amd64 and -fPIC

[Kris Kennaway]

On Tue, Mar 07, 2006 at 07:56:24PM +0100, Roman Neuhauser wrote:

> > > > > If the package includes a library that might be used frequently and doesn't
> > > > > include a shared version please add -fPIC to the amd64 version of the port, for
> > > > > example for math/arpack (and feel free to commit this):
> > > > 
> > > > The best solution is to make the port also build a shared version;
> > > > it's usually not that difficult to modify the makefile.  That way you
> > > > don't have to add nasty hacks.
> > > 
> > >     That doesn't solve the problem, which is: the static library is
> > >     almost useless, and users might actually want or need to use the
> > >     static library.
> > 
> > Why do you say it's useless?  The point of a static library is for
> > static linking, and this works fine on amd64 or any other
> > architecture.
> 
>     I say so because I installed the library (using the port) to use it
>     in a shared library. The link failed with relocation errors. As far
>     as I'm concerned (on amd64, that is), the port is dead weight.

OK, so it just needs to be fixed to build a shared library too (as I
said above).

> > >     net/libpcap only installs lib/libpcap.so if you install into /usr,
> > >     probably because all the dependent ports would need to be taught
> > >     to look in /usr/local/lib first.
> > 
> > I don't know what you're saying here.
>  
>     /usr/lib is walked first, /usr/lib/libpcap.so.N will mask
>     /usr/local/lib/libpcap.so.M

Yep, that's how it works.  Again, what is your point?

> > >     misc/ossp-uuid's ${PREFIX}/lib/libuuid.a (it configures with
> > >     --disable-shared) cannot be used in shared libraries on amd64
> > >     because the port doesn't use -fPIC on this platform.
> > 
> > The bug is presumably the --disable-shared.
> 
>     I'd prefer to link in the .a even if there was a .so.

I don't care what your preference is, it's wrong to expect this to
work (see below).

> > >     Ports that install static libraries *need* to use -fPIC on amd64.
> > 
> > No, they need to also install shared libraries.
> 
>     Ok, to help me understand your view:
> 
>     Do you agree that it's a fact that static libraries installed
>     without -fPIC can be used to create shared libraries on eg. i386?

By accident of the architecture, yes.  The architectures on which this
works are in the minority.

>     Do you agree that it's a fact that static libraries installed
>     without -fPIC *cannot* be used to create shared libraries on eg.
>     amd64?

Yes, relocatable code needs to be used in relocatable libraries on
amd64 and other architectures.  Relocatable code should not be used in
non-relocatable libraries since the extra indirection makes it slower.
This sometimes *makes a measurable performance difference* that is
important when you are trying to optimize for performance.  In fact,
chances are that the port in question is exactly such a case.

Kris
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