linux-kernel - [PATCH RFC 0/2] arm64: Add infrastructure for use of AT

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Message-Id: <20240906-arm64-elf-hwcap3-v1-0-8df1a5e63508@kernel.org>
Date: Fri, 06 Sep 2024 00:05:23 +0100
From: Mark Brown <broonie@...nel.org>
To: Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
 Jonathan Corbet <corbet@....net>
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, Yury Khrustalev <yury.khrustalev@....com>, 
 Wilco Dijkstra <wilco.dijkstra@....com>, 
 linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>
Subject: [PATCH RFC 0/2] arm64: Add infrastructure for use of AT_HWCAP3

Since arm64 has now used all of AT_HWCAP2 it needs to either start using
AT_HWCAP3 (which was recently added for PowerPC) or start allocating
bits 32..61 of AT_HWCAP first.  Those are documented in elf_hwcaps.rst
as unused and in uapi/asm/hwcap.h as unallocated for potential use by
libc, glibc does currently use bits 62 and 63.  This series has the code
for enabling AT_HWCAP3 as a reference.

We will at some point need to bite this bullet but we need to decide if
it's now or later.  Given that we used the high bits of AT_HWCAP2 first
and AT_HWCAP3 is already defined it feels like that might be people's
preference, in order to minimise churn in serieses adding new HWCAPs
it'd be good to get consensus if that's the case or not.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
Mark Brown (2):
      binfmt_elf: Wire up AT_HWCAP3 at AT_HWCAP4
      arm64: Support AT_HWCAP3

 Documentation/arch/arm64/elf_hwcaps.rst |  6 +++---
 arch/arm64/include/asm/cpufeature.h     |  3 ++-
 arch/arm64/include/asm/hwcap.h          |  6 +++++-
 arch/arm64/include/uapi/asm/hwcap.h     |  4 ++++
 arch/arm64/kernel/cpufeature.c          |  6 ++++++
 fs/binfmt_elf.c                         |  6 ++++++
 fs/binfmt_elf_fdpic.c                   |  6 ++++++
 fs/compat_binfmt_elf.c                  | 15 +++++++++++++++
 8 files changed, 47 insertions(+), 5 deletions(-)
---
base-commit: 7c626ce4bae1ac14f60076d00eafe71af30450ba
change-id: 20240905-arm64-elf-hwcap3-7709c5593d34

Best regards,
-- 
Mark Brown <broonie@...nel.org>