Re: New gcc

[Philip Blundell <philb@gnu.org>]

Jim Pick wrote:

>>From what I understand, there should be no compatibility problems with
>running armv3 code on the StrongARM.

Yup, that's correct.

>It might be worthwhile investigating building an armv4 distribution
>which would only contain certain packages that take advantage of the
>armv4 instructions.  This is similar in concept to having an
>i586-optimized distribution containing certain packages to complement
>the i386 distribution.

Another avenue that could be pursued would be to take advantage of the 
mechanism ld.so has for automatically selecting libraries with the appropriate 
optimisation.  We don't currently use this on the ARM, but in theory you could 
install a libc (etc) with ARMv3 instructions and a libc with ARMv4 
instructions, and the linker would choose the right one at run time.  This 
obviously involves less recompiling than building everything with different 
flags, and has less risk attached to it that someone will install the wrong 
version and hose their system.  Of course this only helps if the code that 
will benefit from optimisation is in a shared library.

I've also been thinking about some way to deploy -mapcs-float by default, as 
and when we have enough confidence that it actually works reliably.  I think 
the potential performance gain makes this worthwhile but unfortunately there 
is an ABI compatibility issue again.  Hopefully once more the dynamic linker 
can rescue us.

p.