Re: [cocci] Returning statically allocated nested structs

[Peter Senna Tschudin <peter.senna@gmail.com>]

Thanks Julia,

Your question about nesting inspired me to a simpler solution:

@rule1@
identifier i, s;
position p;
@@
struct i s;
...
return@p s;

@script:python@
p << rule1.p;
s << rule1.s;
@@
cocci.print_main(s, p)

Do I need to worry about calling cocci.print_secs() after the print_main()?

On Thu, Mar 28, 2024 at 11:10 AM Julia Lawall <julia.lawall@inria.fr> wrote:
>
>
>
> On Thu, 28 Mar 2024, Peter Senna Tschudin wrote:
>
> > Hi Julia,
> >
> > Thanks for the reply!
> >
> > On Thu, Mar 28, 2024 at 10:08 AM Julia Lawall <julia.lawall@inria.fr> wrote:
> > >
> > >
> > >
> > > On Thu, 28 Mar 2024, Peter Senna Tschudin wrote:
> > >
> > > > Dear list,
> > > >
> > > > I am trying to come up with a semantic patch to detect uses of nested
> > > > structs, more specifically:
> > > >  - the nested struct is statically allocated
> > > >  - the statically allocated nested struct is returned by a function.
> > > >
> > > > Here is an example:
> > > >
> > > > struct inner {
> > > >
> > > >     /* some inner struct stuff*/
> > > >
> > > > } inner;
> > > >
> > > > struct outer  {
> > > >
> > > >     /* some outer struct stuff*/
> > > >
> > > >     struct inner i; // The kind of nesting I care about
> > > >     struct inner is[SOME_MAGIC_NUMBER]; // The kind of nesting I care about too
> > > >
> > > >     struct inner *ip; // Nah, this is boring. I don't care about boring
> > > > } outer;
> > > >
> > > > void sillyfu() {
> > Argh, that was a typo!
> >
> > struct outer sillyfu() {
> > > >     struct outer ou = { }; // initialization does not matter.
> > > >     struct outer *oup = NULL; // Nah, this is boring. I don't care about boring
> > > >
> > > >     /* some serious silly stuff */
> > > >
> > > >     return ou;
> > >
> > > Not sure to understand.  The return type of the function is void.  Was
> > > that a typo?
> > >
> > > Returning a structure in general seems like something to be concerned
> > > about.  Does it matter that another structure is nested inside?
> >
> > I am not sure if it matters, but it may. The compiler seems to be the
> > arbiter who decides what happens when returning a local struct. It may
> > work, it may not. One theory for not working is variable scope.
> > Returning a local struct may not work due to the local nature of the
> > struct. In this case the compiler would free the memory used by the
> > struct when the function returns, causing undefined behavior. In this
> > scenario the nested struct simply adds another layer of the same
> > problem.
> >
> > Another theory says that the compiler may decide based on the struct
> > size. The compiler may tolerate returning certain struct sizes, but
> > not others.
>
> The following is not tested, but seems like it should be sufficient.
>
> @r@
> identifier i, j, k;
> @@
>
> struct i { ...
>   struct j k;
>   ...
> };
>
> @@
> identifier r.i;
> identifier f,x;
> @@
>
> f(...) {
>   struct i x = ...;
>   ...
> * return x;
> }
>
> julia



-- 
                         Peter