c++ - "dynamically linked at run time but statically aware"- 如何控制加载哪个.so文件？

Question

引用this answer :

There are two Linux C/C++ library types.

• Static libraries (*.a) are archives of object code which are linked with and becomes part of the application. They are created with and can be manipulated using the ar(1) command (i.e. ar -t libfoo.a will list the files in the library/archive).

• Dynamically linked shared object libraries (*.so) can be used in two ways.

  1. The shared object libraries can be dynamically linked at run time but statically aware. The libraries must be available during compile/link phase. The shared objects are not included into the binary executable but are tied to the execution.
  2. The shared object libraries can be dynamically loaded/unloaded and linked during execution using the dynamic linking loader system functions.

制作动态 库是什么意思 tied to the execution ？

这像Windows manifest files吗允许应用程序加载特定的 dll?

控制.so加载的机制是什么？
必须有这样一种机制，否则“编译的”.so 是唯一允许加载的机制，这违背了使其成为动态的目的？

Answer 1

这意味着该库在链接时可用，因此链接器可以验证您从 .so 引用的函数是否存在于 .so 中。优点是对这些函数的调用对您来说是透明的。换句话说，如果您链​​接到 .so 和

int foo(double bar);

你可以这样调用它

int res = foo(4.2);

链接器确保 foo 存在，并且它接受一个 double 类型的参数。之后它将调用站点 int res = ...“链接”到该函数。

在执行期间动态加载/卸载允许您在构建系统上不存在 .so 的情况下进行链接(因此，没有“静态感知”)。作为这种增加的灵 active 的交换，您打开了系统，可能无法在目标 .so 中找到您想要的功能。您的调用序列看起来也比 foo(4.2) 复杂得多，因为您需要完成 dlopen 准备步骤。关于从 .so 调用函数的更多信息在 this Q&A 中.