--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/config/riscv/withmultilib.h	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,51 @@
+/* MULTILIB_DEFAULTS definitions for --with-multilib-list.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published
+   by the Free Software Foundation; either version 3, or (at your
+   option) any later version.
+
+   GCC 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 General Public
+   License for more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#if TARGET_MLIB_ARCH == 1
+
+# if TARGET_MLIB_ABI == 1
+#  define MULTILIB_DEFAULTS {"march=rv32gc", "mabi=ilp32" }
+# elif TARGET_MLIB_ABI == 2
+#  define MULTILIB_DEFAULTS {"march=rv32gc", "mabi=ilp32f" }
+# elif TARGET_MLIB_ABI == 3
+#  define MULTILIB_DEFAULTS {"march=rv32gc", "mabi=ilp32d" }
+# else
+#  error "unsupported TARGET_MLIB_ABI value for rv32gc"
+# endif
+
+#elif TARGET_MLIB_ARCH == 2
+
+# if TARGET_MLIB_ABI == 4
+#  define MULTILIB_DEFAULTS {"march=rv64gc", "mabi=lp64" }
+# elif TARGET_MLIB_ABI == 5
+#  define MULTILIB_DEFAULTS {"march=rv64gc", "mabi=lp64f" }
+# elif TARGET_MLIB_ABI == 6
+#  define MULTILIB_DEFAULTS {"march=rv64gc", "mabi=lp64d" }
+# else
+#  error "unsupported TARGET_MLIB_ABI value for rv64gc"
+# endif
+
+#else
+# error "unsupported TARGET_MLIB_ARCH value"
+#endif