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, 20 insertions, 30 deletions

diff --git a/gdbserver/netbsd-low.cc b/gdbserver/netbsd-low.cc
index 84e34d0..ada92c1 100644
--- a/gdbserver/netbsd-low.cc
+++ b/gdbserver/netbsd-low.cc
@@ -206,20 +206,11 @@ static void
 netbsd_store_waitstatus (struct target_waitstatus *ourstatus, int hoststatus)
 {
   if (WIFEXITED (hoststatus))
-    {
-      ourstatus->kind = TARGET_WAITKIND_EXITED;
-      ourstatus->value.integer = WEXITSTATUS (hoststatus);
-    }
+    ourstatus->set_exited (WEXITSTATUS (hoststatus));
   else if (!WIFSTOPPED (hoststatus))
-    {
-      ourstatus->kind = TARGET_WAITKIND_SIGNALLED;
-      ourstatus->value.sig = gdb_signal_from_host (WTERMSIG (hoststatus));
-    }
+    ourstatus->set_signalled (gdb_signal_from_host (WTERMSIG (hoststatus)));
   else
-    {
-      ourstatus->kind = TARGET_WAITKIND_STOPPED;
-      ourstatus->value.sig = gdb_signal_from_host (WSTOPSIG (hoststatus));
-    }
+    ourstatus->set_stopped (gdb_signal_from_host (WSTOPSIG (hoststatus)));
 }
 
 /* Implement a safe wrapper around waitpid().  */
@@ -258,14 +249,14 @@ netbsd_wait (ptid_t ptid, struct target_waitstatus *ourstatus,
   if (pid == 0)
     {
       gdb_assert (target_options & TARGET_WNOHANG);
-      ourstatus->kind = TARGET_WAITKIND_IGNORE;
+      ourstatus->set_ignore ();
       return null_ptid;
     }
 
   gdb_assert (pid != -1);
 
   /* If the child stopped, keep investigating its status.  */
-  if (ourstatus->kind != TARGET_WAITKIND_STOPPED)
+  if (ourstatus->kind () != TARGET_WAITKIND_STOPPED)
     return wptid;
 
   /* Extract the event and thread that received a signal.  */
@@ -307,12 +298,11 @@ netbsd_wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 	 Ignore exited events for an unknown LWP.  */
       thread_info *thr = find_thread_ptid (wptid);
       if (thr == nullptr)
-	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+	  ourstatus->set_spurious ();
       else
 	{
-	  ourstatus->kind = TARGET_WAITKIND_THREAD_EXITED;
 	  /* NetBSD does not store an LWP exit status.  */
-	  ourstatus->value.integer = 0;
+	  ourstatus->set_thread_exited (0);
 
 	  remove_thread (thr);
 	}
@@ -329,20 +319,19 @@ netbsd_wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 	 not yet reported their PTRACE_LWP_CREATE event.  Ignore
 	 born events for an already-known LWP.  */
       if (find_thread_ptid (wptid))
-	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+	ourstatus->set_spurious ();
       else
 	{
 	  add_thread (wptid, NULL);
-	  ourstatus->kind = TARGET_WAITKIND_THREAD_CREATED;
+	  ourstatus->set_thread_created ();
 	}
       return wptid;
     }
 
   if (code == TRAP_EXEC)
     {
-      ourstatus->kind = TARGET_WAITKIND_EXECD;
-      ourstatus->value.execd_pathname
-	= xstrdup (netbsd_nat::pid_to_exec_file (pid));
+      ourstatus->set_execd
+	(make_unique_xstrdup (netbsd_nat::pid_to_exec_file (pid)));
       return wptid;
     }
 
@@ -356,14 +345,15 @@ netbsd_wait (ptid_t ptid, struct target_waitstatus *ourstatus,
       if (!netbsd_catch_this_syscall(sysnum))
 	{
 	  /* If the core isn't interested in this event, ignore it.  */
-	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+	  ourstatus->set_spurious ();
 	  return wptid;
 	}
 
-      ourstatus->kind
-	= ((code == TRAP_SCE) ? TARGET_WAITKIND_SYSCALL_ENTRY :
-	   TARGET_WAITKIND_SYSCALL_RETURN);
-      ourstatus->value.syscall_number = sysnum;
+      if (code == TRAP_SCE)
+	ourstatus->set_syscall_entry (sysnum);
+      else
+	ourstatus->set_syscall_return (sysnum);
+
       return wptid;
     }
 
@@ -381,7 +371,7 @@ netbsd_wait (ptid_t ptid, struct target_waitstatus *ourstatus,
     }
 
   /* Unclassified SIGTRAP event.  */
-  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+  ourstatus->set_spurious ();
   return wptid;
 }
 
@@ -401,10 +391,10 @@ netbsd_process_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 	 This may also happen on attach, when an event is registered on a thread
 	 that was not fully initialized during the attach stage.  */
       if (wptid.lwp () != 0 && !find_thread_ptid (wptid)
-	  && ourstatus->kind != TARGET_WAITKIND_THREAD_EXITED)
+	  && ourstatus->kind () != TARGET_WAITKIND_THREAD_EXITED)
 	add_thread (wptid, nullptr);
 
-      switch (ourstatus->kind)
+      switch (ourstatus->kind ())
 	{
 	case TARGET_WAITKIND_EXITED:
 	case TARGET_WAITKIND_STOPPED: