Android NDK with static library: linker throws 'undefined reference' all the time - c++

Question

First, I want to say that I've tried all other solutions on SO and the rest of the Internet.
My goal is to build dlib for android as a static library and create shared object as a wrap for JNI.
First part is compiling dlib as a static library. Here is my Android.mk:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := dlib
LOCAL_C_INCLUDES := $(LOCAL_PATH)/../
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/entropy_encoder/entropy_encoder_kernel_2.cpp
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/entropy_encoder/entropy_encoder_kernel_1.cpp
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/all/source.cpp
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/gui_widgets/drawable.cpp
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/gui_widgets/widgets.cpp
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/gui_widgets/base_widgets.cpp
... cut many src files for simplicity.
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/threads/thread_pool_extension.cpp
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/misc_api/misc_api_kernel_1.cpp
LOCAL_SRC_FILES += $(LOCAL_PATH)/../dlib/misc_api/misc_api_kernel_2.cpp
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_C_INCLUDES)
include $(BUILD_STATIC_LIBRARY)
and Application.mk:
NDK_TOOLCHAIN_VERSION := clang
APP_ABI := armeabi-v7a x86
APP_CPPFLAGS := -std=c++11 -frtti -fexceptions -Os
APP_PLATFORM := android-15
APP_STL := c++_static
#APP_CFLAGS+=-DDLIB_NO_GUI_SUPPORT=on
#APP_CFLAGS+=-DDLIB_PNG_SUPPORT=off
APP_CFLAGS+=-DDLIB_JPEG_SUPPORT=on
APP_CFLAGS+=-DDLIB_JPEG_STATIC=on
###
ANDROID_NATIVE_API_LEVEL = 15
ANDROID_NDK_HOST_X64 = true
ANDROID_SDK_TARGET = 15
This works fine. I get my static library (which is 8 times bigger than when compiled with system gcc).
Next I'm trying to create wrap for JNI. My mod.cpp:
#include <jni.h>
#include <string>
#include "dlib/image_processing/frontal_face_detector.h"
extern "C"
JNIEXPORT jstring JNICALL
Java_com_cake_appa_MainActivity_stringFromJNI(
JNIEnv* env,
jobject /* this */) {
std::string hello = "Hello from C++";
dlib::frontal_face_detector detector = dlib::get_frontal_face_detector();
return env->NewStringUTF(hello.c_str());
}
Android.mk:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := dlib
LOCAL_SRC_FILES := $(LOCAL_PATH)/../lib/$(TARGET_ARCH_ABI)/libdlib.a
LOCAL_C_INCLUDES := $(LOCAL_PATH)/../include/
include $(PREBUILT_STATIC_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := mod
LOCAL_C_INCLUDES := $(LOCAL_PATH)/../include/
LOCAL_C_INCLUDES += /usr/include/
LOCAL_SRC_FILES += $(LOCAL_PATH)/../mod.cpp
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_C_INCLUDES)
LOCAL_STATIC_LIBRARIES := dlib
LOCAL_STATIC_LIBRARY := dlib
include $(BUILD_SHARED_LIBRARY)
Application.mk:
NDK_TOOLCHAIN_VERSION := clang
APP_ABI := armeabi-v7a x86
APP_CPPFLAGS := -std=c++11 -frtti -fexceptions -Os
APP_PLATFORM := android-15
APP_STL := c++_static
And what I get when I try to build:
cake#cake-hi:/media/storage/tmp/ndk-wrap$ export NDK_PROJECT_PATH=`pwd`
cake#cake-hi:/media/storage/tmp/ndk-wrap$ /storage/android-sdk/ndk-bundle/ndk-build
[armeabi-v7a] Compile++ thumb: mod <= mod.cpp
[armeabi-v7a] SharedLibrary : libmod.so
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1958: error: undefined reference to 'XClearArea'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1959: error: undefined reference to 'XFlush'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1984: error: undefined reference to 'XVaCreateNestedList'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1985: error: undefined reference to 'XSetICValues'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1986: error: undefined reference to 'XFree'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1834: error: undefined reference to 'XAllocSizeHints'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1840: error: undefined reference to 'XSetNormalHints'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1841: error: undefined reference to 'XFree'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1844: error: undefined reference to 'XResizeWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1846: error: undefined reference to 'XFlush'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1760: error: undefined reference to 'XwcTextListToTextProperty'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1761: error: undefined reference to 'XSetWMName'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1762: error: undefined reference to 'XFree'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1763: error: undefined reference to 'XFlush'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1712: error: undefined reference to 'XDestroyWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1893: error: undefined reference to 'XTranslateCoordinates'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1868: error: undefined reference to 'XMoveWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1869: error: undefined reference to 'XFlush'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1593: error: undefined reference to 'XCreateWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1620: error: undefined reference to 'XCreateFontSet'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1623: error: undefined reference to 'XVaCreateNestedList'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1624: error: undefined reference to 'XCreateIC'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1631: error: undefined reference to 'XFree'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1632: error: undefined reference to 'XFreeStringList'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1642: error: undefined reference to 'XGetICValues'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1644: error: undefined reference to 'XSelectInput'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1652: error: undefined reference to 'XSetWMProtocols'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1668: error: undefined reference to 'XAllocSizeHints'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1674: error: undefined reference to 'XSetNormalHints'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1690: error: undefined reference to 'XDestroyIC'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1692: error: undefined reference to 'XFreeFontSet'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1777: error: undefined reference to 'XMapRaised'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1804: error: undefined reference to 'XUnmapWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:639: error: undefined reference to 'XPending'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:649: error: undefined reference to 'XNextEvent'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:653: error: undefined reference to 'XFilterEvent'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:679: error: undefined reference to 'XInternAtom'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:685: error: undefined reference to 'XChangeProperty'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:794: error: undefined reference to 'XwcLookupString'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:797: