ICorProfilerCallback::ObjectsAllocatedByClass does not work anymore since dotnet 6

[ogxd]

Description

The CLR profiling API callback ICorProfilerCallback::ObjectsAllocatedByClass is not called by the CLR in dotnet 6.

Reproduction Steps

1. Implement the ICorProfilerCallback interface
2. Print to the console in the ObjectsAllocatedByClass callback
3. Eventually also implement ICorProfilerCallback2 and print in the GarbageCollectionStarted callback, so that you you'll see that ObjectsAllocatedByClass is not called when GarbageCollectionStarted is.
4. Use the COR_PRF_MONITOR_GC and COR_PRF_HIGH_MONITOR_NONE event mask 2 flags
5. Attach to a NET 5.0 application: it works.
6. Attach to a NET 6.0 application: it doesn't work anymore, ObjectsAllocatedByClass is not called.

Expected behavior

The ObjectsAllocatedByClass callback should be called for each garbage collection like it used to be before.

Actual behavior

The ObjectsAllocatedByClass callback is never called.

Regression?

Yes

Known Workarounds

No workaround was found

Configuration

dotnet version:

• 6.0.101 (not working)
• 5.0.100 (working)

OS: Windows 11 x64

Other information

Could it be due to these recent changes? @davmason

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Issue Details

---

Description

The CLR profiling API callback ICorProfilerCallback::ObjectsAllocatedByClass is not fired by the CLR in dotnet 6.

Reproduction Steps

• Implement the ICorProfilerCallback interface
• Print to the console in the ObjectsAllocatedByClass callback
• Eventually also implement ICorProfilerCallback2 and print in the GarbageCollectionStarted callback, so that you you'll see that ObjectsAllocatedByClass is not called when GarbageCollectionStarted is.
• Use the COR_PRF_MONITOR_GC and COR_PRF_HIGH_MONITOR_NONE event mask 2 flags
• Attach to a NET 5.0 application: it works.
• Attach to a NET 6.0 application: it doesn't work anymore, ObjectsAllocatedByClass is not called.

Expected behavior

The ObjectsAllocatedByClass callback should be called for each garbage collection like it used to be before.

Actual behavior

The ObjectsAllocatedByClass callback is never called.

Regression?

Yes

Known Workarounds

No workaround was found

Configuration

dotnet version:

• 6.0.101 (not working)
• 5.0.100 (working)

OS: Windows 11 x64

Other information

Could it be due to these recent changes? @davmason

Author:	ogxd
Assignees:	-
Labels:	area-Diagnostics-coreclr, untriaged
Milestone:	-

[ogxd]

So in order the check my hypothesis about the problem coming from theses changes, I installed the latest dotnet 6 SDK before this commit (6.0.100-preview.2.21155.3), and it works as expected: ObjectsAllocatedByClass is called as it should. I hope it will help finding the issue.

[davmason]

Thanks for reporting this @ogxd, it is indeed caused by that change. Specifically this part:

runtime/src/coreclr/vm/proftoeeinterfaceimpl.cpp

Lines 1265 to 1287 in 02e22b0

	bool AllocByClassHelper(Object * pBO, void * pv)
	{
	CONTRACTL
	{
	NOTHROW;
	GC_NOTRIGGER;
	MODE_ANY;
	}
	CONTRACTL_END;
	_ASSERTE(pv != NULL);
	{
	BEGIN_PROFILER_CALLBACK(CORProfilerTrackAllocations());
	// Pass along the call
	g_profControlBlock.AllocByClass(
	(ObjectID) pBO,
	SafeGetClassIDFromObject(pBO),
	pv);
	END_PROFILER_CALLBACK();
	}
	return TRUE;
	}

Line 1277 should be BEGIN_PROFILER_CALLBACK(CORProfilerTrackGC()) and not BEGIN_PROFILER_CALLBACK(CORProfilerTrackAllocations())

I will create a fix sometime soon, we should be able to backport this one to 6.0.

If you (or anyone else out there) are interested in contributing to the runtime, this would be a great first issue. The fix is one line, and then it's just adding a simple test to make sure ObjectsAllocByClass works.

[davmason]

Oh, and it should be possible to work around this by enabling COR_PRF_MONITOR_OBJECT_ALLOCATED, although that is a very expensive thing to enable so I wouldn't suggest enabling that workaround in any production scenario

[ogxd]

Hi @davmason, thanks for the quick reply! A backport fix would be amazing :)
Unfortunately, I can't use COR_PRF_MONITOR_OBJECT_ALLOCATED since the profiler I use is attached to an already running process (using InitializeForAttach(...)), and, from what I understood, it is only possible to use this flag for profilers that are initialized when the profiled app starts (using Initialize(...))

I'll try submitting a fix 👍

[davmason]

For the workaround, it might just work if you set COR_PRF_MONITOR_OBJECT_ALLOCATED even on attach. You won't get the object allocated callbacks, since you need to set those at startup like you mention, but I don't think we prevent you from setting it later in the process.

I would like to see a test if you submit a fix, it hopefully is relatively straightforward but if you get blocked I'm happy to help get you going again.

You need to add a managed testcase, like inlining.csproj/inlining.cs in https://github.com/dotnet/runtime/tree/main/src/tests/profiler/unittest, and then a corresponding native profiler like the one in https://github.com/dotnet/runtime/tree/main/src/tests/profiler/native/inlining.

The managed app should allocate some classes, and then the native profiler should check that the classes it expected to see were allocated and write "PROFILER TEST PASSES" if everything is right.

[davmason]

Oh, nevermind about the workaround. I forgot we whitelist the allowable after attach flags. It won't work

[ogxd]

Thanks for the review and the merge @davmason! Shall I make another PR for an eventual backport to 6.0.0 or do you prefer to handle this on your side?