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

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Message-ID: <20170811092213.mdmzqtm2lp6ltlxt@armageddon.cambridge.arm.com>
Date:   Fri, 11 Aug 2017 10:22:14 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        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 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.

-- 
Catalin