cannot find -lgnustl_static: Compiling Android SDL port with NDK r7

Question

I'm trying to build this port of libSDL for Android, using the new Android NDK r7 release:

https://github.com/pelya/commandergenius

I know I am doing some things to some degree "unsupported": I am using cygwin&windows despite that being mentioned in the README as no longer being supported. That being said, I can hack out shell scripts and solve my problems as necessary and have it compiling but not linking.

So anyways I have compiling working until the linking (sorry for large block, relevant part trimmed below):

/cygdrive/c/and/android-ndk-r7/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-ar crs obj/local/armeabi/libflac.a ./obj/local/armeabi/objs-debug/flac/src/ogg_decoder_aspect.o ./obj/local/armeabi/objs-debug/flac/src/md5.o ./obj/local/armeabi/objs-debug/flac/src/stream_decoder.o ./obj/local/armeabi/objs-debug/flac/src/fixed.o ./obj/local/armeabi/objs-debug/flac/src/memory.o ./obj/local/armeabi/objs-debug/flac/src/stream_encoder.o ./obj/local/armeabi/objs-debug/flac/src/window.o ./obj/local/armeabi/objs-debug/flac/src/cpu.o ./obj/local/armeabi/objs-debug/flac/src/ogg_encoder_aspect.o ./obj/local/armeabi/objs-debug/flac/src/lpc.o ./obj/local/armeabi/objs-debug/flac/src/float.o ./obj/local/armeabi/objs-debug/flac/src/bitmath.o ./obj/local/armeabi/objs-debug/flac/src/metadata_object.o ./obj/local/armeabi/objs-debug/flac/src/ogg_helper.o ./obj/local/armeabi/objs-debug/flac/src/metadata_iterators.o ./obj/local/armeabi/objs-debug/flac/src/bitreader.o ./obj/local/armeabi/objs-debug/flac/src/bitwriter.o ./obj/local/armeabi/objs-debug/flac/src/stream_encoder_framing.o ./obj/local/armeabi/objs-debug/flac/src/crc.o ./obj/local/armeabi/objs-debug/flac/src/format.o ./obj/local/armeabi/objs-debug/flac/src/ogg_mapping.o
C:/and/android-ndk-r7/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/bin/ld.exe: cannot find -lgnustl_static
collect2: ld returned 1 exit status
/cygdrive/c/and/android-ndk-r7/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/arm-linux-androideabi-ar crs obj/local/armeabi-v7a/libflac.a ./obj/local/armeabi-v7a/objs-debug/flac/src/ogg_decoder_aspect.o ./obj/local/armeabi-v7a/objs-debug/flac/src/md5.o ./obj/local/armeabi-v7a/objs-debug/flac/src/stream_decoder.o ./obj/local/armeabi-v7a/objs-debug/flac/src/fixed.o ./obj/local/armeabi-v7a/objs-debug/flac/src/memory.o ./obj/local/armeabi-v7a/objs-debug/flac/src/stream_encoder.o ./obj/local/armeabi-v7a/objs-debug/flac/src/window.o ./obj/local/armeabi-v7a/objs-debug/flac/src/cpu.o ./obj/local/armeabi-v7a/objs-debug/flac/src/ogg_encoder_aspect.o ./obj/local/armeabi-v7a/objs-debug/flac/src/lpc.o ./obj/local/armeabi-v7a/objs-debug/flac/src/float.o ./obj/local/armeabi-v7a/objs-debug/flac/src/bitmath.o ./obj/local/armeabi-v7a/objs-debug/flac/src/metadata_object.o ./obj/local/armeabi-v7a/objs-debug/flac/src/ogg_helper.o ./obj/local/armeabi-v7a/objs-debug/flac/src/metadata_iterators.o ./obj/local/armeabi-v7a/objs-debug/flac/src/bitreader.o ./obj/local/armeabi-v7a/objs-debug/flac/src/bitwriter.o ./obj/local/armeabi-v7a/objs-debug/flac/src/stream_encoder_framing.o ./obj/local/armeabi-v7a/objs-debug/flac/src/crc.o ./obj/local/armeabi-v7a/objs-debug/flac/src/format.o ./obj/local/armeabi-v7a/objs-debug/flac/src/ogg_mapping.o
C:/and/android-ndk-r7/toolchains/arm-linux-androideabi-4.4.3/prebuilt/windows/bin/../lib/gcc/arm-linux-androideabi/4.4.3/../../../../arm-linux-androideabi/bin/ld.exe: cannot find -lgnustl_static
collect2: ld returned 1 exit status

Relevant failure, if you can't parse that wall of text:

ld.exe: cannot find -lgnustl_static

Now, if I look at the Windows NDK release I find gnustl_* files here:

under ./android-ndk-r7/sources:

./cxx-stl/gnu-libstdc++/libs/armeabi/libgnustl_shared.so
./cxx-stl/gnu-libstdc++/libs/armeabi/libgnustl_static.a
./cxx-stl/gnu-libstdc++/libs/armeabi-v7a/libgnustl_shared.so
./cxx-stl/gnu-libstdc++/libs/armeabi-v7a/libgnustl_static.a
./cxx-stl/gnu-libstdc++/libs/x86/libgnustl_shared.so
./cxx-stl/gnu-libstdc++/libs/x86/libgnustl_static.a

I looked also at the linux android NDK distribution and they are packaged the same (only have libgnustl files, built, under the sources directory).

So I have 3 questions:

• why would we be using -l to link libgnustl_static when it's a .a file? Shouldn't that be just including the .a file in the object list, or alternately be -lgnustl_shared?
• why are these files only under "sources"? I would have expected them to be in the "toolchains" library NDK directory. How does anyone ever link against libgnustl?
• Can I copy these files somewhere where they'll be seen by the linker? Just adding their directory with -L hasn't seemed to work, and plus I need to get the right versions linked with the right build target (armeabi vs armeabi-v7 vs x86)

Answer 1

This is a bug in gcc/NDK that manifests itself slightly different on Linux, Cygwin, and Windows (non Cygwin).

Here's what I did to fix it (works for Linux and for one of my developers who is blind and has to use Cygwin)...

• Remove the line that says, APP_STL := gnustl_static from your Application.mk (it's broken in the NDK, and it's broken slightly differently on Linux Cygwin, Windows)

• add a line to $(LOCAL_LDLIBS) in your Android.mk file that says:

  $(NDK_ROOT)/sources/cxx-stl/gnu-libstdc++/4.6/libs/armeabi-v7a/libgnustl_static.a

also add two lines to Android.mk that say:

LOCAL_C_INCLUDES := $(NDK_ROOT)/sources/cxx-stl/gnu-libstdc++/4.6/include
LOCAL_C_INCLUDES += $(NDK_ROOT)/sources/cxx-stl/gnu-libstdc++/4.6/libs/armeabi-v7a/include

The foregoing will accomplish what having, APP_STL := gnustl_static in your Application.mk was supposed to.