From: Pedro Alves <palves@redhat.com>
To: Yao Qi <qiyaoltc@gmail.com>
Cc: gdb-patches@sourceware.org
Subject: Re: [PATCH 3/7] Force to insert software single step breakpoint
Date: Tue, 19 Apr 2016 15:17:00 -0000 [thread overview]
Message-ID: <57164BE8.90202@redhat.com> (raw)
In-Reply-To: <8660vdk5sk.fsf@gmail.com>
On 04/19/2016 03:54 PM, Yao Qi wrote:
> Pedro Alves <palves@redhat.com> writes:
>
>> Another scenario occurred to me:
>>
>> - Thread A is software single-stepping.
>> - Thread B hits single-step breakpoint of thread A.
>> - We pause all threads and set thread B stepping past the
>> single-step breakpoint of thread A.
>>
>> But if the single-step breakpoint is for another thread, then
>> we won't actually manage to have thread B step past it, resulting
>> in spurious re-hits and no-guaranteed forward progress. See
>> e.g., non-stop-fair-events.exp:
>>
>> # On software single-step targets that don't support displaced
>> # stepping, threads keep hitting each others' single-step
>> # breakpoints, and then GDB needs to pause all threads to step
>> # past those. The end result is that progress in the main
>> # thread will be slower and it may take a bit longer for the
>> # signal to be queued; bump the timeout.
>>
>> Sounds like we may need to look at the single-step breakpoint's thread
>> id, and only insert it if it is for the thread that is going to be
>> doing the step-over? We may need to record that in step_over_info and
>> pass more info to stepping_past_instruction_at.
>
> I think this is about any thread specific breakpoint, instead of
> only single-step breakpoint (single-step breakpoint is thread specific
> too). If we are doing step-over for thread A, do we need to insert any
> breakpoints specific to other threads? (my answer is No).
Right, we don't need to insert them, because other threads
will remain stopped while thread A is doing the step-over.
However, given that gdb does not remove/re-insert all breakpoints on
internal stops nowadays, removing thread-specific breakpoints of others
threads will be less efficient than leaving them be, I think. I mean,
you'll get more z0/Z0 traffic than if you leave them inserted.
Thanks,
Pedro Alves
next prev parent reply other threads:[~2016-04-19 15:17 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-23 16:10 [PATCH 0/7 V2] Step over instruction branches to itself Yao Qi
2016-03-23 16:10 ` [PATCH 6/7] Resume the inferior with signal rather than stepping over Yao Qi
2016-04-11 15:29 ` Pedro Alves
2016-03-23 16:10 ` [PATCH 4/7] Insert breakpoint even when the raw breakpoint is found Yao Qi
2016-04-11 14:41 ` Pedro Alves
2016-04-12 9:04 ` Yao Qi
2016-04-12 9:41 ` Pedro Alves
2016-04-25 8:45 ` Yao Qi
2016-03-23 16:10 ` [PATCH 2/7] Deliver signal in hardware single step Yao Qi
2016-04-11 14:10 ` Pedro Alves
2016-04-22 10:54 ` Yao Qi
2016-03-23 16:10 ` [PATCH 1/7] New test case gdb.trace/signal.exp Yao Qi
2016-04-08 16:52 ` Pedro Alves
2016-04-11 8:41 ` Yao Qi
2016-04-11 14:04 ` Pedro Alves
2016-04-22 10:53 ` Yao Qi
2016-04-26 12:57 ` Pedro Alves
2016-04-11 14:08 ` Pedro Alves
2016-03-23 16:10 ` [PATCH 5/7] [GDBserver] Don't error in reinsert_raw_breakpoint if bp->inserted Yao Qi
2016-04-11 14:54 ` Pedro Alves
2016-03-23 16:10 ` [PATCH 3/7] Force to insert software single step breakpoint Yao Qi
2016-04-11 14:31 ` Pedro Alves
2016-04-13 16:21 ` Yao Qi
2016-04-19 14:54 ` Yao Qi
2016-04-19 15:17 ` Pedro Alves [this message]
2016-04-20 7:50 ` Yao Qi
2016-04-22 16:36 ` Pedro Alves
2016-04-25 8:40 ` Yao Qi
2016-03-23 16:26 ` [PATCH 7/7] New test case gdb.base/branch-to-self.exp Yao Qi
2016-04-11 15:34 ` Pedro Alves
2016-04-25 8:58 ` Yao Qi
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