LD
==

命令行选项
----------

.. versionadded:: @2019-02-20
   创建

gcc 使用 `-Wl,` 前缀，例如 `-Wl,--as-needed`\。

* --as-needed

  允许链接器忽略不需要的库。其他两个参数：

  * --no-undefined
  * --no-allow-shlib-undefined

  参考 `Unresolved symbols in shared libraries
  <https://wiki.debian.org/ToolChain/DSOLinking#Unresolved_symbols_in_shared_libraries>`_
  和 `Project:Quality Assurance/As-needed
  <https://wiki.gentoo.org/wiki/Project:Quality_Assurance/As-needed>`_\。

环境变量
--------

* LD_DEBUG

  .. versionadded:: @2011-03-09
     创建


  If LD_DEBUG is set, the linker will dump many useful debug information.
  See help below: ::

    $ LD_DEBUG=help id
    Valid options for the LD_DEBUG environment variable are:

      libs        display library search paths
      reloc       display relocation processing
      files       display progress for input file
      symbols     display symbol table processing
      bindings    display information about symbol binding
      versions    display version dependencies
      scopes      display scope information
      all         all previous options combined
      statistics  display relocation statistics
      unused      determined unused DSOs
      help        display this help message and exit

    To direct the debugging output into a file instead of standard output
    a filename can be specified using the LD_DEBUG_OUTPUT environment variable.

  See following example for a common error
  `cannot open shared object file: No such file or directory`: ::

    $ vim
    vim: error while loading shared libraries: libgcc_s.so.1: cannot open shared object file: No such file or directory
    $ LD_DEBUG=libs vim
         23579:     find library=libSM.so.6 [0]; searching
         ...
         23579:     find library=libgcc_s.so.1 [0]; searching
         23579:      search cache=/etc/ld.so.cache
         23579:       trying file=/usr/lib/gcc/x86_64-pc-linux-gnu/7.3.0/libgcc_s.so.1
         23579:      search path=/lib64/tls/x86_64/x86_64:/lib64/tls/x86_64:/lib64/tls/x86_64:/lib64/tls:/lib64/x86_64/x86_64:/lib64/x86_64:/lib64/x86_64:/lib64:/usr/lib64/tls/x86_64/x86_64:/usr/lib64/tls/x86_64:/usr/lib64/tls/x86_64:/usr/lib64/tls:/usr/lib64/x86_64/x86_64:/usr/lib64/x86_64:/usr/lib64/x86_64:/usr/lib64            (system search path)
         23579:       trying file=/lib64/tls/x86_64/x86_64/libgcc_s.so.1
         23579:       trying file=/lib64/tls/x86_64/libgcc_s.so.1
         23579:       trying file=/lib64/tls/x86_64/libgcc_s.so.1
         23579:       trying file=/lib64/tls/libgcc_s.so.1
         23579:       trying file=/lib64/x86_64/x86_64/libgcc_s.so.1
         23579:       trying file=/lib64/x86_64/libgcc_s.so.1
         23579:       trying file=/lib64/x86_64/libgcc_s.so.1
         23579:       trying file=/lib64/libgcc_s.so.1
         23579:       trying file=/usr/lib64/tls/x86_64/x86_64/libgcc_s.so.1
         23579:       trying file=/usr/lib64/tls/x86_64/libgcc_s.so.1
         23579:       trying file=/usr/lib64/tls/x86_64/libgcc_s.so.1
         23579:       trying file=/usr/lib64/tls/libgcc_s.so.1
         23579:       trying file=/usr/lib64/x86_64/x86_64/libgcc_s.so.1
         23579:       trying file=/usr/lib64/x86_64/libgcc_s.so.1
         23579:       trying file=/usr/lib64/x86_64/libgcc_s.so.1
         23579:       trying file=/usr/lib64/libgcc_s.so.1
         23579:
    vim: error while loading shared libraries: libgcc_s.so.1: cannot open shared object file: No such file or directory