Do not allow a dumped Emacs to be dumped

src/ChangeLog

@@ -1,3 +1,12 @@
+2014-03-21  Daniel Colascione  <dancol@dancol.org>
+
+	Always prohibit dumping a dumped Emacs.
+
+	* emacs.c (might_dump): New variable.
+	(Fdump_emacs): Always prohibit dumping of dumped Emacs.
+	* lisp.h (might_dump): Declare.
+	* unexcw.c (unexec): Remove now-redundant multiple-dump detection code.
+
 2014-03-20  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* doc.c (store_function_docstring): Fix pointer signedness mismatch.

src/emacs.c

@@ -121,6 +121,9 @@ Lisp_Object Vlibrary_cache;
    on subsequent starts.  */
 bool initialized;
 
+/* Set to true if this instance of Emacs might dump.  */
+bool might_dump;
+
 #ifdef DARWIN_OS
 extern void unexec_init_emacs_zone (void);
 #endif
@@ -1631,6 +1634,10 @@ Using an Emacs configured with --with-x-toolkit=lucid does not have this problem
 #endif
 #endif
 
+#ifndef CANNOT_DUMP
+  might_dump = !initialized;
+#endif
+
   initialized = 1;
 
 #ifdef LOCALTIME_CACHE
@@ -2082,6 +2089,9 @@ You must run Emacs in batch mode in order to dump it.  */)
   if (! noninteractive)
     error ("Dumping Emacs works only in batch mode");
 
+  if (!might_dump)
+    error ("Emacs can be dumped only once");
+
 #ifdef GNU_LINUX
 
   /* Warn if the gap between BSS end and heap start is larger than this.  */

src/lisp.h

@@ -800,6 +800,7 @@ extern _Noreturn Lisp_Object wrong_type_argument (Lisp_Object, Lisp_Object);
 
 /* Defined in emacs.c.  */
 extern bool initialized;
+extern bool might_dump;
 
 /* Defined in eval.c.  */
 extern Lisp_Object Qautoload;

src/unexcw.c

@@ -286,13 +286,6 @@ unexec (const char *outfile, const char *infile)
   int ret;
   int ret2;
 
-  if (bss_sbrk_did_unexec)
-    {
-      /* can only dump once */
-      printf ("You can only dump Emacs once on this platform.\n");
-      return;
-    }
-
   report_sheap_usage (1);
 
   infile = add_exe_suffix_if_necessary (infile, infile_buffer);