gdb, gdbserver: make target_waitstatus safe

I stumbled on a bug caused by the fact that a code path read
target_waitstatus::value::sig (expecting it to contain a gdb_signal
value) while target_waitstatus::kind was TARGET_WAITKIND_FORKED.  This
meant that the active union field was in fact
target_waitstatus::value::related_pid, and contained a ptid.  The read
signal value was therefore garbage, and that caused GDB to crash soon
after.  Or, since that GDB was built with ubsan, this nice error
message:

    /home/simark/src/binutils-gdb/gdb/linux-nat.c:1271:12: runtime error: load of value 2686365, which is not a valid value for type 'gdb_signal'

Despite being a large-ish change, I think it would be nice to make
target_waitstatus safe against that kind of bug.  As already done
elsewhere (e.g. dynamic_prop), validate that the type of value read from
the union matches what is supposed to be the active field.

 - Make the kind and value of target_waitstatus private.
 - Make the kind initialized to TARGET_WAITKIND_IGNORE on
   target_waitstatus construction.  This is what most users appear to do
   explicitly.
 - Add setters, one for each kind.  Each setter takes as a parameter the
   data associated to that kind, if any.  This makes it impossible to
   forget to attach the associated data.
 - Add getters, one for each associated data type.  Each getter
   validates that the data type fetched by the user matches the wait
   status kind.
 - Change "integer" to "exit_status", "related_pid" to "child_ptid",
   just because that's more precise terminology.
 - Fix all users.

That last point is semi-mechanical.  There are a lot of obvious changes,
but some less obvious ones.  For example, it's not possible to set the
kind at some point and the associated data later, as some users did.
But in any case, the intent of the code should not change in this patch.

This was tested on x86-64 Linux (unix, native-gdbserver and
native-extended-gdbserver boards).  It was built-tested on x86-64
FreeBSD, NetBSD, MinGW and macOS.  The rest of the changes to native
files was done as a best effort.  If I forgot any place to update in
these files, it should be easy to fix (unless the change happens to
reveal an actual bug).

Change-Id: I0ae967df1ff6e28de78abbe3ac9b4b2ff4ad03b7

1 files changed, 64 insertions, 68 deletions

diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
index 6ea517e..b6820ad 100644
--- a/gdbserver/linux-low.cc
+++ b/gdbserver/linux-low.cc
@@ -450,7 +450,7 @@ linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
   struct thread_info *event_thr = get_lwp_thread (event_lwp);
   struct lwp_info *new_lwp;
 
-  gdb_assert (event_lwp->waitstatus.kind == TARGET_WAITKIND_IGNORE);
+  gdb_assert (event_lwp->waitstatus.kind () == TARGET_WAITKIND_IGNORE);
 
   /* All extended events we currently use are mid-syscall.  Only
      PTRACE_EVENT_STOP is delivered more like a signal-stop, but
@@ -515,7 +515,7 @@ linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
 	  child_lwp->status_pending_p = 0;
 	  child_thr = get_lwp_thread (child_lwp);
 	  child_thr->last_resume_kind = resume_stop;
-	  child_thr->last_status.kind = TARGET_WAITKIND_STOPPED;
+	  child_thr->last_status.set_stopped (GDB_SIGNAL_0);
 
 	  /* If we're suspending all threads, leave this one suspended
 	     too.  If the fork/clone parent is stepping over a breakpoint,
@@ -554,11 +554,9 @@ linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
 
 	  /* Save fork info in the parent thread.  */
 	  if (event == PTRACE_EVENT_FORK)
-	    event_lwp->waitstatus.kind = TARGET_WAITKIND_FORKED;
+	    event_lwp->waitstatus.set_forked (ptid);
 	  else if (event == PTRACE_EVENT_VFORK)
-	    event_lwp->waitstatus.kind = TARGET_WAITKIND_VFORKED;
-
-	  event_lwp->waitstatus.value.related_pid = ptid;
+	    event_lwp->waitstatus.set_vforked (ptid);
 
