As part of the work I've been doing to answer this question about the technical workings of a glitch in Pokémon Red, I've been looking for a way to use a standard debugger to debug a Game Boy ROM. Although many of the emulators I've found have some support for debugging, nothing I've found so far has been helpful.
As a background, as of now I have tried to use the Visual Boy Advance built-in features to do debugging, but they aren't particularly useful for what I'm trying to do. VBA lacks the ability to set breakpoints, and since it steps forward at the level of frames rather than instructions I'm unable to see how the code is executing when I actually need it to. Although VBA says that it supports GDB debugging, I have been completely unable to get it working. I tried cross-compiling GDB for ARM as per the instructions, but could not get GDB to connect to the emulator (it would recognize that there was a program to connect to, but reported that the protocol had been violated). I repeated this with similar success in both Windows with Cygwin and on Ubuntu Linux. A friend and I tried to use Insight/GDB, but ran into exactly the same problems.
I also tried to use the NO$GBA debugger, but it refused to load my ROM for Pokémon Red (and then insulted me by saying that nothing I could try to do would fix it, as the file was just flat-out wrong).
Additionally, I tried downloading this version of Visual Boy Advance that claims to have a debugger in it, but for some reason I can't get it to enable the debugger. Pressing F11 as per its instructions has no effect whatsoever.
I believe that I've done my due diligence trying to get a debugger working, and I'm surprised that not a single one of them has worked. Does anyone know of a simple, straightforward way to debug Game Boy games using standard debugging techniques? I'm interested mostly in being able to put in memory write breakpoints (to see what routine is clobbering certain parts of memory). I would really appreciate it if someone with first-hand experience doing this could provide details on how to do this, as online resources on the subject seem pretty limited.
If you just want to debug your old gameboy games you can also use bgb which has several debugging options such as tracing, breakpoints, profiler and a lot more.
No$GBA is for GBA games; you want NO$GMB. Note that it's very buggy, and without a registered version (which may be impossible to get legitimately) rather crippled.
bgb is free and is very similar to No$GMB, but even buggier.
VBA is supposed to have a debugger, but there are a million different versions out there, so good luck finding the right one.
Check out the site GbaDev.org and look on the forums. This is the best spot on the web for GBA or even GBC questions. I can tell you that there are many versions of VBA and no$ out and about. The No$ you want was technically a pay for version, but Martin Korth hasn't been answering emails or anything for years now and I'm not sure of its status anymore. I can also answer some questions for you personally if you'd like or help you with the debugger.
I was able to go to the no$ main website, download the windows version of no$gmb, and use it to debug when run in B/W mode - should be sufficient for you needs. F12 opens roms, F2 toggles break points, space traces, F3 steps over, Ctrl-G takes you to an address (or symbol), and Ctrl_B allows conditional break points (by far the most powerful feature for you to use.) For instance, (3000)! would set a read/write breakpoint on address 0x3000. (0300..03003)! sets on a range. As you are looking for specific address changes, this is what you want.
VBA-M has a bunch of debugging tools under "Tools" menu, including memory & tile inspectors and a disassembler. It even has support for GDB. I didn't test with any frontends like gdbgui, or VSCode's GDB support, so YMMV, but the other built-in tools look pretty decent.
Go to the releases section for a build for your platform (arch linux also has it in AUR, for easy install in package manager.)
Here it is running some of the tools on a Mac:
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I've been a software developer for over twenty years, programming in C, Perl, SQL, Java, PHP, JavaScript, and recently Python. I've never had a problem I could not debug using some careful thought, and well-placed debugging print statements.
I respect that many people say that my techniques are primitive, and using a real debugger in an IDE is much better. Yet from my observation, IDE users don't appear to debug faster or more successfully than I can, using my stone knives and bear skins. I'm sincerely open to learning the right tools, I've just never been shown a compelling advantage to using visual debuggers.
Moreover, I have never read a tutorial or book that showed how to debug effectively using an IDE, beyond the basics of how to set breakpoints and display the contents of variables.
