Re: [XEN PATCH 2/7] x86/mm: address MISRA C:2012 Rule 2.1

From: Jan Beulich <jbeulich@suse.com>
To: Nicola Vetrini <nicola.vetrini@bugseng.com>
Cc: "Stefano Stabellini" <sstabellini@kernel.org>,
	xen-devel@lists.xenproject.org, consulting@bugseng.com,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>
Subject: Re: [XEN PATCH 2/7] x86/mm: address MISRA C:2012 Rule 2.1
Date: Thu, 14 Dec 2023 08:57:52 +0100	[thread overview]
Message-ID: <21dae6f8-6f79-4952-94e0-1b7c13c7c1a6@suse.com> (raw)
In-Reply-To: <8a49facc4fbf4d3fefb91b9b5bef3305@bugseng.com>

On 13.12.2023 15:44, Nicola Vetrini wrote:
> On 2023-12-12 10:53, Jan Beulich wrote:
>> On 12.12.2023 10:12, Nicola Vetrini wrote:
>>> On 2023-12-12 02:42, Stefano Stabellini wrote:
>>>> On Mon, 11 Dec 2023, Nicola Vetrini wrote:
>>>>> The "return 0" after the swich statement in 'xen/arch/x86/mm.c'
>>>>> is unreachable because all switch clauses end with returns.
>>>>> However, some of them can be substituted with "break"s to allow
>>>>> the "return 0" outside the switch to be reachable.
>>>>>
>>>>> No functional changes.
>>>>
>>>> This is correct but makes the code inconsistent. I would either 
>>>> remove
>>>> the return 0; at the end of arch_memory_op, or do the following:
>>>>
>>>> - initialize rc to 0 at the beginning: int rc = 0;
>>>> - all switch clauses break instead of return;
>>>> - at the end: return rc;
>>>
>>> Given the feedback on the Arm side, the first solution is likely to be
>>> preferred.
>>
>> I wouldn't mind either option, with
>> - the former ensured to be okay with all compiler versions we (still)
>>   support,
> 
> I tested a stripped-down version of the switch on godbolt.org (as far 
> back as gcc-4.8.5) and it doesn't complain. It should be tested on a 
> real Xen build, though.

I didn't fear any issue when going back to just 4.8. Quoting ./README:

      - For x86:
        - GCC 4.1.2_20070115 or later

>> - the latter having the initialize rc to 0 part dropped; imo it's 
>> better
>>   if every case block makes sure to set the intended value explicitly.
> 
> This is a lot of churn, I'd rather avoid it.

Rant (sorry): There's already excessive churn for entirely benign issues
that Misra claims need adjusting.

Jan