diff --git a/build/config.gni b/build/config.gni
index 2a1b78893a02962eb258cf5e72c43bc3e8ad9b42..5ed59b245ff197686a0327e0446b8a350d6527c9 100644
--- a/build/config.gni
+++ b/build/config.gni
@@ -14,7 +14,12 @@
 #
 # Toolchain setup
 
-CLANG_PATH = "${MAPLE_ROOT}/tools/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04"
+if (OLD_OS == "1") {
+  CLANG_PATH = "${MAPLE_ROOT}/tools/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04"
+} else {
+  CLANG_PATH = "/usr"
+}
+
 ANDROID_GCC_PATH = "${MAPLE_ROOT}/tools/gcc"
 ANDROID_CLANG_PATH = "${MAPLE_ROOT}/tools/clang-r353983c"
 GCC_LINARO_PATH = "${MAPLE_ROOT}/tools/gcc-linaro-7.5.0"
diff --git a/build/config/BUILDCONFIG.gn b/build/config/BUILDCONFIG.gn
index 1fa4e65631d70795ce7786eaa966a181bc1001c4..84af356ab1c76de937758fe9e414de9fd090babf 100644
--- a/build/config/BUILDCONFIG.gn
+++ b/build/config/BUILDCONFIG.gn
@@ -31,6 +31,12 @@ MAPLE_ROOT = getenv("MAPLE_ROOT")
 ANDROID_ROOT = "${MAPLE_ROOT}/android"
 MAPLE_BUILD_TYPE = getenv("MAPLE_BUILD_TYPE")
 MAPLE_BUILD_OUTPUT = getenv("MAPLE_BUILD_OUTPUT")
+OLD_OS = getenv("OLD_OS")
+if (OLD_OS == "1") {
+  DESIGNATOR="-Wno-gnu-designator"
+} else {
+  DESIGNATOR="-Wno-c99-designator"
+}
 
 DYNAMICLANG = true
 RC_V2 = true
@@ -108,6 +114,7 @@ cflags_c += [
   "-Werror",
   "-Wdate-time",
   "-Wfloat-equal",
+  "${DESIGNATOR}",
 ]
 
 cflags_cc += [
@@ -120,6 +127,7 @@ cflags_cc += [
   "-Werror",
   "-Wdate-time",
   "-Wfloat-equal",
+  "${DESIGNATOR}",
 ]
 
 if (HOST_ARCH == 64) {
diff --git a/build/core/maple_variables.mk b/build/core/maple_variables.mk
index c28d4b151b79b7e3f7b34de65ede945c51de81e6..a529a6f6aa75684acfb44f26070c49dcf30ee226 100644
--- a/build/core/maple_variables.mk
+++ b/build/core/maple_variables.mk
@@ -18,7 +18,12 @@ LIB_CORE_PATH := $(MAPLE_BUILD_OUTPUT)/libjava-core
 LIB_CORE_JAR := $(LIB_CORE_PATH)/java-core.jar
 LIB_CORE_MPLT := $(LIB_CORE_PATH)/java-core.mplt
 
-CLANG_PATH := $(MAPLE_ROOT)/tools/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04
+ifeq ($(OLD_OS), 1)
+  CLANG_PATH = "${MAPLE_ROOT}/tools/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04"
+else
+  CLANG_PATH = "/usr"
+endif
+
 ANDROID_GCC_PATH := $(MAPLE_ROOT)/tools/gcc
 ANDROID_CLANG_PATH := $(MAPLE_ROOT)/tools/clang-r353983c
 GCC_LINARO_PATH := $(MAPLE_ROOT)/tools/gcc-linaro-7.5.0
@@ -65,13 +70,13 @@ ifeq ($(OPS_ANDROID), 0)
     QEMU_CLANG_FLAGS += -nostdlibinc \
       --gcc-toolchain=$(GCC_LINARO_PATH) \
       --sysroot=$(GCC_LINARO_PATH)/aarch64-linux-gnu/libc \
-      -isystem $(GCC_LINARO_PATH)/bin/../lib/gcc/aarch64-linux-gnu/7.5.0/../../../../aarch64-linux-gnu/include/c++/7.5.0 \
-      -isystem $(GCC_LINARO_PATH)/bin/../lib/gcc/aarch64-linux-gnu/7.5.0/../../../../aarch64-linux-gnu/include/c++/7.5.0/aarch64-linux-gnu \
-      -isystem $(GCC_LINARO_PATH)/bin/../lib/gcc/aarch64-linux-gnu/7.5.0/../../../../aarch64-linux-gnu/include/c++/7.5.0/backward \
-      -isystem $(GCC_LINARO_PATH)/bin/../lib/gcc/aarch64-linux-gnu/7.5.0/include \
-      -isystem $(GCC_LINARO_PATH)/bin/../lib/gcc/aarch64-linux-gnu/7.5.0/include-fixed \
