Index: libc/locale/programs/ld-collate.c
===================================================================
--- libc.orig/locale/programs/ld-collate.c
+++ libc/locale/programs/ld-collate.c
@@ -161,6 +161,24 @@
   size_t line;
 };
 
+/* Data type for toggles.  */
+struct toggle_list_t;
+
+struct toggle_list_t
+{
+  const char *name;
+
+  /* Predecessor in the list.  */
+  struct toggle_list_t *last;
+
+  /* This flag is set when a keyword is undefined.  */
+  int is_undefined;
+
+  /* Where does the branch come from.  */
+  const char *file;
+  size_t line;
+};
+
 /* Sparse table of struct element_t *.  */
 #define TABLE wchead_table
 #define ELEMENT struct element_t *
@@ -214,6 +232,12 @@
   /* This value is used when handling ellipsis.  */
   struct element_t ellipsis_weight;
 
+  /* Known keywords.  */
+  struct toggle_list_t *defined_keywords;
+
+  /* This is a stack of toggle branches.  */
+  struct toggle_list_t *flow_control;
+
   /* Known collating elements.  */
   hash_table elem_table;
 
@@ -1456,6 +1480,56 @@
 }
 
 
+static struct token *
+flow_skip (struct linereader *ldfile, const struct charmap_t *charmap,
+	   struct locale_collate_t *collate)
+{
+  int level = 0;
+  struct token *now;
+  enum token_t nowtok;
+  while (1)
+    {
+      lr_ignore_rest (ldfile, 0);
+      now = lr_token (ldfile, charmap, NULL, NULL, 0);
+      nowtok = now->tok;
+      if (nowtok == tok_eof)
+	break;
+      else if (nowtok == tok_ifdef || nowtok == tok_ifndef)
+	++level ;
+      else if (nowtok == tok_else)
+	{
+	  if (strcmp (collate->flow_control->name, "else") == 0)
+	    lr_error (ldfile,
+		      _("%s: `else' statement at `%s:%d' cannot be followed by another `else' statement"),
+		      "LC_COLLATE", collate->flow_control->name, collate->flow_control->line);
+	  if (level == 0)
+	    {
+	      collate->flow_control->name = "else";
+	      collate->flow_control->file = ldfile->fname;
+	      collate->flow_control->line = ldfile->lineno;
+	      break;
+	    }
+	}
+      else if (nowtok == tok_endif)
+	{
+	  if (level == 0)
+	    {
+	      collate->flow_control = collate->flow_control->last;
+	      break;
+	    }
+	  --level ;
+	}
+    }
+  if (nowtok == tok_eof)
+    WITH_CUR_LOCALE (error (0, 0, _("\
+%s: unterminated `%s' flow control beginning at %s:%d"),
+				 "LC_COLLATE", collate->flow_control->name,
+				 collate->flow_control->file,
+				 collate->flow_control->line));
+  return now;
+}
+
+
 static void
 collate_startup (struct linereader *ldfile, struct localedef_t *locale,
 		 struct localedef_t *copy_locale, int ignore_content)
@@ -3770,6 +3844,205 @@
 			  repertoire, result, nowtok);
 	  break;
 
