From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Date: Wed, 07 Jul 2021 10:45:30 +0000 Subject: Re: [PATCH -tip v8 11/13] x86/unwind: Recover kretprobe trampoline entry Message-Id: <20210707194530.766a9c8364f3b2d7714ca590@kernel.org> List-Id: References: <162399992186.506599.8457763707951687195.stgit@devnote2> <162400002631.506599.2413605639666466945.stgit@devnote2> <20210706004257.9e282b98f447251a380f658f@kernel.org> <20210706111136.7c5e9843@oasis.local.home> <20210707191510.cb48ca4a20f0502ce6c46508@kernel.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Zijlstra Cc: Steven Rostedt , Josh Poimboeuf , Ingo Molnar , X86 ML , Daniel Xu , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kuba@kernel.org, mingo@redhat.com, ast@kernel.org, Thomas Gleixner , Borislav Petkov , kernel-team@fb.com, yhs@fb.com, linux-ia64@vger.kernel.org, Abhishek Sagar , Andrii Nakryiko , wuqiang.matt@bytedance.com On Wed, 7 Jul 2021 12:20:57 +0200 Peter Zijlstra 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. > > > 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 (*). * note that this frame pointer might be used for fixing up the stack trace, but the fixup method depends on the architecture. Thank you, -- Masami Hiramatsu