I was wondering how hard it would be to create a set-up under Windows where a regular ReadFile on certain files is being redirected by the file system to actually run (e.g. ShellExecute) those files, and then the new process' stdout is being used as the file content streamed out to the ReadFile call to the callee...
What I envision the set-up to look like, is that you can configure it to denote a certain folder as 'special', and that this extra functionality is then only available on that folder's content (so it doesn't need to be disk-wide). It might be accessible under a new drive letter, or a path parallel to the source folder; the location it is hooked up to is irrelevant to me.
To those of you that wonder if this is a classic xy problem: it might very well be ;) It's just that this idea has intrigued me, and I want to know what possibilities there are. In my particular case I want to employ it to #include content in my C++ code base, where the actual content included is being made up on the spot, different on each compile round. I could of course also create a script to create such content to include, call it as a pre-build step and leave it at that, but why choose the easy route.
Maybe there are already ready-made solutions for this? I did an extensive Google search for it, but came out empty handed. But then I'm not sure I already know all the keywords involved to do a good search...
When coding up something myself, I think a minifilter driver might be needed intercepting ReadFile calls, but then it must at that spot run usermode apps from kernel space - not a happy marriage I assume. Or use an existing file system driver framework that allows for usermode parts, but I found the price of existing solutions to be too steep for my taste (several thousand dollars).
And I also assume that a standard file system (minifilter) driver might be required to return a consistent file size for such files, although the actual data size returned through ReadFile would of course differ on each call. Not to mention negating any buffering that takes place.
All in all I think that a create-it-yourself solution will take quite some effort, especially when you have never done Windows driver development in your life :) Although I see myself quite capable of learning up on it, the time invested will be prohibitive I think.
Another approach might be to hook ReadFile calls from the process doing the ReadFile - via IAT hooking, or via code injection. But I want this solution to more work 'out-of-the-box', i.e. all ReadFile requests for these special files trigger the correct behavior, regardless of origin. In my case I'd need to intercept my C++ compiler (G++) behavior, but that one is called on the fly by the IDE, so I see no easy way to detect it's startup and hook it up quickly before it does it's ReadFiles. And besides, I only want certain files to be special in this regard; intercepting all ReadFiles for a certain process is overkill.
You want something like FUSE (which I used with profit many times), but for Windows. Apparently there's Dokan, I've never used it but seems to be well known enough (and, at very least, can be used as an inspiration to see "how it's done").
Related
Ok, it may be a bit difficult to explain:
Suppose someone creates a Windows application (using C# or any other language) that uses the GetDesktopWindow() function on the user32.dll to capture a Screenshot and then sends this image to any online service.
Since it's custom made application, no anti-virus software will be able to determine that it's a virus because it's still an unknown application for it. Also, there are legitimate uses for such API, so it's not necessarily a virus, it can be a harmless window capture tool or some kind of espionage tool.
What I want to know is: Is there any way to see what a specific EXE file does regarding the Windows functions? Can I know if "myapp.exe" uses GetDesktopWindow() of user32.dll?
This is only one example. There are plenty other Windows endpoints that I would like to know when they're used by any application.
Is there a way to do that?
It depends to what lengths you want to go doing that. It's essentially a game of cat and mouse - bad actors will attempt to find new ways to circumvent your detection by jumping through some obscure hoops, you will add more sophisticated detection methods for those tricks, they will think of new tricks, and so on.
Also, it depends on whether you want to statically or dynamically determine that, and whether you actually want to know if GetDesktopWindow is called or if "the program gets a handle to the desktop window" (which can be achieved in other ways as well).
Here is a non-exhaustive list of ideas:
You could statically determine whether the function is imported by looking at the import directory. Research the PE file structure to find out more. This article may help.
This method of detection can be easily circumvented by dynamically importing the function using LoadLibrary and GetProcAddress.
You could scan the file for the string GetDesktopWindow to detect possible usage for dynamic import.
