Search code examples
androidandroid-ndkdlopen

Undefined Symbol Error for a Header File in Android NDK

I am using a native library with my Android Studio project. I'm trying to utilize net-snmp, which is a C library (This is, unfortunately, a must-have. I cannot use alternatives as there is a larger native library which depends upon this.). We have compiled these into .so files and have done this correctly (To my knowledge, it compiles without errors in any case.).

However, whenever trying to load these library, I get the following error: java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "endgrent" referenced by "libnetsnmp.so"...

This function is from grp.h which is included in every version of Android NDK. Here is the relavent section of the Android.mk file:

include $(CLEAR_VARS)
LOCAL_MODULE := NetSNMP
LOCAL_SRC_FILES := net-snmp/libnetsnmp.so
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/net-snmp/include
include $(PREBUILT_SHARED_LIBRARY)

I'm kind of new to NDK, but all the undefined symbol errors I found usually referred to it being unable to find the appropriate folder. As far as I know, this should be pulled in by Android NDK. Am I doing something wrong here? Is this just some error unrelated to the makefile?

UPDATE: Even after trying to move the grp.h file over to the includes I already have, I still find the same error.

Solution

  • So I'm pretty sure I figured this out, if someone else happens to have this problem. For some reason or another, this file simply just does not exist. Luckily, this was an alternative route (if it exists, call it instead). However, NDK does not understand if includes (but the compiler does, thus it was not put into the library).

    So it searched for grp.h even though it had not been included. So, it crashed. Removing this, it fixed the error.

    However, for anyone else venturing down this path, we began experiencing problems with the version numbers (it was crashing because it was trying to find 'foo.so.#'). If you make the version void within the makefile and recompile, this should also fix this issue. In future versions of NDK or Android, there may be a fix for version numbers, but there is not as of writing this. So getting rid of the version numbers is your best route right now.