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

2 files changed, 33 insertions, 38 deletions

diff --git a/gdb/nat/fork-inferior.c b/gdb/nat/fork-inferior.c
index c88cf4c..fc19f17 100644
--- a/gdb/nat/fork-inferior.c
+++ b/gdb/nat/fork-inferior.c
@@ -479,7 +479,6 @@ startup_inferior (process_stratum_target *proc_target, pid_t pid, int ntraps,
       ptid_t event_ptid;
 
       struct target_waitstatus ws;
-      memset (&ws, 0, sizeof (ws));
       event_ptid = target_wait (resume_ptid, &ws, 0);
 
       if (last_waitstatus != NULL)
@@ -487,11 +486,11 @@ startup_inferior (process_stratum_target *proc_target, pid_t pid, int ntraps,
       if (last_ptid != NULL)
 	*last_ptid = event_ptid;
 
-      if (ws.kind == TARGET_WAITKIND_IGNORE)
+      if (ws.kind () == TARGET_WAITKIND_IGNORE)
 	/* The inferior didn't really stop, keep waiting.  */
 	continue;
 
-      switch (ws.kind)
+      switch (ws.kind ())
 	{
 	  case TARGET_WAITKIND_SPURIOUS:
 	  case TARGET_WAITKIND_LOADED:
@@ -507,32 +506,28 @@ startup_inferior (process_stratum_target *proc_target, pid_t pid, int ntraps,
 	    target_terminal::ours ();
 	    target_mourn_inferior (event_ptid);
 	    error (_("During startup program terminated with signal %s, %s."),
-		   gdb_signal_to_name (ws.value.sig),
-		   gdb_signal_to_string (ws.value.sig));
+		   gdb_signal_to_name (ws.sig ()),
+		   gdb_signal_to_string (ws.sig ()));
 	    return resume_ptid;
 
 	  case TARGET_WAITKIND_EXITED:
 	    target_terminal::ours ();
 	    target_mourn_inferior (event_ptid);
-	    if (ws.value.integer)
+	    if (ws.exit_status ())
 	      error (_("During startup program exited with code %d."),
-		     ws.value.integer);
+		     ws.exit_status ());
 	    else
 	      error (_("During startup program exited normally."));
 	    return resume_ptid;
 
 	  case TARGET_WAITKIND_EXECD:
 	    /* Handle EXEC signals as if they were SIGTRAP signals.  */
-	    /* Free the exec'ed pathname, but only if this isn't the
-	       waitstatus we are returning to the caller.  */
-	    if (pending_execs != 1)
-	      xfree (ws.value.execd_pathname);
 	    resume_signal = GDB_SIGNAL_TRAP;
 	    switch_to_thread (proc_target, event_ptid);
 	    break;
 
 	  case TARGET_WAITKIND_STOPPED:
-	    resume_signal = ws.value.sig;
+	    resume_signal = ws.sig ();
 	    switch_to_thread (proc_target, event_ptid);
 	    break;
 	}
diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index 0bb87ec..fa0ed56 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -197,8 +197,6 @@ handle_exception (struct target_waitstatus *ourstatus, bool debug_exceptions)
 
   memcpy (&siginfo_er, rec, sizeof siginfo_er);
 
