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

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Message-ID: <CABCJKudGtvVazLpZFdbhe9z-4mx_t16zxzkcwYbdAJriakrWqw@mail.gmail.com>
Date:   Mon, 7 Oct 2019 16:47:20 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, 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 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.

> arch/arm64/kvm/hyp/entry.S:109:87: error: too many positional arguments
>  alternative_insn nop, .inst (0xd500401f | ((0) << 16 | (4) << 5) |
> ((!!1) << 8)), 4, 1
>
>                ^
>
> Since __ALTERNATIVE_CFG now takes one less arg, with your patch?

__ALTERNATIVE_CFG (with two underscores) is only defined for C code,
and this patch doesn't change the definition of _ALTERNATIVE_CFG (with
one underscore) that's used for stand-alone assembly.

Sami