-      -isystem $(GCC_LINARO_PATH)/bin/../lib/gcc/aarch64-linux-gnu/7.5.0/../../../../aarch64-linux-gnu/include \
-      -isystem $(GCC_LINARO_PATH)/bin/../aarch64-linux-gnu/libc/usr/include \
+      -isystem $(GCC_LINARO_PATH)/aarch64-linux-gnu/include/c++/7.5.0 \
+      -isystem $(GCC_LINARO_PATH)/aarch64-linux-gnu/include/c++/7.5.0/aarch64-linux-gnu \
+      -isystem $(GCC_LINARO_PATH)/aarch64-linux-gnu/include/c++/7.5.0/backward \
+      -isystem $(GCC_LINARO_PATH)/lib/gcc/aarch64-linux-gnu/7.5.0/include \
+      -isystem $(GCC_LINARO_PATH)/lib/gcc/aarch64-linux-gnu/7.5.0/include-fixed \
+      -isystem $(GCC_LINARO_PATH)/aarch64-linux-gnu/include \
+      -isystem $(GCC_LINARO_PATH)/aarch64-linux-gnu/libc/usr/include \
       -target aarch64-linux-gnu
 else
     QEMU_CLANG_FLAGS := -Wall -fstack-protector-strong -fPIC -Werror -Wno-unused-command-line-argument \
diff --git a/build/envsetup.sh b/build/envsetup.sh
index 81e8417c653f978114c1d9d76c8b3c82bbc931b3..f61521763c8ce34bbf0e3597cdb8b09521b03046 100644
--- a/build/envsetup.sh
+++ b/build/envsetup.sh
@@ -41,6 +41,14 @@ fi
 export GCOV_PREFIX=${MAPLE_ROOT}/report/gcda
 export GCOV_PREFIX_STRIP=7
 
+OS_VERSION=`lsb_release -r | sed -e "s/^[^0-9]*//" -e "s/\..*//"`
+if [ "$OS_VERSION" = "16" ] || [ "$OS_VERSION" = "18" ]; then
+  OLD_OS=1
+else
+  OLD_OS=0
+fi
+export OLD_OS=${OLD_OS}
+
 # workaround for current build
 if [ "$#" -eq 0 ]; then
 unset MAPLE_BUILD_OUTPUT
diff --git a/doc/cn/DevelopmentPreparation.md b/doc/cn/DevelopmentPreparation.md
index 40d597820ad4618c3fc18d4cfde2b8bfe046fd4d..83be18d14c35ca23d65e5e2517479c8d6e0049ee 100644
--- a/doc/cn/DevelopmentPreparation.md
+++ b/doc/cn/DevelopmentPreparation.md
@@ -10,12 +10,21 @@
 
 ## 开发环境推荐
 
-您需要安装一个64位版本的Ubuntu（推荐Ubuntu 16.04）
+您需要安装一个64位版本的Ubuntu（Ubuntu 16.04，18.04，20.04皆可）
 
 
 ```
+sudo apt-get -y install clang llvm lld libelf-dev libssl-dev python
 sudo apt-get -y install openjdk-8-jdk git-core build-essential zlib1g-dev libc6-dev-i386 g++-multilib gcc-multilib linux-libc-dev:i386
+
+Ubuntu 16.04:
 sudo apt-get -y install gcc-5-aarch64-linux-gnu g++-5-aarch64-linux-gnu
+
+Ubuntu 18.04:
+sudo apt-get -y install gcc-7-aarch64-linux-gnu g++-7-aarch64-linux-gnu
+
+Ubuntu 20.04:
+sudo apt-get -y install gcc-9-aarch64-linux-gnu g++-9-aarch64-linux-gnu
 ```
 
 ## 自动安装工具
@@ -25,7 +34,7 @@ tools/setup_tools.sh
 ```
 
 
-## 安装Clang编译器并完成配置（用于编译方舟编译器代码）
+## 安装Clang编译器并完成配置（用于编译方舟编译器代码，已改为使用系统安装的Clang）
 
 下载**clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04** (具体版本请根据系统版本确定)
 
diff --git a/src/mapleall/mpl2mpl/src/reflection_analysis.cpp b/src/mapleall/mpl2mpl/src/reflection_analysis.cpp
index 4a65fa8c35de1c09bb774b90c66ff9759454ecd7..5ca55d7c60e092923fe0c062a058581c90ecabe0 100755
--- a/src/mapleall/mpl2mpl/src/reflection_analysis.cpp
+++ b/src/mapleall/mpl2mpl/src/reflection_analysis.cpp
@@ -1546,7 +1546,7 @@ void ReflectionAnalysis::GenClassMetaData(Klass &klass) {
   }
   if (structType->IsMIRClassType()) {
     MIRClassType *classType = static_cast<MIRClassType*>(structType);
-    for (TyIdx const kTyIdx : classType->GetInterfaceImplemented()) {
