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

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 =
  { ... };

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
>
>