Re: -fPIC issue

Jakub Jelinek writes:

 > With the exception of Mesa stuff .a XFree86 libraries which are not
 > shipped as shared libs too (.so + .a) aren't performance critical
 > either, and using non-fpic code in them has some bad consequences:

Yes, most of these libraries aren't performance critical.
They don't do much more than providing a C interface
to the underlying request.

 > 1) it means the whole shared libs which link in even one tiny
 >    XFree86 non-fpic .a lib are DT_TEXTREL, which means bigger
 >    overhead when loading them and more unshareable pages.
 > 2) they have more relocations, meaning more time spent in the
 >    dynamic linker on startup.
 > 3) if there are any symbol lookup conflicts, it means those libraries
 >    aren't prelink(8)able, which can mean e.g. that all of KDE
 >    cannot be prelinked [1].

Yes, that's an issue I've learned about today, too.
Thank you for bringing it up here.

I was told prelinking may reduce kde application 
startup time by about 30 to 40 percent. This is 
definitely an aspect to keep in mind.

 > 
 > So IMHO the default XFree86 behaviour, tweakable through imake macros,
 > should be that .a libs which come with a corresponding .so should be
 > -fno-pic while .a libs which don't have a corresponding .so should be
 > -fpic.
 > (Below is a patch I wrote months ago for this).

So far I only marked those libraries that were identified by
toolkits groups as targets of possible encasulation to be build
with -fpic. Currently it is easy enough make ia32 build with pic. 
Just add a:
#define StaticNeedsPicForShared YES
to config/cf/hosts.def. 
Before we decide to add PIC to  more/all .a files without 
corresponding .so we should see if there are arguments 
against this.

 > 
 > As for Mesa, IMHO even libGL.so should be compiled with -fpic, I have some
 > patches which should optimize the performance critical places in there,
 > will test and benchmark them in the following days (had no 3D hardware until
 > recently so couldn't do testing nor measurements) and post them afterwards.
 > 
 > [1] ftp://people.redhat.com/jakub/prelink/
 > 

Have you raised this issue on the MESA/DRI mailing list?
Once you have your benchmarks ready you should do so.

Egbert.