On Tue, Jul 06, 2021 at 12:42:57AM +0900, Masami Hiramatsu wrote: > On Mon, 5 Jul 2021 13:36:14 +0200 > Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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.) I find it bothersome (OCD, sorry :-) that both return trampolines behave differently. Doubly so because I know people (Steve in particular) have been talking about unifying them. Steve, can you clarify the ftrace side here? Afaict return_to_handler() is similarly affected.
