Update to rscons 2.3.0

Move cross compiler to i686-elf-gcc directory.
Automatically build cross compiler using rscons subsidiary script.

.gitignore

@@ -4,3 +4,10 @@
 *.lst
 *.map
 *.bin
+.rscons*
+/i686-elf-gcc/build*/
+/i686-elf-gcc/*.xz
+/i686-elf-gcc/binutils-*/
+/i686-elf-gcc/gcc-*/
+/i686-elf-gcc/i686-elf-gcc/
+/build/

Makefile

@@ -1,88 +1,15 @@
-# Makefile for HOS
-# Josh Holtrop
-# Created: 07/09/04
-
-FLOPPY=/dev/fd0
-FLOPPY_IMAGE=hos.flp
-FLOPPY_MOUNT=./mnt_flp
-GRUB_IMAGE=grub.flp
-INITRD=hos_initrd
-INITRD_DIR=initrd
-INITRD_MOUNT=./mnt_initrd
-INITRD_SIZE=100			#initrd size in kb
-MOUNT=sudo mount
-UMOUNT=sudo umount
-
-# Do not print "Entering directory ..."
-MAKEFLAGS += --no-print-directory
-
-.PHONY:	all clean initrd apps grub_image install install_img depend copy_image bochs bochsq
-
+.PHONY: all
 all:
-	${MAKE} -C kernel
-	${MAKE} -C rmmod
+	./rscons build
 
+.PHONY: run-efi
+run-efi: all
+	qemu-system-x86_64 -bios OVMF.fd -hda build/hos-efi.img
+
+.PHONY: run
+run: all
+	qemu-system-x86_64 -hda build/hos.img
+
+.PHONY: clean
 clean:
-	-${MAKE} -C kernel clean
-	-${MAKE} -C rmmod clean
-	-rm -f *~ *.out hos.flp \#* hos_initrd hos_initrd.gz
-
-apps:
-	${MAKE} -C apps
-
-grub_image:
-	dd if=/dev/zero of=$(GRUB_IMAGE) bs=1024 seek=1440 count=0
-	-mkdir $(FLOPPY_MOUNT)
-	mke2fs -F $(GRUB_IMAGE)
-	$(MOUNT) -t ext2 -o loop $(GRUB_IMAGE) $(FLOPPY_MOUNT)
-	-mkdir -p $(FLOPPY_MOUNT)/boot/grub
-	-cp /boot/grub/stage1 /boot/grub/stage2 /boot/grub/e2fs_stage1_5 $(FLOPPY_MOUNT)/boot/grub
-	$(UMOUNT) $(FLOPPY_MOUNT)
-	-rmdir $(FLOPPY_MOUNT)
-	echo "(fd0) $(GRUB_IMAGE)" > grub_image_device.map.tmp
-	echo "root (fd0)" > grub_commands.tmp
-	echo "setup (fd0)" >> grub_commands.tmp
-	echo "quit" >> grub_commands.tmp
-	grub --device-map grub_image_device.map.tmp < grub_commands.tmp
-	rm grub_commands.tmp
-	rm grub_image_device.map.tmp
-
-copy_image:
-	cp $(GRUB_IMAGE) $(FLOPPY_IMAGE)
-
-install:	FDEV=$(FLOPPY)
-install_img:	FDEV=$(FLOPPY_IMAGE)
-install_img:	MOUNT_FLAGS=-o loop
-install_img: copy_image
-install install_img:
-	-mkdir $(FLOPPY_MOUNT)
-	$(MOUNT) -t ext2 $(MOUNT_FLAGS) $(FDEV) $(FLOPPY_MOUNT)
-	-cp kernel/kernel.bin $(FLOPPY_MOUNT)
-	-cp rmmod/rmmod.bin $(FLOPPY_MOUNT)
-	-cp menu.lst $(FLOPPY_MOUNT)/boot/grub
-	-cp $(INITRD).gz $(FLOPPY_MOUNT)/$(INITRD).gz
-	$(UMOUNT) $(FLOPPY_MOUNT)
-	-rmdir $(FLOPPY_MOUNT)
-
-initrd:
-	dd if=/dev/zero of=$(INITRD) bs=1024 count=$(INITRD_SIZE)
-	mke2fs -Fv -m0 -r0 -i1024 $(INITRD)
-	-mkdir $(INITRD_MOUNT)
-	$(MOUNT) -t ext2 -o loop $(INITRD) $(INITRD_MOUNT)
-	cp -Pr $(INITRD_DIR)/* $(INITRD_MOUNT)
-	$(UMOUNT) $(INITRD_MOUNT)
-	rm -rf $(INITRD_MOUNT)
-	gzip -c $(INITRD) > $(INITRD).gz
-
-depend:
-	${MAKE} -C kernel depend
-
-bochs:
-	bochs
-
-bochsq:
-	echo 'c' | bochs -q
-
-wordcount:
-	find . -regex '\(.*\.[ch]\)\|\(.*\.asm\)\|\(.*\.inc\)\|\(.*\.cpp\)' | xargs cat | wc
-
+	./rscons clean

Rsconscript

@@ -0,0 +1,155 @@
+path_prepend "i686-elf-gcc/i686-elf-gcc/bin"
+
+configure do
+  rscons "i686-elf-gcc"
+  check_c_compiler "i686-elf-gcc"
+  check_program "genext2fs"
+  check_program "grub-mkstandalone"
+  check_program "mformat", on_fail: "Install the mtools package"
+  check_program "xorriso"
+  check_cfg package: "freetype2", on_fail: "Install libfreetype-dev", use: "freetype"
+end
+
+build do
+  require "tmpdir"
+
+  # EFI (w/ GRUB) partition size (MiB)
+  EFI_PART_SIZE = 8
+  # HOS partition size (MiB)
+  HOS_PART_SIZE = 4
+  # Kernel default font size
+  KFONT_SIZE = 15
+
+  class BiosImage < Builder
+    def run(options)
+      unless @cache.up_to_date?(@target, nil, @sources, @env)
+        print_run_message("Generating BIOS boot image #{@target}", nil)
+        Dir.mktmpdir do |tmpdir|
+          # Create iso directory.
+          FileUtils.mkdir_p("#{tmpdir}/iso/boot/grub")
+          File.open("#{tmpdir}/iso/boot/grub/grub.cfg", "wb") do |fh|
+            fh.write(<<EOF)
+set default="0"
+set timeout=1
+menuentry "HOS" {
+  insmod multiboot2
+  multiboot2 /hos.elf
+}
+EOF
+          end
+          @sources.each do |source|
+            FileUtils.cp(source, "#{tmpdir}/iso")
+          end
+          # Build bootable GRUB image.
+          system(*%W[grub-mkrescue -o #{@target} #{tmpdir}/iso], err: "#{@env.build_root}/grub-mkrescue.log")
+        end
+        @cache.register_build(@target, nil, @sources, @env)
+      end
+      true
+    end
+  end
+
+  class EfiImage < Builder
+    def run(options)
+      unless @cache.up_to_date?(@target, nil, @sources, @env)
+        print_run_message("Generating EFI boot 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)
+set default="0"
+set timeout=1
+menuentry "HOS" {
+  insmod part_gpt
+  insmod multiboot2
+  set root=(hd0,gpt2)
+  multiboot2 /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
+
+  class FontGen < Builder
+    def run(options)
+      if @command
+        finalize_command
+      else
+        @sources += ["build/fontgen"]
+        command = %W[build/fontgen #{@sources.first} #{KFONT_SIZE} #{@target}]
+        standard_command("FontGen <target>#{@target}<reset>", command, {})
+      end
+    end
+  end
+
+  class Size < Builder
+    def run(options)
+      if @command
+        finalize_command
+      else
+        @vars["_SOURCES"] = @sources
+        @vars["_TARGET"] = @target
+        command = @env.build_command(%w[${SIZE} ${_SOURCES}], @vars)
+        standard_command("Size <target>#{@target}<reset>", command, stdout: @target)
+      end
+    end
+  end
+
+  # FontGen Environment
+  Environment.new(use: "freetype") do |env|
+    env["CC"] = "gcc"
+    env.Program("build/fontgen", glob("fontgen/**/*.c"))
+  end
+
+  # Kernel Environment
+  Environment.new do |env|
+    env.add_builder(EfiImage)
+    env.add_builder(BiosImage)
+    env.add_builder(FontGen)
+    env.add_builder(Size)
+    env["OBJDUMP"] = "i686-elf-objdump"
+    env["SIZE"] = "i686-elf-size"
+    env["CCFLAGS"] += %w[-ffreestanding -Wall -O2]
+    env["LDFLAGS"] += %w[-ffreestanding -nostdlib -T src/link.ld]
+    env["LDFLAGS"] += %W[-Wl,-Map,${_TARGET}.map]
+    env["LIBS"] += %w[gcc]
+    env.FontGen("^/kfont/kfont.c", "font/Hack-Regular.ttf")
+    env["CPPPATH"] += ["#{env.build_root}/kfont"]
+    env.Program("^/hos.elf", glob("src/**/*.{S,c}") + ["^/kfont/kfont.c"])
+    env.depends("#{env.build_root}/hos.elf", "src/link.ld")
+    env.Disassemble("^/hos.elf.txt", "^/hos.elf")
+    env.Size("^/hos.elf.size", "^/hos.elf")
+    env.EfiImage("build/hos-efi.img", %w[^/hos.elf])
+    env.BiosImage("build/hos.img", %w[^/hos.elf])
+  end
+end

