On Wed 05-09-18 16:26:13, Kirill A. Shutemov wrote: > On Wed, Sep 05, 2018 at 08:48:00AM +0200, Michal Hocko wrote: > > Hi Kirill, > > while looking at something unrelated I have stumbled over %subj and I > > simply do not understand how BUILD_BUG_ON_INVALID is supposed to work > > for page flags checks which are dynamic by definition. > > BUILD_BUG_ON_INVALID is noop without any side effects unless __CHECKER__ > > is enabled when it evaluates to ((void )(sizeof((__force long )(e)))). > > You've read it backwards. BUILD_BUG_ON_INVALID() is not if __CHECKER__ is > enabled. Well, that is what I meant I just reworded the text and kept the negation... > > How is this supposed to work? Am I just confused or BUILD_BUG_ON_INVALID > > is simply not a good fit here and all you wanted is the no side-effect > > nature of it? > > Without CONFIG_DEBUG_VM_PGFLAGS() is basically nop. BUILD_BUG_ON_INVALID() > here is fance version of nop that check that what you've wrote inside > parses fine. That's it. OK, I see it. I somehow implied that this is similar to BUILD_BUG_ON. If this is about pure expression correctness then it finally makes some sense to me. Thanks! -- Michal Hocko SUSE Labs
