linux-nat.c: clean up pending status checking and resuming LWPs

Whenever we resume an LWP, we must clear a few flags and flush the
LWP's register cache.  We actually currently flush the register cache
of all LWPs, but that's unnecessary.  This patch makes us flush the
register cache of only the LWP that is resumed.  Instead of open
coding all that in many places, we use a helper function.

Likewise, we have two fields in the LWP structure where a pending
status may be recorded.  Add a helper predicate that checks both and
use it throughout instead of open coding the checks.

gdb/
2015-01-09  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (linux_resume_one_lwp): New function.
	(resume_lwp): Use lwp_status_pending_p and linux_resume_one_lwp.
	(linux_nat_resume): Use lwp_status_pending_p and
	linux_resume_one_lwp.
	(linux_handle_syscall_trap): Use linux_resume_one_lwp.
	(linux_handle_extended_wait): Use linux_resume_one_lwp.
	(status_callback, running_callback): Use lwp_status_pending_p.
	(lwp_status_pending_p): New function.
	(stop_and_resume_callback): Use lwp_status_pending_p.
	(linux_nat_filter_event): Use linux_resume_one_lwp.
	(linux_nat_wait_1): Always use status_callback to look for an LWP
	with a pending status.  Use linux_resume_one_lwp.
	(resume_stopped_resumed_lwps): Use lwp_status_pending_p and
	linux_resume_one_lwp.

2 files changed, 67 insertions, 120 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index eef41b5..8c7c13b 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,22 @@
 2015-01-09  Pedro Alves  <palves@redhat.com>
 
+	* linux-nat.c (linux_resume_one_lwp): New function.
+	(resume_lwp): Use lwp_status_pending_p and linux_resume_one_lwp.
+	(linux_nat_resume): Use lwp_status_pending_p and
+	linux_resume_one_lwp.
+	(linux_handle_syscall_trap): Use linux_resume_one_lwp.
+	(linux_handle_extended_wait): Use linux_resume_one_lwp.
+	(status_callback, running_callback): Use lwp_status_pending_p.
+	(lwp_status_pending_p): New function.
+	(stop_and_resume_callback): Use lwp_status_pending_p.
+	(linux_nat_filter_event): Use linux_resume_one_lwp.
+	(linux_nat_wait_1): Always use status_callback to look for an LWP
+	with a pending status.  Use linux_resume_one_lwp.
+	(resume_stopped_resumed_lwps): Use lwp_status_pending_p and
+	linux_resume_one_lwp.
+
+2015-01-09  Pedro Alves  <palves@redhat.com>
+
 	* breakpoint.c (bp_location_inserted_here_p): New function,
 	factored out from ...
 	(breakpoint_inserted_here_p): ... here.  Use
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 77aa8e3..2097cb9 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -277,6 +277,8 @@ static void purge_lwp_list (int pid);
 static void delete_lwp (ptid_t ptid);
 static struct lwp_info *find_lwp_pid (ptid_t ptid);
 
+static int lwp_status_pending_p (struct lwp_info *lp);
+
 
 /* Trivial list manipulation functions to keep track of a list of
    new stopped processes.  */
@@ -1508,6 +1510,25 @@ linux_nat_detach (struct target_ops *ops, const char *args, int from_tty)
     linux_ops->to_detach (ops, args, from_tty);
 }
 
+/* Resume execution of the inferior process.  If STEP is nonzero,
+   single-step it.  If SIGNAL is nonzero, give it that signal.  */
+
+static void
+linux_resume_one_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
+{
+  ptid_t ptid;
+
+  lp->step = step;
+  if (linux_nat_prepare_to_resume != NULL)
+    linux_nat_prepare_to_resume (lp);
+  /* Convert to something the lower layer understands.  */
+  ptid = pid_to_ptid (ptid_get_lwp (lp->ptid));
+  linux_ops->to_resume (linux_ops, ptid, step, signo);
+  lp->stopped_by_watchpoint = 0;
+  lp->stopped = 0;
+  registers_changed_ptid (lp->ptid);
+}
+
 /* Resume LP.  */
 
 static void
@@ -1524,8 +1545,7 @@ resume_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
 				"RC: Not resuming %s (vfork parent)\n",
 				target_pid_to_str (lp->ptid));
 	}
-      else if (lp->status == 0
-	       && lp->waitstatus.kind == TARGET_WAITKIND_IGNORE)
+      else if (!lwp_status_pending_p (lp))
 	{
 	  if (debug_linux_nat)
 	    fprintf_unfiltered (gdb_stdlog,
@@ -1536,14 +1556,7 @@ resume_lwp (struct lwp_info *lp, int step, enum gdb_signal signo)
 				 : "0"),
 				step ? "step" : "resume");
 
