[COMMITTED] NaCl: Implement nacl_interface_ext_supply entry point.

diff --git a/sysdeps/nacl/Makefile b/sysdeps/nacl/Makefile
index b51156b..6749a44 100644
--- a/sysdeps/nacl/Makefile
+++ b/sysdeps/nacl/Makefile
@@ -108,7 +108,7 @@  test-wrapper-env = $(test-wrapper-env-only)
 test-wrapper = $(test-wrapper-env) --
 
 ifeq ($(subdir),csu)
-sysdep_routines += nacl_interface_query \
+sysdep_routines += nacl_interface_query nacl_interface_ext_supply \
 		   nacl-interfaces $(call nacl-routines-of,libc)
 endif
 
diff --git a/sysdeps/nacl/Versions b/sysdeps/nacl/Versions
index 4ac56c2..cfc4a08 100644
--- a/sysdeps/nacl/Versions
+++ b/sysdeps/nacl/Versions
@@ -1,12 +1,14 @@ 
 ld {
   GLIBC_PRIVATE {
     __nacl_irt_*;
+    __nacl_supply_interface_rtld;
   }
 }
 
 libc {
   GLIBC_2.22 {
     nacl_interface_query;
+    nacl_interface_ext_supply;
   }
 
   GLIBC_PRIVATE {
diff --git a/sysdeps/nacl/nacl-interfaces.c b/sysdeps/nacl/nacl-interfaces.c
index cb0dcd0..5dbfadd 100644
--- a/sysdeps/nacl/nacl-interfaces.c
+++ b/sysdeps/nacl/nacl-interfaces.c
@@ -121,3 +121,45 @@  __nacl_initialize_interfaces (void)
   initialize_mandatory_interfaces ();
   initialize_optional_interfaces ();
 }
+
+
+static bool
+try_supply (const struct nacl_interface *const start,
+	    const struct nacl_interface *const stop,
+	    uintptr_t *all_tables,
+	    const char *ident, size_t ident_len,
+	    const void *table, size_t tablesize)
+{
+  const struct nacl_interface *i = start;
+  uintptr_t *t = all_tables;
+  while (i < stop)
+    {
+      if (i->table_size == tablesize
+	  && i->namelen == ident_len
+	  && !memcmp (i->name, ident, ident_len))
+	{
+	  memcpy (t, table, tablesize);
+	  return true;
+	}
+
+      t = next_nacl_table (t, i);
+      i = next_nacl_interface (i);
+    }
+
+  return false;
+}
+
+internal_function
+bool
+PASTE_NAME (__nacl_supply_interface_, MODULE_NAME)
+  (const char *ident, size_t ident_len, const void *table, size_t tablesize)
+{
+  return (try_supply (__start_nacl_mandatory_interface_names,
+		      __stop_nacl_mandatory_interface_names,
+		      __start_nacl_mandatory_interface_tables,
+		      ident, ident_len, table, tablesize)
+	  || try_supply (__start_nacl_optional_interface_names,
+			 __stop_nacl_optional_interface_names,
+			 __start_nacl_optional_interface_tables,
+			 ident, ident_len, table, tablesize));
+}
diff --git a/sysdeps/nacl/nacl-interfaces.h b/sysdeps/nacl/nacl-interfaces.h
index 0c886a5..36f3808 100644
--- a/sysdeps/nacl/nacl-interfaces.h
+++ b/sysdeps/nacl/nacl-interfaces.h
@@ -20,6 +20,7 @@ 
 #define _NACL_INTERFACES_H	1
 
 #include <errno.h>
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <sys/types.h>
@@ -73,7 +74,7 @@  next_nacl_interface (const struct nacl_interface *i)
 {
   uintptr_t align = __alignof (*i);
   return (const void *) (((uintptr_t) &i->name[i->namelen] + align - 1)
-                         & -align);
+			 & -align);
 }
 
 #if IS_IN (libpthread)
@@ -94,6 +95,12 @@  next_nacl_interface (const struct nacl_interface *i)
 #undef	NACL_OPTIONAL_INTERFACE
 
 extern void __nacl_initialize_interfaces (void) attribute_hidden;
+extern bool __nacl_supply_interface_libc (const char *ident, size_t ident_len,
+					  const void *table, size_t tablesize)
+  internal_function attribute_hidden;
+extern bool __nacl_supply_interface_rtld (const char *ident, size_t ident_len,
+					  const void *table, size_t tablesize);
+  internal_function;
 
 /* Convenience function for handling IRT call return values.  */
 static inline int
diff --git a/sysdeps/nacl/nacl_interface_ext_supply.c b/sysdeps/nacl/nacl_interface_ext_supply.c
new file mode 100644
index 0000000..a1525be
--- /dev/null
+++ b/sysdeps/nacl/nacl_interface_ext_supply.c
@@ -0,0 +1,42 @@ 
+/* Interface for the user to replace NaCl IRT interface functions.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <nacl-interfaces.h>
+#include <string.h>
+
+size_t
+nacl_interface_ext_supply (const char *interface_ident,
+			   const void *table, size_t tablesize)
+{
+  const size_t ident_len = strlen (interface_ident) + 1;
+
+  /* Most interfaces are in rtld, so try there first.  If other
+     libraries ever get their own tables not used in libc, then we
+     will need some dynamic registration mechanism here to iterate
+     over all libraries' __nacl_supply_interface_libfoo calls.  */
+  if (0
+#ifdef SHARED
+      || __nacl_supply_interface_rtld (interface_ident, ident_len,
+				       table, tablesize)
+#endif
+      || __nacl_supply_interface_libc (interface_ident, ident_len,
+				       table, tablesize))
+    return tablesize;
+
+  return 0;
+}