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

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On Thu, 28 May 2026, Markus Elfring wrote:

> >>>                The question is whether it makes the change that is wanted?
> >>
> >> Unfortunately, not with this test case.
> >
> > And with the semantic patch that you sent previously before deciding to
> > "optimize" it?
> Please compare the involved SmPL code in more detail once more.
>
>
> A)
> @simple_display@
> expression E1, E2;
> identifier F, X;
> initialiser I;
> type T;
> @@
> *T F = I;
>  ...
> *memcmp(&F.X, E1, E2)
>
>
> Markus_Elfring@Sonne:…/Projekte/Coccinelle/Probe> /usr/bin/spatch example_by_Pierrick_Philippe-20260527.c suggestion7_for_Pierrick_Philippe-20260528.cocci
> …
> diff =
> …
>
>
> B)
> @adjusted_display@
> expression E1, E2;
> identifier F, X;
> initialiser I;
> type T;
> @@
> *T F = I;
>  ...
> *memcmp(
> (       &F.X, E1
> |       E1, &F.X
> )       , E2
>        )
>
> Markus_Elfring@Sonne:…/Projekte/Coccinelle/Probe> /usr/bin/spatch example_by_Pierrick_Philippe-20260527.c suggestion6_for_Pierrick_Philippe-20260528.cocci
> …
> [no diff output]
>
>
> Why does the application of such an SmPL disjunction seem to prevent
> an expected difference display anyhow?

The disjunction does not mean what you think it means.  The C language
contains a comma expression, alloowing you to put two expressions together
with a comma in a place that one expression is expected.  That is how your
second semantic patch is being parsed.  Memcmp is considered to be a
two-argument expression where the first argument is a comma expression.
That will not match any real call to memcmp, which is a three argument
function.

To reiterate, for expressions, a dijunction takes only one expression at a
time.  You can't randomly put a disjunction around some fragment of an
argument list.

julia
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