I'm developing a frontend of LLVM IR, and want to attach debug information. I already made the %llvm.dbg.declare works, it can track my variable after this declaration. But I do not understand the another %llvm.dbg.value's purpose, can anyone tell me what situation I should use it? or any examples?
llvm.dbg.declare is sufficient if you're building your code without optimizations (which you should really do). In non-optimized code, locals live on the stack (in allocas) and llvm.dbg.declare tells the debugger where to find them
When trying to debug optimized code, things get murkier because locals can be in registers and there's no actual "memory location" the debugger can examine to always know the value of a local. This is where llvm.dbg.value comes in - it can explicitly notify the debugger that a local has changed, and its new value.
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I am struggling with debugging a model due to missing variable information in the Algorithmic Debugger's Local Browser window. As far as I understand the OpenModelica manuals, when setting a break point within an "algorithm" section and starting the debugger, all variables declared within the model's namespace should automatically show up in the Locals Browser.
Whichever of my own, but also the Modelica Std. Lib. example models I try, the Locals Browser window is always blank.
Is there a way of turning it on manually? Or do I need to add variables somehow manually? Or do I need to set any specific compile flags?
Thanks in advance for your time.
Stephan
Using: OpenModelica 1.17.0~dev-300-g00309fd on Ubuntu, with Modelica Lib. 3.2.3
I'm learning how to use a debugger and wonder if I'm missing the obvious.
My simple script includes two functions that work OK. The main code calls them repeatedly. Is there an easy way to single-step through ONLY the calling code, while the functions and the libraries they use run at normal speed?
I'm using python 2.7 and pyscripter, but I'd imagine that people might want this in other debuggers and languages. Perhaps there's a way to mark sections of code as trusted, and single-step the rest?
With search help from Dani's comment, I found several great explanations elsewhere on Stack Overflow. My favorite, from polygenelubricants on this Eclipse question:
When debugging lines of code, here are the usual scenarios:
(Step Into) A method is about to be invoked, and you want to debug into the code of that method, so the next step is to go into that method and continue debugging step-by-step.
(Step Over) A method is about to be invoked, but you're not interested in debugging this particular invocation, so you want the debugger to execute that method completely as one entire step.
(Step Return) You're done debugging this method step-by-step, and you just want the debugger to run the entire method until it returns as one entire step.
(Resume) You want the debugger to resume "normal" execution instead of step-by-step.
(Line Breakpoint) You don't care how it got there, but if execution reaches a particular line of code, you want the debugger to temporarily pause execution there so you can decide what to do.
Eclipse has other advanced debugging features, but these are the basic
fundamentals.
I have been tracing a BAD_ACCESS error using NSZombieEnabled. As error I get returned:
*** -[MyDocument respondsToSelector:]: message sent to deallocated instance 0x2671b0
I do know what this means,however what surprises me is that I don't call this function anywhere, not in MyDocument.m nor in any imported files.To be exact, I don't call this at all in my whole project. The debugger will not go to the actual code that causes the error, but only shows the assembly code, which, when I click on it, gives me and even bigger list of not understandable numbers.
Does anyone have an idea where this weird "respondsToSelector" could come from? Maybe from frameworks I am using? I am really confused.
Thanks for any help!
respondsToSelector: is widely used in frameworks. For instance, if your class is a delegate or data source (highly likely for MyDocument) the delegating object will use it to determine which delegate methods you support.
In general, the way to find out where a problem like this is happening is to set a breakpoint on objc_exception_throw() (Run->Show->Breakpoints, double-click where it says “Double-Click for Symbol”, type objc_exception_throw) and run under the debugger (Build->Build and Debug - Breakpoints On).
I have some code which generates a large quantity of ArgumentExceptions on one particular line (which is in a different developer's code, so I can't just change it), which are then caught and handled appropriately.
I'm trying to debug ArgumentExceptions which are happening in a different section of code (and are then caught and handled, so I can't just look at unhandled exceptions).
Is there some way to ignore the ArgumentExceptions originating from that particular other line of code, while still breaking on ArgumentExceptions which are thrown elsewhere?
You might be able to do this, but it depends on how the code you want to debug is located relative to the other developer's code, and whether or not you can modify (but not commit your changes) to his code.
The first thing you'll want to do is, at least temporarily, go to menu Tools -> Options -> Debugging in Visual Studio, and tick the "Just My Code" box. I assume this is available even in Express editions, but it may not be, and if it's not available for you I'm afraid the rest of what I have to say probably won't help.
Anyway, once you have that ticked, you will no longer see break-on-throw notifications for code that isn't "yours." This means code that is from an assembly not in your .sln, or code marked with the [DebuggerNonUserCode] attribute from System.Diagnostics. What I usually do then is temporarily decorate the offending methods with [DebuggerNonUserCode] until I'm done debugging what I need to debug, and then revert those changes before checking in to souce control.
