error linking to libgcc.a when cross-compiling for Android, but symbols exists?

Question

I am trying to cross-compile a very simple program for Android that worked with android-ndk-r6b and prior, but does not work on android-ndk-r7 and newer:

Answer 1

Where to find: __aeabi_unwind_cpp_pr0 and other mysterious, undefined functions

(I had a similar problem error to what you describe, but found a different solution, that may be helpful to you or others)

I found 'libgccunwind.a' library in the Google NDK package which defines a number of these mysterious functions (they are functions referenced by libc.a and other libraries in the NDK package, but not defined in a standard library) I found them defined in a libgccunwind.a library in:

\sources\android\gccunwind\libs\armeabi

NM shows that they are defined in that lib from an 'unwind-arm.o' file:

nm libgccunwind.a

unwind-arm.o:
         U _GLOBAL_OFFSET_TABLE_
00000cf8 T _Unwind_Complete
00000cfc T _Unwind_DeleteException
00000ba4 T _Unwind_GetCFA
00000408 t _Unwind_GetGR
00000474 t _Unwind_SetGR
000003c4 T _Unwind_VRS_Get
0000084c T _Unwind_VRS_Pop
00000430 T _Unwind_VRS_Set
00000844 T __aeabi_unwind_cpp_pr0
0000083c W __aeabi_unwind_cpp_pr1
00000834 W __aeabi_unwind_cpp_pr2
         w __cxa_begin_cleanup
         w __cxa_call_unexpected
         w __cxa_type_match
         U __exidx_end
         U __exidx_start
00000d1c T __gnu_Unwind_Backtrace
         w __gnu_Unwind_Find_exidx

Independant of the libgccunwind.a above, I searched for __aeabi_unwind_cpp_pr0 and unwind-arm.c and unwind.c, and found various c source, for example:

http://lxr.free-electrons.com/source/arch/arm/kernel/unwind.c?a=arm

http://opensource.apple.com/source/gcc/gcc-5646/gcc/config/arm/unwind-arm.c

These programs seem to be derived from a similar source. My guess is that these 'unwind_cpp' (and related functions) are called by the functions in libc.a when a function returns or on certain events so that these functions can perform some debugging or tracing operation.

In any event, adding that directory in a -L linker option and -lgccunwind linker option (after the -lc linker option) allowed the linker to find those 'undefined' functions -- and let me get to the next problem I have in cross compiling to ARM systems.