Re: mips64*-*-linux multi arch handling

[Laurent GUERBY <laurent at guerby dot net>]

On Thu, 2009-02-26 at 21:04 +0000, Richard Sandiford wrote:
> Laurent GUERBY <laurent@guerby.net> writes:
> > I was wondering why mips64*-*-linux does not have the same
> > handling of multiarch as powerpc/sparc/x86 in gcc/config.gcc:
> > 32 bits compiler binaries with 32/64 target choice via "-m", --with-cpu
> > and --enable-targets support for configure. Is there any specific reason
> > for this?
> >
> > If reason is "just not done", what model should we follow - copy/paste
> > from? Patch or patch sketch welcomed, we have mips64 machines to play
> > with in the GCC Compile farm :).
> 
> I don't think there's much reason to use a 32-bit compiler binary.
> -mabi=n32 is designed to be an ILP32 ABI that is _mostly_ type-compatible
> with -mabi=32, but with the ability to use 64-bit registers.  And using
> 64-bit registers is fairly important for gcc, because we require 64-bit
> HOST_WIDE_INTs.
> 
> When I did some performance measurements a few years back -- probably
> on a VR413x -- n32 did give a noticeable improvement over o32.

Thanks for your detailed response.

>From what I understand on those box debian and mandriva both
compiled all userspace with -mabi=32 but the kernel is 64. Debian
provides libs for abi=32 (default), n32 and 64 and the -mabi=32 compiled
GCC (4.3.x) supports generating code for the three ABI through various
debian patches. May be Matthias can tell us more about this choice
(I guess this is about compatibility for purely 32 bits mips) and future
debian plans.

Sincerely,

Laurent