linux-kernel - Re: [PATCH v2] [v2] crypto: aes-generic - fix aes-generic regression on powerpc

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Date:   Mon, 17 Sep 2018 09:18:37 +0000
From:   Horia Geanta <horia.geanta@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        Arnd Bergmann <arnd@...db.de>
CC:     "David S. Miller" <davem@...emloft.net>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Richard Biener <rguenther@...e.de>,
        Jakub Jelinek <jakub@....gnu.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] [v2] crypto: aes-generic - fix aes-generic regression
 on powerpc

On 1/20/2018 2:44 AM, Herbert Xu wrote:
> On Mon, Jan 15, 2018 at 05:07:22PM +0100, Arnd Bergmann wrote:
>> My last bugfix added -Os on the command line, which unfortunately caused
>> a build regression on powerpc in some configurations.
>>
>> I've done some more analysis of the original problem and found slightly
>> different workaround that avoids this regression and also results in
>> better performance on gcc-7.0: -fcode-hoisting is an optimization step
>> that got added in gcc-7 and that for all gcc-7 versions causes worse
>> performance.
>>
>> This disables -fcode-hoisting on all compilers that understand the option.
>> For gcc-7.1 and 7.2 I found the same performance as my previous patch
>> (using -Os), in gcc-7.0 it was even better. On gcc-8 I could see no
>> change in performance from this patch. In theory, code hoisting should
>> not be able make things better for the AES cipher, so leaving it
>> disabled for gcc-8 only serves to simplify the Makefile change.
>>
>> Reported-by: kbuild test robot <fengguang.wu@...el.com>
>> Link: https://www.mail-archive.com/linux-crypto@vger.kernel.org/msg30418.html
>> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
>> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83651
>> Fixes: 148b974deea9 ("crypto: aes-generic - build with -Os on gcc-7+")
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> Patch applied.  Thanks.
> 
This fix ("commit 6e36719fbe90213fbba9f50093fa2d4d69b0e93c upstream") is needed
also in 4.14.y stable tree, since it contains commit
7cae67e31292 ("crypto: aes-generic - build with -Os on gcc-7+")

Compilation fails without it:
crypto/aes_generic.o: In function `crypto_aes_set_key':
crypto/aes_generic.c:1300: undefined reference to `_restgpr_31_x'

Thanks,
Horia