[coreboot] IBB and Coreboot

[Melvin Walker]

I am looking to use coreboot on a project, but I am confused about Boot Guard, FSP, Coreboot, and the IBB.
Let's say I purchase a mainboard without Boot Guard enabled that supports coreboot. I build coreboot and put it in flash. I enable Boot Guard with the FIT Tool.
When I boot, Boot Guard will authenticate the IBB.  But, where does the IBB come from?
Does it come from the FSP or is there a ".c" file in the coreboot source repository that reflects what will end up in the IBB?
Melvin