erts: Allow Android cross compilation to target Android 5.0 Lollipop

if_nameindex and if_freenameindex were added in Android 7.0 Nougat
so guard their usages when targeting earlier Android versions.

Update the Android documentation accordingly.

4 files changed, 9 insertions, 6 deletions

diff --git a/HOWTO/INSTALL-ANDROID.md b/HOWTO/INSTALL-ANDROID.md
index 34937b921e..5bef14d68f 100644
--- a/HOWTO/INSTALL-ANDROID.md
+++ b/HOWTO/INSTALL-ANDROID.md
@@ -29,7 +29,7 @@ to generate the configure scripts.
 
 Use the following when compiling a 64-bit version.
 
-    $ export NDK_ABI_PLAT=android24      # When targeting Android 7.0 Nougat
+    $ export NDK_ABI_PLAT=android21      # When targeting Android 5.0 Lollipop
     $ ./otp_build configure \
          --xcomp-conf=./xcomp/erl-xcomp-arm64-android.conf  \
          --without-ssl
@@ -37,7 +37,7 @@ Use the following when compiling a 64-bit version.
 
 Use the following instead when compiling a 32-bit version.
 
-    $ export NDK_ABI_PLAT=androideabi24  # When targeting Android 7.0 Nougat
+    $ export NDK_ABI_PLAT=androideabi21  # When targeting Android 5.0 Lollipop
     $ ./otp_build configure \
          --xcomp-conf=./xcomp/erl-xcomp-arm-android.conf  \
          --without-ssl
diff --git a/erts/emulator/nifs/common/prim_net_nif.c b/erts/emulator/nifs/common/prim_net_nif.c
index 5f7a2716f9..c7ecc99134 100644
--- a/erts/emulator/nifs/common/prim_net_nif.c
+++ b/erts/emulator/nifs/common/prim_net_nif.c
@@ -1109,7 +1109,7 @@ ERL_NIF_TERM nif_if_names(ErlNifEnv*         env,
                           int                argc,
                           const ERL_NIF_TERM argv[])
 {
-#if defined(__WIN32__)
+#if defined(__WIN32__) || (defined(__ANDROID__) && (__ANDROID_API__ < 24))
     return enif_raise_exception(env, MKA(env, "notsup"));
 #else
     ERL_NIF_TERM result;
@@ -1130,7 +1130,10 @@ ERL_NIF_TERM nif_if_names(ErlNifEnv*         env,
 
 
 
-#if !defined(__WIN32__)
+/* if_nameindex and if_freenameindex were added in Android 7.0 Nougat. With
+the Android NDK Unified Headers, check that the build is targeting at least
+the corresponding API level 24. */
+#if !defined(__WIN32__) && !(defined(__ANDROID__) && (__ANDROID_API__ < 24))
 static
 ERL_NIF_TERM nif_names(ErlNifEnv* env)
 {
diff --git a/xcomp/erl-xcomp-arm-android.conf b/xcomp/erl-xcomp-arm-android.conf
index 64f976fce8..1bddd2d8b9 100644
--- a/xcomp/erl-xcomp-arm-android.conf
+++ b/xcomp/erl-xcomp-arm-android.conf
@@ -87,7 +87,7 @@ NDK_SYSROOT=$NDK_ROOT/sysroot
 #   For older Android NDK versions still supporting GCC.
 #CC="arm-linux-androideabi-gcc --sysroot=$NDK_SYSROOT"
 #   For more recent Android NDK versions only supporting Clang/LLVM.
-#NDK_ABI_PLAT=androideabi24  # when targeting Android 7.0 Nougat
+#NDK_ABI_PLAT=androideabi21  # when targeting Android 5.0 Lollipop
 CC="armv7a-linux-$NDK_ABI_PLAT-clang"
 
 # * `CFLAGS' - C compiler flags.
diff --git a/xcomp/erl-xcomp-arm64-android.conf b/xcomp/erl-xcomp-arm64-android.conf
index bedee510e1..e423651fed 100644
--- a/xcomp/erl-xcomp-arm64-android.conf
+++ b/xcomp/erl-xcomp-arm64-android.conf
@@ -85,7 +85,7 @@ NDK_SYSROOT=$NDK_ROOT/sysroot
 # * `CC' - C compiler.
 #
 #   For recent Android NDK versions only supporting Clang/LLVM.
-#NDK_ABI_PLAT=android24  # when targeting Android 7.0 Nougat
+#NDK_ABI_PLAT=android21  # when targeting Android 5.0 Lollipop
 CC="aarch64-linux-$NDK_ABI_PLAT-clang"
 
 # * `CFLAGS' - C compiler flags.