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Harden debug scope update logic
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Based on bug reports like jbevain#816 it seems there are still cases where the IL and scope offsets are out of sync in weird ways. This change modifies the logic to have no potential to cause the `IndexOutOfRangeException`. While I was not able to determine what combination could cause this, it's better this way.

The corner case comes when there's potential problem with the first/second instruction in the method body. The change in this case will potentially make the debug scopes slightly wrong by not pointing to the previous instruction (as there's none). Without having a real repro it's hard to tell what would be a better solution, this way it won't crash and the scopes still make sense.
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@vitek-karas
vitek-karas committed Jan 13, 2022
1 parent 5f69faa commit c4cac56
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Showing 2 changed files with 57 additions and 41 deletions.
13 changes: 9 additions & 4 deletions Mono.Cecil.Cil/MethodBody.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -384,11 +384,16 @@ InstructionOffset ResolveInstructionOffset(InstructionOffset inputOffset, ref In
// resolve by walking the instructions from start and don't cache the result.
int size = 0;
for (int i = 0; i < items.Length; i++) {
//// The array can be larger than the actual size, in which case its padded with nulls at the end
//// so when we reach null, treat it as an end of the IL.
if (items [i] == null)
return new InstructionOffset (i == 0 ? items [0] : items [i - 1]);

if (size == offset)
return new InstructionOffset (items [i]);

if (size > offset)
return new InstructionOffset (items [i - 1]);
return new InstructionOffset (i == 0 ? items [0] : items [i - 1]);

size += items [i].GetSize ();
}
Expand All @@ -407,15 +412,15 @@ InstructionOffset ResolveInstructionOffset(InstructionOffset inputOffset, ref In
// Allow for trailing null values in the case of
// instructions.Size < instructions.Capacity
if (item == null)
return new InstructionOffset (items [i - 1]);
return new InstructionOffset (i == 0 ? items [0] : items [i - 1]);

cache.Instruction = item;

if (cache.Offset == offset)
return new InstructionOffset (cache.Instruction);

if (cache.Offset > offset)
return new InstructionOffset (items [i - 1]);
if (cache.Offset > offset)
return new InstructionOffset (i == 0 ? items [0] : items [i - 1]);

size += item.GetSize ();
}
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85 changes: 48 additions & 37 deletions Test/Mono.Cecil.Tests/ILProcessorTests.cs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -152,16 +152,18 @@ public void Clear ()
AssertOpCodeSequence (new OpCode[] { }, method);
}

[TestCase (RoundtripType.None, false, false)]
[TestCase (RoundtripType.Pdb, false, false)]
[TestCase (RoundtripType.Pdb, true, false)]
[TestCase (RoundtripType.Pdb, true, true)]
[TestCase (RoundtripType.PortablePdb, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false)]
[TestCase (RoundtripType.PortablePdb, true, true)]
public void InsertAfterWithSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes)
[TestCase (RoundtripType.None, false, false, false)]
[TestCase (RoundtripType.Pdb, false, false, false)]
[TestCase (RoundtripType.Pdb, true, false, false)]
[TestCase (RoundtripType.Pdb, true, false, true)]
[TestCase (RoundtripType.Pdb, true, true, false)]
[TestCase (RoundtripType.PortablePdb, false, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, true)]
[TestCase (RoundtripType.PortablePdb, true, true, false)]
public void InsertAfterWithSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes, bool padIL)
{
var methodBody = CreateTestMethodWithLocalScopes ();
var methodBody = CreateTestMethodWithLocalScopes (padIL);
methodBody = RoundtripMethodBody (methodBody, roundtripType, forceUnresolved, reverseScopes);

var il = methodBody.GetILProcessor ();
Expand All @@ -176,16 +178,18 @@ public void InsertAfterWithSymbolRoundtrip (RoundtripType roundtripType, bool fo
methodBody.Method.Module.Dispose ();
}

[TestCase (RoundtripType.None, false, false)]
[TestCase (RoundtripType.Pdb, false, false)]
[TestCase (RoundtripType.Pdb, true, false)]
[TestCase (RoundtripType.Pdb, true, true)]
[TestCase (RoundtripType.PortablePdb, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false)]
[TestCase (RoundtripType.PortablePdb, true, true)]
public void RemoveWithSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes)
[TestCase (RoundtripType.None, false, false, false)]
[TestCase (RoundtripType.Pdb, false, false, false)]
[TestCase (RoundtripType.Pdb, true, false, false)]
[TestCase (RoundtripType.Pdb, true, false, true)]
[TestCase (RoundtripType.Pdb, true, true, false)]
[TestCase (RoundtripType.PortablePdb, false, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, true)]
[TestCase (RoundtripType.PortablePdb, true, true, false)]
public void RemoveWithSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes, bool padIL)
{
var methodBody = CreateTestMethodWithLocalScopes ();
var methodBody = CreateTestMethodWithLocalScopes (padIL);
methodBody = RoundtripMethodBody (methodBody, roundtripType, forceUnresolved, reverseScopes);

var il = methodBody.GetILProcessor ();
Expand All @@ -200,16 +204,18 @@ public void RemoveWithSymbolRoundtrip (RoundtripType roundtripType, bool forceUn
methodBody.Method.Module.Dispose ();
}

