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

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Message-ID: <c0f0eb7e-9e46-10cc-1277-b37fcd48d0be@arm.com>
Date:   Tue, 8 Oct 2019 17:18:53 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Sami Tolvanen <samitolvanen@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Andrew Murray <andrew.murray@....com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: lse: fix LSE atomics with LLVM's integrated
 assembler

On 08/10/2019 16:22, Sami Tolvanen wrote:
> On Mon, Oct 7, 2019 at 2:46 PM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@...glegroups.com> wrote:
>> I'm worried that one of these might lower to LSE atomics without
>> ALTERNATIVE guards by blanketing all C code with `-march=armv8-a+lse`.
> 
> True, that's a valid concern. I think adding the directive to each
> assembly block is the way forward then, assuming the maintainers are
> fine with that.

It's definitely a valid concern in principle, but in practice note that 
lse.h ends up included in ~99% of C files, so the extension is enabled 
more or less everywhere already.

(based on a quick hack involving '#pragma message' and grepping the 
build logs)

Robin.