Default [Q] log or logcat at boot ( not bootanimation )

i am a dev , and i try to make a lightweigh ROM
i decreased size of the rom too much but it doesn't run ( bootloop at boot logo , not bootanimation , i can't see bootanimation )
i know that my work is so crazy but i need it please help
1----- i need logcat to know what happens but logcat is impossible before bootanimation (maybe that is bootlog , i don't know)
i really need to fix it
2----- is there a way to use a emulator to test my rom quickly and see changes by add a file?