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[mono] ILStrip sorts custom attribute table #87923

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merged 4 commits into from
Jun 22, 2023
Merged

[mono] ILStrip sorts custom attribute table #87923

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7ed35f3
ILStrip now sorts custom attribute table to prevent assembly corruption.
jandupej Jun 22, 2023
ff8f623
Whitespace.
jandupej Jun 22, 2023
13c5c97
More whitespace.
jandupej Jun 22, 2023
3a0e328
Commented the final sorting.
jandupej Jun 22, 2023
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26 changes: 25 additions & 1 deletion src/tasks/MonoTargetsTasks/ILStrip/AssemblyStripper/AssemblyStripper.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,16 @@

namespace AssemblyStripper
{
class CustomAttrRowComparer : IComparer
{
public int Compare(object left, object right)
{
CustomAttributeRow row_left = (CustomAttributeRow)left;
CustomAttributeRow row_right = (CustomAttributeRow)right;
return row_left.Parent.RID.CompareTo(row_right.Parent.RID);
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@lambdageek lambdageek Jul 5, 2023 •
edited by akoeplinger
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This is subtly wrong. the problem is that RID on a cecil metadata token masks out the token type.

We actually have to reconstruct the custom attribute coded-index.
something like:

   var leftParentCodedIdx = Utilities.CompressMetadataToken(CodedIndex.HasCustomAttribute, row_left.Parent);
   var rightParentCodedIdx = Utilities.CompressMetadataToken(CodedIndex.HasCustomAttribute, row_right.Parent);
   return leftParentCodedIdx.CompareTo(rightParentCodedIdx);

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This fixed the issue I was running into on #88167

}
}

public class AssemblyStripper
{
AssemblyDefinition assembly;
Expand Down Expand Up @@ -40,6 +50,7 @@ void Strip()
PatchMethods();
PatchFields();
PatchResources();
SortCustomAttributes();
Write();
}

Expand Down Expand Up @@ -192,6 +203,20 @@ void PatchResources()
}
}

// Types that are trimmed away also have their respective rows removed from the
// custom attribute table. This introduces holes in their places, causing the table
// to no longer be sorted by Parent, corrupting the assembly. Runtimes assume ordering
// and may fail to locate the attributes set for a particular type. This step sorts
// the custom attribute table again.
void SortCustomAttributes()
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can you please add a comment about why we need to sort the custom attributes here?

{
CustomAttributeTable table = (CustomAttributeTable)stripped_tables[CustomAttributeTable.RId];
if (table == null)
return;

table.Rows.Sort(new CustomAttrRowComparer());
}

void Write()
{
stripped.MetadataRoot.Accept(metadata_writer);
Expand All @@ -209,7 +234,6 @@ public static void StripAssembly(string assemblyFile, string outputPath)
{
AssemblyDefinition assembly = AssemblyFactory.GetAssembly(assemblyFile);
AssemblyStripper.StripAssembly(assembly, outputPath);

}
}
}