linux-kernel - Re: [PATCH v2 16/18] arm64: crypto: disable LTO for aes-ce-cipher.c

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Date:   Mon, 20 Nov 2017 21:31:29 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Alex Matveev <alxmtvv@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v2 16/18] arm64: crypto: disable LTO for aes-ce-cipher.c

On 20 November 2017 at 21:29, Alex Matveev <alxmtvv@...il.com> wrote:
> On Mon, 20 Nov 2017 15:20:14 +0000
> Mark Rutland <mark.rutland@....com> wrote:
>
>> On Wed, Nov 15, 2017 at 01:34:26PM -0800, Sami Tolvanen wrote:
>> > CONFIG_LTO_CLANG requires the use of clang's integrated assembler,
>> > which doesn't understand the inline assembly in aes-ce-cipher.c.
>> > Disable LTO for the file to work around the issue.
>>
>> Could you elaborate on what the integrated asembler doesn't like?
>>
>> It's not entirely clear at a glance, as the asm in that file doesn't
>> seem to do anything that obscure.
>>
>> Is it a bug?
>
> Turns out, integrated assembler doesn't like this instruction in
> aes_sub():
>         umov    %w[out], v0.4s[0]
>
> Specifically, it barks at "v0.4s[0]" part. And the way I read the spec,
> it's quite correct in not accepting this argument. From UMOV
> description:
>
> UMOV <Wd>, <Vn>.<Ts>[<index>]
>
> ...
>
> <Ts> For the 32-bit variant: is an element size specifier, encoded in
> the "imm5" field. It can have the following values:
>         B       when imm5 = xxxx1
>         H       when imm5 = xxx10
>         S       when imm5 = xx100
>
>
> With "v0.s[0]" it builds fine.
>
> Ard, since this is your code, can you comment? Feels like a typo.
>

Yep.