c - 如何使用静态库 libdl.a 编译程序

Question

我正在尝试编译使用 libdl 库中的 API 的示例代码:

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

int
main(int argc, char **argv)
{
    void *handle;
    double (*cosine)(double);
    char *error;

   handle = dlopen("libm.so", RTLD_LAZY);
    if (!handle) {
        fprintf(stderr, "%s\n", dlerror());
        exit(EXIT_FAILURE);
    }

   dlerror();    /* Clear any existing error */

   /* Writing: cosine = (double (*)(double)) dlsym(handle, "cos");
       would seem more natural, but the C99 standard leaves
       casting from "void *" to a function pointer undefined.
       The assignment used below is the POSIX.1-2003 (Technical
       Corrigendum 1) workaround; see the Rationale for the
       POSIX specification of dlsym(). */

   *(void **) (&cosine) = dlsym(handle, "cos");

   if ((error = dlerror()) != NULL)  {
        fprintf(stderr, "%s\n", error);
        exit(EXIT_FAILURE);
    }

   printf("%f\n", (*cosine)(2.0));
    dlclose(handle);
    exit(EXIT_SUCCESS);
}

我使用以下命令进行编译:--> gcc -static -o foo foo.c -ldl

我收到以下错误:

foo.c:(.text+0x1a): warning: Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking

google了一下，因为我是静态编译的，所以在lib目录下可以找到libdl.a。我也遇到了与 gethostbyname API 相同的问题。静态编译 dl_open 需要添加哪些其他库。

Answer 1

一个可能的问题:

dlsym()

应该在 它被 ma​​in() 引用之前声明或实现。