I have a wxWidgets/GTK based application that works well - except for one installation on an Debian Squeeze ARM system. There it crashes when the user just activates the main window of it. To find the reason for that I added a signal handler to the application and use libunwind out of that signal handler to find the source for the crash. During a test that worked fine, when the software writes e.g. to address 0x0 libunwind correctly points me to the function where that happens.
But the results for the system where the crash appears unexpectedly are a bit strange, they seem to happen outside of my application. One crash comes from a function with no name (here libunwind returns an empty string), and one is caused by "malloc_usable_size", a system function which should never die this way.
So...what to do next? All ideas, suggestions or any other hints are welcome since I'm not sure how to contunue with that problem...
Check for buffer overrun or overwriting some memory unexpectedly for any structures, pointers, memory locations for items returned by library functions.
Check for invalid pointer frees in your code for the library allocated pointers that you are using.
May be using valgrind would also help.
Related
has anyone experience the following issue?
A stack variable getting changed/corrupted after calling ne10 assembly function such as ne10_len_vec2f_neon?
e.g
float gain = 8.0;
ne10_len_vec2f_neon(src, dst, len);
after the call to ne10_len_vec2f_neon, the value of gain changes as its memory is getting corrupted.
1. Note this only happens when the project is compiled in release build but not debug build.
2. Does Ne10 assembly functions preserve registers?
3. Replacing the assembly function call to c equivalent such as ne10_len_vec2f_c and both release and debug build seem to work OK.
thanks for any help on this. Not sure if there's an inherent issue within the program or it is really the call to ne10_len_vec2f_neon causing the corruption with release build.enter code here
I had a quick rummage through the master NEON code here:
https://github.com/projectNe10/Ne10/blob/master/modules/math/NE10_len.neon.s
... and it doesn't really touch address-based stack at all, so not sure it's a stack problem in memory.
However based on what I remember of the NEON procedure call standard q4-q7 (alias d8-d15 or s16-s31) should be preserved by the callee, and as far as I can tell that code is clobbering q4-6 without the necessary save/restore, so it does indeed look like it's clobbering the stack in registers.
In the failed case do you know if gain is still stored in FPU registers, and if yes which ones? If it's stored in any of s16/17/18/19 then this looks like the problem. It also seems plausible that a compiler would choose to use s16 upwards for things it needs to keep across a function call, as it avoids the need to touch in-RAM stack memory.
In terms of a fix, if you perform the following replacements:
s/q4/q8/
s/q5/q9/
s/q6/q10/
in that file, then I think it should work; no means to test here, but those higher register blocks are not callee saved.
I have created a standalone application in Matlab, actually it works, it displays the desired output but it closes immediately, not even enough time to examine the output and read the error message on DOS (standalone mode) that says:
MATLAB:TooManyOutputs
Warning: 1 visible figure(s) exist at MCR Termination
If your application has terminated unexpectedly, please note that
applications generated by the MATLAB Compiler terminate when there are no
visible figure windows. See the documentation for WaitForFiguresToDie and
WAITFORCALLBACKS for more information.
Any help would be appreciated.
Looking at the first line of your message, TooManyOutputs suggests that you have an assignment somewhere of the form
[a b] = somefunction(parameters)
so you want the outputs of somefunction to be put in a and b, but somefunction only returns one parameter. This bug causes your program to terminate, and then MCR realizes the program exits without closing your figure window, causing the later error messages.
If I'm right about TooManyOutputs, you should already have that error message when running your code directly in Matlab; have you tried that before creating a standalone application?
If this doesn't help, you should probably post some of your code to make it clearer where the problem could come from.
I have a matlab script, that every now and them produces the message:
Caught std::exception Exception message is:
bad allocation
Unexpected error status flag encountered. Resetting to proper state.
What could be causing this?
This is a bug in MATLAB, in which some part of MATLAB is not handling a std::bad_alloc exception correctly (std::bad_alloc is an out-of-memory exception thrown from the C++ runtime library).
