RISC-V (+ multiarch in general)

[kivikakk]

• Add ARCH to Makefile, should be either arm64 or riscv64.
  • Parameterise just about everything on this. make ARCH=arm64 qemu and make ARCH=riscv64 qemu each build the correct dainboot/dainkrnl, copy it into target/disk and launch QEMU appropriately.
  • Right now dainboots can live side-by-side (because they're named BOOTAA64.efi and BOOTRISCV64.efi), but the dainkrnls overwrite each other.
    • Fix that.
  • CI compiles and attempts the expect(1)-based E2E test on both.
• Compile in a custom PE header crt0-efi-riscv64.S and ELF loader and self-relocator.
  • This is per Linux, Haiku, U-Boot, etc. What a hack. This took so much work.
    • Working out we had to export our own memcpy and memset to avoid creating a PLT/GOT was big.
• Add our own Arch enum which uses the names arm64 and riscv64, and conditionally compile in things based on that.
• Look for uart@ in the DTB for serial base, in addition to pl011@ and serial@.
  • This gets the QEMU riscv64 virt uart.
• riscv64 bootloader just does fence.i after loading and then jumps to the kernel. No magic.
  • Presumably some magic will be needed when this comes up on hardware. We're using U-Boot in smode on OpenSBI in QEMU.
• Parameterise kernel start:
  • arm64: 0xffffff80_00000000
  • riscv64: 0x00000040_00000000
    • Needed to set the code model to medium explicitly to get this working.
• dainkrnl mostly unported.
  • No MMU bring-up yet, but we're starting.

[kivikakk]

Not done, but I'd like the progress to be visible on master. There's CI changes and arm64 stuff in here too now.