This method of detection can be easily circumvented by packing, encrypting or otherwise obfuscating the name of the dynamically imported function.
You could dynamically observe whether the GetDesktopWindow function gets called by registering an AppInit_DLL or a global hook which is injected into every new process and hook the GetDesktopWindow function from inside the process by overwriting its first bytes with a jump to your own code, notifying your detection component somehow, executing the original bytes and jumping back. (Microsoft Detours can help there.)
This method of detection can be circumvented if the target notices the hook and removes it before calling, since its in its own process space. (You could also do some tricks with acting like a debugger and setting a hardware breakpoint on the first instruction of GetDesktopWindow, but yet again there would be ways to detect or circumvent that since the target could also modify the debug registers.)
You could build a driver that does this from kernel-mode instead, but now we are getting really deep.
Note that until now we focused on the actual GetDesktopWindow function from user32.dll. But what if the target will just use a different way to achieve its goal of getting a desktop window handle?
The desktop window handle for the current thread is stored in the TIB (thread information block) which is accessible via fs:[18] from user mode. You can see this in the GetDesktopWindow source code of ReactOS which is pretty accurate compared to Microsoft's actual implementation (which you can verify by looking at it in a debugger). The target could therefore just access the TIB and extract this value, without even calling GetDesktopWindow at all.
The target could just take a known top-level window such as the shell's hidden compatibility window which you'll get via GetShellWindow() or - to avoid detection of GetShellWindow too - for example FindWindow(NULL, "Program Manager") (or even a newly created window!) and call GetAncestor(hWnd, GA_PARENT) on it to get the desktop window handle.
I'm sure, with some creativity, your adversaries will come up with more clever ideas than these.
Also, if we take this one step further and take a look at the ultimate goal of taking a screenshot, there as well exist other ways to achieve that. First example coming to mind: They could use keybd_event to emulate pressing the PrnSc key and then read the screenshot out of the clipboard data.
So it's all a matter of how far you want to take this.
By the way, you may find the drltrace project interesting - it is a library call tracer.
I'm working on a third-party program that aggregates data from a bunch of different, existing Windows programs. Each program has a mechanism for exporting the data via the GUI. The most brain-dead approach would have me generate extracts by using AutoIt or some other GUI manipulation program to generate the extractions via the GUI. The problem with this is that people might be interacting with the computer when, suddenly, some automated program takes over. That's no good. What I really want to do is somehow have a program run once a day and silently (i.e. without popping up any GUIs) export the data from each program.
My research is telling me that I need to hook each application (assume these applications are always running) and inject a custom DLL to trigger each export. Am I remotely close to being on the right track? I'm a fairly experienced software dev, but I don't know a whole lot about reverse engineering or hooking. Any advice or direction would be greatly appreciated.
Edit: I'm trying to manage the availability of a certain type of professional. Their schedules are stored in proprietary systems. With their permission, I want to install an app on their system that extracts their schedule from whichever system they are using and uploads the information to a central server so that I can present that information to potential clients.
I am aware of four ways of extracting the information you want, both with their advantages and disadvantages. Before you do anything, you need to be aware that any solution you create is not guaranteed and in fact very unlikely to continue working should the target application ever update. The reason is that in each case, you are relying on an implementation detail instead of a pre-defined interface through which to export your data.
Hooking the GUI
The first way is to hook the GUI as you have suggested. What you are doing in this case is simply reading off from what an actual user would see. This is in general easier, since you are hooking the WinAPI which is clearly defined. One danger is that what the program displays is inconsistent or incomplete in comparison to the internal data it is supposed to be representing.
Typically, there are two common ways to perform WinAPI hooking:
DLL Injection. You create a DLL which you load into the other program's virtual address space. This means that you have read/write access (writable access can be gained with VirtualProtect) to the target's entire memory. From here you can trampoline the functions which are called to set UI information. For example, to check if a window has changed its text, you might trampoline the SetWindowText function. Note every control has different interfaces used to set what they are displaying. In this case, you are hooking the functions called by the code to set the display.
