On 03/20/2018 03:06 AM, Linus Torvalds wrote: > On Mon, Mar 19, 2018 at 6:50 PM, Linus Torvalds > <torva...@linux-foundation.org> wrote: >> >> Add it to everything. If it's an invalid optimization, it shouldn't be on. > > IOW, why isn't this just something like > > diff --git a/Makefile b/Makefile > index d65e2e229017..01abedc2e79f 100644 > --- a/Makefile > +++ b/Makefile > @@ -826,6 +826,9 @@ KBUILD_CFLAGS += $(call cc-disable-warning, > pointer-sign) > # disable invalid "can't wrap" optimizations for signed / pointers > KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow) > > +# disable invalid optimization on clang > +KBUILD_CFLAGS += $(call cc-option,-fno-merge-all-constants) > + > # Make sure -fstack-check isn't enabled (like gentoo apparently did) > KBUILD_CFLAGS += $(call cc-option,-fno-stack-check,) > > (whitespace-damaged, but you get the gist of it). > > We disable some optimizations that are technically _valid_, because > they are too dangerous and a bad idea. > > Disabling an optimization that isn't valid EVEN IN THEORY is an > absolute no-brainer, particularly if it has already shown itself to > cause problems. > > We have other situations where we generate multiple static structures > and expect them to be unique. I'm not sure any of them would trigger > the clang rules, but the clang rules are obviously complete garbage > anyway, so who knows? > > That optimization seems to teuly be pure and utter garbage. Clang can > even *see* the address comparison happening in that file. > > Some clang person needs to be publicly shamed for enabling this kind > of garbage by default, particularly since they apparently _knew_ it > was invalid.
Yeah, agree with all the above. I'll respin it to disable globally. Thanks, Linus!
