Re: [PATCHv3 bpf-next 2/5] libbpf: Add uprobe syscall feature detection

[Jiri Olsa]

On Wed, Feb 11, 2026 at 01:45:08PM -0800, Andrii Nakryiko wrote:
> On Wed, Feb 11, 2026 at 12:49 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding uprobe syscall feature detection that will be used
> > in following changes.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> >  tools/lib/bpf/features.c        | 24 ++++++++++++++++++++++++
> >  tools/lib/bpf/libbpf_internal.h |  2 ++
> >  2 files changed, 26 insertions(+)
> >
> > diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> > index b842b83e2480..04a225c7f2c0 100644
> > --- a/tools/lib/bpf/features.c
> > +++ b/tools/lib/bpf/features.c
> > @@ -506,6 +506,27 @@ static int probe_kern_arg_ctx_tag(int token_fd)
> >         return probe_fd(prog_fd);
> >  }
> >
> > +#ifdef __x86_64__
> > +
> > +#ifndef __NR_uprobe
> > +#define __NR_uprobe 336
> > +#endif
> > +
> > +static int probe_uprobe_syscall(int token_fd)
> > +{
> > +       /*
> > +        * If kernel supports uprobe() syscall, it will return -ENXIO when called
> > +        * from the outside of a kernel-generated uprobe trampoline.
> > +        */
> > +       return syscall(__NR_uprobe) < 0 && errno == ENXIO;
> > +}
> > +#else
> > +static int probe_uprobe_syscall(int token_fd)
> > +{
> > +       return 0;
> > +}
> > +#endif
> > +
> >  typedef int (*feature_probe_fn)(int /* token_fd */);
> >
> >  static struct kern_feature_cache feature_cache;
> > @@ -581,6 +602,9 @@ static struct kern_feature_desc {
> >         [FEAT_BTF_QMARK_DATASEC] = {
> >                 "BTF DATASEC names starting from '?'", probe_kern_btf_qmark_datasec,
> >         },
> > +       [FEAT_UPROBE_SYSCALL] = {
> > +               "Kernel supports uprobe syscall", probe_uprobe_syscall,
> 
> this will conflict with libbpf arena relocation fix landed into bpf,
> so let's wait until trees merge.
> 
> But also, this description is going into the middle of a sentence,
> start it with lower case

ok, will change

jirka