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Re: [RFC] Additional targets for powerpc
- From: Ian Lance Taylor <ian at airs dot com>
- To: Steve Munroe <sjmunroe at us dot ibm dot com>
- Cc: libc-alpha at sources dot redhat dot com, gcc at gcc dot gnu dot com, binutils at sourceware dot org, autoconf at gnu dot org, Roland McGrath <roland at redhat dot com>
- Date: 22 Sep 2005 15:40:07 -0700
- Subject: Re: [RFC] Additional targets for powerpc
- References: <OF11BDA2D0.E99C10BD-ON86257084.0077BF90-86257084.007AFAC3@us.ibm.com>
Steve Munroe <sjmunroe@us.ibm.com> writes:
> Retain (compatible with all existing Linux on Power systems)
> powerpc (a synonym for powerpc32)
> powerpc32
> powerpc64
> And add
> power4_32
> power4_64
> power5_32
> power5_64
> ppc970_32
> ppc970_64
> Or alternatively
> powerpc32_power4
> powerpc64_power4
> powerpc32_power5
> powerpc64_power5
> powerpc32_970
> powerpc64_970 I see no need to support a separate (from existing
> powerpc32/64) POWER3 and RS64IV targets at this time. The POWER3 systems
> are quite old and the RS64IV systems are "strongly storage consistent"
> machines. The POWER4, POWER5, and PPC970 processors allow "weak storage
> consistency" and are more aggressively piped for out-of-order instruction
> execution. This is difference requires very different instruction
> scheduling for optimal performance.
> Glibc and other package changes
>
> The changes needed to enable additional targets for glibc include:
>
> * Add the new machine targets to ./scripts/config.sub (and in autoconf)
I think we've found with the i386 and, especially, the MIPS, that this
approach is unwieldy and becomes confusing. Have you considered using
the --with-cpu, --with-arch and --with-tune configure options, instead
of adding a slew of CPU names? I don't know much about glibc
configury, but those options suffice for gcc and the binutils.
The main drawback at present is that there is no way to map from
config.guess to --with-cpu. But I believe that is a solvable problem.
(If people need to support compilers with different default targets on
the same system, they can use --program-prefix.)
Ian