 	  /* The status_pending field contains bits denoting the
 	     extended event, so when the pending event is handled,
@@ -625,7 +623,7 @@ linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
 	}
       else if (cs.report_thread_events)
 	{
-	  new_lwp->waitstatus.kind = TARGET_WAITKIND_THREAD_CREATED;
+	  new_lwp->waitstatus.set_thread_created ();
 	  new_lwp->status_pending_p = 1;
 	  new_lwp->status_pending = status;
 	}
@@ -639,7 +637,7 @@ linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
     }
   else if (event == PTRACE_EVENT_VFORK_DONE)
     {
-      event_lwp->waitstatus.kind = TARGET_WAITKIND_VFORK_DONE;
+      event_lwp->waitstatus.set_vfork_done ();
 
       if (event_lwp->bp_reinsert != 0 && supports_software_single_step ())
 	{
@@ -684,16 +682,16 @@ linux_process_target::handle_extended_wait (lwp_info **orig_event_lwp,
       arch_setup_thread (event_thr);
 
       /* Set the event status.  */
-      event_lwp->waitstatus.kind = TARGET_WAITKIND_EXECD;
-      event_lwp->waitstatus.value.execd_pathname
-	= xstrdup (linux_proc_pid_to_exec_file (lwpid_of (event_thr)));
+      event_lwp->waitstatus.set_execd
+	(make_unique_xstrdup
+	   (linux_proc_pid_to_exec_file (lwpid_of (event_thr))));
 
       /* Mark the exec status as pending.  */
       event_lwp->stopped = 1;
       event_lwp->status_pending_p = 1;
       event_lwp->status_pending = wstat;
       event_thr->last_resume_kind = resume_continue;
-      event_thr->last_status.kind = TARGET_WAITKIND_IGNORE;
+      event_thr->last_status.set_ignore ();
 
       /* Update syscall state in the new lwp, effectively mid-syscall too.  */
       event_lwp->syscall_state = TARGET_WAITKIND_SYSCALL_ENTRY;
@@ -1388,8 +1386,8 @@ get_detach_signal (struct thread_info *thread)
       /* If the thread had been suspended by gdbserver, and it stopped
 	 cleanly, then it'll have stopped with SIGSTOP.  But we don't
 	 want to deliver that SIGSTOP.  */
-      if (thread->last_status.kind != TARGET_WAITKIND_STOPPED
-	  || thread->last_status.value.sig == GDB_SIGNAL_0)
+      if (thread->last_status.kind () != TARGET_WAITKIND_STOPPED
+	  || thread->last_status.sig () == GDB_SIGNAL_0)
 	return 0;
 
       /* Otherwise, we may need to deliver the signal we
@@ -1712,7 +1710,7 @@ lwp_resumed (struct lwp_info *lwp)
      corresponding stop to gdb yet?  If so, the thread is still
      resumed/running from gdb's perspective.  */
   if (thread->last_resume_kind == resume_stop
-      && thread->last_status.kind == TARGET_WAITKIND_IGNORE)
+      && thread->last_status.kind () == TARGET_WAITKIND_IGNORE)
     return 1;
 
   return 0;
@@ -2464,7 +2462,7 @@ linux_process_target::resume_stopped_resumed_lwps (thread_info *thread)
   if (lp->stopped
       && !lp->suspended
       && !lp->status_pending_p
-      && thread->last_status.kind == TARGET_WAITKIND_IGNORE)
+      && thread->last_status.kind () == TARGET_WAITKIND_IGNORE)
     {
       int step = 0;
 
@@ -2710,7 +2708,7 @@ select_event_lwp (struct lwp_info **orig_lp)
 	{
 	  lwp_info *lp = get_thread_lwp (thread);
 
-	  return (thread->last_status.kind == TARGET_WAITKIND_IGNORE
+	  return (thread->last_status.kind () == TARGET_WAITKIND_IGNORE
 		  && thread->last_resume_kind == resume_step
 		  && lp->status_pending_p);
 	});
@@ -2732,7 +2730,7 @@ select_event_lwp (struct lwp_info **orig_lp)
 	  lwp_info *lp = get_thread_lwp (thread);
 
 	  /* Only resumed LWPs that have an event pending. */
-	  return (thread->last_status.kind == TARGET_WAITKIND_IGNORE
+	  return (thread->last_status.kind () == TARGET_WAITKIND_IGNORE
 		  && lp->status_pending_p);
 	});
     }
@@ -2831,17 +2829,17 @@ linux_process_target::stabilize_threads ()
 	 over internal breakpoints and such.  */
       wait_1 (minus_one_ptid, &ourstatus, 0);
 
-      if (ourstatus.kind == TARGET_WAITKIND_STOPPED)
+      if (ourstatus.kind () == TARGET_WAITKIND_STOPPED)
 	{
 	  lwp = get_thread_lwp (current_thread);
 
