linux-kernel - Re: [PATCH v2] uapi/auxvec: Define AT_HWCAP3 and AT

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Date: Thu, 15 Feb 2024 09:16:29 +0100
From: "Arnd Bergmann" <arnd@...nel.org>
To: "Peter Bergner" <bergner@...ux.ibm.com>, linux-api@...r.kernel.org,
 Linux-Arch <linux-arch@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Cc: "Adhemerval Zanella Netto" <adhemerval.zanella@...aro.org>,
 "Szabolcs Nagy" <szabolcs.nagy@....com>, "Nick Piggin" <npiggin@....ibm.com>,
 "Michael Ellerman" <mpe@...erman.id.au>
Subject: Re: [PATCH v2] uapi/auxvec: Define AT_HWCAP3 and AT_HWCAP4 aux vector, entries

On Wed, Feb 14, 2024, at 23:34, Peter Bergner wrote:
> The powerpc toolchain keeps a copy of the HWCAP bit masks in our TCB for fast
> access by the __builtin_cpu_supports built-in function.  The TCB space for
> the HWCAP entries - which are created in pairs - is an ABI extension, so
> waiting to create the space for HWCAP3 and HWCAP4 until we need them is
> problematical.  Define AT_HWCAP3 and AT_HWCAP4 in the generic uapi header
> so they can be used in glibc to reserve space in the powerpc TCB for their
> future use.
>
> I scanned through the Linux and GLIBC source codes looking for unused AT_*
> values and 29 and 30 did not seem to be used, so they are what I went
> with.  This has received Acked-by's from both GLIBC and Linux kernel
> developers and no reservations or Nacks from anyone.
>
> Arnd, we seem to have consensus on the patch below.  Is this something
> you could take and apply to your tree? 
>

I don't mind taking it, but it may be better to use the
powerpc tree if that is where it's actually being used.

If Michael takes it, please add

Acked-by: Arnd Bergmann <arnd@...db.de>

      Arnd