将目标文件符号变为可执行文件中的动态符号

Question

我有几个从构建系统中吐出的目标文件（来自C++）。他们有几个extern "C"-我想在程序中使用的链接符号，并且可以通过其他地方的dlopen/dlsym访问。

当使用gcc编译为可执行文件时，这些符号未使用nm -D <executable-here>（即afaik它们不是动态符号）列出。

如何让它们在编译后的可执行文件中显示为动态符号？

我可以改变目标文件和可执行文件的构建标志，但是改变C++文件在最终可执行文件中的结果（即不是先将它们变成目标文件）是很困难的。

（GCC 4.8，LD 2.24）

编辑：我碰到这个问题，可能会或可能不会是我在问什么，但我不能完全肯定。 Use dlsym on a static binary

Answer 1

你可能想看看--export-dynamic ld的选项：

-E 
    --export-dynamic 
    --no-export-dynamic 
     When creating a dynamically linked executable, using the -E option 
     or the --export-dynamic option causes the linker to add all symbols 
     to the dynamic symbol table. The dynamic symbol table is the set 
     of symbols which are visible from dynamic objects at run time. 

     If you do not use either of these options (or use the 
     --no-export-dynamic option to restore the default behavior), the 
     dynamic symbol table will normally contain only those symbols which 
     are referenced by some dynamic object mentioned in the link. 

     If you use "dlopen" to load a dynamic object which needs to refer 
     back to the symbols defined by the program, rather than some other 
     dynamic object, then you will probably need to use this option when 
     linking the program itself. 

     You can also use the dynamic list to control what symbols should be 
     added to the dynamic symbol table if the output format supports it. 
     See the description of --dynamic-list. 

     Note that this option is specific to ELF targeted ports. PE 
     targets support a similar function to export all symbols from a DLL 
     or EXE; see the description of --export-all-symbols below. 

另外，如果没有链接中的对象是指你的外部符号，你可能想将其付诸--dynamic-list使肯定他们出口。

---

例子：

$ cat test.cc 
#include <stdio.h> 

int main() { 
    printf("Hello, world\n"); 
} 

extern "C" void export_this() { 
    printf("Hello, world from export_this\n"); 
} 

$ g++ -o test -W{all,extra} -Wl,--export-dynamic test.cc 

$ ./test 
Hello, world 

$ nm --dynamic test | grep export_this 
00000000004007f5 T export_this # <---- here you go