Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support to record and check the accessed args

Andrii Nakryiko
2024-03-31T02:34:46Z

On Sat, Mar 30, 2024 at 10:52 AM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Sat, Mar 30, 2024 at 08:27:55AM -0400, Steven Rostedt wrote:
> > On Fri, 29 Mar 2024 16:28:33 -0700
> > Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> >
> > > I thought I'll just ask instead of digging through code, sorry for
> > > being lazy :) Is there any way to pass pt_regs/ftrace_regs captured
> > > before function execution to a return probe (fexit/kretprobe)? I.e.,
> > > how hard is it to pass input function arguments to a kretprobe? That's
> > > the biggest advantage of fexit over kretprobe, and if we can make
> > > these original pt_regs/ftrace_regs available to kretprobe, then
> > > multi-kretprobe will effectively be this multi-fexit.
> >
> > This should be possible with the updates that Masami is doing with the
> > fgraph code.
>
> yes, I have bpf kprobe-multi link support for that [0] (it's on top of
> Masami's fprobe-over-fgraph changes) we discussed that in [1]

Sorry, I forgot the regs/args part, mostly remembering we discussed
session cookie ideas. Thanks for reminder!

>
> jirka
>
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/log/?h=bpf/session_data
> [1] https://lore.kernel.org/bpf/20240228090242.4040210-1-jolsa@kernel.org/