I am building an application and using the x264 library as an encoder. I have built the library for my windows system using MSys/MingW. The library works fine under debug build (note both debug and release builds are using the default VS2010 settings). However, under release an access violation error is thrown at the first call to the x264 library, specifically:
Unhandled exception at 0x00905a4d in StreamTest.exe:
0xC0000005: Access violation.
The error is thrown at this line:
x264_param_default_preset((params), "veryfast", "zerolatency");
While I was figuring out how to compile the library I came across a lot of talk about memory alignment in Windows/Visual Studios and how it wasn't particularly compatible with the alignment expected by x264. For example when compiling in MSys I had to enable --enable-memalign-hack. I am wondering if the source of this error might stem from a memory alignment issue which only manifests itself through some setting in my release build. Unfortunately I know almost nothing about the specifics and so have come here.
Can anyone give me some more information regarding the memory alignment issues and any Visual Studio settings which might cause this? Any other tips/pointers to fix this issue are very welcome.
Thanks.
Edit
From answer below:
From the linked SO question I get the impression he added "build with debugger info" to the OpenCV build? Since I'm building the x264 library through MSys with G++ I'm not sure I can do this. I have checked the build settings for my project, and under both release and debug it has debugger info. Not sure if I missed something in that post, please let me know.
I tried the application verifier. It seems that x264 is trying to execute code from non-executable memory as per the App verifier output:
VERIFIER STOP 0000000000000650: pid 0x1B18:
Attempt to execute code in non-executable memory (first chance).
0000000000905A4D : Address being accessed.
0000000000905A4D : Code performing invalid access.
000000000021EA90 : Exception record. Use .exr to display it.
000000000021E5A0 : Context record. Use .cxr to display it.
Anything to be gathered from this output?
Thanks again.
Refer to a similar issue here, see if that helps you too.
EDIT
Post that you also want to run your application through AppVerifier
EDIT
In my opinion release "Build with debugger info" amounts to turning on -g switch together with optimization switches and turning off any DEBUG macro. Also if you debugger attached (use Gflags ) to start your process with debugger (grab a copy of windbg and use that to debug).
When the Appverifer stops your process use .cxr command to get context information. That should help pointing out the issue.
Related
My code is crashing in the Release configuration but not the Debug configuration. It's only doing this as I exit the program as the very last line 'return(0);' executes. I'm working in the Visual Studio development environment and when it crashes, VS studio offers me the option to 'Debug' the code. When I select that, it leads to an error dialog that pops up saying:
Unhandled exception at 0x00007FF851A0512D (msvcp120d.dll) in myapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.
When I select to 'break' when this exception occurs, it highlights the following function in the xstring file:
void _Free_proxy()
{ // destroy proxy
typename _Alloc::template rebind<_Container_proxy>::other
_Alproxy;
this->_Orphan_all();
_Alproxy.destroy(this->_Myproxy);
_Alproxy.deallocate(this->_Myproxy, 1);
this->_Myproxy = 0;
}
And, especially, the line '_Alproxy.destroy(this->_Myproxy);' is highlighted as the culprit.
I thought the issue might be that my 'release' code is somehow linking to the 'debug' msvcp120d.dll library since that's highlighted in the 1st dialog that pops up - but that may be just because I start using the VS debugger to ID this problem. But even if that is the problem, I'm uncertain how to tell VS to compile with msvcp120.dll for the Release configuration and msvcp120d.dll for the Debug configuration.
(For the record, I'm generating all my code using the 'Multi-threaded DLL (/MD)' flag in the Release configuration and the 'Multi-threaded Debug DLL (/MDd)' in the Debug configuration)
The kicker is that when the Release version crashes, the process enters a 'suspended' state and I'm unable to fully kill it via task manager. And then I can't even recompile a new Release version without restarting my computer!
I don't know how to isolate this problem. Can anyone advise me on how I might fix this?
