On 09/16/2010 11:11 AM, Miles Bader wrote: > I recently wanted to produce both a standalone executable and a shared > library using the same set of object files, and so compiled them all > using -fPIC (as "gcc -shared" demeands it). I made my shared lib, and > also made a normal executable using these object files -- and I > noticed that the resulting executable size was a fair bit smaller > (according to the "size" command) than the previous non-fPIC > executable I had compiled (using non-fPIC object files). > > I haven't done any significant amount of benchmarking on it, but it > didn't seem obviously slower. > > [This is on an x86-64 system, using a g++-snapshot from debian: > gcc (Debian 20100828-1) 4.6.0 20100828 (experimental) [trunk revision 163616] ] > > Is there any general wisdom about the effects of using -fPIC, > especially on code speed? Would it be stupid for me to set up my > configure script to _always_ use -fPIC (even when not needed for a > shared library), when it detects that gcc accepts that option? I don't think it will do much harm, but I don't think it will do much good either. There will be some size increase with PIC, and that will inevitably cause some slowdown. Some processors are better than others: 32-bit x86 isn't so good with PIC. In the main, though, it's only a second-order effect. Andrew.
