NOTES FOR ANDROID PLATFORMS
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.
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_HOME environment to point at NDK directory
as /some/where/android-ndk-<ver>. Both variables are significant at both
configuration and compilation times. 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
./Configure android-arm -D__ANDROID_API__=14
Caveat lector! Earlier OpenSSL versions relied on additional CROSS_SYSROOT
variable set to $ANDROID_NDK_HOME/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_HOME. In such case you have to pass matching
target name to Configure and shouldn't use -D__ANDROID_API__=N. PATH
adjustment becomes simpler, $ANDROID_NDK_HOME/bin:$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