linux-kernel - Re: [RESEND PATCH v2] arm64: lse: fix LSE atomics with LLVM's integrated assembler

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Message-ID: <CABCJKueJ-J5MPj4-qL230iM3Bu8Qc_4wsViRgt2nJD81_EVJLw@mail.gmail.com>
Date:   Thu, 14 Nov 2019 10:15:59 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Andrew Murray <andrew.murray@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [RESEND PATCH v2] arm64: lse: fix LSE atomics with LLVM's
 integrated assembler

On Thu, Nov 14, 2019 at 8:57 AM Will Deacon <will@...nel.org> wrote:
>
> On Thu, Oct 31, 2019 at 12:57:05PM -0700, Sami Tolvanen wrote:
> > Unlike gcc, clang considers each inline assembly block to be independent
> > and therefore, when using the integrated assembler for inline assembly,
> > any preambles that enable features must be repeated in each block.
> >
> > This change defines __LSE_PREAMBLE and adds it to each inline assembly
> > block that has LSE instructions, which allows them to be compiled also
> > with clang's assembler.
>
> Any chance LLVM can be fixed to avoid this bodge in the kernel?

Unfortunately, LLVM developers consider this to be a feature, not a
bug, so it's unlikely that we can change how the integrated assembler
works:

  https://bugs.llvm.org/show_bug.cgi?id=19749

Note that this patch is similar to be604c616ca7 ("arm64: sysreg: Make
mrs_s and msr_s macros work with Clang and LTO"), which worked around
the same issue in the sysreg code.

Sami