linux-kernel - Re: [PATCH] USB: serial: io_edgeport: mark expected switch fall-throughs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20171030235002.Horde.gdw7F_ltZVrS1ZF-scG1Ps1@gator4166.hostgator.com>
Date:   Mon, 30 Oct 2017 23:50:02 -0500
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     David Laight <David.Laight@...lab.com>,
        'Bjørn Mork' <bjorn@...k.no>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: io_edgeport: mark expected switch
 fall-throughs

Hi David, Johan,

Quoting Johan Hovold <johan@...nel.org>:

> On Mon, Oct 30, 2017 at 11:54:33AM +0000, David Laight wrote:
>> From: Bjørn Mork
>> > Sent: 28 October 2017 11:57
>> > > In preparation to enabling -Wimplicit-fallthrough, mark switch cases
>> > > where we are expecting to fall through.
>> > >
>> > > Notice that in this particular case I replaced "...drop on through"
>> > > comments with a proper "fall through" comment on its own line, which
>> > > is what GCC is expecting to find.
>> >
>> > Sounds to me like GCC is the wrong tool for this.  But I would of course
>> > not mind if it was *just* the text.  However, as your patch cleary
>> > shows, the simplified logic leads to real problems:
>> >
>> > > @@ -1819,8 +1819,8 @@ static void process_rcvd_data(struct  
>> edgeport_serial *edge_serial,
>> > >  					edge_serial->rxState = EXPECT_DATA;
>> > >  					break;
>> > >  				}
>> > > -				/* Else, drop through */
>> > >  			}
>> > > +			/* fall through */
>> > >  		case EXPECT_DATA: /* Expect data */
>> > >  			if (bufferLength < edge_serial->rxBytesRemaining) {
>> > >  				rxLen = bufferLength;
>> >
>> >
>> > The original comment clearly marked a *conditional* fall through at the
>> > correct place.  Your patch makes it appear as if there is an
>> > unconditional fall through here.  There is not.  The fallthrough only
>> > applies to one of a number of nested if blocks. There are no less than
>> > 3 break statements in the same case block.
>> >
>> > Not a big deal maybe, just as the lack of any "fall through" comment
>> > isn't a big deal in the first place.  But this change is clearly making
>> > this code harder to read, and the change is therefore harmful IMHO.
>> >
>> > If you can't make -Wimplicit-fallthrough work without removing such
>> > precise fallthrough markings, then my proposal is to drop it and use
>> > some other tool.
>>
>> Just remove the 'else' after the 'break' further up.
>
> Yeah, that might be a good way to resolve this. I was gonna suggest
> adding the "fall though" comment before the case while keeping the
> "Else, drop through" comment in the branch, but removing the else might
> be better.
>

Thanks for the suggestion.

> This code is pretty hard to read as is and could really use some clean
> up...
>

I agree. I'll send a V2 of this patch and then let's see if I can help  
with some code refactoring.

Thank you
--
Gustavo A. R. Silva