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Add explicit layout checks to Crossgen2 #27054

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Oct 31, 2019
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Add explicit layout checks to Crossgen2 #27054

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866b6eb
Add explicit layout checks to Crossgen2 (2nd attempt)
trylek Oct 28, 2019
a51c425
Address Michal's PR feedback
trylek Oct 31, 2019
ff58fb8
Add handling for function pointers per Michal's PR feedback
trylek Oct 31, 2019
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155 changes: 155 additions & 0 deletions src/tools/crossgen2/Common/TypeSystem/Common/ExplicitLayoutValidator.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,155 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using System.Diagnostics;

namespace Internal.TypeSystem
{
public struct ExplicitLayoutValidator
{
private enum FieldLayoutTag : byte
{
Empty,
NonORef,
ORef,
}

private readonly int _pointerSize;

private readonly FieldLayoutTag[] _fieldLayout;

private readonly MetadataType _typeBeingValidated;

private ExplicitLayoutValidator(MetadataType type, int typeSizeInBytes)
{
_typeBeingValidated = type;
_pointerSize = type.Context.Target.PointerSize;
_fieldLayout = new FieldLayoutTag[typeSizeInBytes];
}

public static void Validate(MetadataType type, ComputedInstanceFieldLayout layout)
{
ExplicitLayoutValidator validator = new ExplicitLayoutValidator(type, layout.ByteCountUnaligned.AsInt);
foreach (FieldAndOffset fieldAndOffset in layout.Offsets)
{
validator.AddToFieldLayout(fieldAndOffset.Offset.AsInt, fieldAndOffset.Field.FieldType);
}
}

private void AddToFieldLayout(int offset, TypeDesc fieldType)
{
if (fieldType.IsGCPointer)
{
if (offset % _pointerSize != 0)
{
// Misaligned ORef
ThrowFieldLayoutError(offset);
}
SetFieldLayout(offset, _pointerSize, FieldLayoutTag.ORef);
}
else if (fieldType.IsPointer || fieldType.IsFunctionPointer)
{
SetFieldLayout(offset, _pointerSize, FieldLayoutTag.NonORef);
}
else if (fieldType.IsValueType)
{
if (fieldType.IsByRefLike && offset % _pointerSize != 0)
{
// Misaligned ByRefLike
ThrowFieldLayoutError(offset);
}

MetadataType mdType = (MetadataType)fieldType;
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If the field is a ByRef-like struct, it also needs to be aligned at pointer boundary. This should throw:

[StructLayout(LayoutKind.Explicit)]
ref struct Program
{
    [FieldOffset(2)] Span<int> f;

    static unsafe void Main()
    {
    }
}

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Added alignment check for IsByRefLike within the IsValueType conditional block.

int fieldSize = mdType.InstanceByteCountUnaligned.AsInt;
if (!mdType.ContainsGCPointers)
{
// Plain value type, mark the entire range as NonORef
SetFieldLayout(offset, fieldSize, FieldLayoutTag.NonORef);
}
else
{
if (offset % _pointerSize != 0)
{
// Misaligned struct with GC pointers
ThrowFieldLayoutError(offset);
}

bool[] fieldORefMap = new bool[fieldSize];
MarkORefLocations(mdType, fieldORefMap, offset: 0);
for (int index = 0; index < fieldSize; index++)
{
SetFieldLayout(offset + index, fieldORefMap[index] ? FieldLayoutTag.ORef : FieldLayoutTag.NonORef);
}
}
}
else if (fieldType.IsByRef)
{
if (offset % _pointerSize != 0)
{
// Misaligned pointer field
ThrowFieldLayoutError(offset);
}
SetFieldLayout(offset, _pointerSize, FieldLayoutTag.NonORef);
}
else
{
Debug.Assert(false, fieldType.ToString());
}
}

private void MarkORefLocations(MetadataType type, bool[] orefMap, int offset)
{
// Recurse into struct fields
foreach (FieldDesc field in type.GetFields())
{
if (!field.IsStatic)
{
int fieldOffset = offset + field.Offset.AsInt;
if (field.FieldType.IsGCPointer)
{
for (int index = 0; index < _pointerSize; index++)
{
orefMap[fieldOffset + index] = true;
}
}
else if (field.FieldType.IsValueType)
{
MetadataType mdFieldType = (MetadataType)field.FieldType;
if (mdFieldType.ContainsGCPointers)
{
MarkORefLocations(mdFieldType, orefMap, fieldOffset);
}
}
}
}
}

private void SetFieldLayout(int offset, int count, FieldLayoutTag tag)
{
for (int index = 0; index < count; index++)
{
SetFieldLayout(offset + index, tag);
}
}

private void SetFieldLayout(int offset, FieldLayoutTag tag)
{
FieldLayoutTag existingTag = _fieldLayout[offset];
if (existingTag != tag)
{
if (existingTag != FieldLayoutTag.Empty)
{
ThrowFieldLayoutError(offset);
}
_fieldLayout[offset] = tag;
}
}

private void ThrowFieldLayoutError(int offset)
{
ThrowHelper.ThrowTypeLoadException(ExceptionStringID.ClassLoadExplicitLayout, _typeBeingValidated, offset.ToStringInvariant());
}
}
}
2 changes: 2 additions & 0 deletions src/tools/crossgen2/Common/TypeSystem/Common/MetadataFieldLayoutAlgorithm.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -367,6 +367,8 @@ protected static ComputedInstanceFieldLayout ComputeExplicitFieldLayout(Metadata
computedLayout.ByteCountAlignment = instanceByteSizeAndAlignment.Alignment;
computedLayout.Offsets = offsets;

ExplicitLayoutValidator.Validate(type, computedLayout);

return computedLayout;
}

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3 changes: 3 additions & 0 deletions src/tools/crossgen2/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj
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Expand Up @@ -114,6 +114,9 @@
<Compile Include="..\Common\TypeSystem\Common\CastingHelper.cs">
<Link>TypeSystem\Common\CastingHelper.cs</Link>
</Compile>
<Compile Include="..\Common\TypeSystem\Common\ExplicitLayoutValidator.cs">
<Link>TypeSystem\Common\ExplicitLayoutValidator.cs</Link>
</Compile>
<Compile Include="..\Common\TypeSystem\Common\FunctionPointerType.cs">
<Link>TypeSystem\Common\FunctionPointerType.cs</Link>
</Compile>
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