Builroot and RISCV

buildroot-riscv-kernel.md

// reference: https://popovicu.com/posts/789-kb-linux-without-mmu-riscv/

How to create a linux kernel that can run on a riscv32ima without an MMU.

• Download buildroot
• Untar it and start make menuconfig
• In Target Options
  • Target Architecture select RISCV
  • In Target Architecture Size select 32
  • In Target ABI select ilp32
  • In Target Instruction Variant select Custom architecture
  • Disable:
    • Integer Multiplication and Division
    • Atomic Instructions
    • Single-precision Floating-point
    • Compressed Instructions (should be already disabled)
    • Vector Instructions (should be already disabled)
• Target Binary Format should be set to FLAT
• In Toolchain, in the Thread library implementation section select none (if your processor do not support atomic instruction)
• In Kernel
  • select Linux Kernel
  • select Kernel configuration to Use the architecture default

zig-riscv.md

Compile to basebone RISCV32:

export fn _start() u8 {
  return 42;
}

zig build-exe foo.zig -target riscv32-freestanding-ilp32 -OReleaseSmall