Bootloader: Start work on bootloader

I wrote a fast first stage bootloader and a installer to put it into
a disk image.

bootloader/.gitignore

@@ -0,0 +1,3 @@
+test.img
+build/
+installer/build/

bootloader/arch/x86_64/boot.S

@@ -0,0 +1,287 @@
+# FIXME: don't assume 512 byte sectors
+.set SECTOR_SIZE,		512
+
+.set GPT_HEADER_ADDR,	free_memory_start
+.set GPT_ENTRY_ADDR,	free_memory_start + SECTOR_SIZE
+
+
+
+.code16
+
+#########################################
+#
+# STAGE 1 BOOTLOADER
+#
+# its sole purpose is to load stage2 from
+# bios boot partition
+#
+#########################################
+
+.section .stage1
+
+stage1_start:
+	jmp main
+
+# al:		character to print
+putc:
+	mov $0x0E, %ah
+	int $0x10
+	ret
+
+# ds:si:	null terminated string to print
+puts:
+	push %si
+	push %ax
+
+1:
+	lodsb
+
+	test %al, %al
+	jz 2f
+
+	call putc
+	jmp 1b
+
+2:
+	mov $'\r', %al
+	call putc
+	mov $'\n', %al
+	call putc
+
+	pop %ax
+	pop %si
+	ret
+
+# si:		ptr1
+# di:		ptr2
+# cx:		count
+# return:	1 if equal, 0 otherwise
+memcmp:
+	pushw %si
+	pushw %di
+
+	cld
+	repe cmpsb
+	setzb %al
+
+	popw %di
+	popw %si
+	ret
+
+
+# read sectors from disk
+#
+# bx:eax:	lba start
+# cx:		lba count (has to less than 0x80)
+# dl:		drive number
+# ds:di:	physical address
+#
+# returns only on success
+read_from_disk:
+	push %ax
+	push %si
+
+	# prepare disk read packet
+	mov $disk_address_packet, %si
+	movb $0x10,	0x00(%si)	# packet size
+	movb $0x00,	0x01(%si)	# always 0
+	movw %cx,	0x02(%si)	# lba count
+	movw %di,	0x04(%si)	# offset
+	movw %ds,	0x06(%si)	# segment
+	movl %eax,	0x08(%si)	# 32 bit lower lba
+	movw %bx,	0x0C(%si)	# 16 bit upper lba
+	movw $0,	0x0E(%si)	# zero
+
+	# issue read command
+	clc
+	mov $0x42, %ah
+	int $0x13
+	jc .read_failed
+
+	pop %si
+	pop %ax
+	ret
+
+
+main:
+	# setup segments
+	movw $0, %ax
+	movw %ax, %ds
+	movw %ax, %es
+
+	# setup stack
+	movw %ax, %ss
+	movw $0x7C00, %sp
+
+	# save boot disk number
+	movb %dl, (boot_disk_number)
+
+	# confirm that int 13h extensions are available
+	clc
+	movb $0x41, %ah
+	movw $0x55AA, %bx
+	movb (boot_disk_number), %dl
+	int $0x13
+	jc .no_int13h_ext
+
+	# read gpt header
+	movl $1, %eax
+	movw $0, %bx
+	movw $1, %cx
+	movb (boot_disk_number), %dl
+	movw $GPT_HEADER_ADDR, %di
+	call read_from_disk
+
+	# confirm header (starts with 'EFI PART')
+	cmpl $0x20494645, (GPT_HEADER_ADDR + 0)
+	jne .not_gpt_partition
+	cmpl $0x54524150, (GPT_HEADER_ADDR + 4)
+	jne .not_gpt_partition
+
+	# eax := entry_count
+	movl (GPT_HEADER_ADDR + 80), %eax
+	test %eax, %eax
+	jz .no_bios_boot_partition
