[cryptodev:master 130/134] aes_generic.c:undefined reference to `_restgpr_31_x'

[Arnd Bergmann]

On Fri, Jan 12, 2018 at 10:41 PM, Segher Boessenkool
<segher at kernel.crashing.org> wrote:
> On Fri, Jan 12, 2018 at 10:29:01PM +0100, Arnd Bergmann wrote:
>> On Fri, Jan 12, 2018 at 9:41 PM, Segher Boessenkool
>> <segher at kernel.crashing.org> wrote:
>> > On Fri, Jan 12, 2018 at 08:43:21PM +0100, Arnd Bergmann wrote:
>> >> On Fri, Jan 12, 2018 at 5:39 PM, Segher Boessenkool
>>
>> >> 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 :-(
>>
>> We use -Os only for gcc-7.1 and higher, where it produces faster
>> code for AES and avoids running into
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
>>
>> > Maybe for now just enable it in crtsavres.S always, with a comment?
>> > That -Os workaround is hopefully not going to live long either...
>>
>> It depends on whether or how soon someone comes up with a
>> better fix for PR83356.
>> gcc-8.0.0 is currently not affected by it, so we could limit the
>> workaround (and the hack in crtsavres.S) to gcc-7-only.
>
> I guess you could enable the _x routines whenever you use ubsan?  Ubsan
> will cause much bigger code growth than the handful of insns in those
> routines?

Right, that could work, too. My patch that Herbert merged intentionally
used -Os also for non-UBSAN builds because it turned out to
be much faster (see gcc PR83651), but we could revert that back
to the default and only use the -Os for UBSAN, essentially
addressing only PR83356 but not PR83651.

       Arnd