linux-kernel - Re: New assembler warnings with binutils 2.29

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Message-ID: <CAK8P3a1Bza56jpNcpbSDLXsHL08yiXEnKqNmevNpw_z9iym_qA@mail.gmail.com>
Date:   Fri, 11 Aug 2017 11:34:36 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Michael Collison <michael.collison@....com>
Subject: Re: New assembler warnings with binutils 2.29

On Fri, Aug 11, 2017 at 11:26 AM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> On 11 August 2017 at 10:22, Catalin Marinas <catalin.marinas@....com> wrote:
>> On Thu, Aug 10, 2017 at 01:13:22PM -0700, Laura Abbott wrote:
>>> Fedora rawhide recently upgraded to binutils 2.29 and this seems
>>> to produce new warnings:
>>>
>>> ./arch/arm64/include/asm/assembler.h: Assembler messages:
>>> ./arch/arm64/include/asm/assembler.h:125: Warning: ignoring attempt to redefine built-in register 'lr'
>>>
>>> This is
>>>
>>> /*
>>>  * Register aliases.
>>>  */
>>> lr      .req    x30             // link register
>>
>> Strange, does gas now think 'lr' is a general purpose register (aliased
>> to x30)? It never was and IIRC the toolchain people many years ago
>> refused to add it, hence the alias above in the kernel. I wonder if they
>> added 'fp' as well...
>>
>> We could remove the alias and replace all 'lr' instances with 'x30'
>> throughout the kernel (no too many) or we add some #ifdef around the
>> above based on the binutils version.
>>
>
> This is annoying. Replacing x30 with lr achieves the opposite of the
> intent of the binutils change. And using #ifdefs is inaccurate,
> because you can't really test the binutils version only the GCC
> version, and those are not tightly coupled.
>
> Can you .unreq it?

adding the author of the change to cc

https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=62e20ed45e3da5f3ba695e4ee109317668180fe6

There probably was some reasoning behind the change and an
intended method for using it.

    Arnd