+    for (TyIdx const &kTyIdx : classType->GetInterfaceImplemented()) {
       Klass *interface = klassH->GetKlassFromTyIdx(kTyIdx);
       if (interface == nullptr) {
         MIRType *type = GlobalTables::GetTypeTable().GetTypeFromTyIdx(kTyIdx);
diff --git a/src/mplfe/common/src/fe_type_manager.cpp b/src/mplfe/common/src/fe_type_manager.cpp
index d03ed9d12f2010448cc4149c65306c616e076862..11ea27e59871047ec53e897a1320834a80666c23 100644
--- a/src/mplfe/common/src/fe_type_manager.cpp
+++ b/src/mplfe/common/src/fe_type_manager.cpp
@@ -142,7 +142,7 @@ void FETypeManager::CheckSameNamePolicy() const {
   if (result.size() > 0) {
     WARN(kLncWarn, "========== Structs list with the same name ==========");
   }
-  for (const std::pair<GStrIdx, std::list<GStrIdx>> &item : result) {
+  for (const std::pair<const GStrIdx, std::list<GStrIdx>> &item : result) {
     std::string typeName = GlobalTables::GetStrTable().GetStringFromStrIdx(item.first);
     WARN(kLncWarn, "Type: %s", typeName.c_str());
     for (const GStrIdx &mpltNameIdx : item.second) {
@@ -584,4 +584,4 @@ MIRFunction *FETypeManager::GetMCCFunction(const GStrIdx &funcNameIdx) const {
     return it->second;
   }
 }
-}  // namespace maple
\ No newline at end of file
+}  // namespace maple
diff --git a/src/mplfe/common/src/feir_stmt.cpp b/src/mplfe/common/src/feir_stmt.cpp
index 1c7befe89481d922674f820307844bff91bf0e95..79f2433e9241f27277dd44164c6313a67c0e5b58 100644
--- a/src/mplfe/common/src/feir_stmt.cpp
+++ b/src/mplfe/common/src/feir_stmt.cpp
@@ -449,7 +449,7 @@ FEIRStmtSwitch::~FEIRStmtSwitch() {
 std::list<StmtNode*> FEIRStmtSwitch::GenMIRStmtsImpl(MIRBuilder &mirBuilder) const {
   std::list<StmtNode*> ans;
   CaseVector switchTable(mirBuilder.GetCurrentFuncCodeMpAllocator()->Adapter());
-  for (const std::pair<int32, FEIRStmtPesudoLabel*> &targetPair : mapValueTargets) {
+  for (const std::pair<const int32, FEIRStmtPesudoLabel*> &targetPair : mapValueTargets) {
     CHECK_NULL_FATAL(targetPair.second);
     switchTable.push_back(std::make_pair(targetPair.first, targetPair.second->GetMIRLabelIdx()));
   }
diff --git a/src/mplfe/jbc_input/include/jbc_attr.h b/src/mplfe/jbc_input/include/jbc_attr.h
index 4d6cf42a883d41828ca9476b7408d51ebaa3de11..0fba2413cefd7bffa2bffd48c3abaf6527669166 100644
--- a/src/mplfe/jbc_input/include/jbc_attr.h
+++ b/src/mplfe/jbc_input/include/jbc_attr.h
@@ -166,7 +166,7 @@ class JBCAttrCode : public JBCAttr {
   ~JBCAttrCode();
   void InitLocalVarInfo();
   void SetLoadStoreType() const;
-  const MapleMap<uint32, JBCOp*> &GetInstMap() const {
+  const MapleMap<const uint32, JBCOp*> &GetInstMap() const {
     return instructions;
   }
 
@@ -218,7 +218,7 @@ class JBCAttrCode : public JBCAttr {
   MapleVector<attr::ExceptionTableItem*> exceptions;
   uint16 nAttr;
   MapleVector<JBCAttr*> attrs;
-  MapleMap<uint32, JBCOp*> instructions;
+  MapleMap<const uint32, JBCOp*> instructions;
   JBCAttrMap attrMap;
   JBCAttrLocalVariableInfo localVarInfo;
 };
diff --git a/src/mplfe/jbc_input/src/jbc_attr.cpp b/src/mplfe/jbc_input/src/jbc_attr.cpp
index 977bc653eb9ebb2ba689961c9e0cf0a9d58a468f..f451870e1b0e89829bd4c3dbc00e77b54133ce43 100644
