未定义的引用 - 尽管链接器找到了 lib [英] Undefined reference - despite lib being found by linker

问题描述

我有一个简单的程序来测试 python 开发文件的可用性:

I have a trivial program to test for availability of python development files:

#include<Python.h>
int main(){Py_Initialize(); Py_Finalize(); }

我将它(安装了 python 2.7)编译为 gcc -I/usr/include/python2.7 -lpython2.7 p.c.它在其他机器上运行良好，除了在 Ubuntu 12.04(精确)的大部分干净的 chroot 上我不断得到

I compile it (with python 2.7 installed) as gcc -I/usr/include/python2.7 -lpython2.7 p.c. It works fine on other machines, except that at mostly-clean chroot of Ubuntu 12.04 (precise) I keep getting

/tmp/ccj8Mgjb.o: In function `main':
p.c:(.text+0x5): undefined reference to `Py_Initialize'
p.c:(.text+0xa): undefined reference to `Py_Finalize'
collect2: ld returned 1 exit status

头文件已安装，/usr/lib/libpython2.7.so 存在，但链接器仍然失败.该符号列在.so文件中，gcc正在读取正确的libpython2.7.so:

Headers are installed, /usr/lib/libpython2.7.so exists but the linker nevertheless fails. The symbol is listed in the .so file, and gcc is reading the right libpython2.7.so:

$ nm -D libpython2.7.so.1.0  | grep Py_Initialize
00000000000c9c20 T Py_Initialize
00000000000c9260 T Py_InitializeEx

$ strace -f gcc -I/usr/include/python2.7 -lpython2.7 /tmp/p.c 2>&1 |grep   libpython2.7 |grep open
[pid 10618] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/libpython2.7.so", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10618] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/libpython2.7.a", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10618] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libpython2.7.so", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10618] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libpython2.7.a", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10618] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libpython2.7.so", O_RDONLY) = 7

有什么想法吗?

推荐答案

试试:

gcc -I/usr/include/python2.7 p.c -lpython2.7 

链接器在加载 libpython2.7.a 时还不知道 Py_Initialize 是必需的符号，因此将其丢弃.然后它到达 p.o 并抛出一个关于丢失符号的适合.以这种方式排序将让链接器在后续输入中查找丢失的符号.

the linker doesn't yet know that Py_Initialize is a required symbol when it loads libpython2.7.a, so it tosses it away. And then it gets to p.o and throws a fit about the missing symbol. Ordering it this way will let the linker look for the missing symbol in subsequent inputs.

参见:http://gcc.gnu.org/onlinedocs/gcc/Link-Options.html

在命令的哪个位置编写此选项会有所不同；链接器按照指定的顺序搜索和处理库和目标文件.因此，foo.o -lz bar.o' 在文件 foo.o 之后但在 bar.o 之前搜索库z'.如果 bar.o 引用了 `z' 中的函数，这些函数可能不会被加载.

It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o' searches libraryz' after file foo.o but before bar.o. If bar.o refers to functions in `z', those functions may not be loaded.

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