Use Android NDK 25 and work around Rust/Android incompatibilities.

Use Android NDK 25 since that's GitHub Actions is moving to. SDK level
is the minimum supported, and there are no longer target-specific
allases for `llvm-ar`; update cargo.sh accordingly.

Use the environment variables recommended by the Android documentation.

Work around compatibility issue with Rust and Android NDKs.

Remove out-of-date documentation aboud building for Android.

Author: briansmith

BUILDING.md

@@ -76,12 +76,6 @@ Note in particular that if you are cross-compiling an x86 build on a 64-bit
 version of Linux, then you need to have the proper gcc-multilibs and
 g++-multilibs packages or equivalent installed.
 
-If you generate a standalone NDK toolchain in order to compile your project,
-the wrapper automatically passes flags to the actual compiler to define the
-`__ANDROID_API__` macro. Otherwise, the macro `__ANDROID_API__` must be
-defined with a value of at least 21 on 64-bit targets or 18 on 32-bit targets;
-e.g. export `CFLAGS=-D__ANDROID_API__=21`.
-
 
 Building for Windows ARM64
 --------------------------

mk/cargo.sh

@@ -24,8 +24,12 @@ qemu_arm="qemu-arm -L /usr/arm-linux-gnueabihf"
 # Avoid putting the Android tools in `$PATH` because there are tools in this
 # directory like `clang` that would conflict with the same-named tools that may
 # be needed to compile the build script, or to compile for other targets.
-if [ -n "${ANDROID_SDK_ROOT-}" ]; then
-  android_tools=$ANDROID_SDK_ROOT/ndk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin
+if [ -n "${ANDROID_HOME-}" ]; then
+  ndk_version=25.1.8937393
+  ANDROID_NDK_ROOT=${ANDROID_NDK_ROOT:-${ANDROID_HOME}/ndk/$ndk_version}
+fi
+if [ -n "${ANDROID_NDK_ROOT-}" ]; then
+  android_tools=${ANDROID_NDK_ROOT}/toolchains/llvm/prebuilt/linux-x86_64/bin
 fi
 
 for arg in $*; do
@@ -44,7 +48,7 @@ llvm_version=14
 case $target in
    aarch64-linux-android)
     export CC_aarch64_linux_android=$android_tools/aarch64-linux-android21-clang
-    export AR_aarch64_linux_android=$android_tools/aarch64-linux-android-ar
+    export AR_aarch64_linux_android=$android_tools/llvm-ar
     export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER=$android_tools/aarch64-linux-android21-clang
     ;;
   aarch64-unknown-linux-gnu)
@@ -67,9 +71,9 @@ case $target in
     export CARGO_TARGET_ARM_UNKNOWN_LINUX_GNUEABIHF_RUNNER="$qemu_arm"
     ;;
   armv7-linux-androideabi)
-    export CC_armv7_linux_androideabi=$android_tools/armv7a-linux-androideabi18-clang
-    export AR_armv7_linux_androideabi=$android_tools/arm-linux-androideabi-ar
-    export CARGO_TARGET_ARMV7_LINUX_ANDROIDEABI_LINKER=$android_tools/armv7a-linux-androideabi18-clang
+    export CC_armv7_linux_androideabi=$android_tools/armv7a-linux-androideabi19-clang
+    export AR_armv7_linux_androideabi=$android_tools/llvm-ar
+    export CARGO_TARGET_ARMV7_LINUX_ANDROIDEABI_LINKER=$android_tools/armv7a-linux-androideabi19-clang
     ;;
   armv7-unknown-linux-musleabihf)
     export CC_armv7_unknown_linux_musleabihf=clang-$llvm_version

mk/install-build-tools.sh

@@ -27,12 +27,19 @@ function install_packages {
 use_clang=
 case $target in
 --target*android*)
-  mkdir -p "${ANDROID_SDK_ROOT}/licenses"
-  android_license_file="${ANDROID_SDK_ROOT}/licenses/android-sdk-license"
+  mkdir -p "${ANDROID_HOME}/licenses"
+  ndk_version=25.1.8937393
+  android_license_file="${ANDROID_HOME}/licenses/android-sdk-license"
   accept_android_license=24333f8a63b6825ea9c5514f83c2829b004d1fee
   grep --quiet --no-messages "$accept_android_license" "$android_license_file" \
     || echo $accept_android_license  >> "$android_license_file"
-  "${ANDROID_SDK_ROOT}/cmdline-tools/latest/bin/sdkmanager" ndk-bundle
+  "${ANDROID_HOME}/cmdline-tools/latest/bin/sdkmanager" "ndk;$ndk_version"
+
+  ANDROID_NDK_ROOT=
+  # XXX: Older Rust toolchain versions link with `-lgcc` instead of `-lunwind`;
+  # see https://github.com/rust-lang/rust/pull/85806.
+  find -L ${ANDROID_NDK_ROOT:-${ANDROID_HOME}/ndk/$ndk_version} -name libunwind.a \
+          -execdir sh -c 'echo "INPUT(-lunwind)" > libgcc.a' \;
   ;;
 esac