Is it possible to tell Visual Studio (or any other tool even on any other major operating system) to interpret an address as a beginning of a call stack?
What I'm trying to achieve: we have a library, which uses boost's make_fcontext / jump_fcontext and stores these contexts into a container in order to suspend some calls for later processing.
My question is - is it possible to somehow debug what are these suspended calls? I imagine, that I can tell a debugger/tool something like: "Here's this address, although it's not obvious, it actually points to a call stack, 'parse' it and show it to me like a standard call stack".
No idea if it's theoretically possible, as I don't know boost::context in details, but it sounds achievable.
Has anyone tried to deal with this?
There's a few approaches I can think of, in various flavors of dissatisfying.
You could write your own debugging engine to plug into the IDE, which would allow the manual enumeration of fibers. (You probably don't want to do that.)
You can use a boost::context::fiber instead of a fcontext_t. On Windows, those can be implemented with win32 fibers, so they'll show up in the IDE automatically, with full stack/locals. (You may need to change your Boost config to get this to work, see the docs for details.)
You could look inside the fcontext_t struct, get the EIP and ESP, and copy them into your registers; at that point, the processor will kiiiind of think that it's executing as the fiber. (This is most likely NOT going to work very well.)
Personally I'd go with the second approach. fcontext_t is a bit too low-level to be using directly anyway, unless you have specific exotic needs you haven't mentioned.
I am working on the largest project I've ever worked on, and I've never debugged something like this, so I don't know where to get started.
Some info on the crash:
I am using Visual Studio, and the debugger is completely useless. The only information it gives me is that it appears to be happening during a call to "memcpy". The call stack is completely empty except for the memcpy function, and the local variables are listed but it does not have values for any of them.
It happens occasionally on any computer.
It does not ALWAYS happen under any (known) condition, but it only ever happens under a few conditions. In particular it only happens when a particular type of object is destroyed, although that's not necessarily the direct cause, and investigating the destruction process has not been helpful.
A little more about the project:
It is a game using SFML 2.0, linked statically.
I am not calling memcpy anywhere in my own code.
Some questions:
Where could the call to memcpy be coming from? Is it in SFML or elsewhere?
How do I (using visual studio) get more information on a crash when the debugger isn't working?
This is an answer to "Where could the call to memcpy be coming from?"
In most cases this is the result of a call to the copy constructor of std::string with a this pointer of NULL, or a string operation on an already destructed string. This string can be a member of a class of you, of course.
This in itself won't help you to find the problem when the project is really large. However, you can almost certainly assume that you are using a reference or pointer (or iterator) to a custom object that is already destructed. A most straightforward way to find this access would be by running your program, compiled without optimization and with debug info, in valgrind. Unfortunately that isn't available for windows (see Is there a good Valgrind substitute for Windows?).
The main problem here seems to be that you aren't even getting a backtrace, because that would give a strong hint to where to look into, at least. I'm not familiar with windows though, so I can only guess what is the cause of that. Are you sure you have everything compiled with debug info?
Is there a way in OCaml to get the current call stack programatically? By this, I do not mean inside a debugger but as a function call inside the program that will print the current call stack. I imagine this should not be beyond the capabilities of the byte-code interpreter, especially if debug symbols are available.
I came to this question looking for the same thing, here's my solution
Printexc.get_callstack 5 |> Printexc.raw_backtrace_to_string
(Its actually a pretty good way to familiarize yourself with a new code base)
You can also use ocamldebug, with which you can start your code, compiled in bytecode. In this environment, Printexc.get_backtrace () are far more completes.
For native code one can use glibc's backtrace, though it may not print all stack frames correctly.
Unfortunately, the only way to get a backtrace from inside the code is when an exception is raised, you can then use Printexc.get_backtrace (). It won't give you though the names of the functions, just the locations in the code of what is in the stack, and only if OCaml was able to recover them...
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.
Closed 10 years ago.
In unmanaged C/C++ code, what are the best practices to detect memory leaks? And coding guidelines to avoid? (As if it's that simple ;)
We have used a bit of a silly way in the past: having a counter increment for every memory allocation call and decrement while freeing. At the end of the program, the counter value should be zero.
I know this is not a great way and there are a few catches. (For instance, if you are freeing memory which was allocated by a platform API call, your allocation count will not exactly match your freeing count. Of course, then we incremented the counter when calling API calls that allocated memory.)
I am expecting your experiences, suggestions and maybe some references to tools which simplify this.
If your C/C++ code is portable to *nix, few things are better than Valgrind.
If you are using Visual Studio, Microsoft provides some useful functions for detecting and debugging memory leaks.
I would start with this article:
https://msdn.microsoft.com/en-us/library/x98tx3cf(v=vs.140).aspx
Here is the quick summary of those articles. First, include these headers:
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
Then you need to call this when your program exits:
_CrtDumpMemoryLeaks();
Alternatively, if your program does not exit in the same place every time, you can call this at the start of your program:
_CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF );
Now when the program exits all the allocations that were not free'd will be printed in the Output Window along with the file they were allocated in and the allocation occurrence.
