Compile VIM2Pro Android source code succeed but the update.img doesn't work, what's wrong?

Hollo,
I have downloaded and compiled VIM2Pro Android source code successfully, but,
when download the update.imp onto my VIM2pro board, after KHADAS logo flash 2 times,
the screen black for error, no Android start logo appear… apparently firmware doesn’t work!
I did the compilation as following, can any one tell where may be the problem?

1, I downloaded the android codes according to docs.khadas.com, did the compiling on Ubuntu 19.04, use downloaded toolchains as CROSS_COMPILE=/opt/toolchains/gcc-linaro-6.3.1-2017.02-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-
2, I blocked Werror option in 2 Makefiles, to disable ‘all cc warnings are regarded as errors’, otherwise there are too many!!!
3, export LC_ALL=C, to disable a ‘sizeof…’ error, according to an ‘issue repot…’ solution
4, lacked of ‘compiler-gcc6.h’, I downloaded 1 according an ‘issue repot…’ solution
5, I include “mpi-inline.h” only in mpih-mul.c file, otherwise there will be ‘multi-definition error…’ for mpihelp_add_1 and other 3 inline functions definitions. (included in multi c files) when compiling mpi sub directory.

Thanks!

must use lower compiler then ok.