...

README.md

@@ -2,16 +2,29 @@
 
 ## Dependencies
 
+### Building the kernel
+
 - `make`
-- `grub`
 - `mtools`
 - `x86_64-elf-gcc`
 - `x86_64-elf-ld`
 
+### Creating a disk image
+
+- `grub`
+
 ## Building
 
+### Kernel
+
 ```sh
-make
+make kernel
+```
+
+### Disk image
+
+```sh
+make iso
 ```
 
 ## Running
@@ -19,5 +32,5 @@ make
 After building, run the following:
 
 ```sh
-qemu-system-x86_64 -cdrom .build/nub-os.iso
+qemu-system-i386 -kernel .build/kernel
 ```

grub.cfg

@@ -1,7 +1,6 @@
 menuentry "nub-os" {
-    multiboot2 /boot/kernel
-    boot
+    multiboot /boot/kernel
 }
 
-set default="nub-os"
+set default=0
 set timeout=0

linker.ld

@@ -6,7 +6,7 @@ SECTIONS
 
 	.text BLOCK(4K) : ALIGN(4K)
 	{
-		*(.multiboot2)
+		*(.multiboot)
 		*(.text)
 	}
 

makefile

@@ -1,16 +1,21 @@
-CC = x86_64-elf-gcc
-LD = x86_64-elf-ld
+CC = i386-elf-gcc
+AS = i386-elf-as
+LD = i386-elf-ld
 
-CFLAGS 	= -m64 -ffreestanding -fno-builtin -Wall -Wextra -Wshadow -std=c23
+CFLAGS 	= -m32 -ffreestanding -fno-builtin -Wall -Wextra -Wshadow -std=c23
 LDFLAGS = 
+ASFLAGS = 
 
-SRC_C   := src/kernel.c src/vga.c src/idt.c src/string.c src/keyboard.c
-SRC_ASM := src/boot.asm src/idt_stub.asm
+SRC_C   := src/kernel.c src/string.c src/vga.c
+SRC_ASM := src/boot.s
 
 OBJ_C   := $(SRC_C:src/%.c=.build/%.o)
-OBJ_ASM := $(SRC_ASM:src/%.asm=.build/%.o)
+OBJ_ASM := $(SRC_ASM:src/%.s=.build/%.o)
 OBJS    := $(OBJ_C) $(OBJ_ASM)
 
+kernel: .build/kernel
+	@echo "Kernel created at '.build/kernel'"
+
 iso: .build/nub-os.iso
 	@echo "ISO created at '.build/nub-os.iso'"
 
@@ -20,17 +25,17 @@ clean:
 build-dir:
 	mkdir .build 2>/dev/null || true
 
-.build/nub-os.iso: .build/kernel
+.build/nub-os.iso: .build/kernel grub.cfg
 	mkdir -p .build/nub-os/boot/grub
 	cp grub.cfg .build/nub-os/boot/grub
 	cp .build/kernel .build/nub-os/boot/
 	grub-mkrescue -o .build/nub-os.iso .build/nub-os/
 
-.build/kernel: $(OBJS)
-	$(LD) $(LDFLAGS) -T src/boot.ld -o $@ $^
+.build/kernel: $(OBJS) | linker.ld
+	$(LD) $(LDFLAGS) -m elf_i386 -T linker.ld -o $@ $^
 
