diff --git a/compiler-rt/cmake/Modules/CompilerRTUtils.cmake b/compiler-rt/cmake/Modules/CompilerRTUtils.cmake
--- a/compiler-rt/cmake/Modules/CompilerRTUtils.cmake
+++ b/compiler-rt/cmake/Modules/CompilerRTUtils.cmake
@@ -153,6 +153,7 @@
 
 macro(detect_target_arch)
   check_symbol_exists(__arm__ "" __ARM)
+  check_symbol_exists(__AVR__ "" __AVR)
   check_symbol_exists(__aarch64__ "" __AARCH64)
   check_symbol_exists(__x86_64__ "" __X86_64)
   check_symbol_exists(__i386__ "" __I386)
@@ -170,6 +171,8 @@
   check_symbol_exists(__ve__ "" __VE)
   if(__ARM)
     add_default_target_arch(arm)
+  elseif(__AVR)
+    add_default_target_arch(avr)
   elseif(__AARCH64)
     add_default_target_arch(aarch64)
   elseif(__X86_64)
diff --git a/compiler-rt/cmake/base-config-ix.cmake b/compiler-rt/cmake/base-config-ix.cmake
--- a/compiler-rt/cmake/base-config-ix.cmake
+++ b/compiler-rt/cmake/base-config-ix.cmake
@@ -234,6 +234,8 @@
         test_target_arch(armhf "" "-march=armv7-a" "-mfloat-abi=hard")
         test_target_arch(armv6m "" "-march=armv6m" "-mfloat-abi=soft")
       endif()
+    elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "avr")
+      test_target_arch(avr "__AVR__" "--target=avr")
     elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "aarch32")
       test_target_arch(aarch32 "" "-march=armv8-a")
     elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "aarch64")
diff --git a/compiler-rt/cmake/builtin-config-ix.cmake b/compiler-rt/cmake/builtin-config-ix.cmake
--- a/compiler-rt/cmake/builtin-config-ix.cmake
+++ b/compiler-rt/cmake/builtin-config-ix.cmake
@@ -38,6 +38,7 @@
 
 set(ARM64 aarch64)
 set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k armv8m.main armv8.1m.main)
+set(AVR avr)
 set(HEXAGON hexagon)
 set(X86 i386)
 set(X86_64 x86_64)
@@ -60,7 +61,7 @@
 endif()
 
 set(ALL_BUILTIN_SUPPORTED_ARCH
-  ${X86} ${X86_64} ${ARM32} ${ARM64}
+  ${X86} ${X86_64} ${ARM32} ${ARM64} ${AVR}
   ${HEXAGON} ${MIPS32} ${MIPS64} ${PPC32} ${PPC64}
   ${RISCV32} ${RISCV64} ${SPARC} ${SPARCV9}
   ${WASM32} ${WASM64} ${VE})
diff --git a/compiler-rt/cmake/config-ix.cmake b/compiler-rt/cmake/config-ix.cmake
--- a/compiler-rt/cmake/config-ix.cmake
+++ b/compiler-rt/cmake/config-ix.cmake
@@ -203,8 +203,10 @@
 
 # Detect whether the current target platform is 32-bit or 64-bit, and setup
 # the correct commandline flags needed to attempt to target 32-bit and 64-bit.
+# AVR and MSP430 are omitted since they have 16-bit pointers.
 if (NOT CMAKE_SIZEOF_VOID_P EQUAL 4 AND
-    NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
+    NOT CMAKE_SIZEOF_VOID_P EQUAL 8 AND
+    NOT ${arch} MATCHES "avr|msp430")
   message(FATAL_ERROR "Please use architecture with 4 or 8 byte pointers.")
 endif()
 
diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
--- a/compiler-rt/lib/builtins/CMakeLists.txt
+++ b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -567,6 +567,13 @@
 set(armv8m.main_SOURCES ${arm_SOURCES})
 set(armv8.1m.main_SOURCES ${arm_SOURCES})
 
+# 8-bit AVR MCU
+set(avr_SOURCES
+  avr/mulqi3.S
+  avr/mulhi3.S
+  avr/exit.S
+)
+
 # hexagon arch
 set(hexagon_SOURCES
   hexagon/common_entry_exit_abi1.S
diff --git a/compiler-rt/lib/builtins/avr/exit.S b/compiler-rt/lib/builtins/avr/exit.S
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/builtins/avr/exit.S
@@ -0,0 +1,18 @@
+//===------------ exit.S - global terminator for AVR ----------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+	.text
+	.align 2
+
+	.globl _exit
+	.type  _exit, @function
+
+_exit:
+	cli                 ; Disable all interrupts.
+__stop_program:
+	rjmp __stop_program ; Fall into an infinite loop.
diff --git a/compiler-rt/lib/builtins/avr/mulhi3.S b/compiler-rt/lib/builtins/avr/mulhi3.S
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/builtins/avr/mulhi3.S
@@ -0,0 +1,58 @@
+//===------------ mulhi3.S - int16 multiplication -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// The corresponding C code is something like:
+//
+// int __mulhi3(int A, int B) {
+//   int S = 0;
+//   while (A != 0) {
+//     if (A & 1)
+//       S += B;
+//     A = ((unsigned int) A) >> 1;
+//     B <<= 1;
+//   }
+//   return S;
+// }
+//
+//===----------------------------------------------------------------------===//
+
+	.text
+	.align 2
+
+	.globl __mulhi3
+	.type  __mulhi3, @function
+
+__mulhi3:
+	eor    r28, r28
+	eor    r20, r20
+	eor    r21, r21         ; Initialize the result to 0: `S = 0;`.
+
+__mulhi3_loop:
+	cp     r24, r28
+	cpc    r25, r28         ; `while (A != 0) { ... }`
+	breq   __mulhi3_end     ; End the loop if A is 0.
+
+	mov    r29, r24
+	andi   r29, 1           ; `if (A & 1) { ... }`
+	breq   __mulhi3_loop_a  ; Omit the accumulation (`S += B;`) if  A's LSB is 0.
+
+	add    r20, r22
+	adc    r21, r23         ; Do the accumulation: `S += B;`.
+
+__mulhi3_loop_a:
+	lsr    r25
+	ror    r24              ; `A = ((unsigned int) A) >> 1;`.
+	lsl    r22
+	rol    r23              ; `B <<= 1;`
+
+	rjmp   __mulhi3_loop
+
+__mulhi3_end:
+	mov    r24, r20
+	mov    r25, r21
+	ret
diff --git a/compiler-rt/lib/builtins/avr/mulqi3.S b/compiler-rt/lib/builtins/avr/mulqi3.S
new file mode 100644
--- /dev/null
+++ b/compiler-rt/lib/builtins/avr/mulqi3.S
@@ -0,0 +1,31 @@
+//===------------ mulhi3.S - int8 multiplication --------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// The corresponding C code is something like:
+//
+// int __mulqi3(char A, char B) {
+//   return __mulhi3((int) A, (int) B);
+// }
+//
+//===----------------------------------------------------------------------===//
+
+	.text
+	.align 2
+
+	.globl __mulqi3
+	.type  __mulqi3, @function
+
+__mulqi3:
+	mov    r25, r24
+	lsl    r25
+	sbc    r25, r25         ; Promote A from char to int: `(int) A`.
+	mov    r23, r22
+	lsl    r23
+	sbc    r23, r23         ; Promote B from char to int: `(int) B`.
+	rcall  __mulhi3         ; `__mulhi3((int) A, (int) B);`.
+	ret