我正在尝试编写最小的程序,在运行时也加载我的共享对象(.so)。
不幸的是,尽管进行了错误检查,它还是在运行时挂起:-(
我对我在源代码级别上忽略的内容非常感兴趣。
下面是源代码和运行程序的shell会话。
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): %sn", __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): %sn", __LINE__, reter);
return 1;
}
printf("INFO(%d): Resolved library sample_check() symbol at %pn", __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): %sn", __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shell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$
知道吗?
此处为
(*symver)();
代码取消引用已接收到的内容作为要运行库函数的入口点。这解析为一个随机地址,当被调用时,该地址通常会使程序崩溃。
要解决此问题,请定义
sample_func_t symver = NULL;
其中samle_func_t
由于已经是指针类型
typedef void (*sample_func_t) (void);
(注意*
.)
然后有两种可能分配symver
:
";脏的";一个
symver = dlsym(h_lib, "sample_check");
"脏的";因为编译器可能会发出这样的警告:
ISO C forbids assignment between function pointer and ‘void *’
";"清洁剂";一个
*(void**)(&symver) = dlsym(h_lib, "sample_check");
最后调用这样的函数:
symver(); /* No need to dereference here. */