How to resolve "Relocations in Generic ELF" during ndk-build?

Question

I'm trying to build a static library using a standalone toolchain for a project that has its own build process, which I then wrap with a C++ library and expose to Android (compiled with ndk-build). However, on the ndk-build step I receive the following error:

➜  jni /Users/chrisfosterelli/Library/Android/sdk/ndk-bundle/ndk-build                    
[arm64-v8a] Compile++      : wrapper <= wrapper.cpp
In file included from /Users/chrisfosterelli/workspace/android/jni/wrapper.cpp:9:
In file included from ../prebuild/include/valhalla/meili/universal_cost.h:7:
In file included from ../prebuild/include/valhalla/sif/dynamiccost.h:4:
In file included from ../prebuild/include/valhalla/baldr/directededge.h:5:
../prebuild/include/valhalla/baldr/graphconstants.h:432:11: warning: 21 enumeration values not handled in switch: 'kRoad', 'kRamp', 'kTurnChannel'... [-Wswitch]
  switch (use) {
          ^
1 warning generated.
[arm64-v8a] SharedLibrary  : libwrapper.so
/Users/chrisfosterelli/Library/Android/sdk/ndk-bundle/toolchains/aarch64-linux-android-4.9/prebuilt/darwin-x86_64/lib/gcc/aarch64-linux-android/4.9.x/../../../../aarch64-linux-android/bin/ld: /Users/chrisfosterelli/workspace/android/jni/../prebuild/libvalhalla_meili.a(libvalhalla_meili_la-map_matcher_factory.o): Relocations in generic ELF (EM: 62)
[...above message repeated many times...]
/Users/chrisfosterelli/workspace/android/jni/../prebuild/libvalhalla_meili.a: error adding symbols: File in wrong format
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [/Users/chrisfosterelli/workspace/android/obj/local/arm64-v8a/libwrapper.so] Error 1
➜  jni ls /Users/chrisfosterelli/Library/Android/sdk/ndk-bundle/

This error indicates, as far as I can tell, that I'm trying to mix and match binaries compiled for different architectures. However, from what I can tell the library is the correct architecture:

root@eacbdb1c0e46:/meili/meili2/newtest# ar x libvalhalla_meili.a 
root@eacbdb1c0e46:/meili/meili2/newtest# file libvalhalla_meili_la-map_matcher_factory.o 
libvalhalla_meili_la-map_matcher_factory.o: ELF 64-bit LSB relocatable, ARM aarch64, version 1 (SYSV), not stripped
root@eacbdb1c0e46:/meili/meili2/newtest#

FWIW, these are my current Application.mk,

APP_STL := c++_static
APP_CPPFLAGS := -frtti -std=gnu++11 -D_GLIBCXX_USE_C99
APP_CPPFLAGS += -fexceptions
NDK_TOOLCHAIN_VERSION := clang
APP_LDFLAGS := -latomic
APP_PLATFORM := android-21
APP_ABI := arm64-v8a

and Android.mk,

LOCAL_PATH := $(call my-dir)

# static library info
include $(CLEAR_VARS)
LOCAL_MODULE := libvalhalla_meili
LOCAL_SRC_FILES := ../prebuild/libvalhalla_meili.a
LOCAL_EXPORT_C_INCLUDES := ../prebuild/include
include $(PREBUILT_STATIC_LIBRARY)

# wrapper info
include $(CLEAR_VARS)
LOCAL_C_INCLUDES += ../prebuild/include
LOCAL_MODULE    := wrapper
LOCAL_SRC_FILES := wrapper.cpp
LOCAL_STATIC_LIBRARIES := libvalhalla_meili
include $(BUILD_SHARED_LIBRARY)

Any ideas how to resolve this? I've tried a number of things but all of them lead to more (more obscure) errors, so I'm hoping someone here can point me in the correct direction!

Answer 1

I discovered the problem, but I wish I had a more insightful answer. Apparently the build process had created two library files. The one that I inspected was, of course, ARM64. However the one that I actually copied to the Android device was x86.

So, the error message was correct and so was the library file, but there was more than one file involved. If you're running into the same problem and pretty sure your library is ARM64, double check that's actually the same file that is being compiled into the ndk build!