gdbserver/linux-low: use std::list to store pending signals

Use std::list to store pending signals instead of a manually-managed
linked list.  This is a refactoring.

In the existing code, pending signals are kept in a manually-created
linked list with "prev" pointers.  A new pending signal is thus
inserted to the beginning of the list.  When consuming, GDB goes until
the end of the list, following the "prev" pointers, and processes the
final item.  With this patch, a new item is added to the end of the
list and the item at the front of the list is consumed.  In other
words, the list elements used to be stored in reverse order; with this
patch, they are stored in their order of arrival.  This causes a change
in the debug messages that print the pending signals.  Otherwise, no
behavioral change is expected.

gdbserver/ChangeLog:
2020-06-22  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	Use std::list to stop pending signal instead of manually-created
	linked list.
	* linux-low.h: Include <list>.
	(struct pending_signal): Move here from linux-low.cc.
	(struct lwp_info) <pending_signals>
	<pending_signals_to_report>: Update the type.
	* linux-low.cc (struct pending_signals): Remove.
	(linux_process_target::delete_lwp)
	(linux_process_target::add_lwp)
	(enqueue_one_deferred_signal)
	(dequeue_one_deferred_signal)
	(enqueue_pending_signal)
	(linux_process_target::resume_one_lwp_throw)
	(linux_process_target::thread_needs_step_over)
	(linux_process_target::resume_one_thread)
	(linux_process_target::proceed_one_lwp): Update the use of pending
	signal list.

1 files changed, 32 insertions, 69 deletions

diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index bde6c76..9684922 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -315,13 +315,6 @@ lwp_in_step_range (struct lwp_info *lwp)
   return (pc >= lwp->step_range_start && pc < lwp->step_range_end);
 }
 
-struct pending_signals
-{
-  int signal;
-  siginfo_t info;
-  struct pending_signals *prev;
-};
-
 /* The read/write ends of the pipe registered as waitable file in the
    event loop.  */
 static int linux_event_pipe[2] = { -1, -1 };
@@ -397,7 +390,7 @@ linux_process_target::delete_lwp (lwp_info *lwp)
 
   low_delete_thread (lwp->arch_private);
 
-  free (lwp);
+  delete lwp;
 }
 
 void
@@ -914,7 +907,7 @@ linux_process_target::add_lwp (ptid_t ptid)
 {
   struct lwp_info *lwp;
 
-  lwp = XCNEW (struct lwp_info);
+  lwp = new lwp_info {};
 
   lwp->waitstatus.kind = TARGET_WAITKIND_IGNORE;
 
@@ -2119,7 +2112,6 @@ linux_process_target::maybe_move_out_of_jump_pad (lwp_info *lwp, int *wstat)
 static void
 enqueue_one_deferred_signal (struct lwp_info *lwp, int *wstat)
 {
-  struct pending_signals *p_sig;
   struct thread_info *thread = get_lwp_thread (lwp);
 
   if (debug_threads)
@@ -2128,13 +2120,9 @@ enqueue_one_deferred_signal (struct lwp_info *lwp, int *wstat)
 
   if (debug_threads)
     {
-      struct pending_signals *sig;
-
-      for (sig = lwp->pending_signals_to_report;
-	   sig != NULL;
-	   sig = sig->prev)
+      for (const auto &sig : lwp->pending_signals_to_report)
 	debug_printf ("   Already queued %d\n",
-		      sig->signal);
+		      sig.signal);
 
       debug_printf ("   (no more currently queued signals)\n");
     }
@@ -2144,32 +2132,24 @@ enqueue_one_deferred_signal (struct lwp_info *lwp, int *wstat)
      twice)  */
   if (WSTOPSIG (*wstat) < __SIGRTMIN)
     {
-      struct pending_signals *sig;
-
-      for (sig = lwp->pending_signals_to_report;
-	   sig != NULL;
-	   sig = sig->prev)
+      for (const auto &sig : lwp->pending_signals_to_report)
 	{
-	  if (sig->signal == WSTOPSIG (*wstat))
+	  if (sig.signal == WSTOPSIG (*wstat))
 	    {
 	      if (debug_threads)
 		debug_printf ("Not requeuing already queued non-RT signal %d"
 			      " for LWP %ld\n",
-			      sig->signal,
+			      sig.signal,
 			      lwpid_of (thread));
 	      return;
 	    }
 	}
     }
 
-  p_sig = XCNEW (struct pending_signals);
-  p_sig->prev = lwp->pending_signals_to_report;
-  p_sig->signal = WSTOPSIG (*wstat);
+  lwp->pending_signals_to_report.emplace_back (WSTOPSIG (*wstat));
 
   ptrace (PTRACE_GETSIGINFO, lwpid_of (thread), (PTRACE_TYPE_ARG3) 0,
-	  &p_sig->info);
-
-  lwp->pending_signals_to_report = p_sig;
+	  &lwp->pending_signals_to_report.back ().info);
 }
 
 /* Dequeue one signal from the "signals to report later when out of
@@ -2180,20 +2160,16 @@ dequeue_one_deferred_signal (struct lwp_info *lwp, int *wstat)
 {
   struct thread_info *thread = get_lwp_thread (lwp);
 
