Segmentation fault when doing arithmetic operations on cv::Mat

asked 2014-10-16 16:20:47 -0600

mk
31 ●3

I use some opencv functions in one lib that I build as a shared object (libfoo.so)
In order to have only one .so file loaded in runtime, I use opencv as a static lib (libopencv_*.a) linked in libfoo.so.

Inside libfoo.so I have one static object from a class (Bar), and in the constructor I do some simple cv::Mat operations like:

Bar::Bar(){ barMat = cv::Mat::zeros(...); barMat += 1; } ... static Bar b;

The problem is that I always get a segfault when it reaches the += (or any other arithmetic operation with Mat).

The following is the smallest example I came up with to reproduce the fault:

#include <opencv2/opencv.hpp> class Bug { public: Bug() { cv::Mat M = cv::Mat::zeros(3,3,CV_8U); M += 10; } }; static Bug b; int main(int argc, char** argv){}

Compile with

$ g++ bug.cpp `pkg-config --cflags --libs opencv`

And run

$ ./a.out
Segmentation fault (core dumped)

I already checked another question that seems to be related, but none of the proposed fixes solve my case: http://answers.opencv.org/question/4072/initializing-static-cvmat-with-cvmatzeros-causes/ https://github.com/Itseez/opencv/pull/2558

I compiled OpenCV from 2.4.9 tar.

Can anyone help?

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I think the corresponding issue explains that it was fixed in version 2.4.10. You can also have a look at the github repo and see the differences between the tags.

boaz001 ( 2014-10-17 03:29:13 -0600 )edit

@boaz001 I already tried with the fix proposed for this issue, but it does not solve. I also added some debug msgs in the opencv code, and my program is not breaking inside the functions changed in the pull request: https://github.com/Itseez/opencv/pull/2558

mk ( 2014-10-17 09:12:12 -0600 )edit

Can you debug?You can add -ggdb to the compiler options and start gdb with gdb a.out , then type run and see what happens.

boaz001 ( 2014-10-17 10:26:40 -0600 )edit

Sure! The output is here: http://pastebin.com/FzJZBhJZ I also included a backtrace from gdb.

mk ( 2014-10-17 11:12:51 -0600 )edit

boaz001 I found that arithm_op was trying to access one InputArray that was a noArray() . And since the noArray function returns a static object, it may not be initialized. My workaround was to change the definition of _none in modules/core/src/matrix.cpp:

//static _OutputArray _none;
static _OutputArray noneOutputArray()
{
    static _OutputArray none;
    return &amp;none;
}
#define _none *noneOutputArray()

The define was used to avoid interferences with other code that may be using the _none object. (And to avoid the need to change that code)

I am writing this in the comment because I cannot answer my own question yet. (only tomorrow)

mk ( 2014-10-17 14:32:41 -0600 )edit

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answered 2014-10-20 08:56:24 -0600

mk
31 ●3

I found that arithm_op was trying to access one InputArray that was a noArray() and, since the noArray function returns a static object, it may not be initialized.

My workaround was to change the definition of _none in modules/core/src/matrix.cpp:

//static _OutputArray _none;
static _OutputArray noneOutputArray()
{
    static _OutputArray none;
    return &none;
}
#define _none *noneOutputArray()

The define was used to avoid interferences with other code that may be using the _none object. (And to avoid the need to change that code)

I don't know if this can/will affect the behavior of other parts of OpenCV.

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