On Thu, Jul 14, 2022 at 01:39:25PM -0700, Linus Torvalds wrote: > On Thu, Jul 14, 2022 at 10:02 AM Borislav Petkov <bp@xxxxxxxxx> wrote: > > > > On Thu, Jul 14, 2022 at 09:51:40AM -0700, Linus Torvalds wrote: > > > Oh, absolutely. Doing an -rc7 is normal. > > > > Good. I'm gathering all the fallout fixes and will send them to you on > > Sunday, if nothing unexpected happens. > > Btw, I assume that includes the clang fix for the > x86_spec_ctrl_current section attribute. Yap. Here's the current lineup: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=x86/urgent > That's kind of personally embarrassing that it slipped through: I do > all my normal test builds that I actually *boot* with clang. > > But since I kept all of the embargoed stuff outside my normal trees, > it also meant that the test builds I did didn't have my "this is my > clang tree" stuff in it. > > And so I - like apparently everybody else - only did those builds with gcc. > > And gcc for some reason doesn't care about this whole "you redeclared > that variable with a different attribute" thing. ... so why does clang care? Or, why doesn't gcc care? I guess I need to talk to gcc folks again. > In the 'x86_spec_ctrl_current' case, that nonsensical code _worked_ > (with gcc), because despite the declaration being for a regular > variable, the actual definition was in the proper segment. I'm guessing this is the reason why gcc doesn't fail - it probably looks at the declaration but doesn't care too much about it. And it is the definition that matters. While clang goes, uh, ah, declaration and definition mismatch, I better warn. > But that 'myvariable' thing above does end up being another example of > how we are clearly missing some type checkng in this area. > > I'm not sure if there's any way to get that section mismatch at > compile-time at all. Well, apparently, clang can: arch/x86/kernel/cpu/bugs.c:58:21: error: section attribute is specified on redeclared variable [-Werror,-Wsection] so there's a -Wsection warning which gcc could implement too. > For the static declarations, we could just make DECLARE_PER_CPU() add > some prefix/postfix to the name (and obviously then do it at use time > too). > > We have that '__pcpu_scope_##name' thing to make sure of globally > unique naming due to the whole weak type thing. I wonder if we could > do something similar to verify that "yes, this has been declared as a > percpu variable" at use time? But how? We need to save the info how a var has been declared and then use that info at access time. Yeah, lemme bother compiler guys a bit... -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
