linux-kernel - Re: [PATCH] checkpatch: add new warning when lookup_symbol

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Message-ID: <0f8f1a51-a048-a49b-dde2-90f67f5df7f2@gmx.de>
Date:   Thu, 17 Dec 2020 20:15:52 +0100
From:   Helge Deller <deller@....de>
To:     Joe Perches <joe@...ches.com>, Andy Whitcroft <apw@...onical.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] checkpatch: add new warning when lookup_symbol_name() is
 used

On 12/17/20 7:15 PM, Joe Perches wrote:
> On Thu, 2020-12-17 at 18:42 +0100, Helge Deller wrote:
>> On 12/17/20 6:27 PM, Joe Perches wrote:
>>> On Thu, 2020-12-17 at 18:11 +0100, Helge Deller wrote:
>>>> In most cases people use lookup_symbol_name() to resolve a kernel symbol
>>>> and then print it via printk().
>>>>
>>>> In such cases using the %ps, %pS, %pSR or %pB printk formats are easier
>>>> to use and thus should be preferred.
>>> []
>>>> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
>>> []
>>>> @@ -4317,6 +4317,12 @@ sub process {
>>>>  			     "LINUX_VERSION_CODE should be avoided, code should be for the version to which it is merged\n" . $herecurr);
>>>>  		}
>>>>
>>>> +# avoid lookup_symbol_name()
>>>> +		if ($line =~ /\blookup_symbol_name\b/) {
>>>> +			WARN("PREFER_PRINTK_FORMAT",
>>>> +			     "If possible prefer %ps or %pS printk format string to print symbol name instead of using lookup_symbol_name()\n" . $herecurr);
>>>> +		}
>>>> +
>>>>  # check for uses of printk_ratelimit
>>>>  		if ($line =~ /\bprintk_ratelimit\s*\(/) {
>>>>  			WARN("PRINTK_RATELIMITED",
>>>
>>> Huh?  nak.
>>>
>>> lookup_symbol_name is used in the kernel a grand total of 3 times.
>>
>> Yes, there were much more in the past which got fixed by patches I submitted.
>
> Hi Helge.
>
> Much more may be a bit of an overstatement.
>
> I found 3 instances of lookup_symbol_name removals in 2 patches.
>
> commit 36dbca148bf8e3b8658982aa2256bdc7ef040256
> -		lookup_symbol_name((ulong)pm_power_off, symname);
> -		lookup_symbol_name((ulong)pm_power_off, symname);
> commit da88f9b3113620dcd30fc203236aa53d5430ee98
> -	if (lookup_symbol_name((unsigned long)sym, symname) < 0)
>
> There's a tension between adding tests and newbies that consider
> checkpatch warnings as dicta that must be followed so there would
> be patches submitted eventually against the existing correct uses.
>
> So thanks, but given the very few existing all correct uses of
> this function and the low probability of new uses I'd prefer not
> to apply this.

Ok.

Thanks!
Helge