Re: [cocci] Adjusting attributes for variables with SmPL?

On 5/27/26 10:59, Julia Lawall wrote:
>
> On Wed, 27 May 2026, Pierrick Philippe wrote:
>
>> Hi Markus and Julia,
>>
>> I hope you are doing well.
>>
>> I am now trying to work with structures and basically here is the patch
>> I'd like to generate:
>>
>> ```diff
>> struct foo {
>>     int x;
>>     int y;
>> };
>> int main(void) {
>> -   struct foo f = { 42, 42 };
>> +  struct foo __attribute__((myattr (("x")))) f = { 42, 42 };
>>     int b;
>>     int *c = &b;
>>     int z = memcmp(&f.x, c, sizeof(int));
>>     return z;
>> }
>> ```
>>
>> I used the following semantic patch which is successfully parsed, but
>> not generating any diff:
>>
>> ```cocci
>> @attribute_struct_scalar_type@
>> expression E, E1, E2;
>> type T;
>> identifier F, X;
>> @@
>> -T F = E;
>> +T __attribute__((myattr(("X")))) F = E;
>> ...
>> memcmp(&F.X, E1, E2)
>> ```
> I think that the problem is that { ... } is not actually an expression in
> C.  It's a strange thing that can only exist as part of a declaration.
>
> But you don't want to change it, so you don't need a metavariable for it.
>
> Just write:
>
> - T F =
> + T __attribute__((myattr(("X")))) F =
>   { ... };

It does work indeed, thanks a lot!
Although the metavariable X is not interpreted in the `+` context, could
it be due to the attribute or unrelated?
I think I read something related to attribute not being parsed in `+`
context in the documentation.

>
> Lots of other decompositions are possible.  For example you can also
> write:
>
> T
> + __attribute__((myattr(("X"))))
>   F = { ... };
>
> julia
>
>> The idea is essentially the same than in my previous email, although
>> here I'm working with field access.
>> The semantic patch is clearly inspired from a previous version for
>> integer or float which was successfully parsed and spatch was generating
>> the expected diff.
>>
>> Also, from what I understand from the docs, metavariables of type
>> `field` target field declaration (meaning within the structure type
>> definition specifically).
>> And I could not wrap my head around a way to use it to achieve my goal here.
>> I also tried to used a quite simple semantic patch, which was still not
>> generating any diff and raising a warning ("should f be a metavariable?").
>> And I do not understand why this one is not working since there are
>> basically no metavariables outside the three expressions.
>> Here is the semantic patch in question:
>>
>> ```cocci
>> @attribute_struct_scalar_type_dummy@
>> expression E, E1, E2;
>> @@
>> -struct foo f = E;
>> +struct foo __attribute__((myattr(("x")))) f = E;
>> ...
>> memcmp(&f.x, E1, E2)
>> ```
>>
>> In any case, thank you for your time and your previous answers.
>>
>> Pierrick
>>
> >