加载时间动态链接和运行时动态链接之间的区别 [英] Difference between load-time dynamic linking and run-time dynamic linking

问题描述

将程序加载到内存中时，加载时动态链接和运行时动态链接有什么区别？

When loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?

推荐答案

加载时间链接是指当操作系统将可执行文件/库加载到内存时，由可执行文件（或另一个库）引用的库中的符号被处理。

load-time linking is when symbols in the library, referenced by the executable (or another library) are handled when the executable/library is loaded into memory, by the operating system.

运行时链接是指当您使用操作系统提供的API或通过库在需要时加载DLL或DSO，然后执行符号解析。

Run-time linking is when you use an API provided by the OS or through a library to load a DLL or DSO when you need it, and perform the symbol resolution then.

我比Windows DLL更了解Linux DSO，但原则应该是一样的。 .NET库可能有所不同。

I know more about Linux DSOs than Windows DLL's but the principle should be the same. .NET libraries may differ.

在linux中，插件架构以这种方式完成。您的程序将使用运行时链接加载库并调用某些功能。然后可能卸载它。它还允许导出加载相同符号的多个库，而不会发生冲突。我认为DLL将以相同的方式工作。

In linux, plugin architectures are done this way. Your program will use runtime linking to load up a library and call some functions. Then maybe unload it. It also allows multiple libraries with the same symbols exported to be loaded without clashing. I think DLLs will work in much the same manner.

可执行文件的符号表中有空格，需要填充某些库。这些空格通常是在加载时或编译时填写的。您可以通过使用运行时链接来否定符号表中空格的需要。

Executables have "blank spaces" in their symbol tables that need filling by some library. These blank-spaces are usually filled in at load-time, or compile time. You can negate the need for "blank spaces" in the symbol table by using runtime linking.

运行时链接有用的另一个场景是调试库，或者在运行时从多个ABI / API兼容的库中进行选择。我经常有一个图书馆，说foo和一个叫foo_unstable，并有一个测试应用程序在2之间切换并进行一些测试。

Another scenario where runtime linking is useful is for debugging libraries, or selecting from multiple, ABI/API compatible libraries at runtime. I often have a library, say "foo" and one called "foo_unstable" and have a test app that switches between the 2 and does some testing.

在linux下，看看可执行程序链接到哪个库可以在加载时运行 ldd 命令，并获取输出（on / bin / ls）：

Under linux, to see what libraries an executable links to at load-time you run the ldd command and get output such as (on /bin/ls):

linux-vdso.so.1 =>  (0x00007fff139ff000)
librt.so.1 => /lib64/librt.so.1 (0x0000003c4f200000)
libselinux.so.1 => /lib64/libselinux.so.1 (0x0000003c4fa00000)
libcap.so.2 => /lib64/libcap.so.2 (0x0000003c53a00000)
libacl.so.1 => /lib64/libacl.so.1 (0x0000003c58e0000

操作系统将尝试加载库.so文件），它可能已经在内存中有库。

The operating system will attempt to load the libraries (the .so files) at load-time. It may already have the library in memory.

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