[fedora-arm] About arm choice of toolchain options

[Dennis Gilmore]

On Monday, August 01, 2011 12:35:06 PM DJ Delorie wrote:
> >   What I am trying to understand now is about choice of float abi.
> 
> Not much to understand - each project chooses the abi that best meets
> their goals.  If you want to learn the history, it's all in the mail
> archives.
> 
> > git clone git://fedorapeople.org/~djdelorie/bootstrap.git
> > 
> >   Since I am still very "arm noob" :-) and just yesterday did
> > 
> > the thumb build to learn about thumb, so far, my impression
> > is that the best approach should be to use thumb+softfp.
> 
> If you want to do that, you don't need my bootstrap scripts.  The
> whole *point* of a bootstrap was to bring up an *incompatible* abi
> from scratch.  If you want to use a compatible abi, just keep using
> the armv5 version of Fedora instead.  It was decided long ago that the
> armv7 version of Fedora would use the hardfp abi (hence the project
> name "hardfp bootstrap"), but you can't build hardfp binaries on a
> softfp platform, so we had to start from scratch to do hardfp.

We decided  to keep using soft rather than softfp on armv5 because softfp 
while it can use a hardware floating point unit if its available has the extra 
overhead of working out at runtime if it has a hardware floting point unit or 
not. by making the distinct v7 port and using hardfp we gain the speed of 
using the hardware floating point unit without the runtime overhead.  but since 
softfp and soft are compatiable you could just build using fedora as a base. 
or any other ABI compatiable distro.


> It's also a fun exercise in bootstrapping, to make sure we still can
> do it.
> 
> >   I am kind of trying to figure what "The Industry" says about it,
> 
> If you need someone else's approval, you've missed the point of Free
> Software.  Each project has their own goals, and there is no "The
> Industry" to tell us what to do.  If you want to be part of a project,
> find the one that has the same goals as you do, and join them.
> 
> >   If I understand correctly, neon will have better support for
> > 
> > simd instructions right?
> 
> There are still some armv7 chips that don't have neon, though, so we
> (Fedora) chose to avoid neon for now.

marvell and nvidia armv7 chips dont have neon.  which includes the xo-1.75

Dennis
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