Add NOTES.ANDROID.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5613)

1 files changed, 67 insertions, 0 deletions

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+
+ 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, Mac OS X and Windows, but only Linux
+ version was actually tested. There is no reason to believe that Mac OS X
+ 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 naturally cross-compiled target and you can't use ./config.
+ You have to use ./Configure and name your target explicitly; there are
+ android-arm, android-arm64, android-mips, android-mip64, android-x86
+ and android-x86_64. Do not pass --cross-compile-prefix (as you might
+ be tempted), as it will be "calculated" automatically based on chosen
+ platform. Though you still need to know the prefix to extend your PATH,
+ in order to invoke $(CROSS_COMPILE)gcc and company. (Configure will fail
+ and give you a hint if you get it wrong.) Apart from PATH adjustment
+ you need to set ANDROID_NDK environment to point at NDK directory
+ as /some/where/android-ndk-<ver>. NDK customarily supports multiple
+ Android API levels, e.g. android-14, android-21, etc. By default latest 
+ one available is chosen. If you need to target older platform, pass
+ additional -D__ANDROID_API__=N to Configure. N is numeric value of the
+ target platform version. For example, to compile for ICS on ARM with
+ NDK 10d:
+
+    ANDROID_NDK=/some/where/android-ndk-10d
+    PATH=$ANDROID_NDK/toolchains/arm-linux-androideabi-4.8/prebuild/linux-x86_64/bin:$PATH
+    ./Configure android-arm -D__ANDROID_API__=14
+
+ Caveat lector! Earlier OpenSSL versions relied on additional CROSS_SYSROOT
+ variable set to $ANDROID_NDK/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 passing CC=clang to Configure. In such case
+ PATH needs even more adjustments to cover NDK's clang itself, as well
+ as unprefixed, yet target-specific, ar and ranlib (or not, if you use
+ binutils-multiarch on your Linux).
+
+ 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