configure

@@ -0,0 +1,2 @@
+#!/bin/sh
+exec ./rscons configure "$@"

fontgen/fontgen.c

@@ -0,0 +1,224 @@
+#include <stdlib.h>
+#include <stdint.h>
+#include <ft2build.h>
+#include <stdio.h>
+#include FT_FREETYPE_H
+#include <string.h>
+#include <strings.h>
+#include <ctype.h>
+
+#define N_CHARS 128
+
+#define round_up_26_6(val) (((val) + 63) >> 6u)
+
+int max_advance;
+int max_top = -9999;
+int min_bottom = 9999;
+int line_height;
+int baseline_offset;
+
+typedef struct {
+    int width;
+    int height;
+    int top;
+    int left;
+    uint8_t * bitmap;
+} char_info_t;
+
+static char_info_t char_infos[N_CHARS];
+
+static void load_char(FT_Face face, int char_code)
+{
+    if (FT_Load_Char(face, char_code, FT_LOAD_RENDER) != 0)
+    {
+        return;
+    }
+    int advance = round_up_26_6(face->glyph->advance.x);
+    if (advance > max_advance)
+    {
+        max_advance = advance;
+    }
+    if ((face->glyph->bitmap.width == 0) ||
+            (face->glyph->bitmap.rows == 0))
+    {
+        return;
+    }
+    char_infos[char_code].width = face->glyph->bitmap.width;
+    char_infos[char_code].height = face->glyph->bitmap.rows;
+    char_infos[char_code].top = face->glyph->bitmap_top;
+    if (char_infos[char_code].top > max_top)
+    {
+        max_top = char_infos[char_code].top;
+    }
+    int bottom = char_infos[char_code].top - char_infos[char_code].height;
+    if (bottom < min_bottom)
+    {
+        min_bottom = bottom;
+    }
+    char_infos[char_code].left = face->glyph->bitmap_left;
+    char_infos[char_code].bitmap = malloc(char_infos[char_code].width * char_infos[char_code].height);
+    memcpy(char_infos[char_code].bitmap,
+            face->glyph->bitmap.buffer,
+            char_infos[char_code].width * char_infos[char_code].height);
+}
+
+static const char * bare_header_name(const char * h_file_name)
+{
+    const char * p = rindex(h_file_name, '/');
+    if (p == NULL)
+    {
+        p = h_file_name;
+    }
+    else
+    {
+        p++;
+    }
+    return p;
+}
+
+static char * include_guard_name(const char * h_file_name)
+{
+    const char * p = bare_header_name(h_file_name);
+    char * guard_name = malloc(strlen(p) + 1);
+    strcpy(guard_name, p);
+    char * m = guard_name;
+    while (*m != '\0')
+    {
+        if ('a' <= *m && *m <= 'z')
+        {
+            *m = toupper(*m);
+        }
+        else if (('0' <= *m && *m <= '9') || ('A' <= *m && *m <= 'Z'))
+        {
+            /* no change */
+        }
+        else
+        {
+            *m = '_';
+        }
+        m++;
+    }
+    return guard_name;
+}
+
+static void generate_bytes(FILE * file, const uint8_t * bytes, int count)
+{
+    for (int i = 0; i < count; i++)
+    {
+        if (i % 8 == 0)
+        {
+            fprintf(file, "    ");
+        }
+        fprintf(file, "0x%02xu,", bytes[i]);
+        if ((i + 1) % 8 == 0)
+        {
+            fprintf(file, "\n");
+        }
+        else if (i < (count - 1))
+        {
+            fprintf(file, " ");
+        }
+    }
+    if (count % 8 != 0)
+    {
+        fprintf(file, "\n");
+    }
+}
+
+static void generate(const char * c_file_name)
+{
+    char * h_file_name = malloc(strlen(c_file_name) + 1);
+    strcpy(h_file_name, c_file_name);
+    h_file_name[strlen(h_file_name) - 1] = 'h';
+    char * guard = include_guard_name(h_file_name);
+
+    FILE * h_file = fopen(h_file_name, "wb");
+    fprintf(h_file, "#ifndef %s\n", guard);
+    fprintf(h_file, "#define %s\n\n", guard);
+    fprintf(h_file, "#include <stdint.h>\n");
+    fprintf(h_file, "typedef struct {\n    int width;\n    int height;\n    int top;\n    int left;\n    const uint8_t * bitmap;\n} fontgen_char_info_t;\n");
+    fprintf(h_file, "typedef struct {\n    int line_height;\n    int advance;\n    int baseline_offset;\n    const fontgen_char_info_t ** char_infos;\n} fontgen_font_t;\n");
+    fprintf(h_file, "extern const fontgen_font_t kfont;\n");
+    fprintf(h_file, "#endif\n");
+    fclose(h_file);
+
+    FILE * c_file = fopen(c_file_name, "wb");
+    fprintf(c_file, "#include \"%s\"\n", bare_header_name(h_file_name));
+    fprintf(c_file, "#include <stddef.h>\n");
+    for (int i = 0; i < N_CHARS; i++)
+    {
+        if (char_infos[i].width > 0)
+        {
+            fprintf(c_file, "static const uint8_t char_bitmap_%d[] = {\n", i);
+            generate_bytes(c_file, char_infos[i].bitmap, char_infos[i].width * char_infos[i].height);
+            fprintf(c_file, "};\n");
+        }
+        fprintf(c_file, "static const fontgen_char_info_t char_%d = {\n", i);
+        fprintf(c_file, "    %d,\n", char_infos[i].width);
+        fprintf(c_file, "    %d,\n", char_infos[i].height);
+        fprintf(c_file, "    %d,\n", char_infos[i].top);
+        fprintf(c_file, "    %d,\n", char_infos[i].left);
+        if (char_infos[i].width > 0)
+        {
+            fprintf(c_file, "    char_bitmap_%d,\n", i);
+        }
+        else
+        {
+            fprintf(c_file, "    NULL,\n");
+        }
+        fprintf(c_file, "};\n\n");
+    }
+    fprintf(c_file, "const fontgen_char_info_t * char_infos[] = {\n");
+    for (int i = 0; i < N_CHARS; i++)
+    {
+        fprintf(c_file, "    &char_%d,\n", i);
+    }
+    fprintf(c_file, "};\n");
+    fprintf(c_file, "const fontgen_font_t kfont = {\n");
+    fprintf(c_file, "    %d,\n", line_height);
+    fprintf(c_file, "    %d,\n", max_advance);
+    fprintf(c_file, "    %d,\n", baseline_offset);
+    fprintf(c_file, "    char_infos,\n");
+    fprintf(c_file, "};\n");
+    fclose(c_file);
+}
+
+int main(int argc, char * argv[])
+{
+    /* Expect: font file, size, out file */
+    if (argc != 4)
+    {
+        fprintf(stderr, "Incorrect arguments\n");
+        return 1;
+    }
+    const char * font_file = argv[1];
+    int size = atoi(argv[2]);
+    const char * out_file = argv[3];
+
+    FT_Library ft_library;
+    if (FT_Init_FreeType(&ft_library) != 0)
+    {
+        fprintf(stderr, "Could not initialize freetype\n");
+        return 2;
+    }
+
+    FT_Face face;
+    if (FT_New_Face(ft_library, font_file, 0, &face) != 0)
+    {
+        fprintf(stderr, "Could not open %s\n", font_file);
+        return 3;
+    }
+
+    FT_Set_Pixel_Sizes(face, 0, size);
+
+    for (int i = 0; i < N_CHARS; i++)
+    {
+        load_char(face, i);
+    }
+    line_height = round_up_26_6(face->size->metrics.height);
+    baseline_offset = (line_height - (max_top - min_bottom)) / 2 - min_bottom;
+
+    generate(out_file);
+
+    return 0;
+}

