编译so 文件 gcc -shared -fPIC
-fPIC 是什么意思呢。。。
看GCC手册
-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.
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.
也就是生成与位置无关的代码 windows上面是通过加一个重定位表来实现的 。。
linux 和 windows类似 使用了个 GOT 全局偏移描述表来实习动态的定位 、、
系统加载的时候 会根据加载的地址 修正偏移表里的偏移 这样就实现了代码的执行与代码所在的位置位置无关。。
怎么使用动态链接库呢 shared object
