[PATCH 6/7] Resume the inferior with signal rather than stepping over

Yao Qi
2016-03-23T16:10:03Z

When GDBserver steps over a breakpoint using software single step, it
enqueues the signal, single step and deliver the signal in the next
resume if step over is not needed. In this way, the program won't
receive the signal if the conditional breakpoint is set a branch to
self instruction, because the step over is always needed.

This patch removes the restriction that don't deliver the signal to
the inferior if we are trying to reinsert a breakpoint for software
single step and change the decision on resume vs. step-over when the
LWP has pending signals to deliver.

gdb/gdbserver:

2016-03-23 Yao Qi <yao.qi@linaro.org>

* linux-low.c (LWP_SIGNAL_CAN_BE_DELIVERED): Adjust.
(need_step_over_p): Return zero if the LWP has pending signals
can be delivered on software single step target.
---
gdb/gdbserver/linux-low.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 7e55349..6b72c91 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -4118,7 +4118,6 @@ single_step (struct lwp_info* lwp)
}

/* The signal can be delivered to the inferior if we are not trying to
- reinsert a breakpoint for software single step and not trying to
finish a fast tracepoint collect. Since signal can be delivered in
the step-over, the program may go to signal handler and trap again
after return from the signal handler. We can live with the spurious
@@ -4127,8 +4126,7 @@ single_step (struct lwp_info* lwp)
static int
lwp_signal_can_be_delivered (struct lwp_info *lwp)
{
- return (!(lwp->bp_reinsert != 0 && can_software_single_step ())
- && !lwp->collecting_fast_tracepoint);
+ return !lwp->collecting_fast_tracepoint;
}

/* Resume execution of LWP. If STEP is nonzero, single-step it. If
@@ -4577,6 +4575,20 @@ need_step_over_p (struct inferior_list_entry *entry, void *dummy)
return 0;
}

+ /* On software single step target, resume the inferior with signal
+ rather than stepping over. */
+ if (can_software_single_step ()
+ && lwp->pending_signals != NULL
+ && lwp_signal_can_be_delivered (lwp))
+ {
+ if (debug_threads)
+ debug_printf ("Need step over [LWP %ld]? Ignoring, has pending"
+ " signals.\n",
+ lwpid_of (thread));
+
+ return 0;
+ }
+
saved_thread = current_thread;
current_thread = thread;

--
1.9.1