Bad data can cause ILVerify to throw IndexOutOfRangeException

[masonwheeler]

Description

While attempting to use ILVerify to diagnose a compiler output problem, it instead blew up in my face, dumping an IndexOutOfRangeException stack trace on me.

Reproduction Steps

1. Install .NET 5.
2. Install ILVerify.
3. Download this test case and unzip it to a new folder.
4. Open PowerShell and CD to that folder.
5. ilverify .\testcase.dll -r "C:\Program Files\dotnet\shared\Microsoft.NETCore.App\5.0.13\*.dll" -r "Boo.Lang.dll" (Adjust .NET 5 path as needed)

Expected behavior

A correct program should not throw "boneheaded exceptions."

A diagnostic tool should provide helpful diagnostic information about the nature of errors encountered.

Actual behavior

Error: System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at Internal.IL.ILImporter.CreateBasicBlock(Int32 offset)
   at Internal.IL.ILImporter.FindBasicBlocks()
   at Internal.IL.ILImporter.Verify()
   at ILVerify.Verifier.VerifyMethod(EcmaModule module, MethodIL methodIL, MethodDefinitionHandle methodHandle)
   at ILVerify.Verifier.VerifyMethods(EcmaModule module, IEnumerable`1 methodHandles)+MoveNext()
   at ILVerify.Verifier.Verify(PEReader peReader, MethodDefinitionHandle methodHandle)+MoveNext()
   at ILVerify.Program.VerifyMethods(PEReader peReader, EcmaModule module, String path, Int32& numErrors, Int32& verifiedMethodCounter, Int32& methodCounter)
   at ILVerify.Program.VerifyAssembly(PEReader peReader, EcmaModule module, String path)
   at ILVerify.Program.Run()
   at ILVerify.Program.Run(Options options)

Configuration

.NET 5, Windows 10, x64

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Issue Details

---

Description

While attempting to use ILVerify to diagnose a compiler output problem, it instead blew up in my face, dumping an IndexOutOfRangeException stack trace on me.

Reproduction Steps

1. Install .NET 5.
2. Install ILVerify.
3. Download this test case and unzip it to a new folder.
4. Open PowerShell and CD to that folder.
5. ilverify .\testcase.dll -r "C:\Program Files\dotnet\shared\Microsoft.NETCore.App\5.0.13\*.dll" -r "Boo.Lang.dll" (Adjust .NET 5 path as needed)

Expected behavior

A correct program should not throw "boneheaded exceptions."

A diagnostic tool should provide helpful diagnostic information about the nature of errors encountered.

Actual behavior

Error: System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at Internal.IL.ILImporter.CreateBasicBlock(Int32 offset)
   at Internal.IL.ILImporter.FindBasicBlocks()
   at Internal.IL.ILImporter.Verify()
   at ILVerify.Verifier.VerifyMethod(EcmaModule module, MethodIL methodIL, MethodDefinitionHandle methodHandle)
   at ILVerify.Verifier.VerifyMethods(EcmaModule module, IEnumerable`1 methodHandles)+MoveNext()
   at ILVerify.Verifier.Verify(PEReader peReader, MethodDefinitionHandle methodHandle)+MoveNext()
   at ILVerify.Program.VerifyMethods(PEReader peReader, EcmaModule module, String path, Int32& numErrors, Int32& verifiedMethodCounter, Int32& methodCounter)
   at ILVerify.Program.VerifyAssembly(PEReader peReader, EcmaModule module, String path)
   at ILVerify.Program.Run()
   at ILVerify.Program.Run(Options options)

Configuration

.NET 5, Windows 10, x64

Author:	masonwheeler
Assignees:	-
Labels:	untriaged, area-ILVerification
Milestone:	-

[jkotas]

Error: System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at Internal.IL.ILImporter.CreateBasicBlock(Int32 offset)
   at Internal.IL.ILImporter.FindBasicBlocks()
   at Internal.IL.ILImporter.Verify()
   at ILVerify.Verifier.VerifyMethod(EcmaModule module, MethodIL methodIL, MethodDefinitionHandle methodHandle)
   at ILVerify.Verifier.VerifyMethods(EcmaModule module, IEnumerable`1 methodHandles)+MoveNext()
   at ILVerify.Verifier.Verify(PEReader peReader, MethodDefinitionHandle methodHandle)+MoveNext()
   at ILVerify.Program.VerifyMethods(PEReader peReader, EcmaModule module, String path, Int32& numErrors, Int32& verifiedMethodCounter, Int32& methodCounter)
   at ILVerify.Program.VerifyAssembly(PEReader peReader, EcmaModule module, String path)
   at ILVerify.Program.Run()
   at ILVerify.Program.Run(Options options)

[MichalStrehovsky]

peverify message:

[IL]: Error: [foo.exe : <Module>::main][offset 0x00000000] Code size is zero.
1 Error(s) Verifying empty.exe

The best fix is to add a check for length being zero in FindBasicBlocks and have that call ReportZeroSizedMethod (a new method; similar to the other ReportXXX method calls in ILImporter.cs). The ReportZeroSizedMethod method would be defined in ILImporter.Verify.cs file and report the error similar to how the other Report methods do it there.

It won't be possible to make a unit test for this because ILAsm will never generate a method with an empty body (it will put a ret there for you), so unit test can be skipped.

[masonwheeler]

There is actually a check for this already in InitialPass. Unfortunately, its name notwithstanding, InitialPass is called after FindBasicBlocks.