May 2017 | Page 2 of 3 | The Old New Thing

Why do my PDF file associations get reset every time I restart?

Raymond ChenMay 17, 2017May 17, 201705/17/17

A customer reported that each time they restart their Windows 10 PC, the file association for PDF documents keeps getting reset to the default, which is Microsoft Edge. They use the "Set Default Programs" control panel to change the default handler to Program X, but the changes don't stick past a reboot. The feature team for file ...

There’s a group policy for Action Center, and another one for Action Center

Raymond ChenMay 16, 2017May 16, 201705/16/17

A customer wanted to know how to disable the Action Center, the control panel that lets you access settings for the firewall, SmartScreen, that sort of thing. The reason is that the customer is developing a locked-down system with a fixed set of applications, and they want to disable notifications about the settings that are locked down, since...

At least it wasn’t on a Web page with the warning “Beware of the leopard”

Raymond ChenMay 15, 2017May 15, 201705/15/17

In my discussion of the effect of ASLR on DLL rebasing, I wondered how vtables and other function pointers were handled in position-independent code. Commenter kantos replied, "It appears from a cursory google search that…" I wanted to find out more, so I did some searching but couldn't find anything, so I asked for help with that ...

A question about avoiding page faults the first time newly-allocated memory is accessed

Raymond ChenMay 12, 2017May 12, 201705/12/17

A customer had a question about memory allocation. When allocating memory with malloc and new, the memory is not loaded into the physical memory immediately. Instead, the memory is placed in RAM only when the application writes to the memory address. The process of moving pages into physical memory incurs page faults. In order to avoid page ...

How to calculate the resulting security descriptor of a child object without creating it

Raymond ChenMay 11, 2017May 11, 201705/11/17

The CreatePrivateObjectSecurity function is part of a family of functions intended for programs that implement security descriptors for their own custom objects. Normally, you would let the kernel object manager deal with security descriptors, but if your object isn't a kernel object, then you have to do your own security ...

Revised notes on the reliability of FlushFileBuffers

Raymond ChenMay 10, 2017May 10, 201705/10/17

Some time ago, I wrote on the hard drives that lie about flushing file buffers (and the drivers who love them). Here's a check-in on what's happened over the past few years. As things stand today, you can rely on FlushFileBuffers committing your changes to physical disk. (Noting of course that this operation is expensive and may not...

The early Windows phone devices were liquid-cooled, sort of

Raymond ChenMay 9, 2017May 9, 201705/9/17

Jim Lyon shares this story about early Windows phone devices: I remember during early development of Windows phones, our solution to the overheating problems. You would get two cans of soda from the fridge, set one on the desk, set the phone on top of that, and set the other on top of the phone. You were then good for an hour or so. We ...

Couldn’t we fix the lackey catastrophe by using #pragma init_seg(user)?

Raymond ChenMay 8, 2017May 8, 201705/8/17

The lackey catastrophe is the nickname I gave to a problem where the lackey hired by the C runtime to destruct global objects runs too late. Specifically, it may run after other DLLs have already shut down, which means that you will have a problem if there is an object whose destructor relies on one of those already-shut-down DLLs. Commenter ...

Remember that in a stack trace, the addresses are return addresses, not call addresses

Raymond ChenMay 5, 2017May 5, 201705/5/17

You may be faced with a stack trace like this: But when you go to look at, say, line 930 of the file uicontroller.cpp, you don't see a call to UpdateDisplay: Why is the debugger saying that the call to UpdateDisplay came from line 930 when there's no call to UpdateDisplay anywhere in sight? Recall that the stack trace ...

The interaction between AppBars and Windows 10 virtual desktops

Raymond ChenMay 4, 2017May 4, 201705/4/17

A customer had a question about the interaction between Application Desktop Toolbars (commonly known as AppBars) and Windows 10 virtual desktops. "When we create our AppBar, it is shown on all virtual desktops. Is this expected behavior? Can I limit it to only one virtual desktop?" Yes, this is expected behavior. AppBars modify the work area ...

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