i686-elf-gcc/Rsconscript

@@ -0,0 +1,17 @@
+configure do
+  check_c_compiler "gcc"
+  check_program "make"
+  check_program "bison"
+  check_program "flex"
+  check_program "texi2any", on_fail: "Install the texinfo package"
+  check_program "wget"
+  check_lib "gmp", on_fail: "Install the libgmp-dev package"
+  check_lib "mpc", on_fail: "Install the libmpc-dev package"
+  check_lib "mpfr", on_fail: "Install the libmpfr-dev package"
+end
+
+build do
+  unless File.exist?("i686-elf-gcc")
+    system("./build.sh")
+  end
+end

i686-elf-gcc/build.sh

@@ -0,0 +1,64 @@
+#!/bin/bash
+
+BINUTILS_VERSION="2.35"
+BINUTILS_CHECKSUM="1b11659fb49e20e18db460d44485f09442c8c56d5df165de9461eb09c8302f85"
+GCC_VERSION="10.2.0"
+GCC_CHECKSUM="b8dd4368bb9c7f0b98188317ee0254dd8cc99d1e3a18d0ff146c855fe16c1d8c"
+
+if [ ! -e binutils-${BINUTILS_VERSION}.tar.xz ]; then
+  wget -O binutils-${BINUTILS_VERSION}.tar.xz https://ftp.gnu.org/gnu/binutils/binutils-${BINUTILS_VERSION}.tar.xz
+fi
+
+if [[ ! `sha256sum binutils-${BINUTILS_VERSION}.tar.xz` =~ $BINUTILS_CHECKSUM ]]; then
+  echo "Invalid binutils-${BINUTILS_VERSION}.tar.xz checksum"
+  exit
+fi
+
+if [ ! -d binutils-${BINUTILS_VERSION} ]; then
+  tar xJf binutils-${BINUTILS_VERSION}.tar.xz
+fi
+
+if [ ! -e gcc-${GCC_VERSION}.tar.xz ]; then
+  wget -O gcc-${GCC_VERSION}.tar.xz https://ftp.gnu.org/gnu/gcc/gcc-${GCC_VERSION}/gcc-${GCC_VERSION}.tar.xz
+fi
+
+if [[ ! `sha256sum gcc-${GCC_VERSION}.tar.xz` =~ $GCC_CHECKSUM ]]; then
+  echo "Invalid gcc-${GCC_VERSION}.tar.xz checksum"
+  exit
+fi
+
+if [ ! -d gcc-${GCC_VERSION} ]; then
+  tar xJf gcc-${GCC_VERSION}.tar.xz
+fi
+
+export PREFIX="$PWD/i686-elf-gcc"
+export TARGET="i686-elf"
+export PATH="$PREFIX/bin:$PATH"
+
+function build_binutils()
+{
+  rm -rf build-binutils
+  mkdir -p build-binutils
+  (
+    cd build-binutils
+    ../binutils-${BINUTILS_VERSION}/configure --target="$TARGET" --prefix="$PREFIX" --with-sysroot --disable-nls --disable-werror && \
+    make && \
+    make install
+  )
+}
+
+function build_gcc()
+{
+  rm -rf build-gcc
+  mkdir -p build-gcc
+  (
+    cd build-gcc
+    ../gcc-${GCC_VERSION}/configure --target="$TARGET" --prefix="$PREFIX" --disable-nls --enable-languages=c,c++ --without-headers && \
+    make all-gcc && \
+    make all-target-libgcc && \
+    make install-gcc && \
+    make install-target-libgcc
+  )
+}
+
+build_binutils && build_gcc

i686-elf-gcc/clean.sh

@@ -0,0 +1,2 @@
+#!/bin/sh
+rm -rf build build-* binutils* gcc-*

i686-elf-gcc/configure

@@ -0,0 +1,2 @@
+#!/bin/sh
+exec ../rscons configure

src/boot.S

@@ -0,0 +1,18 @@
+.global hos_start
+.type hos_start, @function
+hos_start:
+    /* Set stack pointer. */
+    mov $_stack_end, %esp
+ 
+    /* Jump to C. */
+    push $0
+    push $0
+    push $0
+    push %ebx
+    call hos_main
+ 
+    cli
+1:  hlt
+    jmp 1b
+ 
+.size hos_start, . - hos_start