+
+	# edx:eax := eax * entry_size
+	mull (GPT_HEADER_ADDR + 84)
+	test %edx, %edx
+	jnz .too_gpt_big_entries
+
+	# sector count := (arr_size + SECTOR_SIZE - 1) / SECTOR_SIZE
+	pushl %eax
+	addl $(SECTOR_SIZE - 1), %eax
+	movl $SECTOR_SIZE, %ecx
+	divl %ecx
+	movl %eax, %ecx
+	popl %eax
+
+	# start lba
+	movl (GPT_HEADER_ADDR + 72), %eax
+	movw (GPT_HEADER_ADDR + 76), %bx
+
+	movb (boot_disk_number), %dl
+	movw $GPT_ENTRY_ADDR, %di
+	call read_from_disk
+
+	# NOTE: 'only' 0xFFFF partitions supported
+	movw (GPT_HEADER_ADDR + 80), %cx
+
+.loop_entries:
+	push %cx
+	movw $16, %cx
+	movw $bios_boot_guid, %si
+	call memcmp
+	pop %cx
+
+	testb %al, %al
+	jnz .bios_boot_found
+
+	# add entry size to entry pointer
+	addw (GPT_HEADER_ADDR + 84), %di
+
+	loop .loop_entries
+	jmp .no_bios_boot_partition
+
+.bios_boot_found:
+	# first lba
+	movl 32(%di), %eax
+	movw $0, %bx
+
+	# count := last lba - first lba + 1
+	movl 40(%di), %ecx
+	subl %eax, %ecx
+	addl $1, %ecx
+
+	# calculate stage2 sector count
+	movw $((stage2_end - stage2_start + SECTOR_SIZE - 1) / SECTOR_SIZE), %cx
+
+	movb (boot_disk_number), %dl
+	movw $stage2_start, %di
+
+	call read_from_disk
+	jmp stage2_start
+
+print_and_halt:
+	call puts
+halt:
+	hlt
+	jmp halt
+
+.no_int13h_ext:
+	mov $no_int13_ext_msg, %si
+	jmp print_and_halt
+
+.read_failed:
+	mov $read_failed_msg, %si
+	jmp print_and_halt
+
+.not_gpt_partition:
+	mov $not_gpt_partition_msg, %si
+	jmp print_and_halt
+
+.no_bios_boot_partition:
+	mov $no_bios_boot_partition_msg, %si
+	jmp print_and_halt
+
+.too_gpt_big_entries:
+	mov $too_gpt_big_entries_msg, %si
+	jmp print_and_halt
+
+
+
+# 21686148-6449-6E6F-744E-656564454649
+bios_boot_guid:
+	.long 0x21686148		# little endian
+	.word 0x6449			# little endian
+	.word 0x6E6F			# little endian
+	.word 0x4E74			# big endian
+	.quad 0x494645646565	# big endian
+
+no_int13_ext_msg:
+	.asciz "no INT 13h ext"
+
+read_failed_msg:
+	.asciz "read error"
+
+not_gpt_partition_msg:
+	.asciz "not gpt"
+
+no_bios_boot_partition_msg:
+	.asciz "no bios boot partition"
+
+too_gpt_big_entries_msg:
+	.asciz "too big GPT array"
+
+boot_disk_number:
+	.skip 1
+
+disk_address_packet:
+	.skip 16
+
+
+
+#########################################
+#
+# STAGE 2 BOOTLOADER
+#
+#########################################
+
+.section .stage2
+stage2_start:
+	# clear screen and enter 80x25 text mode
+	movb $0x03, %al
+	movb $0x00, %ah
+	int $0x10
+
+	# print hello message
+	movw $hello_msg, %si
+	call puts
+
+1:
+	jmp 1b
+
+hello_msg:
+	.asciz "This is banan-os bootloader"
+
+stage2_end:

