Messages in this thread |  | | From | Guo Ren <> | Date | Sat, 11 Jul 2020 09:32:01 +0800 | Subject | Re: [PATCH v2 6/6] riscv: Add KPROBES_ON_FTRACE supported |
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Thx Masami,
On Fri, Jul 10, 2020 at 9:50 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > Hi Guo, > > On Thu, 9 Jul 2020 02:19:14 +0000 > guoren@kernel.org wrote: > > > +/* Ftrace callback handler for kprobes -- called under preepmt disabed */ > > +void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > > + struct ftrace_ops *ops, struct pt_regs *regs) > > +{ > > + struct kprobe *p; > > + struct kprobe_ctlblk *kcb; > > + > > + p = get_kprobe((kprobe_opcode_t *)ip); > > + if (unlikely(!p) || kprobe_disabled(p)) > > + return; > > + > > + kcb = get_kprobe_ctlblk(); > > + if (kprobe_running()) { > > + kprobes_inc_nmissed_count(p); > > + } else { > > + /* > > + * The regs->epc hasn't been saved by SAVE_ALL in mcount-dyn.S > > + * So no need to resume it, just for kprobe handler. > > + */ > > + instruction_pointer_set(regs, ip); > > + __this_cpu_write(current_kprobe, p); > > + kcb->kprobe_status = KPROBE_HIT_ACTIVE; > > + if (!p->pre_handler || !p->pre_handler(p, regs)) { > > + /* > > + * Emulate singlestep (and also recover regs->pc) > > + * as if there is a nop > > + */ > > + instruction_pointer_set(regs, > > + (unsigned long)p->addr + MCOUNT_INSN_SIZE); > > + if (unlikely(p->post_handler)) { > > + kcb->kprobe_status = KPROBE_HIT_SSDONE; > > + p->post_handler(p, regs, 0); > > + } > > Hmm, don't you need restoring the previous instruction pointer here? look at riscv mcount-dyn.S SAVE_ALL function, sp frame lay out like this: ----------------------- | return address | ----------------------- | frame pointer | ----------------------- | pt_regs x1-x31| ----------------------- It's not a complete pt_regs for the handler, so modifing regs->ip is no use.
> If you don't support modifying the instruction pointer in the handler, We can modify ip like this if necessary: *(unsigned long *)((unsigned long)regs + sizeof(struct pt_regs) + 8) = xxx;
> it must not be compatible with kprobes. Why, can you show related codes? thank you very much.
> > Now BPF function override and function error injection depends on > this behevior, so could you consider to support it in the "ftrace" > implementation at first? (And if it is enabled, you can enable the > livepatch on RISCV too) Great message!
But can you show me codes that bpf and err-jnject using the behavior? Thx
I'll try to fix up it :)
-- Best Regards Guo Ren
ML: https://lore.kernel.org/linux-csky/
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