gdb: additional debug output in infrun.c and linux-nat.c

While working on some of the recent patches relating to vfork handling
I found this debug output very helpful, I'd like to propose adding
this into GDB.

With debug turned off there should be no user visible changes after
this commit.

gdb/infrun.c

@@ -435,6 +435,11 @@ show_follow_fork_mode_string (struct ui_file *file, int from_tty,
 static bool
 follow_fork_inferior (bool follow_child, bool detach_fork)
 {
+  INFRUN_SCOPED_DEBUG_ENTER_EXIT;
+
+  infrun_debug_printf ("follow_child = %d, detach_fork = %d",
+		       follow_child, detach_fork);
+
   target_waitkind fork_kind = inferior_thread ()->pending_follow.kind ();
   gdb_assert (fork_kind == TARGET_WAITKIND_FORKED
 	      || fork_kind == TARGET_WAITKIND_VFORKED);
@@ -543,6 +548,13 @@ holding the child stopped.  Try \"set detach-on-fork\" or \
 	  parent_inf->thread_waiting_for_vfork_done
 	    = detach_fork ? inferior_thread () : nullptr;
 	  parent_inf->pspace->breakpoints_not_allowed = detach_fork;
+
+	  infrun_debug_printf
+	    ("parent_inf->thread_waiting_for_vfork_done == %s",
+	     (parent_inf->thread_waiting_for_vfork_done == nullptr
+	      ? "nullptr"
+	      : (parent_inf->thread_waiting_for_vfork_done
+		 ->ptid.to_string ().c_str ())));
 	}
     }
   else
@@ -727,6 +739,8 @@ set_last_target_status_stopped (thread_info *tp)
 static bool
 follow_fork ()
 {
+  INFRUN_SCOPED_DEBUG_ENTER_EXIT;
+
   bool follow_child = (follow_fork_mode_string == follow_fork_mode_child);
   bool should_resume = true;
 
@@ -996,6 +1010,8 @@ proceed_after_vfork_done (thread_info *thread)
 static void
 handle_vfork_child_exec_or_exit (int exec)
 {
+  INFRUN_SCOPED_DEBUG_ENTER_EXIT;
+
   struct inferior *inf = current_inferior ();
 
   if (inf->vfork_parent)
@@ -1127,6 +1143,8 @@ handle_vfork_child_exec_or_exit (int exec)
 static void
 handle_vfork_done (thread_info *event_thread)
 {
+  INFRUN_SCOPED_DEBUG_ENTER_EXIT;
+
   /* We only care about this event if inferior::thread_waiting_for_vfork_done is
      set, that is if we are waiting for a vfork child not under our control
      (because we detached it) to exec or exit.
@@ -1142,8 +1160,6 @@ handle_vfork_done (thread_info *event_thread)
       return;
     }
 
-  INFRUN_SCOPED_DEBUG_ENTER_EXIT;
-
   /* We stopped all threads (other than the vforking thread) of the inferior in
      follow_fork and kept them stopped until now.  It should therefore not be
      possible for another thread to have reported a vfork during that window.
@@ -3407,6 +3423,8 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
 
   thread_info *cur_thr = inferior_thread ();
 
+  infrun_debug_printf ("cur_thr = %s", cur_thr->ptid.to_string ().c_str ());
+
   /* Fill in with reasonable starting values.  */
   init_thread_stepping_state (cur_thr);
 
@@ -3463,8 +3481,10 @@ proceed (CORE_ADDR addr, enum gdb_signal siggnal)
   if (!cur_thr->control.in_infcall)
     set_running (resume_target, resume_ptid, true);
 
-  infrun_debug_printf ("addr=%s, signal=%s", paddress (gdbarch, addr),
+  infrun_debug_printf ("addr=%s, signal=%s, resume_ptid=%s",
-		       gdb_signal_to_symbol_string (siggnal));
+		       paddress (gdbarch, addr),
+		       gdb_signal_to_symbol_string (siggnal),
+		       resume_ptid.to_string ().c_str ());
 
   annotate_starting ();
 

gdb/linux-nat.c

@@ -1293,6 +1293,11 @@ get_detach_signal (struct lwp_info *lp)
 static void
 detach_one_lwp (struct lwp_info *lp, int *signo_p)
 {
+  LINUX_NAT_SCOPED_DEBUG_ENTER_EXIT;
+
+  linux_nat_debug_printf ("lwp %s (stopped = %d)",
+			  lp->ptid.to_string ().c_str (), lp->stopped);
+
   int lwpid = lp->ptid.lwp ();
   int signo;
 
@@ -1363,6 +1368,10 @@ detach_one_lwp (struct lwp_info *lp, int *signo_p)
   else
     signo = *signo_p;
 
+  linux_nat_debug_printf ("preparing to resume lwp %s (stopped = %d)",
+			  lp->ptid.to_string ().c_str (),
+			  lp->stopped);
+
   /* Preparing to resume may try to write registers, and fail if the
      lwp is zombie.  If that happens, ignore the error.  We'll handle
      it below, when detach fails with ESRCH.  */
@@ -1395,6 +1404,8 @@ detach_callback (struct lwp_info *lp)
 void
 linux_nat_target::detach (inferior *inf, int from_tty)
 {
+  LINUX_NAT_SCOPED_DEBUG_ENTER_EXIT;
+
   struct lwp_info *main_lwp;
   int pid = inf->pid;
 
@@ -3122,13 +3133,13 @@ static ptid_t
 linux_nat_wait_1 (ptid_t ptid, struct target_waitstatus *ourstatus,
 		  target_wait_flags target_options)
 {
+  LINUX_NAT_SCOPED_DEBUG_ENTER_EXIT;
+
   sigset_t prev_mask;
   enum resume_kind last_resume_kind;
   struct lwp_info *lp;
   int status;
 
-  linux_nat_debug_printf ("enter");
-
   /* The first time we get here after starting a new inferior, we may
      not have added it to the LWP list yet - this is the earliest
      moment at which we know its PID.  */
@@ -3228,7 +3239,7 @@ linux_nat_wait_1 (ptid_t ptid, struct target_waitstatus *ourstatus,
 
       if (target_options & TARGET_WNOHANG)
 	{
-	  linux_nat_debug_printf ("exit (ignore)");
+	  linux_nat_debug_printf ("no interesting events found");
 
 	  ourstatus->set_ignore ();
 	  restore_child_signals_mask (&prev_mask);
@@ -3314,7 +3325,7 @@ linux_nat_wait_1 (ptid_t ptid, struct target_waitstatus *ourstatus,
   else
     *ourstatus = host_status_to_waitstatus (status);
 
-  linux_nat_debug_printf ("exit");
+  linux_nat_debug_printf ("event found");
 
   restore_child_signals_mask (&prev_mask);
 
@@ -3410,6 +3421,8 @@ ptid_t
 linux_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 			target_wait_flags target_options)
 {
+  LINUX_NAT_SCOPED_DEBUG_ENTER_EXIT;
+
   ptid_t event_ptid;
 
   linux_nat_debug_printf ("[%s], [%s]", ptid.to_string ().c_str (),
@@ -3589,6 +3602,8 @@ linux_nat_target::kill ()
 void
 linux_nat_target::mourn_inferior ()
 {
+  LINUX_NAT_SCOPED_DEBUG_ENTER_EXIT;
+
   int pid = inferior_ptid.pid ();
 
   purge_lwp_list (pid);