StefanNienhuis/ARMBareMetal

Experimenting with ARM Bare Metal programming.

ARM Bare Metal

An experiment with bare metal C on ARM processors. Emulated using QEMU on the Cortex A72.

This repository is just some sample code and scripts (and some details on macOS/M1 support). See the sources below for actual guides.

Details

Cross compiling GCC and binutils is required. See https://wiki.osdev.org for details.

hello-world/ is a very basic kernel implementation.

uart/ is a very basic UART driver implementation.

Warning: This is likely the worst C code you will ever see (especially in the UART driver). C is not my area of expertise and especially not at this low level.

macOS

This was all done in macOS on an M1 Mac, which required some workarounds and different arguments.

For starters, I had to apply some patches to GCC to make it all work on my M1 Mac. See richfelker/musl-cross-make#116 (comment).

gmp, mpc, mpfr and libiconv had to be installed (through something like Homebrew), either because they were not included or were very outdated.

binutils configure options:

--target=$TARGET --prefix=$PREFIX --enable-interwork --enable-multilib --disable-nls --disable-werror

gcc configure options:

--target=$TARGET --prefix=$PREFIX --disable-nls --enable-languages=c,c++ --without-headers --enable-interwork --enable-multilib --with-gmp=/opt/homebrew --with-mpc=/opt/homebrew --with-mpfr=/opt/homebrew --with-libiconv-prefix=/opt/homebrew/opt/libiconv

Sources

• https://wiki.osdev.org/, specifically
  • https://wiki.osdev.org/User:Zesterer/Bare_Bones
  • https://wiki.osdev.org/Bare_Bones
  • https://wiki.osdev.org/GCC_Cross-Compiler
• https://github.com/freedomtan/aarch64-bare-metal-qemu (boot assembly)
• https://developer.arm.com/documentation/ddi0183/ (UART specification)
• https://github.com/qemu/qemu/blob/master/hw/arm/virt.c (UART memory mapping)
• richfelker/musl-cross-make#116 (comment) (M1 GCC patches)