First version

.cargo/config.toml

@@ -1,2 +0,0 @@
-[unstable]
-bindeps = true

.gitignore

@@ -1 +1,5 @@
-/target
+/kernel/target
+/build
+/binutils
+/gcc
+/opt

Makefile

@@ -0,0 +1,23 @@
+.PHONY: all build test clean
+
+all: build
+
+build:
+	rm -rf build
+	rm -rf kernel/target
+	mkdir build
+	i686-elf-as -o build/boot.o boot.s
+	cd kernel; cargo build
+	cp kernel/target/i686-unknown-bare/debug/kernel.elf build/geos.bin
+	mkdir -p build/isodir/boot/grub
+	cp build/geos.bin build/isodir/boot/geos.bin
+	cp grub.cfg build/isodir/boot/grub/grub.cfg
+	grub-mkrescue -o build/geos.iso build/isodir
+
+test: build
+	qemu-system-i386 -cdrom build/geos.iso
+
+clean:
+	rm -rf kernel/target
+	rm -rf build
+

boot.s

@@ -0,0 +1,109 @@
+/* Declare constants for the multiboot header. */
+.set ALIGN,    1<<0             /* align loaded modules on page boundaries */
+.set MEMINFO,  1<<1             /* provide memory map */
+.set FLAGS,    ALIGN | MEMINFO  /* this is the Multiboot 'flag' field */
+.set MAGIC,    0x1BADB002       /* 'magic number' lets bootloader find the header */
+.set CHECKSUM, -(MAGIC + FLAGS) /* checksum of above, to prove we are multiboot */
+
+/* 
+Declare a multiboot header that marks the program as a kernel. These are magic
+values that are documented in the multiboot standard. The bootloader will
+search for this signature in the first 8 KiB of the kernel file, aligned at a
+32-bit boundary. The signature is in its own section so the header can be
+forced to be within the first 8 KiB of the kernel file.
+*/
+.section .multiboot
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
+
+/*
+The multiboot standard does not define the value of the stack pointer register
+(esp) and it is up to the kernel to provide a stack. This allocates room for a
+small stack by creating a symbol at the bottom of it, then allocating 16384
+bytes for it, and finally creating a symbol at the top. The stack grows
+downwards on x86. The stack is in its own section so it can be marked nobits,
+which means the kernel file is smaller because it does not contain an
+uninitialized stack. The stack on x86 must be 16-byte aligned according to the
+System V ABI standard and de-facto extensions. The compiler will assume the
+stack is properly aligned and failure to align the stack will result in
+undefined behavior.
+*/
+.section .bss
+.align 16
+stack_bottom:
+.skip 16384 # 16 KiB
+stack_top:
+
+/*
+The linker script specifies _start as the entry point to the kernel and the
+bootloader will jump to this position once the kernel has been loaded. It
+doesn't make sense to return from this function as the bootloader is gone.
+*/
+.section .text
+.global _start
+.type _start, @function
+_start:
+	/*
+	The bootloader has loaded us into 32-bit protected mode on a x86
+	machine. Interrupts are disabled. Paging is disabled. The processor
+	state is as defined in the multiboot standard. The kernel has full
+	control of the CPU. The kernel can only make use of hardware features
+	and any code it provides as part of itself. There's no printf
+	function, unless the kernel provides its own <stdio.h> header and a
+	printf implementation. There are no security restrictions, no
+	safeguards, no debugging mechanisms, only what the kernel provides
+	itself. It has absolute and complete power over the
+	machine.
+	*/
+
+	/*
+	To set up a stack, we set the esp register to point to the top of the
+	stack (as it grows downwards on x86 systems). This is necessarily done
+	in assembly as languages such as C cannot function without a stack.
+	*/
+	mov $stack_top, %esp
+
+	/*
+	This is a good place to initialize crucial processor state before the
+	high-level kernel is entered. It's best to minimize the early
+	environment where crucial features are offline. Note that the
+	processor is not fully initialized yet: Features such as floating
+	point instructions and instruction set extensions are not initialized
+	yet. The GDT should be loaded here. Paging should be enabled here.
+	C++ features such as global constructors and exceptions will require
+	runtime support to work as well.
+	*/
+
+	/*
+	Enter the high-level kernel. The ABI requires the stack is 16-byte
+	aligned at the time of the call instruction (which afterwards pushes
+	the return pointer of size 4 bytes). The stack was originally 16-byte
+	aligned above and we've pushed a multiple of 16 bytes to the
+	stack since (pushed 0 bytes so far), so the alignment has thus been
+	preserved and the call is well defined.
+	*/
+	call kernel_main
+
+	/*
+	If the system has nothing more to do, put the computer into an
+	infinite loop. To do that:
+	1) Disable interrupts with cli (clear interrupt enable in eflags).
+	   They are already disabled by the bootloader, so this is not needed.
+	   Mind that you might later enable interrupts and return from
+	   kernel_main (which is sort of nonsensical to do).
+	2) Wait for the next interrupt to arrive with hlt (halt instruction).
+	   Since they are disabled, this will lock up the computer.
+	3) Jump to the hlt instruction if it ever wakes up due to a
+	   non-maskable interrupt occurring or due to system management mode.
+	*/
+	cli
+1:	hlt
+	jmp 1b
+
+/*
+Set the size of the _start symbol to the current location '.' minus its start.
+This is useful when debugging or when you implement call tracing.
+*/
+.size _start, . - _start

grub.cfg

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+menuentry "geos" {
+	multiboot /boot/geos.bin
+}