What am I missing? What makes IDE debugging tools so much more effective than thoughtful use of diagnostic print statements?
Can you suggest resources (tutorials, books, screencasts) that show the finer techniques of IDE debugging?
Sweet answers! Thanks much to everyone for taking the time. Very illuminating. I voted up many, and voted none down.
Some notable points:
Debuggers can help me do ad hoc inspection or alteration of variables, code, or any other aspect of the runtime environment, whereas manual debugging requires me to stop, edit, and re-execute the application (possibly requiring recompilation).
Debuggers can attach to a running process or use a crash dump, whereas with manual debugging, "steps to reproduce" a defect are necessary.
Debuggers can display complex data structures, multi-threaded environments, or full runtime stacks easily and in a more readable manner.
Debuggers offer many ways to reduce the time and repetitive work to do almost any debugging tasks.
Visual debuggers and console debuggers are both useful, and have many features in common.
A visual debugger integrated into an IDE also gives you convenient access to smart editing and all the other features of the IDE, in a single integrated development environment (hence the name).
Some examples of some abilities that an IDE debugger will give you over trace messages in code:
View the call stack at any point in time, giving you a context for your current stack frame.
Step into libraries that you are not able to re-compile for the purposes of adding traces (assuming you have access to the debug symbols)
Change variable values while the program is running
Edit and continue - the ability to change code while it is running and immediately see the results of the change
Be able to watch variables, seeing when they change
Be able to skip or repeat sections of code, to see how the code will perform. This allows you to test out theoretical changes before making them.
Examine memory contents in real-time
Alert you when certain exceptions are thrown, even if they are handled by the application.
Conditional breakpointing; stopping the application only in exceptional circumstances to allow you to analyse the stack and variables.
View the thread context in multi-threaded applications, which can be difficult to achieve with tracing (as the traces from different threads will be interleaved in the output).
In summary, print statements are (generally) static and you'll need to re-compile to get additional information if your original statements weren't detailed enough. The IDE removes this static barrier, giving you a dynamic toolkit at your fingertips.
When I first started coding, I couldn't understand what the big deal with debuggers was and I thought I could achieve anything with tracing (granted, that was on unix and the debugger was GDB). But once you learn how to properly use a graphical debugger, you don't want to go back to print statements.
An IDE debugger lets you change the
values of variables at run-time.
An IDE
debugger lets you see the value of
variables you didn't know you wanted
to see when execution began.
An IDE
debugger lets you see the call stack
and examine the state of the
function passed weird values.
(think this function is called from
hundreds of places, you don't know
where these weird values are coming
from)
An IDE debugger lets you
conditionally break execution at any
point in code, based on a condition,
not a line number.
An IDE debugger will let you examine the state of the program in the case of an unhandled exception instead of just crapping out.
Here's one thing that you definitely cannot debug with "print" statement, which is when a customer brings you memory dump and says "your program crashed, can you tell me why?"
Print statements all through your code reduces readability.
Adding and removing them for debug purposes only is time consuming
Debuggers track the call stack making it easy to see where you are
Variables can be modified on the fly
Adhoc commands can be executed during a pause in execution to assist diagnosing
Can be used IN CONJUNCTION with print statements : Debug.Write("...")
I think debugging using print statements is a lost art, and very important for every developer to learn. Once you know how to do that, certain classes of bugs become much easier to debug that way than through an IDE. Programmers who know this technique also have a really good feel of what's useful information to put in a log message (not to mention you'll actually end up reading the log) for non-debugging purposes as well.
That said, you really should know how to use the step-through debugger, since for a different class of bugs it is WAY easier. I'll leave it up to the other excellent answers already posted to explain why :)
Off the top of my head:
Debugging complex objects - Debuggers allow you to step deep into an object's innards. If your object has, say, an array of array of complex objects, print statements will only get you so far.
