Add legacy Android build support & patches

Enable building older Python releases for Android using a legacy patched cross-build flow and add necessary patches and tooling. Changes include:

- Add android/android-env.sh to configure NDK/r27d toolchain, environment variables, and cross-compile flags.
- Add multiple patches (bldlibrary, grp, python_for_build_deps, soname, sysroot_paths) to fix cross-compilation, linking and packaging issues on Android.
- Update build scripts to be version-aware:
  - .github workflow now packages armeabi-v7a for Python < 3.13.
  - android/build-all.sh selects ABIs based on Python version (3.13+ uses official tool, older versions include armeabi-v7a and x86).
  - android/build.sh applies patches and either uses the legacy cross-build flow (for <= 3.12) with prebuilt libs and custom configure/make/install steps or uses CPython's Android/android.py for 3.13+.
  - Set CCSHARED, CONFIG_SITE, sysroot include/lib paths and other flags needed for current NDKs and cross-compilation.
- Add ABI-to-host mappings for armeabi-v7a and x86 in android/abi-to-host.sh.
- Improve NDK detection in android/package-for-dart.sh to prefer locally installed NDKs.
- Update android/README.md to document the two build flows (3.12 legacy vs 3.13+ official) and ABI support.

These changes allow building and packaging older Python versions for a wider set of Android ABIs and fix several cross-compile/link/runtime issues encountered when targeting Android.

Author: FeodorFitsner

.github/workflows/build-python.yml

@@ -79,6 +79,11 @@ jobs:
           tar -czf dist/python-android-mobile-forge-$PYTHON_VERSION_SHORT.tar.gz install support
           bash ./package-for-dart.sh install "$PYTHON_VERSION" arm64-v8a
           bash ./package-for-dart.sh install "$PYTHON_VERSION" x86_64
+          read version_major version_minor < <(echo "$PYTHON_VERSION" | sed -E 's/^([0-9]+)\.([0-9]+).*/\1 \2/')
+          version_int=$((version_major * 100 + version_minor))
+          if [ $version_int -lt 313 ]; then
+            bash ./package-for-dart.sh install "$PYTHON_VERSION" armeabi-v7a
+          fi
       - uses: actions/upload-artifact@v4
         with:
           name: python-android

android/README.md

@@ -1,15 +1,15 @@
 # Python for Android
 
-Scripts and CI jobs for building Python 3.13 for Android.
+Scripts and CI jobs for building Python for Android.
 
 * Can be run on both Linux and macOS.
-* Builds Python 3.13.x only.
-* Creates Python installation with a structure suitable for https://github.com/flet-dev/mobile-forge
-* Uses CPython's official `Android/android.py` build flow.
+* Python 3.12 uses the legacy patched cross-build flow.
+* Python 3.13+ uses CPython's official `Android/android.py` build flow.
+* Creates Python installation with a structure suitable for https://github.com/flet-dev/mobile-forge.
 
 ## Usage
 
-To build Python for a specific ABI (`arm64-v8a` or `x86_64`):
+To build Python for a specific ABI:
 
 ```
 ./build.sh 3.13.12 arm64-v8a
@@ -21,7 +21,9 @@ To build all ABIs:
 ./build-all.sh 3.13.12
 ```
 
-For Python 3.13+, official CPython Android tooling currently supports `arm64-v8a` and `x86_64`.
+ABI support:
+* Python 3.12: `arm64-v8a`, `armeabi-v7a`, `x86_64`, `x86`
+* Python 3.13+: `arm64-v8a`, `x86_64`
 
 ## Credits
 

android/abi-to-host.sh

@@ -1,7 +1,13 @@
 case ${abi:?} in
+    armeabi-v7a)
+        HOST=arm-linux-androideabi
+        ;;
     arm64-v8a)
         HOST=aarch64-linux-android
         ;;
+    x86)
+        HOST=i686-linux-android
+        ;;
     x86_64)
         HOST=x86_64-linux-android
         ;;