src/fb.c

@@ -0,0 +1,116 @@
+#include "fb.h"
+#include <stddef.h>
+#include "mem.h"
+
+static struct {
+    uint32_t * addr;
+    uint32_t width;
+    uint32_t height;
+    uint32_t pitch;
+} fb;
+
+static inline uint32_t build_pixel(uint8_t r, uint8_t g, uint8_t b)
+{
+    return (r << 16u) | (g << 8u) | b;
+}
+
+static inline void fb_set_pixel(int x, int y, uint8_t r, uint8_t g, uint8_t b)
+{
+    fb.addr[fb.pitch * y + x] = build_pixel(r, g, b);
+}
+
+void fb_clear(void)
+{
+    memset32(fb.addr, 0u, fb.pitch * fb.height);
+}
+
+void fb_init(uint32_t * addr, uint32_t width, uint32_t height, uint32_t pitch)
+{
+    fb.addr = addr;
+    fb.width = width;
+    fb.height = height;
+    fb.pitch = pitch / 4u;
+    fb_clear();
+}
+
+uint32_t * fb_addr(void)
+{
+    return fb.addr;
+}
+
+bool fb_ready(void)
+{
+    return fb.addr != NULL;
+}
+
+uint32_t fb_width(void)
+{
+    return fb.width;
+}
+
+uint32_t fb_height(void)
+{
+    return fb.height;
+}
+
+void fb_blend_alpha8(const uint8_t * bitmap, int width, int height, int pitch, int x, int y, uint8_t r, uint8_t g, uint8_t b)
+{
+    if (((x + width) <= 0) || (x >= (int)fb.width) || ((y + height) <= 0) || (y >= (int)fb.height))
+    {
+        return;
+    }
+    if (x < 0)
+    {
+        width += x;
+        bitmap += (-x);
+        x = 0;
+    }
+    if (y < 0)
+    {
+        height += y;
+        bitmap += ((-y) * pitch);
+        y = 0;
+    }
+    if ((x + width) > (int)fb.width)
+    {
+        width = (int)fb.width - x;
+    }
+    if ((y + height) > (int)fb.height)
+    {
+        height = (int)fb.height - y;
+    }
+    uint32_t * target = &fb.addr[fb.pitch * y + x];
+    for (int row = 0; row < height; row++)
+    {
+        for (int col = 0; col < width; col++)
+        {
+            uint32_t alpha = bitmap[col];
+            uint32_t current_pixel = target[col];
+            uint8_t cr = (current_pixel >> 16u) & 0xFFu;
+            uint8_t cg = (current_pixel >> 8u) & 0xFFu;
+            uint8_t cb = current_pixel & 0xFFu;
+            uint8_t pr = alpha * r / 255u;
+            uint8_t pg = alpha * g / 255u;
+            uint8_t pb = alpha * b / 255u;
+            uint32_t current_alpha = 255u - alpha;
+            uint32_t pixel = build_pixel(
+                    pr + current_alpha * cr / 255u,
+                    pg + current_alpha * cg / 255u,
+                    pb + current_alpha * cb / 255u);
+            target[col] = pixel;
+        }
+        bitmap += pitch;
+        target += fb.pitch;
+    }
+}
+
+void fb_fill(int x, int y, int width, int height, uint8_t r, uint8_t g, uint8_t b)
+{
+    uint32_t * target = &fb.addr[fb.pitch * y + x];
+    uint32_t pixel = build_pixel(r, g, b);
+    for (int row = 0; row < height; row++)
+    {
+        memset32(target, pixel, width);
+        target += fb.pitch;
+    }
+}

src/fb.h

@@ -0,0 +1,16 @@
+#ifndef FB_H
+#define FB_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+void fb_init(uint32_t * addr, uint32_t width, uint32_t height, uint32_t pitch);
+bool fb_ready(void);
+uint32_t * fb_addr(void);
+uint32_t fb_width(void);
+uint32_t fb_height(void);
+void fb_blend_alpha8(const uint8_t * bitmap, int width, int height, int pitch, int x, int y, uint8_t r, uint8_t g, uint8_t b);
+void fb_fill(int x, int y, int width, int height, uint8_t r, uint8_t g, uint8_t b);
+void fb_clear(void);
+
+#endif

src/fb_text.c

@@ -0,0 +1,11 @@
+#include "fb_text.h"
+#include "kfont.h"
+#include "fb.h"
+
+void fb_text_render_char(int c, int x, int y, uint8_t r, uint8_t g, uint8_t b)
+{
+    const fontgen_char_info_t * char_info = kfont.char_infos[c];
+    y += kfont.line_height - kfont.baseline_offset - char_info->top;
+    x += char_info->left;
+    fb_blend_alpha8(char_info->bitmap, char_info->width, char_info->height, char_info->width, x, y, r, g, b);
+}

src/fb_text.h

@@ -0,0 +1,8 @@
+#ifndef FB_TEXT_H
+#define FB_TEXT_H
+
+#include <stdint.h>
+
+void fb_text_render_char(int c, int x, int y, uint8_t r, uint8_t g, uint8_t b);
+
+#endif

src/gdt.S

@@ -0,0 +1,16 @@
+.global gdt_set
+.extern gdtr
+.type gdt_set, @function
+gdt_set:
+    lgdt gdtr
+    jmp $0x8, $gdt_set_reload
+gdt_set_reload:
+    mov $0x10, %ax
+    mov %ax, %ds
+    mov %ax, %es
+    mov %ax, %fs
+    mov %ax, %gs
+    mov %ax, %ss
+    ret
+
+.size gdt_set, . - gdt_set

src/gdt.c

@@ -0,0 +1,20 @@
+#include "gdt.h"
+
+static const gdt_entry_t gdt_entries[] = {
+    /* Null descriptor */
+    0u,
+    /* Code segment for kernel */
+    gdt_build_entry(0u, 0xFFFFFu, 1u, 0u, 1u, 1u, 0u, 1u, 0u, 1u, 1u, 0u),
+    /* Data segment for kernel */
+    gdt_build_entry(0u, 0xFFFFFu, 1u, 0u, 1u, 0u, 0u, 1u, 0u, 1u, 1u, 0u),
+};
+
+gdtr_t gdtr;
+
+void gdt_init(void)
+{
+    gdtr.size = sizeof(gdt_entries);
+    gdtr.offset_lower = (uintptr_t)gdt_entries & 0xFFFFu;
+    gdtr.offset_upper = (uintptr_t)gdt_entries >> 16u;
+    gdt_set();
+}

src/gdt.h

@@ -0,0 +1,34 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include <stdint.h>
+
+typedef struct {
+    uint16_t size;
+    uint16_t offset_lower;
+    uint16_t offset_upper;
+    uint16_t _reserved;
+} gdtr_t;
+
+typedef uint64_t gdt_entry_t;
+#define gdt_build_entry(base, limit, pr, privl, s, ex, dc, rw, ac, gr, sz, l) \
+    (gdt_entry_t)( \
+            (((gdt_entry_t)base << 32) & 0xFF00000000000000ull) | /* Base 0:15 */ \
+            (((gdt_entry_t)gr & 0x1u) << 55) | /* Granularity (0 = bytes, 1 = blocks) */ \
+            (((gdt_entry_t)sz & 0x1u) << 54) | /* Size (0 = 16-bit, 1 = 32-bit) */ \
+            (((gdt_entry_t)l & 0x1u) << 53) | /* L flag (x86_64 code) */ \
+            (((gdt_entry_t)limit << 32) & 0x000F000000000000ull) | /* Limit 16:19 */ \
+            (((gdt_entry_t)pr & 0x1u) << 47) | /* Present flag */ \
+            (((gdt_entry_t)privl & 0x3u) << 45) | /* Privilege (ring level) */ \
+            (((gdt_entry_t)s & 0x1u) << 44) | /* Type (0 = system, 1 = code/data) */ \
+            (((gdt_entry_t)ex & 0x1u) << 43) | /* Executable flag */ \
+            (((gdt_entry_t)dc & 0x1u) << 42) | /* Direction/Conforming */ \
+            (((gdt_entry_t)rw & 0x1u) << 41) | /* Readable/Writable */ \
+            (((gdt_entry_t)ac & 0x1u) << 40) | /* Accessed flag */ \
+            (((gdt_entry_t)base << 16) & 0x000000FFFFFF0000ull) | /* Base 0:23 */ \
+             ((gdt_entry_t)limit & 0x000000000000FFFFull)) /* Limit 0:15 */
+
+void gdt_init(void);
+void gdt_set(void);
+
+#endif

