xref: /openssl/NOTES-ANDROID.md (revision 2d321448)
1Notes for Android platforms
2===========================
3
4 Requirement details
5 -------------------
6
7 Beside basic tools like perl and make, you'll need to download the Android
8 NDK. It's available for Linux, macOS and Windows, but only Linux
9 version was actually tested. There is no reason to believe that macOS
10 wouldn't work. And as for Windows, it's unclear which "shell" would be
11 suitable, MSYS2 might have best chances. NDK version should play lesser
12 role, the goal is to support a range of most recent versions.
13
14 Configuration
15 -------------
16
17 Android is a cross-compiled target and you can't rely on `./Configure`
18 to find out the configuration target for you.  You have to name your
19 target explicitly; there are `android-arm`, `android-arm64`, `android-mips`,
20 `android-mip64`, `android-x86`, `android-x86_64` and `android-riscv64`
21 (`*MIPS` targets are no longer supported with NDK R20+).
22
23 Do not pass --cross-compile-prefix (as you might be tempted), as it
24 will be "calculated" automatically based on chosen platform. However,
25 you still need to know the prefix to extend your PATH, in order to
26 invoke `$(CROSS_COMPILE)clang` [`*gcc` on NDK 19 and lower] and company.
27 (`./Configure` will fail and give you a hint if you get it wrong.)
28
29 Apart from `PATH` adjustment, you need to set `ANDROID_NDK_ROOT` environment
30 to point at the `NDK` directory. If you're using a side-by-side NDK the path
31 will look something like `/some/where/android-sdk/ndk/<ver>`, and for a
32 standalone NDK the path will be something like `/some/where/android-ndk-<ver>`.
33 Both variables are significant at both configuration and compilation times.
34 The NDK customarily supports multiple Android API levels, e.g. `android-14`,
35 `android-21`, etc. By default, latest API level is chosen. If you need to target
36 an older platform pass the argument `-D__ANDROID_API__=N` to `Configure`,
37 with `N` being the numerical value of the target platform version. For example,
38 to compile for Android 10 arm64 with a side-by-side NDK r20.0.5594570
39
40    export ANDROID_NDK_ROOT=/home/whoever/Android/android-sdk/ndk/20.0.5594570
41    PATH=$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
42    ./Configure android-arm64 -D__ANDROID_API__=29
43    make
44
45 Older versions of the NDK have GCC under their common prebuilt tools
46 directory, so the bin path will be slightly different. EG: to compile
47 for ICS on ARM with NDK 10d:
48
49    export ANDROID_NDK_ROOT=/some/where/android-ndk-10d
50    PATH=$ANDROID_NDK_ROOT/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin:$PATH
51    ./Configure android-arm -D__ANDROID_API__=14
52    make
53
54 Caveat lector! Earlier OpenSSL versions relied on additional `CROSS_SYSROOT`
55 variable set to `$ANDROID_NDK_ROOT/platforms/android-<api>/arch-<arch>` to
56 appoint headers-n-libraries' location. It's still recognized in order
57 to facilitate migration from older projects. However, since API level
58 appears in `CROSS_SYSROOT` value, passing `-D__ANDROID_API__=N` can be in
59 conflict, and mixing the two is therefore not supported. Migration to
60 `CROSS_SYSROOT`-less setup is recommended.
61
62 One can engage clang by adjusting PATH to cover the same NDK's clang. Just
63 keep in mind that if you miss it, Configure will try to use gcc...
64 Also, PATH would need even further adjustment to cover unprefixed, yet
65 target-specific, ar and ranlib. It's possible that you don't need to
66 bother, if binutils-multiarch is installed on your Linux system.
67
68 Another option is to create so called "standalone toolchain" tailored
69 for single specific platform including Android API level, and assign its
70 location to `ANDROID_NDK_ROOT`. In such case, you have to pass matching
71 target name to Configure and shouldn't use `-D__ANDROID_API__=N`. `PATH`
72 adjustment becomes simpler, `$ANDROID_NDK_ROOT/bin:$PATH` suffices.
73
74 Running tests (on Linux)
75 ------------------------
76
77 This is not actually supported. Notes are meant rather as inspiration.
78
79 Even though build output targets alien system, it's possible to execute
80 test suite on Linux system by employing qemu-user. The trick is static
81 linking. Pass -static to Configure, then edit generated Makefile and
82 remove occurrences of -ldl and -pie flags. You would also need to pick
83 API version that comes with usable static libraries, 42/2=21 used to
84 work. Once built, you should be able to
85
86    env EXE_SHELL=qemu-<arch> make test
87
88 If you need to pass additional flag to qemu, quotes are your friend, e.g.
89
90    env EXE_SHELL="qemu-mips64el -cpu MIPS64R6-generic" make test
91