Re: [PATCH 08/13] bpf: Add kprobe link for attaching raw kprobes

Jiri Olsa
2022-01-06T08:41:55Z

On Wed, Jan 05, 2022 at 08:30:56PM -0800, Andrii Nakryiko wrote:
> On Tue, Jan 4, 2022 at 12:10 AM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > Adding new link type BPF_LINK_TYPE_KPROBE to attach kprobes
> > directly through register_kprobe/kretprobe API.
> >
> > Adding new attach type BPF_TRACE_RAW_KPROBE that enables
> > such link for kprobe program.
> >
> > The new link allows to create multiple kprobes link by using
> > new link_create interface:
> >
> > struct {
> > __aligned_u64 addrs;
> > __u32 cnt;
> > __u64 bpf_cookie;
>
> I'm afraid bpf_cookie has to be different for each addr, otherwise
> it's severely limiting. So it would be an array of cookies alongside
> an array of addresses

ok

>
> > } kprobe;
> >
> > Plus new flag BPF_F_KPROBE_RETURN for link_create.flags to
> > create return probe.
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > include/linux/bpf_types.h | 1 +
> > include/uapi/linux/bpf.h | 12 +++
> > kernel/bpf/syscall.c | 191 ++++++++++++++++++++++++++++++++-
> > tools/include/uapi/linux/bpf.h | 12 +++
> > 4 files changed, 211 insertions(+), 5 deletions(-)
> >
>
> [...]
>
> > @@ -1111,6 +1113,11 @@ enum bpf_link_type {
> > */
> > #define BPF_F_SLEEPABLE (1U << 4)
> >
> > +/* link_create flags used in LINK_CREATE command for BPF_TRACE_RAW_KPROBE
> > + * attach type.
> > + */
> > +#define BPF_F_KPROBE_RETURN (1U << 0)
> > +
>
> we have plenty of flexibility to have per-link type fields, so why not
> add `bool is_retprobe` next to addrs and cnt?

well I thought if I do that, people would suggest to use the empty
flags field instead ;-)

we can move it there as you suggest, but I wonder it's good idea to
use bool in uapi headers, because the bool size definition is vague

jirka

>
> > /* When BPF ldimm64's insn[0].src_reg != 0 then this can have
> > * the following extensions:
> > *
> > @@ -1465,6 +1472,11 @@ union bpf_attr {
> > */
> > __u64 bpf_cookie;
> > } perf_event;
> > + struct {
> > + __aligned_u64 addrs;
> > + __u32 cnt;
> > + __u64 bpf_cookie;
> > + } kprobe;
> > };
> > } link_create;
> >
>
> [...]
>