src/hos_main.c

@@ -0,0 +1,25 @@
+#include <stdint.h>
+#include "fb.h"
+#include "mbinfo.h"
+#include "klog.h"
+#include "gdt.h"
+#include "mm.h"
+
+void hos_main(uint32_t mbinfo_addr)
+{
+    gdt_init();
+    if (!mbinfo_init(mbinfo_addr))
+    {
+        return;
+    }
+    if (!fb_ready())
+    {
+        return;
+    }
+    klog_init();
+    klog_printf("Welcome to HOS!\n");
+    mm_init();
+    mbinfo_load();
+    klog_printf("Found %dKB of usable RAM\n", mm_get_total_ram() / 1024u);
+    klog_printf("Kernel is %dKB at 0x%x\n", mm_get_kernel_size() / 1024u, mm_get_kernel_address());
+}

src/hos_printf.c

@@ -0,0 +1,281 @@
+#include "hos_printf.h"
+#include <stdint.h>
+#include <stdbool.h>
+#include "string.h"
+
+static size_t format_dec(char * buffer, int32_t v)
+{
+    size_t sz = 0u;
+    bool printing = false;
+    if (v < 0)
+    {
+        buffer[sz++] = '-';
+        v = -v;
+    }
+    for (int32_t div = 1000000000; div >= 1; div /= 10)
+    {
+        int32_t digit = v / div;
+        v %= div;
+        if ((digit != 0) || (div == 1))
+        {
+            printing = true;
+        }
+        if (printing)
+        {
+            buffer[sz++] = digit + '0';
+        }
+    }
+    return sz;
+}
+
+static size_t format_dec64(char * buffer, int64_t v)
+{
+    size_t sz = 0u;
+    bool printing = false;
+    if (v < 0)
+    {
+        buffer[sz++] = '-';
+        v = -v;
+    }
+    for (int64_t div = 1000000000000000000; div >= 1; div /= 10)
+    {
+        int64_t digit = v / div;
+        v %= div;
+        if ((digit != 0) || (div == 1))
+        {
+            printing = true;
+        }
+        if (printing)
+        {
+            buffer[sz++] = digit + '0';
+        }
+    }
+    return sz;
+}
+
+static size_t format_udec(char * buffer, int32_t v)
+{
+    size_t sz = 0u;
+    for (int32_t div = 1000000000u; div >= 1u; div /= 10u)
+    {
+        int32_t digit = v / div;
+        v %= div;
+        if ((digit != 0) || (sz > 0u) || (div == 1))
+        {
+            buffer[sz++] = digit + '0';
+        }
+    }
+    return sz;
+}
+
+static size_t format_udec64(char * buffer, uint64_t v)
+{
+    size_t sz = 0u;
+    for (uint64_t div = 10000000000000000000u; div >= 1u; div /= 10u)
+    {
+        uint64_t digit = v / div;
+        v %= div;
+        if ((digit != 0) || (sz > 0u) || (div == 1))
+        {
+            buffer[sz++] = digit + '0';
+        }
+    }
+    return sz;
+}
+
+static size_t format_hex(char * buffer, uint32_t v, bool upper)
+{
+    const char upper_hex[] = "0123456789ABCDEF";
+    const char lower_hex[] = "0123456789abcdef";
+    size_t sz = 0u;
+    for (int i = 28; i >= 0; i -= 4)
+    {
+        uint8_t n = (v >> i) & 0xFu;
+        if ((sz > 0u) || (n != 0u) || (i == 0))
+        {
+            buffer[sz] = upper ? upper_hex[n] : lower_hex[n];
+            sz++;
+        }
+    }
+    return sz;
+}
+
+static size_t format_hex64(char * buffer, uint64_t v, bool upper)
+{
+    const char upper_hex[] = "0123456789ABCDEF";
+    const char lower_hex[] = "0123456789abcdef";
+    size_t sz = 0u;
+    for (int i = 60; i >= 0; i -= 4)
+    {
+        uint8_t n = (v >> i) & 0xFu;
+        if ((sz > 0u) || (n != 0u) || (i == 0))
+        {
+            buffer[sz] = upper ? upper_hex[n] : lower_hex[n];
+            sz++;
+        }
+    }
+    return sz;
+}
+
+static void pad_write(const stream_t * stream, const char * data, size_t length, bool leading_zero, bool left_just, size_t width)
+{
+    if (left_just)
+    {
+        stream->write(data, length);
+        while (length < width)
+        {
+            stream->write1(' ');
+            length++;
+        }
+    }
+    else
+    {
+        char fill = leading_zero ? '0' : ' ';
+        size_t l = length;
+        while (l < width)
+        {
+            stream->write1(fill);
+            l++;
+        }
+        stream->write(data, length);
+    }
+}
+
+void hos_vprintf(const stream_t * stream, const char * fmt, va_list va)
+{
+    bool in_conv = false;
+    char c;
+    char buffer[22];
+    size_t width;
+    bool leading_zero;
+    bool left_just;
+    bool long_flag;
+    size_t length;
+    while ((c = *fmt))
+    {
+        if (in_conv)
+        {
+            switch (c)
+            {
+            case '%':
+                stream->write1('%');
+                break;
+            case 'X':
+                {
+                    if (long_flag)
+                    {
+                        uint64_t v = va_arg(va, uint64_t);
+                        length = format_hex(buffer, v, true);
+                    }
+                    else
+                    {
+                        uint32_t v = va_arg(va, uint32_t);
+                        length = format_hex(buffer, v, true);
+                    }
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
+                }
+                break;
+            case 'c':
+                {
+                    char ch = va_arg(va, int);
+                    pad_write(stream, &ch, 1u, leading_zero, left_just, width);
+                }
+                break;
+            case 'd':
+                {
+                    if (long_flag)
+                    {
+                        int64_t v = va_arg(va, int64_t);
+                        length = format_dec64(buffer, v);
+                    }
+                    else
+                    {
+                        int32_t v = va_arg(va, int32_t);
+                        length = format_dec(buffer, v);
+                    }
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
+                }
+                break;
+            case 's':
+                {
+                    const char * s = va_arg(va, const char *);
+                    pad_write(stream, s, strlen(s), leading_zero, left_just, width);
+                }
+                break;
+            case 'u':
+                {
+                    if (long_flag)
+                    {
+                        uint64_t v = va_arg(va, uint64_t);
+                        length = format_udec64(buffer, v);
+                    }
+                    else
+                    {
+                        uint32_t v = va_arg(va, uint32_t);
+                        length = format_udec(buffer, v);
+                    }
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
+                }
+                break;
+            case 'x':
+                {
+                    if (long_flag)
+                    {
+                        uint64_t v = va_arg(va, uint64_t);
+                        length = format_hex64(buffer, v, false);
+                    }
+                    else
+                    {
+                        uint32_t v = va_arg(va, uint32_t);
+                        length = format_hex(buffer, v, false);
+                    }
+                    pad_write(stream, buffer, length, leading_zero, left_just, width);
+                }
+                break;
+            }
+            in_conv = false;
+        }
+        else if (c == '%')
+        {
+            in_conv = true;
+            width = 0u;
+            leading_zero = false;
+            left_just = false;
+            long_flag = false;
+            if (fmt[1] == '-')
+            {
+                left_just = true;
+                fmt++;
+            }
+            if (fmt[1] == '0')
+            {
+                leading_zero = true;
+                fmt++;
+            }
+            while (('0' <= fmt[1]) && (fmt[1] <= '9'))
+            {
+                width *= 10u;
+                width += (fmt[1] - '0');
+                fmt++;
+            }
+            if (fmt[1] == 'l')
+            {
+                long_flag = true;
+                fmt++;
+            }
+        }
+        else
+        {
+            stream->write1(c);
+        }
+        fmt++;
+    }
+}
+
+void hos_printf(const stream_t * stream, const char * fmt, ...)
+{
+    va_list va;
+    va_start(va, fmt);
+    hos_vprintf(stream, fmt, va);
+    va_end(va);
+}