Update
The code for this project is quite large - so distilling it to a minimal version that exhibits the same behavior, while usually a valid way to track a bug, would be a pretty big task. I was hoping that there was some method to log the processes and figure out which one is calling msvcp120d.dll #Niall, I generated the dependency graph and it is huge. Without giving away anything proprietary, attached is a global view of the graph.
Dependency graph of entire solution
Is there any tool to track which is calling msvcp120d.dll?
#Niall Thank you! The software at Dependencywalker.com was fantastic. I was able to use it to determine the library causing the problem and track down the error. It turns out that I had previously (months ago, dumbly) set a system path to the debug version of that library. So even though my project was properly directed to link to the release version of the library, at runtime, my executable was linking to the debug version of the *.dll file!
I deleted the path variable and now make sure a copy of the proper *.dll file is in my Release or Debug directory. Then it all runs and shuts down fine.
Thanks to all who provided assistance.
I set Qt Creator to break when a C++ exception is thrown:
I then tested it with this code:
try {
throw std::runtime_error("error");
} catch (std::exception &e) {
qDebug("%s", e.what());
}
But it didn't break on throw std::runtime_error("error");. I'm using CDB, not GDB, because I'm using the MSVC Kit.
Edit: There is another question where CDB is working for the OP, even if slowly. So it should work in principle. My configuration is: Qt Creator 3.3.0, compiling with Qt4/MSVC 9.0 (x86), the debugger is CDB 6.2.9200.16384.
Edit 2: This is what I'm getting in the CDB log window (I made a diff between the CDB log with and without the breakpoint):
<bu100400 CxxThrowException
<!qtcreatorcdbext.breakpoints -t 1 -v
<!qtcreatorcdbext.pid -t 2
dATTEMPT SYNC
d*** Bp expression 'CxxThrowException' contains symbols not qualified with module name.
1 breakpoint(s) pending...
*** Unable to resolve unqualified symbol in Bp expression 'CxxThrowException' from module 'C:\Windows\WinSxS\x86_microsoft.windows.common-controls_6595b64144ccf1df_5.82.7601.18201_none_ec80f00e8593ece5\comctl32.dll'.
Full CDB log (in case needed): http://pastebin.com/jhNRy9bE
Edit 3: #HansPassant's explained why it fails in the comments:
Keep in mind that you are using a very old version of MSVC++, big changes at VS2012. The pastebin shows it being out of sync pretty badly, never getting to the DLL that contains __CxxThrowException#8 (MSVCR90D.dll) before the exception is thrown. It is simple with the sxe debugger command, automatic break when any exception is thrown.. Maybe you shouldn't be using QT's UI at all, it looks too gimpy. – Hans Passant 10 hours ago
Just look at the trace, the debugger shows what DLLs it is searching for "CxxThrowException". It never gets to msvcr90d.dll. And the exception is thrown while it is searching for the symbol after which it all ends. Completely out of sync. – Hans Passant 56 mins ago
I'll just write up why this is going wrong, a workaround is going to be difficult to find. The debugger trace in your pastebin tells the tale.
The basic issue is that the communication between the debugger and the QT front-end is rather poor. And in your case it gets out of sync, QT doesn't wait long enough for the debugger to complete the command. QT tries to set a breakpoint on the msvcr90d.dll!__CxxThrowException#8 function, the one that raises a C++ exception in the Microsoft CRT. This function can be present in more than one executable file if the program uses multiple CRTs. A pretty common mishap, caused by building with /MT. And sometimes intentional if you use a well-isolated DLL that you interface with by using COM.
This takes a while as you might imagine, the complaint in the linked question, the debugger has to plow through the symbol information for every DLL that's loaded. It will take especially long if the PDB for the DLL needs to be downloaded from the symbol server and doesn't otherwise get cached so it is available the next time you debug. Not your issue afaict, it does setup the cache location to C:\Users\sasho\AppData\Local\Temp\symbolcache. Go have a look-see to verify that you do see PDBs for the operating system DLLs there.
