[llvm-zorg] Use ndk21 for buildbot

[vitalybuka]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

109–110

we don't want to do that, the point of this bot to test clang and compiler_rt from master

[vitalybuka]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

95

maybe link errors because it includes libc++, but then sets -stdlib=libstdc++ ?

[oontvoo]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

95

Without the include, I was getting missing header errors (eg., <vector>, <limits>, etc)
(I have also tried setting stdlib=libc++ )

[oontvoo]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

95

Oh, I see. compiler-rt passed stdlib=libstdc++, and that overrode libc++.

********************
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90
FAIL: AddressSanitizer-aarch64-android :: TestCases/uar_and_exceptions.cpp (458 of 485)
******************** TEST 'AddressSanitizer-aarch64-android :: TestCases/uar_and_exceptions.cpp' FAILED ********************
Script:
--
: 'RUN: at line 2';     /mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/llvm-project/compiler-rt/test/sanitizer_common/android_commands/android_compile.py  /mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/llvm_build64/bin/clang  --driver-mode=g++ -stdlib=libstdc++ -fsanitize=address -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls -gline-tables-only  -pie -fuse-ld=gold --target=aarch64-linux-android --sysroot=/mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/android_ndk/standalone-aarch64/sysroot -B/mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/android_ndk/standalone-aarch64  -shared-libasan -O0 /mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/llvm-project/compiler-rt/test/asan/TestCases/uar_and_exceptions.cpp -o /mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/compiler_rt_build_android_aarch64/test/asan/AARCH64AndroidConfig/TestCases/Output/uar_and_exceptions.cpp.tmp
: 'RUN: at line 3';   env ASAN_OPTIONS=abort_on_error=0:detect_stack_use_after_return=1  /mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/compiler_rt_build_android_aarch64/test/asan/AARCH64AndroidConfig/TestCases/Output/uar_and_exceptions.cpp.tmp

[oontvoo]

updated to use the right API, depending on the device and use libc++

[oontvoo]

updated

[srhines]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

76

@danalbert Should we be adding this kind of autodetection (to look in $_arch-linux-android) to Clang directly? How does this work for NDK users today?

[vitalybuka]

Thank you!
I tried yesterday myself but didn't figureout "-stdlib=libc++ -I/$ANDROID_TOOLCHAIN/sysroot/usr/include/c++/v1"" part.

May I ask you to move ANDROID_HAS_ELF_TLS and ANDROID_HAS_ELF_TLS into a separate patch so we can keep ndk upgrade only to see how it works for the bot?

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

52

double spaces?

52

not sure about this part
we build ndk and all this for particular platform no mater what devices are available
the script is going to run all tests on all available devices

56

"-lt 21" for consistency?

63

can we use cmake rule to detect that? like link trivial program?

134

check buildbot_android.sh
ANDROID_HAS_ELF_TLS here is from the last arch and can mismatch

Can be solved by reordering of
build_android_ndk aarch64 arm64
configure_android aarch64 aarch64-linux-android

but I would prefer if we detect with ANDROID_HAS_ELF_TLS
isn't this crt property so we can test from cmake if it links?

[vitalybuka]

actually I see a lot of test failing with v21 on 93953d411a0fc240e10237fea34aaff43e8f0ff5 on x86 emulator

-
Exit Code: 1

Command Output (stderr):
--
/usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/compiler-rt/test/ubsan/TestCases/ImplicitConversion/integer-arithmetic-value-change.c:160:14: error: CHECK-V0: expected string not found in input
// CHECK-V0: {{.*}}integer-arithmetic-value-change.c:900:10: runtime error: implicit conversion from type '{{.*}}' (aka 'unsigned int') of value 4294967295 (32-bit, unsigned) to type '{{.*}}' (aka 'int') changed the value to -1 (32-bit, signed)
             ^
<stdin>:1:1: note: scanning from here
CANNOT LINK EXECUTABLE "/data/local/tmp/Output/usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/ubsan/AddressSanitizer-i386/TestCases/ImplicitConversion/Output/integer-arithmetic-value-change.c.tmp": cannot locate symbol "_ZTIN10__cxxabiv117__class_type_infoE" referenced by "/data/local/tmp/Output/libclang_rt.asan-i686-android.so"...
^

Input file: <stdin>
Check file: /usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/compiler-rt/test/ubsan/TestCases/ImplicitConversion/integer-arithmetic-value-change.c

-dump-input=help explains the following input dump.