The ability to step past code - Debuggers will also allow you to skip past code you don't want to execute. True, you could do this manually as well, but it's that much more code you have to inject.
As alternative to debug in IDE you can try great Google Chrome extension PHP Console with php library that allows to:
See errors & exception in Chrome JavaScript console & in notification popups.
Dump any type variable.
Execute PHP code remotely.
Protect access by password.
Group console logs by request.
Jump to error file:line in your text editor.
Copy error/debug data to clipboard (for testers).
I haven't been developing for nearly 20 years, but I find that using a IDE / debugger I can :
see all kinds of things I might not have thought to have included in a print statement
step through code to see if it matches the path I thought it would take
set variables to certain values to make code take certain branches
One reason to use the IDE might be that modern IDEs support more than simple breakpoints. For example, Visual Studio offers the following advanced debugging features:
define conditional breakpoints (break only if a condition is met, or only on the n-th time the statement at the breakpoint is executed)
break on an unhandled exception or whenever a (specific) ecxeption is to be thrown
change variable while debugging
repeating a piece of code by setting the next line to be executed
etc.
Also, when using the debugger, you won't have to remove all your print statements once you have finished debugging.
In my experience, simple printouts have one huge advantage that no one seems to mention.
The problem with an IDE debugger is that everything happens at real time. You halt the program at a certain time, then you step through the steps one at a time and it is impossible to go back if you suddenly want to see what happened before. This is completley at odds with how our brain works. The brain collects information, and gradually forms an oppinion. It might be necessary to iterate the events several times in doing so, but once you have stepped past a certain point, you cannot go back.
In contrast to this, a selected series of printouts/logging gives you a "spatial projection of the temporal events". It gives you a complete story of what happened, and you can go back and fourth several times very easily by just scrolling up and down. It makes it easy to answer questions like "did A occur before B happened". It can make you see patterns you wernt even looking for.
So in my experience. IDE and debuggers are fantastic tools to solve simple problems when something in one single call-stack went wrong, and explore the current state of the machine at a certain crash.
However, when we approach more difficoult problems where gradual changing of state is involved. Where for example one algorithm corrupted a data structure, that in turn caused anohter algorithm to fail. Or if we want to answer questions like "how often do this happen", "do things happen in the order and in the way as I imagine them to happen". etc. Then the "old fashined" logging/printout technique has a clear advantage.
The best things is to use either technique when it is most suitable, for example use logging/printouts to get to some bugs, and pause at a breakpoint where we need to explore the current state more in detail.
There are also hybrid approaches. For example, when you do console.log(object) you get a data-structure widget in the log that you can expand and explore more in detail.This is many times a clear advantage over a "dead" text log.
One thing that I'm surprised I haven't seen in another answer is that the 2 debugging methods are not mutually exclusive.
printf debugging can work quite nicely even if you're using a standard debugger (whether IDE based or not). In particular with a logging framework so you can leave all or most of in the released product to help with diagnosing customer problems.
As noted in pretty much all the other answers here, the key nice thing about a standard debugger is that it allows you to more easily examine (and potentially change) the details of the program state. You don't have to know up front what you might want to look at - it's all available at your fingertips (more or less).
Because debugging multi-threaded applications with print statements will drive you bananas. Yes you can still do it with print statements but you'd need a lot of them and unravelling the sequential print out of statements to emulate the multi-threaded executiong would take a long long time.
Human brains are only single-threaded unfortunately.
Since you asked for pointers to books... As far as Windows debugging goes, John Robbins has several editions of a good book on Windows debugging:
Debugging Applications for Microsoft .NET and Microsoft Windows
Note that the most recent edition (Debugging Microsoft .NET 2.0 Applications) is .NET only, so you might want an older one (like in the first link) if you want native code debugging (it covers both .NET and native).
I personally feel the answer is as simple as "A integrated debugger/IDE gives you a wealth of different information quickly without the need for punching in commands. The information tends to be there in front of you without you haven't tell it what to show you.
