[libc++][Android] Support libc++ testing on Android (#69274)

I could probably break this commit into more pieces.

---

This patch adds libc++ support for Android L (Android 5.0+) and up,
tested using the Android team's current compiler, a recent version of
the AOSP sysroot, and the x86[-64] Android Emulator.

CMake and Lit Configuration:

Add runtimes/cmake/android/Arch-${ARCH}.cmake files that configure CMake
to cross-compile to Android without using CMake's built-in NDK support
(which only works with an actual packaged NDK).

Add libcxx/cmake/caches/AndroidNDK.cmake that builds and tests libc++
(and libc++abi) for Android. This file configures libc++ to match what
the NDK distributes, e.g.:
- libc++_shared.so (includes libc++abi objects, there is no
libc++abi.so). libunwind is linked statically but not exported.
 - libc++_static.a (does not include libc++abi) and libc++abi.a
 - `std::__ndk1` namespace
- All the libraries are built with `__ANDROID_API__=21`, even when they
are linked to something targeting a higher API level.

(However, when the Android LLVM team builds these components, they do
not use these CMake cache files. Instead they use Python scripts to
configure the builds. See
https://android.googlesource.com/toolchain/llvm_android/.)

Add llvm-libc++[abi].android-ndk.cfg.in files that test the Android
NDK's libc++_shared.so. These files can target old or new Android
devices. The Android LLVM team uses these test files to test libc++ for
both arm/arm64 and x86/x86_64 architectures.

The Android testing mode works by setting %{executor} to adb_run.py,
which uses `adb push` and `adb shell` to run tests remotely. adb_run.py
always runs tests as the "shell" user even on an old emulator where "adb
unroot" doesn't work. The script has workarounds for old Android
devices. The script uses a Unix domain socket on the host
(--job-limit-socket) to restrict concurrent adb invocations. Compiling
the tests is a major part of libc++ testing run-time, so it's desirable
to exploit all the host cores without overburdening the test devices,
which can have far fewer cores.

BuildKite CI:

Add a builder to run-buildbot, `android-ndk-*`, that uses Android Clang
and an Android sysroot to build libc++, then starts an Android emulator
container to run tests.

Run the emulator and an adb server in a separate Docker container
(libcxx-ci-android-emulator), and create a separate Docker image for
each emulator OS system image. Set ADB_SERVER_SOCKET to connect to the
container's adb server. Running the only adb server inside the container
makes cleanup more reliable between test runs, e.g. the adb client
doesn't create a `~/.android` directory and the adb server can be
restarted along with the emulator using docker stop/run. (N.B. The
emulator insists on connecting to an adb server and will start one
itself if it can't connect to one.)

The suffix to the android-ndk-* job is a label that concisely specifies
an Android SDK emulator image. e.g.:
 - "system-images;android-21;default;x86" ==> 21-def-x86
 - "system-images;android-33;google_apis;x86_64" ==> 33-goog-x86_64

Fixes: https://github.com/llvm/llvm-project/issues/69270
Differential Revision: https://reviews.llvm.org/D139147

1 files changed, 40 insertions, 0 deletions

diff --git a/libcxxabi/test/configs/llvm-libc++abi-android-ndk.cfg.in b/libcxxabi/test/configs/llvm-libc++abi-android-ndk.cfg.in
new file mode 100644
index 0000000..f2cb62a
--- /dev/null
+++ b/libcxxabi/test/configs/llvm-libc++abi-android-ndk.cfg.in
@@ -0,0 +1,40 @@
+# This testing configuration handles running the test suite against LLVM's
+# libc++abi using adb and a libc++_shared.so library on Android.
+
+lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
+
+import re
+import site
+
+site.addsitedir(os.path.join('@LIBCXX_SOURCE_DIR@', 'utils'))
+
+import libcxx.test.android
+import libcxx.test.config
+import libcxx.test.params
+
+config.substitutions.append(('%{flags}',
+    '--sysroot @CMAKE_SYSROOT@' if '@CMAKE_SYSROOT@' else ''
+))
+config.substitutions.append(('%{compile_flags}',
+    '-nostdinc++ -I %{include} -I %{cxx-include} -I %{cxx-target-include} %{maybe-include-libunwind} -I %{libcxx}/test/support -I %{libcxx}/src -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS'
+))
+
+# The NDK library is called "libc++_shared.so". Use LD_LIBRARY_PATH to find
+# libc++_shared.so because older Bionic dynamic loaders don't support rpath
+# lookup. The Android libc++ shared library exports libc++abi, so we don't need
+# to link with -lc++abi.
+config.substitutions.append(('%{link_flags}',
+    '-nostdlib++ -L %{lib} -lc++_shared'
+))
+config.substitutions.append(('%{exec}',
+    '%{executor}' +
+    ' --job-limit-socket ' + libcxx.test.android.adb_job_limit_socket() +
+    ' --prepend-path-env LD_LIBRARY_PATH /data/local/tmp/libc++ --execdir %T -- '
+))
+
+libcxx.test.config.configure(
+    libcxx.test.params.DEFAULT_PARAMETERS,
+    libcxx.test.features.DEFAULT_FEATURES,
+    config,
+    lit_config
+)