SetWindowsHookEx. Under the covers, this works similarly to DLL injection and in this case is really just another method for you to extend/subvert the control flow of messages received by controls. What you want to do in this case is hook the window procedures of each child control. For example, when an item is added to a ComboBox, it would receive a CB_ADDSTRING message. In this case, you are hooking the messages that are received when the display changes.
One caveat with this approach is that it will only work if the target is using or extending WinAPI controls.
Reading from the GUI
Instead of hooking the GUI, you can alternatively use WinAPI to read directly from the target windows. However, in some cases this may not be allowed. There is not much to do in this case but to try and see if it works. This may in fact be the easiest approach. Typically, you will send messages such as WM_GETTEXT to query the target window for what it is currently displaying. To do this, you will need to obtain the exact window hierarchy containing the control you are interested in. For example, say you want to read an edit control, you will need to see what parent window/s are above it in the window hierarchy in order to obtain its window handle.
Reading from memory (Advanced)
This approach is by far the most complicated but if you are able to fully reverse engineer the target program, it is the most likely to get you consistent data. This approach works by you reading the memory from the target process. This technique is very commonly used in game hacking to add 'functionality' and to observe the internal state of the game.
Consider that as well as storing information in the GUI, programs often hold their own internal model of all the data. This is especially true when the controls used are virtual and simply query subsets of the data to be displayed. This is an example of a situation where the first two approaches would not be of much use. This data is often held in some sort of abstract data type such as a list or perhaps even an array. The trick is to find this list in memory and read the values off directly. This can be done externally with ReadProcessMemory or internally through DLL injection again. The difficulty lies mainly in two prerequisites:
Firstly, you must be able to reliably locate these data structures. The problem with this is that code is not guaranteed to be in the same place, especially with features such as ASLR. Colloquially, this is sometimes referred to as code-shifting. ASLR can be defeated by using the offset from a module base and dynamically getting the module base address with functions such as GetModuleHandle. As well as ASLR, a reason that this occurs is due to dynamic memory allocation (e.g. through malloc). In such cases, you will need to find a heap address storing the pointer (which would for example be the return of malloc), dereference that and find your list. That pointer would be prone to ASLR and instead of a pointer, it might be a double-pointer, triple-pointer, etc.
The second problem you face is that it would be rare for each list item to be a primitive type. For example, instead of a list of character arrays (strings), it is likely that you will be faced with a list of objects. You would need to further reverse engineer each object type and understand internal layouts (at least be able to determine offsets of primitive values you are interested in in terms of its offset from the object base). More advanced methods revolve around actually reverse engineering the vtable of objects and calling their 'API'.
You might notice that I am not able to give information here which is specific. The reason is that by its nature, using this method requires an intimate understanding of the target's internals and as such, the specifics are defined only by how the target has been programmed. Unless you have knowledge and experience of reverse engineering, it is unlikely you would want to go down this route.
Hooking the target's internal API (Advanced)
As with the above solution, instead of digging for data structures, you dig for the internal API. I briefly covered this with when discussing vtables earlier. Instead of doing this, you would be attempting to find internal APIs that are called when the GUI is modified. Typically, when a view/UI is modified, instead of directly calling the WinAPI to update it, a program will have its own wrapper function which it calls which in turn calls the WinAPI. You simply need to find this function and hook it. Again this is possible, but requires reverse engineering skills. You may find that you discover functions which you want to call yourself. In this case, as well as being able to locate the location of the function, you have to reverse engineer the parameters it takes, its calling convention and you will need to ensure calling the function has no side effects.
I would consider this approach to be advanced. It can certainly be done and is another common technique used in game hacking to observe internal states and to manipulate a target's behaviour, but is difficult!
The first two methods are well suited for reading data from WinAPI programs and are by far easier. The two latter methods allow greater flexibility. With enough work, you are able to read anything and everything encapsulated by the target but requires a lot of skill.
