linux-kernel - Re: [PATCH v4 1/2] ARM: use arch_extension directive instead of arch argument

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Message-ID: <20190619173354.z5znqao6iveoffc7@localhost>
Date:   Wed, 19 Jun 2019 10:33:54 -0700
From:   Olof Johansson <olof@...om.net>
To:     Stefan Agner <stefan@...er.ch>
Cc:     arm@...nel.org, linux@...linux.org.uk, arnd@...db.de,
        ard.biesheuvel@...aro.org, robin.murphy@....com, nico@...xnic.net,
        f.fainelli@...il.com, rjui@...adcom.com, sbranden@...adcom.com,
        bcm-kernel-feedback-list@...adcom.com, kgene@...nel.org,
        krzk@...nel.org, robh@...nel.org, ssantosh@...nel.org,
        jason@...edaemon.net, andrew@...n.ch, gregory.clement@...tlin.com,
        sebastian.hesselbarth@...il.com, tony@...mide.com,
        marc.w.gonzalez@...e.fr, mans@...sr.com, ndesaulniers@...gle.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] ARM: use arch_extension directive instead of arch
 argument

On Tue, May 28, 2019 at 12:40:50AM +0200, Stefan Agner 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 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. Also make sure to use ".arch armv7-a" in case a v6/v7
> multi-platform kernel is being built.
> 
> 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@...er.ch>
> Acked-by: Mans Rullgard <mans@...sr.com>
> Acked-by: Arnd Bergmann <arnd@...db.de>
> Acked-by: Krzysztof Kozlowski <krzk@...nel.org>
> ---
> Changes since v1:
> - Explicitly specify assembler architecture as armv7-a to avoid
>   build issues when bulding v6/v7 multi arch kernel.
> 
> Changes since v2:
> - Add armv7-a also in mach-tango
> - Move .arch armv7-a outside of ifdef'ed area in sleep44xx.S
>   to make the kernel compile also without CONFIG_SMP/PM.
> 
> Changes since v3:
> - Rebase on top of v5.2-rc2

Thanks, applied to arm/soc.


-Olof