6.4.2 and 6.5

[Michel Dänzer]

On Tue, 2006-05-16 at 09:13 -0600, Marcelo E. Magallón wrote:
> 
> On 5/16/06, Michel Dänzer <daenzer at debian.org> wrote:
> > On Mon, 2006-05-15 at 12:06 -0600, Marcelo E. Magallón wrote:
> > >
> > > Now it's your turn to tell me that PowerPC is screwed up :-)
> >
> > The attached patch makes the arch specific packages build here, and they
> > seem to work fine as well.
> 
> Ok, let me try to explain why this is wrong, and how the build system
> works, perhaps starting on the why.

Note that I didn't mean to present this as a solution, just as more
evidence to point out how it breaks.


> Mesa supports architecture-specific optimizations in the form of
> hand-written assembler code.  Last time I looked at this there wasn't
> such a thing as run-time switching between the optimized and
> non-optimized versions of the code (which is not so hard to do, given
> that Mesa already supports switching between entry points).
> 
> Given the not so weird requirement by Debian that packages should work
> on certain old architectures (e.g. i486) and given the user's desire
> to have optimized versions of almost anything and given that profiling
> (by me) has shown that certain sets of compiler flags plus these
> hand-written optimizations actually have some impact in performance I
> decided to provide arch-optimized packages.
> 
> The first and the last statements are incompatible with each other if
> you take into account the first paragraph.
> 
> In order to provide these architecture-optimized packages we *HAVE* to
> provide non-optimized versions.  This is the reason why Mesa builds
> the source several times.  Otherwise random programs will fail with
> "Illegal instruction" and the user won't understand why.

I understand all this, but Mesa doesn't contain any PPC assembly code
yet, and it doesn't use any build flags that prevent the code from
running on older machines either. In fact, /lib/ld.so.1 doesn't seem to
contain any sub-architecture specific paths. The only thing that needs
overriding for powerpc at this point is the list of drivers.


> Now, if debian/README.build is not clear enough, please provide a patch.

All I can say right now is that contrary to what this says, the build
tried to act on the gl-debian-dri_powerpc target even though it wasn't
listed in libdir.map and failed.


-- 
Earthling Michel Dänzer           |          http://tungstengraphics.com
Libre software enthusiast         |          Debian, X and DRI developer