Another point of concern which may or may not relate to your case is how easy it will be to update your solution to work should the target every be updated. With the first two methods, it is more likely no changes or small changes have to be made. With the second two methods, even a small change in source code can cause a relocation of the offsets you are relying upon. One method of dealing with this is to use byte signatures to dynamically generate the offsets. I wrote another answer some time ago which addresses how this is done.
What I have written is only a brief summary of the various techniques that can be used for what you want to achieve. I may have missed approaches, but these are the most common ones I know of and have experience with. Since these are large topics in themselves, I would advise you ask a new question if you want to obtain more detail about any particular one. Note that in all of the approaches I have discussed, none of them suffer from any interaction which is visible to the outside world so you would have no problem with anything popping up. It would be, as you describe, 'silent'.
This is relevant information about detouring/trampolining which I have lifted from a previous answer I wrote:
If you are looking for ways that programs detour execution of other
processes, it is usually through one of two means:
Dynamic (Runtime) Detouring - This is the more common method and is what is used by libraries such as Microsoft Detours. Here is a
relevant paper where the first few bytes of a function are overwritten
to unconditionally branch to the instrumentation.
(Static) Binary Rewriting - This is a much less common method for rootkits, but is used by research projects. It allows detouring to be
performed by statically analysing and overwriting a binary. An old
(not publicly available) package for Windows that performs this is
Etch. This paper gives a high-level view of how it works
conceptually.
Although Detours demonstrates one method of dynamic detouring, there
are countless methods used in the industry, especially in the reverse
engineering and hacking arenas. These include the IAT and breakpoint
methods I mentioned above. To 'point you in the right direction' for
these, you should look at 'research' performed in the fields of
research projects and reverse engineering.
I am writing a scriptable game engine, for which I have a large number of classes that perform various tasks. The size of the engine is growing rapidly, and so I thought of splitting the large executable up into dll modules so that only the components that the game writer actually uses can be included. When the user compiles their game (which is to say their script), I want the correct dll's to be part of the final executable. I already have quite a bit of overlay data, so I figured I might be able to store the dll's as part of this block. My question boils down to this:
Is it possible to trick LoadLibrary to start reading the file at a certain offset? That would save me from having to either extract the dll into a temporary file which is not clean, or alternatively scrapping the automatic inclusion of dll's altogether and simply instructing my users to package the dll's along with their games.
Initially I thought of going for the "load dll from memory" approach but rejected it on grounds of portability and simply because it seems like such a horrible hack.
Any thoughts?
Kind regards,
Philip Bennefall
You are trying to solve a problem that doesn't exist. Loading a DLL doesn't actually require any physical memory. Windows creates a memory mapped file for the DLL content. Code from the DLL only ever gets loaded when your program calls that code. Unused code doesn't require any system resources beyond reserved memory pages. You have 2 billion bytes worth of that on a 32-bit operating system. You have to write a lot of code to consume them all, 50 megabytes of machine code is already a very large program.
The memory mapping is also the reason you cannot make LoadLibrary() do what you want to do. There is no realistic scenario where you need to.
Look into the linker's /DELAYLOAD option to improve startup performance.
I think every solution for that task is "horrible hack" and nothing more.
Simplest way that I see is create your own virtual drive that present custom filesystem and hacks system access path from one real file (compilation of your libraries) to multiple separate DLL-s. For example like TrueCrypt does (it's open-source). And than you may use LoadLibrary function without changes.
But only right way I see is change your task and don't use this approach. I think you need to create your own script interpreter and compiler, using structures, pointers and so on.
The main thing is that I don't understand your benefit from use of libraries. I think any compiled code in current time does not weigh so much and may be packed very good. Any other resources may be loaded dynamically at first call. All you need to do is to organize the working cycles of all components of the script engine in right way.
