From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Eric Biederman <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 1/4] arm64/cpufeature: Store elf_hwcaps as an array rather than unsigned long
Date: Wed, 29 Jun 2022 13:06:10 +0100 [thread overview]
Message-ID: <YrxAMspHoLn3CaPk@arm.com> (raw)
In-Reply-To: <Yrw7EthwLfJVQE9V@sirena.org.uk>
The 06/29/2022 12:44, Mark Brown wrote:
> On Wed, Jun 29, 2022 at 11:01:43AM +0100, Szabolcs Nagy wrote:
>
> > the reason i slightly preferred AT_HWCAP3 was that AT_HWCAP
> > is a bit special in ld.so: library lookups can depend on a
> > glibc internal 64bit "hwcap" value that is historically
> > AT_HWCAP but since that does not use all bits, some targets
> > reused the top bits for high level platform abis which we
> > may want to do on aarch64 too. it should be possible to make
> > "hwcap" separate from AT_HWCAP (i.e. the bottom 32bits of
> > "hwcap" just happens to come from AT_HWCAP but the top is
> > defined by glibc), but that would be awkward to do in the
> > ld.so code if AT_HWCAP started using the top bits too.
> > (i think we cannot change the "hwcap" bits once they are
> > allocated because they are in the ld.so.cache file.)
>
> So when you were saying that bits 62 and 63 were reserved it's actually
> potentially all the top 32 bits but only in plain AT_HWCAP?
>
currently only bits 62 and 63 are reserved and only in plain AT_HWCAP.
and yes it might be useful to reserve all top 32bits of AT_HWCAP.
(for glibc internal reasons those are easy to use for ld.so extensions).
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next prev parent reply other threads:[~2022-06-29 12:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-20 12:54 [PATCH v2 0/4] arm64: Add AT_HWCAP3 Mark Brown
2022-06-20 12:54 ` [PATCH v2 1/4] arm64/cpufeature: Store elf_hwcaps as an array rather than unsigned long Mark Brown
2022-06-28 14:21 ` Will Deacon
2022-06-28 15:06 ` Mark Brown
2022-06-29 10:01 ` Szabolcs Nagy
2022-06-29 11:44 ` Mark Brown
2022-06-29 12:06 ` Szabolcs Nagy [this message]
2022-06-29 13:55 ` Catalin Marinas
2022-06-29 15:07 ` Mark Brown
2022-06-20 12:54 ` [PATCH v2 2/4] elf: Allow architectures to provide AT_HWCAP3 Mark Brown
2022-06-20 12:54 ` [PATCH v2 3/4] arm64/cpufeature: Support AT_HWCAP3 Mark Brown
2022-06-20 12:54 ` [PATCH v2 4/4] arm64/hwcap: Support FEAT_EBF16 Mark Brown
2022-07-05 17:53 ` [PATCH v2 0/4] arm64: Add AT_HWCAP3 Mark Brown
2022-07-06 9:02 ` Szabolcs Nagy
2022-07-06 10:08 ` Marc Zyngier
2022-07-06 13:48 ` Mark Brown
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