Add more modern build script for kernel and disk image based on osdev Bare Bones template

GRUB is not identifying the kernel as multiboot compatible. Possibly
because I am using x86_64 instead of i686. Need to investigate further.

Rsconscript

@@ -1,3 +1,71 @@
 configure do
   check_c_compiler "x86_64-elf-gcc", on_fail: "Install cross compiler from x86_64-cross directory"
+  check_program "genext2fs"
+  check_program "grub-mkstandalone"
+  check_program "mformat", on_fail: "Install the mtools package"
+end
+
+build do
+  require "tmpdir"
+
+  # EFI (w/ GRUB) partition size (MiB)
+  EFI_PART_SIZE = 8
+  # HOS partition size (MiB)
+  HOS_PART_SIZE = 4
+
+  class Image < Builder
+    def run(options)
+      unless @cache.up_to_date?(@target, nil, @sources, @env)
+        print_run_message("Generating disk image #{@target}", nil)
+        Dir.mktmpdir do |tmpdir|
+          # Build a standalone GRUB.
+          File.open("#{tmpdir}/grub.cfg", "wb") do |fh|
+            fh.write(<<EOF)
+insmod part_gpt
+configfile (hd0,gpt2)/grub.cfg
+EOF
+          end
+          system(*%W[grub-mkstandalone -O x86_64-efi -o #{tmpdir}/BOOTX64.EFI boot/grub/grub.cfg=#{tmpdir}/grub.cfg])
+          # Create EFI partition.
+          system(*%W[dd if=/dev/zero of=#{tmpdir}/efi.part bs=1M count=#{EFI_PART_SIZE}], err: "/dev/null")
+          system(*%W[mformat -i #{tmpdir}/efi.part ::])
+          system(*%W[mmd -i #{tmpdir}/efi.part ::/EFI])
+          system(*%W[mmd -i #{tmpdir}/efi.part ::/EFI/BOOT])
+          system(*%W[mcopy -i #{tmpdir}/efi.part #{tmpdir}/BOOTX64.EFI ::/EFI/BOOT])
+          # Create ext2 HOS partition.
+          FileUtils.mkdir_p("#{tmpdir}/ext2")
+          @sources.each do |source|
+            FileUtils.cp(source, "#{tmpdir}/ext2")
+          end
+          File.open("#{tmpdir}/ext2/grub.cfg", "wb") do |fh|
+            fh.write(<<EOF)
+insmod part_gpt
+insmod multiboot
+set root=(hd0,gpt2)
+multiboot /hos.elf
+EOF
+          end
+          system(*%W[genext2fs -b #{HOS_PART_SIZE * 1024} -d #{tmpdir}/ext2 #{tmpdir}/ext2.part])
+          # Create full disk image.
+          system(*%W[dd if=/dev/zero of=#{@target} bs=1M count=#{EFI_PART_SIZE + HOS_PART_SIZE + 2}], err: "/dev/null")
+          system(*%W[parted -s #{@target} mklabel gpt])
+          system(*%W[parted -s #{@target} mkpart efi 1MiB #{EFI_PART_SIZE + 1}MiB])
+          system(*%W[parted -s #{@target} mkpart hos #{EFI_PART_SIZE + 1}MiB #{EFI_PART_SIZE + HOS_PART_SIZE + 1}MiB])
+          system(*%W[dd if=#{tmpdir}/efi.part of=#{@target} bs=1M seek=1 conv=notrunc], err: "/dev/null")
+          system(*%W[dd if=#{tmpdir}/ext2.part of=#{@target} bs=1M seek=#{1 + EFI_PART_SIZE} conv=notrunc], err: "/dev/null")
+        end
+        @cache.register_build(@target, nil, @sources, @env)
+      end
+      true
+    end
+  end
+
+  Environment.new do |env|
+    env.add_builder(Image)
+    env["CCFLAGS"] += %w[-ffreestanding -Wall -O2]
+    env["LDFLAGS"] += %w[-ffreestanding -nostdlib -T src/link.ld]
+    env["LIBS"] += %w[gcc]
+    env.Program("^/hos.elf", glob("src/**/*.{S,c}"))
+    env.Image("build/hos.img", %w[^/hos.elf])
+  end
 end

src/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

src/kernel_main.c

@@ -0,0 +1,9 @@
+#include <stdint.h>
+
+void kernel_main(void)
+{
+    for (;;)
+    {
+        (*(volatile uint16_t *)0xB8000)++;
+    }
+}

src/link.ld

@@ -0,0 +1,43 @@
+/* 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
+{
+	/* Begin putting sections at 1 MiB, a conventional place for kernels to be
+	   loaded at by the bootloader. */
+	. = 1M;
+ 
+	/* First put the multiboot header, as it is required to be put very early
+	   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. */
+}