bootloader/arch/x86_64/linker.ld

@@ -0,0 +1,11 @@
+SECTIONS
+{
+	. = 0x7C00;
+	.stage1 : { *(.stage1*) }
+
+	. = ALIGN(512);
+	.stage2 : { *(.stage2) }
+
+	. = ALIGN(512);
+	free_memory_start = .;
+}

bootloader/build-and-run.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+
+set -e
+
+CURRENT_DIR=$(dirname $(realpath $0))
+
+INSTALLER_DIR=$CURRENT_DIR/installer
+INSTALLER_BUILD_DIR=$INSTALLER_DIR/build
+
+BUILD_DIR=$CURRENT_DIR/build
+DISK_IMAGE_PATH=$CURRENT_DIR/test.img
+
+if ! [ -d $INSTALLER_BUILD_DIR ]; then
+	mkdir -p $INSTALLER_BUILD_DIR
+	cd $INSTALLER_BUILD_DIR
+	cmake ..
+fi
+
+cd $INSTALLER_BUILD_DIR
+make
+
+cd $CURRENT_DIR
+
+echo creating clean disk image
+truncate --size 0 $DISK_IMAGE_PATH
+truncate --size 50M $DISK_IMAGE_PATH
+echo -ne 'g\nn\n\n\n+1M\nt 1\n4\nw\n' | fdisk $DISK_IMAGE_PATH > /dev/null
+
+mkdir -p $BUILD_DIR
+
+echo compiling bootloader
+x86_64-banan_os-as arch/x86_64/boot.S -o $BUILD_DIR/bootloader.o
+
+echo linking bootloader
+x86_64-banan_os-ld -nostdlib -T arch/x86_64/linker.ld $BUILD_DIR/bootloader.o -o $BUILD_DIR/bootloader
+
+echo installing bootloader
+$INSTALLER_BUILD_DIR/x86_64-banan_os-bootloader-installer $BUILD_DIR/bootloader $DISK_IMAGE_PATH
+
+if [ "$1" == "debug" ] ; then
+	QEMU_FLAGS="-s -S"
+fi
+
+echo running qemu
+qemu-system-x86_64 $QEMU_FLAGS --drive format=raw,file=test.img

bootloader/installer/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(x86_64-banan_os-bootloader-installer CXX)
+
+set(SOURCES
+    crc32.cpp
+    ELF.cpp
+    GPT.cpp
+    GUID.cpp
+	main.cpp
+)
+
+add_executable(x86_64-banan_os-bootloader-installer ${SOURCES})
+target_compile_options(x86_64-banan_os-bootloader-installer PUBLIC -O2 -std=c++20)

bootloader/installer/ELF.cpp

@@ -0,0 +1,140 @@
+#include "ELF.h"
+
+#include <cassert>
+#include <cerrno>
+#include <cstring>
+#include <fcntl.h>
+#include <iostream>
+#include <sys/mman.h>
+#include <unistd.h>
+
+ELFFile::ELFFile(std::string_view path)
+	: m_path(path)
+{
+	m_fd = open(m_path.c_str(), O_RDONLY);
+	if (m_fd == -1)
+	{
+		std::cerr << "Could not open '" << m_path << "': " << std::strerror(errno) << std::endl;
+		return;
+	}
+
+	if (fstat(m_fd, &m_stat) == -1)
+	{
+		std::cerr << "Could not stat '" << m_path << "': " << std::strerror(errno) << std::endl;
+		return;
+	}
+
+	void* mmap_addr = mmap(nullptr, m_stat.st_size, PROT_READ, MAP_PRIVATE, m_fd, 0);
+	if (mmap_addr == MAP_FAILED)
+	{
+		std::cerr << "Could not mmap '" << m_path << "': " << std::strerror(errno) << std::endl;
+		return;
+	}
+	m_mmap = reinterpret_cast<uint8_t*>(mmap_addr);
+
+	if (!validate_elf_header())
+		return;
+
+	m_success = true;
+}
+
+ELFFile::~ELFFile()
+{
+	if (m_mmap)
+		munmap(m_mmap, m_stat.st_size);
+	m_mmap = nullptr;
+
+	if (m_fd != -1)
+		close(m_fd);
+	m_fd = -1;
+}
+
+const Elf64_Ehdr& ELFFile::elf_header() const
+{
+	return *reinterpret_cast<Elf64_Ehdr*>(m_mmap);
+}
+
+bool ELFFile::validate_elf_header() const
+{
+	if (m_stat.st_size < sizeof(Elf64_Ehdr))
+	{
+		std::cerr << m_path << " is too small to be a ELF executable" << std::endl;
+		return false;
+	}
+
+	const auto& elf_header = this->elf_header();
+
+	if (
+		elf_header.e_ident[EI_MAG0] != ELFMAG0 ||
+		elf_header.e_ident[EI_MAG1] != ELFMAG1 ||
+		elf_header.e_ident[EI_MAG2] != ELFMAG2 ||
+		elf_header.e_ident[EI_MAG3] != ELFMAG3
+	)
+	{
+		std::cerr << m_path << " doesn't have an ELF magic number" << std::endl;
+		return false;
+	}
+
+	if (elf_header.e_ident[EI_CLASS] != ELFCLASS64)
+	{
+		std::cerr << m_path << " is not 64 bit ELF" << std::endl;
+		return false;
+	}
+
+	if (elf_header.e_ident[EI_DATA] != ELFDATA2LSB)
+	{
+		std::cerr << m_path << " is not in little endian format" << std::endl;
+		return false;
+	}
+
+	if (elf_header.e_ident[EI_VERSION] != EV_CURRENT)
+	{
+		std::cerr << m_path << " has unsupported version" << std::endl;
+		return false;
+	}
+
+	if (elf_header.e_type != ET_EXEC)
+	{
+		std::cerr << m_path << " is not an executable ELF file" << std::endl;
+		return false;
+	}
+
+	if (elf_header.e_machine != EM_X86_64)
+	{
+		std::cerr << m_path << " is not an x86_64 ELF file" << std::endl;
+		return false;
+	}
+
+	return true;
+}
+
+const Elf64_Shdr& ELFFile::section_header(std::size_t index) const
+{
+	const auto& elf_header = this->elf_header();
+	assert(index < elf_header.e_shnum);
+	const uint8_t* section_array_start = m_mmap + elf_header.e_shoff;
+	return *reinterpret_cast<const Elf64_Shdr*>(section_array_start + index * elf_header.e_shentsize);
+}
+
+std::string_view ELFFile::section_name(const Elf64_Shdr& section_header) const
+{
+	const auto& elf_header = this->elf_header();
+	assert(elf_header.e_shstrndx != SHN_UNDEF);
+	const auto& section_string_table = this->section_header(elf_header.e_shstrndx);
+	const char* string_table_start = reinterpret_cast<const char*>(m_mmap + section_string_table.sh_offset);
+	return string_table_start + section_header.sh_name;
+}
+
+std::optional<std::span<const uint8_t>> ELFFile::find_section(std::string_view name) const
+{
+	const auto& elf_header = this->elf_header();
+	for (std::size_t i = 0; i < elf_header.e_shnum; i++)
+	{
+		const auto& section_header = this->section_header(i);
+		auto section_name = this->section_name(section_header);
+		if (section_name != name)
+			continue;
+		return std::span<const uint8_t>(m_mmap + section_header.sh_offset, section_header.sh_size);
+	}
+	return {};
+}

