linux-kernel - Re: [PATCH] EDAC: remove unnecessary static in edac_fake_inject

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Message-ID: <6698a3ad-bb52-7297-a10b-818304c96d38@embeddedor.com>
Date:   Sun, 23 Jul 2017 01:25:56 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        Borislav Petkov <bp@...en8.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        cocci@...teme.lip6.fr
Subject: Re: [PATCH] EDAC: remove unnecessary static in
 edac_fake_inject_write()



On 07/23/2017 12:53 AM, Julia Lawall wrote:
>
>
> On Sun, 23 Jul 2017, Gustavo A. R. Silva wrote:
>
>> Hi Julia,
>>
>> On 07/23/2017 12:07 AM, Julia Lawall wrote:
>>>
>>>
>>> On Sat, 22 Jul 2017, Gustavo A. R. Silva wrote:
>>>
>>>> Hi Julia, Borislav,
>>>>
>>>> On 07/22/2017 11:22 AM, Gustavo A. R. Silva wrote:
>>>>> Hi all,
>>>>>
>>>>> On 07/22/2017 01:36 AM, Borislav Petkov wrote:
>>>>>> On Fri, Jul 21, 2017 at 10:08:12PM +0200, Julia Lawall wrote:
>>>>>>> Someone pointed out that the rule is probably not OK when the
>>>>>>> address of
>>>>>>> the static variable is taken, because then it is likely being used
>>>>>>> as
>>>>>>> permanent storage.
>>>>>>
>>>>>> Makes sense to me.
>>>>>>
>>>>>>> An improved rule is:
>>>>>>
>>>>>> Do you think it is worth having it in scripts/coccinelle/ ?
>>>>>>
>>>>>> I don't think Gustavo would mind putting it there :)
>>>>>>
>>>>>
>>>>> Absolutely, I'd be glad to help out. :)
>>>>>
>>>>
>>>> I've been working on this issue today and, in my opinion, this script is
>>>> even
>>>> better:
>>>>
>>>> @bad exists@
>>>> position p;
>>>> identifier x;
>>>> expression e;
>>>> type T;
>>>> @@
>>>>
>>>> static T x@p;
>>>> ... when != x = e
>>>> x = <+...x...+>
>>>>
>>>> @worse1 exists@
>>>> position p;
>>>> identifier x;
>>>> type T;
>>>> @@
>>>>
>>>> static T x@p;
>>>> ...
>>>> return &x;
>>>>
>>>> @worse2 exists@
>>>> position p;
>>>> identifier x;
>>>> type T;
>>>> @@
>>>>
>>>> static T *x@p;
>>>> ...
>>>> return x;
>>>>
>>>> @@
>>>> identifier x;
>>>> expression e;
>>>> type T;
>>>> position p != {bad.p,worse1.p,worse2.p};
>>>> @@
>>>>
>>>> -static
>>>>   T x@p;
>>>>   ... when != x
>>>>       when strict
>>>> ?x = e;
>>>>
>>>> It ignores all the cases in which the address of the static variable is
>>>> returned to the caller function.
>>>
>>> I don't understand why you want to restrict the address of a variable case
>>> to returns.  Storing the address in a field of a structure that has a
>>> lifetime beyond the function body is a problem as well.
>>>
>>
>> Yeah, I totally agree and, personally I consider that a bad coding practice.
>> But I think those kinds of issues should be addressed in a different script.
>
> I don't understand the response at all.  My point was that you have taken
> a very general reason to not apply the change, ie the presence of &x
> anywhere, and limited it to a special case: you don't apply the change
> when there exists return &x and you do apply the script when there exits
> a->b = &x.  But the change is not safe to apply in both cases.
>

I see your point now.

>
>>
>>> On the other hand returning the value stored in a static variable is not a
>>> problem.  That value exists independently of the variable that contains
>>> it.  The variable that conains it doesn't need to live on in any way.
>>>
>>
>> Yeah, I agree, but I don't see exactly where this argument is coming from ?
>>
>> Notice that for both worse1 and worse2, what is returned is the address, not
>> the value of the static variable. At least that was my intention, unless I
>> maybe missing something ?
>
> return x returns the value of x.  It does not return the address of x.
>

You are right, I missed that one. Thank you for pointing it out.

Lesson learned, your original script should remain as is. :)

Have a good day,
Thank you!
-- 
Gustavo A. R. Silva