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

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Message-ID: <CABCJKufxncBPOx6==57asbMF_On=g1sZAv+w6RnqHJFSwOSeTw@mail.gmail.com>
Date:   Mon, 7 Oct 2019 14:24:18 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrew Murray <andrew.murray@....com>,
        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: lse: fix LSE atomics with LLVM's integrated assembler

On Mon, Oct 7, 2019 at 1:28 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
> I tried adding `.arch armv8-a+lse` directives to all of the inline asm:
> https://github.com/ClangBuiltLinux/linux/issues/573#issuecomment-535098996

Yes, I had a similar patch earlier. I feel like using a command line
parameter here is cleaner, but I'm fine with either solution.

> One thing to be careful about is that blankets the entire kernel in
> `+lse`, allowing LSE atomics to be selected at any point.

Is that a problem? The current code allows LSE instructions with gcc
in any file that includes <asm/lse.h>, which turns out to be quite a
few places.

Sami