--- a/src/mplfe/jbc_input/src/jbc_attr.cpp
+++ b/src/mplfe/jbc_input/src/jbc_attr.cpp
@@ -253,7 +253,7 @@ std::list<std::string> JBCAttrLocalVariableInfo::EmitToStrings() const {
   std::list<std::string> ans;
   std::stringstream ss;
   ans.emplace_back("===== Local Variable Info =====");
-  for (const std::pair<std::pair<uint16, uint16>, JavaAttrLocalVariableInfoItem> &itemPair : itemMap) {
+  for (const std::pair<const std::pair<uint16, uint16>, JavaAttrLocalVariableInfoItem> &itemPair : itemMap) {
     const JavaAttrLocalVariableInfoItem &item = itemPair.second;
     ss.str("");
     ss << "slot[" << item.slotIdx << "]: ";
diff --git a/src/mplfe/jbc_input/src/jbc_function.cpp b/src/mplfe/jbc_input/src/jbc_function.cpp
index c502004181b604a692325234f7b08992ffdab472..022160c379ad70e8fe52606629b6f5c79d8e726d 100644
--- a/src/mplfe/jbc_input/src/jbc_function.cpp
+++ b/src/mplfe/jbc_input/src/jbc_function.cpp
@@ -318,8 +318,8 @@ bool JBCFunction::CheckJVMStackResult() {
 }
 
 bool JBCFunction::PreBuildJsrInfo(const jbc::JBCAttrCode &code) {
-  const MapleMap<uint32, jbc::JBCOp*> &instMap = code.GetInstMap();
-  for (const std::pair<uint32, jbc::JBCOp*> &it : instMap) {
+  const MapleMap<const uint32, jbc::JBCOp*> &instMap = code.GetInstMap();
+  for (const std::pair<const uint32, jbc::JBCOp*> &it : instMap) {
     uint32 pc = it.first;
     jbc::JBCOp *op = it.second;
     ASSERT_NOT_NULL(op);
@@ -353,8 +353,8 @@ bool JBCFunction::PreBuildJsrInfo(const jbc::JBCAttrCode &code) {
 
 bool JBCFunction::BuildStmtFromInstruction(const jbc::JBCAttrCode &code) {
   GeneralStmt *stmt = nullptr;
-  const MapleMap<uint32, jbc::JBCOp*> &instMap = code.GetInstMap();
-  for (const std::pair<uint32, jbc::JBCOp*> &it : instMap) {
+  const MapleMap<const uint32, jbc::JBCOp*> &instMap = code.GetInstMap();
+  for (const std::pair<const uint32, jbc::JBCOp*> &it : instMap) {
     uint32 pc = it.first;
     const jbc::JBCOp *op = it.second;
     ASSERT(op != nullptr, "null ptr check");
@@ -416,7 +416,7 @@ GeneralStmt *JBCFunction::BuildStmtFromInstructionForSwitch(const jbc::JBCOp &op
   GeneralStmt *stmt = uniStmt.get();
   stmt->SetFallThru(false);
   const jbc::JBCOpSwitch &opSwitch = static_cast<const jbc::JBCOpSwitch&>(op);
-  for (const std::pair<int32, uint32> &targetInfo : opSwitch.GetTargets()) {
+  for (const std::pair<const int32, uint32> &targetInfo : opSwitch.GetTargets()) {
     GeneralStmt *target = BuildAndUpdateLabel(targetInfo.second, uniStmt);
     static_cast<JBCStmtInstBranch*>(stmt)->AddSucc(target);
   }
@@ -491,7 +491,7 @@ void JBCFunction::BuildStmtForTry(const jbc::JBCAttrCode &code) {
     rawInfo[std::make_pair(start, end)].push_back(handlerPC);
   }
   BuildTryInfo(rawInfo, outMapStartEnd, outMapStartCatch);
-  for (const std::pair<uint32, uint32> &startEnd : outMapStartEnd) {
+  for (const std::pair<const uint32, uint32> &startEnd : outMapStartEnd) {
     // Try
     JBCStmtPesudoTry *stmtTry =
         static_cast<JBCStmtPesudoTry*>(RegisterGeneralStmt(std::make_unique<JBCStmtPesudoTry>()));
