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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sat, 23 Mar 2019 21:06:56 +0100
Message-ID: <CAK8P3a0XBN+noCkdGT_TYfPNY1j9CcVH8mTjh_mQL3w+Z6jfaw@mail.gmail.com>
Subject: Re: [PATCH 1/3] ARM: use arch_extension directive instead of arch argument
To:     Stefan Agner <stefan@agner.ch>
Cc:     Russell King - ARM Linux <linux@armlinux.org.uk>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Ray Jui <rjui@broadcom.com>,
        Scott Branden <sbranden@broadcom.com>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
        Kukjin Kim <kgene@kernel.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Rob Herring <robh@kernel.org>,
        Santosh Shilimkar <ssantosh@kernel.org>,
        Jason Cooper <jason@lakedaemon.net>,
        Andrew Lunn <andrew@lunn.ch>,
        Gregory CLEMENT <gregory.clement@bootlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>,
        Tony Lindgren <tony@atomide.com>,
        Marc Gonzalez <marc.w.gonzalez@free.fr>,
        Mans Rullgard <mans@mansr.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Sat, Mar 23, 2019 at 4:52 PM Stefan Agner <stefan@agner.ch> wrote:
>
> The LLVM Target parser currently does not allow to specify the security
> extension as part of -march (see also LLVM Bug 40186 [0]). When trying
> to use Clang with LLVM's integrated assembler, this leads to a build
> errors such as this:
>   clang-8: error: the clang compiler does not support '-Wa,-march=armv7-a+sec'
>
> Use ".arch_extension sec" to enable the security extension in a more
> portable fasion.
>
> Note that this is technically not exactly the same as the old code
> checked for availabilty of the security extension by calling as-instr.
> However, there are already other sites which use ".arch_extension sec"
> unconditionally, hence de-facto we need an assembler capable of
> ".arch_extension sec" already today (arch/arm/mm/proc-v7.S). The
> arch extension "sec" is available since binutils 2.21 according to
> its documentation [1].
>
> [0] https://bugs.llvm.org/show_bug.cgi?id=40186
> [1] https://sourceware.org/binutils/docs-2.21/as/ARM-Options.html
>
> Signed-off-by: Stefan Agner <stefan@agner.ch>

This sounds like a good idea. I think we have platform specific
minimum toolchain versions elsewhere, but I don't see a problem
with raising the minimum version for all the armv7ve platforms.

I've added this patch to my randconfig test queue, but please
send it to arm@kernel.org for inclusion when you have
collected more Acks.

Do you have a git tree with other patches required for the
integrated assembler? I might try that out as well with
my randconfig tree. At the moment I'm building with
clang-8 and a small number of patches on top.

Acked-by: Arnd Bergmann <arnd@arndb.de>