linux-kernel - Re: [PATCH 1/2] ARM: drop unnecessary WASM

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Date:   Tue, 5 Mar 2019 16:47:55 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Stefan Agner <stefan@...er.ch>,
        Russell King <linux@...linux.org.uk>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>, julien.thierry@....com,
        LKML <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Kristof Beyls <Kristof.Beyls@....com>,
        Peter Smith <Peter.Smith@....com>
Subject: Re: [PATCH 1/2] ARM: drop unnecessary WASM

On Tue, Mar 5, 2019 at 3:39 PM Robin Murphy <robin.murphy@....com> wrote:
>
> Hi Stefan,
>
> On 2019-03-05 10:18 pm, Stefan Agner wrote:
> > The W macro for generating wide instructions when targeting Thumb-2
> > is not required for the preload data instructions (pld, pldw) since
> > they are only available as wide instructions. The GNU assembler seems
> > to work with or without the .w appended when compiling an Thumb-2
> > kernel. However, Clang's integrated assembler does not consider the
> > .w variants as valid instructions:
> >
> >    ./arch/arm/include/asm/processor.h:133:5: error: invalid instruction
> >                            "pldw.w\t%a0 \n"
> >                             ^
> >    <inline asm>:2:1: note: instantiated into assembly here
> >    pldw.w  [r0]
> >    ^
> >    1 error generated.
>
> Have you filed a bug against Clang for that? Something like "pldwal.w"

Yes; please.  For each deficiency you find, please file a bug.  We're
working on identifying what's missing from Clang's integrated
assembler support.  Given the list of issues, it's easier to estimate
how much effort is needed, which helps us allocate resources towards
fixing those issues better.

It would be good to know if pldw.w is valid under UAL or not.

Hopefully, the ARM kernel team can stress the importance of assembler
support for their ISA to their LLVM team.
-- 
Thanks,
~Nick Desaulniers