Input was:
<<<<<<
           1: CANNOT LINK EXECUTABLE "/data/local/tmp/Output/usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/ubsan/AddressSanitizer-i386/TestCases/ImplicitConversion/Output/integer-arithmetic-value-change.c.tmp": cannot locate symbol "_ZTIN10__cxxabiv117__class_type_infoE" referenced by "/data/local/tmp/Output/libclang_rt.asan-i686-android.so"...
check:160     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
           2: Aborted 
check:160     ~~~~~~~~
>>>>>>

Do they work for you?

[oontvoo]

In D89924#2348784, @vitalybuka wrote:

actually I see a lot of test failing with v21 on 93953d411a0fc240e10237fea34aaff43e8f0ff5 on x86 emulator

Sorry, forgot to mention compiler-rt needs to set stdlib=libc++ too. Right now, they are using stdlibc++. (Or better yet, change the default value of the cmake variable ANDROID_NDK_VERSION=21)
(This is why you're getting these undefined symbols).

I'll send a patch for that soon.

[oontvoo]

updated

[oontvoo]

May I ask you to move ANDROID_HAS_ELF_TLS and ANDROID_HAS_ELF_TLS into a separate patch so we can keep ndk upgrade only to see how it works for the bot?

Done - removed the ANDROID_HAS_ELF_TLS part.

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

52

It should match the platform/arch to the right device and its libc API level??

I'm concerned that if you say want to build for 29 (with elf-tls), then run it on 25 (without TLS support) it won't load.

[oontvoo]

Use the libc++_shared.so under sysroot rather than searching for it.
(In the new NDKs, there are a bunch of libc++_shared.so for different archs)

[oontvoo]

updated

[oontvoo]

Set cmake ndk-version variable

[vitalybuka]

BTW zorg repo is frozen right now for buildbot migration, we need to wait week or so before able to commit.

zorg/buildbot/builders/sanitizers/buildbot_android.sh

28

let's remove r21 here and set global ANDROID_NDK_VERSION=21 in buildbot_android_functions

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

35

here we build compiler for the host and we don't use NDK at all

52

That is a problem but I'd like focus this patch only on 16->21 update keeping as much as possible unchanged, including ANDROID_API,
please move entire check_android_api into a separate patch

76

I suspect they each clang-* from NDK has hard coded value.
Here we share single clang binary for all platforms

134

it would be nice to have single place for "21"

[oontvoo]

updated diff

[oontvoo]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

134

but I would prefer if we detect with ANDROID_HAS_ELF_TLS
isn't this crt property so we can test from cmake if it links?

I've moved the ANDROID_HAS_ELF_TLS to a different patch. So will close this for now.

[oontvoo]

updated

[oontvoo]

(rebase)

[danalbert]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

6

Don't you want the fixed version? r21d is the latest.

56

These values are in $NDK/meta/platforms.json if you want to remove the hard coding.

The minimum isn't right either. The minimum for current NDKs is 16. It's only the LP64 ABIs that have a minimum of 21. Don't know if that matters here. *We* certainly care about testing API 16, but we also aren't using zorg to do that.

72–83

This isn't needed any more. You can just use clang directly with the appropriate target (e.g. aarch64-linux-android24) and it works. I'm guessing it's the case that you're only using the NDK for its sysroot and using your own clang/linker/ar/etc here, in which case you just need to make sure you pass --sysroot $NDK/toolchains/llvm/prebuilt/linux-x86_64/sysroot when invoking clang.

76

Looks unnecessary to me. make_standalone_toolchain.py is no longer the common approach, but we do have tests that say it should work fine without this.