error: undefined reference to 'XwcLookupString'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:731: error: undefined reference to 'XAllocSizeHints'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:737: error: undefined reference to 'XSetNormalHints'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:745: error: undefined reference to 'XResizeWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:752: error: undefined reference to 'XMoveWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1050: error: undefined reference to 'XCheckIfEvent'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:697: error: undefined reference to 'XChangeProperty'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:717: error: undefined reference to 'XSendEvent'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:804: error: undefined reference to 'XLookupString'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1018: error: undefined reference to 'XDestroyWindow'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1223: error: undefined reference to 'XInitImage'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1225: error: undefined reference to 'XCreateGC'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1227: error: undefined reference to 'XPutImage'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1229: error: undefined reference to 'XFreeGC'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1266: error: undefined reference to 'XGetModifierMapping'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1272: error: undefined reference to 'XkbKeycodeToKeysym'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1294: error: undefined reference to 'XFreeModifiermap'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1365: error: undefined reference to 'XSetSelectionOwner'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1423: error: undefined reference to 'XInternAtom'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1424: error: undefined reference to 'XGetSelectionOwner'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1436: error: undefined reference to 'XConvertSelection'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1441: error: undefined reference to 'XPeekIfEvent'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1444: error: undefined reference to 'XGetWindowProperty'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1461: error: undefined reference to 'XGetWindowProperty'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1468: error: undefined reference to 'XwcTextPropertyToTextList'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1473: error: undefined reference to 'XwcFreeStringList'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1485: error: undefined reference to 'XwcFreeStringList'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:1934: error: undefined reference to 'XScreenNumberOfScreen'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:334: error: undefined reference to 'XOpenDisplay'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:337: error: undefined reference to 'XOpenDisplay'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:369: error: undefined reference to 'XFreeFontSet'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:371: error: undefined reference to 'XCreateFontSet'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:376: error: undefined reference to 'XExtentsOfFontSet'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:379: error: undefined reference to 'XFreeStringList'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:322: error: undefined reference to 'XwcTextExtents'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:388: error: undefined reference to 'XFreeGC'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:389: error: undefined reference to 'XFreePixmap'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:393: error: undefined reference to 'XDefaultDepth'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:393: error: undefined reference to 'XCreatePixmap'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:394: error: undefined reference to 'XCreateGC'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:398: error: undefined reference to 'XSetForeground'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:399: error: undefined reference to 'XSetBackground'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:400: error: undefined reference to 'XFillRectangle'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:401: error: undefined reference to 'XSetForeground'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:328: error: undefined reference to 'XwcDrawString'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:405: error: undefined reference to 'XGetImage'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:313: error: undefined reference to 'XAllocColor'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:435: error: undefined reference to 'XQueryColor'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:449: error: undefined reference to 'XFreeGC'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:450: error: undefined reference to 'XFreeFontSet'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:451: error: undefined reference to 'XFreePixmap'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_widgets/nativefont.h:452: error: undefined reference to 'XCloseDisplay'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:148: error: undefined reference to 'XPutBackEvent'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:153: error: undefined reference to 'XSendEvent'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:160: error: undefined reference to 'XCloseIM'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:163: error: undefined reference to 'XCloseDisplay'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:191: error: undefined reference to 'XInitThreads'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:203: error: undefined reference to 'XOpenDisplay'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:208: error: undefined reference to 'XOpenDisplay'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:225: error: undefined reference to 'XInternAtom'
/media/storage/tmp/ndk-dlib/jni/../dlib/all/../gui_core/gui_core_kernel_2.cpp:272: error: undefined reference to 'XCreateWindow'
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
/media/storage/android-sdk/ndk-bundle/build/core/build-binary.mk:677: recipe for target '/media/storage/tmp/ndk-wrap/obj/local/armeabi-v7a/libmod.so' failed
make: *** [/media/storage/tmp/ndk-wrap/obj/local/armeabi-v7a/libmod.so] Error 1
Linker says it can't find X libraries. I guess, my system package libx11-dev:i386 won't do anything. Tried LOCAL_ALLOW_UNDEFINED_SYMBOLS := true which results in endless build which eats all system memory (6 GiB process).
Same thing happens to OpenCV, but undefined references are with something else.
I'm on Debian 9.3 x86_64.

Answer 1

LOCAL_C_INCLUDES += /usr/include/
Don't do this; these header files are not compatible with Android. Android does not use glibc.
I guess, my system package libx11-dev:i386 won't do anything.
No, it won't, but you do need to get your dependency from somewhere. You'll need to build that library for Android and include it (or rewrite your code to not use that library).