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Secrets of Windows-95 Programming
Review by Lou Grinzo
Copyright (C) Dr. Dobb's Journal, March, 1996
Matt Pietrek, author of Windows Internals and coauthor (with Andrew
Schulman and Dave Maxey) of Undocumented Windows is back. His recently
published Windows-95 System Programming Secrets is a 760-page volume
so densely packed with details about the inner workings of Windows 95 that
it's hard to believe it was written by someone outside of Redmond. If you're
familiar with Pietrek's earlier books, you may wonder if Secrets
is Undocumented Windows-95, or if its more akin to Windows-95
Internals. As it turns out, its much closer to Internals than
Undocumented, but its a more useful and better book than either.
Pietrek gives us only ten chapters, the first clue that he covers topics
in exhaustive detail. The chapters are as follows: Putting Windows 95 in
Perspective; Whats New in Windows 95; Modules, Processes, and Threads; USER
and GDI Subsystems; Memory Management; VWINKERNEL32386 (Pietreks contraction
of VWIN32.VXD, KERNEL32.DLL, and KRNL386.EXE); Win16 Modules and Tasks;
The Portable Executable and COFF OBJ Formats; Spelunking on Your Own; and
Writing a Win32 API Spy.
After starting off with a good overview of Windows 95 and its place in the
Microsoft world, the book begins its heavy lifting in Chapter 3. Microsoft
Systems Journal editor Eric Maffei mentions in the foreword that Pietrek
has a degree in physics. Normally, I don't care about such biographical
material, but in this case, it's surprisingly relevant. Read this book and
you'll likely imagine Pietrek firing up his personal bit accelerator to
whack Windows 95 with high-energy ones and zeros, causing structures and
functions, documented and otherwise, to fly out in all directions. Pietrek
then collects the pieces and presents them to the reader in the form of
numerous pseudocode listings and detailed structure definitions. This approach
and underlying philosophy explain the strengths and one potential weakness
of this book.
Secrets is packed with details not likely documented anywhere else,
certainly not to this extent. Some of my favorites include the following:
- How to create and run Ring 0 code from within a Ring 3 application
program.
- How Windows 95 invokes dozens of INT 21h services from 32-bit code,
including KERNEL32.DLL.
- Thread-local storage (declared via __declspec(thread), not allocated
via TlsAlloc() calls) is available to a DLL only if it is implicitly loaded
by a program.
- The presence of Krn32Mutex, another mutex besides the now-infamous
Win16Mutex, which apparently controls access to certain parts of the kernel
(although Pietrek only mentions it in passing).
- KERNEL32 functions that can be blocked by the Win16Mutex, even though
Microsoft says this isnt the case.
The biggest eyebrow raiser of all is that Windows 95 fudges the free system
resource numbers. At boot time, Windows takes a snapshot of its resources
and then biases all ensuing calculations; 80 percent free system resources
no longer means 80 percent of all resources but 80 percent of what was free
after the system booted and already used part of the total. You get the
idea. A complete listing of the goodies would fill several pages.
There's one drawback to Pietrek's approach, however. Secrets is almost
entirely descriptive, and it sometimes leaves the reader to draw conclusions.
For example, Pietrek talks about the mechanisms for locating DLL-resident
routines by name or by export ordinal. He says it's more efficient to use
ordinals instead of function names when establishing linkage between an
.EXE and a .DLL, since no system memory is needed to store the list of names.
This is true as far as it goes, but it overlooks one of the truly perverse
situations that can trip up a Windows programan .EXE and .DLL that don't
agree on the mapping of ordinals to functions.
For example, if a DLL is changed after its matching EXE is built and the
DLL now assigns the ordinal 5 to Fred() instead of Barney(), the application
can accidentally call Fred(), even though its source refers to the function
as Barney(). Given that programs are often used with the wrong .DLLs in
the real world, this can lead to disaster. Secrets is an excellent
scientific treatment but offers little advice on application engineering.
In all fairness, such coverage isn't the book's intent, either stated or
implied, but it's something readers should keep in mind as they watch Pietrek
crack Windows 95 like a walnut.
At a time when most Windows programmers are struggling just to stay current
with the latest releases of compilers, frameworks, and third-party libraries,
it's natural to ask what place an under the covers book has on our already
sagging shelves. While not directly justifying his book, Pietrek himself
addresses this issue on page 184, where, after detailing some of the hoops
one of his sample programs had to jump through, he says:
The black box approach to programming that Microsoft wants us
to take is nice when writing Hello World programs, but it fails miserably
when attempting to write anything other than toy applications.
I couldn't agree more. Microsoft is largely responsible for making the creation
of robust, intelligent, and accommodating 32-bit Windows programs as tough
as it is. The Win32 documentation seems vast, almost luxurious, until you
begin serious work and you discover its shortcomings, like the fact that
extended error codes aren't documented, and numerous APIs are documented
either incorrectly or so poorly that you must burn precious time testing
them to see how they really work (or debugging your code once you, or your
users, see that your assumptions were wrong). This sorry situation creates
a genuine need for third-party books that fill in the gaps. Secrets
provides so much solid information and does it in such an enjoyable and
readable fashion that, even at $50.00, its easily one of the best titles
you can add to your Windows shelf.
Windows 95 System Programming Secrets
Matt Pietrek
IDG Books Worldwide, 1995
759 pp., $49.95
ISBN 1-56884-318-6
Electronic Review of Computer Books
Created 5/1/96 / Last modified 6/7/96 / webmaster@ercb.com