I am making a protocol, client and server which provide file transfer functionality similar to FTP (among other features). One difference between my protocol and FTP is that I would like to store a copy of the remote server's directory structure in a local cache. The server will only be running on Windows (written in C++) so any applicable Win32 API calls would be appreciated (if any). When initially connected, the client requests the immediate children (both files and directories, just like "ls" or "dir" with no options), then when a user navigates into a directory, this step repeats with the new parent like you might expect.
Of course, most of the time, if the same directory of a given server is requested twice by a client, the directory's contents will be the same. Therefore I would like to cache the results of each directory listing on the client. I would like a simple way of implementing this, but it would need to take into account expiring cache entries because of file/directory access and modification time and name changes, which is the tricky part. I would ideally like something which would enable almost instant directory listings by the client, with something like a hash which takes into account not only file contents, but also changes in subdirectories' contents' filenames, data, modification and access dates, etc.
This is NOT something that could completely rely on FileSystemWatcher (or similar) objects because it would need to maintain this cache even if the program is only run occasionally. Of course these would be nice to help maintain the cache, but that's only part of the problem.
My best(?) idea so far is using FindFirstFile() and FindNextFile(), and sorting (somehow), concatenating and hashing values found in the WIN32_FIND_DATA structs (with file contents maybe), and using that as a token for expiration (just to indicate change in any of these fields). Then I would have one of these tokens for each directory. When a directory is requested, the server would hash everything and compare that to the cached hash provided by the client, and if it's different, return the normal data, otherwise an HTTP 304 equivalent. Is there a less elaborate way of doing something like this? Does "directory last modified date" take into account every one of its subdirectories' files' modification dates under all circumstances? I'm sure that the built-in Windows indexing service has something like this but ideally I wouldn't need to rely on it.
Because this service is for file sharing, something involving hashes would be especially nice so that I could automatically and efficiently find other people who are sharing a given file, but that's less of a concern then hosing the disk during the hash calculation.
I'm wondering what others who are more experienced than I am with programming would do to solve this problem (rsync and subversion have solved similar problems but not identical).
You're asking a lot of a File System Implementation of Very Little Brain (with apologies to A. A. Milne).
This is actually well-trammeled ground and you'd do well to look at the existing literature on distributed filesystems. AFS comes to mind as an example of a very well studied approach.
I doubt you'll be able to come up with something useful and accurate without doing some serious homework. Put another way, 'twould be folly to ignore all the prior art.
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Interview question-
Often its pretty easier to debug a program once you have trouble with your code.You can put watches,breakpoints and etc.Life is much easier because of debugger.
But how to debug a program without a debugger?
One possible approach which I know is simply putting print statements in your code wherever you want to check for the problems.
Are there any other approaches other than this?
As its a general question, its not restricted to any specific language.So please share your thoughts on how you would have done it?
EDIT- While submitting your answer, please mention a useful resource (if you have any) about any concept. e.g. Logging
This will be lot helpful for those who don't know about it at all.(This includes me, in some cases :)
UPDATE: Michal Sznajderhas put a real "best" answer and also made it a community wiki.Really deserves lots of up votes.
Actually you have quite a lot of possibilities. Either with recompilation of source code or without.
With recompilation.
Additional logging. Either into program's logs or using system logging (eg. OutputDebugString or Events Log on Windows). Also use following steps:
Always include timestamp at least up to seconds resolution.
Consider adding thread-id in case of multithreaded apps.
Add some nice output of your structures
Do not print out enums with just %d. Use some ToString() or create some EnumToString() function (whatever suits your language)
... and beware: logging changes timings so in case of heavily multithreading you problems might disappear.
More details on this here.
Introduce more asserts
Unit tests
"Audio-visual" monitoring: if something happens do one of
use buzzer
play system sound
flash some LED by enabling hardware GPIO line (only in embedded scenarios)
Without recompilation
If your application uses network of any kind: Packet Sniffer or I will just choose for you: Wireshark
If you use database: monitor queries send to database and database itself.
