Re: [PATCH 11/12] Use reinsert_breakpoint for vCont;s

Yao Qi
2016-06-14T13:14:58Z

Pedro Alves <palves@redhat.com> writes:

>> @@ -4293,7 +4313,7 @@ linux_resume_one_lwp_throw (struct lwp_info *lwp,
>>
>> step = maybe_hw_step (thread);
>> }
>> - else
>> + else if (lwp->resume != NULL && lwp->resume->kind != resume_step)
>> {
>> /* If the thread isn't doing step-over, there shouldn't be any
>> reinsert breakpoints. */
>
> Consider (non-stop RSP):
>
> -> vCont;s:1
> <- OK
> -> vCont;s:2
> <- OK
>
> The handling of the second vCont sets thread 1's lwp->resume to NULL.

If so, the assert won't be called for thread 1.

> The lwp->resume pointer is only meaningful within linux_resume
> and its callees. (But this function is called in other contexts.)
>

When I wrote the patch, it took me a while to think about this condition
check. I wanted to remove this condition and assert, but finally
decided to leave it there, as it is not harmful. If lwp->resume is only
meaningful within linux_resume and its callees, how about remove the
condition check and assert here?

>> @@ -5009,12 +5033,52 @@ linux_resume (struct thread_resume *resume_info, size_t n)
>> debug_printf ("Resuming, no pending status or step over needed\n");
>> }
>>
>> + /* Before we resume the threads, if resume_step is requested by GDB,
>> + stop all threads and install reinsert breakpoints. */
>
> Looking again, I think the rationale for stopping threads should
> be mentioned here, as it's not obvious.
>

How about this,

/* Before we resume the threads, if resume_step is requested by GDB,
we need to access the inferior memory to install reinsert
breakpoints, so stop all threads. */

>> @@ -5110,7 +5174,8 @@ proceed_one_lwp (struct inferior_list_entry *entry, void *except)
>> if (debug_threads)
>> debug_printf (" stepping LWP %ld, client wants it stepping\n",
>> lwpid_of (thread));
>> - step = 1;
>> +
>> + step = maybe_hw_step (thread);
>> }
>> else if (lwp->bp_reinsert != 0)
>> {
>> @@ -5176,6 +5241,30 @@ proceed_all_lwps (void)
>> if (debug_threads)
>> debug_printf ("Proceeding, no step-over needed\n");
>>
>> + /* Re-install the reinsert breakpoints on software single step target
>> + if the client wants it step. */
>> + if (can_software_single_step ())
>
> Not immediately obvious to why is this necessary. Where were they
> removed in the first place? I'm it must be necessary, but maybe
> extending the comment helps.

How about this

/* On software single step target, we removed reinsert breakpoints
after we get any events from the inferior. If the client wants
thread step, re-install these reinsert breakpoints. */

--
Yao (齐尧)