Does Android compiler honor -Wall?

Question

I'm trying to build a shared object with the following recipe in our Android.mk. The shared object is based on a C++ library.

include $(CLEAR_VARS)
LOCAL_MODULE := cryptopp_shared
LOCAL_SRC_FILES := $(addprefix $(CRYPTOPP_PATH),$(CRYPTOPP_SRC_FILES))
LOCAL_CPP_FLAGS := -Wall
LOCAL_CPP_FEATURES := rtti exceptions
LOCAL_LDFLAGS := -Wl,--exclude-libs,ALL -Wl,--as-needed

LOCAL_EXPORT_CFLAGS := $(LOCAL_CFLAGS)
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/..

LOCAL_STATIC_LIBRARIES := cpufeatures

include $(BUILD_SHARED_LIBRARY)

The library builds mostly OK. Some options are not being honored, like -Wall. Other options like -Wl,--exclude-libs,ALL are being honored.

The docs for Android.mk is here, but it does not discuss removing or filtering options.

Why is Android's build system not honoring all of our flags?

---

Here is the build command we used. I build from the library's root directory:

ndk-build V=1 APP_ABI=armeabi-v7a NDK_PROJECT_PATH="$PWD" 
    NDK_APPLICATION_MK="$PWD/Application.mk"

The odd thing is, all of our source files are C++ and none of the source files were built with -Wall. However, we import Android's cpufeatures library, it is one C source file, and it was built with -Wall:

/opt/android-ndk-r16b/toolchains/llvm/prebuilt/linux-x86_64/bin/clang -MMD -MP -
MF /home/cryptopp/obj/local/armeabi-v7a/objs/cpufeatures/cpu-features.o.d -gcc-t
oolchain /opt/android-ndk-r16b/toolchains/arm-linux-androideabi-4.9/prebuilt/lin
ux-x86_64 -fpic -ffunction-sections -funwind-tables -fstack-protector-strong -Wn
o-invalid-command-line-argument -Wno-unused-command-line-argument -no-canonical-
prefixes -fno-integrated-as -g -target armv7-none-linux-androideabi18 -march=arm
v7-a -mfloat-abi=softfp -mfpu=vfpv3-d16 -mthumb -Os -DNDEBUG  -I/opt/android-ndk
-r16b/sources/android/cpufeatures   -DANDROID -Wall -Wextra -Werror -D__ANDROID_
API__=18 -Wa,--noexecstack -Wformat -Werror=format-security  --sysroot /opt/andr
oid-ndk-r16b/sysroot -isystem /opt/android-ndk-r16b/sysroot/usr/include/arm-linu
x-androideabi -c  /opt/android-ndk-r16b/sources/android/cpufeatures/cpu-features
.c -o /home/cryptopp/obj/local/armeabi-v7a/objs/cpufeatures/cpu-features.o

Given I used LOCAL_CPP_FLAGS := -Wall I would think the opposite would happen - all C++ source files would build with -Wall, and the one C file would build without.

Answer 1

It's a mere typo, you need LOCAL_CPPFLAGS, only one _ there.

As for cpu-features.c, it receives -Wall because $(NDK_ROOT)/sources/android/cpufeatures/Android.mk requires this in LOCAL_CFLAGS.