加载时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

加载时链接是指可执行文件(或其他库)引用的库中的符号在可执行文件/库加载到内存时被处理，通过操作系统.

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，但原理应该是相同的..NET 库可能会有所不同.

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

在 linux 中，插件架构是这样完成的.您的程序将使用运行时链接来加载库并调用一些函数.然后也许卸载它.它还允许加载具有相同符号的多个库而不会发生冲突.我认为 DLL 将以几乎相同的方式工作.

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"，需要一些库来填充.这些空格通常在加载时或编译时填充.您可以使用运行时链接来消除符号表中对空格"的需求.

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，或在运行时从多个 ABI/API 兼容库中进行选择.我经常有一个库，比如foo"和一个名为foo_unstable"的库，并且有一个测试应用程序可以在两者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，要查看可执行文件在加载时链接到哪些库，请运行 ldd 命令并获取输出，例如 (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

操作系统将在加载时尝试加载库(.so 文件).它可能已经在内存中拥有该库.

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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