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

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Date:   Fri, 11 Aug 2017 11:17:02 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
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 11 August 2017 at 10:34, Arnd Bergmann <arnd@...db.de> wrote:
> 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

Of course, I meant replacing lr with x30 in our code.

>> 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