Update Android build instr. for ARMv8, PIE, etc.

* Include information on how to do a 64-bit ARMv8 build with the latest
NDK
* Suggest -fPIE and -pie as default CFLAGS (required for android-16 and
later.
* Remove -fstrict-aliasing flag (-Wall already includes it)

diff --git a/BUILDING.txt b/BUILDING.txt
index 062641220020971a732af20c2b40d68faa57f280..c68225b47fbb75129adf9672183def7164cd36f3 100644 (file)
--- a/BUILDING.txt
+++ b/BUILDING.txt
@@ -436,18 +436,25 @@ a general recipe script that can be modified for your specific needs.
   # Set these variables to suit your needs
   NDK_PATH={full path to the "ndk" directory-- for example, /opt/android/ndk}
   BUILD_PLATFORM={the platform name for the NDK package you installed--
-    for example, "windows-x86" or "linux-x86_64"}
-  TOOLCHAIN_VERSION={"4.6", "4.8", etc.  This corresponds to a toolchain
-    directory under ${NDK_PATH}/toolchains/.}
+    for example, "windows-x86" or "linux-x86_64" or "darwin-x86_64"}
+  TOOLCHAIN_VERSION={"4.8", "4.9", "clang3.5", etc.  This corresponds to a
+    toolchain directory under ${NDK_PATH}/toolchains/.}
   ANDROID_VERSION={The minimum version of Android to support-- for example,
-    "9", "19", etc.}
+    "16", "19", etc.  "21" or later is required for a 64-bit build.}
 
+  # 32-bit ARMv7 build
   HOST=arm-linux-androideabi
-  TOOLCHAIN=${NDK_PATH}/toolchains/${HOST}-${TOOLCHAIN_VERSION}/prebuilt/${BUILD_PLATFORM}
   SYSROOT=${NDK_PATH}/platforms/android-${ANDROID_VERSION}/arch-arm
-  ANDROID_INCLUDES="-I${SYSROOT}/usr/include -I${TOOLCHAIN}/include"
   ANDROID_CFLAGS="-march=armv7-a -mfloat-abi=softfp -fprefetch-loop-arrays \
-    -fstrict-aliasing --sysroot=${SYSROOT}"
+    --sysroot=${SYSROOT}"
+
+  # 64-bit ARMv8 build
+  HOST=aarch64-linux-android
+  SYSROOT=${NDK_PATH}/platforms/android-${ANDROID_VERSION}/arch-arm64
+  ANDROID_CFLAGS="--sysroot=${SYSROOT}"
+
+  TOOLCHAIN=${NDK_PATH}/toolchains/${HOST}-${TOOLCHAIN_VERSION}/prebuilt/${BUILD_PLATFORM}
+  ANDROID_INCLUDES="-I${SYSROOT}/usr/include -I${TOOLCHAIN}/include"
   export CPP=${TOOLCHAIN}/bin/${HOST}-cpp
   export AR=${TOOLCHAIN}/bin/${HOST}-ar
   export AS=${TOOLCHAIN}/bin/${HOST}-as
@@ -459,11 +466,14 @@ a general recipe script that can be modified for your specific needs.
   export STRIP=${TOOLCHAIN}/bin/${HOST}-strip
   cd {build_directory}
   sh {source_directory}/configure --host=${HOST} \
-    CFLAGS="${ANDROID_INCLUDES} ${ANDROID_CFLAGS} -O3" \
+    CFLAGS="${ANDROID_INCLUDES} ${ANDROID_CFLAGS} -O3 -fPIE" \
     CPPFLAGS="${ANDROID_INCLUDES} ${ANDROID_CFLAGS}" \
-    LDFLAGS="${ANDROID_CFLAGS}" --with-simd ${1+"$@"}
+    LDFLAGS="${ANDROID_CFLAGS} -pie" --with-simd ${1+"$@"}
   make
 
+If building for Android 4.0.x (API level < 16) or earlier, remove -fPIE from
+CFLAGS and -pie from LDFLAGS.
+
 
 *******************************************************************************
 **     Building on Windows (Visual C++ or MinGW)