linux-kernel - Re: [linux-stable-rc:linux-5.15.y 6874/8723] arch/arm/lib/xor-neon.c:30:2: warning: This code requires at least version 4.6 of GCC

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Message-ID: <Yt3KObFVIUI2mFGt@zx2c4.com>
Date:   Mon, 25 Jul 2022 00:39:53 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     kernel test robot <lkp@...el.com>, ardb@...nel.org
Cc:     "Justin M. Forbes" <jforbes@...oraproject.org>,
        llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Jason A. Donenfeld" <zx2c4@...nel.org>
Subject: Re: [linux-stable-rc:linux-5.15.y 6874/8723]
 arch/arm/lib/xor-neon.c:30:2: warning: This code requires at least version
 4.6 of GCC

Hi Ard,

On Mon, Jul 25, 2022 at 04:14:48AM +0800, kernel test robot wrote:
> All warnings (new ones prefixed by >>):
> 
> >> arch/arm/lib/xor-neon.c:30:2: warning: This code requires at least version 4.6 of GCC [-W#warnings]
>    #warning This code requires at least version 4.6 of GCC
>     ^
>    1 warning generated.
> 
> 
> vim +30 arch/arm/lib/xor-neon.c
> 
> 01956597cbc46d Ard Biesheuvel 2013-05-17  16  
> 01956597cbc46d Ard Biesheuvel 2013-05-17  17  /*
> 01956597cbc46d Ard Biesheuvel 2013-05-17  18   * Pull in the reference implementations while instructing GCC (through
> 01956597cbc46d Ard Biesheuvel 2013-05-17  19   * -ftree-vectorize) to attempt to exploit implicit parallelism and emit
> 01956597cbc46d Ard Biesheuvel 2013-05-17  20   * NEON instructions.
> 01956597cbc46d Ard Biesheuvel 2013-05-17  21   */
> 01956597cbc46d Ard Biesheuvel 2013-05-17  22  #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
> 01956597cbc46d Ard Biesheuvel 2013-05-17  23  #pragma GCC optimize "tree-vectorize"
> 01956597cbc46d Ard Biesheuvel 2013-05-17  24  #else
> 01956597cbc46d Ard Biesheuvel 2013-05-17  25  /*
> 01956597cbc46d Ard Biesheuvel 2013-05-17  26   * While older versions of GCC do not generate incorrect code, they fail to
> 01956597cbc46d Ard Biesheuvel 2013-05-17  27   * recognize the parallel nature of these functions, and emit plain ARM code,
> 01956597cbc46d Ard Biesheuvel 2013-05-17  28   * which is known to be slower than the optimized ARM code in asm-arm/xor.h.
> 01956597cbc46d Ard Biesheuvel 2013-05-17  29   */
> 01956597cbc46d Ard Biesheuvel 2013-05-17 @30  #warning This code requires at least version 4.6 of GCC
> 01956597cbc46d Ard Biesheuvel 2013-05-17  31  #endif
> 01956597cbc46d Ard Biesheuvel 2013-05-17  32  

Does this file need a depends on ≥4.6 thing in Kconfig? Or is something
else happening here since 4.6 isn't even supported by the kernel these
days?

Jason