@@ -620,8 +620,8 @@ void JBCFunction::BuildStmtForInstComment(const jbc::JBCAttrCode &code) {
   uint16 currLineNum = 0xFFFF;  // use 0xFFFF as invalid line number
   std::stringstream ss;
   const jbc::JBCConstPool &constPool = method.GetConstPool();
-  const MapleMap<uint32, jbc::JBCOp*> &instMap = code.GetInstMap();
-  for (const std::pair<uint32, jbc::JBCOp*> &it : instMap) {
+  const MapleMap<const uint32, jbc::JBCOp*> &instMap = code.GetInstMap();
+  for (const std::pair<const uint32, jbc::JBCOp*> &it : instMap) {
     uint32 pc = it.first;
     jbc::JBCOp *op = it.second;
     if (mapPCLineNum.find(pc) != mapPCLineNum.end()) {
diff --git a/src/mplfe/jbc_input/src/jbc_function_context.cpp b/src/mplfe/jbc_input/src/jbc_function_context.cpp
index c2ab16a5b97514d7677b61a345ddd363eb5afdc7..f0b594d8c50a80c56ce13d829b9be247351a3d73 100644
--- a/src/mplfe/jbc_input/src/jbc_function_context.cpp
+++ b/src/mplfe/jbc_input/src/jbc_function_context.cpp
@@ -39,7 +39,7 @@ void JBCFunctionContext::ArrangeStmts() {
    *   comment
    *   inst
    */
-  for (const std::pair<uint32, GeneralStmt*> &pcInst : mapPCStmtInst) {
+  for (const std::pair<const uint32, GeneralStmt*> &pcInst : mapPCStmtInst) {
     uint32 pc = pcInst.first;
     GeneralStmt *stmtInst = pcInst.second;
     if (mapPCEndTryStmt.find(pc) != mapPCEndTryStmt.end()) {
@@ -80,4 +80,4 @@ const FEIRType *JBCFunctionContext::GetSlotType(uint16 slotIdx) const {
   const jbc::JavaAttrLocalVariableInfoItem &info = localVarInfo.GetItemByStart(slotIdx, startPC);
   return info.feirType;
 }
-}  // namespace maple
\ No newline at end of file
+}  // namespace maple
diff --git a/test/testsuite/maple.py b/test/testsuite/maple.py
index 393950c88be11e82a789f322a569d1175a737b7b..8f9b86cd4f943382e2cd44ae3ae5d72be11803f8 100644
--- a/test/testsuite/maple.py
+++ b/test/testsuite/maple.py
@@ -219,7 +219,11 @@ def do_prepare(components, info, maple_root):
     maple_out_path = os.environ.get("MAPLE_BUILD_OUTPUT")
     maple_out_lib_path = maple_out_path + "/ops"
     maple_out_bin_path = maple_out_path + "/bin/"
-    gnu_bin_path = maple_root + "/tools/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04/bin/"
+    old_os = os.environ.get("OLD_OS")
+    if old_os == "1":
+      gnu_bin_path = maple_root + "/tools/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04/bin/"
+    elif old_os == "0":
+      gnu_bin_path = "/usr/bin/"
     as_options = "-g3 -O2 -x assembler-with-cpp -march=armv8-a -target aarch64-linux-gnu -c "
     cc_options = "-g3 -O2 -c -march=armv8-a -target aarch64-linux-gnu"
     cxx_options = "-g3 -O2 -c -fPIC -march=armv8-a -target aarch64-linux-gnu"
diff --git a/tools/setup_tools.sh b/tools/setup_tools.sh
index 34a9b7943b526f31abed1500cd356d7e7e83079d..f3945849bc6a1691063f6954b2a68da76fc1b74b 100755
--- a/tools/setup_tools.sh
+++ b/tools/setup_tools.sh
@@ -31,9 +31,43 @@ ANDROID_SRCDIR=$MAPLE_ROOT/../android/$ANDROID_VERSION
 
 ANDROID_DIR=$MAPLE_ROOT/android
 
+if [ "$OLD_OS" == "1" ]; then
+  if [ ! -f $TOOLS/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04/bin/clang ]; then
+    cd $TOOLS
+    echo Start wget llvm-8.0.0 ...