kernel/.cargo/config.toml

@@ -0,0 +1,9 @@
+[build]
+target = "i686-unknown-bare.json"
+
+[unstable]
+build-std-features = ["compiler-builtins-mem"]
+build-std = ["core", "compiler_builtins"]
+
+[target."i686-unknown-bare"]
+linker = "i686-elf-gcc"

kernel/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "kernel"
+version = "0.1.0"

kernel/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "kernel"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

kernel/i686-unknown-bare.json

@@ -0,0 +1,25 @@
+{
+  "llvm-target": "i686-unknown-none",
+  "data-layout": "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i128:128-f64:32:64-f80:32-n8:16:32-S128",
+  "arch": "x86",
+  "target-endian": "little",
+  "target-pointer-width": "32",
+  "target-c-int-width": "32",
+  "os": "none",
+  "executables": true,
+  "linker-flavor": "gcc",
+  "linker": "i686-elf-gcc",
+  "panic-strategy": "abort",
+  "disable-redzone": true,
+  "features": "-sse,+soft-float",
+  "dynamic-linking": false,
+  "relocation-model": "pic",
+  "code-model": "kernel",
+  "exe-suffix": ".elf",
+  "has-rpath": false,
+  "no-default-libraries": true,
+  "position-independent-executables": false,
+  "pre-link-args": {
+    "gcc": ["-T", "../linker.ld", "-ffreestanding", "-nostdlib", "-lgcc", "../build/boot.o"]
+  }
+}

kernel/src/main.rs

@@ -0,0 +1,23 @@
+#![no_std]
+#![no_main]
+
+#[no_mangle]
+pub extern "C" fn kernel_main() -> ! {
+    let vga_buffer = 0xb8000 as *mut u8;
+
+    let string: &[u8] = b":3";
+    for (i, &byte) in string.iter().enumerate() {
+        unsafe {
+            *vga_buffer.offset(i as isize * 2) = byte;
+            *vga_buffer.offset(i as isize * 2 + 1) = 0xf;
+        }
+    }
+
+
+    loop {}
+}
+ 
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}

linker.ld

@@ -0,0 +1,52 @@
+/* The bootloader will look at this image and start execution at the symbol
+   designated as the entry point. */
+ENTRY(_start)
+ 
+/* Tell where the various sections of the object files will be put in the final
+   kernel image. */
+SECTIONS
+{
+	/* It used to be universally recommended to use 1M as a start offset,
+	   as it was effectively guaranteed to be available under BIOS systems.
+	   However, UEFI has made things more complicated, and experimental data
+	   strongly suggests that 2M is a safer place to load. In 2016, a new
+	   feature was introduced to the multiboot2 spec to inform bootloaders
+	   that a kernel can be loaded anywhere within a range of addresses and
+	   will be able to relocate itself to run from such a loader-selected
+	   address, in order to give the loader freedom in selecting a span of
+	   memory which is verified to be available by the firmware, in order to
+	   work around this issue. This does not use that feature, so 2M was
+	   chosen as a safer option than the traditional 1M. */
+	. = 2M;
+ 
+	/* First put the multiboot header, as it is required to be put very early
+	   in the image or the bootloader won't recognize the file format.
+	   Next we'll put the .text section. */
+	.text BLOCK(4K) : ALIGN(4K)
+	{
+		*(.multiboot)
+		*(.text)
+	}
+ 
+	/* Read-only data. */
+	.rodata BLOCK(4K) : ALIGN(4K)
+	{
+		*(.rodata)
+	}
+ 
+	/* Read-write data (initialized) */
+	.data BLOCK(4K) : ALIGN(4K)
+	{
+		*(.data)
+	}
+ 
+	/* Read-write data (uninitialized) and stack */
+	.bss BLOCK(4K) : ALIGN(4K)
+	{
+		*(COMMON)
+		*(.bss)
+	}
+ 
+	/* The compiler may produce other sections, by default it will put them in
+	   a segment with the same name. Simply add stuff here as needed. */
+}

rust-toolchain

@@ -1 +0,0 @@
-nightly

shell.nix

@@ -1,20 +1,35 @@
 { pkgs ? import <nixpkgs> {} }:
-pkgs.mkShell rec {
+
+let
+  crossPkgs = pkgs.pkgsCross.aarch64-multiplatform;
+in pkgs.mkShell rec {
 	buildInputs = with pkgs; [
       clang
       llvmPackages_17.bintools
       rustup
 	  qemu
+      grub2
+      libisoburn
+      bison
+      flex
+      gmp
+      libmpc
+      mpfr
+      texinfo
+      isl
     ];
-    RUSTC_VERSION = pkgs.lib.readFile ./rust-toolchain;
+    RUSTC_VERSION = "nightly";
+    hardeningDisable = [ "all" ];
     # https://github.com/rust-lang/rust-bindgen#environment-variables
     LIBCLANG_PATH = pkgs.lib.makeLibraryPath [ pkgs.llvmPackages_latest.libclang.lib ];
 	shellHook = ''
+      rustup default nightly
 	  rustup component add llvm-tools-preview
 	  rustup component add rust-analyzer
 	  rustup target add x86_64-unknown-none
       export PATH=$PATH:''${CARGO_HOME:-~/.cargo}/bin
-      export PATH=$PATH:''${RUSTUP_HOME:-~/.rustup}/toolchains/$RUSTC_VERSION-x86_64-unknown-linux-gnu/bin/
+      export PATH=$PATH:''${RUSTUP_HOME:-~/.rustup}/toolchains/nightly-x86_64-unknown-linux-gnu/bin/
+      export PATH=$PATH:$PWD/opt/bin
       '';
     # Add precompiled library to rustc search path
     RUSTFLAGS = (builtins.map (a: ''-L ${a}/lib'') [