Python C API - 使用比较函数导致'分段错误'

Question

我目前正在尝试学习用C编写Python扩展,一切似乎进展顺利.但是,当我尝试使用比较功能时,它们都会导致Segmentaion故障.例如:

#include "Python.h"

int test(void) {
    int result;
    printf("Before compare...\n");
    result = PyObject_Compare(PyInt_FromLong(1), PyInt_FromLong(3));
    printf("result= %d\n", result);
    return 0;   
}

test()从Python 执行(我使用ctypes)给出以下输出:

Before compare...
Segmentation fault

对于其他比较函数,我发生这种情况,例如:PyObject_cmp......等

任何帮助表示赞赏,谢谢.

更多信息:

我首先将文件(test.c)编译为共享库:

$> python-config --cflags
-I/usr/include/python2.7 -I/usr/include/python2.7 -fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes
$> python-config --ldflags
-L/usr/lib/python2.7/config -lpthread -ldl -lutil -lm -lpython2.7 -Xlinker -export-dynamic -Wl,-O1 -Wl,-Bsymbolic-functions

$> gcc -c $(python-config --cflags) ./test.c -o test.o
$> gcc -shared  ./test.o  $(python-config --ldflags) -o libtest.so

然后我从Python开始这样的功能:

import ctypes
testlib = ctypes.CDLL('./libtest.so')

testlib.test()

编辑:

使用Viktor给出的测试

$> gcc -o dlltest test.c -ldl
$> gdb dlltest
(gdb) run
Starting program: dlltest 
[Thread debugging using libthread_db enabled]
Cannot find new threads: generic error
(gdb) 

所以我这样做了:

$> LD_PRELOAD=libpthread-2.13.so gdb dlltest
(gdb) run
Starting program: dlltest
[Thread debugging using libthread_db enabled]
Before compare...
result= -1
[Inferior 1 (process 3274) exited normally]
(gdb)

编辑2:

>$ gdb --args python frompython.py
(gdb) run
Starting program: /usr/bin/python frompython.py
[Thread debugging using libthread_db enabled]
Before compare...

Program received signal SIGSEGV, Segmentation fault.
0x080a855b in PyObject_Compare ()
(gdb) backtrace
#0  0x080a855b in PyObject_Compare ()
#1  0x005225d8 in test () at ./testmod.c:29
#2  0x005181ca in ffi_call_SYSV ()
   from /usr/lib/python2.7/lib-dynload/_ctypes.so
#3  0x00517eff in ffi_call () from /usr/lib/python2.7/lib-dynload/_ctypes.so
#4  0x00510312 in _ctypes_callproc ()
   from /usr/lib/python2.7/lib-dynload/_ctypes.so
#5  0x0050788d in ?? () from /usr/lib/python2.7/lib-dynload/_ctypes.so
#6  0x0805dc31 in PyObject_Call ()
#7  0x080f81c1 in PyEval_EvalFrameEx ()
#8  0x080fd804 in PyEval_EvalCodeEx ()
#9  0x080fe177 in PyEval_EvalCode ()
#10 0x0811acd0 in ?? ()
#11 0x0811b8e9 in PyRun_FileExFlags ()
#12 0x0811c4cc in PyRun_SimpleFileExFlags ()
#13 0x0812c7c6 in Py_Main ()
#14 0x0805da0b in main ()
(gdb) 

Answer 1

在'test()'函数中没有初始化Python的解释器(没有Py_Initialize调用).

PyInt_FromLong()返回一个指向内部数组的指针,在你的情况下它是未初始化的.因此,您获得一些无效指针并将其传递给Py_Compare()函数会导致解释器崩溃.

有关初始化的详细信息,请参见此处:http: //docs.python.org/c-api/init.html#initializing-and-finalizing-the-interpreter

至少尝试在test()函数的开头添加"Py_Initialize()"调用.

编辑:

有趣的是,如果你使用这个编程从C运行libtest.test,那么GDB的堆栈跟踪会是什么:

#include <dlfcn.h>

typedef int (*fcn)();

int main()
{
    void* dll = dlopen("libtest.so", RTLD_LAZY);

    /* dlerror checks here */

    fcn Test = (fcn)dlsym(dll, "test");

    Test();

    dclose(dll);

    return 0;
}

EDIT2:

1. 编译测试(gcc -o dlltest test.c -ldl)

2. 运行"gdb dlltest"

3. 在gdb提示符下键入命令"run"

4. 看它是否崩溃

5. 如果是,请在gdb的提示符下键入backtrace.

EDIT3:

目前尚不清楚坠机的位置.尝试添加"fflush(stdout);" 在每次printf()调用之后,确保打印错误.

如果基于python的应用程序中出现"result = -1",则错误在ctypes中,而不在libtest.so中.