[oontvoo]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

76

I suspect they each clang-* from NDK has hard coded value.

seems plausible

I'm guessing it's the case that you're only using the NDK for its sysroot and using your own clang/linker/ar/etc here, in which case you >just need to make sure you pass --sysroot $NDK/toolchains/llvm/prebuilt/linux-x86_64/sysroot when invoking clang.

I've tried using the prebuilt sysroot but unfortunately it didn't work. (Can't find -lc++ and -lgcc)

eg., this failed during Cmake compiler check

[2/2] Linking C executable cmTC_1a555
FAILED: cmTC_1a555 
: && /mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/llvm_build64/bin/clang --target=i686-linux-android --sysroot=/mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/android_ndk/toolchains/llvm/prebuilt/linux-x86_64/sysroot -B/mnt/ssd/repo/buildbot/d_emulated_tls/run_dir/android_ndk/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib  -pie CMakeFiles/cmTC_1a555.dir/testCCompiler.c.o  -o cmTC_1a555   && :
/usr/bin/ld: cannot find -lgcc

[oontvoo]

download r21d package (instead of r21)

[danalbert]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

76

It can't find libc++ because you didn't specify an API level. -target i686-linux-android21 finds libc++.

libgcc is part of the toolchain rather than the Android system. For that you need to add -gcc-toolchain $NDK/toolchains/llvm/prebuilt/linux-x86_64. Sorry, forgot that step :)

(you could also try using libclangrt instead of libgcc, but we haven't finished that migration, so unless that's what you're trying to test I wouldn't recommend that just yet)

[oontvoo]

updated

[oontvoo]

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

76

Thanks. Specifying the -gcc-toolchain in addition to adding the API level to target got it to work.

[oontvoo]

rebase

[oontvoo]

updated diff

[vitalybuka]

In D89924#2360974, @oontvoo wrote:

updated diff

does this version pass tests with emulator on master?
I see a lot of CANNOT LINK EXECUTABLE

******************** TEST 'AddressSanitizer-i386-android :: TestCases/strcspn-1.c' FAILED ********************
Script:
--
: 'RUN: at line 2';     /usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/compiler-rt/test/sanitizer_common/android_commands/android_compile.py  /usr/local/google/home/vitalybuka/slow/bbot/llvm_build64/bin/clang  -fsanitize=address -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls -gline-tables-only  -pie -fuse-ld=gold --target=i686-linux-android24 --sysroot=/usr/local/google/home/vitalybuka/slow/bbot/android_ndk/toolchains/llvm/prebuilt/linux-x86_64/sysroot -gcc-toolchain /usr/local/google/home/vitalybuka/slow/bbot/android_ndk/toolchains/llvm/prebuilt/linux-x86_64  -B/usr/local/google/home/vitalybuka/slow/bbot/android_ndk/toolchains/llvm/prebuilt/linux-x86_64  -shared-libasan /usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/compiler-rt/test/asan/TestCases/strcspn-1.c -o /usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/asan/I386AndroidConfig/TestCases/Output/strcspn-1.c.tmp && env ASAN_OPTIONS=abort_on_error=0:strict_string_checks=true not  /usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/asan/I386AndroidConfig/TestCases/Output/strcspn-1.c.tmp 2>&1 | FileCheck /usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/compiler-rt/test/asan/TestCases/strcspn-1.c
: 'RUN: at line 5';   env ASAN_OPTIONS=abort_on_error=0:intercept_strspn=false  /usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/asan/I386AndroidConfig/TestCases/Output/strcspn-1.c.tmp 2>&1
--
Exit Code: 1

Command Output (stderr):
--
/usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/compiler-rt/test/asan/TestCases/strcspn-1.c:17:11: error: CHECK: expected string not found in input
 // CHECK:'s1'{{.*}} <== Memory access at offset {{[0-9]+}} partially overflows this variable
          ^
<stdin>:1:1: note: scanning from here
CANNOT LINK EXECUTABLE "/data/local/tmp/Output/usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/asan/I386AndroidConfig/TestCases/Output/strcspn-1.c.tmp": cannot locate symbol "_ZTIN10__cxxabiv117__class_type_infoE" referenced by "/data/local/tmp/Output/libclang_rt.asan-i686-android.so"...
^

Input file: <stdin>
Check file: /usr/local/google/home/vitalybuka/src/llvm.git/llvm-project/compiler-rt/test/asan/TestCases/strcspn-1.c

-dump-input=help explains the following input dump.