-  ourstatus->kind = TARGET_WAITKIND_STOPPED;
-
   /* Record the context of the current thread.  */
   thread_rec (ptid_t (current_event.dwProcessId, current_event.dwThreadId, 0),
 	      DONT_SUSPEND);
@@ -207,53 +205,53 @@ handle_exception (struct target_waitstatus *ourstatus, bool debug_exceptions)
     {
     case EXCEPTION_ACCESS_VIOLATION:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_ACCESS_VIOLATION");
-      ourstatus->value.sig = GDB_SIGNAL_SEGV;
+      ourstatus->set_stopped (GDB_SIGNAL_SEGV);
       if (handle_access_violation (rec))
 	return HANDLE_EXCEPTION_UNHANDLED;
       break;
     case STATUS_STACK_OVERFLOW:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_STACK_OVERFLOW");
-      ourstatus->value.sig = GDB_SIGNAL_SEGV;
+      ourstatus->set_stopped (GDB_SIGNAL_SEGV);
       break;
     case STATUS_FLOAT_DENORMAL_OPERAND:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_DENORMAL_OPERAND");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case EXCEPTION_ARRAY_BOUNDS_EXCEEDED:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_ARRAY_BOUNDS_EXCEEDED");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_FLOAT_INEXACT_RESULT:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_INEXACT_RESULT");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_FLOAT_INVALID_OPERATION:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_INVALID_OPERATION");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_FLOAT_OVERFLOW:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_OVERFLOW");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_FLOAT_STACK_CHECK:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_STACK_CHECK");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_FLOAT_UNDERFLOW:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_UNDERFLOW");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_FLOAT_DIVIDE_BY_ZERO:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_DIVIDE_BY_ZERO");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_INTEGER_DIVIDE_BY_ZERO:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_INTEGER_DIVIDE_BY_ZERO");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case STATUS_INTEGER_OVERFLOW:
       DEBUG_EXCEPTION_SIMPLE ("STATUS_INTEGER_OVERFLOW");
-      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      ourstatus->set_stopped (GDB_SIGNAL_FPE);
       break;
     case EXCEPTION_BREAKPOINT:
 #ifdef __x86_64__
@@ -263,7 +261,7 @@ handle_exception (struct target_waitstatus *ourstatus, bool debug_exceptions)
 	     on startup, first a BREAKPOINT for the 64bit ntdll.dll,
 	     then a WX86_BREAKPOINT for the 32bit ntdll.dll.
 	     Here we only care about the WX86_BREAKPOINT's.  */
-	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+	  ourstatus->set_spurious ();
 	  ignore_first_breakpoint = false;
 	}
       else if (wow64_process)
@@ -277,45 +275,45 @@ handle_exception (struct target_waitstatus *ourstatus, bool debug_exceptions)
 	     unconditionally.  */
 	  DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT");
 	  rec->ExceptionCode = DBG_CONTROL_C;
-	  ourstatus->value.sig = GDB_SIGNAL_INT;
+	  ourstatus->set_stopped (GDB_SIGNAL_INT);
 	  break;
 	}
 #endif
       /* FALLTHROUGH */
     case STATUS_WX86_BREAKPOINT:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT");
-      ourstatus->value.sig = GDB_SIGNAL_TRAP;
+      ourstatus->set_stopped (GDB_SIGNAL_TRAP);
       break;
     case DBG_CONTROL_C:
       DEBUG_EXCEPTION_SIMPLE ("DBG_CONTROL_C");
-      ourstatus->value.sig = GDB_SIGNAL_INT;
+      ourstatus->set_stopped (GDB_SIGNAL_INT);
       break;
     case DBG_CONTROL_BREAK:
       DEBUG_EXCEPTION_SIMPLE ("DBG_CONTROL_BREAK");
-      ourstatus->value.sig = GDB_SIGNAL_INT;
+      ourstatus->set_stopped (GDB_SIGNAL_INT);
       break;
     case EXCEPTION_SINGLE_STEP:
     case STATUS_WX86_SINGLE_STEP:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_SINGLE_STEP");
-      ourstatus->value.sig = GDB_SIGNAL_TRAP;
+      ourstatus->set_stopped (GDB_SIGNAL_TRAP);
       break;
     case EXCEPTION_ILLEGAL_INSTRUCTION:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_ILLEGAL_INSTRUCTION");
-      ourstatus->value.sig = GDB_SIGNAL_ILL;
+      ourstatus->set_stopped (GDB_SIGNAL_ILL);
       break;
     case EXCEPTION_PRIV_INSTRUCTION:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_PRIV_INSTRUCTION");
-      ourstatus->value.sig = GDB_SIGNAL_ILL;
+      ourstatus->set_stopped (GDB_SIGNAL_ILL);
       break;
     case EXCEPTION_NONCONTINUABLE_EXCEPTION:
       DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_NONCONTINUABLE_EXCEPTION");
-      ourstatus->value.sig = GDB_SIGNAL_ILL;
+      ourstatus->set_stopped (GDB_SIGNAL_ILL);
       break;
     case MS_VC_EXCEPTION:
       DEBUG_EXCEPTION_SIMPLE ("MS_VC_EXCEPTION");
       if (handle_ms_vc_exception (rec))
 	{
-	  ourstatus->value.sig = GDB_SIGNAL_TRAP;
+	  ourstatus->set_stopped (GDB_SIGNAL_TRAP);
 	  result = HANDLE_EXCEPTION_IGNORED;
 	  break;
 	}
@@ -329,11 +327,13 @@ handle_exception (struct target_waitstatus *ourstatus, bool debug_exceptions)
 	(unsigned) current_event.u.Exception.ExceptionRecord.ExceptionCode,
 	host_address_to_string (
 	  current_event.u.Exception.ExceptionRecord.ExceptionAddress));
-      ourstatus->value.sig = GDB_SIGNAL_UNKNOWN;
+      ourstatus->set_stopped (GDB_SIGNAL_UNKNOWN);
       break;
     }
 
-  last_sig = ourstatus->value.sig;
+  if (ourstatus->kind () == TARGET_WAITKIND_STOPPED)
+    last_sig = ourstatus->sig ();
+
   return result;
 
 #undef DEBUG_EXCEPTION_SIMPLE