-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 pro-
gram starts (the dynamic loader is not part of GCC; it is part
of the operating system). If the GOT size for the linked execu-
table 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 there
fore 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.
When this flag is set, the macros __pic__ and __PIC__ are defined to 1.
-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, PowerPC and SPARC.
Position-independent code requires special support, and therefore
works only on certain machines.
When this flag is set, the macros __pic__ and __PIC__ are defined to 2.
2 回答
如果您的目标模块将在共享库中使用，则始终需要“位置无关代码” . 它依赖于高度平台，并且会产生一些开销 .
您必须在amd64上明确指定它而不是x386的原因只是它恰好是x86的默认值，而不是amd64 .
另请注意，“-fpic”和“-fPIC”之间的区别：
好的答案在这里详细描述：http://www.technovelty.org/code/c/amd64-pic.html .
解释的基本要点是i386架构隐式取消引用每个函数的帧指针（在链接页面的最后一段解释） . 此过程会产生一些额外开销，因此在新的64位体系结构中，这种解除引用开销作为优化被消除 .
从链接角度来看，这种优化的结果是，除非将64位代码显式编译为与位置无关的代码，否则它将生成使用其执行上下文的偏移量进行硬编码的代码 .
这是对链接页面中内容的不完美解释，但它足以满足我的目的 .