=== modified file 'src/fileio.c'
--- src/fileio.c	2014-09-02 11:41:22 +0000
+++ src/fileio.c	2014-09-02 11:47:45 +0000
@@ -1179,11 +1179,11 @@
 	      char newdir_utf8[MAX_UTF8_PATH];
 
 	      filename_from_ansi (newdir, newdir_utf8);
-	      tem = build_string (newdir_utf8);
+	      tem = alloca_string (newdir_utf8);
 	    }
 	  else
 #endif
-	    tem = build_string (newdir);
+	    tem = alloca_string (newdir);
 	  newdirlen = SBYTES (tem);
 	  if (multibyte && !STRING_MULTIBYTE (tem))
 	    {
@@ -1215,7 +1215,7 @@
 	      /* `getpwnam' may return a unibyte string, which will
 		 bite us since we expect the directory to be
 		 multibyte.  */
-	      tem = build_string (newdir);
+	      tem = alloca_string (newdir);
 	      newdirlen = SBYTES (tem);
 	      if (multibyte && !STRING_MULTIBYTE (tem))
 		{
@@ -1249,7 +1249,7 @@
 	    adir = NULL;
 	  else if (multibyte)
 	    {
-	      Lisp_Object tem = build_string (adir);
+	      Lisp_Object tem = alloca_string (adir);
 
 	      tem = DECODE_FILE (tem);
 	      newdirlen = SBYTES (tem);
@@ -1350,7 +1350,7 @@
 	    getcwd (adir, adir_size);
 	  if (multibyte)
 	    {
-	      Lisp_Object tem = build_string (adir);
+	      Lisp_Object tem = alloca_string (adir);
 
 	      tem = DECODE_FILE (tem);
 	      newdirlen = SBYTES (tem);

=== modified file 'src/lisp.h'
--- src/lisp.h	2014-09-02 06:49:40 +0000
+++ src/lisp.h	2014-09-02 12:31:01 +0000
@@ -4459,6 +4459,25 @@
   memcpy (alloca (SBYTES (string) + 1),		\
 	  SSDATA (string), SBYTES (string) + 1)
 
+/* Create temporary Lisp_String.  Use alloca and do not disturb GC.  */
+
+#define alloca_string(str)					\
+  ({ Lisp_Object string;					\
+     struct Lisp_String *s;					\
+     ptrdiff_t nchars, nbytes, size = strlen (str);		\
+     parse_str_as_multibyte ((const unsigned char *) str,	\
+			     size, &nchars, &nbytes);		\
+     s = alloca (sizeof *s + nbytes + 1);			\
+     s->data = (unsigned char *) s + sizeof (*s);		\
+     memcpy (s->data, str, nbytes);				\
+     s->data[size] = '\0';					\
+     s->intervals = NULL;					\
+     if (nbytes == nchars || nbytes != size)			\
+       s->size = size, s->size_byte = -1;			\
+     else							\
+       s->size = nchars, s->size_byte = nbytes;		\
+     XSETSTRING (string, s); string; })
+  
 /* Set up the name of the machine we're running on.  */
 extern void init_system_name (void);