Insert breakpoint even when the raw breakpoint is found

When GDBserver inserts a breakpoint, it looks for raw breakpoint, if
the raw breakpoint is found, increase its refcount, and return.  This
doesn't work when it steps over a breakpoint using software single
step and the underneath instruction of breakpoint is branch to self.

When stepping over a breakpoint on ADDR using software single step,
GDBserver uninsert the breakpoint, so the corresponding raw breakpoint
RAW's 'inserted' flag is zero.  Then, GDBserver insert single step
breakpoint at the same address ADDR because the instruction is branch
to self, the same raw brekapoint RAW is found, and increase the
refcount.  However, the raw breakpoint is not inserted, and the
program won't stop.

gdb/gdbserver:

2016-04-25  Pedro Alves  <palves@redhat.com>
	    Yao Qi  <yao.qi@linaro.org>

	* mem-break.c (set_raw_breakpoint_at): Create a raw breakpoint
	object.  Insert it if it is not inserted yet.  Increase the
	refcount and link it into the proc's raw breakpoint list.

1 files changed, 28 insertions, 20 deletions

diff --git a/gdb/gdbserver/mem-break.c b/gdb/gdbserver/mem-break.c
index b06f8e9..419db9e 100644
--- a/gdb/gdbserver/mem-break.c
+++ b/gdb/gdbserver/mem-break.c
@@ -390,6 +390,7 @@ set_raw_breakpoint_at (enum raw_bkpt_type type, CORE_ADDR where, int kind,
 {
   struct process_info *proc = current_process ();
   struct raw_breakpoint *bp;
+  struct cleanup *old_chain = make_cleanup (null_cleanup, NULL);
 
   if (type == raw_bkpt_type_sw || type == raw_bkpt_type_hw)
     {
@@ -408,32 +409,39 @@ set_raw_breakpoint_at (enum raw_bkpt_type type, CORE_ADDR where, int kind,
   else
     bp = find_raw_breakpoint_at (where, type, kind);
 
-  if (bp != NULL)
+  if (bp == NULL)
     {
-      bp->refcount++;
-      return bp;
+      bp = XCNEW (struct raw_breakpoint);
+      bp->pc = where;
+      bp->kind = kind;
+      bp->raw_type = type;
+      make_cleanup (xfree, bp);
     }
 
-  bp = XCNEW (struct raw_breakpoint);
-  bp->pc = where;
-  bp->kind = kind;
-  bp->refcount = 1;
-  bp->raw_type = type;
-
-  *err = the_target->insert_point (bp->raw_type, bp->pc, bp->kind, bp);
-  if (*err != 0)
+  if (!bp->inserted)
     {
-      if (debug_threads)
-	debug_printf ("Failed to insert breakpoint at 0x%s (%d).\n",
-		      paddress (where), *err);
-      free (bp);
-      return NULL;
+      *err = the_target->insert_point (bp->raw_type, bp->pc, bp->kind, bp);
+      if (*err != 0)
+	{
+	  if (debug_threads)
+	    debug_printf ("Failed to insert breakpoint at 0x%s (%d).\n",
+			  paddress (where), *err);
+
+	  do_cleanups (old_chain);
+	  return NULL;
+	}
+
+      bp->inserted = 1;
     }
 
-  bp->inserted = 1;
-  /* Link the breakpoint in.  */
-  bp->next = proc->raw_breakpoints;
-  proc->raw_breakpoints = bp;
+  discard_cleanups (old_chain);
+
+  /* Link the breakpoint in, if this is the first reference.  */
+  if (++bp->refcount == 1)
+    {
+      bp->next = proc->raw_breakpoints;
+      proc->raw_breakpoints = bp;
+    }
   return bp;
 }