The ease in which the information can be retrieved is what makes them better than just command-line debugging, or "printf" debugging.
Advantages of a debugger over a printf (note not an IDE debugger but any debugger)
Can set watchpoints.
This is one of my favourite ways of finding memory corruptions
Can debug a binary that you can't recompile at the moment
Can debug a binary that takes a long time to recompile
Can change variables on the fly
Can call functions on the fly
Doesn't have the problem where debug statemenets are not flushed and hence timing issue can not be debugged acuratly
Debuggers help with core dumps, print statements dont'
This is what I use most on VS.NET debugging windows:
Call stack, which is also a great way to figure out someone else's code
Locals & Watches.
Immediate window, which is basically a C# console and also lets me change variable contents, initialize stuff etc.
The ability to skip a line, set the next statement to be executed somewhere else.
The ability to hover over variables and have a tool-tip showing me their values.
In summary, it gives me a 360 degree view of the state of my executing code, not just a small window.
Never found a book teaching this kind of stuff, but then again, it seems to be quite simple, it's pretty much WYSIWYG.
A debugger can attach to a running process
Often easier to debug threaded code from a debugger
With an IDE debugger you can see the values of ALL the variables in the current scope (all the way up the call stack) whenever you halt execution.
Print statements can be great but dumping so much information to the screen at any given place can produce a whole lot of print statements.
Also, many IDE debuggers let you type in and evaluate methods, and evaluate members while you are halted, which further increases the amount of print statements you'd have to do.
I do feel that debuggers are better for some languages than for others however...
My general opinion is that IDE debuggers are absolutely, amazingly wonderful for managed languages like Java or C#, are fairly useful for C++, and are not very useful for scripting languages like Python (but it could be that I just haven't tried a good debugger for any scripting languages yet).
I absolutely love the debugger in IntelliJ IDEA when I do Java development. I just use print statements when I use Python.
As someone said above: Debugger != IDE.
gdb and (back in the day) TurboDebugger (stand-alone) work just fine for the languages they support[ed], thank you. (or an even older technology: Clipper debugger linked into the xBase executable itself) -- none of these required an IDE
Also, though C/++ coding is more rare, printf statements sometimes mask off the very bug you are trying to find! (initialization problems in auto vars on the stack, for instance, or memory allocation/alignment)
Finally, as others stated, you can use both. Some real-time-ish problems almost require a print, or at least a judicious "*video_dbg = ( is_good ? '+' : '-');" somewhere into video memory. My age is showing, this was under DOS :-)
TMTOWTDI
In addition to much of what the other posters have said, I really like stepping through one line at a time along with the computer, as it forces me to think about one line at a time. Often I will catch the bug without even looking at variable values simply because I am forced to look at it as I click the 'next line' button. However, I don't think my answer will help you, Bill, because you probably have this skill already.
As far as learning resources go, I haven't used any -- I just explore all the menus and options.
Is this even real question from real programmer?
Anyone who spent even 5 mins debugging with print statements and debugging with IDE - it will OCCUR to him/her without even asking!
I've used both prints and IDEs for debugging and I would much rather debug using an IDE. The only time for me when that doesn't work is in time critical situations (like debugging online games) where you litter the code with print statements and then look at the log files after it has gone horribly wrong. Then if you still cannot figure it out, add more prints and repeat.
Just wanted to mention a useful feature of a console debugger vs printf and vs debugger in an IDE.
You can attach to a remote application (obvioustly, compiled in DEBUG mode) and inspect its state dumping the debugger output to a file using POSIX tee utility. Compared to printf, you can choose where to output the state in run-time.
It helped me a lot when I was debugging Adobe Flash applications deployed in an agressive environment. You just need to define some actions that print required state in each breakpoint, start the console debugger with fdb | tee output.log, and walk through some breakpoints. After that you can print the log and analyse the information by thorough comparison of the state in different breakpoints.
Unfortunatelly, this feature [logging to a file] is rarely available in GUI debuggers, making developers compare the state of objects in their head.
