Messages in this thread | | | Date | Sun, 4 Jan 2015 19:40:12 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC 8/8] ARM64: Add uprobe support |
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On 01/04, Pratyush Anand wrote: > > On Friday 02 January 2015 10:53 PM, Oleg Nesterov wrote: >> But the main question is: why do we need add/find_ss_context ?? Please >> explain. >> > > See arch/arm64/kernel/debug-monitors.c: call_step_hook > > Unlike breakpoint exception, there is no ESR info check for step > exception. So, it is the responsibility of step handler > (uprobe_single_step_handler) to make sure that exception was generated > for it.
Yes, yes, this is clear. My point was, we can (I think) rely on uprobe_post_sstep_notifier() which checks ->active_uprobe != NULL.
And I guess you understood what I meant, but since I wasn't clear let me repeat to ensure we really understand each other.
Can't
uprobe_single_step_handler(regs, esr) { if (user_mode(regs) && uprobe_post_sstep_notifier(regs)) return HANDLED; return ERROR; }
work without this step_ctx logic?
If everything is correct, the probed task can execute a single (xol) insn in user-mode before the trap. If ->active_uprobe is set we know that we expect the ss trap in user-mode, and nothing else except this xol insn can generate it?
Perhaps arm64 needs additional checks, I dunno... If you think that the ->active_uprobe check is not enough you can probably also verify that "utask->state = UTASK_SSTEP" and/or "regs->pc - 4 == utask->xol_vaddr", but so far it seems to me that these additional checks can only make sense under WARN_ON().
Oleg.
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