RISC-V: Generic library routines and assembly

This patch contains code that is more specific to the RISC-V ISA than it
is to Linux.  It contains string and math operations, C wrappers for
various assembly instructions, stack walking code, and uaccess.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

arch/riscv/lib/udivdi3.S

@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2016-2017 Free Software Foundation, Inc.
+ *
+ *   This program 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, version 2.
+ *
+ *   This program 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.
+ */
+
+  .globl __udivdi3
+__udivdi3:
+  mv    a2, a1
+  mv    a1, a0
+  li    a0, -1
+  beqz  a2, .L5
+  li    a3, 1
+  bgeu  a2, a1, .L2
+.L1:
+  blez  a2, .L2
+  slli  a2, a2, 1
+  slli  a3, a3, 1
+  bgtu  a1, a2, .L1
+.L2:
+  li    a0, 0
+.L3:
+  bltu  a1, a2, .L4
+  sub   a1, a1, a2
+  or    a0, a0, a3
+.L4:
+  srli  a3, a3, 1
+  srli  a2, a2, 1
+  bnez  a3, .L3
+.L5:
+  ret