Enables building examples with Android NDK

Soft enable runtime cpu detect for armv7-android target, so that it
can be disabled and remove dependency on 'cpufeatures' lib.
Change the arm_cpu_caps implementation selection such that 'no rtcd' takes
precedence over system type.

Switch to use -mtune instead of -mcpu. NDK was complaining about
-mcpu=cortex-a8 conflicting with -march=armv7-a, not sure why.

Add a linker flag to fix some cortex-a8 bug, as suggested by NDK Dev
Guide.

Examples:
Configure for armv7+neon:

./configure --target=armv7-android-gcc \
            --sdk-path=/path/to/android/ndk \
            --disable-runtime-cpu-detect \
            --enable-realtime-only \
            --disable-unit-tests

...armv7 w/o neon:

./configure --target=armv7-android-gcc \
            --sdk-path=/path/to/android/ndk \
            --disable-runtime-cpu-detect \
            --enable-realtime-only \
            --disable-neon \
            --cpu=cortex-a9 \
            --disable-unit-tests

Change-Id: I37e2c0592745208979deec38f7658378d4bd6cfa

3 files changed, 53 insertions, 31 deletions

diff --git a/build/make/Android.mk b/build/make/Android.mk
index 6fcd4aec3..d54639aa6 100644
--- a/build/make/Android.mk
+++ b/build/make/Android.mk
@@ -34,8 +34,15 @@
 # Application.mk in the jni directory that contains:
 # APP_ABI := armeabi-v7a
 #
+# By default libvpx will detect at runtime the existance of NEON extension.
+# For this we import the 'cpufeatures' module from the NDK sources.
+# libvpx can also be configured without this runtime detection method.
+# Configuring with --disable-runtime-cpu-detect will assume presence of NEON.
+# Configuring with --disable-runtime-cpu-detect --disable-neon will remove any
+# NEON dependency.
+
 # To change to building armeabi, run ./libvpx/configure again, but with
-# --target=arm5te-android-gcc and and modify the Application.mk file to
+# --target=arm5te-android-gcc and modify the Application.mk file to
 # set APP_ABI := armeabi
 #
 # Running ndk-build will build libvpx and include it in your project.
@@ -166,7 +173,9 @@ LOCAL_MODULE := libvpx
 
 LOCAL_LDLIBS := -llog
 
-LOCAL_STATIC_LIBRARIES := cpufeatures
+ifeq ($(CONFIG_RUNTIME_CPU_DETECT),yes)
+  LOCAL_STATIC_LIBRARIES := cpufeatures
+endif
 
 $(foreach file, $(LOCAL_SRC_FILES), $(LOCAL_PATH)/$(file)): vpx_rtcd.h
 
@@ -196,4 +205,7 @@ ifeq ($(CONFIG_VP8_ENCODER), yes)
     $(LIBVPX_PATH)/vp8/encoder/asm_enc_offsets.c))
 endif
 
+ifeq ($(CONFIG_RUNTIME_CPU_DETECT),yes)
 $(call import-module,cpufeatures)
+endif
+
diff --git a/build/make/configure.sh b/build/make/configure.sh
index 575a394ff..9a520a997 100755
--- a/build/make/configure.sh
+++ b/build/make/configure.sh
@@ -773,17 +773,23 @@ process_common_toolchain() {
             check_add_asflags --defsym ARCHITECTURE=${arch_int}
             tune_cflags="-mtune="
             if [ ${tgt_isa} == "armv7" ]; then
+                check_add_cflags  -march=armv7-a -mfloat-abi=softfp
+                check_add_asflags -march=armv7-a -mfloat-abi=softfp
+
                 if enabled neon
                 then
                     check_add_cflags -mfpu=neon #-ftree-vectorize
                     check_add_asflags -mfpu=neon
                 fi
-                check_add_cflags -march=armv7-a -mcpu=cortex-a8 -mfloat-abi=softfp
-                check_add_asflags -mcpu=cortex-a8 -mfloat-abi=softfp  #-march=armv7-a
+
+                if [ -z "${tune_cpu}" ]; then
+                    tune_cpu=cortex-a8
+                fi
             else
                 check_add_cflags -march=${tgt_isa}
                 check_add_asflags -march=${tgt_isa}
             fi
+
             enabled debug && add_asflags -g
             asm_conversion_cmd="${source_path}/build/make/ads2gas.pl"
             ;;
@@ -851,12 +857,17 @@ process_common_toolchain() {
             add_cflags "--sysroot=${alt_libc}"
             add_ldflags "--sysroot=${alt_libc}"
 
-            add_cflags "-I${SDK_PATH}/sources/android/cpufeatures/"
+            # linker flag that routes around a CPU bug in some
+            # Cortex-A8 implementations (NDK Dev Guide)
+            add_ldflags "-Wl,--fix-cortex-a8"
 
             enable pic
             soft_enable realtime_only
             if [ ${tgt_isa} == "armv7" ]; then
-                enable runtime_cpu_detect
+                soft_enable runtime_cpu_detect
+            fi
+            if enabled runtime_cpu_detect; then
+                add_cflags "-I${SDK_PATH}/sources/android/cpufeatures"
             fi
           ;;
 
diff --git a/vpx_ports/arm_cpudetect.c b/vpx_ports/arm_cpudetect.c
index ebe428df3..ff37ed173 100644
--- a/vpx_ports/arm_cpudetect.c
+++ b/vpx_ports/arm_cpudetect.c
@@ -32,8 +32,30 @@ static int arm_cpu_env_mask(void)
     return env && *env ? (int)strtol(env, NULL, 0) : ~0;
 }
 
+#if !CONFIG_RUNTIME_CPU_DETECT
 
-#if defined(_MSC_VER)
+int arm_cpu_caps(void)
+{
+    int flags;
+    int mask;
+    if (!arm_cpu_env_flags(&flags))
+    {
+        return flags;
+    }
+    mask = arm_cpu_env_mask();
+#if defined(HAVE_EDSP)
+    flags |= HAS_EDSP;
+#endif
+#if defined(HAVE_MEDIA)
+    flags |= HAS_MEDIA;
+#endif
+#if defined(HAVE_NEON)
+    flags |= HAS_NEON;
+#endif
+    return flags & mask;
+}
+
+#elif defined(_MSC_VER)
 /*For GetExceptionCode() and EXCEPTION_ILLEGAL_INSTRUCTION.*/
 #define WIN32_LEAN_AND_MEAN
 #define WIN32_EXTRA_LEAN
@@ -189,30 +211,7 @@ int arm_cpu_caps(void)
     return flags & mask;
 }
 #endif // defined(__linux__)
-#elif !CONFIG_RUNTIME_CPU_DETECT
-
-int arm_cpu_caps(void)
-{
-    int flags;
-    int mask;
-    if (!arm_cpu_env_flags(&flags))
-    {
-        return flags;
-    }
-    mask = arm_cpu_env_mask();
-#if defined(HAVE_EDSP)
-    flags |= HAS_EDSP;
-#endif
-#if defined(HAVE_MEDIA)
-    flags |= HAS_MEDIA;
-#endif
-#if defined(HAVE_NEON)
-    flags |= HAS_NEON;
-#endif
-    return flags & mask;
-}
-
 #else
 #error "--enable-runtime-cpu-detect selected, but no CPU detection method " \
- "available for your platform. Reconfigure without --enable-runtime-cpu-detect."
+ "available for your platform. Reconfigure with --disable-runtime-cpu-detect."
 #endif