-  if (lwp->pending_signals_to_report != NULL)
+  if (!lwp->pending_signals_to_report.empty ())
     {
-      struct pending_signals **p_sig;
+      const pending_signal &p_sig = lwp->pending_signals_to_report.front ();
 
-      p_sig = &lwp->pending_signals_to_report;
-      while ((*p_sig)->prev != NULL)
-	p_sig = &(*p_sig)->prev;
-
-      *wstat = W_STOPCODE ((*p_sig)->signal);
-      if ((*p_sig)->info.si_signo != 0)
+      *wstat = W_STOPCODE (p_sig.signal);
+      if (p_sig.info.si_signo != 0)
 	ptrace (PTRACE_SETSIGINFO, lwpid_of (thread), (PTRACE_TYPE_ARG3) 0,
-		&(*p_sig)->info);
-      free (*p_sig);
-      *p_sig = NULL;
+		&p_sig.info);
+
+      lwp->pending_signals_to_report.pop_front ();
 
       if (debug_threads)
 	debug_printf ("Reporting deferred signal %d for LWP %ld.\n",
@@ -2201,13 +2177,9 @@ dequeue_one_deferred_signal (struct lwp_info *lwp, int *wstat)
 
       if (debug_threads)
 	{
-	  struct pending_signals *sig;
-
-	  for (sig = lwp->pending_signals_to_report;
-	       sig != NULL;
-	       sig = sig->prev)
+	  for (const auto &sig : lwp->pending_signals_to_report)
 	    debug_printf ("   Still queued %d\n",
-			  sig->signal);
+			  sig.signal);
 
 	  debug_printf ("   (no more queued signals)\n");
 	}
@@ -4050,15 +4022,11 @@ linux_process_target::stop_all_lwps (int suspend, lwp_info *except)
 static void
 enqueue_pending_signal (struct lwp_info *lwp, int signal, siginfo_t *info)
 {
-  struct pending_signals *p_sig = XNEW (struct pending_signals);
-
-  p_sig->prev = lwp->pending_signals;
-  p_sig->signal = signal;
-  if (info == NULL)
-    memset (&p_sig->info, 0, sizeof (siginfo_t));
+  lwp->pending_signals.emplace_back (signal);
+  if (info == nullptr)
+    memset (&lwp->pending_signals.back ().info, 0, sizeof (siginfo_t));
   else
-    memcpy (&p_sig->info, info, sizeof (siginfo_t));
-  lwp->pending_signals = p_sig;
+    lwp->pending_signals.back ().info = *info;
 }
 
 void
@@ -4154,7 +4122,7 @@ linux_process_target::resume_one_lwp_throw (lwp_info *lwp, int step,
      inferior right now.  */
   if (signal != 0
       && (lwp->status_pending_p
-	  || lwp->pending_signals != NULL
+	  || !lwp->pending_signals.empty ()
 	  || !lwp_signal_can_be_delivered (lwp)))
     {
       enqueue_pending_signal (lwp, signal, info);
@@ -4263,21 +4231,16 @@ linux_process_target::resume_one_lwp_throw (lwp_info *lwp, int step,
 
   /* If we have pending signals, consume one if it can be delivered to
      the inferior.  */
-  if (lwp->pending_signals != NULL && lwp_signal_can_be_delivered (lwp))
+  if (!lwp->pending_signals.empty () && lwp_signal_can_be_delivered (lwp))
     {
-      struct pending_signals **p_sig;
-
-      p_sig = &lwp->pending_signals;
-      while ((*p_sig)->prev != NULL)
-	p_sig = &(*p_sig)->prev;
+      const pending_signal &p_sig = lwp->pending_signals.front ();
 
-      signal = (*p_sig)->signal;
-      if ((*p_sig)->info.si_signo != 0)
+      signal = p_sig.signal;
+      if (p_sig.info.si_signo != 0)
 	ptrace (PTRACE_SETSIGINFO, lwpid_of (thread), (PTRACE_TYPE_ARG3) 0,
-		&(*p_sig)->info);
+		&p_sig.info);
 
-      free (*p_sig);
-      *p_sig = NULL;
+      lwp->pending_signals.pop_front ();
     }
 
   if (debug_threads)
@@ -4570,7 +4533,7 @@ linux_process_target::thread_needs_step_over (thread_info *thread)
   /* On software single step target, resume the inferior with signal
      rather than stepping over.  */
   if (supports_software_single_step ()
-      && lwp->pending_signals != NULL
+      && !lwp->pending_signals.empty ()
       && lwp_signal_can_be_delivered (lwp))
     {
       if (debug_threads)
@@ -4787,7 +4750,7 @@ linux_process_target::resume_one_thread (thread_info *thread,
 	     midway through moving the LWP out of the jumppad, and we
 	     will report the pending signal as soon as that is
 	     finished.  */
-	  if (lwp->pending_signals_to_report == NULL)
+	  if (lwp->pending_signals_to_report.empty ())
 	    send_sigstop (lwp);
 	}
 
@@ -4966,7 +4929,7 @@ linux_process_target::proceed_one_lwp (thread_info *thread, lwp_info *except)
     }
 
   if (thread->last_resume_kind == resume_stop
-      && lwp->pending_signals_to_report == NULL
+      && lwp->pending_signals_to_report.empty ()
       && (lwp->collecting_fast_tracepoint
 	  == fast_tpoint_collect_result::not_collecting))
     {