+	case tok_define:
+	  /* Ignore the rest of the line if we don't need the input of
+	     this line.  */
+	  if (ignore_content)
+	    {
+	      lr_ignore_rest (ldfile, 0);
+	      break;
+	    }
+
+	  arg = lr_token (ldfile, charmap, result, NULL, verbose);
+	  if (arg->tok != tok_ident)
+	    goto err_label;
+	  else
+	    {
+	      struct toggle_list_t *runp = collate->defined_keywords;
+	      char *name;
+
+	      while (runp != NULL)
+		if (strncmp (runp->name, arg->val.str.startmb,
+			     arg->val.str.lenmb) == 0
+		    && runp->name[arg->val.str.lenmb] == '\0')
+		  break;
+		else
+		  runp = runp->last;
+
+	      if (runp != NULL && runp->is_undefined == 0)
+		{
+		  lr_ignore_rest (ldfile, 0);
+		  break;
+		}
+
+	      if (runp == NULL)
+		{
+		  runp = (struct toggle_list_t *) xcalloc (1, sizeof (*runp));
+		  runp->last = collate->defined_keywords;
+		  collate->defined_keywords = runp;
+		}
+	      else
+		{
+		  free ((char *) runp->name);
+		  runp->is_undefined = 0;
+		}
+
+	      name = (char *) xmalloc (arg->val.str.lenmb + 1);
+	      memcpy (name, arg->val.str.startmb, arg->val.str.lenmb);
+	      name[arg->val.str.lenmb] = '\0';
+	      runp->name = name;
+	    }
+	  lr_ignore_rest (ldfile, 1);
+	  break;
+
+	case tok_undef:
+	  /* Ignore the rest of the line if we don't need the input of
+	     this line.  */
+	  if (ignore_content)
+	    {
+	      lr_ignore_rest (ldfile, 0);
+	      break;
+	    }
+
+	  arg = lr_token (ldfile, charmap, result, NULL, verbose);
+	  if (arg->tok != tok_ident)
+	    goto err_label;
+	  else
+	    {
+	      struct toggle_list_t *runp = collate->defined_keywords;
+	      while (runp != NULL)
+		if (strncmp (runp->name, arg->val.str.startmb,
+			     arg->val.str.lenmb) == 0
+		    && runp->name[arg->val.str.lenmb] == '\0')
+		{
+		  runp->is_undefined = 1;
+		  break;
+		}
+		else
+		  runp = runp->last;
+	    }
+	  lr_ignore_rest (ldfile, 1);
+	  break;
+
+	case tok_ifdef:
+	  /* Ignore the rest of the line if we don't need the input of
+	     this line.  */
+	  if (ignore_content)
+	    {
+	      lr_ignore_rest (ldfile, 0);
+	      break;
+	    }
+
+	  arg = lr_token (ldfile, charmap, result, NULL, verbose);
+	  if (arg->tok != tok_ident)
+	    goto err_label;
+	  else
+	    {
+	      struct toggle_list_t *runp = collate->defined_keywords;
+	      struct toggle_list_t *flow = (struct toggle_list_t *) xcalloc (1, sizeof (*runp));
+	      flow->name = "ifdef";
+	      flow->file = ldfile->fname;
+	      flow->line = ldfile->lineno;
+	      flow->last = collate->flow_control;
+	      collate->flow_control = flow;
+
+	      while (runp != NULL)
+		if (strncmp (runp->name, arg->val.str.startmb,
+			     arg->val.str.lenmb) == 0
+		    && runp->name[arg->val.str.lenmb] == '\0')
+		  break;
+		else
+		  runp = runp->last;
+
+	      if (runp == NULL)
+		{
+		  now = flow_skip(ldfile, charmap, collate);
+		  if (now->tok == tok_eof)
+		    WITH_CUR_LOCALE (error (0, 0, _("\
+%s: unterminated `%s' flow control"), "LC_COLLATE", collate->flow_control->name));
+		}
+	    }
+	  lr_ignore_rest (ldfile, 1);
+	  break;
+
+	case tok_ifndef:
+	  /* Ignore the rest of the line if we don't need the input of
+	     this line.  */
+	  if (ignore_content)
+	    {
+	      lr_ignore_rest (ldfile, 0);
+	      break;
+	    }
+
+	  arg = lr_token (ldfile, charmap, result, NULL, verbose);
+	  if (arg->tok != tok_ident)
+	    goto err_label;
+	  else
+	    {
+	      struct toggle_list_t *runp = collate->defined_keywords;
+	      struct toggle_list_t *flow = (struct toggle_list_t *) xcalloc (1, sizeof (*runp));
+	      flow->name = "ifndef";
+	      flow->file = ldfile->fname;
+	      flow->line = ldfile->lineno;
+	      flow->last = collate->flow_control;
+	      collate->flow_control = flow;
+
+	      while (runp != NULL)
+		if (strncmp (runp->name, arg->val.str.startmb,
+			     arg->val.str.lenmb) == 0
+		    && runp->name[arg->val.str.lenmb] == '\0')
+		  break;
+		else
+		  runp = runp->last;
+
+	      if (runp != NULL)
+		{
+		  now = flow_skip(ldfile, charmap, collate);
+		  if (now->tok == tok_eof)
+		    WITH_CUR_LOCALE (error (0, 0, _("\
+%s: unterminated `%s' flow control"), "LC_COLLATE", collate->flow_control->name));
+		}
+	    }
+	  lr_ignore_rest (ldfile, 1);
+	  break;
+
+	case tok_else:
+	  /* Ignore the rest of the line if we don't need the input of
+	     this line.  */
+	  if (ignore_content)
+	    {
+	      lr_ignore_rest (ldfile, 0);
+	      break;
+	    }
+
+	  if (strcmp (collate->flow_control->name, "else") == 0)
+	    lr_error (ldfile,
+		      _("%s: `else' statement at `%s:%d' cannot be followed by another `else' statement"),
+		      "LC_COLLATE", collate->flow_control->name, collate->flow_control->line);
+	  collate->flow_control->name = "else";
+	  collate->flow_control->file = ldfile->fname;
+	  collate->flow_control->line = ldfile->lineno;
+	  now = flow_skip(ldfile, charmap, collate);
+	  if (now->tok == tok_eof)
+	    WITH_CUR_LOCALE (error (0, 0, _("\
+%s: unterminated `%s' flow control"), "LC_COLLATE", collate->flow_control->name));
+	  break;
+
+	case tok_endif:
+	  /* Ignore the rest of the line if we don't need the input of
+	     this line.  */
+	  if (ignore_content)
+	    {
+	      lr_ignore_rest (ldfile, 0);
+	      break;
+	    }
+
+	  if (collate->flow_control == NULL)
+	    goto err_label;
+	  else
+	    collate->flow_control = collate->flow_control->last;
+	  break;
+
 	case tok_end:
 	  /* Next we assume `LC_COLLATE'.  */
 	  if (!ignore_content)
@@ -3799,6 +4072,12 @@
 	      else if (state == 5)
 		WITH_CUR_LOCALE (error (0, 0, _("\
 %s: missing `reorder-sections-end' keyword"), "LC_COLLATE"));
+	      if (collate->flow_control != NULL)
+		WITH_CUR_LOCALE (error (0, 0, _("\
+%s: unterminated `%s' flow control beginning at %s:%d"),
+				 "LC_COLLATE", collate->flow_control->name,
+				 collate->flow_control->file,
+				 collate->flow_control->line));
 	    }
 	  arg = lr_token (ldfile, charmap, result, NULL, verbose);
 	  if (arg->tok == tok_eof)