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[release/6.0] Add explicit null-check for tailcalls to VSD (#62769)
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* Add explicit null-check for tailcalls to VSD

There is already a comment that this is necessary, but it is only being
done for x86 tailcalls via jit helper. Do it for normal tailcalls to VSD
as well.

Fix #61486

* Revert cleanup to make potential backport easier

Co-authored-by: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
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github-actions[bot] and jakobbotsch authored Jan 7, 2022
1 parent a8b733b commit d575a6f
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Showing 3 changed files with 63 additions and 9 deletions.
18 changes: 9 additions & 9 deletions src/coreclr/jit/morph.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -7896,6 +7896,15 @@ GenTree* Compiler::fgMorphPotentialTailCall(GenTreeCall* call)
// Avoid potential extra work for the return (for example, vzeroupper)
call->gtType = TYP_VOID;

// The runtime requires that we perform a null check on the `this` argument before
// tail calling to a virtual dispatch stub. This requirement is a consequence of limitations
// in the runtime's ability to map an AV to a NullReferenceException if
// the AV occurs in a dispatch stub that has unmanaged caller.
if (call->IsVirtualStub())
{
call->gtFlags |= GTF_CALL_NULLCHECK;
}

// Do some target-specific transformations (before we process the args,
// etc.) for the JIT helper case.
if (tailCallViaJitHelper)
Expand Down Expand Up @@ -8622,15 +8631,6 @@ void Compiler::fgMorphTailCallViaJitHelper(GenTreeCall* call)
JITDUMP("fgMorphTailCallViaJitHelper (before):\n");
DISPTREE(call);

// The runtime requires that we perform a null check on the `this` argument before
// tail calling to a virtual dispatch stub. This requirement is a consequence of limitations
// in the runtime's ability to map an AV to a NullReferenceException if
// the AV occurs in a dispatch stub that has unmanaged caller.
if (call->IsVirtualStub())
{
call->gtFlags |= GTF_CALL_NULLCHECK;
}

// For the helper-assisted tail calls, we need to push all the arguments
// into a single list, and then add a few extra at the beginning or end.
//
Expand Down
45 changes: 45 additions & 0 deletions src/tests/JIT/Regression/JitBlue/Runtime_61486/Runtime_61486.cs
Original file line number Diff line number Diff line change
@@ -0,0 +1,45 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Reflection;
using System.Runtime.CompilerServices;

public class Runtime_61486
{
public static int Main()
{
var my = new My(new My(null));
var m = my.GetType().GetMethod("M");
try
{
m.Invoke(my, null);
return -1;
}
catch (TargetInvocationException ex) when (ex.InnerException is NullReferenceException)
{
return 100;
}
}

public interface IFace
{
void M();
}

public class My : IFace
{
private IFace _face;

public My(IFace face)
{
_face = face;
}

// We cannot handle a null ref inside a VSD if the caller is not
// managed frame. This test is verifying that JIT null checks ahead of
// time in this case.
[MethodImpl(MethodImplOptions.AggressiveOptimization)]
public void M() => _face.M();
}
}
Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<Optimize>True</Optimize>
</PropertyGroup>
<ItemGroup>
<Compile Include="$(MSBuildProjectName).cs" />
</ItemGroup>
</Project>

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