linux g++ 将 64 位共享库代码链接到静态库

Question

上下文:我可以创建一个链接到静态库的共享对象库，在 32 位 Linux 上没有任何问题。当我在 64 位 Linux 上尝试相同的构建时，我看到了这个链接器错误:

• 创建共享对象时不能使用针对“局部符号”的重定位 R_X86_64_32S；重新编译 -fPIC

这个错误在网络上很常见。解决方案是使用位置无关代码(-fPIC)编译静态链接库。

我不明白的是为什么 32 位版本不需要这样做。有人可以帮忙吗？

Answer 1

如果您的目标模块将在共享库中使用，则始终需要“位置独立代码”。它高度依赖于平台，并且会产生一些开销。

您必须在 amd64 而不是 x386 上明确指定它的原因很简单，它恰好是 x86 的默认设置，而不是 amd64。

还要注意“-fpic”和“-fPIC”之间的区别:

-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.