How to repack after extracting system.img?

[fulalas]

Sorry to ask such a silly question, but I love the project and just wanted to included hosts file and remove a few apks, however, after extracting system.img using simg2img and mounting, I'm failing to repack to a valid img file using make_ext4fs and finally img2simg, which gives the following output:

img2simg: sparse.cpp:131: int write_all_blocks(sparse_file*, output_file*): Assertion ``pad >= 0' failed.
Aborted

I read some tutorials saying that I should have file_contexts (when running make_ext4fs), but I couldn't find it anywhere. Thanks!