alt.hn

6/28/2026 at 9:53:58 AM

DLL that was not present in memory despite not being formally unloaded

 https://devblogs.microsoft.com/oldnewthing/20260625-00/?p=112467

by ibobev

6/28/2026 at 12:38:34 PM

Part two:

https://devblogs.microsoft.com/oldnewthing/20260626-00/?p=11...

by masfuerte

6/28/2026 at 1:02:31 PM

Part 1 was interesting; it isn't clear why he split that into a Part 2 since it adds little to the story and is a paragraph long.

by Someone1234

6/28/2026 at 2:07:51 PM

I assume the fact it is a third party application means debugging gets harder, and the business case for doing so is weaker/none.

But I would hope that some kind of reverse debugger triggered on one of these crashes would make it pretty simple to say "who wrote this 01".

by londons_explore

6/28/2026 at 8:12:21 PM

You usually hope that TTD points to the culprit in such situations. But once I encountered single-byte corruption that didn't make any sense in TTD trace, there was good value at write and next read was garbage. I never discovered whether that was CPU bug, corruption by GPU shaders, stray kernel writes, or whatever.(I think it's unlikely that CPU bug would manifest with both native and TTD-instrumented runs. Corrupted byte was inside heap allocated memory so it shouldn't be in GPU pagetables at all. Kernel writes wouldn't appear in TTD trace, so really I think that was most likely issue, but how to debug that...)

by garaetjjte

6/28/2026 at 3:22:45 PM

You could also look at modules loaded into all of those processes that crashed this way.

by microgpt

6/28/2026 at 1:17:18 PM

Might have been an “I need to look into this” segueing into “ never mind”?

by taneq

6/28/2026 at 4:49:15 PM

Part-2 is more than a paragraph and is logically distinct from Part-1. In this, Raymond actually gets the crucial clue from another colleague's debugging efforts which leads him to identify that the bottom byte of HMODULE of the DLL gets overwritten by <something> which is the root cause of the bug; viz.

The “DLL unmapped from memory” crash is just an alternate manifestation of the “somebody is writing 01 bytes to places they shouldn’t” bug. The original bug had a larger bucket spray than we initially thought.

Part-2 is the essence of the solution while Part-1 is a series of investigations and inferences.

by rramadass

6/28/2026 at 12:27:28 PM

> The good news for the shell32 team is that they are off the hook; they are the victim. The bad news is that we don’t know who the culprit is.

The story of software development through the ages.

by zabzonk

6/28/2026 at 1:09:19 PM

When you’ve eliminated all possible explanation, it’s time to pack it in.

by brookst

6/28/2026 at 1:19:40 PM

Oh man, my journey from idealistic “there is always an explanation” youth to “some days it do be like that, and we may never know why” in a nutshell.

by taneq

6/28/2026 at 3:04:38 PM

Or, as the original article suggests, blame someone else.

by zabzonk

6/28/2026 at 1:31:29 PM

What MSFT support policy do you need to have the legendary Raymond Chen take a look at it?

I say this because we've reported a bunch of Windows bugs (mainly running Windows under virtualization) and getting them to pay attention at all is an up-hill battle.

by rwmj

6/28/2026 at 1:49:35 PM

> What MSFT support policy do you need to have the legendary Raymond Chen take a look at it?

If you have to ask, you can't afford it.

by hackyhacky

6/28/2026 at 7:15:42 PM

If you can reproduce it reliably and doing so generates some form of telemetry, then just set up some automation to keep doing that in a loop. From as many machines as possible.

No comment is offered on if I have ever gotten a bug noticed this way.

by xmodem

6/28/2026 at 6:28:02 PM

Perhaps it’s a matter of subjective interest!

Often that’s how these things go.

by DANmode

6/28/2026 at 2:33:38 PM

>I asked for the 100 most recent crashes in that third party program and put them into a pivot table so I could see the distribution.

Always wondered if crash reporting is some kind of shady business. It's good to know it does, at minimum, do what it promises and give valuable crash data to MS.

by 1970-01-01

6/28/2026 at 6:31:07 PM

Shady, as in, where does that data end up after MS collects it, and why?

by DANmode

6/28/2026 at 12:48:20 PM

I see posts like this, this deep dive into the call stacks and am always humbled and reminded of the limits of my knowledge about computers and programs.

by kumarvvr

6/28/2026 at 1:10:21 PM

Goes both ways, author probably knows little about FPGA programming, React or PyTorch.

by dist-epoch

6/28/2026 at 1:02:24 PM

Not a programmer?

by Panzer04

6/28/2026 at 1:18:11 PM

I am, for 20 years now. I do embedded stuff too. Still.

by kumarvvr

6/28/2026 at 1:35:47 PM

I'm a bit surprised you don't run into things like this then :). Do you use GDB and the like at all?

Or do you mean all the windows specific stuff etc, I guess I was more imaging the call stack etc.

