NOTES.ANDROID

   1
   2  NOTES FOR ANDROID PLATFORMS
   3  ===========================
   4
   5  Requirement details
   6  -------------------
   7
   8  Beside basic tools like perl and make you'll need to download the Android
   9  NDK. It's available for Linux, Mac OS X and Windows, but only Linux
  10  version was actually tested. There is no reason to believe that Mac OS X
  11  wouldn't work. And as for Windows, it's unclear which "shell" would be
  12  suitable, MSYS2 might have best chances. NDK version should play lesser
  13  role, the goal is to support a range of most recent versions.
  14
  15  Configuration
  16  -------------
  17
  18  Android is a naturally cross-compiled target and you can't use ./config.
  19  You have to use ./Configure and name your target explicitly; there are
  20  android-arm, android-arm64, android-mips, android-mip64, android-x86
  21  and android-x86_64 (*MIPS targets are no longer supported with NDK R20+).
  22  Do not pass --cross-compile-prefix (as you might be tempted), as it will
  23  be "calculated" automatically based on chosen platform. Though you still
  24  need to know the prefix to extend your PATH, in order to invoke
  25  $(CROSS_COMPILE)clang [*gcc on NDK 19 and lower] and company. (Configure
  26  will fail and give you a hint if you get it wrong.) Apart from PATH
  27  adjustment you need to set ANDROID_NDK_ROOT environment to point at the
  28  NDK directory. If you're using a side-by-side NDK the path will look
  29  something like /some/where/android-sdk/ndk/<ver>, and for a standalone
  30  NDK the path will be something like /some/where/android-ndk-<ver>.
  31  Both variables are significant at both configuration and compilation times.
  32  The NDK customarily supports multiple Android API levels, e.g. android-14,
  33  android-21, etc. By default latest API level is chosen. If you need to
  34  target an older platform pass the argument -D__ANDROID_API__=N to Configure,
  35  with N being the numerical value of the target platform version. For example,
  36  to compile for Android 10 arm64 with a side-by-side NDK r20.0.5594570
  37
  38         export ANDROID_NDK_ROOT=/home/whoever/Android/android-sdk/ndk/20.0.5594570
  39         PATH=$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
  40         ./Configure android-arm64 -D__ANDROID_API__=29
  41         make
  42
  43  Older versions of the NDK have GCC under their common prebuilt tools directory, so the bin path
  44  will be slightly different. EG: to compile for ICS on ARM with NDK 10d:
  45
  46     export ANDROID_NDK_ROOT=/some/where/android-ndk-10d
  47     PATH=$ANDROID_NDK_ROOT/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin:$PATH
  48     ./Configure android-arm -D__ANDROID_API__=14
  49     make
  50
  51  Caveat lector! Earlier OpenSSL versions relied on additional CROSS_SYSROOT
  52  variable set to $ANDROID_NDK_ROOT/platforms/android-<api>/arch-<arch> to
  53  appoint headers-n-libraries' location. It's still recognized in order
  54  to facilitate migration from older projects. However, since API level
  55  appears in CROSS_SYSROOT value, passing -D__ANDROID_API__=N can be in
  56  conflict, and mixing the two is therefore not supported. Migration to
  57  CROSS_SYSROOT-less setup is recommended.
  58
  59  One can engage clang by adjusting PATH to cover same NDK's clang. Just
  60  keep in mind that if you miss it, Configure will try to use gcc...
  61  Also, PATH would need even further adjustment to cover unprefixed, yet
  62  target-specific, ar and ranlib. It's possible that you don't need to
  63  bother, if binutils-multiarch is installed on your Linux system.
  64
  65  Another option is to create so called "standalone toolchain" tailored
  66  for single specific platform including Android API level, and assign its
  67  location to ANDROID_NDK_ROOT. In such case you have to pass matching
  68  target name to Configure and shouldn't use -D__ANDROID_API__=N. PATH
  69  adjustment becomes simpler, $ANDROID_NDK_ROOT/bin:$PATH suffices.
  70
  71  Running tests (on Linux)
  72  ------------------------
  73
  74  This is not actually supported. Notes are meant rather as inspiration.
  75
  76  Even though build output targets alien system, it's possible to execute
  77  test suite on Linux system by employing qemu-user. The trick is static
  78  linking. Pass -static to Configure, then edit generated Makefile and
  79  remove occurrences of -ldl and -pie flags. You would also need to pick
  80  API version that comes with usable static libraries, 42/2=21 used to
  81  work. Once built, you should be able to
  82
  83     env EXE_SHELL=qemu-<arch> make test
  84
  85  If you need to pass additional flag to qemu, quotes are your friend, e.g.
  86
  87     env EXE_SHELL="qemu-mips64el -cpu MIPS64R6-generic" make test