This strategy works for most programs. However, it becomes difficult or impossible in certain cases. Using third party libraries that do some initialization on startup may cause other objects to appear in the memory dump and can make tracking down your leaks difficult. Also, if any of your classes have members with the same name as any of the memory allocation routines( such as malloc ), the CRT debug macros will cause problems.
There are other techniques explained in the MSDN link referenced above that could be used as well.
In C++: use RAII. Smart pointers like std::unique_ptr, std::shared_ptr, std::weak_ptr are your friends.
As a C++ Developer here's some simply guidelines:
Use pointers only when absolutely necessary
If you need a pointer, doublecheck if a SmartPointer is a possibility
Use the GRASP Creator pattern.
As for the detection of memory leaks personally I've always used Visual Leak Detector and find it to be very useful.
I've been using DevStudio for far too many years now and it always amazes me just how many programmers don't know about the memory analysis tools that are available in the debug run time libraries. Here's a few links to get started with:
Tracking Heap Allocation Requests - specifically the section on Unique Allocation Request Numbers
_CrtSetDbgFlag
_CrtSetBreakAlloc
Of course, if you're not using DevStudio then this won't be particularly helpful.
I’m amazed no one mentioned DebugDiag for Windows OS.
It works on release builds, and even at the customer site.
(You just need to keep your release version PDBs, and configure DebugDiag to use Microsoft public symbol server)
Visual Leak Detector is a very good tool, altough it does not supports the calls on VC9 runtimes (MSVCR90D.DLL for example).
Microsoft VC++ in debug mode shows memory leaks, although it doesn't show where your leaks are.
If you are using C++ you can always avoid using new explicitly: you have vector, string, auto_ptr (pre C++11; replaced by unique_ptr in C++11), unique_ptr (C++11) and shared_ptr (C++11) in your arsenal.
When new is unavoidable, try to hide it in a constructor (and hide delete in a destructor); the same works for 3rd party APIs.
There are various replacement "malloc" libraries out there that will allow you to call a function at the end and it will tell you about all the unfreed memory, and in many cases, who malloced (or new'ed) it in the first place.
If you're using MS VC++, I can highly recommend this free tool from the codeproject:
leakfinder by Jochen Kalmbach.
You simply add the class to your project, and call
InitAllocCheck(ACOutput_XML)
DeInitAllocCheck()
before and after the code you want to check for leaks.
Once you've build and run the code, Jochen provides a neat GUI tool where you can load the resulting .xmlleaks file, and navigate through the call stack where each leak was generated to hunt down the offending line of code.
Rational's (now owned by IBM) PurifyPlus illustrates leaks in a similar fashion, but I find the leakfinder tool actually easier to use, with the bonus of it not costing several thousand dollars!
Never used it myself, but my C friends tell me Purify.
If you're using Visual Studio it might be worth looking at Bounds Checker. It's not free, but it's been incredibly helpful in finding leaks in my code. It doesn't just do memory leaks either, but also GDI resource leaks, WinAPI usage errors, and other stuff. It'll even show you where the leaked memory was initialized, making it much easier to track down the leak.
I think that there is no easy answer to this question. How you might really approach this solution depends on your requirements. Do you need a cross platform solution? Are you using new/delete or malloc/free (or both)? Are you really looking for just "leaks" or do you want better protection, such as detecting buffer overruns (or underruns)?
If you are working on the windows side, the MS debug runtime libraries have some basic debug detection functionality, and as another has already pointed out, there are several wrappers that can be included in your source to help with leak detection. Finding a package that can work with both new/delete and malloc/free obviously gives you more flexibility.
I don't know enough about the unix side to provide help, although again, others have.
But beyond just leak detection, there is the notion of detecting memory corruption via buffer overruns (or underruns). This type of debug functionality is I think more difficult than plain leak detection. This type of system is also further complicated if you are working with C++ objects because polymorhpic classes can be deleted in varying ways causing trickiness in determining the true base pointer that is being deleted. I know of no good "free" system that does decent protection for overruns. we have written a system (cross platform) and found it to be pretty challenging.
I'd like to offer something I've used at times in the past: a rudimentary leak checker which is source level and fairly automatic.
I'm giving this away for three reasons:
You might find it useful.
Though it's a bit krufty, I don't let that embarass me.
Even though it's tied to some win32 hooks, that should be easy to alleviate.
There are things of which you must be careful when using it: don't do anything that needs to lean on new in the underlying code, beware of the warnings about cases it might miss at the top of leakcheck.cpp, realize that if you turn on (and fix any issues with) the code that does image dumps, you may generate a huge file.
The design is meant to allow you to turn the checker on and off without recompiling everything that includes its header. Include leakcheck.h where you want to track checking and rebuild once. Thereafter, compile leakcheck.cpp with or without LEAKCHECK #define'd and then relink to turn it on and off. Including unleakcheck.h will turn it off locally in a file. Two macros are provided: CLEARALLOCINFO() will avoid reporting the same file and line inappropriately when you traverse allocating code that didn't include leakcheck.h. ALLOCFENCE() just drops a line in the generated report without doing any allocation.