Input was:
<<<<<<
          1: CANNOT LINK EXECUTABLE "/data/local/tmp/Output/usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/asan/I386AndroidConfig/TestCases/Output/strcspn-1.c.tmp": cannot locate symbol "_ZTIN10__cxxabiv117__class_type_infoE" referenced by "/data/local/tmp/Output/libclang_rt.asan-i686-android.so"...
check:17     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
          2: Aborted 
check:17     ~~~~~~~~
          3: error: Aborted
check:17     ~~~~~~~~~~~~~~
>>>>>>

[oontvoo]

In D89924#2361276, @vitalybuka

does this version pass tests with emulator on master?

Yes, worked for me.
Though i'm not sure you meant llvm-project master? or emulator with aosp-master image?
I've tested it with latest llvm-project on a Q image.

CANNOT LINK EXECUTABLE "/data/local/tmp/Output/usr/local/google/home/vitalybuka/slow/bbot/compiler_rt_build_android_i686/test/asan/I386AndroidConfig/TestCases/Output/strcspn-1.c.tmp": cannot locate symbol "_ZTIN10cxxabiv117class_type_infoE" referenced by "/data/local/tmp/Output/libclang_rt.asan-i686-android.so"...

This seems strange. The test is C. Why is it looking for _ZTIN10cxxabiv117class_type_infoE ?

[oontvoo]

P.S: For completeness, I've re-tested with aosp-master. I didn't see the link errors you saw, but did see 16 Scudo test failures. Looked a like unrelated issues, because same errors also seen with the old zorg script
https://pastebin.ubuntu.com/p/bTDc7Vj9TD/

Failed Tests (16):
  AddressSanitizer-i386-android :: TestCases/throw_invoke_test.cpp
  SanitizerCommon-asan-i386-Android :: Linux/mallopt.cpp
  Scudo-i386 :: aligned-new.cpp
  Scudo-i386 :: alignment.c
  Scudo-i386 :: double-free.cpp
  Scudo-i386 :: fsanitize.c
  Scudo-i386 :: interface.cpp
  Scudo-i386 :: memalign.c
  Scudo-i386 :: mismatch.cpp
  Scudo-i386 :: options.cpp
  Scudo-i386 :: overflow.c
  Scudo-i386 :: quarantine.c
  Scudo-i386 :: rss.c
  Scudo-i386 :: sized-delete.cpp
  Scudo-i386 :: sizes.cpp
  Scudo-i386 :: threads.c

[vitalybuka]

I use internal emulator, I've sent you how to run it.
master means llvm-project master, no other patches (20a3931f8fadb9c13b4868d1b0124498b014b1d5)
zorg:
237d0b4da0c0df5ffec99ce30e62b3acc7d15c3c no errors
237d0b4da0c0df5ffec99ce30e62b3acc7d15c3c+this patch: can't link

[oontvoo]

In D89924#2363156, @vitalybuka wrote:

I use internal emulator, I've sent you how to run it.

Thanks! was able to repro the errors.

So what I've got so far. This only occurs for 25 or older. (Didn't get the errors when testing this patch with Pie or newer images)

A closer. look at the error, cannot locate symbol "_ZTIN10cxxabiv117class_type_infoE" referenced by "/data/local/tmp/Output/libclang_rt.asan-i686-android.so"...
(note that this symbol is defined in libc++_shared.so ) So maybe somewhere it was confusing libc++ and libstdc++ ?

@srhines @danalbert Is there any subtlety we don't know about?

[oontvoo]

Update compiler-rt build to set -DSANITIZER_CXX_ABl=libcxxabi (which is similar to what the ndk build does).
This should fix the undefined symbols issue.

