linux-kernel - Re: [PATCH] arm64: fix alternatives with LLVM's integrated assembler

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Message-ID: <20191015000017.66jkcya6zzbi7qqc@willie-the-truck>
Date:   Tue, 15 Oct 2019 01:00:18 +0100
From:   Will Deacon <will@...nel.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] arm64: fix alternatives with LLVM's integrated assembler

On Mon, Oct 07, 2019 at 04:47:20PM -0700, Sami Tolvanen wrote:
> On Mon, Oct 7, 2019 at 2:34 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> > Should the definition of the ALTERNATIVE macro
> > (arch/arm64/include/asm/alternative.h#L295) also be updated in this
> > patch to not pass `1` as the final parameter?
> 
> No, that's the default value for cfg in case the caller omits the
> parameter, and it's still needed.
> 
> > I get one error on linux-next that looks related:
> > $ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang AS=clang
> > -j71 arch/arm64/kvm/
> > ...
> 
> This patch only touches the inline assembly version (i.e. when
> compiling without -no-integrated-as), while with AS=clang you are
> using clang also for stand-alone assembly code. I believe some
> additional work is needed before we can do that.

Is there any benefit from supporting '-no-integrated-as' but not 'AS=clang'?
afaict, you have to hack the top-level Makefile for that.

Will