https://wiki.osdev.org/Bare_Bones + my Makefile and .gitignore

8 files changed, 389 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..8f8bb8c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+build
+isodir
+myos.iso
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..f3f5b47
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,26 @@
+BUILD_DIR=build
+ISO_DIR=isodir
+
+.PHONY: all
+all: $(BUILD_DIR)/myos.bin
+	grub-file --is-x86-multiboot $(BUILD_DIR)/myos.bin
+	mkdir -p $(ISO_DIR)/boot/grub
+	cp $(BUILD_DIR)/myos.bin $(ISO_DIR)/boot/myos.bin
+	cp grub.cfg $(ISO_DIR)/boot/grub/grub.cfg
+	grub-mkrescue -o myos.iso $(ISO_DIR)
+
+$(BUILD_DIR)/boot.o: boot.s
+	mkdir -p $(BUILD_DIR)
+	i686-elf-as boot.s -o $(BUILD_DIR)/boot.o
+
+$(BUILD_DIR)/kernel.o: kernel.c
+	mkdir -p $(BUILD_DIR)
+	i686-elf-gcc -c kernel.c -o $(BUILD_DIR)/kernel.o -std=gnu99 -ffreestanding -O2 -Wall -Wextra
+
+$(BUILD_DIR)/myos.bin: $(BUILD_DIR)/kernel.o $(BUILD_DIR)/boot.o
+	mkdir -p $(BUILD_DIR)
+	i686-elf-gcc -T linker.ld -o $(BUILD_DIR)/myos.bin -ffreestanding -O2 -nostdlib $(BUILD_DIR)/boot.o $(BUILD_DIR)/kernel.o -lgcc
+
+.PHONY: clean
+clean:
+	rm -rf $(BUILD_DIR) $(ISO_DIR) myos.iso
diff --git a/boot.asm b/boot.asm
new file mode 100644
index 0000000..94b4c57
--- /dev/null
+++ b/boot.asm
@@ -0,0 +1,90 @@
+; Declare constants for the multiboot header.
+MBALIGN  equ  1 << 0            ; align loaded modules on page boundaries
+MEMINFO  equ  1 << 1            ; provide memory map
+FLAGS    equ  MBALIGN | MEMINFO ; this is the Multiboot 'flag' field
+MAGIC    equ  0x1BADB002        ; 'magic number' lets bootloader find the header
+CHECKSUM equ -(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
+	dd MAGIC
+	dd FLAGS
+	dd 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:
+resb 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.
+; Declare _start as a function symbol with the given symbol size.
+section .text
+global _start:function (_start.end - _start)
+_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 our
+	; 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 esp, stack_top
+ 
+	; 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 isnot 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 since pushed a multiple of 16 bytes to the
+	; stack since (pushed 0 bytes so far) and the alignment is thus
+	; preserved and the call is well defined.
+        ; note, that if you are building on Windows, C functions may have "_" prefix in assembly: _kernel_main
+	extern kernel_main
+	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
+.hang:	hlt
+	jmp .hang
+.end: 
diff --git a/boot.s b/boot.s
new file mode 100644
index 0000000..172fd14
--- /dev/null
+++ b/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 instuctions 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
diff --git a/grub.cfg b/grub.cfg
new file mode 100644
index 0000000..b2f8404
--- /dev/null
+++ b/grub.cfg
@@ -0,0 +1,3 @@
+menuentry "myos" {
+	multiboot /boot/myos.bin
+}
diff --git a/kernel.c b/kernel.c
new file mode 100644
index 0000000..0516f16
--- /dev/null
+++ b/kernel.c
@@ -0,0 +1,114 @@
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+ 
+/* Check if the compiler thinks you are targeting the wrong operating system. */
+#if defined(__linux__)
+#error "You are not using a cross-compiler, you will most certainly run into trouble"
+#endif
+ 
+/* This tutorial will only work for the 32-bit ix86 targets. */
+#if !defined(__i386__)
+#error "This tutorial needs to be compiled with a ix86-elf compiler"
+#endif
+ 
+/* Hardware text mode color constants. */
+enum vga_color {
+	VGA_COLOR_BLACK = 0,
+	VGA_COLOR_BLUE = 1,
+	VGA_COLOR_GREEN = 2,
+	VGA_COLOR_CYAN = 3,
+	VGA_COLOR_RED = 4,
+	VGA_COLOR_MAGENTA = 5,
+	VGA_COLOR_BROWN = 6,
+	VGA_COLOR_LIGHT_GREY = 7,
+	VGA_COLOR_DARK_GREY = 8,
+	VGA_COLOR_LIGHT_BLUE = 9,
+	VGA_COLOR_LIGHT_GREEN = 10,
+	VGA_COLOR_LIGHT_CYAN = 11,
+	VGA_COLOR_LIGHT_RED = 12,
+	VGA_COLOR_LIGHT_MAGENTA = 13,
+	VGA_COLOR_LIGHT_BROWN = 14,
+	VGA_COLOR_WHITE = 15,
+};
+ 
+static inline uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg) 
+{
+	return fg | bg << 4;
+}
+ 
+static inline uint16_t vga_entry(unsigned char uc, uint8_t color) 
+{
+	return (uint16_t) uc | (uint16_t) color << 8;
+}
+ 
+size_t strlen(const char* str) 
+{
+	size_t len = 0;
+	while (str[len])
+		len++;
+	return len;
+}
+ 
+static const size_t VGA_WIDTH = 80;
+static const size_t VGA_HEIGHT = 25;
+ 
+size_t terminal_row;
+size_t terminal_column;
+uint8_t terminal_color;
+uint16_t* terminal_buffer;
+ 
+void terminal_initialize(void) 
+{
+	terminal_row = 0;
+	terminal_column = 0;
+	terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
+	terminal_buffer = (uint16_t*) 0xB8000;
+	for (size_t y = 0; y < VGA_HEIGHT; y++) {
+		for (size_t x = 0; x < VGA_WIDTH; x++) {
+			const size_t index = y * VGA_WIDTH + x;
+			terminal_buffer[index] = vga_entry(' ', terminal_color);
+		}
+	}
+}
+ 
+void terminal_setcoor(uint8_t color) 
+{
+	terminal_color = color;
+}
+ 
+void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) 
+{
+	const size_t index = y * VGA_WIDTH + x;
+	terminal_buffer[index] = vga_entry(c, color);
+}
+ 
+void terminal_putchar(char c) 
+{
+	terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
+	if (++terminal_column == VGA_WIDTH) {
+		terminal_column = 0;
+		if (++terminal_row == VGA_HEIGHT)
+			terminal_row = 0;
+	}
+}
+ 
+void terminal_write(const char* data, size_t size) 
+{
+	for (size_t i = 0; i < size; i++)
+		terminal_putchar(data[i]);
+}
+ 
+void terminal_writestring(const char* data) 
+{
+	terminal_write(data, strlen(data));
+}
+ 
+void kernel_main(void) 
+{
+	/* Initialize terminal interface */
+	terminal_initialize();
+ 
+	/* Newline support is left as an exercise. */
+	terminal_writestring("Hello, kernel World!\n");
+}
diff --git a/linker.ld b/linker.ld
new file mode 100644
index 0000000..38ddd94
--- /dev/null
+++ b/linker.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. */
+}
diff --git a/qemu.sh b/qemu.sh
new file mode 100755
index 0000000..8080024
--- /dev/null
+++ b/qemu.sh
@@ -0,0 +1 @@
+qemu-system-x86_64 -cdrom myos.iso