c++ - 通过 python ctypes 使用时，opencv 调用共享库段错误

Question

每当我使用 ctypes 将共享库 (.so) 加载到 Python 中并调用其中一个使用 OpenCV 过滤器引擎(如 cvErode 或 cvDilate)的过程时，解释器就会在 OpenCV 代码深处产生段错误。如果我在 C 程序中使用 dlopen 加载相同的库并调用相同的过程，一切正常。

我在另一篇文章中读到，它可能与 gcc 使用的 ABI 有关，并且 python 必须使用与 python 解释器编译时使用的相同版本的 gcc 进行编译才能工作。但是在我的例子中，它都是 4.4.5，所以这应该不是问题。 OpenCV 库也是使用相同版本的 gcc 编译的。

如何构建共享库:

g++ -g -shared -lopencv_core -lopencv_imgproc -lopencv_calib3d -lopencv_video -lopencv_features2d -lopencv_ml -lopencv_highgui -lopencv_objdetect -lopencv_contrib -lopencv_legacy -o thumbsplit.so thumbsplit.cpp

共享库是如何包装的:

extern "C" {

int is_thumbsheet(char * image_path){
    Image image;
    image.read(image_path);
    int width = image.columns();
    int height = image.rows();
    int BOUND_CHANGE = 7000;
    int test_height = 0;

    if( width > height ){
        return 0;
    }else{
        test_height = width;
    }
    vector<int> test_rows = getRows(image, width, test_height, BOUND_CHANGE);
    vector<int> test_cols = getCols(image, width, test_height, BOUND_CHANGE);

    vector<Box> test_boxes = createBoxes(test_rows,test_cols,width,height);
    if( test_boxes.size() > 6 ){
        return 1;
    }else{
        return 0;
    }
}

int cut_thumbs(char * image_path, char * thumb_path){
    Image image;
    image.read(image_path);
    int width = image.columns();
    int height = image.rows();
    int BOUND_CHANGE = 7000;
    vector<int> rows = getRows(image, width, height, BOUND_CHANGE);
    vector<int> cols = getCols(image, width, height, BOUND_CHANGE);

    //drawDebugLines(rows, cols, width, height);

    vector<Box> boxes = createBoxes(rows,cols,width,height);
    //printBoxes(boxes);
    char path[0x100];
    for( int i=0 ; i < boxes.size() ; i++ ){
        sprintf(path, "%s%d.jpg", thumb_path, i);
        boxes[i].saveBox(image, path);
    }


    return 0;
}

} // C

如何在 python 中加载共享库过程:

import ctypes, os

def load_lib():
lib_path = "%s/%s"%(os.path.realpath(os.path.dirname(__file__)), "thumbsplit.so")
lib = ctypes.CDLL(lib_path)
return lib

def is_thumbsheet(image_path):

lib = load_lib()
if lib.is_thumbsheet(image_path):
    return True
else:
    return False

def cut_thumbs(image_path, thumbs_path):

lib = load_lib()
lib.cut_thumbs(image_path, thumbs_path)

is_thumbsheet("/home/rolf/test/imageproc/full9.jpg") # this segfaults

GDB 输出:

$ gdb python
GNU gdb (GDB) 7.0.1-debian
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/bin/python...(no debugging symbols found)...done.
(gdb) run thumbsheet.py
Starting program: /usr/bin/python thumbsheet.py
[Thread debugging using libthread_db enabled]
0xb6330a12

Program received signal SIGSEGV, Segmentation fault.
0xb76fe2dc in cv::FilterEngine::start(cv::Size_<int>, cv::Rect_<int>, int) () from /usr/local/lib/libopencv_imgproc.so.2.3
(gdb) info stack
#0  0xb76fe2dc in cv::FilterEngine::start(cv::Size_<int>, cv::Rect_<int>, int) () from /usr/local/lib/libopencv_imgproc.so.2.3
#1  0xb76feb41 in cv::FilterEngine::start(cv::Mat const&, cv::Rect_<int> const&, bool, int) ()
   from /usr/local/lib/libopencv_imgproc.so.2.3
#2  0xb770a52b in cv::FilterEngine::apply(cv::Mat const&, cv::Mat&, cv::Rect_<int> const&, cv::Point_<int>, bool) ()
   from /usr/local/lib/libopencv_imgproc.so.2.3
#3  0xb764bf8a in cv::morphOp(int, cv::_InputArray const&, cv::_OutputArray const&, cv::_InputArray const&, cv::Point_<int>, int, int, cv::Scalar_<double> const&) () from /usr/local/lib/libopencv_imgproc.so.2.3
#4  0xb764d2ce in cv::erode(cv::_InputArray const&, cv::_OutputArray const&, cv::_InputArray const&, cv::Point_<int>, int, int, cv::Scalar_<double> const&) () from /usr/local/lib/libopencv_imgproc.so.2.3
#5  0xb764d62e in cvErode () from /usr/local/lib/libopencv_imgproc.so.2.3
#6  0xb7fd7adb in seperate::findSeperatedBoxes (img=0x8351d70) at seperate.cpp:189
#7  0xb7fd7fcf in seperate::trySeperatedBoxes (img=0x8351d70, percentage_boxed=0xbfffefec) at seperate.cpp:202
#8  0xb7fda00c in is_thumbsheet (image_path=0xb7c1bf74 "/home/rolf/test/imageproc/full9.jpg") at thumbsplit.cpp:39
#9  0xb7a047df in ffi_call_SYSV () from /usr/lib/python2.6/lib-dynload/_ctypes.so
#10 0xb7a0461e in ffi_call () from /usr/lib/python2.6/lib-dynload/_ctypes.so
#11 0xb79ff27d in _CallProc () from /usr/lib/python2.6/lib-dynload/_ctypes.so
#12 0xb79f6d7e in ?? () from /usr/lib/python2.6/lib-dynload/_ctypes.so
#13 0x0806232a in PyObject_Call ()
#14 0x080e016b in PyEval_EvalFrameEx ()
#15 0x080e18b0 in PyEval_EvalFrameEx ()
#16 0x080e2507 in PyEval_EvalCodeEx ()
#17 0x080e2607 in PyEval_EvalCode ()
#18 0x080ffcbd in PyRun_FileExFlags ()
#19 0x080fff22 in PyRun_SimpleFileExFlags ()
#20 0x0805dd81 in Py_Main ()
#21 0x0805cf6b in main ()
(gdb) x/i 0xb76fe2dc
0xb76fe2dc <_ZN2cv12FilterEngine5startENS_5Size_IiEENS_5Rect_IiEEi+1212>:   movdqa %xmm3,0x30(%esp)
(gdb)

GCC/G++ 版本:

$ python
Python 2.6.6 (r266:84292, Dec 27 2010, 00:02:40) 
[GCC 4.4.5] on linux2

$ gcc --version
gcc (Debian 4.4.5-8) 4.4.5

$ g++ --version
g++ (Debian 4.4.5-8) 4.4.5

OpenCV 是 2.3.1 版，是使用此版本的 gcc (4.4.5-8) 从源代码构建的

Answer 1

我找到了解决方案。对于 SSE 指令，堆栈需要重新对齐为 16 字节。如果我使用 -mstackrealign 构建共享库，它可以完美地从 python 加载和调用。

Qt, GCC, SSE and stack alignment