-	  if (linux_nat_prepare_to_resume != NULL)
-	    linux_nat_prepare_to_resume (lp);
-	  linux_ops->to_resume (linux_ops,
-				pid_to_ptid (ptid_get_lwp (lp->ptid)),
-				step, signo);
-	  lp->stopped = 0;
-	  lp->step = step;
-	  lp->stopped_by_watchpoint = 0;
+	  linux_resume_one_lwp (lp, step, signo);
 	}
       else
 	{
@@ -1637,7 +1650,6 @@ linux_nat_resume (struct target_ops *ops,
   gdb_assert (lp != NULL);
 
   /* Remember if we're stepping.  */
-  lp->step = step;
   lp->last_resume_kind = step ? resume_step : resume_continue;
 
   /* If we have a pending wait status for this thread, there is no
@@ -1667,7 +1679,7 @@ linux_nat_resume (struct target_ops *ops,
 	}
     }
 
-  if (lp->status || lp->waitstatus.kind != TARGET_WAITKIND_IGNORE)
+  if (lwp_status_pending_p (lp))
     {
       /* FIXME: What should we do if we are supposed to continue
 	 this thread with a signal?  */
@@ -1690,14 +1702,7 @@ linux_nat_resume (struct target_ops *ops,
   if (resume_many)
     iterate_over_lwps (ptid, linux_nat_resume_callback, lp);
 
-  /* Convert to something the lower layer understands.  */
-  ptid = pid_to_ptid (ptid_get_lwp (lp->ptid));
-
-  if (linux_nat_prepare_to_resume != NULL)
-    linux_nat_prepare_to_resume (lp);
-  linux_ops->to_resume (linux_ops, ptid, step, signo);
-  lp->stopped_by_watchpoint = 0;
-  lp->stopped = 0;
+  linux_resume_one_lwp (lp, step, signo);
 
   if (debug_linux_nat)
     fprintf_unfiltered (gdb_stdlog,
@@ -1861,14 +1866,7 @@ linux_handle_syscall_trap (struct lwp_info *lp, int stopping)
      subsequent syscall.  Simply resume using the inf-ptrace layer,
      which knows when to use PT_SYSCALL or PT_CONTINUE.  */
 
-  /* Note that gdbarch_get_syscall_number may access registers, hence
-     fill a regcache.  */
-  registers_changed ();
-  if (linux_nat_prepare_to_resume != NULL)
-    linux_nat_prepare_to_resume (lp);
-  linux_ops->to_resume (linux_ops, pid_to_ptid (ptid_get_lwp (lp->ptid)),
-			lp->step, GDB_SIGNAL_0);
-  lp->stopped = 0;
+  linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
   return 1;
 }
 
@@ -2062,23 +2060,14 @@ linux_handle_extended_wait (struct lwp_info *lp, int status,
 		    fprintf_unfiltered (gdb_stdlog,
 					"LHEW: resuming new LWP %ld\n",
 					ptid_get_lwp (new_lp->ptid));
-		  if (linux_nat_prepare_to_resume != NULL)
-		    linux_nat_prepare_to_resume (new_lp);
-		  linux_ops->to_resume (linux_ops, pid_to_ptid (new_pid),
-					0, GDB_SIGNAL_0);
-		  new_lp->stopped = 0;
+		  linux_resume_one_lwp (new_lp, 0, GDB_SIGNAL_0);
 		}
 	    }
 
 	  if (debug_linux_nat)
 	    fprintf_unfiltered (gdb_stdlog,
 				"LHEW: resuming parent LWP %d\n", pid);
-	  if (linux_nat_prepare_to_resume != NULL)
-	    linux_nat_prepare_to_resume (lp);
-	  linux_ops->to_resume (linux_ops,
-				pid_to_ptid (ptid_get_lwp (lp->ptid)),
-				0, GDB_SIGNAL_0);
-	  lp->stopped = 0;
+	  linux_resume_one_lwp (lp, 0, GDB_SIGNAL_0);
 	  return 1;
 	}
 
