From: Robin Murphy <robin.murphy@arm.com>
To: Mark Rutland <mark.rutland@arm.com>, Ard Biesheuvel <ardb@kernel.org>
Cc: Eric Biggers <ebiggers@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Mark Brown <broonie@kernel.org>,
linux-crypto@vger.kernel.org, Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 0/3] arm64: Open code .arch_extension
Date: Wed, 25 Mar 2020 12:24:53 +0000 [thread overview]
Message-ID: <ea521053-1f55-dbab-2d34-0773fd4dcac5@arm.com> (raw)
In-Reply-To: <20200325120224.GA34330@C02TD0UTHF1T.local>
On 2020-03-25 12:03 pm, Mark Rutland wrote:
> On Wed, Mar 25, 2020 at 12:54:10PM +0100, Ard Biesheuvel wrote:
>> On Wed, 25 Mar 2020 at 12:50, Mark Brown <broonie@kernel.org> wrote:
>>> Since BTI is a mandatory feature of v8.5 there is no BTI arch_extension,
>>> you can only enable it by moving the base architecture to v8.5. You'd
>>> need to use .arch and that feels likely to find us sharp edges to run
>>> into.
>>
>> I think we should talk to the toolchain folks about this. Even if
>> .arch_extension today does not support the 'bti' argument, it *is*
>> most definitely an architecture extension, even it it is mandatory in
>> v8.5 (given that v8.5 is itself an architecture extension).
>
> It certianly seems unfortunate, as it goes against the premise of having
> HINT space instructions. Most software will want to enable HINT space
> instructions from ARMv8.x but nothing else to ensure binary
> compatibility with existing hardware.
>
> I see the same is true for pointer authentication judging by:
>
> https://sourceware.org/binutils/docs/as/AArch64-Extensions.html#AArch64-Extensions
>
> ... so worth raising with toolchain folk as a general principle even if
> we have to bodge around it for now.
Indeed, in general, just because a feature is mandatory in v8.n doesn't
necessarily mean it can't be included in a v8.(n-1) implementation which
may not have the *other* mandatory parts of v8.n which ".arch
armv8.<n>-a" would let through.
Robin.
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next prev parent reply other threads:[~2020-03-25 12:25 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 11:41 [PATCH 0/3] arm64: Open code .arch_extension Mark Brown
2020-03-25 11:41 ` [PATCH 1/3] arm64: asm: Provide macro to control enabling architecture extensions Mark Brown
2020-03-25 11:41 ` [PATCH 2/3] arm64: lib: Use ARM64_EXTENSIONS() Mark Brown
2020-03-25 11:41 ` [PATCH 3/3] arm64: crypto: " Mark Brown
2020-03-25 11:45 ` [PATCH 0/3] arm64: Open code .arch_extension Ard Biesheuvel
2020-03-25 11:50 ` Mark Brown
2020-03-25 11:54 ` Ard Biesheuvel
2020-03-25 12:01 ` Mark Brown
2020-03-25 12:03 ` Mark Rutland
2020-03-25 12:24 ` Robin Murphy [this message]
2020-04-22 18:00 ` Catalin Marinas
2020-04-23 11:18 ` Mark Brown
2020-04-23 11:59 ` Catalin Marinas
2020-04-23 13:40 ` Catalin Marinas
2020-03-25 12:31 ` Mark Rutland
2020-03-25 13:26 ` Ard Biesheuvel
2020-03-25 13:30 ` Mark Brown
2020-03-25 13:27 ` Mark Brown
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