No insult was intended XD

by Panzer04

6/28/2026 at 1:49:05 PM

As someone who has debugged his fair share of tricky low-level issues, the parts that I find impressive in his blog posts are things such as "then we look at the bytes in memory and oh yeah, this looks like an exception record". I would usually not think to do that (or be able to recognise it as easily as I presume he did).

by FartyMcFarter

6/28/2026 at 6:14:27 PM

I assume it's mostly just something you learn to recognize after decades of poking at the same things. I remember being impressed with Thiago (Qt developer) being able to immediately tell if a pointer was heap allocated, invalid/unaligned, etc. until I spent more time poring over /proc/*/maps and in gdb. Never figured out how he could tell someone's Qt version just from an strace excerpt, though.

by Chu4eeno

6/28/2026 at 7:41:26 PM

> Never figured out how he could tell someone's Qt version just from an strace excerpt, though.

Sonames might be a big clue? Otherwise, initialization order changes maybe? Sometimes there's enough file content in an strace to be able to see a strong indicator?

Those are just guesses, I do a lot more debugging with pcaps rather than straces. Although you do often want to determine which side of the syscall caused whatever you're seeing in the pcap.

by toast0

6/28/2026 at 1:43:48 PM

I have done everything from desktop apps to web apps and a bunch in between. Regular debugging is good enough for me. Never had the need to go down into call stack level.

Even with embedded programming, regular C debugger has always been enough.

by kumarvvr

6/28/2026 at 12:24:21 PM

That's some doggedly determined back tracing to uncover an unexpected heisenbug (loose meaning).

  So a total of 46% of the crashes were due to this rogue force-unload of a DLL. This is a case of bucket spray, where a single underlying cause generates a large number of different types of crashes.

by defrost

6/28/2026 at 12:35:53 PM

We've not yet seen sufficient evidence this is any type of heisenbug.

by chrisjj

6/28/2026 at 1:10:27 PM

Looking more closely would resolve it one way or the other.

by brookst

6/28/2026 at 1:23:36 PM

My hat.

by defrost

6/28/2026 at 1:22:28 PM

It's not, by the article, in a strict taxonomy.

In a wider sloppier sense some use the term for bugs that are hard to pin down and exhibit wide behaviours.

by defrost

6/28/2026 at 2:09:28 PM

How big and important third-party vendor must be for Raymond Chen to dissect its coredumps?

by nopurpose

6/28/2026 at 2:17:39 PM

Given his seniority, it could also be that he picks whatever bugs he wants to work on. Whether that is from personal interest, frequency of crashes or any other criteria.

When you're at that level in a company, it's rare that someone would be micromanaging what you work on at all times.

by FartyMcFarter

6/28/2026 at 2:56:42 PM

Windows COM is super weird and way over engineered.

by IChooseY0u

6/28/2026 at 3:06:24 PM

I actually think COM is an amazing bit of engineering considering its intended use case.

It still feels like a much more advanced way of sharing compiled libraries between different languages than the current default of "export a C ABI and communicate across the barrier via primitive sticks and stones."

COM isn't perfect but I still find it impressive especially since COM/OLE are 40 years old at this point.

by rpeden

6/28/2026 at 3:24:59 PM

It basically is that. It's a standardized sticks and stones. Plus objects for some reason. But I don't think the objects are a bad thing - it allows multiple implementations of sometimes to co-exist - consider using two different GPUs from different vendors at the same time. It took a really long time and a bunch of hacks to make OpenGL support that, but DirectX could always do it (at least at the API level) by just creating two different ID3DDevice objects backed by different code from different DLLs both loaded at the same time.

OpenGL basically loads the GPU driver DLL that directly implements the OpenGL functions while Direct3D uses a COM object with a vtable so it can easily have two different ones.

by microgpt

6/28/2026 at 2:56:08 PM

The fact that Raymond Chen is debugging these kind of issues, tells me Microsoft is short on staff that has his particular set of skills, handing him the hairiest issues from the annals of Windows. The new hires are probably all about .NET and JavaScript and what have you -- whatever Microsoft is about these days. I doubt it's C/C++. Chen is probably on standby and is paid handsomely as a de-facto VIP consultant. He is a legend, but he's becoming somewhat of a vintage developer.

by hackrmn

6/28/2026 at 4:29:27 PM

Managed dump analysis in windbg was a thing. It’s been many years since I’ve needed it, though. Service telemetry improved quickly thereafter.

by forestry

6/28/2026 at 8:23:58 PM

It is still a thing, just not a very common one since the debugger in VS has become more ergonomic and powerful. But windbg is still the king here, for the most advanced analysis of both managed and unmanaged code and it isn't even close to be honest once you learn the arcane commands and incatations

by algorithmsRcool

6/28/2026 at 4:33:50 PM

Feed the info and code to Claude, it'll diagnose and fix this. You're welcome, Microsoft.

by antonvs