+    wget https://releases.llvm.org/8.0.0/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04.tar.xz
+    echo unpacking clang+llvm ...
+    tar xf clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04.tar.xz
+    echo Downloaded clang+llvm.
+  fi
+fi
+
+if [ "$android_env" == "android" ]; then
+  if [ ! -f $TOOLS/android-ndk-r21/ndk-build ]; then
+    cd $TOOLS
+    wget https://dl.google.com/android/repository/android-ndk-r21d-linux-x86_64.zip
+    echo unpacking android ndk ...
+    unzip android-ndk-r21d-linux-x86_64.zip > /dev/null
+    mv android-ndk-r21d android-ndk-r21
+    echo Downloaded android ndk.
+  fi
+
+  if [ ! -L $TOOLS/gcc ]; then
+    cd $TOOLS
+    ln -s ../android/prebuilts/gcc .
+    echo Linked gcc.
+  fi
+
+  if [ ! -L $TOOLS/clang-r353983c ]; then
+    cd $TOOLS
+    ln -s ../android/prebuilts/clang/host/linux-x86/clang-r353983c .
+    echo Linked clang.
+  fi
+fi
+
 if [ ! -f $TOOLS/ninja/ninja ]; then
   cd $TOOLS
-  echo Start wget ninja..............
+  echo Start wget ninja ...
   mkdir -p ./ninja
   cd ./ninja || exit 3
   wget https://github.com/ninja-build/ninja/releases/download/v1.10.0/ninja-linux.zip
@@ -43,24 +77,15 @@ fi
 
 if [ ! -f $TOOLS/gn/gn ]; then
   cd $TOOLS
-  echo Start clone gn..................
+  echo Start clone gn ...
   git clone https://gitee.com/xlnb/gn_binary.git gn
   chmod +x gn/gn
   echo Downloaded gn.
 fi
 
-if [ ! -f $TOOLS/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04/bin/clang ]; then
-  cd $TOOLS
-  echo Start wget llvm-8.0.0........................
-  wget https://releases.llvm.org/8.0.0/clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04.tar.xz
-  echo unpacking clang+llvm ...
-  tar xf clang+llvm-8.0.0-x86_64-linux-gnu-ubuntu-16.04.tar.xz
-  echo Downloaded clang+llvm.
-fi
-
 if [ ! -f $TOOLS/gcc-linaro-7.5.0/bin/aarch64-linux-gnu-gcc ]; then
   cd $TOOLS
-  echo Start wget gcc-linaro-7.5.0...................
+  echo Start wget gcc-linaro-7.5.0 ...
   wget https://releases.linaro.org/components/toolchain/binaries/latest-7/aarch64-linux-gnu/gcc-linaro-7.5.0-2019.12-i686_aarch64-linux-gnu.tar.xz
   echo unpacking gcc ...
   tar xf gcc-linaro-7.5.0-2019.12-i686_aarch64-linux-gnu.tar.xz
@@ -68,18 +93,9 @@ if [ ! -f $TOOLS/gcc-linaro-7.5.0/bin/aarch64-linux-gnu-gcc ]; then
   echo Downloaded gcc aarch64 compiler.
 fi
 
-if [ ! -f $TOOLS/android-ndk-r21/ndk-build ] && [ "$android_env" == "android" ]; then
-  cd $TOOLS
-  wget https://dl.google.com/android/repository/android-ndk-r21d-linux-x86_64.zip
-  echo unpacking android ndk ...