src/hos_printf.h

@@ -0,0 +1,10 @@
+#ifndef HOS_PRINTF_H
+#define HOS_PRINTF_H
+
+#include "stream.h"
+#include <stdarg.h>
+
+void hos_vprintf(const stream_t * stream, const char * fmt, va_list va);
+void hos_printf(const stream_t * stream, const char * fmt, ...);
+
+#endif

src/klog.c

@@ -0,0 +1,103 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdarg.h>
+#include "klog.h"
+#include "kfont.h"
+#include "fb.h"
+#include "fb_text.h"
+#include "stream.h"
+#include "hos_printf.h"
+#include "mem.h"
+
+static struct {
+    size_t console_width;
+    size_t console_height;
+    size_t x;
+    size_t y;
+    bool need_shift;
+} klog;
+
+static void shift_line(void)
+{
+    uint32_t * fb = fb_addr();
+    uint32_t w = fb_width();
+    size_t console_fb_line_words = w * kfont.line_height;
+    for (size_t row = 0u; row < klog.console_height; row++)
+    {
+        memcpy32(fb, fb + console_fb_line_words, console_fb_line_words);
+        fb += console_fb_line_words;
+    }
+    fb_fill(0, kfont.line_height * (klog.console_height - 1u), w, kfont.line_height, 0u, 0x2Cu, 0x55u);
+}
+
+static void klog_fb_write1(char c)
+{
+    if (klog.need_shift)
+    {
+        shift_line();
+        klog.need_shift = false;
+    }
+    if (c == '\n')
+    {
+        if (klog.y == (klog.console_height - 1u))
+        {
+            klog.need_shift = true;
+        }
+        else
+        {
+            klog.y++;
+        }
+        klog.x = 0u;
+    }
+    else
+    {
+        int px = klog.x * kfont.advance;
+        int py = klog.y * kfont.line_height;
+        fb_text_render_char(c, px, py, 0xFFu, 0x80u, 0u);
+        klog.x++;
+        if (klog.x == klog.console_width)
+        {
+            if (klog.y == (klog.console_height - 1u))
+            {
+                klog.need_shift = true;
+            }
+            else
+            {
+                klog.y++;
+            }
+            klog.x = 0u;
+        }
+    }
+}
+
+static void klog_fb_write(const char * src, size_t length)
+{
+    for (size_t i = 0u; i < length; i++)
+    {
+        klog_fb_write1(src[i]);
+    }
+}
+
+static const stream_t klog_fb_stream = {
+    klog_fb_write,
+    klog_fb_write1,
+};
+
+void klog_init(void)
+{
+    klog.console_width = fb_width() / kfont.advance;
+    klog.console_height = fb_height() / kfont.line_height;
+    klog.x = 0u;
+    klog.y = 0u;
+    klog.need_shift = false;
+    fb_fill(0, 0, fb_width(), fb_height(), 0u, 0x2Cu, 0x55u);
+}
+
+void klog_printf(const char * fmt, ...)
+{
+    va_list va;
+    va_start(va, fmt);
+    hos_vprintf(&klog_fb_stream, fmt, va);
+    va_end(va);
+}

src/klog.h

@@ -0,0 +1,7 @@
+#ifndef KLOG_H
+#define KLOG_H
+
+void klog_init(void);
+void klog_printf(const char * fmt, ...);
+
+#endif

src/link.ld

@@ -0,0 +1,41 @@
+ENTRY(hos_start)
+
+SECTIONS
+{
+    . = 1M;
+    _hos_mem_start = .;
+
+    .text BLOCK(4K) : ALIGN(4K)
+    {
+        *(.multiboot)
+        *(.text)
+    }
+
+    .rodata BLOCK(4K) : ALIGN(4K)
+    {
+        *(.rodata)
+    }
+
+    .data BLOCK(4K) : ALIGN(4K)
+    {
+        *(.data)
+    }
+
+    _stack_size = 16K;
+    .stack (NOLOAD) : ALIGN(4K)
+    {
+        _stack_start = .;
+        . = . + _stack_size;
+        _stack_end = .;
+    }
+
+    .bss BLOCK(4K) : ALIGN(4K)
+    {
+        *(COMMON)
+        *(.bss)
+    }
+
+    . = ALIGN(4K);
+
+    _hos_mem_end = .;
+}

