On Sat, Mar 30, 2024 at 10:52 AM Jiri Olsa [off-list ref] wrote:

On Sat, Mar 30, 2024 at 08:27:55AM -0400, Steven Rostedt wrote:

quoted

On Fri, 29 Mar 2024 16:28:33 -0700
Andrii Nakryiko [off-list ref] wrote:

quoted

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/ (local)