-  unzip android-ndk-r21d-linux-x86_64.zip > /dev/null
-  mv android-ndk-r21d android-ndk-r21
-  echo Downloaded android ndk.
-fi
-
 if [ ! -f $MAPLE_ROOT/third_party/d8/lib/d8.jar ]; then
   cd $TOOLS
-  echo Start clone d8...............
+  echo Start clone d8 ...
   git clone https://gitee.com/xlnb/r8-d81513.git
   mkdir -p $MAPLE_ROOT/third_party/d8/lib
   cp -f r8-d81513/d8/lib/d8.jar $MAPLE_ROOT/third_party/d8/lib
@@ -88,38 +104,26 @@ fi
 
 if [ ! -d $MAPLE_ROOT/third_party/icu ]; then
   cd $TOOLS
-  echo Start clone ICU4C..............
+  echo Start clone ICU4C ...
   git clone https://gitee.com/xlnb/icu4c.git
   mkdir -p $MAPLE_ROOT/third_party/icu
   cp -r icu4c/lib/ $MAPLE_ROOT/third_party/icu/
   echo Downloaded icu4c libs
 fi
 
-# download and build andriod source
+# download prebuilt andriod
 if [ ! -d $ANDROID_DIR/out/target/product/generic_arm64 ]; then
   cd $TOOLS
-  echo Start clone AOSP CORE LIB...........
+  echo Start clone AOSP CORE LIB ...
   git clone https://gitee.com/xlnb/aosp_core_bin.git
   cp -r aosp_core_bin/android $MAPLE_ROOT/
   cp -r aosp_core_bin/libjava-core $MAPLE_ROOT/ 
   echo Downloaded AOSP CORE LIB
 fi
 
-if [ ! -L $TOOLS/gcc ] && [ "$android_env" == "android" ]; then
-  cd $TOOLS
-  ln -s ../android/prebuilts/gcc .
-  echo Linked gcc.
-fi
-
-if [ ! -L $TOOLS/clang-r353983c ] && [ "$android_env" == "android" ]; then
-  cd $TOOLS
-  ln -s ../android/prebuilts/clang/host/linux-x86/clang-r353983c .
-  echo Linked clang.
-fi
-
 if [ ! -f $MAPLE_ROOT/third_party/libdex/prebuilts/aarch64-linux-gnu/libz.so.1.2.8 ]; then
   cd $TOOLS
-  echo Start wget libz.............................
+  echo Start wget libz ...
   wget http://ports.ubuntu.com/pool/main/z/zlib/zlib1g_1.2.8.dfsg-2ubuntu4_arm64.deb
   mkdir -p libz_extract
   dpkg --extract zlib1g_1.2.8.dfsg-2ubuntu4_arm64.deb libz_extract
@@ -129,3 +133,19 @@ if [ ! -f $MAPLE_ROOT/third_party/libdex/prebuilts/aarch64-linux-gnu/libz.so.1.2
   echo Downloaded libz.
 fi
 
+# install qemu-user 2.5
+if [ ! -f $MAPLE_ROOT/tools/qemu/done ]; then
+  cd $TOOLS
+  echo Start wget qemu-user ...
+  rm -rf qemu
+  mkdir -p qemu
+  cd qemu
+  wget http://security.ubuntu.com/ubuntu/pool/universe/q/qemu/qemu-user_2.5+dfsg-5ubuntu10.48_amd64.deb
+  echo Install qemu-aarch64 ...
+  # use the following to make sure only the specific version of qemu-user is isstalled
+  # the first version sometimes insists to install the system default qemu-user.
+  # sudo apt install ./qemu-user_2.5+dfsg-5ubuntu10.48_amd64.deb
+  sudo dpkg -i ./qemu-user_2.5+dfsg-5ubuntu10.48_amd64.deb || sudo apt install -f
+  touch done
+  echo Installed qemu-aarch64
+fi