Re: [Cocci] Adding a line to a function after all variable declarations

[Fuad Tabba <tabba@google.com>]

On Thu, May 27, 2021 at 11:26 AM Julia Lawall <julia.lawall@inria.fr> wrote:
>
>
>
> On Thu, 27 May 2021, Julia Lawall wrote:
>
> >
> >
> > On Thu, 27 May 2021, Fuad Tabba wrote:
> >
> > > Hi,
> > >
> > > I'm trying to write a semantic patch that would add a new line to a
> > > function, but would like that line to come after all local variables
> > > (if any) have been declared. For example (distilled from what I am
> > > actually trying to accomplish):
> > >
> > > @@
> > > identifier f, s;
> > > @@
> > > f(..., struct mystruct *s, ...) {
> > > /* after any variable declarations*/
> > > + x = s->x;
> > >  ...
> > >  }
> > >
> > > I would like it to patch as follows:
> > >
> > > int function(struct mystruct *s) {
> > > + x = s->x;
> > > return 0;
> > > }
> > >
> > > as well as
> > >
> > > int function(struct mystruct *s)
> > > {
> > > int y;
> > > + x = s->x;
> > > return 0;
> > > }
> > >
> > > or
> > >
> > > int function(struct mystruct *s)
> > > {
> > > int y, z = 10;
> > > float f;
> > > + x = s->x;
> > > return 0;
> > > }
> > >
> > > Any suggestions on how I could do that?
> >
> > @@
> > @@
> >
> > f(...) {
> > ... when != S
> > + new_code
> > S
> > ... when any
> > }
>
> Sorry, that was not quite right.  The first S should be S1 and the second
> S should be S2, ie they should be different.  S1 and S2 should be
> statement metavariables and f should be an identifier metavariable.

Thanks Julia. That works for my distilled example, but teaches me a
lesson not to assume that the parts I've omitted aren't relevant. :)
Here's the actual semantic patch I'm trying to write, and I can't get
that quite to work:

@@
expression a, b;
identifier vcpu;
fresh identifier vcpu_ctxt = vcpu ## "_ctxt";
iterator name kvm_for_each_vcpu;
identifier fc;
@@
kvm_for_each_vcpu(a, vcpu, b)
 {
/* hop over any declarations */
+ vcpu_ctxt = &vcpu->arch.ctxt;
<+...
fc(..., vcpu, ...)
...+>
 }

So I'm trying to add the line "vcpu_ctxt = &vcpu->arch.ctxt" after any
declarations, only if there's a function in that block that's using
vcpu. This works, but the vcpu_ctxt assignment is of course always
added first, before any declarations.

Doing the following partially works, but it of course misses the case
where the function call with vcpu comes immediately after the
vcpu_ctxt assignment. Removing S2 altogether gives me a parse error.

@@
expression a, b;
identifier vcpu;
fresh identifier vcpu_ctxt = vcpu ## "_ctxt";
iterator name kvm_for_each_vcpu;
identifier fc;
statement S1, S2;
@@
kvm_for_each_vcpu(a, vcpu, b)
 {
 ... when != S1
+ vcpu_ctxt = &vcpu->arch.ctxt;
 S2;
<+...
fc(..., vcpu, ...)
...+>
 }

Thanks again,
/fuad

> julia
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