-fPIC在构建共享库时意味着什么？

Question

我知道' -fPIC'选项与解决各个模块之间的地址和独立性有关,但我不确定它的真正含义.你可以解释吗？

Answer 1

PIC代表位置独立代码

并引述man gcc:

如果目标机器受支持,则发出与位置无关的代码,适用于动态链接并避免对全局偏移表的大小进行任何限制.此选项对m68k,PowerPC和SPARC产生影响.与位置无关的代码需要特殊支持,因此仅适用于某些机器.

在这些提到的体系结构上构建共享对象(*.so)时使用它.

Answer 2

的f是选项"控制接口约定在代码生成中使用的"在gcc前缀

该PIC代表"位置无关的代码",它的一个专业化fpic的M68K和SPARC.

编辑:在阅读0x6adb015引用的文档的第11页和coryan的评论后,我做了一些更改:

此选项仅对共享库有意义,并且您告诉操作系统您正在使用全局偏移表GOT.这意味着您的所有地址引用都与GOT相关,并且代码可以在多个进程中共享.

否则,如果没有此选项,加载程序将必须自行修改所有偏移量.

不用说,我们几乎总是使用-fpic/PIC.

Answer 3

man gcc 说:

-fpic
  Generate position-independent code (PIC) suitable for use in a shared
  library, if supported for the target machine. Such code accesses all
  constant addresses through a global offset table (GOT). The dynamic
  loader resolves the GOT entries when the program starts (the dynamic
  loader is not part of GCC; it is part of the operating system). If
  the GOT size for the linked executable exceeds a machine-specific
  maximum size, you get an error message from the linker indicating
  that -fpic does not work; in that case, recompile with -fPIC instead.
  (These maximums are 8k on the SPARC and 32k on the m68k and RS/6000.
  The 386 has no such limit.)

  Position-independent code requires special support, and therefore
  works only on certain machines. For the 386, GCC supports PIC for
  System V but not for the Sun 386i. Code generated for the
  IBM RS/6000 is always position-independent.

-fPIC
  If supported for the target machine, emit position-independent code,
  suitable for dynamic linking and avoiding any limit on the size of
  the global offset table.  This option makes a difference on the m68k
  and the SPARC.

  Position-independent code requires special support, and therefore
  works only on certain machines.