-owners.md if you want to be subscribed.

[vitek-karas]

@jkurdek Jeremi who did the Vector3 intrinsics work?

[jkurdek]

It might have been me, will look into that

[tannergooding]

There's probably a mismatch between the handling for locals (where Vector3 is often given 16 bytes of storage for efficiency) as compared to the handling for fields (where it should always strictly be 12 bytes of storage).
-- This is notably how RyuJIT handles it, but I vaguely recall Mono doing something similar

[BradChase2011]

Is there a current workaround besides moving fields? Is there a current expectation of when this will be fixed? In the next .net update? This has completely killed our ios/macos development.