Re: new checkpatch flexible array test ? (was Re: [PATCH v4 12/14] gunyah: rsc_mgr: Add RPC for console services)

From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Joe Perches <joe@perches.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Elliot Berman <quic_eberman@quicinc.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Bjorn Andersson <quic_bjorande@quicinc.com>,
	Murali Nalajala <quic_mnalajal@quicinc.com>,
	Trilok Soni <quic_tsoni@quicinc.com>,
	Srivatsa Vaddagiri <quic_svaddagi@quicinc.com>,
	Carl van Schaik <quic_cvanscha@quicinc.com>,
	Andy Gross <agross@kernel.org>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	Jassi Brar <jassisinghbrar@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Marc Zyngier <maz@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Jonathan Corbet <corbet@lwn.net>, Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Arnd Bergmann <arnd@arndb.de>,
	devicetree@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: new checkpatch flexible array test ? (was Re: [PATCH v4 12/14] gunyah: rsc_mgr: Add RPC for console services)
Date: Mon, 31 Oct 2022 13:23:54 -0500	[thread overview]
Message-ID: <89eca382-fca3-28f9-eac7-f855f2efb598@embeddedor.com> (raw)
In-Reply-To: <04ade5f54bd3dc658cb8606c98b0b1fe34a97383.camel@perches.com>

On 10/3/22 00:38, Joe Perches wrote:
> On Mon, 2022-10-03 at 07:29 +0200, Greg Kroah-Hartman wrote:
>> On Sun, Oct 02, 2022 at 06:46:30PM -0700, Joe Perches wrote:
>>> On Fri, 2022-09-30 at 14:22 +0200, Greg Kroah-Hartman wrote:
>>>> On Wed, Sep 28, 2022 at 12:56:31PM -0700, Elliot Berman wrote:
>>>>> Gunyah resource manager defines a simple API for virtual machine log
>>>>> sharing with the console service.
>>> []
>>>>> diff --git a/include/linux/gunyah_rsc_mgr.h b/include/linux/gunyah_rsc_mgr.h
>>> []
>>>>> +struct gh_rm_notif_vm_console_chars {
>>>>> +	u16 vmid;
>>>>> +	u16 num_bytes;
>>>>> +	u8 bytes[0];
>>>>
>>>> Please do not use [0] for new structures, otherwise we will just have to
>>>> fix them up again as we are trying to get rid of all of these from the
>>>> kernel. Just use "bytes[];" instead.
>>>
>>> Maybe a checkpatch addition like:
>>> ---
> []
>>> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> []
>>> @@ -3948,6 +3948,17 @@ sub process {
>>>   			}
>>>   		}
>>>   
>>> +# check for zero length array declarations in likely structs
>>> +		if ($line =~ /^\+\t($Declare\s*$Ident)\s*\[\s*0\s*\]\s*;\s*$/ &&
>>> +		    defined $lines[$linenr] &&
>>> +		    $lines[$linenr] =~ /^[\+ ]\}\s*(?:__\w+\s*(?:$balanced_parens)?)\s*;\s*$/) {

This sounds great. We need the same for one-element arrays. :)
Both zero-length and one-element arrays are deprecated.

> 
> This should actually be:
> 
> 		    $lines[$linenr] =~ /^[\+ ]\}(?:\s*__\w+\s*(?:$balanced_parens)?)*\s*;\s*$/) {

I agree. Thanks.

> 
> as it was missing a * for uses like
> 
> 	int foo[0];
> } __packed __aligned(4);
> 
> and uses without any attribute at all
> 
>>> +			if (WARN("FLEXIBLE_ARRAY_ZERO",
>>> +				 "Prefer flexible length array declarations with [] over [0]\n" . $herecurr) &&
>>> +			    $fix) {
>>> +				$fixed[$fixlinenr] =~ s/\[\s*0\s*\]/[]/;
>>> +			}
>>> +		}
>>> +
>>>   # check for multiple consecutive blank lines
>>>   		if ($prevline =~ /^[\+ ]\s*$/ &&
>>>   		    $line =~ /^\+\s*$/ &&
>>
>> This is a question for Gustavo, who did all the work here.  Gustavo,
>> does the above checkpatch change look good to you?

Yep; the idea is great. :)

Another alternative to stop those fake flex-arrays from entering the codebase
is to run Coccinelle scripts during linux-next builds, as suggested by Elena
Reshetova at LSSEU a couple of months ago.

However, if these can be stopped with checkpatch it'd be really helpful, as well.

Thanks
--
Gustavo