Exception in clrjit.dll when using .NET 9.0

[melfon]

Description

Fail to open an dll built with .NET 9.0 /clr:netcore.

It works fine with .NET 8.0, but with .NET 9.0 it only works during debugging and if Suppress JIT optimization on module load is enabled. It never works in release.

It is somehow connected to the main application loading the dll. It works if the main app is written in C#.

Reproduction Steps

Created a simple app to reproduce the problem.
DllExport

Run DebugTestApp to see the problem. Debug uses NetApp, which works.

Works fine if using .NET 8, but crashes if using .NET 9.

Expected behavior

As with .NET 8.0

Actual behavior

'TestApp.exe' (Win32): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\9.0.2\clrjit.dll'. Symbol loading disabled by Include/Exclude setting.
Exception thrown at 0x00007FFB66DF53EB (clrjit.dll) in TestApp.exe: 0xC000008E: Floating-point division by zero (parameters: 0x0000000000000000, 0x0000000000001924).

Regression?

Works with .NET 8

Known Workarounds

Enable Suppress JIT optimization on module load in VS to get it working during debugging within VS. It never works in release.

Configuration

No response

Other information

No response

[EgorBo]

Does not repro for me in .NET 9.0 and Release assuming I repeated the steps correctly

I changed TFM to net9.0 for NetApp.csproj and ran it under Release (with "Enable Suppress JIT optimization on module load i" disabled)

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[melfon]

The problem is with the TestApp. Use DllExport to reproduce the problem, DebugTestApp fails, DebugTestApp.NET8 works. NetApp is only used to show that somehow the problem is dependent on the application calling the dll.

You can also test it by starting TestApp directly from the browser. DllExportTest\bin\Release\TestApp.exe will fail.

[EgorBo]

The problem is with the TestApp. Use DllExport to reproduce the problem, DebugTestApp fails, DebugTestApp.NET8 works. NetApp is only used to show that somehow the problem is dependent on the application calling the dll.

You can also test it by starting TestApp directly from the browser. DllExportTest\bin\Release\TestApp.exe will fail.

@melfon not sure I follow - I cloned you rerpo with C# and C++ project. but then there is also a standalone binary (it's not managed) - is there a source for it?

[AndyAyersMS]

I can repro, the error is in profile synthesis:

clrjit.dll!ProfileSynthesis::GaussSeidelSolver() Line 1416
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.cpp(1416)
[Inline Frame] clrjit.dll!ProfileSynthesis::ComputeBlockWeights() Line 1113
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.cpp(1113)
clrjit.dll!ProfileSynthesis::Run(ProfileSynthesisOption option) Line 100
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.cpp(100)
[Inline Frame] clrjit.dll!ProfileSynthesis::Run(Compiler *) Line 37
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.h(37)
clrjit.dll!Compiler::fgIncorporateProfileData() Line 2919
	at D:\a\_work\1\s\src\coreclr\jit\fgprofile.cpp(2919)
[Inline Frame] clrjit.dll!Phase::Run() Line 61
	at D:\a\_work\1\s\src\coreclr\jit\phase.cpp(61)
[Inline Frame] clrjit.dll!DoPhase(Compiler *) Line 143
	at D:\a\_work\1\s\src\coreclr\jit\phase.h(143)
clrjit.dll!Compiler::compCompile(void * * methodCodePtr, unsigned int * methodCodeSize, JitFlags * compileFlags) Line 4642

Here change is 100 and oldWeight is 0.

@melfon I wonder if something in the host changes the FP exception modes. Normally this computation would not raise an exception and just compute infinity.

[melfon]

The problem is with the TestApp. Use DllExport to reproduce the problem, DebugTestApp fails, DebugTestApp.NET8 works. NetApp is only used to show that somehow the problem is dependent on the application calling the dll.
You can also test it by starting TestApp directly from the browser. DllExportTest\bin\Release\TestApp.exe will fail.

@melfon not sure I follow - I cloned you rerpo with C# and C++ project. but then there is also a standalone binary (it's not managed) - is there a source for it?

@EgorBo The problem is that sometimes I have external apps, in this case the TestApp that will load a dll.
DllExport creates a very simple dll that TestApp will load and call the exported method Load() in dllmain.cpp. Normally the load method will call some C# class, but the problem can be reproduced even without that. I had no problem doing this before with NET8, but it fails with NET9.

Use configuration DebugTestApp with DllExport project and you should be able to reproduce the error.

[melfon]

I can repro, the error is in profile synthesis:

clrjit.dll!ProfileSynthesis::GaussSeidelSolver() Line 1416
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.cpp(1416)
[Inline Frame] clrjit.dll!ProfileSynthesis::ComputeBlockWeights() Line 1113
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.cpp(1113)
clrjit.dll!ProfileSynthesis::Run(ProfileSynthesisOption option) Line 100
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.cpp(100)
[Inline Frame] clrjit.dll!ProfileSynthesis::Run(Compiler *) Line 37
	at D:\a\_work\1\s\src\coreclr\jit\fgprofilesynthesis.h(37)
clrjit.dll!Compiler::fgIncorporateProfileData() Line 2919
	at D:\a\_work\1\s\src\coreclr\jit\fgprofile.cpp(2919)
[Inline Frame] clrjit.dll!Phase::Run() Line 61
	at D:\a\_work\1\s\src\coreclr\jit\phase.cpp(61)
[Inline Frame] clrjit.dll!DoPhase(Compiler *) Line 143
	at D:\a\_work\1\s\src\coreclr\jit\phase.h(143)
clrjit.dll!Compiler::compCompile(void * * methodCodePtr, unsigned int * methodCodeSize, JitFlags * compileFlags) Line 4642

Here change is 100 and oldWeight is 0.

@melfon I wonder if something in the host changes the FP exception modes. Normally this computation would not raise an exception and just compute infinity.

That at least explains the division by zero.

[AndyAyersMS]

See for example the discussion in #109997 -- if you want to modify FP exceptional behavior you have to be careful to restore it before invoking any .NET code.

[melfon]

Ok, now I understand. So there is a difference in behavior between NET8 and NET9. To get this working in NET9, the main application has to disable zero division checks. I recompiled TestApp.exe and got it working. This could cause a problem for older apps that can not be recompiled.

[AndyAyersMS]

AFAIK this FP mode sensitivity is not a new requirement in .NET 9. But in .NET 9 it may now be exposed in more places.

[AndyAyersMS]

Though it looks like as good citizens we should probably avoid depending on divide by zero in that one spot in the JIT. I will put up a PR, though not sure if it will qualify for backporting to .NET 9.

[melfon]

Though it looks like as good citizens we should probably avoid depending on divide by zero in that one spot in the JIT. I will put up a PR, though not sure if it will qualify for backporting to .NET 9.

@AndyAyersMS Thanks for the support and quick response!

[AndyAyersMS]

FYI I have put this up for consideration as a .NET 9 fix: #113418 -- will update this once a decision is made.