I've already read the gcc manpage, but I still can't understand the difference between -fpic and -fPIC. Can someone explain it, in a very simple and clear way?
Related questions:
http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html
Use -fPIC or -fpic to generate position independent code. Whether to use -fPIC or -fpic to generate position independent code is target-dependent. The -fPIC choice always works, but may produce larger code than -fpic (mnenomic to remember this is that PIC is in a larger case, so it may produce larger amounts of code). Using -fpic option usually generates smaller and faster code, but will have platform-dependent limitations, such as the number of globally visible symbols or the size of the code. The linker will tell you whether it fits when you create the shared library. When in doubt, I choose -fPIC, because it always works.
From the Gcc manual page:
When generating code for shared libraries, -fpic implies -msmall-data and -fPIC implies -mlarge-data.
Where:
-msmall-data
-mlarge-data
When -mexplicit-relocs is in effect, static data is accessed via
gp-relative relocations. When -msmall-data is used, objects 8
bytes long or smaller are placed in a small data area (the
".sdata" and ".sbss" sections) and are accessed via 16-bit
relocations off of the $gp register. This limits the size of the
small data area to 64KB, but allows the variables to be directly
accessed via a single instruction.
The default is -mlarge-data. With this option the data area is
limited to just below 2GB. Programs that require more than 2GB
of data must use "malloc" or "mmap" to allocate the data in the
heap instead of in the program's data segment.
When generating code for shared libraries, -fpic implies
-msmall-data and -fPIC implies -mlarge-data.
来源：https://stackoverflow.com/questions/3544035/what-is-the-difference-between-fpic-and-fpic-gcc-parameters