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Date: Tue, 28 Nov 2017 12:05:12 -0600 From: "Gustavo A. R. Silva" <garsilva@...eddedor.com> To: Thomas Gleixner <tglx@...utronix.de> Cc: Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org> Subject: Re: [PATCH] x86/syscalls: Mark expected switch fall-throughs Quoting Thomas Gleixner <tglx@...utronix.de>: > On Mon, 27 Nov 2017, Gustavo A. R. Silva wrote: > >> In preparation to enabling -Wimplicit-fallthrough, mark switch cases >> where we are expecting to fall through. > >> case 0: >> if (!n--) break; >> *args++ = regs->bx; >> + /* fall through */ > > And these gazillions of pointless comments help enabling of > -Wimplicit-fallthrough in which way? > The -Wimplicit-fallthrough option was added to GCC 7. We want to add that option to the top-level Makefile so we can have the compiler help us not make mistakes as missing "break"s or "continue"s. This also documents the intention for humans and provides a way for analyzers to report issues or ignore False Positives. So prior to adding such option to the Makefile, we have to properly add a code comment wherever the code is intended to fall through. During the process of placing these comments I have identified actual bugs (missing "break"s/"continue"s) in a variety of components in the kernel, so I think this effort is valuable. Lastly, such a simple comment in the code can save a person plenty of time during a code review. Thanks -- Gustavo A. R. Silva
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