Hello Computor!

This is an example EFI module that makes use of clang, [make,] and optionally qemu.

Using Make for automatic build

Update gitmodules using git submodule update --init --recursive. Then, you may make and run the emulated efi using make -f .mk qemu

Manually

Clang compiles the special efi binary type on many operating systems without extra steps.

Install clang

If you already have clang installed and updated, you may skip this step.

On archlinux, install clang and lld package using pacman. sudo pacman -S clang lld On debian-based systems (Ubuntu...): sudo apt install clang-13 lld --install-suggests

On windows

Download the latest release installer from their github release page. At the time of writing, it can be found here: https://github.com/llvm/llvm-project/releases/download/llvmorg-13.0.0/LLVM-13.0.0-win64.exe This should install clang and lld.

Compile EFI executable manually

For each source file ending in .c, compile ***.c to objects ***.o (replace MYPROGRAM with your source code file name): clang -target x86_64-unknown-windows -ffreestanding -fshort-wchar -mno-red-zone -Iextern/efi -o MYPROGRAM.o -c MYPROGRAM.c

Then collect all these objects to generate your efi binary (replace MYQUBIC and FIRST/SECOND/.../LAST with your generated objects): clang -target x86_64-unknown-windows -nostdlib -Wl,-entry:efi_main -Wl,-subsystem:efi_application -fuse-ld=lld-link -o MYQUBIC.efi FIRST.o SECOND.o .... LAST.o

You've now created the operating-system-independent binary for your computor.

Run on Qemu

Perhaps you don't want to go through the hassle of rebooting your PC, like myself. In this case, you can run it in a virtual machine!

Install qemu

On archlinux, the command sudo pacman -S qemu will install it.

On ubuntu, enter this into a terminal: sudo apt update && sudo apt install qemu-kvm qemu virt-manager virt-viewer libvirt-clients libvirt-daemon-system bridge-utils virtinst libvirt-daemon

On windows, a qemu executable may be found here: https://qemu.weilnetz.de/w64/qemu-w64-setup-20211215.exe

On macOS, it may be installed using brew install qemu.

Install OVMF (Open Virtual Machine Firmware)

I will include OVMF_CODE.fd and OVMF_VARS.fd for reference use. You may choose to install it on your system.

In archlinux, it may be installed using the command: sudo pacman -S edk2-ovmf

Run in qemu

The qemu command may be different on varying systems. On some, it is qemu-kvm. On others, qemu alone is used. On mine, the relevant command is qemu-system-x86_64.

In the directory where you built your efi binary, create a new directory named, i,e., BOOT, and move your program (MYQUBIC.efi) there.

From your terminal, run this command (replacing qemu-* with the appropriate name for your system [typing qemu, and then hittng TAB will help to find it]):

qemu-system-x86_64 -enable-kvm -drive if=pflash,format=raw,readonly=on,file=OVMF_CODE.fd -drive if=pflash,format=raw,file=OVMF_VARS.fd -drive index=0,format=raw,file=fat:rw:BOOT

Run on baremetal

If you wish to run bare instead of in QEMU, copy the binary to a thumb drive, insert it into your pc, load the EFI shell.

EFI Shell

With the EFI Shell loaded, it should list a mapping table, somewhat similar to this:

Mapping table
      FS0: Alias(s):HD0a1:;BLK1:
          PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)
     BLK0: Alias(s):
          PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)
     BLK2: Alias(s):
          PciRoot(0x0)/Pci(0x1,0x1)/Ata(0x0)

If it does not, you may type map to see it. In this case, FS0 contains my binary. To enter it, one types the command FS0: From here, the commands ls or dir should show that previously created program. For instance,

FS0:\> ls
Directory of: FS0:\
01/17/2022  11:48               3,072  MYQUBIC.efi
          1 File(s)       3,072 bytes

If you see the program, in this instance named "MYQUBIC.efi", you run it simply by entering:

FS0:\> MYQUBIC.efi

dsphinx / hellocomputor