How to recompile with -fPIC

问题

I was trying to reinstall my ffmpeg, following this guide, on my ARM Ubuntu machine. Unfortunately, when I compile a program which uses this lib I get the following failure:

/usr/bin/ld: /usr/local/lib/libavcodec.a(amrnbdec.o): relocation R_ARM_MOVW_ABS_NC against `a local symbol\' can not be used when making a shared object; recompile with -fPIC
/usr/local/lib/libavcodec.a: could not read symbols: Bad value
collect2: ld returned 1 exit status

Now I would like to recompile it with -fPIC like the compiler is suggesting but I have no idea how. Any help is appreciated.

回答1:

in brief, the error means that you can't use a static library to be linked w/ a dynamic one. The correct way is to have a libavcodec compiled into .so instead of .a, so the other .so library you are trying to build will link well.

the shortest way to do so is to add --enable-shared at ./configure options. or even you may try to disable shared (or static) libraries at all... you choose what is suitable for you!

回答2:

Have a look at this page.

you can try globally adding the flag using: export CXXFLAGS="$CXXFLAGS -fPIC"

回答3:

After the configure step you probably have a makefile. Inside this makefile look for CFLAGS (or similar). puf -fPIC at the end and run make again. In other words -fPIC is a compiler option that has to be passed to the compiler somewhere.

回答4:

I hit this same issue trying to install Dashcast on Centos 7. The fix was adding -fPIC at the end of each of the CFLAGS in the x264 Makefile. Then I had to run make distclean for both x264 and ffmpeg and rebuild.

回答5:

I had this problem when building FFMPEG static libraries (e.g. libavcodec.a) for Android x86_64 target platform (using Android NDK clang). When statically linking with my library the problem occured although all FFMPEG C -> object files (*.o) were compiled with -fPIC compile option:

x86_64/libavcodec.a(h264_qpel_10bit.o): 
requires dynamic R_X86_64_PC32 reloc against 'ff_pw_1023' 
which may overflow at runtime; recompile with -fPIC

The problem occured only for libavcodec.a and libswscale.a.

Source of this problem is that FFMPEG has assembler optimizations for x86* platforms e.g. the reported problem cause is in libavcodec/h264_qpel_10bit.asm -> h264_qpel_10bit.o.

When producing X86-64 bit static library (e.g. libavcodec.a) it looks like assembler files (e.g. libavcodec/h264_qpel_10bit.asm) uses some x86 (32bit) assembler commands which are incompatible when statically linking with x86-64 bit target library since they don't support required relocation type.

Possible solutions:

compile all ffmpeg files with no assembler optimizations (for ffmpeg this is configure option: --disable-asm)
produce dynamic libraries (e.g. libavcodec.so) and link them in your final library dynamically

I chose 1) and it solved the problem.

Reference: https://tecnocode.co.uk/2014/10/01/dynamic-relocs-runtime-overflows-and-fpic/