This is how to make a program that runs directly on UEFI.
==> This was done on Ubuntu 20 -> download qemu (virtual machine), gcc (c compiler), ovmf(enalbes UEFI in QEMU), gnu-efi (c libraries and dependancies for efi development) sudo apt-get install gcc sudo apt-get install qemu sudo apt-get install virt-manager libvirt-daemon ovmf
-> Create efimain.c This is the efi application #include <efi.h> #include <efilib.h>
EFI_STATUS EFIAPI efi_main (EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE *SystemTable) { InitializeLib(ImageHandle, SystemTable); Print(L"Hello, world!\n"); return EFI_SUCCESS; }
-> Build efimain.c paying special attention to the paths of the efi libraries you downloaded -> Also makes efi disk image (dd command) #!/bin/bash
gcc efimain.c
-c
-fno-stack-protector
-fpic
-fshort-wchar
-mno-red-zone
-I /usr/include/efi
-I /usr/include/efi/x86_64
-DEFI_FUNCTION_WRAPPER
-o efimain.o
ld efimain.o
/usr/lib/crt0-efi-x86_64.o
-nostdlib
-znocombreloc
-T /usr/lib/elf_x86_64_efi.lds
-shared
-Bsymbolic
-L /usr/lib
-l:libgnuefi.a
-l:libefi.a
-o efimain.so
objcopy -j .text
-j .sdata
-j .data
-j .dynamic
-j .dynsym
-j .rel
-j .rela
-j .reloc
--target=efi-app-x86_64
efimain.so
efimain.efi
dd if=/dev/zero of=/home/divan/prog/os/uefi.img bs=512 count=93750
-> Create patitions on disk and prepare disk. gdisk /home/divan/prog/os/uefi.img
gdisk output and user commans below........... GPT fdisk (gdisk) version 0.8.10
Partition table scan: MBR: not present BSD: not present APM: not present GPT: not present
Creating new GPT entries.
Command (? for help): o <==== This option deletes all partitions and creates a new protective MBR. Proceed? (Y/N): y
Command (? for help): n <==== Partition number (1-128, default 1): 1 <==== First sector (34-93716, default = 2048) or {+-}size{KMGTP}: 2048 <==== Last sector (2048-93716, default = 93716) or {+-}size{KMGTP}: 93716 <==== Current type is 'Linux filesystem' Hex code or GUID (L to show codes, Enter = 8300): ef00 <=== Changed type of partition to 'EFI System'
Command (? for help): w <====
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING PARTITIONS!!
Do you want to proceed? (Y/N): y <==== OK; writing new GUID partition table (GPT) to uefi.img. Warning: The kernel is still using the old partition table. The new table will be used at the next reboot. The operation has completed successfully.
-> Mount image and copy UEFI app to image. Note that loop0 might already be in use, in that case just specify another. I used "sudo losetup -l" to check for an unused one and used 17 sudo losetup --offset 1048576 --sizelimit 46934528 /dev/loop17 /home/divan/prog/os/uefi.img sudo mkdosfs -F 32 /dev/loop17 sudo mount /dev/loop17 /mnt sudo cp /home/divan/prog/os/efimain.efi /mnt/ sudo umount /mnt sudo losetup -d /dev/loop0
-> Launch qemu with UEFI and use disk image we made sudo qemu-system-x86_64 -cpu qemu64 -bios /usr/share/ovmf/OVMF.fd -drive file="/home/divan/prog/os/uefi.img",if=ide
-> Inside machine. Wait for boot. Mine took a few minutes. I thought it was broken but the errors recieved seem to not be a problem. FS0: ls efimain.efi