On Thu, Jul 06, 2023 at 03:29:08PM -0700, Andrii Nakryiko wrote:
> On Fri, Jun 30, 2023 at 1:34 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding support for bpf_get_func_ip helper being called from
> > ebpf program attached by uprobe_multi link.
> >
> > It returns the ip of the uprobe.
> >
> > Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > kernel/trace/bpf_trace.c | 33 ++++++++++++++++++++++++++++++---
> > 1 file changed, 30 insertions(+), 3 deletions(-)
> >
>
> A slight aside related to bpf_get_func_ip() support in
> uprobe/uretprobe. We just had a conversation with Alastair and Jordan
> (cc'ed) about bpftrace and using bpf_get_func_ip() there with
> uretprobes, and it seems like it doesn't work.
>
> Is that intentional or we just missed that bpf_get_func_ip() doesn't
> work with uprobes/uretprobes? Do you think it would be hard to add
> support for them for bpf_get_func_ip()? It's a very useful helper,
> would be nice to have it working in all cases where it has meaningful
> behavior (and I think it does for uprobe and uretprobe).
I'm not sure we discussed at the time we added this helper,
but I see same problem as we had with kprobes where we need
to know if the probe is on the start of the symbol
we use KPROBE_FLAG_ON_FUNC_ENTRY flag for that in kprobe's
get_func_ip helper version:
BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
{
struct kprobe *kp = kprobe_running();
if (!kp || !(kp->flags & KPROBE_FLAG_ON_FUNC_ENTRY))
return 0;
return get_entry_ip((uintptr_t)kp->addr);
}
I don't think we can have same flag for uprobe, we don't have
the binary symbol data as we have for kernel
I guess the app needs to store regs->ip and match it against symbol
addresses in user space
jirka
>
> Thanks!
>
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 4ef51fd0497f..f5a41c1604b8 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -88,6 +88,7 @@ static u64 bpf_kprobe_multi_cookie(struct bpf_run_ctx *ctx);
> > static u64 bpf_kprobe_multi_entry_ip(struct bpf_run_ctx *ctx);
> >
>
> [...]