bootloader/installer/ELF.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <cstdint>
+#include <optional>
+#include <span>
+#include <string_view>
+#include <string>
+#include <sys/stat.h>
+
+#include <elf.h>
+
+class ELFFile
+{
+public:
+	ELFFile(std::string_view path);
+	~ELFFile();
+
+	const Elf64_Ehdr& elf_header() const;
+	std::optional<std::span<const uint8_t>> find_section(std::string_view name) const;
+
+	bool success() const { return m_success; }
+
+	std::string_view path() const { return m_path; }
+
+private:
+	const Elf64_Shdr& section_header(std::size_t index) const;
+	std::string_view section_name(const Elf64_Shdr&) const;
+	bool validate_elf_header() const;
+
+private:
+	const std::string	m_path;
+	bool				m_success	{ false };
+	int					m_fd		{ -1 };
+	struct stat			m_stat		{ };
+	uint8_t*			m_mmap		{ nullptr };
+};

bootloader/installer/GPT.cpp

@@ -0,0 +1,171 @@
+#include "crc32.h"
+#include "GPT.h"
+
+#include <cassert>
+#include <cerrno>
+#include <cstring>
+#include <fcntl.h>
+#include <iostream>
+#include <sys/mman.h>
+#include <unistd.h>
+
+// FIXME: don't assume 512 byte sectors
+#define SECTOR_SIZE 512
+
+GPTFile::GPTFile(std::string_view path)
+	: m_path(path)
+{
+	m_fd = open(m_path.c_str(), O_RDWR);
+	if (m_fd == -1)
+	{
+		std::cerr << "Could not open '" << m_path << "': " << std::strerror(errno) << std::endl;
+		return;
+	}
+
+	if (fstat(m_fd, &m_stat) == -1)
+	{
+		std::cerr << "Could not stat '" << m_path << "': " << std::strerror(errno) << std::endl;
+		return;
+	}
+
+	void* mmap_addr = mmap(nullptr, m_stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, m_fd, 0);
+	if (mmap_addr == MAP_FAILED)
+	{
+		std::cerr << "Could not mmap '" << m_path << "': " << std::strerror(errno) << std::endl;
+		return;
+	}
+	m_mmap = reinterpret_cast<uint8_t*>(mmap_addr);
+
+	if (!validate_gpt_header())
+		return;
+
+	m_success = true;
+}
+
+GPTFile::~GPTFile()
+{
+	if (m_mmap)
+		munmap(m_mmap, m_stat.st_size);
+	m_mmap = nullptr;
+
+	if (m_fd != -1)
+		close(m_fd);
+	m_fd = -1;
+}
+
+MBR& GPTFile::mbr()
+{
+	return *reinterpret_cast<MBR*>(m_mmap);
+}
+
+const GPTHeader& GPTFile::gpt_header() const
+{
+    return *reinterpret_cast<GPTHeader*>(m_mmap + SECTOR_SIZE);
+}
+
+bool GPTFile::install_bootcode(std::span<const uint8_t> boot_code)
+{
+	auto& mbr = this->mbr();
+
+	if (boot_code.size() > sizeof(mbr.boot_code))
+	{
+		std::cerr << m_path << ": can't fit " << boot_code.size() << " bytes of boot code in mbr (max is " << sizeof(mbr.boot_code) << ")" << std::endl;
+		return false;
+	}
+
+	// copy boot code
+	memcpy(mbr.boot_code, boot_code.data(), boot_code.size());
+
+	// setup mbr
+	mbr.unique_mbr_disk_signature = 0xdeadbeef;
+	mbr.unknown = 0;
+	mbr.signature = 0xAA55;
+
+	// setup mbr partition records
+	mbr.partition_records[0].boot_indicator = 0x00;
+	mbr.partition_records[0].starting_chs[0] = 0x00;
+	mbr.partition_records[0].starting_chs[1] = 0x02;