Use virtual machines to test exactly the same OS/hardware setup as your system is running on.
Use some kind of system calls monitor. This includes
On Unix box strace or dtrace
On Windows tools from former Sysinternals tools like http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx, ProcessExplorer and alike
In case of Windows GUI stuff: check out Spy++ or for WPF Snoop (although second I didn't use)
Consider using some profiling tools for your platform. It will give you overview on thing happening in your app.
[Real hardcore] Hardware monitoring: use oscilloscope (aka O-Scope) to monitor signals on hardware lines
Source code debugging: you sit down with your source code and just pretend with piece of paper and pencil that you are computer. Its so called code analysis or "on-my-eyes" debugging
Source control debugging. Compare diffs of your code from time when "it" works and now. Bug might be somewhere there.
And some general tips in the end:
Do not forget about Text to Columns and Pivot Table in Excel. Together with some text tools (awk, grep or perl) give you incredible analysis pack. If you have more than 32K records consider using Access as data source.
Basics of Data Warehousing might help. With simple cube you may analyse tons of temporal data in just few minutes.
Dumping your application is worth mentioning. Either as a result of crash or just on regular basis
Always generate you debug symbols (even for release builds).
Almost last but not least: most mayor platforms has some sort of command line debugger always built in (even Windows!). With some tricks like conditional debugging and break-print-continue you can get pretty good result with obscure bugs
And really last but not least: use your brain and question everything.
In general debugging is like science: you do not create it you discover it. Quite often its like looking for a murderer in a criminal case. So buy yourself a hat and never give up.
First of all, what does debugging actually do? Advanced debuggers give you machine hooks to suspend execution, examine variables and potentially modify state of a running program. Most programs don't need all that to debug them. There are many approaches:
Tracing: implement some kind of logging mechanism, or use an existing one such as dtrace(). It usually worth it to implement some kind of printf-like function that can output generally formatted output into a system log. Then just throw state from key points in your program to this log. Believe it or not, in complex programs, this can be more useful than raw debugging with a real debugger. Logs help you know how you got into trouble, while a debugger that traps on a crash assumes you can reverse engineer how you got there from whatever state you are already in. For applications that you use other complex libraries that you don't own that crash in the middle of them, logs are often far more useful. But it requires a certain amount of discipline in writing your log messages.
Program/Library self-awareness: To solve very specific crash events, I often have implemented wrappers on system libraries such as malloc/free/realloc which extensions that can do things like walk memory, detect double frees, attempts to free non-allocated pointers, check for obvious buffer over-runs etc. Often you can do this sort of thing for your important internal data types as well -- typically you can make self-integrity checks for things like linked lists (they can't loop, and they can't point into la-la land.) Even for things like OS synchronization objects, often you only need to know which thread, or what file and line number (capturable by __FILE__, __LINE__) the last user of the synch object was to help you work out a race condition.
If you are insane like me, you could, in fact, implement your own mini-debugger inside of your own program. This is really only an option in a self-reflective programming language, or in languages like C with certain OS-hooks. When compiling C/C++ in Windows/DOS you can implement a "crash-hook" callback which is executed when any program fault is triggered. When you compile your program you can build a .map file to figure out what the relative addresses of all your public functions (so you can work out the loader initial offset by subtracting the address of main() from the address given in your .map file). So when a crash happens (even pressing ^C during a run, for example, so you can find your infinite loops) you can take the stack pointer and scan it for offsets within return addresses. You can usually look at your registers, and implement a simple console to let you examine all this. And voila, you have half of a real debugger implemented. Keep this going and you can reproduce the VxWorks' console debugging mechanism.
Another approach, is logical deduction. This is related to #1. Basically any crash or anomalous behavior in a program occurs when it stops behaving as expected. You need to have some feed back method of knowing when the program is behaving normally then abnormally. Your goal then is to find the exact conditions upon which your program goes from behaving correctly to incorrectly. With printf()/logs, or other feedback (such as enabling a device in an embedded system -- the PC has a speaker, but some motherboards also have a digital display for BIOS stage reporting; embedded systems will often have a COM port that you can use) you can deduce at least binary states of good and bad behavior with respect to the run state of your program through the instrumentation of your program.