[vitalybuka]

small changes and disable failing tests

zorg/buildbot/builders/sanitizers/buildbot_android.sh

 LLVM=$ROOT/llvm
 CMAKE_COMMON_OPTIONS="${CMAKE_COMMON_OPTIONS:-}"
 CMAKE_COMMON_OPTIONS="${CMAKE_COMMON_OPTIONS:-} -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_PARALLEL_LINK_JOBS=20"
 
 if [ -e /usr/include/plugin-api.h ]; then
   CMAKE_COMMON_OPTIONS="${CMAKE_COMMON_OPTIONS} -DLLVM_BINUTILS_INCDIR=/usr/include"
 fi
 
-clobber
+#clobber
 
-download_android_tools r16
+download_android_tools r21
 
 # Stage 1
 
 build_stage1_clang_at_revison
 ### From now on we use just-built Clang as a host compiler ###
 
-buildbot_update
+#buildbot_update
+LLVM=$ROOT/llvm-project/llvm
 
 CMAKE_COMMON_OPTIONS="$CMAKE_COMMON_OPTIONS -DLLVM_ENABLE_ASSERTIONS=ON"
 
 build_stage2_android
 
 # Android NDK has no iconv.h which is requred by LIBXML2.
 CMAKE_COMMON_OPTIONS="${CMAKE_COMMON_OPTIONS} -DLLVM_LIBXML2_ENABLED=OFF"
 
-build_android_ndk aarch64 arm64
-build_android_ndk arm arm
+#build_android_ndk aarch64 arm64
+#build_android_ndk arm arm
 build_android_ndk i686 x86
 
 echo @@@BUILD_STEP run cmake@@@
-configure_android aarch64 aarch64-linux-android
+#configure_android aarch64 aarch64-linux-android
 # Testing armv7 instead of plain arm to work around
 # https://code.google.com/p/android/issues/detail?id=68779
-configure_android arm armv7-linux-androideabi
+#configure_android arm armv7-linux-androideabi
 configure_android i686 i686-linux-android
 
-build_android aarch64
-build_android arm
+#build_android aarch64
+#build_android arm
 build_android i686
 
 # Arm hardware is temporarily offline
 test_android i686:x86 # aarch64:arm64-v8a arm:armeabi-v7a

zorg/buildbot/builders/sanitizers/buildbot_android_functions.sh

 #!/usr/bin/env bash
 
 CLOBBER="android_ndk android-ndk-* platform-tools *.zip shards_* test_android_* tested_arch_*"
 STAGE2_CLOBBER="compiler_rt_build_android_* llvm_build_android_*"
 STAGE1_CLOBBER="llvm_build64 ${STAGE2_CLOBBER}"
 
 function download_android_tools {
   local VERSION=android-ndk-$1
   local FILE_NAME=${VERSION}-linux-x86_64.zip
   local NDK_URL=https://dl.google.com/android/repository/${FILE_NAME}
   local NDK_DIR=android_ndk
   if  [[ "$(cat ${NDK_DIR}/android_ndk_url)" != ${NDK_URL} ]] ; then
     echo @@@BUILD_STEP downloading Android NDK@@@
     [[ -d ${NDK_DIR} ]] && rm -rf ${NDK_DIR}
if  [[ ! -d platform-tools ]] ; then
     wget https://dl.google.com/android/repository/${FILE_NAME}
     unzip ${FILE_NAME} > /dev/null
   fi
   export PATH=$ROOT/platform-tools/:$PATH
 }
 
 function build_stage2_android() {
   # Build self-hosted tree with fresh Clang and -Werror.
   local CMAKE_OPTIONS="${CMAKE_COMMON_OPTIONS} -DLLVM_ENABLE_WERROR=ON ${STAGE1_AS_COMPILER} -DCMAKE_C_FLAGS=-gmlt -DCMAKE_CXX_FLAGS=-gmlt"
   CMAKE_OPTIONS="${CMAKE_OPTIONS} -DLLVM_ENABLE_PROJECTS='clang;compiler-rt;lld'"
 
   echo @@@BUILD_STEP bootstrap clang@@@
   rm -rf ${STAGE2_CLOBBER}
 
   mkdir -p llvm_build64
   if  [[ "$(cat llvm_build64/CMAKE_OPTIONS)" != "${CMAKE_OPTIONS}" ]] ; then
     (cd llvm_build64 && cmake ${CMAKE_OPTIONS} -DLLVM_BUILD_EXTERNAL_COMPILER_RT=ON $LLVM && \
        echo ${CMAKE_OPTIONS} > CMAKE_OPTIONS) || echo @@@STEP_FAILURE@@@
   fi
   ninja -C llvm_build64 || echo @@@STEP_FAILURE@@@
 }
 
