[PATCH 7/8] Use reinsert_breakpoint for vCont;s

Yao Qi
2016-05-20T15:13:08Z

This patch is to teach GDBserver using software single step to handle
vCont;s. Simply speaking, if the thread's resume request is resume_step,
install reinsert breakpoint at the next pcs when GDBserver is about to
resume threads. These reinsert breakpoints of a thread are removed,
when GDBserver gets an event from that thread. Note that GDBserver may
or may not report this event back to GDB.

gdb/gdbserver:

2016-05-20 Yao Qi <yao.qi@linaro.org>

* linux-low.c (resume_stopped_resumed_lwps): If resume request
is resume_step, either set step to 1 or assert that reinsert
breakpoints are installed.
(linux_wait_1): Stop all threads, remove reinsert breakpoints,
and unstop them.
(linux_resume_one_thread): If resume request is resume_step,
either set step to 1 or assert that reinsert breakpoints are
installed.
(linux_resume): Install reinsert breakpoints if the thread is
requested to resume_step.
(proceed_one_lwp): If resume request is resume_step,
either set step to 1 or assert that reinsert breakpoints are
installed.
(proceed_all_lwps): Install reinsert breakpoints if the thread is
requested to resume_step.
---
gdb/gdbserver/linux-low.c | 125 ++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 121 insertions(+), 4 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index d5f7097..22cf51a 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -2526,7 +2526,18 @@ resume_stopped_resumed_lwps (struct inferior_list_entry *entry)
&& !lp->status_pending_p
&& thread->last_status.kind == TARGET_WAITKIND_IGNORE)
{
- int step = thread->last_resume_kind == resume_step;
+ int step = 0;
+
+ if (thread->last_resume_kind == resume_step)
+ {
+ if (can_hardware_single_step ())
+ step = 1;
+ else
+ {
+ /* GDBserver must insert reinsert breakpoint for vCont;s. */
+ gdb_assert (has_reinsert_breakpoints (thread));
+ }
+ }

if (debug_threads)
debug_printf ("RSRL: resuming stopped-resumed LWP %s at %s: step=%d\n",
@@ -3477,6 +3488,18 @@ linux_wait_1 (ptid_t ptid,
return ignore_event (ourstatus);
}

+ /* Remove reinsert breakpoints for resume_step. */
+ if (can_software_single_step ()
+ && current_thread->last_resume_kind == resume_step
+ && has_reinsert_breakpoints (current_thread))
+ {
+ stop_all_lwps (1, event_child);
+
+ delete_reinsert_breakpoints (current_ptid);
+
+ unstop_all_lwps (1, event_child);
+ }
+
/* Note that all addresses are always "out of the step range" when
there's no range to begin with. */
in_step_range = lwp_in_step_range (event_child);
@@ -4796,7 +4819,6 @@ linux_resume_one_thread (struct inferior_list_entry *entry, void *arg)
{
struct thread_info *thread = (struct thread_info *) entry;
struct lwp_info *lwp = get_thread_lwp (thread);
- int step;
int leave_all_stopped = * (int *) arg;
int leave_pending;

@@ -4865,10 +4887,22 @@ linux_resume_one_thread (struct inferior_list_entry *entry, void *arg)

if (!leave_pending)
{
+ int step = 0;
+
if (debug_threads)
debug_printf ("resuming LWP %ld\n", lwpid_of (thread));

- step = (lwp->resume->kind == resume_step);
+ if (lwp->resume->kind == resume_step)
+ {
+ if (can_hardware_single_step ())
+ step = 1;
+ else
+ {
+ /* GDBserver must insert reinsert breakpoint for vCont;s. */
+ gdb_assert (has_reinsert_breakpoints (thread));
+ }
+ }
+
linux_resume_one_lwp (lwp, step, lwp->resume->sig, NULL);
}
else
@@ -4909,6 +4943,7 @@ linux_resume (struct thread_resume *resume_info, size_t n)
struct thread_info *need_step_over = NULL;
int any_pending;
int leave_all_stopped;
+ int resume_step_is_handled = 0;

if (debug_threads)
{
@@ -4952,12 +4987,57 @@ 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. */
+ if (!leave_all_stopped && can_software_single_step ())
+ {
+ struct inferior_list_entry *inf, *tmp;
+
+ if (debug_threads)
+ debug_printf ("Handle resume_step.\n");
+
+ ALL_INFERIORS (&all_threads, inf, tmp)
+ {
+ struct thread_info *thread = (struct thread_info *) inf;
+ struct lwp_info *lwp = get_thread_lwp (thread);
+
+ if (lwp->resume != NULL && lwp->resume->kind == resume_step)
+ {
+ struct thread_info *saved_thread;
+
+ if (!resume_step_is_handled)
+ {
+ stop_all_lwps (0, NULL);
+
+ if (debug_threads)
+ debug_printf ("Done stopping all threads.\n");
+
+ resume_step_is_handled = 1;
+ }
+
+ saved_thread = current_thread;
+ current_thread = thread;
+ install_software_single_step_breakpoints (lwp);
+ current_thread = saved_thread;
+
+ if (debug_threads)
+ debug_printf ("Insert breakpoint for resume_step LWP %ld\n",
+ lwpid_of (thread));
+ }
+ }
+
+ if (debug_threads)
+ debug_printf ("Handle resume_step. Done\n");
+ }
+
/* Even if we're leaving threads stopped, queue all signals we'd
otherwise deliver. */
find_inferior (&all_threads, linux_resume_one_thread, &leave_all_stopped);

if (need_step_over)
start_step_over (get_thread_lwp (need_step_over));
+ else if (resume_step_is_handled)
+ unstop_all_lwps (0, NULL);

if (debug_threads)
{
@@ -5054,7 +5134,14 @@ 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;
+
+ if (can_hardware_single_step ())
+ step = 1;
+ else
+ {
+ /* GDBserver must insert reinsert breakpoint for vCont;s. */
+ gdb_assert (has_reinsert_breakpoints (thread));
+ }
}
else if (lwp->bp_reinsert != 0)
{
@@ -5124,6 +5211,36 @@ 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 ())
+ {
+ struct inferior_list_entry *inf, *tmp;
+
+ ALL_INFERIORS (&all_threads, inf, tmp)
+ {
+ struct thread_info *thread = (struct thread_info *) inf;
+
+ if (thread->last_resume_kind == resume_step)
+ {
+ struct lwp_info *lwp = get_thread_lwp (thread);
+ struct thread_info *saved_thread;
+
+ saved_thread = current_thread;
+ current_thread = thread;
+
+ if (!has_reinsert_breakpoints (thread))
+ install_software_single_step_breakpoints (lwp);
+
+ current_thread = saved_thread;
+
+ if (debug_threads)
+ debug_printf ("Insert breakpoint for resume_step LWP %ld\n",
+ lwpid_of (thread));
+ }
+ }
+ }
+
find_inferior (&all_threads, proceed_one_lwp, NULL);
}

--
1.9.1