By the way, my opinion is that one should plan where and what to debug before staring a debugger.
Well another thing is that if you join a new old project and nobody really knows how the code is doing what it's doing, then you can't debug by echoing variables/objects/... b/c you have no idea what code is executed at all.
At my job I am facing exactly that kind of situation and visual XDebuging helps me getting an idea about what is going on and where, at all.
Best regards
Raffael
In addition to the many things that have been already mentioned, one of the most important advantages of a debugger over printf is that using printf statements assumes that you know in which function the bug resides. In many cases you don't, so you have to make a few guesses and add print statements to many other functions in order to localise it. The bug may be in framework code or somewhere far removed from where you think it is. In a debugger it is far easier to set breakpoints to examine the state in different areas of the code and at different points in time.
Also, a decent debugger will let you do printf-style debugging by attaching conditions and actions to breakpoints, so that you still retain the benefits of printf debugging, but without modifying the code.
Debugging in an IDE is invaluable in an environment where error logs and shell access are unavailable, such as a shared host. In that case, an IDE with a remote debugger is the only tool which allows you to do simple things such as view stderr or stdout.
A problem with using print statements is it makes a mess of your code. IE, you have a function with 10 parts to it and you know it crashes somewhere, but you're not sure where. So you add in 10 extra print statements to pinpoint where the bug is. Once you've found and solved your bug, you now have to clean up by removing all of those print statements. Maybe you'll do that. Maybe you'll forget and it'll end up in production and your user's console will be full of debug prints.
Wauw, do I like this question. I never dared to pose it...
It seems that people just have different ways of working.
For me what works best is:
Having a solid mind model of my code, including memory management
Using instrumentation (like print statements) to follow what's happening.
I've earned my living programming for over 40 years now, working at non-trivial technical and scientific applications in C++ and Python daily, and I have the personal experience that a debugger doesn't help me a bit.
I don't say that's good. I don't say that's bad. I just want to share it.
It's not just debugging. An IDE helps you build better software faster in a lot of ways:
refactoring tools
intellisense to make api's more discoverable, or remind of exact spelling/case of familiar items(not much use if you've used the same system for 15 years, but that's rare)
save on typing by autocompleting variable and class names
find certain kinds of errors before you even start to compile
Automatically jump to variable/method/class declarations/definitions, even if they're not in the same file or folder.
Break on unhandled and handled exceptions
I could go on.
Is it possible to remotely debug a process started outside VB6?
The application is a VB6 application with quite a few dll/ocx resources. I am attempting to setup a ClickOnce deployment, using Registration-Free COM, of the VB6 app but have been getting errors when it executes.
My understanding of the way that VB6 redirects COM registerations will probably mean that this is not possible but I thought someone might have a better idea.
To support Darryl's answer suggesting Windbg - here's a 2006 blog post by a Microsoft guy about using Windbg with VB6, and 2004 blog post by another Microsoft guy with a brief introduction to Windbg.
EDIT: Just to make it totally clear. Windbg is a free standalone debugger from Microsoft. Compile your VB6 EXEs, DLLs and OCXs into native code with symbols (create PDB files) and you will be able to debug your ClickOnce application.
Key excerpt from the blog:
If you have limited access to the server machine then you can use the
remote debugging facilities of WinDbg. Attach a copy of WinDbg to the
process in the usual way and then turn it in to a debugging server
(check out .server in the WinDbg help). You can then connect to it
remotely from the File menu of WinDbg. It will be just like being
there except for the lack of noise from the server room fans. When
debugging a remote, your copy of WinDbg is just a very smart terminal
so all extensions, symbols and so on have to be on the remote server.
You set this up the exact same way for any DLL, VB6 or .NET.
The symbols for your component will not load until your component does
and so you have to let the server run at least that long. You can put
a break in early in your VB code if you want to stop the debugger at
that point but if you do, remember that it will stop there every time
through the code. Let’s assume that you let it run and then break in.