@@ -2556,20 +2545,7 @@ status_callback (struct lwp_info *lp, void *data)
   if (!lp->resumed)
     return 0;
 
-  if (lp->waitstatus.kind != TARGET_WAITKIND_IGNORE)
-    {
-      /* A ptrace event, like PTRACE_FORK|VFORK|EXEC, syscall event,
-	 or a pending process exit.  Note that `W_EXITCODE(0,0) ==
-	 0', so a clean process exit can not be stored pending in
-	 lp->status, it is indistinguishable from
-	 no-pending-status.  */
-      return 1;
-    }
-
-  if (lp->status != 0)
-    return 1;
-
-  return 0;
+  return lwp_status_pending_p (lp);
 }
 
 /* Return non-zero if LP isn't stopped.  */
@@ -2578,9 +2554,7 @@ static int
 running_callback (struct lwp_info *lp, void *data)
 {
   return (!lp->stopped
-	  || ((lp->status != 0
-	       || lp->waitstatus.kind != TARGET_WAITKIND_IGNORE)
-	      && lp->resumed));
+	  || (lwp_status_pending_p (lp) && lp->resumed));
 }
 
 /* Count the LWP's that have had events.  */
@@ -2611,6 +2585,17 @@ select_singlestep_lwp_callback (struct lwp_info *lp, void *data)
     return 0;
 }
 
+/* Returns true if LP has a status pending.  */
+
+static int
+lwp_status_pending_p (struct lwp_info *lp)
+{
+  /* We check for lp->waitstatus in addition to lp->status, because we
+     can have pending process exits recorded in lp->status and
+     W_EXITCODE(0,0) happens to be 0.  */
+  return lp->status != 0 || lp->waitstatus.kind != TARGET_WAITKIND_IGNORE;
+}
+
 /* Select the Nth LWP that has had a SIGTRAP event.  */
 
 static int
@@ -2774,7 +2759,7 @@ stop_and_resume_callback (struct lwp_info *lp, void *data)
       if (lp != NULL)
 	{
 	  if (lp->last_resume_kind == resume_stop
-	      && lp->status == 0)
+	      && !lwp_status_pending_p (lp))
 	    {
 	      /* The core wanted the LWP to stop.  Even if it stopped
 		 cleanly (with SIGSTOP), leave the event pending.  */
@@ -2786,7 +2771,7 @@ stop_and_resume_callback (struct lwp_info *lp, void *data)
 	      lp->status = W_STOPCODE (SIGSTOP);
 	    }
 
-	  if (lp->status == 0)
+	  if (!lwp_status_pending_p (lp))
 	    {
 	      if (debug_linux_nat)
 		fprintf_unfiltered (gdb_stdlog,
@@ -2977,13 +2962,7 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
 	{
 	  /* This is a delayed SIGSTOP.  */
 
-	  registers_changed ();
-
-	  if (linux_nat_prepare_to_resume != NULL)
-	    linux_nat_prepare_to_resume (lp);
-	  linux_ops->to_resume (linux_ops,
-				pid_to_ptid (ptid_get_lwp (lp->ptid)),
-				lp->step, GDB_SIGNAL_0);
+	  linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
 	  if (debug_linux_nat)
 	    fprintf_unfiltered (gdb_stdlog,
 				"LLW: %s %s, 0, 0 (discard SIGSTOP)\n",
@@ -2991,7 +2970,6 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
 				"PTRACE_SINGLESTEP" : "PTRACE_CONT",
 				target_pid_to_str (lp->ptid));
 
-	  lp->stopped = 0;
 	  gdb_assert (lp->resumed);
 
 	  /* Discard the event.  */
@@ -3012,19 +2990,13 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
       /* This is a delayed SIGINT.  */
       lp->ignore_sigint = 0;
 
-      registers_changed ();
-      if (linux_nat_prepare_to_resume != NULL)
-	linux_nat_prepare_to_resume (lp);
-      linux_ops->to_resume (linux_ops, pid_to_ptid (ptid_get_lwp (lp->ptid)),
-			    lp->step, GDB_SIGNAL_0);
+      linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
       if (debug_linux_nat)
 	fprintf_unfiltered (gdb_stdlog,
 			    "LLW: %s %s, 0, 0 (discard SIGINT)\n",
 			    lp->step ?
 			    "PTRACE_SINGLESTEP" : "PTRACE_CONT",
 			    target_pid_to_str (lp->ptid));
-
-      lp->stopped = 0;
       gdb_assert (lp->resumed);
 
