On my Ubuntu 21.03 host, I follow the coreboot doc to build a simple ROM: https://doc.coreboot.org/tutorial/part1.html
This is the steps I take and a few screenshot below. This coreboot’s payload is a ELF coreinfo application.
sudo apt-get install -y bison build-essential curl flex git gnat libncurses5-dev m4 zlib1g-dev git clone https://review.coreboot.org/coreboot cd coreboot make crossgcc-i386 CPUS=$(nproc) make -C payloads/coreinfo olddefconfig make -C payloads/coreinfo make menuconfig select 'Mainboard' menu Beside 'Mainboard vendor' should be '(Emulation)' Beside 'Mainboard model' should be 'QEMU x86 i440fx/piix4' select < Exit > select 'Payload' menu select 'Add a Payload' choose 'An Elf executable payload' select 'Payload