即使 nm 指示该符号存在于共享库中，也未定义对符号的引用

这里可能出了什么问题？我有以下简单的课程：

#include  "libmnl/libmnl.h"

int main() {
    struct mnl_socket *a = mnl_socket_open(12);
}

运行一个简单的之后gcc编译（gcc -lmnl main.c）我收到以下错误：

/tmp/cch3GjuS.o: In function `main':
main.c:(.text+0xe): undefined reference to `mnl_socket_open'
collect2: ld returned 1 exit status

在共享库上运行 nm 显示它确实已找到：

aatteka@aatteka-Dell1:/tmp$ nm -D /usr/lib/libmnl.so | grep mnl_socket_open
0000000000001810 T mnl_socket_open

Ubuntu 12.04 上发生这种情况。这libmnl-dev and libmnl0软件包已安装。这strace的输出gcc表明ld正在使用那个 *.so 文件：

[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.so", 0x7fff2a39b470) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.so", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.a", 0x7fff2a39b4d0) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.a", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.so", 0x7fff2a39b470) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.so", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.a", 0x7fff2a39b4d0) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.a", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libmnl.so", {st_mode=S_IFREG|0644, st_size=18608, ...}) = 0
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libmnl.so", O_RDONLY) = 7

库必须列在使用它们的对象之后（更准确地说，只有当库包含满足在遇到时已知的未定义引用的符号时，才会使用库）。移动-lmnl到命令结束。