* alloc.c (valid_pointer_p): Use pipe, not open.

This fixes some permissions issues when debugging.

src/ChangeLog

 2011-07-18  Paul Eggert  <eggert@cs.ucla.edu>
 
+	* alloc.c (valid_pointer_p): Use pipe, not open.
+	This fixes some permissions issues when debugging.
+
 	* fileio.c (Fcopy_file): Adjust mode if fchown fails.  (Bug#9002)
 	If fchown fails to set both uid and gid, try to set just gid,
 	as that is sometimes allowed.  Adjust the file's mode to eliminate

src/alloc.c

@@ -4415,18 +4415,18 @@ valid_pointer_p (void *p)
 #ifdef WINDOWSNT
   return w32_valid_pointer_p (p, 16);
 #else
-  int fd;
+  int fd[2];
 
   /* Obviously, we cannot just access it (we would SEGV trying), so we
      trick the o/s to tell us whether p is a valid pointer.
      Unfortunately, we cannot use NULL_DEVICE here, as emacs_write may
      not validate p in that case.  */
 
-  if ((fd = emacs_open ("__Valid__Lisp__Object__", O_CREAT | O_WRONLY | O_TRUNC, 0666)) >= 0)
+  if (pipe (fd) == 0)
     {
-      int valid = (emacs_write (fd, (char *)p, 16) == 16);
-      emacs_close (fd);
-      unlink ("__Valid__Lisp__Object__");
+      int valid = (emacs_write (fd[1], (char *) p, 16) == 16);
+      emacs_close (fd[1]);
+      emacs_close (fd[0]);
       return valid;
     }