+	mbr.partition_records[0].starting_chs[2] = 0x00;
+	mbr.partition_records[0].os_type = 0xEE;
+	mbr.partition_records[0].ending_chs[0] = 0xFF;
+	mbr.partition_records[0].ending_chs[1] = 0xFF;
+	mbr.partition_records[0].ending_chs[2] = 0xFF;
+	mbr.partition_records[0].starting_lba = 1;
+	mbr.partition_records[0].size_in_lba = 0xFFFFFFFF;
+	memset(&mbr.partition_records[1], 0x00, sizeof(MBRPartitionRecord));
+	memset(&mbr.partition_records[2], 0x00, sizeof(MBRPartitionRecord));
+	memset(&mbr.partition_records[3], 0x00, sizeof(MBRPartitionRecord));
+
+	return true;
+}
+
+bool GPTFile::write_partition(std::span<const uint8_t> data, GUID type_guid)
+{
+	auto partition = find_partition(type_guid);
+	if (!partition.has_value())
+	{
+		std::cerr << m_path << ": could not find partition with type " << type_guid << std::endl;
+		return false;
+	}
+
+	const std::size_t partition_size = (partition->ending_lba - partition->starting_lba + 1) * SECTOR_SIZE;
+
+	if (data.size() > partition_size)
+	{
+		std::cerr << m_path << ": can't fit " << data.size() << " bytes of data to partition of size " << partition_size << std::endl;
+		return false;
+	}
+
+	memcpy(m_mmap + partition->starting_lba * SECTOR_SIZE, data.data(), data.size());
+
+	return true;
+}
+
+std::optional<GPTPartitionEntry> GPTFile::find_partition(const GUID& type_guid) const
+{
+	const auto& gpt_header = this->gpt_header();
+	const uint8_t* partition_entry_array_start = m_mmap + gpt_header.partition_entry_lba * SECTOR_SIZE;
+	for (std::size_t i = 0; i < gpt_header.number_of_partition_entries; i++)
+	{
+		const auto& partition_entry = *reinterpret_cast<const GPTPartitionEntry*>(partition_entry_array_start + i * gpt_header.size_of_partition_entry);
+		if (partition_entry.type_guid != type_guid)
+			continue;
+		return partition_entry;
+	}
+	return {};
+}
+
+bool GPTFile::validate_gpt_header() const
+{
+    if (SECTOR_SIZE + m_stat.st_size < sizeof(GPTHeader))
+    {
+		std::cerr << m_path << " is too small to have GPT header" << std::endl;
+        return false;
+    }
+
+    auto gpt_header = this->gpt_header();
+
+    if (std::memcmp(gpt_header.signature, "EFI PART", 8) != 0)
+    {
+		std::cerr << m_path << " doesn't contain GPT partition header signature" << std::endl;
+		return false;
+    }
+
+	const uint32_t header_crc32 = gpt_header.header_crc32;
+
+	gpt_header.header_crc32 = 0;
+	if (header_crc32 != crc32_checksum(reinterpret_cast<uint8_t*>(&gpt_header), gpt_header.header_size))
+	{
+		std::cerr << m_path << " has non-matching header crc32" << std::endl;
+		return false;
+	}
+
+	const std::size_t partition_array_size = gpt_header.number_of_partition_entries * gpt_header.size_of_partition_entry;
+	if (gpt_header.partition_entry_array_crc32 != crc32_checksum(m_mmap + gpt_header.partition_entry_lba * SECTOR_SIZE, partition_array_size))
+	{
+		std::cerr << m_path << " has non-matching partition entry crc32" << std::endl;
+		return false;
+	}
+
+    return true;
+}

