bpf: Use an UNUSED id for bpf_session_cookie without FPROBE

Commit Message

Sebastian Andrzej Siewior May 29, 2024, 12:44 p.m. UTC

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 <[e-mail]>
---
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Alexei Starovoitov May 29, 2024, 4:18 p.m. UTC | #1

On Wed, May 29, 2024 at 5:44 AM Sebastian Andrzej Siewior
<[e-mail]> 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 <[e-mail]>
> ---
>  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

Jiri Olsa May 29, 2024, 7:34 p.m. UTC | #2

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
> <[e-mail]> 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 <[e-mail]>
> > ---
> >  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

Sebastian Andrzej Siewior May 31, 2024, 7:15 a.m. UTC | #3

On 2024-05-29 21:34:25 [+0200], Jiri Olsa wrote:
> > > +#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?

Now that I look again, ifdef CONFIG_FPROBE isn't enough it requires
additionally CONFIG_UPROBE_EVENTS.
So the suggested snippet does not work if CONFIG_UPROBE_EVENTS is not
enabled.

> thanks,
> jirka

Sebastian

Patch

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
 
 static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
 {