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

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Date:   Fri, 11 Aug 2017 10:26:06 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: New assembler warnings with binutils 2.29

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?