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Re: [PATCH] Don't set random_signal for single step breakpoint
- From: Pedro Alves <palves at redhat dot com>
- To: Yao Qi <qiyaoltc at gmail dot com>, gdb-patches at sourceware dot org
- Date: Mon, 26 Sep 2016 07:15:54 -0400
- Subject: Re: [PATCH] Don't set random_signal for single step breakpoint
- Authentication-results: sourceware.org; auth=none
- References: <1474866074-21720-1-git-send-email-yao.qi@linaro.org>
On 09/26/2016 01:01 AM, Yao Qi wrote:
> I happen to see the code, and find the comments are out of date,
> because single-step breakpoint is not transparent to the breakpoint
> module. If one thread hits another thread's single-step breakpoint,
> random_signal should be zero. IOW, if random_signal is one, the
> thread shouldn't hit any single-step breakpoints. This patch is to
> remove this piece of code.
Hmm, not sure. This hunk does predate the move to have single-step
breakpoints be regular breakpoints, but, OTOH, the single-step breakpoints
are deleted before the bpstat handling takes place:
/* Pull the single step breakpoints out of the target. */
if (ecs->event_thread->suspend.stop_signal == GDB_SIGNAL_TRAP)
{
...
/* However, before doing so, if this single-step breakpoint was
actually for another thread, set this thread up for moving
past it. */
if (!thread_has_single_step_breakpoint_here (ecs->event_thread,
aspace, pc))
{
if (single_step_breakpoint_inserted_here_p (aspace, pc))
{
ecs->hit_singlestep_breakpoint = 1;
...
delete_just_stopped_threads_single_step_breakpoints ();
bpstat_clear (&ecs->event_thread->control.stop_bpstat);
...
ecs->event_thread->control.stop_bpstat
= bpstat_stop_status (get_regcache_aspace (get_current_regcache ()),
stop_pc, ecs->ptid, &ecs->ws);
/* See if the breakpoints module can explain the signal. */
random_signal
= !bpstat_explains_signal (ecs->event_thread->control.stop_bpstat,
ecs->event_thread->suspend.stop_signal);
So I wonder whether this:
/* Maybe this was a trap for a software breakpoint that has since
been removed. */
if (random_signal && target_stopped_by_sw_breakpoint ())
{
is masking the need for the hunk you're proposing to remove.
What happens if you hack your target to no longer support
target_stopped_by_sw_breakpoint ?
The commit that added the code in question (2adfaa28b5,
eliminate thread-hop code) predates that (the whole
moribund breakpoints -> siginfo.si_code change).
Thanks,
Pedro Alves