From: Ben Pfaff <blp@cs.stanford.edu>
Date: Mon, 20 Sep 2004 06:44:03 +0000 (+0000)
Subject: Introduce PID_ERROR as an invalid exec return value.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8a0c402207a9c4b0dc58f417ae3bc169c6f62f0f;p=pintos-anon

Introduce PID_ERROR as an invalid exec return value.
Make shell example check for invalid join return,
because passing an invalid value to exec is allowed to kill the
process.
---

diff --git a/src/lib/user/syscall.h b/src/lib/user/syscall.h
index d0a2250..188576d 100644
--- a/src/lib/user/syscall.h
+++ b/src/lib/user/syscall.h
@@ -5,6 +5,7 @@
 #include <debug.h>
 
 typedef int pid_t;
+#define PID_ERROR ((pid_t) -1)
 
 void halt (void) NO_RETURN;
 void exit (int status) NO_RETURN;
diff --git a/src/tests/userprog/shell.c b/src/tests/userprog/shell.c
index 905e18b..7b9570a 100644
--- a/src/tests/userprog/shell.c
+++ b/src/tests/userprog/shell.c
@@ -23,6 +23,12 @@ main (void)
       
       /* Execute command. */
       if (cp > command) 
-        join (exec (command));
+        {
+          pid_t pid = exec (command);
+          if (pid != PID_ERROR)
+            join (pid);
+          else
+            printf ("exec failed\n");
+        }
     }
 }