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Date:   Wed, 25 Nov 2020 14:09:29 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     James Bottomley <James.Bottomley@...senpartnership.com>,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
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Subject: Re: [Intel-wired-lan] [PATCH 000/141] Fix fall-through warnings for Clang

On Wed, Nov 25, 2020 at 1:33 PM Finn Thain <fthain@...egraphics.com.au> wrote:
>
> Or do you think that a codebase can somehow satisfy multiple checkers and
> their divergent interpretations of the language spec?

Have we found any cases yet that are divergent? I don't think so.  It
sounds to me like GCC's cases it warns for is a subset of Clang's.
Having additional coverage with Clang then should ensure coverage for
both.

> > This is not a shiny new warning; it's already on for GCC and has existed
> > in both compilers for multiple releases.
> >
>
> Perhaps you're referring to the compiler feature that lead to the
> ill-fated, tree-wide /* fallthrough */ patch series.
>
> When the ink dries on the C23 language spec and the implementations figure
> out how to interpret it then sure, enforce the warning for new code -- the
> cost/benefit analysis is straight forward. However, the case for patching
> existing mature code is another story.

I don't think we need to wait for the ink to dry on the C23 language
spec to understand that implicit fallthrough is an obvious defect of
the C language.  While the kernel is a mature codebase, it's not
immune to bugs.  And its maturity has yet to slow its rapid pace of
development.
-- 
Thanks,
~Nick Desaulniers

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