Re: [PATCH 2/2] Enable range stepping for ARM on GDBServer

Yao Qi
2016-09-01T16:44:38Z

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[sigh, I am testing my arm range stepping patches today...]

On Thu, Sep 1, 2016 at 4:59 PM, Pedro Alves <palves@redhat.com> wrote:
>>>
>>>> I'm sorry I can't be more helpful at the moment but I wanted to post
>>>> this issue before I have to leave for a while.
>>>
>>> Understood. Does enabling range stepping unblock something else?
>>
>> It would unblock ARM tracepoints, as per Yao's requirements...
>
> Tracepoints make gdbserver single-step and then not report the event
> to gdb, so I do see the parallel with range-stepping. Throwing
> while-stepping into the equation would make it even more clear.
>

Range-stepping makes gdbserver single-step and then not report the event
to gdb if thread pc is within the range. It is similar to tracepoint, but much
simpler.

Both range-stepping and tracepoing needs to remove reinsert_breakpoint
when gdbserver gets an event but doesn't report it back to gdb. However,
gdbserver doesn't do so now. That is the reason I believe we need to
support range-stepping first, and I am working on this (but interrupted by
7.12 release). The draft patch attached removes reinsert_breakpoint when
gdbserver gets an event but not to report it back to gdb.

Beside "removing reinsert_breakpoint on gdbserver internal event", we'd
better to think that "each backend unwinders don't have to worry about
unavailable data". I posted a draft here
https://sourceware.org/ml/gdb-patches/2016-05/msg00060.html, I need
some review comments. Pedro,
can you take a look? This is not a hard requirement for ARM tracepoint
support.

--
Yao (齐尧)

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diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 45061ac..2f30bc1 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -3662,17 +3662,31 @@ linux_wait_1 (ptid_t ptid,
(*the_low_target.set_pc) (regcache, event_child->stop_pc);
}

- /* We may have finished stepping over a breakpoint. If so,
- we've stopped and suspended all LWPs momentarily except the
- stepping one. This is where we resume them all again. We're
- going to keep waiting, so use proceed, which handles stepping
- over the next breakpoint. */
- if (debug_threads)
- debug_printf ("proceeding all threads.\n");
-
if (step_over_finished)
- unsuspend_all_lwps (event_child);
+ {
+ /* If we have finished stepping over a breakpoint, we've
+ stopped and suspended all LWPs momentarily except the
+ stepping one. This is where we resume them all again.
+ We're going to keep waiting, so use proceed, which
+ handles stepping over the next breakpoint. */
+ unsuspend_all_lwps (event_child);
+ }
+ else
+ {
+ /* Remove the singlestep breakpoints if any. Note that
+ there isn't singlestep breakpoint if we finished stepping
+ over. */
+ if (can_software_single_step ()
+ && has_reinsert_breakpoints (current_thread))
+ {
+ stop_all_lwps (0, event_child);
+ delete_reinsert_breakpoints (current_thread);
+ unstop_all_lwps (0, event_child);
+ }
+ }

+ if (debug_threads)
+ debug_printf ("proceeding all threads.\n");
proceed_all_lwps ();
return ignore_event (ourstatus);
}