linux - 动态加载时的库路径？

Question

如何从库本身获取共享库的路径？

换句话说，假设库 X 是使用 dlopen() 加载的，我如何才能从库本身中访问用于加载所述库的路径？

请注意，我不能让首先加载库的代理将此参数交给我。

更新:这是处理静态变量的方法:

std::string wdir;

namespace {
    class dynamic_library_load_unload_handler {
         public:
              dynamic_library_load_unload_handler(){
                    Dl_info dl_info;
                    dladdr((void *) NP_Initialize, &dl_info);

                    std::string path(dl_info.dli_fname);
                    wdir = path.substr( 0, path.find_last_of( '/' ) +1 );
              }
              ~dynamic_library_load_unload_handler(){
                    // Code to execute when the library is unloaded
              }
    } dynamic_library_load_unload_handler_hook;
}

Answer 1

动态链接器实际上会搜索几个地方来找到每个动态库。这些包括(来自 man ld.so):

• 环境变量 LD_LIBRARY_PATH 给出的路径
• 烘焙到二进制文件中的路径将库加载到 DT_RUNPATH 条目下
• 缓存文件/etc/ld.so.cache
• /lib 和/usr/lib

如果您想获取特定共享库的路径，我会推荐dladdr 函数。从手册页:

The function dladdr() takes a function pointer and tries to resolve name and file where it is located. Information is stored in the Dl_info structure:

typedef struct {
    const char *dli_fname;  /* Pathname of shared object that
                               contains address */
    void       *dli_fbase;  /* Address at which shared object
                               is loaded */
    const char *dli_sname;  /* Name of nearest symbol with address
                               lower than addr */
    void       *dli_saddr;  /* Exact address of symbol named
                               in dli_sname */
} Dl_info;

If no symbol matching addr could be found, then dli_sname and dli_saddr are set to NULL.

dladdr() returns 0 on error, and non-zero on success.

所以你只要给它一个函数指针，它就会给你提供它的文件的名称和一堆其他信息。因此，例如，您可以让库中的构造函数自行调用它以找出库的完整路径:

#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdio.h>

__attribute__((constructor))
void on_load(void) {
    Dl_info dl_info;
    dladdr((void *)on_load, &dl_info);
    fprintf(stderr, "module %s loaded\n", dl_info.dli_fname);
}

此函数也适用于具有相同语义的 OS X。