On Sat, Jul 01, 2023 at 11:40:05AM +0800, Yafang Shao wrote:
> On Fri, Jun 30, 2023 at 4:34 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding support to specify cookies array for uprobe_multi link.
> >
> > The cookies array share indexes and length with other uprobe_multi
> > arrays (offsets/ref_ctr_offsets).
> >
> > The cookies[i] value defines cookie for i-the uprobe and will be
> > returned by bpf_get_attach_cookie helper when called from ebpf
> > program hooked to that specific uprobe.
> >
> > Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > include/uapi/linux/bpf.h | 1 +
> > kernel/bpf/syscall.c | 2 +-
> > kernel/trace/bpf_trace.c | 45 +++++++++++++++++++++++++++++++---
> > tools/include/uapi/linux/bpf.h | 1 +
> > 4 files changed, 44 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index a236139f08ce..4103f395593b 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -1592,6 +1592,7 @@ union bpf_attr {
> > __aligned_u64 path;
> > __aligned_u64 offsets;
> > __aligned_u64 ref_ctr_offsets;
> > + __aligned_u64 cookies;
>
> Could you pls. explain why the 'cookies' is defined as a pointer ? Are
> there real use cases to define different cookies for different probes
> in a single uprobe_multi ? Why can't we just use one cookie for all
> probes? Per my understanding, the cookie is used to identify the user
> or the application, rather than each probe.
>
> We also defined it the same way in kprobe_multi...
yes, each probed function (or symbol/offset for uprobe) can get
its own cookie and we use that to get probe-specific config in
generic bpf program with the bpf_get_attach_cookie helper
jirka
