Re: coccinelle: adjustments for array.cocci?

From: Markus Elfring <markus.elfring@web.de>
Date: Nov 17, 2019, 07:56 UTC
Message-ID: <57b5d1c9-72c1-6fff-a242-90f5f24f0972@web.de>
In-Reply-To: <fc56b970-4ca1-7734-c4bb-f57cae7a273f@web.de>

Show 12 quoted lines

>> @@
>> expression dst, src, n, E;
>> @@
>>  memcpy(dst, src, sizeof(
>> +                        *(
>>                            E
>> -                           [...]
>> +                         )
>>                          ) * n
>>        )
>
> That's longer and looks more complicated to me

I point another possibility out to express a change specification by the means of the semantic patch language. How would you think about such SmPL code if the indentation will be reduced?

Show 10 quoted lines

> than what we currently have:
>   @@
>   expression dst, src, n, E;
>   @@
>     memcpy(dst, src, n * sizeof(
>   - E[...]
>   + *(E)
>     ))
>
> Avoiding to duplicate E doesn't seem to be worth it.

I show other development preferences occasionally.

> I can see that indenting the sizeof parameter and parentheses could
> improve readability, though.

Thanks that you can follow such coding style aspects.

Show 29 quoted lines

>> @@
>> type T;
>> T *ptr;
>> T[] arr;
>> expression E, n;
>> @@
>>  memcpy(
>> (       ptr, E, sizeof(
>> -                      *(ptr)
>> +                      T
>>                       ) * n
>> |       arr, E, sizeof(
>> -                      *(arr)
>> +                      T
>>                       ) * n
>> |       E, ptr, sizeof(
>> -                      *(ptr)
>> +                      T
>>                       ) * n
>> |       E, arr, sizeof(
>> -                      *(arr)
>> +                      T
>>                       ) * n
>> )
>>        )
>
> This still fails to regenerate two of the changes from 921d49be86
> (use COPY_ARRAY for copying arrays, 2019-06-15), at least with for me
> (and Coccinelle 1.0.4).

Would you become keen to find the reasons out for unexpected data processing results (also by the software combination “Coccinelle 1.0.8-00004-g842075f7”) at this place?

But this transformation rule can probably be omitted if the usage of SmPL disjunctions will be increased in a subsequent rule, can't it?

Show 24 quoted lines

>> @@
>> type T;
>> T* dst_ptr, src_ptr;
>> T[] dst_arr, src_arr;
>> expression n, x;
>> @@
>> -memcpy
>> +COPY_ARRAY
>>        (
>> (       dst_ptr
>> |       dst_arr
>> )
>>        ,
>> (       src_ptr
>> |       src_arr
>> )
>> -      , (n) * \( sizeof(T) \| sizeof(*(x)) \)
>> +      , n
>>        )
>
> That x could be anything -- it's not tied to the element size of source
> or destination.  Such a transformation might change the meaning of the
> code, as COPY_ARRAY will use the element size of the destination behind
> the scenes.  So that doesn't look safe to me.

Would you like to use the SmPL code “*( \( src_ptr \| src_arr \) )” instead?

Show 18 quoted lines

>> @@
>> type T;
>> T* dst, src, ptr;
>> expression n;
>> @@
>> (
>> -memmove
>> +MOVE_ARRAY
>>         (dst, src
>> -                , (n) * \( sizeof(* \( dst \| src \) ) \| sizeof(T) \)
>> +                , n
>>         )
>> |
>> -ptr = xmalloc((n) * \( sizeof(*ptr) \| sizeof(T) \))
>> +ALLOC_ARRAY(ptr, n)
>> );
>
> memmove/MOVE_ARRAY and xmalloc/ALLOC_ARRAY are quite different;

These functions provide another programming interface.

> why would we want to jam transformations for them into the same rule
> like this?

Possible nicer run time characteristics by the Coccinelle software.

> The only overlap seems to be n.

These case distinctions can share also the metavariable “T” for the desired source code deletion.

> Handling memmove/MOVE_ARRAY and memcpy/COPY_ARRAY together would make
> more sense, as they take the same kinds of parameters.

Would you like to adjust the SmPL code in such a design direction?

> I didn't know that disjunctions can be specified inline using \(, \|
> and \), though.  Rules can be much more compact that way.

I hope that more corresponding software improvements can be achieved.

> Mixing languages like that can also be quite confusing.

I agree to this development concern.

Show 7 quoted lines

>> Now I observe that the placement of space characters can be a coding style
>> concern at four places for adjusted lines by the generated patch.
>> Would you like to clarify remaining issues for pretty-printing
>> in such use cases?
>
> Ideally, generated code should adhere to Documentation/CodingGuidelines,
> so that it can be accepted without requiring hand-editing.

But how does the software situation look like if the original source code would contain coding style issues?

It seems to be possible to specify SmPL code in a way so that even questionable code layout would be preserved by an automatic transformation.

Regards, Markus