Attaching the debugger to a process doesn't seem to do anything - c++

I've got a C++ application that doesn't quite work right. When I ask VisualStudio to run it, it runs just fine. But when I copy the compiled binary to its final location, it whinges about some sort of permissions problem.
I would dearly love to know exactly where it's getting stuck. According to this MSDN article, it's supposed to be possible to attach the VisualStudio debugger to an arbitrary process. But when I do this... nothing happens.
I copy my compiled binary to the right place, and run it. I leave it running, and switch back to VS. Go to Debug → Attach to process… and select my running program. VS clearly goes into debug mode, but... I can't see anything. The call stack is blank, it won't tell me what code is running... I can't do anything!
(Again: There's no error message. It seems to have connected just fine. It's just that nothing happens.)
Clearly a debugger that won't let you do anything is utterly pointless, so this obviously isn't what's supposed to happen. How do I make it so VS will actually show me what's running, let me poke variables, step through stuff, etc. You know, debug stuff?
(Again, this is unmanaged C++ code compiled to native machine code.)

The "Break All" button will break into a running process that you are attached to. It's the one that looks like a pause button.

Related

Edit and Continue in VS2019

I've just updated a major C++ project from VS2010 to VS2019, and I'm having problems getting Edit and Continue to work like it used to, specifically in relation to the 'Require source files to exactly match the original version' setting (which I will refer to as the 'require match' setting, because it's shorter).
I'm used to running my program, making changes to the source code while it's running, then setting a breakpoint to catch the running application just before the changed code. When the breakpoint is hit, I could hit F5 to rebuild and continue.
In VS2019, it seems that Edit and Continue will not work without the 'require match' setting, but setting breakpoints in existing code cannot be done with 'require match' once any changes are made.
There's a couple of workarounds, but none are ideal. It's possible to turn on "require match" to build and run the program, then after some code changes are made, turn it off to set the breakpoint, then turn it back on again for the rebuild and continue. That's a huge pain. It's possible to use pause and continue to force a rebuild of any edits, but this only works if the code change is complete enough to build. If I want to break to inspect a variable, this doesn't work. Once or twice I did manage to set a breakpoint on changed code, and it automatically went to the stale code, which is acceptable, but I can't get this to happen now. Also, now I have breakpoints that are showing as valid on edited code that has been rebuilt and I know is running, but the breakpoints are not being hit.
Any solutions here, or does Edit and Continue simply not work as well as it used to?
Here's some pictures...
Firstly, while my program is running, I made some change to surfdraw_panels.cpp, then went to add a breakpoint. It shows the following message...
Then loads up a [stale] version of the code, with the breakpoint set in the stale code...
Other times, when I make a change, I get a different result, and it won't allow me to set a breakpoint at all... In VS2010, it was possible to turn off the 'require match' setting and still use 'Edit and continue', but VS2019 will not allow this, even though it is still the recommended 'solution' in the message!
Github project that shows the issue is below. It's a simple MFC app, dialog based, created by the new project wizard in VS2019. There is a single button on the dialog, and some simple code to do something in the button. To recreate the problem, start the app in the debugger, then make a change to OnBnClickedButton1(), and then try to set a breakpoint.
https://github.com/surfdabbler/MFCApplication1
Not quite understand your specific situation and operation, because there are not some pictures and code to explain the issue in detail.
But this function which I used could break into the changed code during debugging with require match option. You should move your cursor back to the changed code and then Debug the below code step by step. And when you move the cursor back to the changed code, vc++ project will rebuild the changed code automatically and you do not have to stop debugging and restart build.
Update 1
I also faced the same behavior in my side. And since we could not handle the issue here any more, I reported the issue on our DC Forum.
You can vote it and add any comments if I did not describe the issue in detail so that it will get more Microsoft's attention. And I hope the Team will give you a satisfactory reply.

Was GDB listing the code as I stepped through, or was I only dreaming?

Years ago, when I last had call to use GDB to debug a Linux server, I seem to remember seeing a listing of the code that was being executed. Perhaps it was just the current line +/- five lines or so. I think i also remember it redrawing the entire console, every time I executed a command, so that the code listing was always at the top of the screen.
Now that I am once again in need of GDB's assistance, is my memory playing cruel tricks on me? Or does such a mode actually exist?
The documentation I'm finding online just points me at the 'l' command to list code. That looks like it has some potential, but there doesn't seem to be a way to get it to dynamically update as I step/next my way through the code.
If it's significant, I'm running Ubuntu on a dedicated Linux machine, and (since the program uses OpenGL) the actual debugging is going on inside a Weston Compositor terminal window.

