ArcBoot v0

A uefi bootloader for riscv, arm and x86. Comes in the form of a single executable.

• the source code contains a single executable target and no libraries. By default, builds for aarch64
• build arcutils first, then use that to build, run and test arcboot

TODO

• get uart working properly on qemu
• get linker scripts to work properly and setup certain sections for bootloader stage 1 [ ]

Design

Like Oreboot and GRUB, Arcboot is a multiboot UEFI bootloader. For stages 1 and 2 after platform firmware starts and loads the image (BIN or ELF) into RAM.

• should be flashed onto a drive on its own FAT32 partition. The / partition should be saved for the kernel. Instead the FAT partition should have a /boot dir with extra config files for runtime boot (stages 1 and 2)
• the /boot fat32 partition can then be mounted on /boot on the main VFS filesystem root

ELF Runner

Kernel images can be built as an ELF executable or just a binary blob in the case of ARM.

• arcboot sets up a stack, heap, bss, etc. for the kernel
• it then sets up 48 bit paging and goes into S-Mode. Then it can pass control to the loaded kernel code

No support for 39/52/64 bit paging yet.

RISC-V

RISC-V systems should implement SBI. Arcboot uses rust-sbi and loads an SEE before loading a kernel ELF image.

• Neutron-riscv compiles an ecall subsystem for simpler hw management
• I think SBI handles a lot of the multicore scheduling though IDK

ARM

ARM systems have better capabilities than RISCV ones on the market. Usually more library and driver support as well.

• There are things like vector tables and stuff for bare metal cortex M. I assume a generic aarch64 setup with rings 0-3. Usually a multicore Cortex-A system
• And any usual data structures and boot methods

Graphics

• an ARM based GPU like Mali or PowerVR can be used with ARM/RISCV processors. Neutron loads driver modules for those components based on MMIO. Arcboot tells Neutron via ACPI the graphics units available
• Neutron should load its 3D graphics subsystem when a supported GPU is detected by ACPI

QEMU

Arcboot should be flashed onto a vhd file. QEMU should be run with OVMF firmware.

To specify the vhd file --disk=<main_disk.vhd>. If everything goes well, QEMU should be able to load Arcboot into the host memory and hand off control to it in pseudo M mode.