[gentoo-dev] [[e-mail]: Re: 64-bit.eclass]

[Aron Griffis]

I think it's important all developers see this, so I'm forwarding it to
gentoo-core and gentoo-dev...  (I'm referring to the text from Daniel,
not necessarily the fact that I screwed up ;-)

----- Forwarded message from Daniel Robbins <drobbins@g.o> -----

From: Daniel Robbins <drobbins@g.o>
Organization: Gentoo Technologies, Inc.
Date: Wed, 10 Dec 2003 18:02:35 -0700
To: Aron Griffis <agriffis@g.o>
Cc: alpha@g.o, amd64@g.o, ia64@g.o
Subject: Re: 64-bit.eclass

On Wed, 2003-12-10 at 17:03, Aron Griffis wrote:
> Hi all,
>
> I committed 64-bit.eclass today which contains a single function:
> 64-bit.  The point is to be able to recognize when you're building for a
> 64-bit architecture in a way where we can change the implementation as
> needed.

OK, there are a couple of problems with this approach:

1) Adding -fPIC to the compile flags makes all the code relocatable,
which is not the "right" solution for many packages (unless they are
pure libraries)

2) Lack of -fPIC is not a 64-bit issue in the first place, so there's no
reason to have a "fix" associated with 64-bit.eclass. The problems tend
to pop up on non-x86 systems, but it's really the fault of the Makefiles
in these packages. The shipped Makefiles may (barely) work on x86, but
they are not valid for non-x86 systems.

The Makefiles happen to "work" on x86 because x86 supports non-PIC
shared libraries, but it can only support them by doing text relocs.

When a non-PIC shared library is used on x86, the dynamic loader is
forced to create a private in-memory copy of the lib for every process
using the library (after fixing up addresses in each copy so it can be
used.) This means that if a package breaks during compile due to no
-fPIC on alpha, ia64 and amd64, it also happens to be wasting a lot of
memory on x86 (but nevertheless, the library does "work" on x86, even
though it's technically broken.) 

The correct solution is to:

1) find the specific sources where -fPIC is needed (and this should just
be in cases of library code, not executables)

2) make a patch to the Makefile/configure stuff to add -fPIC to these
areas only.

3) send patch upstream to fix their standard build scripts

4) Use the patch on *all* architectures, including x86 (to avoid the
text-reloc/memory wastage issue on x86)

Then you have the right solution.

Then, the problem is really fixed. Virtually all of the -fPIC issues can
be tracked down to a bad Makefile. Again, it isn't a 64-bit or 
arch-specific quirk, but an issue of a broken Makefile, so the solution
needs to be focused on fixing the Makefile for all arches.

Regards,

Daniel



----- End forwarded message -----

-- 
Aron Griffis
Gentoo Linux Developer (alpha / ia64 / ruby / vim)
Key fingerprint = E3B6 8734 C2D6 B5E5 AE76  FB3A 26B1 C5E3 2010 4EB0