交叉编译opencv：undefined reference to `png_riffle_palette_neon

• 错误

usr/lib/gcc-cross/aarch64-linux-gnu/8/../../../../aarch64-linux-gnu/bin/ld: ../../lib/libopencv_imgcodecs.so.4.2.0: undefined reference to `png_riffle_palette_neon'
collect2: error: ld returned 1 exit status
make[2]: *** [apps/annotation/CMakeFiles/opencv_annotation.dir/build.make:89：bin/opencv_annotation] 错误 1
make[1]: *** [CMakeFiles/Makefile2:3746：apps/annotation/CMakeFiles/opencv_annotation.dir/all] 错误 2      

• 解决办法

方法一：无效

进入到3rdparty/libpng，在CMakeLists.txt顶端增加：

set(ENABLE_NEON ON)      

方法二：有效

${HOME}/

opencv

-3.3.1/3rdparty/libpng/pngpriv.h

/*# if (defined(ARM_NEON) || defined(__ARM_NEON)) && */
 
if defined(PNG_ARM_NEON) && (defined(ARM_NEON) || defined(__ARM_NEON)) && \      

如上所示，把上面的一行注释掉，增加下面一行。再次make即可。