August 2013 | The Old New Thing

Can an x64 function repurpose parameter home space as general scratch space?

Raymond ChenAugust 30, 2013Aug 30, 201308/30/13

We saw some time ago that the x64 calling convention in Windows reserves space for the register parameters on the stack, in case the called function wants to spill them. But can the called function use the memory for other purposes, too? You sort of already know the answer to this question. Consider this function: How would a naïve

How can I write to a file only as long as nobody's looking?

Raymond ChenAugust 29, 2013Aug 29, 201308/29/13

A customer wanted to know how to detect that the user has opened Notepad to view a particular file. They had come up with method based on polling and sniffing the Notepad title bar, but they found that it consumed a lot of CPU. (They hadn't noticed yet that it doesn't localize, and that it can trigger false positives since Notepad shows only t

The format of data and custom resources

Raymond ChenAugust 28, 2013Aug 28, 201308/28/13

Continuing the highly-sporadic series of Win32 resource formats, today we'll look at the format of RT_DATA resources, which are declared in resource files as RCDATA. Also the format of custom resources, which are declared in resource files by just giving the custom resource name or ordinal as the second word on the declaration. The format is

How can I find out which process and user is modifying a file?

Raymond ChenAugust 27, 2013Aug 27, 201308/27/13

When troubleshooting a problem, you may discover that a file is being modified that shouldn't, and you figure out would be nice if there were some way of finding out which process is modifying the file (so you can get it to stop). Enter the security auditing system. Every securable object has an associated system access control list (SACL) w

The challenge of improvisational historical comedy

Raymond ChenAugust 26, 2013Aug 26, 201308/26/13

I dreamed that one of my friends signed me up for some sort of combination Punk'd/Thank God You're Here improv show without my knowledge, and I had to explain how her husband had unwittingly coined some nonspecific Internet meme.

Why doesn't the "Automatically move pointer to the default button in a dialog box" work for nonstandard dialog boxes, and how do I add it to my own nonstandard dialog boxes?

Raymond ChenAugust 26, 2013Aug 26, 201308/26/13

The Mouse control panel has a setting called Automatically move pointer to the default button in a dialog box, known informally as Snap to default button or simply Snap To. You may have discovered that it doesn't work for all dialog boxes. Why not? The Snap To feature is implemented by the dialog manager. When the window is shown and the se

If I attach a file to an existing completion port, do I have to close the completion port handle a second time?

Raymond ChenAugust 23, 2013Aug 23, 201308/23/13

There are two ways of calling the CreateIOCompletionPort function. You can pass a null pointer as the ExistingCompletionPort parameter, indicating that you would like to create a brand new completion port, associated with the file handle you passed (if you passed one). Or you can pass the handle of an existing comple

All I/O on a synchronous file handle is serialized; that's why it's called a synchronous file handle

Raymond ChenAugust 22, 2013Aug 22, 201308/22/13

File handles are synchronous by default. If you want asynchronous file handles, you need to pass the FILE_FLAG_OVERLAPPED flag when you create the handle. And all operations on a synchronous file handle are serialized. You'd think this was a simple and obvious rule, but "Someone" finds it "very surprising that operations can block which only

Adding a confirmation dialog to every drag/drop operation does not solve the problem

Raymond ChenAugust 21, 2013Aug 21, 201308/21/13

A customer wanted to know how to enable a confirmation dialog whenever the user inadvertently perform a drag/drop operation in Explorer to move files within a volume. For example, if I have an S drive mapped to \\server\share, I would like to display the confirmation dialog when users inadvertently drag and drop a file or folder within the S

Microspeak: The train

Raymond ChenAugust 20, 2013Aug 20, 201308/20/13

Work on Windows occurs in several different branches of the source code, and changes in one branch propagate to other branches. The goal is to push changes toward the trunk on a regular cadence. I will illustrate with an extremely simplified example because the complexities aren't really important. Consider this branch structure: Suppose f

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