Re: [RFC PATCH v2 3/8] rethook: Add a generic return hook

[Masami Hiramatsu <mhiramat@kernel.org>]

On Fri, 14 Jan 2022 16:18:13 +0100
Jiri Olsa <jolsa@redhat.com> wrote:

> On Thu, Jan 13, 2022 at 10:15:32PM +0900, Masami Hiramatsu wrote:
> > On Thu, 13 Jan 2022 13:25:52 +0100
> > Jiri Olsa <jolsa@redhat.com> wrote:
> > 
> > > On Wed, Jan 12, 2022 at 11:03:22PM +0900, Masami Hiramatsu wrote:
> > > > Add a return hook framework which hooks the function
> > > > return. Most of the idea came from the kretprobe, but
> > > > this is independent from kretprobe.
> > > > Note that this is expected to be used with other
> > > > function entry hooking feature, like ftrace, fprobe,
> > > > adn kprobes. Eventually this will replace the
> > > > kretprobe (e.g. kprobe + rethook = kretprobe), but
> > > > at this moment, this is just a additional hook.
> > > 
> > > this looks similar to the code kretprobe is using now
> > 
> > Yes, I've mostly re-typed the code :)
> > 
> > > would it make sense to incrementaly change current code to provide
> > > this rethook interface? instead of big switch of current kretprobe
> > > to kprobe + new rethook interface in future?
> > 
> > Would you mean modifying the kretprobe instance code to provide
> > similar one, and rename it at some point?
> > My original idea is to keep the current kretprobe code and build
> > up the similar one, and switch to it at some point. Actually,
> > I don't want to change the current kretprobe interface itself,
> > but the backend will be changed. For example, current kretprobe
> > has below interface.
> > 
> > struct kretprobe {
> >         struct kprobe kp;
> >         kretprobe_handler_t handler;
> >         kretprobe_handler_t entry_handler;
> >         int maxactive;
> >         int nmissed;
> >         size_t data_size;
> >         struct freelist_head freelist;
> >         struct kretprobe_holder *rph;
> > };
> > 
> > My idea is switching it to below.
> > 
> > struct kretprobe {
> >         struct kprobe kp;
> >         kretprobe_handler_t handler;
> >         kretprobe_handler_t entry_handler;
> >         int maxactive;
> >         int nmissed;
> >         size_t data_size;
> >         struct rethook *rethook;
> > };
> 
> looks good, will this be a lot of changes?

Yes and no, we can easily replace the kretprobe generic trampoline
callback (since it almost same, and have same feature), but it also
needs to update per-arch kretprobe trampoline to rethook trampoline.

> could you include it in the patchset?

Let me try, but since it involves many archs (which support kretprobes)
it may take a time to be merged.

Thank you,

> 
> thanks,
> jirka
> 
> > 
> > Of course 'kretprobe_instance' may need to be changed...
> > 
> > struct kretprobe_instance {
> > 	struct rethook_node;
> > 	char data[];
> > };
> > 
> > But even though, since there is 'get_kretprobe(ri)' wrapper, user
> > will be able to access the 'struct kretprobe' from kretprobe_instance
> > transparently.
> > 
> > Thank you,
> > 
> > 
> > -- 
> > Masami Hiramatsu <mhiramat@kernel.org>
> > 
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>