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Thu, 15 Feb 2024 14:39:26 +0000 (GMT) Message-ID: Date: Thu, 15 Feb 2024 08:39:26 -0600 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] uapi/auxvec: Define AT_HWCAP3 and AT_HWCAP4 aux vector, entries Content-Language: en-US To: Arnd Bergmann , linux-api@vger.kernel.org, Linux-Arch , "linux-kernel@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" References: From: Peter Bergner In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: U0zh-cXg3ppxx8BiWtZDI9TVoSkYhrAq X-Proofpoint-GUID: U0zh-cXg3ppxx8BiWtZDI9TVoSkYhrAq X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-02-15_13,2024-02-14_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxscore=0 impostorscore=0 spamscore=0 priorityscore=1501 mlxlogscore=319 phishscore=0 malwarescore=0 suspectscore=0 bulkscore=0 lowpriorityscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2402150117 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Szabolcs Nagy , Nick Piggin , Adhemerval Zanella Netto Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 2/15/24 2:16 AM, Arnd Bergmann wrote: > 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. So this is not a powerpc only patch, but we may be the first arch to use it. Szabolcs mentioned that aarch64 was pretty quickly filling up their AT_HWCAP2 and that they will eventually require using AT_HWCAP3 as well. If you still think this should go through the powerpc tree, I can check on that. Peter