From: Catalin Marinas <catalin.marinas@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Mark Brown <broonie@kernel.org>, Will Deacon <will@kernel.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH 1/2] arm64: lib: Use .arch_extension
Date: Wed, 25 Mar 2020 11:05:04 +0000 [thread overview]
Message-ID: <20200325110504.GK3901@mbp> (raw)
In-Reply-To: <CAKv+Gu-wPyPufNah5FJ2VrKA5MUNZTDpJrWu+1oXEmrQwqDDdQ@mail.gmail.com>
On Tue, Mar 24, 2020 at 11:17:05PM +0100, Ard Biesheuvel wrote:
> On Tue, 24 Mar 2020 at 19:58, Mark Brown <broonie@kernel.org> wrote:
> >
> > On Tue, Mar 24, 2020 at 07:19:17PM +0100, Ard Biesheuvel wrote:
> > > On Mon, 23 Mar 2020 at 20:18, Mark Brown <broonie@kernel.org> wrote:
> >
> > > > order to generate BTI landing pads. We did this due to a lack of
> > > > support for the .arch_extension gas feature in older versions of the
> > > > clang built in assembler but since current versions of clang now have
> > > > support for .arch_extension we can use that.
> >
> > > This is not 100% accurate. Support for .arch_extension was added to
> > > GAS/aarch64 much later, so we should at least double check that it
> > > works on the oldest binutils that we do support.
> >
> > Ah, OK - the information I figured out from history was misleading
> > sorry.
> >
> > We've already got quite a lot of usages of .arch_extension in the kernel
> > for arm and a couple for arm64 (one in TF and another for LSE).
>
> ARM had support for this way before it was added to AArch64 as well.
> In the LSE case, it doesn't matter since LSE itself was not
> implemented by the assembler before that. For other things, we should
> really avoid .arch_extension as long as we still support binutils <
> 2.26
Good point. So we can add .arch_extension for new features which are
already dependent on newer gas options.
I'll drop this patch for now but we should try to find a solution
because of the overriding effect of .arch. In self-contained .S files
(like crypto) that's not an issue but once we start adding more
architecture feature in a single file, things will get more complicated.
--
Catalin
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next prev parent reply other threads:[~2020-03-25 11:05 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-23 19:18 [PATCH 1/2] arm64: lib: Use .arch_extension Mark Brown
2020-03-23 19:18 ` [PATCH 2/2] arm64: crypto: " Mark Brown
2020-03-24 16:45 ` Catalin Marinas
2020-03-24 16:48 ` [PATCH 1/2] arm64: lib: " Catalin Marinas
2020-03-24 18:19 ` Ard Biesheuvel
2020-03-24 18:58 ` Mark Brown
2020-03-24 22:17 ` Ard Biesheuvel
2020-03-25 11:05 ` Catalin Marinas [this message]
2020-03-25 11:07 ` Mark Brown
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