A related method is logical deduction with respect to code versions. Often a program was working perfectly at one state, but some later version is not longer working. If you use good source control, and you enforce a "top of tree must always be working" philosophy amongst your programming team, then you can use a binary search to find the exact version of the code at which the failure occurs. You can use diffs then to deduce what code change exposes the error. If the diff is too large, then you have the task of trying to redo that code change in smaller steps where you can apply binary searching more effectively.
Just a couple suggestions:
1) Asserts. This should help you work out general expectations at different states of the program. As well familiarize yourself with the code
2) Unit tests. I have used these at times to dig into new code and test out APIs
One word: Logging.
Your program should write descriptive debug lines which include a timestamp to a log file based on a configurable debug level. Reading the resultant log files gives you information on what happened during the execution of the program. There are logging packages in every common programming language that make this a snap:
Java: log4j
.Net: NLog or log4net
Python: Python Logging
PHP: Pear Logging Framework
Ruby: Ruby Logger
C: log4c
I guess you just have to write fine-grain unit tests.
I also like to write a pretty-printer for my data structures.
I think the rest of the interview might go something like this...
Candidate: So you don't buy debuggers for your developers?
Interviewer: No, they have debuggers.
Candidate: So you are looking for programmers who, out of masochism or chest thumping hamartia, make things complicated on themselves even if they would be less productive?
Interviewer: No, I'm just trying to see if you know what you would do in a situation that will never happen.
Candidate: I suppose I'd add logging or print statements. Can I ask you a similar question?
Interviewer: Sure.
Candidate: How would you recruit a team of developers if you didn't have any appreciable interviewing skill to distinguish good prospects based on relevant information?
Peer review. You have been looking at the code for 8 hours and your brain is just showing you what you want to see in the code. A fresh pair of eyes can make all the difference.
Version control. Especially for large teams. If somebody changed something you rely on but did not tell you it is easy to find a specific change set that caused your trouble by rolling the changes back one by one.
On *nix systems, strace and/or dtrace can tell you an awful lot about the execution of your program and the libraries it uses.
Binary search in time is also a method: If you have your source code stored in a version-control repository, and you know that version 100 worked, but version 200 doesn't, try to see if version 150 works. If it does, the error must be between version 150 and 200, so find version 175 and see if it works... etc.
use println/log in code
use DB explorer to look at data in DB/files
write tests and put asserts in suspicious places
More generally, you can monitor side effects and output of the program, and trigger certain events in the program externally.
A Print statement isn't always appropriate. You might use other forms of output such as writing to the Event Log or a log file, writing to a TCP socket (I have a nice utility that can listen for that type of trace from my program), etc.
For programs that don't have a UI, you can trigger behavior you want to debug by using an external flag such as the existence of a file. You might have the program wait for the file to be created, then run through a behavior you're interested in while logging relevant events.
Another file's existence might trigger the program's internal state to be written to your logging mechanism.
like everyone else said:
Logging
Asserts
Extra Output
&
your favorite task manager or process
explorer
links here and here
Another thing I have not seen mentioned here that I have had to use quite a bit on embedded systems is serial terminals.
You can cannot a serial terminal to just about any type of device on the planet (I have even done it to embedded CPUs for hydraulics, generators, etc). Then you can write out to the serial port and see everything on the terminal.
You can get real fancy and even setup a thread that listens to the serial terminal and responds to commands. I have done this as well and implemented simple commands to dump a list, see internal variables, etc all from a simple 9600 baud RS-232 serial port!
Spy++ (and more recently Snoop for WPF) are tremendous for getting an insight into Windows UI bugs.
A nice read would be Delta Debugging from Andreas Zeller. It's like binary search for debugging