src/mbinfo.c

@@ -0,0 +1,100 @@
+#include "multiboot2.h"
+#include "fb.h"
+#include "mem.h"
+#include <stdint.h>
+#include "klog.h"
+#include "mm.h"
+
+static uint32_t mbinfo[2048];
+
+static void mbinfo_process_tag(const multiboot2_info_tag_t * tag)
+{
+    switch (tag->type)
+    {
+    case MULTIBOOT2_INFO_BOOT_COMMAND_LINE:
+        {
+            multiboot2_info_boot_command_line_t * cl =
+                (multiboot2_info_boot_command_line_t *)tag;
+            klog_printf("Kernel boot command line: '%s'\n", cl->string);
+        }
+        break;
+
+    case MULTIBOOT2_INFO_BOOT_LOADER_NAME:
+        {
+            multiboot2_info_boot_loader_name_t * bln =
+                (multiboot2_info_boot_loader_name_t *)tag;
+            klog_printf("Boot loader: '%s'\n", bln->string);
+        }
+        break;
+
+    case MULTIBOOT2_INFO_MEMORY_MAP:
+        {
+            multiboot2_info_memory_map_t * mmap_info =
+                (multiboot2_info_memory_map_t *)tag;
+            size_t sz = sizeof(mmap_info->header) +
+                sizeof(mmap_info->entry_size) +
+                sizeof(mmap_info->entry_version);
+            multiboot2_info_memory_map_entry_t * entry = &mmap_info->entries[0];
+            for (;;)
+            {
+                sz += mmap_info->entry_size;
+                if (sz > mmap_info->header.size)
+                {
+                    break;
+                }
+                if (entry->type == MULTIBOOT2_MEMORY_MAP_TYPE_RAM)
+                {
+                    klog_printf("Memory region %16lx : %16lx\n",
+                            entry->base_addr,
+                            entry->length);
+                    mm_register_ram_region(entry->base_addr, entry->length);
+                }
+                entry = (multiboot2_info_memory_map_entry_t *)((uintptr_t)entry + mmap_info->entry_size);
+            }
+        }
+        break;
+
+    case MULTIBOOT2_INFO_FRAMEBUFFER_INFO:
+        {
+            multiboot2_info_framebuffer_info_t * fbinfo =
+                (multiboot2_info_framebuffer_info_t *)tag;
+            fb_init((uint32_t *)(uintptr_t)fbinfo->framebuffer_addr,
+                    fbinfo->framebuffer_width,
+                    fbinfo->framebuffer_height,
+                    fbinfo->framebuffer_pitch);
+        }
+        break;
+    }
+}
+
+static void process_tags(const multiboot2_info_tag_t * tag, bool init)
+{
+    while (tag->type != 0u)
+    {
+        if ((init && (tag->type == MULTIBOOT2_INFO_FRAMEBUFFER_INFO)) ||
+                (!init && (tag->type != MULTIBOOT2_INFO_FRAMEBUFFER_INFO)))
+        {
+            mbinfo_process_tag(tag);
+        }
+        tag = multiboot2_info_next_tag(tag);
+    }
+}
+
+bool mbinfo_init(uint32_t mbinfo_addr)
+{
+    multiboot2_info_header_t * mbinfo_header = (multiboot2_info_header_t *)mbinfo_addr;
+    if (mbinfo_header->total_size <= sizeof(mbinfo))
+    {
+        memcpy32(mbinfo, mbinfo_header, mbinfo_header->total_size / 4u);
+        multiboot2_info_tag_t * tag = (multiboot2_info_tag_t *)(mbinfo + sizeof(multiboot2_info_header_t) / 4u);
+        process_tags(tag, true);
+        return true;
+    }
+    return false;
+}
+
+void mbinfo_load(void)
+{
+    multiboot2_info_tag_t * tag = (multiboot2_info_tag_t *)(mbinfo + sizeof(multiboot2_info_header_t) / 4u);
+    process_tags(tag, false);
+}

src/mbinfo.h

@@ -0,0 +1,10 @@
+#ifndef MBINFO_H
+#define MBINFO_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+bool mbinfo_init(uint32_t mbinfo_addr);
+void mbinfo_load(void);
+
+#endif

src/mem.h

@@ -0,0 +1,49 @@
+#ifndef MEM_H
+#define MEM_H
+
+#include <stddef.h>
+
+static inline void memcpy(void * dest, const void * src, size_t n)
+{
+    uint32_t r0, r1, r2;
+    __asm__ __volatile__ (
+            "cld\n\t"
+            "rep movsb"
+            : "=&c" (r0), "=&S" (r1), "=&D" (r2)
+            : "2" (dest), "1" (src), "0" (n)
+            : "memory");
+}
+
+static inline void memcpy32(void * dest, const void * src, size_t count)
+{
+    uint32_t r0, r1, r2;
+    __asm__ __volatile__ (
+            "cld\n\t"
+            "rep movsd"
+            : "=&c" (r0), "=&S" (r1), "=&D" (r2)
+            : "2" (dest), "1" (src), "0" (count)
+            : "memory");
+}
+
+static inline void * memmove(void * dest, const void * src, size_t count)
+{
+    return __builtin_memmove(dest, src, count);
+}
+
+static inline void * memset(void * dest, int val, size_t count)
+{
+    return __builtin_memset(dest, val, count);
+}
+
+static inline void memset32(void * dest, uint32_t val, size_t count)
+{
+    uint32_t r0, r1;
+    __asm__ __volatile__ (
+            "cld\n\t"
+            "rep stosl"
+            : "=&c" (r0), "=&D" (r1)
+            : "a" (val), "1" (dest), "0" (count)
+            : "memory");
+}
+
+#endif

src/mm.c

@@ -0,0 +1,91 @@
+#include "mm.h"
+
+typedef struct mm_page_entry_s {
+    size_t count;
+    struct mm_page_entry_s * next;
+} mm_region_entry_t;
+
+static mm_region_entry_t * mm_next_free_region;
+static size_t mm_free_pages;
+static size_t mm_total_ram;
+static size_t kernel_start_address;
+static size_t kernel_size;
+
+extern uint8_t _hos_mem_start;
+extern uint8_t _hos_mem_end;
+
+static void mm_add_ram_region(size_t base, size_t size)
+{
+    mm_region_entry_t * region = (mm_region_entry_t *)base;
+    size_t pages = size / PAGE_SIZE;
+    region->count = pages;
+    region->next = mm_next_free_region;
+    mm_next_free_region = region;
+    mm_total_ram += size;
+    mm_free_pages = pages;
+}
+
+void mm_register_ram_region(uint64_t base, size_t size)
+{
+    /* Ignore any RAM region above 4GB. */
+    if (base >= 0x100000000ull)
+    {
+        return;
+    }
+    if ((base + size) > 0x100000000ull)
+    {
+        size = (size_t)(0x100000000ull - base);
+    }
+    size_t end_address = mm_page_floor((size_t)base + size);
+    size_t start_address = mm_page_ceil(base);
+    size = end_address - start_address;
+    if (size < PAGE_SIZE)
+    {
+        return;
+    }
+    size_t kernel_end_address = kernel_start_address + kernel_size;
+    /* Add regions before and after kernel RAM. */
+    if (start_address < kernel_start_address)
+    {
+        /* RAM region begins before kernel RAM. */
+        size_t this_sz = size;
+        if ((start_address + this_sz) > kernel_start_address)
+        {
+            this_sz = kernel_start_address - start_address;
+        }
+        mm_add_ram_region(start_address, this_sz);
+    }
+    if ((start_address + size) > kernel_end_address)
+    {
+        /* RAM region ends after kernel RAM. */
+        size_t this_sz = size;
+        if (start_address < kernel_end_address)
+        {
+            this_sz = (start_address + size) - kernel_end_address;
+            start_address = kernel_end_address;
+        }
+        mm_add_ram_region(start_address, this_sz);
+    }
+}
+
+void mm_init(void)
+{
+    kernel_start_address = mm_page_floor((size_t)&_hos_mem_start);
+    kernel_size = mm_page_ceil((size_t)&_hos_mem_end - kernel_start_address);
+    mm_total_ram = kernel_size;
+}
+
+size_t mm_get_total_ram(void)
+{
+    return mm_total_ram;
+}
+
+size_t mm_get_kernel_address(void)
+{
+    return kernel_start_address;
+}
+
+size_t mm_get_kernel_size(void)
+{
+    return kernel_size;
+}

src/mm.h

@@ -0,0 +1,25 @@
+#ifndef MM_H
+#define MM_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+#define PAGE_SIZE 4096u
+
+static inline size_t mm_page_floor(size_t bytes)
+{
+    return bytes & ~(PAGE_SIZE - 1u);
+}
+
+static inline size_t mm_page_ceil(size_t bytes)
+{
+    return (bytes + PAGE_SIZE - 1u) & ~(PAGE_SIZE - 1u);
+}
+
+void mm_init(void);
+void mm_register_ram_region(uint64_t base, size_t size);
+size_t mm_get_total_ram(void);
+size_t mm_get_kernel_address(void);
+size_t mm_get_kernel_size(void);
+
+#endif

