Re: [Cocci] linux: special logic in repetitive tests

Re: [Cocci] linux: special logic in repetitive tests

[Markus Elfring]

> There is a block of if tests against the same variable
> in include/linux/mtd/pfow.h that likely is defective

I wonder about this interpretation.


> Likely the first test should be something like
>
> 	if ((prog_status & 0x03) == 0x03)

Why would you prefer such a code variant?


> Is there a way for cocci to find this style of bitwise logic defect?

* Probably, yes.

* How often will this implementation detail really be a “defect”?

* Where do you stumble on difficulties to express a corresponding source code
  search pattern by the means of the semantic patch language?

Regards,
Markus
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Re: [Cocci] linux: special logic in repetitive tests

[Joe Perches]

On Tue, 2020-03-31 at 08:28 +0200, Markus Elfring wrote:
> > There is a block of if tests against the same variable
> > in include/linux/mtd/pfow.h that likely is defective
> 
> I wonder about this interpretation.

Wonder harder.

If something is (& 3) it is also either (& 2 || & 1)
so why have both below the first test?

> * How often will this implementation detail really be a “defect”?

Moderately likely.

> * Where do you stumble on difficulties to express a corresponding source code
>   search pattern by the means of the semantic patch language?

#defines, shifts, masks


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Re: [Cocci] linux: special logic in repetitive tests

[Markus Elfring]

> Wonder harder.
>
> If something is (& 3) it is also either (& 2 || & 1)
> so why have both below the first test?

I can interpret the source code example in the way that the number
of set bits are checked.
I can eventually become concerned around the preferred coding style
because of the usage of these constant values.
Would you like to check the use of bit fields?


>> * Where do you stumble on difficulties to express a corresponding source code
>>   search pattern by the means of the semantic patch language?
>
> #defines, shifts, masks

You come along the usual development challenges for the safe handling
of possible code variations.
With which approach would you like to start and perform further
source code analysis?

Regards,
Markus
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Re: [Cocci] linux: special logic in repetitive tests

[Markus Elfring]

> Wonder harder.
>
> If something is (& 3) it is also either (& 2 || & 1)
> so why have both below the first test?

Would you occasionally prefer to use enumeration values together with
switch statements at such source code places?

Regards,
Markus
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