Re: libm accuracy, eglibc compared to glibc -- solved

[Mark Hatle <mark.hatle@windriver.com>]

On 3/21/14, 7:10 AM, Mats Kärrman wrote:
> Hi,
>
> On: Thursday, March 13, 2014 11:36 AM, Mats Kärrman wrote:
>> My "home made" hard float tune for PowerPC looks like this:
>>
>> ------------------------------------------------------------------
>> # Tune for the e300c3 core
>> require conf/machine/include/tune-ppce300c3.inc
>>
>> # Use hardware floating point
>> AVAILTUNES += "ppce300c3hf"
>> TUNE_FEATURES_tune-ppce300c3hf = "m32 fpu-hard ppce300c3"
>> TUNE_PKGARCH_tune-ppce300c3hf = "ppce300c3hf"
>> PACKAGE_EXTRA_ARCHS_tune-ppce300c3hf = "${PACKAGE_EXTRA_ARCHS_tune-powerpc} ppce300c3hf"
>> DEFAULTTUNE = "ppce300c3hf"
>> ------------------------------------------------------------------
>>
>
> I found the reason for the error (deviance) in the sqrt function. glibc has
> special code for PowerPC 603e core (e300 is an optimized variant of 603e).
> By adding the following line to the tuning I now get the same result as
> for all other environments that I've tried:
>
> GLIBC_EXTRA_OECONF += "${@bb.utils.contains("TUNE_FEATURES", "ppce300c3", "-with-cpu=603e", "", d)}"
>
> Does anyone know about the reason for having soft-float as the default and
> only available alternative for e300c2/3 tunings?

My guess is because e300 e300c2 were both soft-float designs.  And e300c3 is the 
first hard float design.

The e300c3 should inherit and use the 603e directly.  This includes definiting 
the TUNE_FEATURES that the 603e does.  If it doesn't do that, I'd suggest it's a 
mistake.

The default 603e tune should include:

GLIBC_EXTRA_OECONF += "${@bb.utils.contains("TUNE_FEATURES", "ppc603e", 
"-with-cpu=603e", "", d)}"

or similar already -- and should already be hard float enabled.  (ppc603e 
soft-float should be the alternative -- as it is significantly rarer and the 
deviation.)

> Would it be worthwhile to send a patch to add the hf tuning to OE-core?

As the e300c3 should be hard float, we shouldn't have the 'hf' designation. 
Otherwise, we should ensure the e300c3 tune is correctly configured.

> In that case what tests should be performed before that and what (related)
> tests are performed by the OE auto-builder?
>
> BR // Mats
>