Re: Reason for 10.2 -fPIC requirement
On Sun, Sep 18, 2005 at 05:28:44PM +0200, Loïc Minier wrote:
> Hi,
>
> Policy 10.2: "The shared version of a library must be compiled with
> -fPIC".
>
> This is a "must", but I couldn't find where the requirement comes from
> (I only checked the changelog).
>
> I'm currently trying to resolve Debian bug #268603 where mpeg2dec is
> built with -fPIC on i386 only. As far as I understood it, -fPIC is a
> 10% performance improvement on i386 only, and a much smaller
> improvement on most other arches because they usually have more
> registers. I also have read that -fPIC is borken on some !i386 arches.
I guess you mean not using -fPIC is a performance improvement,
and ffmpeg is only not using it on i386.
> Would someone please sched some light on the origins of this
> requirement? If this requirement is only to save memory in most cases,
> would it be reasonable to permit building with -fPIC by changing this
> "must" in a "should"?
The problem is that on some architectures not using -fPIC will
just not work (hppa, amd64, alpha) while on others it's the
default (atleast ia64). I don't now about other arches. As I
understand it, i386 really is the only arch that supports non-pic
code in a shared object.
There are also ways to avoid the relocations, and I really
recommend everybody making a shared library reads Ulrich
Drepper's dso howto:
http://people.redhat.com/drepper/dsohowto.pdf
Kurt
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