bootloader/installer/GPT.h

@@ -0,0 +1,88 @@
+#pragma once
+
+#include "GUID.h"
+
+#include <cstdint>
+#include <optional>
+#include <span>
+#include <string_view>
+#include <string>
+#include <sys/stat.h>
+
+struct MBRPartitionRecord
+{
+	uint8_t boot_indicator;
+	uint8_t starting_chs[3];
+	uint8_t os_type;
+	uint8_t ending_chs[3];
+	uint32_t starting_lba;
+	uint32_t size_in_lba;
+} __attribute__((packed));
+
+struct MBR
+{
+	uint8_t boot_code[440];
+	uint32_t unique_mbr_disk_signature;
+	uint16_t unknown;
+	MBRPartitionRecord partition_records[4];
+	uint16_t signature;
+} __attribute__((packed));
+static_assert(sizeof(MBR) == 512);
+
+struct GPTPartitionEntry
+{
+	GUID type_guid;
+	GUID partition_guid;
+	uint64_t starting_lba;
+	uint64_t ending_lba;
+	uint64_t attributes;
+	uint16_t name[36];
+};
+static_assert(sizeof(GPTPartitionEntry) == 128);
+
+struct GPTHeader
+{
+	char signature[8];
+	uint32_t revision;
+	uint32_t header_size;
+	uint32_t header_crc32;
+	uint32_t reserved;
+	uint64_t my_lba;
+	uint64_t alternate_lba;
+	uint64_t first_usable_lba;
+	uint64_t last_usable_lba;
+	GUID disk_guid;
+	uint64_t partition_entry_lba;
+	uint32_t number_of_partition_entries;
+	uint32_t size_of_partition_entry;
+	uint32_t partition_entry_array_crc32;
+} __attribute__((packed));
+static_assert(sizeof(GPTHeader) == 92);
+
+class GPTFile
+{
+public:
+	GPTFile(std::string_view path);
+	~GPTFile();
+
+	bool install_bootcode(std::span<const uint8_t>);
+	bool write_partition(std::span<const uint8_t>, GUID type_guid);
+
+	const GPTHeader& gpt_header() const;
+
+	bool success() const { return m_success; }
+
+	std::string_view path() const { return m_path; }
+
+private:
+	MBR& mbr();
+	bool validate_gpt_header() const;
+	std::optional<GPTPartitionEntry> find_partition(const GUID& type_guid) const;
+
+private:
+	const std::string	m_path;
+	bool				m_success	{ false };
+	int					m_fd		{ -1 };
+	struct stat			m_stat		{ };
+	uint8_t*			m_mmap		{ nullptr };
+};

bootloader/installer/GUID.cpp

@@ -0,0 +1,26 @@
+#include "GUID.h"
+
+#include <iomanip>
+#include <cstring>
+
+bool GUID::operator==(const GUID& other) const
+{
+	return std::memcmp(this, &other, sizeof(GUID)) == 0;
+}
+
+std::ostream& operator<<(std::ostream& out, const GUID& guid)
+{
+	auto flags = out.flags();
+	out << std::hex << std::setfill('0');
+	out << std::setw(8) << guid.component1 << '-';
+	out << std::setw(4) << guid.component2 << '-';
+	out << std::setw(4) << guid.component3 << '-';
+
+	out << std::setw(2);
+	for (int i = 0; i < 2; i++) out << +guid.component45[i];
+	out << '-';
+	for (int i = 2; i < 6; i++) out << +guid.component45[i];
+
+	out.flags(flags);
+	return out;
+}

