Re: [PATCH bpf-next v8 04/11] bpf: support fsession for bpf_session_is_return

[Menglong Dong]

On Sat, Jan 10, 2026 at 11:38 AM Menglong Dong <menglong.dong@xxxxxxxxx> wrote:
>
> On 2026/1/10 10:40, Alexei Starovoitov wrote:
> > On Wed, Jan 7, 2026 at 6:25 PM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
> > >
> > > +       } else if (func_id == special_kfunc_list[KF_bpf_session_is_return]) {
> > > +               if (prog->expected_attach_type == BPF_TRACE_FSESSION)
> > > +                       addr = (unsigned long)bpf_fsession_is_return;
> >
> > ...
> >
> > > +bool bpf_fsession_is_return(void *ctx)
> > > +{
> > > +       /* This helper call is inlined by verifier. */
> > > +       return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN));
> > > +}
> > > +
> >
> > Why do this specialization and introduce a global function
> > that will never be called, since it will be inlined anyway?
>
> Ah, the specialization and the definition of the global function
> is not unnecessary. I thought that it's kinda fallback solution
      ^
typo: is not necessary

> that we define the function even if it is inlined by the verifier.
>
> >
> > Remove the first hunk and make the 2nd a comment instead of a real function?
>
> Agree. So it will be:
>
> +static bool bpf_fsession_is_return(void *ctx)
> +{
> +       /* This helper call is implemented and inlined by the verifier, and the logic is:
> +         *   return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN));
> +         */
> +        return false;
> +}
>
> >
> >
>
>
>
>