sh: Make exit without parameters from EXIT trap POSIX-compliant.

It should use the original exit status, just like falling off the
end of the trap handler.

Outside an EXIT trap, 'exit' is still equivalent to 'exit $?'.

bin/sh/main.c

@@ -341,10 +341,7 @@ exitcmd(int argc, char **argv)
 	if (stoppedjobs())
 		return 0;
 	if (argc > 1)
-		exitstatus = number(argv[1]);
+		exitshell(number(argv[1]));
 	else
-		exitstatus = oexitstatus;
-	exitshell(exitstatus);
-	/*NOTREACHED*/
-	return 0;
+		exitshell_savedstatus();
 }

bin/sh/trap.c

@@ -80,6 +80,9 @@ static volatile sig_atomic_t gotsig[NSIG];
 static int ignore_sigchld;	/* Used while handling SIGCHLD traps. */
 volatile sig_atomic_t gotwinch;
 
+static int exiting;		/* exitshell() has been called */
+static int exiting_exitstatus;	/* value passed to exitshell() */
+
 static int getsigaction(int, sig_t *);
 
 
@@ -477,11 +480,22 @@ setinteractive(int on)
  */
 void
 exitshell(int status)
+{
+	TRACE(("exitshell(%d) pid=%d\n", status, getpid()));
+	exiting = 1;
+	exiting_exitstatus = status;
+	exitshell_savedstatus();
+}
+
+void
+exitshell_savedstatus(void)
 {
 	struct jmploc loc1, loc2;
 	char *p;
 
-	TRACE(("exitshell(%d) pid=%d\n", status, getpid()));
+	if (!exiting)
+		exiting_exitstatus = oexitstatus;
+	exitstatus = oexitstatus = exiting_exitstatus;
 	if (setjmp(loc1.loc)) {
 		goto l1;
 	}
@@ -498,5 +512,5 @@ l1:   handler = &loc2;			/* probably unnecessary */
 #if JOBS
 	setjobctl(0);
 #endif
-l2:   _exit(status);
+l2:   _exit(exiting_exitstatus);
 }

bin/sh/trap.h

@@ -46,3 +46,4 @@ void onsig(int);
 void dotrap(void);
 void setinteractive(int);
 void exitshell(int) __dead2;
+void exitshell_savedstatus(void) __dead2;

tools/regression/bin/sh/builtins/exit3.0

@@ -0,0 +1,5 @@
+# $FreeBSD$
+
+# exit without arguments differs from exit $? in an EXIT trap.
+
+trap 'false; exit' 0