+function check_android_api {
+  if [ -z ${ANDROID_API+x} ]; then
+    # If ANDROID_API was not specified, then use the one from the device.
+    ANDROID_API=$(adb shell getprop ro.build.version.sdk)
+  fi
+  
+  # Re-adjust it since the current NDK supports API levels in the range [21,29].
+  if [[ $ANDROID_API -gt 29  || $ANDROID_API -lt 21 ]]; then
+    echo "API level $ANDROID_API is not supported."
+    ANDROID_API=29
+  fi
+  
+  echo "Building for Android API level $ANDROID_API" 
+}
+
 function build_android_ndk {
   local NDK_DIR=android_ndk
   local _arch=$1
   local _ndk_arch=$2
+
+  check_android_api
   if [[ ! -d $NDK_DIR/standalone-$_arch ]] ; then 
     echo @@@BUILD_STEP building Android NDK for $_arch@@@
-    $NDK_DIR/build/tools/make_standalone_toolchain.py --api 24 --force --arch $_ndk_arch --stl=libc++ --install-dir $NDK_DIR/standalone-$_arch
+    $NDK_DIR/build/tools/make_standalone_toolchain.py --api $ANDROID_API --force --arch $_ndk_arch --stl=libc++ --install-dir $NDK_DIR/standalone-$_arch
+
+    # Move the [shared] objects and libraries back to expected sysroot layout.
+    # Or it won't be able to find -lc++
+    local _source=$ROOT/$NDK_DIR/standalone-$_arch/sysroot/usr/lib/$_arch-linux-android
+    local _target=$ROOT/$NDK_DIR/standalone-$_arch/sysroot/usr/lib
+    mv $_source/*.so $_target/.
+    mv $_source/*.a $_target/.
+
+    mv $_source/$ANDROID_API/*.so $_target/.
+    mv $_source/$ANDROID_API/*.o $_target/.
+    mv $_source/$ANDROID_API/*.a $_target/.
   fi
 }
 
 function configure_android { # ARCH triple
   local _arch=$1
   local _triple=$2
 
   local ANDROID_TOOLCHAIN=$ROOT/android_ndk/standalone-$_arch
   local ANDROID_LIBRARY_OUTPUT_DIR=$(ls -d $ROOT/llvm_build64/lib/clang/* | tail -1)
   local ANDROID_EXEC_OUTPUT_DIR=$ROOT/llvm_build64/bin
   local ANDROID_FLAGS="--target=$_triple --sysroot=$ANDROID_TOOLCHAIN/sysroot -B$ANDROID_TOOLCHAIN"
-  local ANDROID_CXX_FLAGS="$ANDROID_FLAGS -stdlib=libstdc++"
+  local ANDROID_CXX_FLAGS="$ANDROID_FLAGS -stdlib=libc++ -I/$ANDROID_TOOLCHAIN/sysroot/usr/include/c++/v1"
 
+  local CLANG_PATH=$ROOT/llvm_build64/bin/clang
+  local CLANGXX_PATH=$ROOT/llvm_build64/bin/clang++
   # Always clobber android build tree.
   # It has a hidden dependency on clang (through CXX) which is not known to
   # the build system.
   rm -rf compiler_rt_build_android_$_arch
   mkdir -p compiler_rt_build_android_$_arch
   rm -rf llvm_build_android_$_arch
   mkdir -p llvm_build_android_$_arch
 
