From: Segher Boessenkool <segher@kernel.crashing.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
<linux-crypto@vger.kernel.org>,
kbuild test robot <fengguang.wu@intel.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Herbert Xu <herbert@gondor.apana.org.au>,
kbuild-all@01.org
Subject: Re: [cryptodev:master 130/134] aes_generic.c:undefined reference to `_restgpr_31_x'
Date: Fri, 12 Jan 2018 14:41:55 -0600 [thread overview]
Message-ID: <20180112204154.GM21977@gate.crashing.org> (raw)
In-Reply-To: <CAK8P3a39=PVpwiSk_3CjRnYBawhXqMatHKSsHCd2KHCgR+Zmyg@mail.gmail.com>
On Fri, Jan 12, 2018 at 08:43:21PM +0100, Arnd Bergmann wrote:
> 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.
Ah ok. Right.
> 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?
There is no such thing, sorry. Would be very hard to implement, and
older compilers will never get it, so it won't help you anyway :-(
Maybe for now just enable it in crtsavres.S always, with a comment?
That -Os workaround is hopefully not going to live long either...
Segher
next prev parent reply other threads:[~2018-01-12 20:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-12 14:11 [cryptodev:master 130/134] aes_generic.c:undefined reference to `_restgpr_31_x' kbuild test robot
2018-01-12 14:55 ` Arnd Bergmann
2018-01-12 16:39 ` Segher Boessenkool
2018-01-12 19:43 ` Arnd Bergmann
2018-01-12 20:41 ` Segher Boessenkool [this message]
2018-01-12 21:29 ` Arnd Bergmann
2018-01-12 21:41 ` Segher Boessenkool
2018-01-12 21:45 ` Arnd Bergmann
2018-01-12 22:10 ` Segher Boessenkool
2018-01-14 21:40 ` Arnd Bergmann
2018-01-15 0:21 ` Segher Boessenkool
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