[PATCH 1/8] Switch to current thread before finish_step_over

[Yao Qi <qiyaoltc@gmail.com>]

This patch adds some sanity check that reinsert breakpoints must be
there when doing step-over on software single step target.  The check
triggers an assert when running forking-threads-plus-breakpoint.exp
on arm-linux target,

 gdb/gdbserver/linux-low.c:4714: A problem internal to GDBserver has been detected.^M
 int finish_step_over(lwp_info*): Assertion `has_reinsert_breakpoints ()' failed.

the error happens when GDBserver has already resumed a thread of
process A for step-over (and wait for it hitting reinsert breakpoint),
but receives detach request for process B from GDB, which is shown in
the backtrace below,

 (gdb) bt
 #2  0x000228aa in finish_step_over (lwp=0x12bbd98) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:4703
 #3  0x00025a50 in finish_step_over (lwp=0x12bbd98) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:4749
 #4  complete_ongoing_step_over () at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:4760
 #5  linux_detach (pid=25228) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/linux-low.c:1503
 #6  0x00012bae in process_serial_event () at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/server.c:3974
 #7  handle_serial_event (err=<optimized out>, client_data=<optimized out>) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/server.c:4347
 #8  0x00016d68 in handle_file_event (event_file_desc=<optimized out>) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/event-loop.c:429
 #9  0x000173ea in process_event () at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/event-loop.c:184
 #10 start_event_loop () at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/event-loop.c:547
 #11 0x0000aa2c in captured_main (argv=<optimized out>, argc=<optimized out>) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/server.c:3719
 #12 main (argc=<optimized out>, argv=<optimized out>) at /home/yao/SourceCode/gnu/gdb/git/gdb/gdbserver/server.c:3804

the sanity check tries to find the reinsert breakpoint from process B,
but nothing is found.  It is wrong, we need to search in process A,
since we started step-over of a thread of process A.

 (gdb) p lwp->thread->entry.id
 $3 = {pid = 25120, lwp = 25131, tid = 0}
 (gdb) p current_thread->entry.id
 $4 = {pid = 25228, lwp = 25228, tid = 0}

This patch switched current_thread to the step we are doing step-over
in complete_ongoing_step_over.

gdb/gdbserver:

2016-05-19  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (linux_resume_one_lwp_throw): Call
	has_reinsert_breakpoints.
	(finish_step_over): Likewise.
	(proceed_one_lwp): Likewise.
	* mem-break.c (has_reinsert_breakpoints): New function.
	* mem-break.h (has_reinsert_breakpoints): Declare.
---
 gdb/gdbserver/linux-low.c | 30 +++++++++++++++++++++++++-----
 gdb/gdbserver/mem-break.c | 22 ++++++++++++++++++++++
 gdb/gdbserver/mem-break.h |  4 ++++
 3 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 81134b0..8e8f710 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -4218,6 +4218,11 @@ linux_resume_one_lwp_throw (struct lwp_info *lwp,
 
 	  step = 1;
 	}
+      else
+	{
+	  gdb_assert (step == 0);
+	  gdb_assert (has_reinsert_breakpoints (proc));
+	}
     }
 
   if (fast_tp_collecting == 1)
@@ -4705,7 +4710,10 @@ finish_step_over (struct lwp_info *lwp)
 	 because we were stepping over a breakpoint, and we hold all
 	 threads but LWP stopped while doing that.  */
       if (!can_hardware_single_step ())
-	delete_reinsert_breakpoints ();
+	{
+	  gdb_assert (has_reinsert_breakpoints (current_process ()));
+	  delete_reinsert_breakpoints ();
+	}
 
       step_over_bkpt = null_ptid;
       return 1;
@@ -4741,7 +4749,13 @@ complete_ongoing_step_over (void)
 
       lwp = find_lwp_pid (step_over_bkpt);
       if (lwp != NULL)
-	finish_step_over (lwp);
+	{
+	  struct thread_info *saved_thread = current_thread;
+
+	  current_thread = get_lwp_thread (lwp);
+	  finish_step_over (lwp);
+	  current_thread = saved_thread;
+	}
       step_over_bkpt = null_ptid;
       unsuspend_all_lwps (lwp);
     }
@@ -5017,6 +5031,7 @@ proceed_one_lwp (struct inferior_list_entry *entry, void *except)
       send_sigstop (lwp);
     }
 
+  step = 0;
   if (thread->last_resume_kind == resume_step)
     {
       if (debug_threads)
@@ -5029,10 +5044,15 @@ proceed_one_lwp (struct inferior_list_entry *entry, void *except)
       if (debug_threads)
 	debug_printf ("   stepping LWP %ld, reinsert set\n",
 		      lwpid_of (thread));
-      step = 1;
+
+      if (can_hardware_single_step ())
+	step = 1;
+      else
+	{
+	  /* GDBserver must insert reinsert breakpoint for step-over.  */
+	  gdb_assert (has_reinsert_breakpoints (get_thread_process (thread)));
+	}
     }
-  else
-    step = 0;
 
   linux_resume_one_lwp (lwp, step, 0, NULL);
   return 0;
diff --git a/gdb/gdbserver/mem-break.c b/gdb/gdbserver/mem-break.c
index 363d7ca..3313459 100644
--- a/gdb/gdbserver/mem-break.c
+++ b/gdb/gdbserver/mem-break.c
@@ -1553,6 +1553,28 @@ reinsert_breakpoints_at (CORE_ADDR pc)
     }
 }
 
+int
+has_reinsert_breakpoints (struct process_info *proc)
+{
+  struct breakpoint *bp, **bp_link;
+
+  bp = proc->breakpoints;
+  bp_link = &proc->breakpoints;
+
+  while (bp)
+    {
+      if (bp->type == reinsert_breakpoint)
+	return 1;
+      else
+	{
+	  bp_link = &bp->next;
+	  bp = *bp_link;
+	}
+    }
+
+  return 0;
+}
+
 void
 reinsert_all_breakpoints (void)
 {
diff --git a/gdb/gdbserver/mem-break.h b/gdb/gdbserver/mem-break.h
index 4d9a76c..b84dc1e 100644
--- a/gdb/gdbserver/mem-break.h
+++ b/gdb/gdbserver/mem-break.h
@@ -163,6 +163,10 @@ void delete_reinsert_breakpoints (void);
 
 void reinsert_breakpoints_at (CORE_ADDR where);
 
+/* Process PROC has reinsert breakpoints or not.  */
+
+int has_reinsert_breakpoints (struct process_info *proc);
+
 /* Uninsert breakpoints at WHERE (and change their status to
    uninserted).  This still leaves the breakpoints in the table.  */
 
-- 
1.9.1