On 2021/7/7 PM9:29, Masami Hiramatsu wrote:
On Wed, 7 Jul 2021 19:45:30 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
On Wed, 7 Jul 2021 12:20:57 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
On Wed, Jul 07, 2021 at 07:15:10PM +0900, Masami Hiramatsu wrote:
I actually don't want to keep this feature because no one use it.
(only systemtap needs it?)
Yeah, you mentioned systemtap, but since that's out-of-tree I don't
care. Their problem.
Yeah, maybe it is not hard to update.
Anyway, if we keep the idea-level compatibility (not code level),
what we need is 'void *data' in the struct kretprobe_instance.
User who needs it can allocate their own instance data for their
kretprobes when initialising it and sets in their entry handler.
Then we can have a simple kretprobe_instance.
When would you do the alloc? When installing the retprobe, but that
might be inside the allocator, which means you can't call the allocator
etc.. :-)
Yes, so the user may need to allocate a pool right before register_kretprobe().
(whether per-kretprobe or per-task or global pool, that is user's choice.)
If we look at struct ftrace_ret_stack, it has a few fixed function
fields. The calltime one is all that is needed for the kretprobe
example code.
kretprobe consumes 3 fields, a pointer to 'struct kretprobe' (which
stores callee function address in 'kretprobe::kp.addr'), a return
address and a frame pointer (*).
> Oops, I forgot to add "void *data" for storing user data.
Should use "struct kretprobe_holder *rph", since "struct kretprobe" belongs
to 3rd-party module (which might be unloaded any time).
User's own pool might not work if the module can be unloaded. Better manage
the pool in kretprobe_holder, which needs no changes from user side.
