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Date:   Tue, 1 Dec 2020 17:08:49 +0300
From:   Dan Carpenter <dan.carpenter@oracle.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Kees Cook <keescook@chromium.org>, alsa-devel@alsa-project.org,
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Subject: Re: [PATCH 000/141] Fix fall-through warnings for Clang
Message-ID: <20201201140849.GH2767@kadam>
References: <cover.1605896059.git.gustavoars@kernel.org>
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 <202011201129.B13FDB3C@keescook>
 <20201120115142.292999b2@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
 <202011220816.8B6591A@keescook>
 <CAKwvOdntVfXj2WRR5n6Kw7BfG7FdKpTeHeh5nPu5AzwVMhOHTg@mail.gmail.com>
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On Mon, Nov 23, 2020 at 05:32:51PM -0800, Nick Desaulniers wrote:
> On Sun, Nov 22, 2020 at 8:17 AM Kees Cook <keescook@chromium.org> wrote:
> >
> > On Fri, Nov 20, 2020 at 11:51:42AM -0800, Jakub Kicinski wrote:
> > > If none of the 140 patches here fix a real bug, and there is no change
> > > to machine code then it sounds to me like a W=2 kind of a warning.
> >
> > FWIW, this series has found at least one bug so far:
> > https://lore.kernel.org/lkml/CAFCwf11izHF=g1mGry1fE5kvFFFrxzhPSM6qKAO8gxSp=Kr_CQ@mail.gmail.com/
> 
> So looks like the bulk of these are:
> switch (x) {
>   case 0:
>     ++x;
>   default:
>     break;
> }

This should not generate a warning.

> 
> I have a patch that fixes those up for clang:
> https://reviews.llvm.org/D91895
> 
> There's 3 other cases that don't quite match between GCC and Clang I
> observe in the kernel:
> switch (x) {
>   case 0:
>     ++x;
>   default:
>     goto y;
> }
> y:;

This should generate a warning.

> 
> switch (x) {
>   case 0:
>     ++x;
>   default:
>     return;
> }

Warn for this.


> 
> switch (x) {
>   case 0:
>     ++x;
>   default:
>     ;
> }

Don't warn for this.

If adding a break statement changes the flow of the code then warn about
potentially missing break statements, but if it doesn't change anything
then don't warn about it.

regards,
dan carpenter