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@xxxxxxxxxxxxxxxxxxx> 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
