Cannot profile exception performance possibly due to stack walking issue

[GSPP]

It appears impossible to profile the CPU usage of exceptions. There seems to be some issue with stack walking.

        while (true)
        {
            try
            {
                var reader = new Utf8JsonReader(new byte[] { (byte)'{' });
                while (reader.Read()) ;
            }
            catch
            {
            }
        }

Process Explorer shows a truncated stack with unusual 0x0000 entries:

PerfView loses track of where the time is spent:

Note, that 95% of the time is unaccounted for and it appears as if JSON code calls into Main.

DotTrace shows a lot of time spent in "Unsafe Stack Walking" but in the wrong place:

There might be some quicks in how the tools are functioning. But it seems that the basic stack walking data available to profilers is broken.

Environment:

• In 3.0.100-preview7-012821
• Windows 10
• Latest Windows SDK for dbghelp.dll
• Latest PerfView

[sywhang]

I just tried to repro this issue but didn't have much success.

Here is what I did:

Compile the following program under the name exceptionperf.exe in 3.0 Preview 7 official build (preview-7-012821) on Windows 10:

using System;
using System.Text.Json;

namespace exceptionperf
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                try
                {
                    var reader = new Utf8JsonReader(new byte[] { (byte)'{' });
                    while (reader.Read()) ;
                }
                catch
                {
                }
            }
        }
    }
}

2. Capture dump using WinDbg (and process explorer). I observed the following stack which doesn't contain the 0x0000 entry you had:
   

3. Tried to profile the app using PerfView and got the following calltree:
   

The calltree does show that the majority of time is spent processing exception.

I tried using different previews (5 and 6) and still could not repro the issue.

@dotnet/dotnet-diag Can anyone try to repro this issue? If this really is broken then I think it can be a serious issue and we should investigate.

[GSPP]

I emailed dumps and here is a repro solution:

ExceptionStackRepro.zip

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