 	  /* Lock it.  */
 	  lwp_suspended_inc (lwp);
 
-	  if (ourstatus.value.sig != GDB_SIGNAL_0
+	  if (ourstatus.sig () != GDB_SIGNAL_0
 	      || current_thread->last_resume_kind == resume_stop)
 	    {
-	      wstat = W_STOPCODE (gdb_signal_to_host (ourstatus.value.sig));
+	      wstat = W_STOPCODE (gdb_signal_to_host (ourstatus.sig ()));
 	      enqueue_one_deferred_signal (lwp, &wstat);
 	    }
 	}
@@ -2877,7 +2875,7 @@ ignore_event (struct target_waitstatus *ourstatus)
      another target_wait call.  */
   async_file_mark ();
 
-  ourstatus->kind = TARGET_WAITKIND_IGNORE;
+  ourstatus->set_ignore ();
   return null_ptid;
 }
 
@@ -2892,9 +2890,9 @@ linux_process_target::filter_exit_event (lwp_info *event_child,
   if (!last_thread_of_process_p (pid_of (thread)))
     {
       if (cs.report_thread_events)
-	ourstatus->kind = TARGET_WAITKIND_THREAD_EXITED;
+	ourstatus->set_thread_exited (0);
       else
-	ourstatus->kind = TARGET_WAITKIND_IGNORE;
+	ourstatus->set_ignore ();
 
       delete_lwp (event_child);
     }
@@ -2965,7 +2963,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
   bp_explains_trap = 0;
   trace_event = 0;
   in_step_range = 0;
-  ourstatus->kind = TARGET_WAITKIND_IGNORE;
+  ourstatus->set_ignore ();
 
   auto status_pending_p_any = [&] (thread_info *thread)
     {
@@ -3006,7 +3004,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 	  debug_exit ();
 	}
 
-      ourstatus->kind = TARGET_WAITKIND_IGNORE;
+      ourstatus->set_ignore ();
       return null_ptid;
     }
   else if (pid == -1)
@@ -3018,7 +3016,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 	  debug_exit ();
 	}
 
-      ourstatus->kind = TARGET_WAITKIND_NO_RESUMED;
+      ourstatus->set_no_resumed ();
       return null_ptid;
     }
 
@@ -3030,8 +3028,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
     {
       if (WIFEXITED (w))
 	{
-	  ourstatus->kind = TARGET_WAITKIND_EXITED;
-	  ourstatus->value.integer = WEXITSTATUS (w);
+	  ourstatus->set_exited (WEXITSTATUS (w));
 
 	  if (debug_threads)
 	    {
@@ -3044,8 +3041,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 	}
       else
 	{
-	  ourstatus->kind = TARGET_WAITKIND_SIGNALLED;
-	  ourstatus->value.sig = gdb_signal_from_host (WTERMSIG (w));
+	  ourstatus->set_signalled (gdb_signal_from_host (WTERMSIG (w)));
 
 	  if (debug_threads)
 	    {
@@ -3057,7 +3053,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 	    }
 	}
 
-      if (ourstatus->kind == TARGET_WAITKIND_EXITED)
+      if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
 	return filter_exit_event (event_child, ourstatus);
 
       return ptid_of (current_thread);
@@ -3252,8 +3248,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 
 	      if (stabilizing_threads)
 		{
-		  ourstatus->kind = TARGET_WAITKIND_STOPPED;
-		  ourstatus->value.sig = GDB_SIGNAL_0;
+		  ourstatus->set_stopped (GDB_SIGNAL_0);
 
 		  if (debug_threads)
 		    {
@@ -3378,7 +3373,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 		   || (gdb_breakpoint_here (event_child->stop_pc)
 		       && gdb_condition_true_at_breakpoint (event_child->stop_pc)
 		       && gdb_no_commands_at_breakpoint (event_child->stop_pc))
-		   || event_child->waitstatus.kind != TARGET_WAITKIND_IGNORE);
+		   || event_child->waitstatus.kind () != TARGET_WAITKIND_IGNORE);
 
   run_breakpoint_commands (event_child->stop_pc);
 
