[Cocci] cocci: char* indexing style for linux

[lars@metafoo.de (Lars-Peter Clausen)]

On 08/17/2014 07:42 PM, Julia Lawall wrote:
>
>
> On Sun, 17 Aug 2014, Joe Perches wrote:
>
>> On Sun, 2014-08-17 at 18:09 +0200, SF Markus Elfring wrote:
>>>> I would prefer to be able to convert
>>>> 	*(skb->data + frame_size / 2 + 10)
>>>> not to
>>>> 	(skb->data + frame_size / 2)[10]
>>>> but to
>>>> 	skb->data[frame_size / 2 + 10]
>>>>
>>>> but I don't know how.
>>>
>>> How do you think about a bit more fine-tuning for the desired semantic
>>> patch?
>>
>> Not sure I understand what you are requesting.
>>
>>> Can it be that the pattern "*(foo + e)" is too generic for any source
>>> code place?
>>
>> I don't think so as any type or combination of
>> arithmetic operations would then need to be specified
>> by the spatch input script.
>>
>>> Would you like to try out the specification of a few more elements
>>> instead of a single expression here?
>>
>> Not really.
>>
>> I think a precedence specification capability like first
>> pointer match followed by longest arithmetic match would
>> perhaps be a better generic facility.
>
> Isn't the problem already solved? If not, I will look into it.

I think for these kinds of problems it would be helpful to have a 
metavariable type that is somewhere in the middle of idexpression and 
expression. Something that matches an identifier or accessing a field in an 
identifier, or a field of a field of an identifier and so on.

In the past I had cocci scripts where I ended up doing

(
id->fld1
|
id->fld1.fld2
|
id->fld1.fld2.fld3
...
)

to kind of make this work.

- Lars