This operation is tricky, the debugger doesn't give a good signal that it is done searching the DLLs. What the QT should do is verify the debugger feedback against the list of DLLs it obtained. It does not do that, it issues the g command before the debugger is done searching. Could be a timeout that is too short but it actually looks like QT doesn't count on the debugger performing this command in the background. A convenience to a human, not exactly very helpful here :)
There ought to be a way to configure CDB to not perform this search in the background. This is well-hidden, I don't see anything in the debugger.chm help file but it probably wasn't updated in a while. Google doesn't help either. I'd recommend you ask a question about it. Most significantly perhaps is that you have a rather major mismatch in version numbers. The compiler you use is 2008 vintage, the debugger is quite new, SDK 8.0 version, I can't tell what QT version you use.
So a possible workaround is to intentionally use an older version of CDB, one that's more likely to have been tested with the QT front-end version you use. Download the corresponding SDK version, version 6.0 matches the VS2008 time frame. I think the "Debugging Tools for Windows" was still a separate download back then and not yet included in the SDK. Another workaround is to stop relying on the friendly QT front-end and learn to drive CDB from the command prompt. Moderately more useful is WINDBG, uses the same debugging engine but has a GUI interface. Just moderate, it is still mostly prompt driven. You do lose several days of your life learning the commands however. Getting the debugger to break when an exception is thrown is trivial, use the sxe command.
There are a number of errors going on here but I'm sure they are all linked, so first off I'm getting Access violation reading location exceptions at locations (generally near 0x00000000)
but I only get these exceptions in release and not in debug, even if i setup debugging to do so. Also I found where the error happens but when I step over that it goes in to a complete unrelated function that is not called in the line or in any of the functions in that line of code. But when similar code is called it still goes to this unrelated function but doesn't fail. This all only happens in release versions. I know which piece of code is causing the error as if I comment it out its all fine. Also in the watch window in release all the numbers are wrong most of the time, which has never been a problem but it could help also a added some code to it to output the values of variables to a file and the variables are all fine, the pointers are sensible, but when the exception happens it always says their 0x00000020 but when I look at the log they are fine. This is in 32 bit , but on 64 bit windows 7 in c++. Please any help would be good!
Visual Studio's debugger will cause the program to use a debug heap that can hide uninitialized memory if you use the option "Start with Debugging" to start your program, in release or debug. You can try to run your program built in the Debug configuration without the debugger attached, and then use the Attach to Process... option in the debug menu to attach to your executable.
If this doesn't help, I recommend using windbg to debug your program. For help getting started with windbg, take a look at the answers on this question.
Once windbg is configured and symbol paths are set up, you can use the "!analyze -v" option once the program crashes to get a lot of information about the crash automatically.
I have a problem with my C++ application. It was developed on a 32bit pc, on Microsoft Visual Studio 2008, and now I am trying to run it on a 64bit pc.
On my 32bit pc it works fine; on the 64bit pc, Visual Studio does not give any compilation problem, but then on execution gives wrong results.
And I have undestood why.
In the code, I define a variable, of tipe "dag", that is a structure for a direct acyclic graph. By debugging the software, I noticed that, although I declared it, later the software is not able to insert data in it, and the debugger says:
CXX0017: Error: symbol "dags" not found
Here's my code:
Dag<int64_t>* dags = new Dag<int64_t>();
dags = getDagsFromRequest2(request, dags);
The very strange thing is that, if I follow the flow inside getDagsFromRequest2() function, I can clearly see that dags variable is full of data: on "quickwatch", it shows 2342 nodes inside it. But when I come back from getDagsFromRequest2() function to this part of the code, debugger says "CXX0017: Error: symbol "dags" not found". How is it possible?
You can also see this screenshot from my Visual Studio debug set.
What could be the problem?