       /* Discard the event.  */
@@ -3133,46 +3105,17 @@ linux_nat_wait_1 (struct target_ops *ops,
   block_child_signals (&prev_mask);
 
 retry:
-  lp = NULL;
   status = 0;
 
   /* First check if there is a LWP with a wait status pending.  */
-  if (ptid_equal (ptid, minus_one_ptid) || ptid_is_pid (ptid))
-    {
-      /* Any LWP in the PTID group that's been resumed will do.  */
-      lp = iterate_over_lwps (ptid, status_callback, NULL);
-      if (lp)
-	{
-	  if (debug_linux_nat && lp->status)
-	    fprintf_unfiltered (gdb_stdlog,
-				"LLW: Using pending wait status %s for %s.\n",
-				status_to_str (lp->status),
-				target_pid_to_str (lp->ptid));
-	}
-    }
-  else if (ptid_lwp_p (ptid))
+  lp = iterate_over_lwps (ptid, status_callback, NULL);
+  if (lp != NULL)
     {
       if (debug_linux_nat)
 	fprintf_unfiltered (gdb_stdlog,
-			    "LLW: Waiting for specific LWP %s.\n",
-			    target_pid_to_str (ptid));
-
-      /* We have a specific LWP to check.  */
-      lp = find_lwp_pid (ptid);
-      gdb_assert (lp);
-
-      if (debug_linux_nat && lp->status)
-	fprintf_unfiltered (gdb_stdlog,
 			    "LLW: Using pending wait status %s for %s.\n",
 			    status_to_str (lp->status),
 			    target_pid_to_str (lp->ptid));
-
-      /* We check for lp->waitstatus in addition to lp->status,
-	 because we can have pending process exits recorded in
-	 lp->status and W_EXITCODE(0,0) == 0.  We should probably have
-	 an additional lp->status_p flag.  */
-      if (lp->status == 0 && lp->waitstatus.kind == TARGET_WAITKIND_IGNORE)
-	lp = NULL;
     }
 
   if (!target_can_async_p ())
@@ -3388,12 +3331,7 @@ retry:
 	     other threads to run.  On the other hand, not resuming
 	     newly attached threads may cause an unwanted delay in
 	     getting them running.  */
-	  registers_changed ();
-	  if (linux_nat_prepare_to_resume != NULL)
-	    linux_nat_prepare_to_resume (lp);
-	  linux_ops->to_resume (linux_ops,
-				pid_to_ptid (ptid_get_lwp (lp->ptid)),
-				lp->step, signo);
+	  linux_resume_one_lwp (lp, lp->step, signo);
 	  if (debug_linux_nat)
 	    fprintf_unfiltered (gdb_stdlog,
 				"LLW: %s %s, %s (preempt 'handle')\n",
@@ -3403,7 +3341,6 @@ retry:
 				(signo != GDB_SIGNAL_0
 				 ? strsignal (gdb_signal_to_host (signo))
 				 : "0"));
-	  lp->stopped = 0;
 	  goto retry;
 	}
 
@@ -3523,8 +3460,7 @@ resume_stopped_resumed_lwps (struct lwp_info *lp, void *data)
 
   if (lp->stopped
       && lp->resumed
-      && lp->status == 0
-      && lp->waitstatus.kind == TARGET_WAITKIND_IGNORE)
+      && !lwp_status_pending_p (lp))
     {
       struct regcache *regcache = get_thread_regcache (lp->ptid);
       struct gdbarch *gdbarch = get_regcache_arch (regcache);
@@ -3547,13 +3483,7 @@ resume_stopped_resumed_lwps (struct lwp_info *lp, void *data)
 			    paddress (gdbarch, pc),
 			    lp->step);
 
-      registers_changed ();
-      if (linux_nat_prepare_to_resume != NULL)
-	linux_nat_prepare_to_resume (lp);
-      linux_ops->to_resume (linux_ops, pid_to_ptid (ptid_get_lwp (lp->ptid)),
-			    lp->step, GDB_SIGNAL_0);
-      lp->stopped = 0;
-      lp->stopped_by_watchpoint = 0;
+      linux_resume_one_lwp (lp, lp->step, GDB_SIGNAL_0);
     }
 
   return 0;