Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 28 Nov 2017 12:05:12 -0600
Message-ID: <20171128120512.Horde.1mz61Up1PsNtyHbrjWmK8L7@gator4166.hostgator.com>
From:   "Gustavo A. R. Silva" <garsilva@embeddedor.com>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] x86/syscalls: Mark expected switch fall-throughs
References: <20171127235253.GA20384@embeddedor.com>
 <alpine.DEB.2.20.1711281448520.1723@nanos>
In-Reply-To: <alpine.DEB.2.20.1711281448520.1723@nanos>
User-Agent: Horde Application Framework 5
Content-Type: text/plain; charset=utf-8; format=flowed; DelSp=Yes
MIME-Version: 1.0
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


Quoting Thomas Gleixner <tglx@linutronix.de>:

> 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


From 1585317989981270721@xxx Tue Nov 28 13:50:50 +0000 2017
X-GM-THRID: 1585265423856272058
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread