5

我正在尝试编写在运行时加载我的共享对象(.so)的最小程序。

不幸的是,尽管进行了错误检查,它仍会在运行时挂起:-(

我对我在源代码级别忽略的内容非常感兴趣。

源代码和运行我的程序的 shell 会话如下。

文件“libsample.c”:

#include <stdio.h>

void sample_check(void)
{
    printf("INFO: Function sample_check() called.\n");
}

文件“test.c”:

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

typedef void (*sample_func_t) (void);

int main(void)
{
    setbuf(stdout, NULL);
    setbuf(stderr, NULL);
    void* h_lib = dlopen("./libsample.so.1", RTLD_LAZY); // RTLD_LAZY || RTLD_NOW
    if (! h_lib)
    {
        fprintf(stderr, "ERROR(%d): %s\n", __LINE__, dlerror());
        return 1;
    }

    sample_func_t* symver = NULL;
    dlerror();
    symver = dlsym(h_lib, "sample_check");
    char* reter = dlerror();
    if (reter)
    {
        fprintf(stderr, "ERROR(%d): %s\n", __LINE__, reter);
        return 1;
    }

    printf("INFO(%d): Resolved library sample_check() symbol at %p\n", __LINE__, symver);
    printf("INFO(%d): About to call library sample_check() ...\n", __LINE__);
    (*symver)();
    printf("INFO(%d): sample_check() called !\n", __LINE__);

    int retcl = dlclose(h_lib);
    if (retcl)
    {
        fprintf(stderr, "ERROR(%d): %s\n", __LINE__, dlerror());
        return 1;
    }

    return 0;
}

文件“构建”:

#! /bin/bash

echo "Begin of compilation ..."

rm test test.o libsample.so.1 libsample.so.1.0.1 libsample.o 2>/dev/null

gcc -fpic -c -o libsample.o libsample.c || exit 1

gcc -shared -Wl,-soname,libsample.so.1 -o libsample.so.1.0.1 libsample.o || exit 1

ln -s libsample.so.1.0.1 libsample.so.1 || exit 1

gcc -c -o test.o test.c || exit 1

gcc -o test test.o -ldl || exit 1

echo "Compilation successful !"

我的外壳会话日志:

valentin@valentin-SATELLITE-L875-10G:~/PROGRAMMING/C/Libraries/libsample$ 
valentin@valentin-SATELLITE-L875-10G:~/PROGRAMMING/C/Libraries/libsample$ ./build 
Begin of compilation ...
Compilation successful !
valentin@valentin-SATELLITE-L875-10G:~/PROGRAMMING/C/Libraries/libsample$ ./test 
INFO(27): Resolved library sample_check() symbol at 0x7f5e96df86f0
INFO(28): About to call library sample_check() ...
Erreur de segmentation
valentin@valentin-SATELLITE-L875-10G:~/PROGRAMMING/C/Libraries/libsample$ 

任何想法 ?

4

1 回答 1

3

这里

 (*symver)();

代码取消引用作为要运行的库函数的入口点接收到的内容。这会解析为一个随机地址,该地址在被调用时通常会使程序崩溃。

要修复此定义

sample_func_t symver = NULL;

wheresamle_func_t已经是指针类型,因为

typedef void (*sample_func_t) (void);

(注意*。)

那么有两种分配的可能性symver

  1. “肮脏”的那个

     symver = dlsym(h_lib, "sample_check");
    

    “脏”,因为编译器可能会发出如下警告:

     ISO C forbids assignment between function pointer and ‘void *’
    
  2. “清洁工”之一

     *(void**)(&symver) = dlsym(h_lib, "sample_check");
    

最后像这样调用函数:

symver(); /* No need to dereference here. */
于 2015-12-06T12:42:31.093 回答