@@ -3448,7 +3443,7 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 
   if (debug_threads)
     {
-      if (event_child->waitstatus.kind != TARGET_WAITKIND_IGNORE)
+      if (event_child->waitstatus.kind () != TARGET_WAITKIND_IGNORE)
 	{
 	  std::string str
 	    = target_waitstatus_to_string (&event_child->waitstatus);
@@ -3589,14 +3584,14 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 	unstop_all_lwps (1, event_child);
     }
 
-  if (event_child->waitstatus.kind != TARGET_WAITKIND_IGNORE)
+  if (event_child->waitstatus.kind () != TARGET_WAITKIND_IGNORE)
     {
       /* If the reported event is an exit, fork, vfork or exec, let
 	 GDB know.  */
 
       /* Break the unreported fork relationship chain.  */
-      if (event_child->waitstatus.kind == TARGET_WAITKIND_FORKED
-	  || event_child->waitstatus.kind == TARGET_WAITKIND_VFORKED)
+      if (event_child->waitstatus.kind () == TARGET_WAITKIND_FORKED
+	  || event_child->waitstatus.kind () == TARGET_WAITKIND_VFORKED)
 	{
 	  event_child->fork_relative->fork_relative = NULL;
 	  event_child->fork_relative = NULL;
@@ -3604,10 +3599,13 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 
       *ourstatus = event_child->waitstatus;
       /* Clear the event lwp's waitstatus since we handled it already.  */
-      event_child->waitstatus.kind = TARGET_WAITKIND_IGNORE;
+      event_child->waitstatus.set_ignore ();
     }
   else
-    ourstatus->kind = TARGET_WAITKIND_STOPPED;
+    {
+      /* The actual stop signal is overwritten below.  */
+      ourstatus->set_stopped (GDB_SIGNAL_0);
+    }
 
   /* Now that we've selected our final event LWP, un-adjust its PC if
      it was a software breakpoint, and the client doesn't know we can
@@ -3627,9 +3625,15 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
 
   if (WSTOPSIG (w) == SYSCALL_SIGTRAP)
     {
-      get_syscall_trapinfo (event_child,
-			    &ourstatus->value.syscall_number);
-      ourstatus->kind = event_child->syscall_state;
+      int syscall_number;
+
+      get_syscall_trapinfo (event_child, &syscall_number);
+      if (event_child->syscall_state == TARGET_WAITKIND_SYSCALL_ENTRY)
+	ourstatus->set_syscall_entry (syscall_number);
+      else if (event_child->syscall_state == TARGET_WAITKIND_SYSCALL_RETURN)
+	ourstatus->set_syscall_return (syscall_number);
+      else
+	gdb_assert_not_reached ("unexpected syscall state");
     }
   else if (current_thread->last_resume_kind == resume_stop
 	   && WSTOPSIG (w) == SIGSTOP)
@@ -3637,19 +3641,17 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
       /* A thread that has been requested to stop by GDB with vCont;t,
 	 and it stopped cleanly, so report as SIG0.  The use of
 	 SIGSTOP is an implementation detail.  */
-      ourstatus->value.sig = GDB_SIGNAL_0;
+      ourstatus->set_stopped (GDB_SIGNAL_0);
     }
   else if (current_thread->last_resume_kind == resume_stop
 	   && WSTOPSIG (w) != SIGSTOP)
     {
       /* A thread that has been requested to stop by GDB with vCont;t,
 	 but, it stopped for other reasons.  */
-      ourstatus->value.sig = gdb_signal_from_host (WSTOPSIG (w));
-    }
-  else if (ourstatus->kind == TARGET_WAITKIND_STOPPED)
-    {
-      ourstatus->value.sig = gdb_signal_from_host (WSTOPSIG (w));
+      ourstatus->set_stopped (gdb_signal_from_host (WSTOPSIG (w)));
     }
+  else if (ourstatus->kind () == TARGET_WAITKIND_STOPPED)
+    ourstatus->set_stopped (gdb_signal_from_host (WSTOPSIG (w)));
 
   gdb_assert (step_over_bkpt == null_ptid);
 
@@ -3657,11 +3659,11 @@ linux_process_target::wait_1 (ptid_t ptid, target_waitstatus *ourstatus,
     {
       debug_printf ("wait_1 ret = %s, %d, %d\n",
 		    target_pid_to_str (ptid_of (current_thread)),
-		    ourstatus->kind, ourstatus->value.sig);
+		    ourstatus->kind (), ourstatus->sig ());
       debug_exit ();
     }
 
