Re: [PATCH 3/3] Add basic PowerPC core tune config

[Kumar Gala <galak@kernel.crashing.org>]

On Jul 26, 2011, at 8:59 AM, Richard Purdie wrote:

> On Tue, 2011-07-26 at 08:47 -0500, Kumar Gala wrote:
>> On Jul 26, 2011, at 7:44 AM, Richard Purdie wrote:
>> 
>>> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
>>> ---
>>> meta/conf/machine/include/powerpc/arch-powerpc.inc |   45 +++++++++++++++++++-
>>> meta/conf/machine/include/tune-ppc603e.inc         |   12 ++++-
>>> meta/conf/machine/include/tune-ppce300c2.inc       |   12 ++++-
>>> meta/conf/machine/include/tune-ppce500.inc         |   13 ++++--
>>> meta/conf/machine/include/tune-ppce500mc.inc       |   12 ++++-
>>> meta/conf/machine/include/tune-ppce500v2.inc       |   12 ++++-
>>> 6 files changed, 88 insertions(+), 18 deletions(-)
>> 
>> One thing I'm wondering about as we do this is the ability to pass
>> --with-cpu to gcc & [e]glibc configure to pickup proper optimized cfgs
>> & libs for a given target.
> 
> As far as I can tell, gcc 4.x has no --with-cpu option. We pass the
> correct march and mtune options to the compiler at runtime through
> CFLAGS and friends.

Hmm, gcc still supports this:

http://gcc.gnu.org/install/configure.html

--with-cpu=cpu
--with-cpu-32=cpu
--with-cpu-64=cpu
Specify which cpu variant the compiler should generate code for by default. cpu will be used as the default value of the -mcpu= switch. This option is only supported on some targets, including ARM, i386, M68k, PowerPC, and SPARC. The --with-cpu-32 and --with-cpu-64 options specify separate default CPUs for 32-bit and 64-bit modes; these options are only supported for i386, x86-64 and PowerPC. 

http://gcc.gnu.org/install/specific.html

powerpc-*-*
You can specify a default version for the -mcpu=cpu_type switch by using the configure option --with-cpu-cpu_type.

> You're already found the way to pass configuration to *libc using values
> in TARGET_FPU to pickup the right configuration.
> 
> Is there a use case we're missing?

Yes, for [e]glibc we have optimized libc functions for a given / specific PPC processor.  So we need someway to tell configure this.

- k