From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Date: Mon, 05 Jul 2021 15:42:57 +0000 Subject: Re: [PATCH -tip v8 11/13] x86/unwind: Recover kretprobe trampoline entry Message-Id: <20210706004257.9e282b98f447251a380f658f@kernel.org> List-Id: References: <162399992186.506599.8457763707951687195.stgit@devnote2> <162400002631.506599.2413605639666466945.stgit@devnote2> 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 On Mon, 5 Jul 2021 13:36:14 +0200 Peter Zijlstra wrote: > On Fri, Jun 18, 2021 at 04:07:06PM +0900, Masami Hiramatsu wrote: > > @@ -549,7 +548,15 @@ bool unwind_next_frame(struct unwind_state *state) > > (void *)orig_ip); > > goto err; > > } > > - > > + /* > > + * There is a small chance to interrupt at the entry of > > + * kretprobe_trampoline where the ORC info doesn't exist. > > + * That point is right after the RET to kretprobe_trampoline > > + * which was modified return address. So the @addr_p must > > + * be right before the regs->sp. > > + */ > > + state->ip = unwind_recover_kretprobe(state, state->ip, > > + (unsigned long *)(state->sp - sizeof(long))); > > state->regs = (struct pt_regs *)sp; > > state->prev_regs = NULL; > > state->full_regs = true; > > @@ -562,6 +569,9 @@ bool unwind_next_frame(struct unwind_state *state) > > (void *)orig_ip); > > goto err; > > } > > + /* See UNWIND_HINT_TYPE_REGS case comment. */ > > + state->ip = unwind_recover_kretprobe(state, state->ip, > > + (unsigned long *)(state->sp - sizeof(long))); > > > > if (state->full_regs) > > state->prev_regs = state->regs; > > Why doesn't the ftrace case have this? That is, why aren't both return > trampolines having the same general shape? Ah, this strongly depends what the trampoline code does. For the kretprobe case, the PUSHQ at the entry of the kretprobe_trampoline() does not covered by UNWIND_HINT_FUNC. Thus it needs to find 'correct_ret_addr' by the frame pointer (which is next to the sp). "kretprobe_trampoline:\n" #ifdef CONFIG_X86_64 /* Push fake return address to tell the unwinder it's a kretprobe */ " pushq $kretprobe_trampoline\n" UNWIND_HINT_FUNC But I'm not so sure how ftrace treat it. It seems that the return_to_handler() doesn't care such case. (anyway, return_to_handler() does not return but jump to the original call-site, in that case, the information will be lost.) Thank you, -- Masami Hiramatsu