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The Old New Thing

August 2004 - The Old New Thing

Reading a contract from the other side: Application publishers

August 31, 2004 Aug 31, 2004 08/31/04
Raymond Chen
In an earlier article, I gave an example of reading a contract from the other side. Here's another example of how you can read a specification and play the role of the operating system. I chose this particular example because somebody wanted to do this and didn't realize that everything they needed was already documented; they just needed to...
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Importance of alignment even on x86 machines, part 2

August 30, 2004 Aug 30, 2004 08/30/04
Raymond Chen
The various Interlocked functions (InterlockedIncrement, and so on) require that the variable being updated be properly aligned, even on x86, a platform where the CPU silently fixes unaligned memory access invisibly. If you pass an unaligned pointer to one of the Interlocked functions, the operation will still succeed, but the result won't ...

The sociology of the mobile phone

August 30, 2004 Aug 30, 2004 08/30/04
Raymond Chen
It has become obvious by now that the mobile phone has changed the way people interact. These two papers were forwaded to me by a colleague, whose summary I am shamelessly lifting from heavily. First is a short paper titled Exploring the implications for social identity of the new sociology of the mobile phone. The much more fascinating...

Importance of alignment even on x86 machines

August 27, 2004 Aug 27, 2004 08/27/04
Raymond Chen
Sometimes unaligned memory access will hang the machine. Some video cards do not let you access all the video memory at one go. Instead, you are given a window into which you can select which subset of video memory ("bank") you want to see. For example, the EGA video card had 256K of memory, split into four 64K banks. If you wanted to access...

Why do some structures end with an array of size 1?

August 26, 2004 Aug 26, 2004 08/26/04
Raymond Chen
Some Windows structures are variable-sized, beginning with a fixed header, followed by a variable-sized array. When these structures are declared, they often declare an array of size 1 where the variable-sized array should be. For example: typedef struct _TOKEN_GROUPS { DWORD GroupCount; SID_AND_ATTRIBUTES Groups[ANYSIZE_ARRAY]; } ...
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Why can’t you treat a FILETIME as an __int64?

August 25, 2004 Aug 25, 2004 08/25/04
Raymond Chen
The FILETIME structure represents a 64-bit value in two parts: typedef struct _FILETIME { DWORD dwLowDateTime; DWORD dwHighDateTime; } FILETIME, *PFILETIME; You may be tempted to take the entire FILETIME structure and access it directly as if it were an __int64. After all, its memory layout exactly matches that of a 64-bit (little-...

Beware of non-null-terminated registry strings

August 24, 2004 Aug 24, 2004 08/24/04
Raymond Chen
Even though a value is stored in the registry as REG_SZ, this doesn't mean that the value actually ends with a proper null terminator. At the bottom, the registry is just a hierarchically-organized name/value database. And you can lie and get away with it. Lots of people lie about their registry data. You'll find lots of things that ...
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Summary of the recent spate of /3GB articles

August 22, 2004 Aug 22, 2004 08/22/04
Raymond Chen
A table of contents now that the whole thing is over. I hope. I'm not sure how successful this series has been, though, for it appears that even people who have read the articles continue to confuse virtual address space with physical address space. (Or maybe this person is merely mocking a faulty argument? I can't tell for sure...