The "Unexpected error status flag encountered. Resetting to proper state." is an internal diagnostic - you shouldn't see it unless MATLAB has gotten into a bad state, which in this case is happening because it's encountering the bad_alloc someplace where it was not expected. Recent versions of MATLAB have fixed most of these issues, except in extremely low-memory situations (like, there's less than 1 kilobyte of free memory left). What version are you using?
My best guess is that your script is trying to allocate some memory and failing. The occurrence of such an error will depend on the availability of memory on your computer at the time allocation is attempted. The available memory will vary according to what is going on at the time in other programs, the operating system, even the state of your Matlab session.
For a more accurate diagnosis, you'll have to tell us more, maybe even post your script.
It was happening to me, and it turned out I had too many files open. fclose('all') set everything back to normal, and I made sure that all my fopen were followed by fclose.
I have a pretty weird problem in my iPhone app which is, I think, related to memory getting corrupted:
At one point, I need to sort an array, which I do with -[sortArrayUsingFunction].
The result is not correct unless I either allocate some memory with something like void *test = malloc(2 * sizeof( int )) before the method call or have, e.g., a call to NSLog() (which is never invoked) in the sorting function.
In other words: the sorting only works if I slightly increase the memory that was used before calling the sorting function. I think this is because at some point, memory gets corrupted.
How do you debug something like this?
It sounds like some of your code is using already released objects. A lot of help with debugging this kind of errors is provided in Apple’s great Mac OS X Debugging Magic tech note, especially the foundation part.
For your case I'd disable autorelease pools (setting the environment variable NSEnableAutoreleasePool=NO) or use the zombie feature (NSZombieEnabled=YES) to find places where you send messages to released objects.
Try running your program in the simulator under Valgrind:
http://valgrind.org/
And how to use it under the simulator:
http://landonf.bikemonkey.org/code/iphone/iPhone_Simulator_Valgrind.20081224.html
You may have to change the VALGRIND path in the code example depending on where it gets installed.
Such things can be a challenge to debug. There are some tools for detecting out-of-bounds accesses and such on other platforms, so I presume there would be something for the iPhone, however I don't know of any.
Perhaps you should store two copies of the array, and compare them for differences. Print out the differences. The nature of the "junk" that was introduced to one of the arrays might give a hint as to where it came from.
Also just go through the code that runs before this point, and re-read it (or better yet, get someone else to read it). You might spot a bug.
I have this line of code (splits is an instance variable):
splits = [[NSMutableArray alloc] initWithObjects:[NSMutableArray array]];
This code is obviously wrong (it should be nil-terminated), however it runs fine in the simulator, even though it throws an EXC_BAD_ACCESS on the device. My question is why does the simulator not throw an error?
Kyle
The actual outcome depends on the memory contents. It is quite possible that the memory layout on the simulator contains a zero right after the address of the first parameter (the anonymous array). This zero gets interpreted as if you would close the argument list with nil and everything works fine. (P.S. There is an interesting macro called NS_REQUIRES_NIL_TERMINATION for such cases, although it obviously would not help here.)
The iPhone has much less memory than your computer. The area in memory for the stack could have been set to 0x00 (nil) before being used by the initWithObjects function. When the parameters are sent to the initWithObjects function and the stack is alloated, that memory space on the computer is more likely to be preset to 0x00 than the iPhone because the same memory space is used less often. So it is likely that the nil is being read from a spot in memory set to 0 already.
If you fill up your memory on your computer, and then run the simulator, the simulator may be more likely to crash like the iPhone.
Buffer overflows result in undefined behavior. They are not guaranteed to cause an access violation (or even a noticeable bug). On modern machines, they will cause an access violation if you happen to step on "someone else's" memory, but probably not if you're just reading junk from your own stack.
Basically, you just need to be careful, and can try tools like Mudflap and Valgrind to help you out (these particular two are more meant for C/C++, and I don't know how well they apply to Obj-C).