On Monday 05 January 2015 12:10 AM, Oleg Nesterov wrote:
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?
Yes,yes, no need of 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?
Yes, I do see any value addition in saving xol_vaddr in ss_ctx->match_addr.
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().
Yes.
~Pratyush
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