bootloader/installer/GUID.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <cstdint>
+#include <ostream>
+
+struct GUID
+{
+	uint32_t component1;
+	uint16_t component2;
+	uint16_t component3;
+	// last 2 components are combined so no packed needed
+	uint8_t component45[8];
+
+	bool operator==(const GUID& other) const;
+};
+
+std::ostream& operator<<(std::ostream& out, const GUID& guid);
+
+// unused		00000000-0000-0000-0000-000000000000
+static constexpr GUID unused_guid = {
+	0x00000000,
+	0x0000,
+	0x0000,
+	{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }
+};
+
+// bios boot	21686148-6449-6E6F-744E-656564454649
+static constexpr GUID bios_boot_guid = {
+	0x21686148,
+	0x6449,
+	0x6E6F,
+	{ 0x74, 0x4E, 0x65, 0x65, 0x64, 0x45, 0x46, 0x49 }
+};

bootloader/installer/build.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+g++ -O2 -std=c++20 main.cpp crc32.cpp ELF.cpp GPT.cpp GUID.cpp -o install-bootloader

bootloader/installer/crc32.cpp

@@ -0,0 +1,80 @@
+#include "crc32.h"
+
+static constexpr uint32_t crc32_table[256] =
+{
+	0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA,
+	0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
+	0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
+	0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
+	0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,
+	0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
+	0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC,
+	0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
+	0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
+	0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
+	0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940,
+	0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
+	0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116,
+	0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
+	0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
+	0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
+	0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A,
+	0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
+	0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818,
+	0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
+	0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
+	0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
+	0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C,
+	0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
+	0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
+	0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
+	0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
+	0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
+	0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086,
+	0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
+	0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4,
+	0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
+	0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
+	0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
+	0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,
+	0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
+	0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE,
+	0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
+	0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
+	0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
+	0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252,
+	0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
+	0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60,
+	0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
+	0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
+	0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
+	0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04,
+	0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
+	0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A,
+	0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
+	0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
+	0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
+	0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E,
+	0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
+	0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
+	0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
+	0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
+	0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
+	0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0,
+	0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
+	0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6,
+	0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,
+	0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
+	0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D,
+};
+
+uint32_t crc32_checksum(const uint8_t* data, std::size_t count)
+{
+	uint32_t crc32 = 0xFFFFFFFF;
+	for (size_t i = 0; i < count; i++)
+	{
+		uint8_t index = (crc32 ^ data[i]) & 0xFF;
+		crc32 = (crc32 >> 8) ^ crc32_table[index];
+	}
+	return crc32 ^ 0xFFFFFFFF;
+}

bootloader/installer/crc32.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+
+uint32_t crc32_checksum(const uint8_t* data, std::size_t count);

bootloader/installer/main.cpp

@@ -0,0 +1,41 @@
+#include "ELF.h"
+#include "GPT.h"
+
+#include <iostream>
+
+int main(int argc, char** argv)
+{
+	using namespace std::string_view_literals;
+
+	if (argc != 3)
+	{
+		std::fprintf(stderr, "usage: %s BOOTLOADER DISK_IMAGE}\n", argv[0]);
+		return 1;
+	}
+
+	ELFFile bootloader(argv[1]);
+	if (!bootloader.success())
+		return 1;
+
+	auto stage1 = bootloader.find_section(".stage1"sv);
+	auto stage2 = bootloader.find_section(".stage2"sv);
+	if (!stage1.has_value() || !stage2.has_value())
+	{
+		std::cerr << bootloader.path() << " doesn't contain .stage1 and .stage2 sections" << std::endl;
+		return 1;
+	}
+
+	GPTFile disk_image(argv[2]);
+	if (!disk_image.success())
+		return 1;
+
+	if (!disk_image.install_bootcode(*stage1))
+		return 1;
+	std::cout << "wrote stage1 bootloader" << std::endl;
+
+	if (!disk_image.write_partition(*stage2, bios_boot_guid))
+		return 1;
+	std::cout << "wrote stage2 bootloader" << std::endl;
+
+	return 0;
+}