Messages in this thread | | | Date | Fri, 15 Jul 2022 16:03:47 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 5.15 00/78] 5.15.55-rc1 review |
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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@alien8.de> 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
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