If you list the loaded symbols for your module with "x MyModule!*"
then you will see all of your functions together with a lot of symbols
bundled in there for you. VB adds interfaces and symbols quite
unashamedly but you don’t generally need to worry about those. One
thing that will probably look strange is that all class/method syntax
with the C++ double colon convention instead of the friendly little
dot. WinDbg doesn’t understand that VB is different and it is treated
just like any DLL with symbols.
From here, you can set breakpoints in the usual way (bp etc) and step
through code. You can also open up VB source code modules and set
breakpoints in them with F9 although the VB file extensions are not in
the source file type dropdown. Stepping through the code is revealing
but might be a little alarming if you have not seen the code that VB
generates for you before. You will be stepping through the assembler
and there is a lot of COM goo in there. Hresults get checked a lot.
You will probably need to refer to the source often to work out where
you are since it takes a bit of practice to be able to know what the
source code looked like. Variants are especially challenging because
VB does a lot of work for you there and what looks like a simple
equation can result in a great deal of code. Optimised code is even
harder because the order of execution is often very different from
what you might expect and it is harder than usual to see the data.
Data is not easy to get at this way. When you look at local variables
(dv is the command) then you may see that variables are simply listed
as eclipsed which means that the memory is being used for something
else as well within the function lifetime or that the name is not
unique in this context. Enums just show as integers or longs and
objects show as pointers. In fact, they always were exactly that but
the VB IDE hides that from you. VB strings are COM BSTRs (and
accordingly Unicode) under the covers and byte arrays are really char
arrays. You might be surprised to discover that VB strings are Unicode
as VB appears to have no support for anything but ANSI. That is
because the Ruby forms engine was ANSI only. The runtime converts the
Unicode strings to ANSI for Ruby and API calls although there are ways
to pass Unicode if you want.
You are not going to be able to get at the Err, App or Printer objects
since you would need to go through a lot of internal and completely
undocumented structures to get at them. Even if you could get there,
they would just be raw data without the accessor functions that you
use in VB. If you need to look at any of those fields, your best bet
is to embed debug code in the source code to copy their values to
somewhere that you can get at.
You can step in to the VB runtime if you want but it probably won’t be
very revealing if you are trying to debug your application. If you do,
you will notice that VB’s internals are very COM influenced. The
influence was actually two way since some COM ideas came from VB
originally.
You may see exceptions when running your code. Null reference
exceptions (i.e dereferencing a null pointer) are not uncommon or
anything to worry about. They will show up as first chance C000005
exceptions with a 0 or almost 0 address. The runtime will sometimes do
that if there are objects set to nothing but that is safe because the
only possible values are null or a valid value. You will also see
exceptions if your code does lookups in collections and the value is
not there. Because exceptions are now so expensive, you probably want
to avoid doing that if you can. Another exception that you will
commonly see is c000008f. If you look the number up then you will find
that it is a floating point inexact result exception. It is used in a
different meaning here – since we don’t generate real floating point
inexact result exceptions, they can safely be thrown to indicate VB
errors of the normal trappable type.
Debugging hangs and crashes in VB components is done very much in the
same way as with any other unmanaged component but it is just a little
harder because of the compilations described above. If you have to try
debugging VB code this way, I would strongly recommend that you start
on a "Hello world" application and work your way up. All the things
that may VB an easy language to code in make it a terrible language to
debug.
I believe that when debugging in VB6, it does not attach to a running binary but instead interprets the code within it's own process. This is why the Task Manager and Win32 APIs show VB6.exe as the running app when debugging.
Also as you say, VB6 sometimes short-circuits calls to COM libraries so intercepting these calls is not always possible.
You're probably going to have to resort to intelligent logging (i.e. log the values of variables around the points where the errors you are getting occur in the hope of locating the line of code it occurs on, and/or the state of relevant variables.)
Good luck
Have you tried windbg? Just make sure you have pdb files for the project.