Thanks a lot
There are a few possibilities to consider:
Running in Release builds. Switch to a Debug build.
Using a Debug build that has optimizations enabled and/or debug information disabled. Disable the optimizations and enable the debug information (look in another project for the relevant settings).
A corrupt build of some sort. Clean and rebuild the entire solution.
Memory corruption which is preventing the debugger from displaying the variable. Ensure that no memory issues exist with a tool like Valgrind.
A VS bug. This report for VS2010 seems to suggest a known bug with similar characteristics for example. Ensure all patches and hotfixes for VS2008 are installed.
The variable dags is defined as your code compiles. The error you see is simply related to the debugger. I am guessing it is caused by running the application in Release mode which sometimes causes confusing and wrong watches values. Try changing the mode to debug(there is a drop down from which you can choose the build mode).
EDIT: as you say you are running in Debug mode, my next guess is that this behavior could be caused by stack corruption. Try using valgrind to detect if that is the case. It may take a while to start with it,but it is worth it and will detect if you have some memory corruption.
I'm trying to generate a release build for a C++ application that I've written. The application runs fine (debug & release) when you run it from within VS2008; but when you run the executable it crashes nearly every single time.
Now, is there a hack so I can run this application as a standalone application without having to run through all of the code and finding the bug that is causing it?
Thanks in advance.
In short, no.
you will have to find the bug, if it works within VS, then I'd hazard a guess that it is a timing issue, possibly you're overwriting shared thread data, this would be less likely (though still possible to see) inside VS as its being run in a debug environment which slows it down a bit.
If you want help finding your bug, then tell us more. Otherwise, build your release with debug symbols (pdbs), install DrWatson as the system debugger and run it standalone. When it crashes DrWatson will create a minidump file, load this into WinDbg (my favourite) and you'll be able to see exactly where your bug is (it'll even tell you that the dump contains an exception and show you it by default. You need to add your source code path and path to your symbols in WinDbg to get it to do this correctly).
Then you will also know how to diagnose crashes when the app is run on-site too.
Are you loading external resources? If you are check that your relative paths are correct in the C++ program.
One possibility is that your program uses uninitialized heap data. Launching a program from the debugger enables the NT debug heap, which causes the heap allocator to fill new memory blocks with a fill pattern, and also enables some heap checking. Launching the same program from outside the debugger leaves the NT debug heap disabled, but if the program was linked against the debug version of the C runtime, then the CRT debug heap will still be enabled.
A much less likely possibility is that your program requires SeDebugPrivilege to be set in its process token. The debugger enables this privilege in its process token, which has the side effect that all programs launched from the debugger inherit this privilege. If your program tries to use OpenProcess()/ReadProcessMemory()/WriteProcessMemory() and doesn't handle errors correctly, it's conceivable that it could crash.
There are a few possibilities. Besides what has already been mentioned, running an app from Visual Studio will execute in the same security context as the Visual Studio instance. So if, for instance, you are working on Vista, you might be hitting an unhandled security violation if you're trying to access protected files, or the registry.
What if you build a debug version and run it standalone? Does it crash? If so, you can usually break into the debugger from there and get a call stack to see what the malfunction is.
From the details you've given, it sounds like there may be a library issue. Are you running the program on the same computer? If not then you'll also have to deploy the appropriate libraries for your application. If you are running on the same computer but outside of the dev environment, ensure that your application can see the appropriate libraries.
Best way i have found to debug in release is to create a crash dump when an crash happens and the dump then allows me to load debug symbols on my dev computer and find out whats going on. More info here: http://www.debuginfo.com/articles/effminidumps.html
You can also go to file => open in Visual Studio and open the .exe, so you are not starting it under the debugger per se. Not sure if it will help.
http://blogs.msdn.com/saraford/archive/2008/08/21/did-you-know-you-can-debug-an-executable-that-isn-t-a-part-of-a-visual-studio-project-without-using-tools-attach-to-process-296.aspx