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

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Message-ID: <CABCJKufHzQamE5+JtH0J4TyS05kutkty_7GwJ6w8T-szdCwHvg@mail.gmail.com>
Date:   Tue, 8 Oct 2019 16:59:25 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Andrew Murray <andrew.murray@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        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: [PATCH v2] arm64: lse: fix LSE atomics with LLVM's integrated assembler

On Tue, Oct 8, 2019 at 4:31 PM Andrew Murray <andrew.murray@....com> wrote:
> This looks good to me. I can build and boot in a model with both Clang
> (9.0.6) and GCC (7.3.1) and boot a guest without anything going bang.

Great, thank you for testing this!

> Though when I build with AS=clang, e.g.
>
> make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CC=clang AS=clang Image

Note that this patch only fixes issues with inline assembly, which
should at some point allow us to drop -no-integrated-as from clang
builds. I believe there are still other fixes needed before AS=clang
works.

> I get errors like this:
>
>   CC      init/main.o
> In file included from init/main.c:17:
> In file included from ./include/linux/module.h:9:
> In file included from ./include/linux/list.h:9:
> In file included from ./include/linux/kernel.h:12:
> In file included from ./include/linux/bitops.h:26:
> In file included from ./arch/arm64/include/asm/bitops.h:26:
> In file included from ./include/asm-generic/bitops/atomic.h:5:
> In file included from ./include/linux/atomic.h:7:
> In file included from ./arch/arm64/include/asm/atomic.h:16:
> In file included from ./arch/arm64/include/asm/cmpxchg.h:14:
> In file included from ./arch/arm64/include/asm/lse.h:13:
> In file included from ./include/linux/jump_label.h:117:
> ./arch/arm64/include/asm/jump_label.h:24:20: error: expected a symbol reference in '.long' directive
>                  "      .align          3                       \n\t"
>                                                                   ^
> <inline asm>:4:21: note: instantiated into assembly here
>                 .long           1b - ., "" - .
>                                            ^
>
> I'm assuming that I'm doing something wrong?

No, this particular issue will be fixed in clang 10:
https://github.com/ClangBuiltLinux/linux/issues/500

Sami