It's not as elegant as I'd like (I'd love a "never break on throws from this site again" checkbox in the exception assistant), but it's better than nothing.
I believe there may be other debugger settings that could interact with how "Just My Code" works, so if this doesn't work for you let me know and I'll try to get a more accurate picture of what my settings look like when I do this.
If you are talking about the "Break On Throw" exception feature then no there is not. It is strictly a type based feature only and does not have any way to control for what section of the code throws the exception.
Your best bet is to just place breakpoints on all of the lines which throw or temporarily suspend throwing an exception from the one place that you care about.
If you know how you are calling it, I would set the break point in your code and then step into (F11) from there. You could also smack the programmer until they fix their code, which would have the effect of making you feel better (unless you are a pacifist) and maybe they won't have so many ArgumentExceptions in their code (which would probably make you feel better even if you are a pacifist).
Sounds like using exceptions as flow control. If the one you're trying to debug occurs later in the program, you can try to attach the debugger later, or you can wait until after the program is running to turn on breaking when an ArgumentException is thrown.
Try to limit the scope as well - if the exception you're interested in derives from but is not exactly ArgumentException, break on that one instead.
Tell the other developer to fix his code.
Edit: In .NET 4, you can attach a handler to the AppDomain.FirstChanceException event, filter out non-ArgumentException excepitons and filter out the bad one based on the call stack.
The links in the comments are great.
i think Conditional Breakpoints are what you're looking for here. You can do this by right clicking your breakpoint and clicking the Condition... menu item.
I have a workspace for running an H.263 Video Encoder in a loop for 31 times i.e. the main is executed 31 times to generate 31 different encoded bit streams. This MS Visual Studio 2005 Workspace has all C source files. When i create a "DEBUG" configuration for the workspace and build and execute it, it runs fine, i.e. it generates all the 31 output files as expected.
But when I set the configuration of the workspace to "RELEASE" mdoe, and repeat the process, the encoder crashes at some test case run.
Now to debug this is verified following:
Analyzed the code to see if there was any variable initialization being missed out in every run of the encoder
Checked the various Workspace(Solution) options in both the modes (DEBUG and RELEASE).
There are some obvious differences, but i turned the optimization related options explicitly same in both modes.
But still could not nail the problem and find a fix for that. Any pointers?
-Ajit.
It's hard to say what the problem might be without carefully inspecting the code. However...
One of the differences between debug and release builds is how the function call stack frame is set up. There are certain classes of bad things you can do (like calling a function with the wrong number of arguments) that are not fatal in a debug build but crash horribly in a release build. Perhaps you could try changing the stack frame related options (I forget what they're called, sorry) in the release build to the same as the debug build and see whether that helps.
Another thing might be to enable all the warnings you possibly can, and fix them all.
Could be a concurrency problem of two threads. The DEBUG configuration slows the execution down, so the problem does not occur. But, only a guess.
Interesting problem.. Are you sure you have no conditional compilation code lurking around that is not being compiled in release mode? i.e:
#if (DEBUG)
// Debug Code here
#else
// Release Code here
#endif
Thats the only thing I can really think of.. Never experienced anything like this myself..
Can you add the debug symbols to the release build and run it in the debugger to see where and why it crashed?
Yeah, those bastard crashes are the hardest to fix. Fortunatly, there are some steps you can do that will give you clues before you resort to manually looking at the code and hope to find the needle.
When does it crash? At every test? At a specific test? What does that test does that the others don't?
What's the error? If it's an access violation, is there a pattern to where it happens? If the addresses are low, it might mean there is an uninitialised pointer somewhere.
Is the program crashing with Debug configuration but without the debugger attached? If so, it's most likely a thread synchronisation problem as John Smithers pointed out.
Have you tried running the code through an analyser such as Purify? It's slow but it's usually worth the wait.
Try to debug the release configuration anyway. It will only dump assemblies but it can still give you an indication of what happens such as if the code pointer jumps in the middle of garbage or hits a breakpoint in an external library.
Are you on an Intel architecture? If not, watch for memory alignement errors, they hard crash without warning on some architectures and those codec algorithm tend to create those situations a lot since they are overly optimized.
Are you sure there are no precompile directives that, say, ignores some really important code in Release mode but allows them in Debug?
Also, have you implemented any logging that might point out to the precise assembly that's throwing the error?
I would look at the crash in more detail - if it's crashing in a test case, then it sounds pretty easily reproducible, which is usually most of the challenge.
Another thing to consider: in debug mode, the variables are initialized with 0xCCCCCCCC instead of zero. That might have some nasty side effects.