   (cd llvm_build_android_$_arch && cmake \
     -DLLVM_ENABLE_WERROR=OFF \
-    -DCMAKE_C_COMPILER=$ROOT/llvm_build64/bin/clang \
-    -DCMAKE_CXX_COMPILER=$ROOT/llvm_build64/bin/clang++ \
+    -DCMAKE_C_COMPILER=$CLANG_PATH \
+    -DCMAKE_CXX_COMPILER=$CLANGXX_PATH \
     -DCMAKE_ASM_FLAGS="$ANDROID_FLAGS" \
     -DCMAKE_C_FLAGS="$ANDROID_FLAGS" \
     -DCMAKE_CXX_FLAGS="$ANDROID_CXX_FLAGS" \
     -DCMAKE_EXE_LINKER_FLAGS="-pie" \
     -DCMAKE_SKIP_RPATH=ON \
     -DLLVM_BUILD_RUNTIME=OFF \
     -DLLVM_TABLEGEN=$ROOT/llvm_build64/bin/llvm-tblgen \
     ${CMAKE_COMMON_OPTIONS} \
     $LLVM || echo @@@STEP_FAILURE@@@) &
 
   local COMPILER_RT_OPTIONS="$(readlink -f $LLVM/../compiler-rt)"
   
   (cd compiler_rt_build_android_$_arch && cmake \
-    -DCMAKE_C_COMPILER=$ROOT/llvm_build64/bin/clang \
-    -DCMAKE_CXX_COMPILER=$ROOT/llvm_build64/bin/clang++ \
+    -DCMAKE_C_COMPILER=$CLANG_PATH \
+    -DCMAKE_CXX_COMPILER=$CLANGXX_PATH \
     -DLLVM_CONFIG_PATH=$ROOT/llvm_build64/bin/llvm-config \
     -DCOMPILER_RT_BUILD_BUILTINS=OFF \
     -DCOMPILER_RT_INCLUDE_TESTS=ON \
     -DCOMPILER_RT_ENABLE_WERROR=ON \
     -DCMAKE_ASM_FLAGS="$ANDROID_FLAGS" \
     -DCMAKE_C_FLAGS="$ANDROID_FLAGS" \
     -DCMAKE_CXX_FLAGS="$ANDROID_CXX_FLAGS" \
     -DANDROID=1 \
     -DCOMPILER_RT_TEST_COMPILER_CFLAGS="$ANDROID_FLAGS" \
     -DCOMPILER_RT_TEST_TARGET_TRIPLE=$_triple \
     -DCOMPILER_RT_OUTPUT_DIR="$ANDROID_LIBRARY_OUTPUT_DIR" \
     -DCOMPILER_RT_EXEC_OUTPUT_DIR="$ANDROID_EXEC_OUTPUT_DIR" \
     -DLLVM_LIT_ARGS="-sv --show-unsupported --show-xfail" \
     ${CMAKE_COMMON_OPTIONS} \
     ${COMPILER_RT_OPTIONS} || echo @@@STEP_FAILURE@@@) &
 }
 
function test_arch_on_device {
   local _arch=$1
   local _serial=$2
   local _build_id=$3
   local _build_flavor=$4
 
   export DEVICE_DESCRIPTION=$_arch/$_build_flavor/$_build_id
 
   ANDROID_TOOLCHAIN=$ROOT/android_ndk/standalone-$_arch
-  LIBCXX_SHARED=$(find $ANDROID_TOOLCHAIN/ -name libc++_shared.so | head -1)
+  LIBCXX_SHARED=$ROOT/$NDK_DIR/standalone-$_arch/sysroot/usr/lib/libc++_shared.so
   SYMBOLIZER_BIN=$ROOT/llvm_build_android_$_arch/bin/llvm-symbolizer
   RT_DIR=$($ROOT/llvm_build64/bin/clang -print-resource-dir)/lib/linux
   COMPILER_RT_BUILD_DIR=$ROOT/compiler_rt_build_android_$_arch
   export ADB=adb
   export DEVICE_ROOT=/data/local/tmp/Output
   export ANDROID_SERIAL=$_serial
   echo "Serial $_serial"