Getting debug output from a crashed VS2010 application

Question: Can I set up VS2010 so it automatically writes debug output to a file?
Motivation: I have a DirectX 9 application that I'm trying to debug. I've noticed that when my application is fullscreen, it may crash under certain conditions. Normally I would just check my logs or DirectX debug output. However, the way my program crashes prevents that. It freezes and does not respond to any my attempts to end it (including "End Process" from task manager). Moreover, it also freezes my VS2010, and so VS doesn't respond to any commands either. The only way out of this whole thing that I've found is to End VS process. This, however, also destroys the output I'd very much like to read.
Now I see two ways out of this. First is to write all the debug info to a file but I have no idea how to do it. Second is to make my application crash in a more friendly way, but this seems like a difficult task.
Probably MiniDumpWriteMiniDump(..) helps on this. You can at any time dump the current state of the process to a file. After that, you can open the dumps with Visual Studio and analyze the state of the process - this includes callstacks of every thread, variable values...
Try to identify conditions in which your process crashes and write one or more dumps.
Another try is to install the Windows Debugging Tools and use WinDbg to debug your application. This is not as comfortable as Visual Studio, but allows a deeper insight.
Edit:
If there are debug statements made with OutputDebugString(..), you can use DebugView (from Microsoft, earlier Sysinternals) to display it.

How can I debug a program when debugger fails

I am debugging an Iphone program with the simulator in xCode and I have one last issue to resolve but I need help resolving it for the following reason: when it happens the program goes into debugging mode but no errors appear (no BAD ACCESS appears) and it does not show where the code fails. Putting some variables as global helps me to see their values to start pin pointing where the bug is but before I go into this fully I would like to know what techniques/tools you guys use to debug these situations.
If it helps Im debugging the following: I merged some code into the SpeakHere demo. The code was added in the C++ modules of the program (AQRecorder.h and .mm). I seem to have pinpointed the problem code in a function I wrote.
My favourite is always to add debugging code and log it to a file. This allows me so report any and all information I need to resolve the issue if the debugger is not working properly.
I normally control the debugging code by use of a flag which I can manipulate at run time or by the command line.
If the error is (and it probably is) a memory management issue, printing log entries is really not going to help.
I would reccomend learning how to use Instruments, and use its tools to track down the memory leak when it occurs rather than waiting until the application crashes later on.

Debugger question

I have a bug I am chasing (I think its a deadlock). When I run the code it hangs without the debugger flagging an error, so after a while I try pressing the pause (break all) button. The debugger then reports "The process appears to be deadlocked...". I then can see that all the threads are held up at lines saying EnterCriticalSection except for one which is already inside a critical section. When I look at the thread that is inside the C.S. with the debugger I see a green arrow, accompanied by a tiny blue circle pointing at a line with GetWindowText... as below:
// stuff A
{
GetWindowText(editwin[a].child_window_handle,existing_text,MAX_TEXT_SIZE-1);
}
// stuff B
If I hover the mouse over the green arrow I see the text "this is the next statement to execute when this thread returns from the current function". Now this has stumped me because I don't know if it means that it is stuck inside "stuff A" and is waiting to come back or its stuck inside GetWindowText and has somehow got stuck inside that. The arguments to GetWindowText all look sensible to me. If I click on "step into" I get the message "Unable to step. The process has been soft broken".
EDIT: stuff A is in fact the statement:
if (buf_ptr != NULL)
Usually a green arrow beside a line of code means "this is the next line that would be executed, if not for the fact we're stuck somewhere in a deeper stack frame." However, VS makes it impossible to say for sure based on the info provided so far...
[EDIT - of course, deep knowledge of Win32 can provide a very good guess - see the answer by "mos" for a likely explanation based on the GetWindowText() API's known pitfalls]
As mentioned, what Visual Studio shows you is sometimes misleading. To get a closer view of exactly what is happening you need to turn off some non-helpful "features" that VS enables by default. In Tools -> Options -> Debugging -> General, make sure:
Enable address-level debugging = ON
Enable Just My Code = OFF
Enable Source Server support = ON
This should allow you to:
1) break on / step over / etc the exact instruction that's causing the deadlock
2) see the full stack trace up to that point, regardless of module(s)
3) see source code whenever available, assuming your symbol & source servers are configured correctly
Your problem is that GetWindowText actually sends a message to the other window and waits for it to return. If that window is owned by another thread that is waiting for a critical section, GetWindowText will wait forever.
You're stuck inside GetWindowText, and have created a deadlock.
As the previous responses suggest, your code is stuck inside "Stuff A".
Can I suggest another tool for your tool-belt?
I usually find it much easier to debug native synchronization problems using WinDbg.
just launch your program in WinDbg, point to the correct symbols and all the info will be right there for your investigation using the !locks, !cs and k commands.
If you're new to WinDbg, you'll find that the internet is full with information about it. I recommend reading Advanced Windows Debugging as well.
It's a little bit difficult to start, comparing to the user friendly VS Debugger but every minute you'll invest in learning how to use it will save you hours of debugging further down the road.
Assuming your question is "Is this normal", then yes, the debugger usually shows the statement after the one stuck on a critical section.