"undefined reference" build error during init build

[Jaejyn Shin]

Dear Android developers

I want to add some feature into the libselinux using libutils

   - libselinux: external/libselinux

   - libutils: system/core/libutils

The libselinux build succeeded, but the init(system/core/init) build failed.

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target StaticExecutable: init (my_project/target/product/my_project/obj/EXECUTABLES/init_intermediates/LINKED/init)

my_project/target/product/my_project/obj/STATIC_LIBRARIES/libselinux_intermediates/libselinux.a(dump_stack.o): In function `dump_stack_android':

my_source/android/external/libselinux/src/dump_stack.cpp:5: undefined reference to `android::CallStack::CallStack()'

my_source/android/external/libselinux/src/dump_stack.cpp:6: undefined reference to `android::CallStack::update(int, int)'

my_source/android/external/libselinux/src/dump_stack.cpp:6: undefined reference to `android::CallStack::~CallStack()'

collect2: error: ld returned 1 exit status

make: *** [my_project/target/product/my_project/obj/EXECUTABLES/init_intermediates/LINKED/init] Error 1

make: Leaving directory `my_project/android'

#### make failed to build some targets (19 seconds) ####

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I modified my source like it.

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external/libselinux/Android.mk [modified source]

LOCAL_SRC_FILES := $(common_SRC_FILES) $(common_HOST_FILES) src/android.c

+LOCAL_SRC_FILES := $(common_SRC_FILES) $(common_HOST_FILES) src/android.c src/dump_stack.cpp

 LOCAL_MODULE:= libselinux

 LOCAL_MODULE_TAGS := eng

-LOCAL_STATIC_LIBRARIES := libmincrypt

+LOCAL_STATIC_LIBRARIES := libmincrypt libutils

external/libselinux/src/dump_stack.cpp [new_file]

+#include <utils/CallStack.h>

+using namespace android;

+extern "C" void dump_stack_android(void)

+{

+        CallStack stack;

+        stack.update();

+//      stack.dump();

+ }

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Please help me to solve this build error.

Thank you

Best regards