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Message-ID: <CAHk-=wi0ePNgwLfk8yddABjnZh+gcL9dV2E8mxLKfb=8LHFQ-g@mail.gmail.com> Date: Fri, 6 Sep 2024 17:48:09 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Nathan Chancellor <nathan@...nel.org> Cc: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, llvm@...ts.linux.dev Subject: Re: [GIT PULL] KVM fixes for Linux 6.11-rc7 On Fri, 6 Sept 2024 at 16:40, Nathan Chancellor <nathan@...nel.org> wrote: > > This was brought up to GCC at one point and they considered its current > behavior as working as intended from my understanding: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91432 Their argument seems to be "the missing fallthrough has no effect". Which is true. But they seem to be missing that it has no effect *NOW*. One major problem case is that people tend to add new cases to the end of a switch() statement, not counting that final "default: break". So the "it doesn't have any effect NOW" is true, but the next time somebody edits that and doesn't check warnings, it *will* have very strange behavior, and it won't be affecting the newly added case, but some entirely unrelated previous case. So I really think the lack of warnings is a gcc mis-feature. It leaves code in a bad situation going forward. Oh well. Many times I have had to disable warnings entirely because they have too many false positives, so I guess the occasional "doesn't warn enough" is still a better problem to have. And at least we have (a) clang warning about it and (b) require the warnings going forward and use -Werror, so at least for the kernel the "when somebody edits that code, you get surprising behavior" case _will_ get noticed. Linus
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