Re: [PATCH] bpf: Use an UNUSED id for bpf_session_cookie without FPROBE

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, May 29, 2024 at 09:18:48AM -0700, Alexei Starovoitov wrote:
> On Wed, May 29, 2024 at 5:44 AM Sebastian Andrzej Siewior
> <bigeasy@linutronix.de> wrote:
> >
> > bpf_session_cookie() is only available with CONFIG_FPROBE=y leading to
> > an unresolved symbol otherwise.
> >
> > Use BTF_ID_UNUSED instead of bpf_session_cookie for CONFIG_FPROBE=n.
> >
> > Fixes: 5c919acef8514 ("bpf: Add support for kprobe session cookie")
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> >  kernel/bpf/verifier.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 77da1f438becc..436f72bfcb9b9 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -11124,7 +11124,11 @@ BTF_ID(func, bpf_iter_css_task_new)
> >  #else
> >  BTF_ID_UNUSED
> >  #endif
> > +#ifdef CONFIG_FPROBE
> >  BTF_ID(func, bpf_session_cookie)
> > +#else
> > +BTF_ID_UNUSED
> > +#endif
> 
> Instead of this fix..
> Jiri,
> maybe remove ifdef CONFIG_FPROBE hiding of this kfunc
> in kernel/tace/bpf_trace.c ?
> The less ifdef-s the better. imo

yes, that seems to work

Sebastian, do you want to send it as v2 or should I post it?

thanks,
jirka


---
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f5154c051d2c..cc90d56732eb 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3519,7 +3519,6 @@ static u64 bpf_uprobe_multi_entry_ip(struct bpf_run_ctx *ctx)
 }
 #endif /* CONFIG_UPROBES */
 
-#ifdef CONFIG_FPROBE
 __bpf_kfunc_start_defs();
 
 __bpf_kfunc bool bpf_session_is_return(void)
@@ -3568,4 +3567,3 @@ static int __init bpf_kprobe_multi_kfuncs_init(void)
 }
 
 late_initcall(bpf_kprobe_multi_kfuncs_init);
-#endif