linux-kernel - Re: [PATCH net-next] intel: Mark expected switch fall-throughs

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Date:   Wed, 23 Jan 2019 09:44:48 -0800
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] intel: Mark expected switch fall-throughs

On Wed, 2019-01-23 at 11:11 -0600, Gustavo A. R. Silva wrote:
> Hi Jeffrey,
> 
> On 1/23/19 11:04 AM, Jeff Kirsher wrote:
> > On Wed, 2019-01-23 at 01:48 -0600, Gustavo A. R. Silva wrote:
> > > In preparation to enabling -Wimplicit-fallthrough, mark switch
> > > cases
> > > where we are expecting to fall through.
> > > 
> > > This patch fixes the following warnings:
> > > 
> > > drivers/net/ethernet/intel/igb/e1000_82575.c:636:6: warning: this
> > > statement may fall through [-Wimplicit-fallthrough=]
> > > drivers/net/ethernet/intel/igb/igb_main.c:6710:6: warning: this
> > > statement may fall through [-Wimplicit-fallthrough=]
> > > drivers/net/ethernet/intel/i40e/i40e_xsk.c:237:3: warning: this
> > > statement may fall through [-Wimplicit-fallthrough=]
> > > 
> > > Warning level 3 was used: -Wimplicit-fallthrough=3
> > > 
> > > This patch is part of the ongoing efforts to enabling
> > > -Wimplicit-fallthrough.
> > > 
> > > Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> > > ---
> > >   drivers/net/ethernet/intel/i40e/i40e_xsk.c   | 3 ++-
> > >   drivers/net/ethernet/intel/igb/e1000_82575.c | 2 +-
> > >   drivers/net/ethernet/intel/igb/igb_main.c    | 2 +-
> > >   3 files changed, 4 insertions(+), 3 deletions(-)
> > 
> > NAK on the igb changes.  There is already a "fall through" code
> > comment
> > which is fine, adding a hyphen does not make the comment any more
> > readable.
> > 
> 
> Those comments are not fine. They trigger the warnings I mention in
> the
> commit log. With this patch such warnings are fixed.
> 
> Notice that warning level 3 was used: -Wimplicit-fallthrough=3

This is a "false positive" based on the compiler option definition:

-Wimplicit-fallthrough=3 case sensitively matches a wide range of
regular expressions, listed in the GCC manual. E.g., all of these are
accepted:
/* Falls through. */
/* fall-thru */
/* Else falls through. */
/* FALLTHRU */
/* … falls through … */
etc.

You should be looking to fix the problem with the compiler option,
which is reporting "acceptable" code comments.

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