Re: [PATCH] x86/syscalls: Mark expected switch fall-throughs

[Gustavo A. R. Silva]

Quoting Thomas Gleixner <tglx@xxxxxxxxxxxxx>:

> 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