[TestCase (RoundtripType.None, false, false)]
[TestCase (RoundtripType.Pdb, false, false)]
[TestCase (RoundtripType.Pdb, true, false)]
[TestCase (RoundtripType.Pdb, true, true)]
[TestCase (RoundtripType.PortablePdb, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false)]
[TestCase (RoundtripType.PortablePdb, true, true)]
public void ReplaceWithSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes)
[TestCase (RoundtripType.None, false, false, false)]
[TestCase (RoundtripType.Pdb, false, false, false)]
[TestCase (RoundtripType.Pdb, true, false, false)]
[TestCase (RoundtripType.Pdb, true, false, true)]
[TestCase (RoundtripType.Pdb, true, true, false)]
[TestCase (RoundtripType.PortablePdb, false, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, true)]
[TestCase (RoundtripType.PortablePdb, true, true, false)]
public void ReplaceWithSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes, bool padIL)
{
var methodBody = CreateTestMethodWithLocalScopes ();
var methodBody = CreateTestMethodWithLocalScopes (padIL);
methodBody = RoundtripMethodBody (methodBody, roundtripType, forceUnresolved, reverseScopes);

var il = methodBody.GetILProcessor ();
Expand All @@ -224,16 +230,18 @@ public void ReplaceWithSymbolRoundtrip (RoundtripType roundtripType, bool forceU
methodBody.Method.Module.Dispose ();
}

[TestCase (RoundtripType.None, false, false)]
[TestCase (RoundtripType.Pdb, false, false)]
[TestCase (RoundtripType.Pdb, true, false)]
[TestCase (RoundtripType.Pdb, true, true)]
[TestCase (RoundtripType.PortablePdb, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false)]
[TestCase (RoundtripType.PortablePdb, true, true)]
public void EditBodyWithScopesAndSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes)
[TestCase (RoundtripType.None, false, false, false)]
[TestCase (RoundtripType.Pdb, false, false, false)]
[TestCase (RoundtripType.Pdb, true, false, false)]
[TestCase (RoundtripType.Pdb, true, false, true)]
[TestCase (RoundtripType.Pdb, true, true, false)]
[TestCase (RoundtripType.PortablePdb, false, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, false)]
[TestCase (RoundtripType.PortablePdb, true, false, true)]
[TestCase (RoundtripType.PortablePdb, true, true, false)]
public void EditBodyWithScopesAndSymbolRoundtrip (RoundtripType roundtripType, bool forceUnresolved, bool reverseScopes, bool padIL)
{
var methodBody = CreateTestMethodWithLocalScopes ();
var methodBody = CreateTestMethodWithLocalScopes (padIL);
methodBody = RoundtripMethodBody (methodBody, roundtripType, forceUnresolved, reverseScopes);

var il = methodBody.GetILProcessor ();
Expand Down Expand Up @@ -320,13 +328,16 @@ static void AssertLocalScope (MethodBody methodBody, ScopeDebugInformation scope
Assert.IsTrue (scope.End.IsEndOfMethod);
}

static MethodBody CreateTestMethodWithLocalScopes ()
static MethodBody CreateTestMethodWithLocalScopes (bool padILWithNulls)
{
var module = ModuleDefinition.CreateModule ("TestILProcessor", ModuleKind.Dll);
var type = new TypeDefinition ("NS", "TestType", TypeAttributes.Public | TypeAttributes.Abstract | TypeAttributes.Sealed, module.ImportReference (typeof (object)));
module.Types.Add (type);

var methodBody = CreateTestMethod (OpCodes.Nop, OpCodes.Ldloc_0, OpCodes.Nop, OpCodes.Ldloc_1, OpCodes.Nop, OpCodes.Ldloc_2, OpCodes.Nop);
if (padILWithNulls)
methodBody.Instructions.Capacity += 10;

var method = methodBody.Method;
method.ReturnType = module.ImportReference (typeof (void));
type.Methods.Add (method);
Expand Down

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