-  if (ourstatus->kind == TARGET_WAITKIND_EXITED)
+  if (ourstatus->kind () == TARGET_WAITKIND_EXITED)
     return filter_exit_event (event_child, ourstatus);
 
   return ptid_of (current_thread);
@@ -3712,7 +3714,7 @@ linux_process_target::wait (ptid_t ptid,
     }
   while ((target_options & TARGET_WNOHANG) == 0
 	 && event_ptid == null_ptid
-	 && ourstatus->kind == TARGET_WAITKIND_IGNORE);
+	 && ourstatus->kind () == TARGET_WAITKIND_IGNORE);
 
   /* If at least one stop was reported, there may be more.  A single
      SIGCHLD can signal more than one child stop.  */
@@ -3813,15 +3815,9 @@ mark_lwp_dead (struct lwp_info *lwp, int wstat)
   /* Store in waitstatus as well, as there's nothing else to process
      for this event.  */
   if (WIFEXITED (wstat))
-    {
-      lwp->waitstatus.kind = TARGET_WAITKIND_EXITED;
-      lwp->waitstatus.value.integer = WEXITSTATUS (wstat);
-    }
+    lwp->waitstatus.set_exited (WEXITSTATUS (wstat));
   else if (WIFSIGNALED (wstat))
-    {
-      lwp->waitstatus.kind = TARGET_WAITKIND_SIGNALLED;
-      lwp->waitstatus.value.sig = gdb_signal_from_host (WTERMSIG (wstat));
-    }
+    lwp->waitstatus.set_signalled (gdb_signal_from_host (WTERMSIG (wstat)));
 
   /* Prevent trying to stop it.  */
   lwp->stopped = 1;
@@ -4087,7 +4083,7 @@ linux_process_target::resume_one_lwp_throw (lwp_info *lwp, int step,
   if (lwp->stopped == 0)
     return;
 
-  gdb_assert (lwp->waitstatus.kind == TARGET_WAITKIND_IGNORE);
+  gdb_assert (lwp->waitstatus.kind () == TARGET_WAITKIND_IGNORE);
 
   fast_tpoint_collect_result fast_tp_collecting
     = lwp->collecting_fast_tracepoint;
@@ -4351,7 +4347,7 @@ linux_set_resume_request (thread_info *thread, thread_resume *resume, size_t n)
 	    {
 	      if (debug_threads)
 		debug_printf ("already %s LWP %ld at GDB's request\n",
-			      (thread->last_status.kind
+			      (thread->last_status.kind ()
 			       == TARGET_WAITKIND_STOPPED)
 			      ? "stopped"
 			      : "stopping",
@@ -4382,8 +4378,8 @@ linux_set_resume_request (thread_info *thread, thread_resume *resume, size_t n)
 	      struct lwp_info *rel = lwp->fork_relative;
 
 	      if (rel->status_pending_p
-		  && (rel->waitstatus.kind == TARGET_WAITKIND_FORKED
-		      || rel->waitstatus.kind == TARGET_WAITKIND_VFORKED))
+		  && (rel->waitstatus.kind () == TARGET_WAITKIND_FORKED
+		      || rel->waitstatus.kind () == TARGET_WAITKIND_VFORKED))
 		{
 		  if (debug_threads)
 		    debug_printf ("not resuming LWP %ld: has queued stop reply\n",
@@ -4771,7 +4767,7 @@ linux_process_target::resume_one_thread (thread_info *thread,
 
       /* For stop requests, we're done.  */
       lwp->resume = NULL;
-      thread->last_status.kind = TARGET_WAITKIND_IGNORE;
+      thread->last_status.set_ignore ();
       return;
     }
 
@@ -4818,7 +4814,7 @@ linux_process_target::resume_one_thread (thread_info *thread,
 	debug_printf ("leaving LWP %ld stopped\n", lwpid_of (thread));
     }
 
-  thread->last_status.kind = TARGET_WAITKIND_IGNORE;
+  thread->last_status.set_ignore ();
   lwp->resume = NULL;
 }
 
@@ -4918,7 +4914,7 @@ linux_process_target::proceed_one_lwp (thread_info *thread, lwp_info *except)
     }
 
   if (thread->last_resume_kind == resume_stop
-      && thread->last_status.kind != TARGET_WAITKIND_IGNORE)
+      && thread->last_status.kind () != TARGET_WAITKIND_IGNORE)
     {
       if (debug_threads)
 	debug_printf ("   client wants LWP to remain %ld stopped\n",