linux-kernel - Re: [PATCH] Makefile: Globally enable fall-through warning

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Message-ID: <c5140ba1-5971-2158-4aaa-5999a66ba0ec@roeck-us.net>
Date:   Sun, 28 Jul 2019 11:12:58 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] Makefile: Globally enable fall-through warning

On 7/28/19 10:31 AM, Gustavo A. R. Silva wrote:
> 
> 
> On 7/28/19 12:14 PM, Guenter Roeck wrote:
>> Hi Gustavo,
>>
>> On Sun, Jul 28, 2019 at 11:42:28AM -0500, Gustavo A. R. Silva wrote:
>>> Hi Guenter,
>>>
>>> On 7/28/19 8:58 AM, Guenter Roeck wrote:
>>>> On Thu, Jun 06, 2019 at 07:46:17PM -0500, Gustavo A. R. Silva wrote:
>>>>> Now that all the fall-through warnings have been addressed in the
>>>>> kernel, enable the fall-through warning globally.
>>>>>
>>>>
>>>> Not really "all".
>>>>
>>>> powerpc:85xx/sbc8548_defconfig:
>>>>
>>>> arch/powerpc/kernel/align.c: In function ‘emulate_spe’:
>>>> arch/powerpc/kernel/align.c:178:8: error: this statement may fall through
>>>>
>>>> Plus many more similar errors in the same file.
>>>>
>>>> All sh builds:
>>>>
>>>> arch/sh/kernel/disassemble.c: In function 'print_sh_insn':
>>>> arch/sh/kernel/disassemble.c:478:8: error: this statement may fall through
>>>>
>>>> Again, this is seen in several places.
>>>>
>>>> mips:cavium_octeon_defconfig:
>>>>
>>>> arch/mips/cavium-octeon/octeon-usb.c: In function 'dwc3_octeon_clocks_start':
>>>> include/linux/device.h:1499:2: error: this statement may fall through
>>>>
>>>> None of those are from recent changes. And this is just from my small
>>>> subset of test builds.
>>>>
>>>
>>> Thank you for letting me know about this. I don't have access to build
>>> infrastructure like yours.
>>>
>>
>> I am always happy to run test builds on my infrastructure.
>>
> 
> Thank you!
> 
>>> My build infrastructure is similar to that of Linus.
>>>
>>> But if you send me all of those I can create a patch and send it back
>>> to you to make sure what you see is addressed. If we can coordinate for
>>> this it'd be great for everybody. :)
>>>
>>
>> Just have a look at the output of https://kerneltests.org/builders/,
>> in the 'master' and/or 'next' column. There are many additional warnings
>> in 'next'. Only downside is that you won't see the warnings unless there
>> are also build errors, but -next tends to have lots of those.
>>
> 
> I see.
> 
> mm... for some reason I'm not able to establish connection with that site...
> 

What is your host's IP address ? It might be auto-filtered; the site is hosted
on my own server and is under constant attack. Any subnet originating a sequence
of attacks will be blocked automatically.

Thanks,
Guenter

>> Just wondering ... wouldn't it be possible to run a coccinelle script
>> to identify those problems automatically, without depending on compile
>> warnings ? Or smatch/sparse, maybe ?
>>
> 
> That was a common question from people along the whole process. The short
> answer is: no. The reason for that is that Coccinelle is not a sophisticated
> enough tool to determine if we are dealing with a false positive or an actual
> bug.
> 
> That's why a code audit was needed.
> 
> Thanks
> --
> Gustavo
> 
> 
> 
> 
> 
>