android/android-env.sh

@@ -0,0 +1,138 @@
+# This script must be sourced with the following variables already set:
+: ${HOST:?}  # GNU target triplet
+
+# You may also override the following:
+: ${api_level:=24}  # Minimum Android API level the build will run on
+: ${PREFIX:-}  # Path in which to find required libraries
+
+NDK_VERSION=r27d
+
+# Print all messages on stderr so they're visible when running within build-wheel.
+log() {
+    echo "$1" >&2
+}
+
+fail() {
+    log "$1"
+    exit 1
+}
+
+# When moving to a new version of the NDK, carefully review the following:
+#
+# * https://developer.android.com/ndk/downloads/revision_history
+#
+# * https://android.googlesource.com/platform/ndk/+/ndk-rXX-release/docs/BuildSystemMaintainers.md
+#   where XX is the NDK version. Do a diff against the version you're upgrading from, e.g.:
+#   https://android.googlesource.com/platform/ndk/+/ndk-r25-release..ndk-r26-release/docs/BuildSystemMaintainers.md
+if [[ -z "${NDK_HOME-}" ]]; then
+    NDK_HOME=$HOME/ndk/$NDK_VERSION
+    echo "NDK_HOME environment variable is not set."
+    if [ ! -d $NDK_HOME ]; then
+        echo "Installing NDK $NDK_VERSION to $NDK_HOME"
+
+        if [ $(uname) = "Darwin" ]; then
+            seven_zip=$downloads/7zip/7zz
+            if ! test -f $seven_zip; then
+                echo "Installing 7-zip"
+                mkdir -p $(dirname $seven_zip)
+                cd $(dirname $seven_zip)
+                curl -#OL https://www.7-zip.org/a/7z2301-mac.tar.xz
+                tar -xf 7z2301-mac.tar.xz
+                cd -
+            fi
+
+            ndk_dmg=android-ndk-$NDK_VERSION-darwin.dmg
+            if ! test -f $downloads/$ndk_dmg; then
+                echo ">>> Downloading $ndk_dmg"
+                curl -#L -o $downloads/$ndk_dmg https://dl.google.com/android/repository/$ndk_dmg
+            fi
+
+            cd $downloads
+            $seven_zip x -snld $ndk_dmg
+            mkdir -p $(dirname $NDK_HOME)
+            mv Android\ NDK\ */AndroidNDK*.app/Contents/NDK $NDK_HOME
+            rm -rf Android\ NDK\ *
+            cd -
+        else
+            ndk_zip=android-ndk-$NDK_VERSION-linux.zip
+            if ! test -f $downloads/$ndk_zip; then
+                echo ">>> Downloading $ndk_zip"
+                curl -#L -o $downloads/$ndk_zip https://dl.google.com/android/repository/$ndk_zip
+            fi
+            cd $downloads
+            unzip -oq $ndk_zip
+            mkdir -p $(dirname $NDK_HOME)
+            mv android-ndk-$NDK_VERSION $NDK_HOME
+            cd -
+            echo "NDK installed to $NDK_HOME"
+        fi
+    else
+        echo "NDK $NDK_VERSION is already installed in $NDK_HOME"
+    fi
+else
+    echo "NDK home: $NDK_HOME"
+fi
+
+if [ $HOST = "arm-linux-androideabi" ]; then
+    clang_triplet=armv7a-linux-androideabi
+else
+    clang_triplet=$HOST
+fi
+
+# These variables are based on BuildSystemMaintainers.md above, and
+# $NDK_HOME/build/cmake/android.toolchain.cmake.
+toolchain=$(echo $NDK_HOME/toolchains/llvm/prebuilt/*)
+export AR="$toolchain/bin/llvm-ar"
+export AS="$toolchain/bin/llvm-as"
+export CC="$toolchain/bin/${clang_triplet}${api_level}-clang"
+export CXX="${CC}++"
+export LD="$toolchain/bin/ld"
+export NM="$toolchain/bin/llvm-nm"
+export RANLIB="$toolchain/bin/llvm-ranlib"
+export READELF="$toolchain/bin/llvm-readelf"
+export STRIP="$toolchain/bin/llvm-strip"
+
+# The quotes make sure the wildcard in the `toolchain` assignment has been expanded.
+for path in "$AR" "$AS" "$CC" "$CXX" "$LD" "$NM" "$RANLIB" "$READELF" "$STRIP"; do
+    if ! [ -e "$path" ]; then
+        fail "$path does not exist"
+    fi
+done
+
+export CFLAGS="-D__BIONIC_NO_PAGE_SIZE_MACRO"
+export LDFLAGS="-Wl,--build-id=sha1 -Wl,--no-rosegment -Wl,-z,max-page-size=16384"
+
+# Unlike Linux, Android does not implicitly use a dlopened library to resolve
+# relocations in subsequently-loaded libraries, even if RTLD_GLOBAL is used
+# (https://github.com/android/ndk/issues/1244). So any library that fails to
+# build with this flag, would also fail to load at runtime.
+LDFLAGS="$LDFLAGS -Wl,--no-undefined"
+
+# Many packages get away with omitting -lm on Linux, but Android is stricter.
+LDFLAGS="$LDFLAGS -lm"
+
+# -mstackrealign is included where necessary in the clang launcher scripts which are
+# pointed to by $CC, so we don't need to include it here.
+if [ $HOST = "arm-linux-androideabi" ]; then
+    CFLAGS="$CFLAGS -march=armv7-a -mthumb"
+fi
+
+if [ -n "${PREFIX:-}" ]; then
+    abs_prefix=$(realpath $PREFIX)
+    CFLAGS="$CFLAGS -I$abs_prefix/include"
+    LDFLAGS="$LDFLAGS -L$abs_prefix/lib"
+
+    export PKG_CONFIG="pkg-config --define-prefix"
+    export PKG_CONFIG_LIBDIR="$abs_prefix/lib/pkgconfig"
+fi
+
+# When compiling C++, some build systems will combine CFLAGS and CXXFLAGS, and some will
+# use CXXFLAGS alone.
+export CXXFLAGS=$CFLAGS
+
+# Use the same variable name as conda-build
+if [ $(uname) = "Darwin" ]; then
+    export CPU_COUNT=$(sysctl -n hw.ncpu)
+else
+    export CPU_COUNT=$(nproc)
+fi

android/build-all.sh

@@ -2,7 +2,16 @@
 set -euo pipefail
 
 python_version=${1:?}
-abis="arm64-v8a x86_64"
+read version_major version_minor < <(
+    echo "$python_version" | sed -E 's/^([0-9]+)\.([0-9]+).*/\1 \2/'
+)
+version_int=$((version_major * 100 + version_minor))
+
+if [ $version_int -ge 313 ]; then
+    abis="arm64-v8a x86_64"
+else
+    abis="arm64-v8a armeabi-v7a x86_64 x86"
+fi
 
 for abi in $abis; do
     bash ./build.sh $python_version $abi