我细读glibc的时候我通过套接字code来了，可有人解释这是怎么回事？ [英] I was perusing glibc when I came across the socket code, can someone explain what is going on?

问题描述

下面是我在浏览来源：​​<一个href=\"http://sourceware.org/git/?p=glibc.git;a=tree;f=socket;h=8217353b094378659dae035c0619f6495172523c;hb=2543fef229599e8a6e4feeea65ca2dd3f984154f\">glibc来源。我特别的问题是从这一组特定的功能：<一href=\"http://sourceware.org/git/?p=glibc.git;a=tree;f=socket;h=8217353b094378659dae035c0619f6495172523c;hb=2543fef229599e8a6e4feeea65ca2dd3f984154f\">socket库。

Here is the source I was browsing: glibc source. My particular question arises from this particular set of functions: socket library.

例如（大部分功能都设置了这种方式）的插座/ bind.c 来源：

For example(most of the functions are set up this way) socket/bind.c's source is:

  19 #include <errno.h>
  20 #include <sys/socket.h>
  21 
  22 /* Give the socket FD the local address ADDR (which is LEN bytes long).  */
  23 int
  24 __bind (fd, addr, len)
  25      int fd;
  26      __CONST_SOCKADDR_ARG addr;
  27      socklen_t len;
  28 {
  29   __set_errno (ENOSYS);
  30   return -1;
  31 }
  32 
  33 weak_alias (__bind, bind)
  34 
  35 stub_warning (bind)
  36 #include <stub-tag.h>

我承认我没有花很多的时间，但究竟哪里是code的实际功能，这是怎么回事？这是一个很好用的模式？

I admit I didn't spend a lot of time, but where exactly is the code for the actual function and what is going on? Is this a well used paradigm?

推荐答案

的 __绑定函数是一个的存根：它看起来像外部真实的东西（相同的原型），但不进行必要的函数的函数

The __bind function is a stub: it's a function that looks externally like the real thing (same prototype) but does not perform the requisite function.

的<一个href=\"http://sourceware.org/git/?p=glibc.git;a=blob;f=include/libc-symbols.h;h=252141eb0111269d721c501b1bcac0cd94c3305a;hb=2543fef229599e8a6e4feeea65ca2dd3f984154f#l110\"><$c$c>weak_alias宏告诉链接器绑定是要为 __绑定弱别名。也就是说，绑定的定义是弱符号。如果有一个名为绑定符号，没有其他的定义，这个定义代表;如果有绑定的另一个（非弱）的定义则该非弱定义站和弱定义将被忽略。弱别名是一个弱符号是另一个符号的别名（而不是让在自己的权利的定义）。在<一个href=\"http://sourceware.org/git/?p=glibc.git;a=blob;f=include/libc-symbols.h;h=252141eb0111269d721c501b1bcac0cd94c3305a;hb=2543fef229599e8a6e4feeea65ca2dd3f984154f#l280\"><$c$c>stub_warning宏将导致链接器，如果使用了弱别名发出警告。

The weak_alias macro tells the linker that bind is to be a weak alias for __bind. That is, this definition of bind is a weak symbol. If there is no other definition of a symbol called bind, this definition stands; if there is another (non-weak) definition of bind then that non-weak definition stands and the weak definition is ignored. A weak alias is a weak symbol that is an alias of another symbol (as opposed to having a definition in its own right). The stub_warning macro causes the linker to emit a warning if that weak alias is used.

真正落实绑定的依赖于操作系统的Glibc编译为上。在赫德，它<$c$c>sysdeps/mach/hurd/bind.c.在Linux上，绑定是一个系统调用：有Glibc源码，只有组装code没有C code吧。 绑定在<一个提供href=\"http://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/bind.S;h=7719ad0be8bb6c2ad6c2722393b44f148a19de1c;hb=2543fef229599e8a6e4feeea65ca2dd3f984154f\"><$c$c>sysdeps/unix/sysv/linux/bind.S其中重用插座的体系结构相关的定义 sysdeps / UNIX / SYSV / Linux的/ ** / socket.S 或端口/ sysdeps / UNIX / SYSV / Linux的/ * / socket.S 。这些定义都是围绕着底层的系统调用的所有包装薄，注意该参数和返回值复制到适当的寄存器。

The real implementation of bind depends on the operating system that Glibc is compiled for. On Hurd, it is defined in sysdeps/mach/hurd/bind.c. On Linux, bind is a system call: there is no C code for it in the Glibc source, only assembly code. bind is provided in sysdeps/unix/sysv/linux/bind.S which reuses the architecture-dependent definition of socket in sysdeps/unix/sysv/linux/**/socket.S or ports/sysdeps/unix/sysv/linux/*/socket.S. Those definitions are all thin wrappers around the underlying system call, taking care to copy the argument and the return values into the proper registers.

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