[TF-A] How to load some images in BL31?

Hi all,

I want to load a specific image in BL31. But when I call load_auth_image(). It says

"in function `load_image': trusted-firmware-a/common/bl_common.c:87: undefined reference to `plat_get_image_source'"

Also, the io_read, io_size and etc. are undefined reference.

I find other BL files (bl1, bl2) will call the load_auth_image() in their main functions or sub-functions. If I want to implement it on BL31, what should I do? Should I modify the Makefile?

Sincerely, Wang