From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [cryptodev:master 130/134] aes_generic.c:undefined reference to `_restgpr_31_x'
Date: Fri, 12 Jan 2018 20:43:21 +0100
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To: Segher Boessenkool <segher@kernel.crashing.org>
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On Fri, Jan 12, 2018 at 5:39 PM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:

>> or why the aes_generic implementation needs this on
>> powerpc when built with 'gcc -Os'. FWIW, the -Os change was needed
>> to work around a possible kernel stack overflow that can happen with
>> gcc-7.2, see https://patchwork.kernel.org/patch/10143607/ and
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
>
> The _x versions are smaller but slower; that's why they are used with -Os.
> Apparently nothing else was built with -Os (and the other needed flags)
> before.

Ah, that explains it, the definition is in arch/powerpc/lib/crtsavres.S,
but inside of #ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE.

We could theoretically work around it by turning that into
"#if defined(CONFIG_CC_OPTIMIZE_FOR_SIZE) ||
defined(CONFIG_CRYPTO_AES)", but that seems rather ugly.

My earlier patch already tried to be more specific, turning very
specific optimizations off rather than moving from -O2 to -Os,
but that turned out to lead to significantly worse performance,
where -Os improved performance slightly. Is there a way
to ask powerpc compilers to use mostly -Os but not the
specific thing that makes it link to _restgpr_31_x?

       Arnd