From: Catalin Marinas <catalin.marinas@arm.com>
To: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: Mark Brown <broonie@kernel.org>, Will Deacon <will@kernel.org>,
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 14:55:55 +0100 [thread overview]
Message-ID: <YrxZ6w2N6vR/M17P@arm.com> (raw)
In-Reply-To: <YrwjB7NdYOlZP2gV@arm.com>
On Wed, Jun 29, 2022 at 11:01:43AM +0100, Szabolcs Nagy wrote:
> The 06/28/2022 16:06, Mark Brown wrote:
> > On Tue, Jun 28, 2022 at 03:21:25PM +0100, Will Deacon wrote:
> > > On Mon, Jun 20, 2022 at 01:54:48PM +0100, Mark Brown wrote:
> > > > +/* Note that bits 62 and 63 of each AT_HWCAP are reserved */
> >
> > > Can you expand a bit on this comment, please? It's not clear who has
> > > reserved those bits (e.g. kernel or userspace) and why having two bit
> > > reserved means we are limited to 32 instead of 62 bits.
> >
> > It's also not clear to me why they're reserved, I didn't manage to dig
> > far enough into the history to figure that out - I believe it's a glibc
> > thing, or at least something glibc now expects. Indeed I can't
> > immediately dig up the specific reference now. Szabolcs?
>
> only the top two bits of AT_HWCAP are reserved for glibc.
> (bits of AT_HWCAP2 are not reserved.)
>
> we did the 32bit limit because of ilp32 and i requested to
> keep following that.
>
> there is no precedent for using more than 32bit AT_HWCAP nor
> precedent for using AT_HWCAP3.
[...]
> - start using top bits of AT_HWCAP2 but not of AT_HWCAP.
> (this is the least amount of work for now)
That's a bit more appealing to me in the short term, though we may still
end up with AT_HWCAP3 at some point. Is anyone still thinking seriously
about ILP32?
--
Catalin
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next prev parent reply other threads:[~2022-06-29 13:57 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
2022-06-29 13:55 ` Catalin Marinas [this message]
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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