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Re: [PATCH] Add hwcap2 bits for POWER9
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Tulio Magno Quites Machado Filho <tuliom at linux dot vnet dot ibm dot com>
- Cc: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>, libc-alpha at sourceware dot org, linuxppc-dev at lists dot ozlabs dot org, Steve Munroe <munroesj at linux dot vnet dot ibm dot com>
- Date: Mon, 11 Jan 2016 15:48:50 -0500
- Subject: Re: [PATCH] Add hwcap2 bits for POWER9
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- References: <568C272D dot 6000705 at linux dot vnet dot ibm dot com> <87egdsi4om dot fsf at totoro dot br dot ibm dot com> <1452267366 dot 5201 dot 12 dot camel at vnet dot ibm dot com> <568FE3D0 dot 7080008 at linaro dot org> <87wprgdu3u dot fsf at totoro dot br dot ibm dot com> <5693C861 dot 9030308 at redhat dot com> <87bn8revra dot fsf at totoro dot br dot ibm dot com>
On 01/11/2016 02:55 PM, Tulio Magno Quites Machado Filho wrote:
> "Carlos O'Donell" <firstname.lastname@example.org> writes:
>> On 01/11/2016 10:16 AM, Tulio Magno Quites Machado Filho wrote:
>>> Adhemerval Zanella <email@example.com> writes:
>>>> On 08-01-2016 13:36, Peter Bergner wrote:
>>>>> On Fri, 2016-01-08 at 11:25 -0200, Tulio Magno Quites Machado Filho wrote:
>>>>>> Peter, this solves the issue you reported previously .
>>>>>>  https://sourceware.org/ml/libc-alpha/2015-12/msg00522.html
>>>>> Agreed, thanks. I'll also add the POWER9 support to the GCC side
>>>>> of the patch now that the glibc code is upstream.
>>>> I do not see these bits being added in kernel side yet and GLIBC usual
>>>> only sync these kind of bits *after* they are included in kernel side.
>>>> So I would advise to either get these pieces (kernel support and hwcap
>>>> advertise) in kernel before 2.23 release, otherwise revert the patches.
>>> It has just been sent to the correspondent Linux mailing list:
>> Please revert the changes from glibc until you checkin support to linux
>> kernel mainline.
>> Leaving these bits in increases the risk that someone uses to deploy a glibc
>> that then may have the wrong value.
> Could you clarify this statement, please?
> I fail to see how they could have the wrong value.
Until it is checked into the mainline kernel it is not canonical.
That's the rule. There are no other discussions to be had.
The single rule avoids discussions like "it can never be wrong because that's
what our ABI says it is."
> However, I do agree with the concerns raised by Peter and Adhemerval: glibc
> should be in sync with the kernel by the time of the release in order to
> guarantee both bits are reserved for the exact same goal and we should have
> both AT_HWCAP and AT_PLATFORM supporting the new processor.
> With that said, I was planning to revert both commits d2de9ef7 and b1f19b8e
> if we don't get the kernel patch accepted into the powerpc tree in time for
> the release 2.23.
Exactly. That's perfect. We can backport them to 2.23.1 if you get in later.