gcc选项-fPIC的问题

linkejin

首先-fpic,gcc手册上说是编译共享库库
-fPIC,gcc手册上说是动态链接

是不是-fPIC就是支持动态链接的共享库？

Configured with: /dw/gaoming/x01tool/buildroot/toolchain_build_arm/gcc-4.0.1/configure --prefix=/dw/buildroot/build_arm/staging_dir --build=i386-pc-linux-gnu --host=i386-pc-linux-gnu --target=arm-linux-uclibc --enable-languages=c,c++ --disable-__cxa_atexit --enable-target-optspace --with-gnu-ld --disable-shared --disable-nls --enable-threads --enable-multilib
Thread model: posix
gcc version 4.0.1

这个工具链在编译时候加上－fPIC选项和不加fPIC是有区别的，加了可以达到共享库的效果

Configured with: ../gcc-3.4.2/configure --prefix=/opt/toolchains/uclibc-crosstools_gcc-3.4.2_uclibc-20050502/ --target=mips-linux-uclibc --build=mips-linux --host=mips-linux --enable-target-optspace --disable-nls --with-gnu-ld --enable-shared --enable-languages=c,c++ --enable-threads --infodir=/opt/toolchains/uclibc-crosstools_gcc-3.4.2_uclibc-20050502/info --mandir=/opt/toolchains/uclibc-crosstools_gcc-3.4.2_uclibc-20050502/man --disable-__cxa_atexit --disable-checking --with-arch=mips32
Thread model: posix
gcc version 3.4.2

这个工具链加不加fPIC都可以达到共享库的效果

我看他们的区别就是--disable-shared  --enable-shared
我的理解是gcc enable－shared后就不用加fPIC选项了，不知道是否正确

另外我想知道，机器上已经装好gcc了，我如何在命令行中改变gcc的配置？

zhuhefang2006

-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 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 16k on the m88k,
           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, m88k, and the Sparc.

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