Index: compiler-rt/lib/builtins/CMakeLists.txt
===================================================================
--- compiler-rt/lib/builtins/CMakeLists.txt
+++ compiler-rt/lib/builtins/CMakeLists.txt
@@ -557,6 +557,7 @@
 set(riscv_SOURCES ${GENERIC_SOURCES} ${GENERIC_TF_SOURCES})
 set(riscv32_SOURCES
   riscv/mulsi3.S
+  riscv/muldi3.S
   ${riscv_SOURCES}
 )
 set(riscv64_SOURCES ${riscv_SOURCES})
Index: compiler-rt/lib/builtins/riscv/muldi3.S
===================================================================
--- /dev/null
+++ compiler-rt/lib/builtins/riscv/muldi3.S
@@ -0,0 +1,28 @@
+//===--- muldi3.S - Implement __muldi3 Interger Multiplication routine  ---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#if !defined(__riscv_mul) && __riscv_xlen == 64
+        .text
+        .align 2
+
+        .globl __muldi3
+        .type  __muldi3, @function
+__muldi3:
+        mv     a2, a0
+        mv     a0, zero
+.L1:
+        andi   a3, a1, 1
+        beqz   a3, .L2
+        add    a0, a0, a2
+.L2:
+        srli   a1, a1, 1
+        slli   a2, a2, 1
+        bnez   a1, .L1
+        ret
+#endif
+