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diff --git a/NOTES-ANDROID.md b/NOTES-ANDROID.md new file mode 100644 index 0000000000..e1e7370d26 --- /dev/null +++ b/NOTES-ANDROID.md @@ -0,0 +1,90 @@ +NOTES FOR ANDROID PLATFORMS +=========================== + + Requirement details + ------------------- + + Beside basic tools like perl and make you'll need to download the Android + NDK. It's available for Linux, macOS and Windows, but only Linux + version was actually tested. There is no reason to believe that macOS + wouldn't work. And as for Windows, it's unclear which "shell" would be + suitable, MSYS2 might have best chances. NDK version should play lesser + role, the goal is to support a range of most recent versions. + + Configuration + ------------- + + Android is a cross-compiled target and you can't rely on `./Configure` + to find out the configuration target for you. You have to name your + target explicitly; there are `android-arm`, `android-arm64`, `android-mips`, + `android-mip64`, `android-x86` and `android-x86_64` (`*MIPS` targets are no + longer supported with NDK R20+). + + Do not pass --cross-compile-prefix (as you might be tempted), as it + will be "calculated" automatically based on chosen platform. However, + you still need to know the prefix to extend your PATH, in order to + invoke `$(CROSS_COMPILE)clang` [`*gcc` on NDK 19 and lower] and company. + (`./Configure` will fail and give you a hint if you get it wrong.) + + Apart from `PATH` adjustment you need to set `ANDROID_NDK_ROOT` environment + to point at the `NDK` directory. If you're using a side-by-side NDK the path + will look something like `/some/where/android-sdk/ndk/<ver>`, and for a + standalone NDK the path will be something like `/some/where/android-ndk-<ver>`. + Both variables are significant at both configuration and compilation times. + The NDK customarily supports multiple Android API levels, e.g. `android-14`, + `android-21`, etc. By default latest API level is chosen. If you need to target + an older platform pass the argument `-D__ANDROID_API__=N` to `Configure`, + with `N` being the numerical value of the target platform version. For example, + to compile for Android 10 arm64 with a side-by-side NDK r20.0.5594570 + + export ANDROID_NDK_ROOT=/home/whoever/Android/android-sdk/ndk/20.0.5594570 + PATH=$ANDROID_NDK_ROOT/toolchains/llvm/prebuilt/linux-x86_64/bin:$ANDROID_NDK_ROOT/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin:$PATH + ./Configure android-arm64 -D__ANDROID_API__=29 + make + + Older versions of the NDK have GCC under their common prebuilt tools + directory, so the bin path will be slightly different. EG: to compile + for ICS on ARM with NDK 10d: + + export ANDROID_NDK_ROOT=/some/where/android-ndk-10d + PATH=$ANDROID_NDK_ROOT/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin:$PATH + ./Configure android-arm -D__ANDROID_API__=14 + make + + Caveat lector! Earlier OpenSSL versions relied on additional `CROSS_SYSROOT` + variable set to `$ANDROID_NDK_ROOT/platforms/android-<api>/arch-<arch>` to + appoint headers-n-libraries' location. It's still recognized in order + to facilitate migration from older projects. However, since API level + appears in `CROSS_SYSROOT` value, passing `-D__ANDROID_API__=N` can be in + conflict, and mixing the two is therefore not supported. Migration to + `CROSS_SYSROOT`-less setup is recommended. + + One can engage clang by adjusting PATH to cover same NDK's clang. Just + keep in mind that if you miss it, Configure will try to use gcc... + Also, PATH would need even further adjustment to cover unprefixed, yet + target-specific, ar and ranlib. It's possible that you don't need to + bother, if binutils-multiarch is installed on your Linux system. + + Another option is to create so called "standalone toolchain" tailored + for single specific platform including Android API level, and assign its + location to `ANDROID_NDK_ROOT`. In such case you have to pass matching + target name to Configure and shouldn't use `-D__ANDROID_API__=N`. `PATH` + adjustment becomes simpler, `$ANDROID_NDK_ROOT/bin:$PATH` suffices. + + Running tests (on Linux) + ------------------------ + + This is not actually supported. Notes are meant rather as inspiration. + + Even though build output targets alien system, it's possible to execute + test suite on Linux system by employing qemu-user. The trick is static + linking. Pass -static to Configure, then edit generated Makefile and + remove occurrences of -ldl and -pie flags. You would also need to pick + API version that comes with usable static libraries, 42/2=21 used to + work. Once built, you should be able to + + env EXE_SHELL=qemu-<arch> make test + + If you need to pass additional flag to qemu, quotes are your friend, e.g. + + env EXE_SHELL="qemu-mips64el -cpu MIPS64R6-generic" make test |