linux-kernel - Re: [PATCH 1/3] arm64: vdso32: drop the test for dmb ishld

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Date:   Wed, 13 Oct 2021 09:55:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, llvm@...ts.linux.dev,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Christian Biesinger <cbiesinger@...gle.com>,
        Simon Marchi <simon.marchi@...ymtl.ca>
Subject: Re: [PATCH 1/3] arm64: vdso32: drop the test for dmb ishld

On Wed, Oct 13, 2021 at 1:46 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> Binutils added support for this instruction in commit
> e797f7e0b2bedc9328d4a9a0ebc63ca7a2dbbebc which shipped in 2.34 (just
> missing the 2.33 release) but was cherry-picked into 2.33 in commit
> 27a50d6755bae906bc73b4ec1a8b448467f0bea1. Thanks to Christian and Simon
> for helping me with the patch archaeology.
>
> According to Documentation/process/changes.rst, the minimum supported
> version of binutils is 2.33. Since all supported versions of GAS support
> this instruction, drop the assembler invocation, preprocessor
> flags/guards, and the cross assembler macro that's now unused.
>
> This also avoids a recursive self reference in a follow up cleanup
> patch.
>
> Cc: Christian Biesinger <cbiesinger@...gle.com>
> Cc: Simon Marchi <simon.marchi@...ymtl.ca>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

This change looks good, but I think we should do the same for the gcc
version check:

> -#if __LINUX_ARM_ARCH__ >= 8 && defined(CONFIG_AS_DMB_ISHLD)
> +#if __LINUX_ARM_ARCH__ >= 8
>  #define aarch32_smp_mb()       dmb(ish)
>  #define aarch32_smp_rmb()      dmb(ishld)
>  #define aarch32_smp_wmb()      dmb(ishst)

gcc-4.8 already supported -march=armv8, and we require gcc-5.1 now, so both
this #if/#else construct and the corresponding "cc32-option,-march=armv8-a"
check should be obsolete now.

       Arnd