Re: [PATCH RFC bpf-next 0/4] bpf: Add support to attach return prog in kprobe multi

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Feb 15, 2024 at 11:27:22AM -0500, Steven Rostedt wrote:
> On Wed, 14 Feb 2024 21:55:03 +0100
> Jiri Olsa <olsajiri@gmail.com> wrote:
> 
> 
> > Masami,
> > we recently discussed the possibility to store data between entry/return probe,
> > IIUC your current patchset [0] allows that, but it seems to be shared across all
> > the tracers for the given function (__ftrace_return_to_handler).. is the plan to
> > make the shadow stack per tracer and function? /cc Steven
> 
> The shadow stack is per task, but it saves unique data per tracer per function.
> 
> It allows up to 16 different tracers attached to function graph tracing at
> a time, as there is a limited shadow stack size, which all the attached
> tracers use. Now you can create your own shadow stack per user (bpf
> program?) and have a single registered function graph user that will demux
> the data coming in and out of the function.

ok, I guess that's fgraph_reserve_data/fgraph_retrieve_data api

we'd like to share data between bpf programs executed from entry
and exit handlers, that should do it

thanks,
jirka