April 2018 | The Old New Thing

The seasoned pianist’s guide to musical collaborators

Raymond ChenApril 30, 2018Apr 30, 201804/30/18

The wife of one of my relatives is a classical pianist. She shared with me her hot takes on musicians she collaborates with.¹ As you might expect for a pianist, she is hired to do a lot of accompaniment. I learned that she makes makes more money from bad musicians than from good ones. For one thing, bad musicians are generally ...

I don’t know how I managed to be presenting at the same conference as Dona Sarkar

Raymond ChenApril 30, 2018Apr 30, 201804/30/18

Dona Sarkar is an aspiring fashion designer, a fashion blogger, a book author, and head of the Windows Insiders program. She's also way cooler than I will ever be. Here's her proposed title slide for one of her presentations at the Build 2018 conference.¹ OKAY! Finally making progress on our #MSBuild talk #1 pic.twitter.com/9q4ork4pzZ&...

A cute hidden message in a image to entertain you while you wait

Raymond ChenApril 27, 2018Apr 27, 201804/27/18

In one of the internal Microsoft special-interest group mailing lists, someone pointed out that the Windows 10 Mail app contains a cute hidden message: Hint: The people who noticed were members of the Ham Radio special-interest group. Answer: The pattern of long and short dashes that are used to suggest motion spell out, in Morse code, ...

How can I have my program execute some code only if run from the Visual Studio debugger?

Raymond ChenApril 26, 2018Apr 26, 201804/26/18

A customer wanted their program to operate in a special mode if it is being debugged from inside the Visual Studio development environment. Say, if being run from Visual Studio via the "Start with debugging" menu, it should display a diagnostic window that contains additional information. You should think twice before you do this. Sure. you ...

Microspeak: Tented

Raymond ChenApril 25, 2018Apr 25, 201804/25/18

Here's a citation for the Microspeak term tented from an old Microsoft job listing that is no longer available, maybe because the req has been filled. You and your team will decide how the Office clients and services measure their success in performance sensitive areas like latency, memory/disk footprint, and battery life not only for the ...

It rather involved being on the other side of this airtight hatchway: Passing invalid parameters from kernel mode to another kernel-mode function corrupts the kernel (who knew?)

Raymond ChenApril 24, 2018Apr 24, 201804/24/18

A customer reported a vulnerability in a kernel function, let's call it kfunc. The kernel-mode kfunc function doesn't validate any of the pointers passed to it. As a result, you can pass anything you want as the output pointer, and it will blindly try to write to it. If you pass null, you will crash the kernel. Or if you pass a pointer to ...

The early history of redundant function pointer casts: MakeProcInstance

Raymond ChenApril 23, 2018Apr 23, 201804/23/18

If you look through old code, you see a lot of redundant function pointer casts. (If you're writing new code, you should get rid of as many function pointer casts as possible, because a function pointer cast is a bug waiting to happen.) Why does old code have so many redundant function pointer casts? Because back in the old days, they weren't...

The MIPS R4000, part 15: Code walkthrough

Raymond ChenApril 20, 2018Apr 20, 201804/20/18

Today we're going to take a relatively small function and watch what the compiler did with it. The function is this guy from the C runtime library, although I've simplified it a bit to avoid some distractions. Here's the corresponding disassembly: On entry, the parameters to a function are passed in a0 through a3. This function has only one ...

The MIPS R4000, part 14: Common patterns

Raymond ChenApril 19, 2018Apr 19, 201804/19/18

Okay, now that we see how function calls work, we can demonstrate some common code sequences. If you are debugging through MIPS code, you'll need to be able to recognize these different types of calling sequences in order to keep your bearings. Non-virtual calls generally look like this: The parameters could be set up in any order, and there...

The MIPS R4000, part 13: Function prologues and epilogues

Raymond ChenApril 18, 2018Apr 18, 201804/18/18

We saw last time how functions are called. Today we'll look at the receiving end of a function call. As noted earlier, all functions (except for lightweight leaf functions) must declare unwind codes in the module metadata so that the kernel can figure out what to do if an exception occcurs. The stack for a typical function looks like this...

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