Again, please realize that I haven't used this in a while and you may have to work with it a bit. I'm dropping it in to illustrate the idea. If there turns out to be sufficient interest, I'd be willing to work up an example, updating the code in the process, and replace the contents of the following URL with something nicer that includes a decently syntax-colored listing.
You can find it here: http://www.cse.ucsd.edu/~tkammeye/leakcheck.html
For Linux:
Try Google Perftools
There are a lot of tools that do similar alloc/free counting, the pros of Goolge Perftools:
Quite fast (in comparison to valgrind: very fast)
Comes with nice graphical display of results
Has other useful capabilities: cpu-profiling, memory-usage profiling...
The best defense against leaks is a program structure which minimizes the use of malloc. This is not only good from a programming perspective, but also improves performance and maintainability. I'm not talking about using other things in place of malloc, but in terms of re-using objects and keeping very explicit tabs on all objects being passed around rather than allocating willy-nilly like one often gets used to in languages with garbage collectors like Java.
For example, a program I work on has a bunch of frame objects representing image data. Each frame object has sub-data, which the frame's destructor frees. The program keeps a list of all frames that are allocated, and when it needs a new one, checks a list of unused frame objects to see if it can re-use an existing one rather than allocate a new one. On shutdown, it just iterates through the list, freeing everything.
I would recommend using Memory Validator from software verify.
This tool proved itself to be of invaluable help to help me track down memory leaks and to improve the memory management of the applications i am working on.
A very complete and fast tool.
Are you counting the allocs and frees by interpolating your own syscall functions which record the calls and then pass the call to the real function?
This is the only way you can keep track of calls originating from code that you haven't written.
Have a look at the man page for ld.so. Or ld.so.1 on some systems.
Also do Google LD_PRELOAD and you'll find some interesting articles explaining the technique over on www.itworld.com.
At least for MS VC++, the C Runtime library has several functions that I've found helpful in the past. Check the MSDN help for the _Crt* functions.
Paul Nettle's mmgr is a long time favourite tool of mine. You include mmgr.h in your source files, define TEST_MEMORY, and it delivers a textfile full of memory problems that occurred during a run of your app.
General Coding Guideline:
Resources should be deallocated at the same "layer" (function/class/library) where they are allocated.
If this is not possible, try to use some automatic deallocation (boost shared pointer...)
Memory debugging tools are worth their weight in gold but over the years I've found that two simple ideas can be used to prevent most memory/resource leaks from being coded in the first place.
Write release code immediatly after writing the acquisition code for the resources you want to allocate. With this method its harder to "forget" and in some sense forces one to seriously think of the lifecycle of resources being used upfront instead of as an aside.
Use return as sparringly as possible. What is allocated should only be freed in one place if possible. The conditional path between acquisition of resource and release should be designed to be as simple and obvious as possible.
At the top of this list (when I read it) was valgrind. Valgrind is excellent if you are able to reproduce the leak on a test system. I've used it with great success.
What if you've just noticed that the production system is leaking right now and you have no idea how to reproduce it in test? Some evidence of what's wrong is captured in the state of that production system, and it might be enough to provide an insight on where the problem is so you can reproduce it.
That's where Monte Carlo sampling comes into the picture. Read Raymond Chen's blog article,
“The poor man's way of identifying memory leaks” and then check out my implementation (assumes Linux, tested only on x86 and x86-64)
http://github.com/tialaramex/leakdice/tree/master
Working on Motorola cell phones operating system, we hijacked memory allocation library to observe all memory allocations. It helped to find a lot of problems with memory allocations.
Since prevention is better then curing, I would recommend to use static analysis tool like Klockwork or PC-Lint
Valgrind is a nice option for Linux. Under MacOS X, you can enable the MallocDebug library which has several options for debugging memory allocation problems (see the malloc manpage, the "ENVIRONMENT" section has the relevant details). The OS X SDK also includes a tool called MallocDebug (usually installed in /Developer/Applications/Performance Tools/) that can help you to monitor usage and leaks.
Detect:
Debug CRT
Avoid:
Smart pointers, boehm GC
A nice malloc, calloc and reallloc replacement is rmdebug, it's pretty simple to use. It is much faster to then valgrind, so you can test your code extensively. Of course it has some downsides, once you found a leak you probably still need to use valgrind to find where the leak appears and you can only test mallocs that you do directly. If a lib leaks because you use it wrong, rmdebug won't find it.
http://www.hexco.de/rmdebug/
Most memory profilers slow my large complex Windows application to the point where the results are useless. There is one tool that works well for finding leaks in my application: UMDH - http://msdn.microsoft.com/en-us/library/ff560206%28VS.85%29.aspx
Mtrace appears to be the standard built-in one for linux. The steps are :
set up the environment variable MALLOC_TRACE in bash
MALLOC_TRACE=/tmp/mtrace.dat
export MALLOC_TRACE;
Add #include <mcheck.h> to the top of you main source file
Add mtrace(); at the start of main and muntrace(); at the bottom (before the return statement)
compile your program with the -g switch for debug information
run your program
display leak info with mtrace your_prog_exe_name /tmp/mtrace.dat
(I had to install the mtrace perl script first on my fedora system with yum install glibc_utils )