src/multiboot2.h

@@ -0,0 +1,127 @@
+#ifndef MULTIBOOT2_H
+#define MULTIBOOT2_H
+
+#include <stdint.h>
+
+#define MULTIBOOT2_MAGIC 0xE85250D6u
+#define MULTIBOOT2_ARCHITECTURE_I386 0u
+
+typedef struct {
+    uint32_t magic;
+    uint32_t architecture;
+    uint32_t header_length;
+    uint32_t checksum;
+} multiboot2_header_t;
+#define multiboot2_header(magic, architecture, header_length) \
+    {(magic), (architecture), (header_length), (uint32_t)(0x100000000u - (magic) - (architecture) - (header_length))}
+#define multiboot2_header_default() \
+    multiboot2_header(MULTIBOOT2_MAGIC, MULTIBOOT2_ARCHITECTURE_I386, sizeof(multiboot2_header_t))
+
+typedef struct {
+    uint16_t type;
+    uint16_t flags;
+    uint32_t size;
+} multiboot2_tag_t;
+#define multiboot2_end_tag() {0u, 0u, 8u}
+
+typedef struct {
+    multiboot2_tag_t header;
+    uint32_t width;
+    uint32_t height;
+    uint32_t depth;
+    uint32_t _padding;
+} multiboot2_framebuffer_tag_t;
+#define multiboot2_framebuffer_tag(width, height, depth) \
+    {{5u, 0u, 20u}, width, height, depth}
+
+#define MULTIBOOT2_INFO_TAG_ALIGNMENT 8u
+#define MULTIBOOT2_INFO_BOOT_COMMAND_LINE 1u
+#define MULTIBOOT2_INFO_BOOT_LOADER_NAME 2u
+#define MULTIBOOT2_INFO_MODULES 3u
+#define MULTIBOOT2_INFO_BASIC_MEMORY_INFO 4u
+#define MULTIBOOT2_INFO_BIOS_BOOT_DEVICE 5u
+#define MULTIBOOT2_INFO_MEMORY_MAP 6u
+#define MULTIBOOT2_INFO_VBE_INFO 7u
+#define MULTIBOOT2_INFO_FRAMEBUFFER_INFO 8u
+#define MULTIBOOT2_INFO_ELF_SYMBOLS 9u
+#define MULTIBOOT2_INFO_APM_TABLE 10u
+#define MULTIBOOT2_INFO_EFI_32BIT_SYSTEM_TABLE_POINTER 11u
+#define MULTIBOOT2_INFO_EFI_64BIT_SYSTEM_TABLE_POINTER 12u
+#define MULTIBOOT2_INFO_SMBIOS_TABLES 13u
+#define MULTIBOOT2_INFO_ACPI_OLD_RSDP 14u
+#define MULTIBOOT2_INFO_NETWORKING_INFO 16u
+#define MULTIBOOT2_INFO_EFI_MEMORY_MAP 17u
+#define MULTIBOOT2_INFO_EFI_BOOT_SERVICES_NOT_TERMINATED 18u
+#define MULTIBOOT2_INFO_EFI_32BIT_IMAGE_HANDLE_POINTER 19u
+#define MULTIBOOT2_INFO_EFI_64BIT_IMAGE_HANDLE_POINTER 20u
+#define MULTIBOOT2_INFO_IMAGE_LOAD_BASE_PHYSICAL_ADDRESS 21u
+
+typedef struct {
+    uint32_t total_size;
+    uint32_t _reserved;
+} multiboot2_info_header_t;
+
+typedef struct {
+    uint32_t type;
+    uint32_t size;
+} multiboot2_info_tag_t;
+#define multiboot2_info_next_tag(current_tag) \
+    (multiboot2_info_tag_t *)(((uintptr_t)current_tag + current_tag->size + MULTIBOOT2_INFO_TAG_ALIGNMENT - 1u) & ~(MULTIBOOT2_INFO_TAG_ALIGNMENT - 1u))
+
+typedef struct {
+    multiboot2_info_tag_t header;
+    char string[];
+} multiboot2_info_boot_command_line_t;
+
+typedef struct {
+    multiboot2_info_tag_t header;
+    char string[];
+} multiboot2_info_boot_loader_name_t;
+
+typedef struct {
+    multiboot2_info_tag_t header;
+    uint32_t mem_lower;
+    uint32_t mem_upper;
+} multiboot2_info_basic_memory_info_t;
+
+#define MULTIBOOT2_MEMORY_MAP_TYPE_RAM 1u
+#define MULTIBOOT2_MEMORY_MAP_TYPE_ACPI 3u
+#define MULTIBOOT2_MEMORY_MAP_TYPE_PRESERVE 4u
+#define MULTIBOOT2_MEMORY_MAP_TYPE_DEFECTIVE 5u
+
+typedef struct {
+    uint64_t base_addr;
+    uint64_t length;
+    uint32_t type;
+    uint32_t _reserved;
+} multiboot2_info_memory_map_entry_t;
+
+typedef struct {
+    multiboot2_info_tag_t header;
+    uint32_t entry_size;
+    uint32_t entry_version;
+    multiboot2_info_memory_map_entry_t entries[];
+} multiboot2_info_memory_map_t;
+
+typedef struct {
+    multiboot2_info_tag_t header;
+    uint16_t vbe_mode;
+    uint16_t vbe_interface_set;
+    uint16_t vbe_interface_off;
+    uint16_t vbe_interface_len;
+    uint8_t vbe_control_info[512];
+    uint8_t vbe_mode_info[256];
+} multiboot2_info_vbe_info_t;
+
+typedef struct {
+    multiboot2_info_tag_t header;
+    uint64_t framebuffer_addr;
+    uint32_t framebuffer_pitch;
+    uint32_t framebuffer_width;
+    uint32_t framebuffer_height;
+    uint8_t framebuffer_bpp;
+    uint8_t framebuffer_type;
+    uint8_t _reserved;
+} multiboot2_info_framebuffer_info_t;
+
+#endif

src/multiboot_header.c

@@ -0,0 +1,12 @@
+#include "multiboot2.h"
+
+/* Multiboot2 Header. */
+struct {
+    multiboot2_header_t header;
+    multiboot2_framebuffer_tag_t framebuffer_tag;
+    multiboot2_tag_t end_tag;
+} multiboot_header __attribute__((section(".multiboot"))) = {
+    multiboot2_header_default(),
+    multiboot2_framebuffer_tag(1600u, 900u, 32u),
+    multiboot2_end_tag(),
+};

src/stream.h

@@ -0,0 +1,12 @@
+#ifndef STREAM_H
+#define STREAM_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct {
+    void (*write)(const char * src, size_t length);
+    void (*write1)(char c);
+} stream_t;
+
+#endif

src/string.h

@@ -0,0 +1,26 @@
+#ifndef STRING_H
+#define STRING_H
+
+#include <stddef.h>
+
+static inline size_t strlen(const char * s)
+{
+    size_t r = 0u;
+    while (*s++ != (char)0)
+    {
+        r++;
+    }
+    return r;
+}
+
+static inline char * strcpy(char * dest, const char * src)
+{
+    return __builtin_strcpy(dest, src);
+}
+
+static inline char * strncpy(char * dest, const char * src, size_t n)
+{
+    return __builtin_strncpy(dest, src, n);
+}
+
+#endif