 .build/%.o: src/%.c | build-dir
 	$(CC) $(CFLAGS) -c -o $@ $<
 
-.build/%.o: src/%.asm | build-dir
-	nasm -f elf64 -o $@ $<
+.build/%.o: src/%.s | build-dir
+	$(AS) $(ASFLAGS) -o $@ $<

src/boot.asm

@@ -1,204 +0,0 @@
-%define MAGIC       0xe85250d6
-%define ARCH        0
-%define LEN         header_end - header_start
-%define CHECKSUM    -(MAGIC + ARCH + LEN)
-
-section .multiboot2
-header_start:
-align 4
-    dd MAGIC
-    dd ARCH
-    dd LEN
-    dd CHECKSUM
-    dw 0
-    dd 8
-header_end:
-
-section .bss
-align 16
-    resb 16384
-stack_top:
-
-align 4096
-pml4_table:
-    resb 4096
-pdp_table:
-    resb 4096
-pd_table:
-    resb 4096
-
-section .text
-bits 32
-global _start
-_start:
-    cli
-    mov esp, stack_top
-
-    ; Check if CPU supports 64-bit mode
-    call check_multiboot
-    call check_cpuid
-    call check_long_mode
-
-    ; Set up paging for 64-bit mode
-    call set_up_page_tables
-    call enable_paging
-
-    ; Load GDT and jump to 64-bit mode
-    lgdt [gdt64.pointer]
-    jmp gdt64.code:long_mode_start
-
-check_multiboot:
-    cmp eax, 0x36d76289
-    jne .no_multiboot
-    ret
-
-.no_multiboot:
-    mov al, 'M'
-    jmp error
-
-check_cpuid:
-    ; Copy flags to eax through the stack
-    pushfd
-    pop eax
-
-    ; Copy flags to ecx for a later comparison
-    mov ecx, eax
-
-    ; Flit the cpuid bit
-    xor eax, 1 << 21
-
-    ; Copy eax (with the flipped cpuid bit) back to flags
-    push eax
-    popfd
-
-    ; Copy flags back to eax. The cpiuid bit will be flipped if cpuid is supported
-    pushfd
-    pop eax
-
-    ; Restore flags from the original flags stored in ecx
-    push ecx
-    popfd
-
-    ; Compare eax and ecx. If thry are equal, cpuid is not supported
-    cmp eax, ecx
-    je .no_cpuid
-    ret
-
-.no_cpuid:
-    mov al, 'I'
-    jmp error
-
-check_long_mode:
-    ; Test if extended processor info is available
-    mov eax, 0x80000000
-    cpuid
-    cmp eax, 0x80000001
-    jb .no_long_mode
-
-    ; Test if long mode is available
-    mov eax, 0x80000001
-    cpuid
-    test edx, 1 << 29
-    jz .no_long_mode
-    ret
-
-.no_long_mode:
-    mov al, 'L'
-    jmp error
-
-; todo(nub): This is copy pasted. I will research hat it does later
-set_up_page_tables:
-    ; Map first PML4 entry to PDP table
-    mov eax, pdp_table
-    or eax, 0b11 ; present + writable
-    mov [pml4_table], eax
-
-    ; Map first PDP entry to PD table
-    mov eax, pd_table
-    or eax, 0b11 ; present + writable
-    mov [pdp_table], eax
-
-    ; Map each PD entry to a huge 2MiB page
-    mov ecx, 0         ; counter variable
-.map_pd_table:
-    ; Map ecx-th PD entry to a huge page that starts at address (2MiB * ecx)
-    mov eax, 0x200000  ; 2MiB
-    mul ecx            ; Start address of ecx-th page
-    or eax, 0b10000011 ; present + writable + huge
-    mov [pd_table + ecx * 8], eax ; Map ecx-th entry
-
-    inc ecx            ; Increase counter
-    cmp ecx, 512       ; If counter == 512, the whole PD table is mapped
-    jne .map_pd_table  ; Else map the next entry
-
-    ret
-
-; todo(nub): This is copy pasted. I will research hat it does later
-enable_paging:
-    ; Load PML4 to cr3 register (cpu uses this to access the PML4 table)
-    mov eax, pml4_table
-    mov cr3, eax
-
-    ; Enable PAE-flag in cr4 (Physical Address Extension)
-    mov eax, cr4
-    or eax, 1 << 5
-    mov cr4, eax
-
-    ; Set the long mode bit in the EFER MSR (model specific register)
-    mov ecx, 0xC0000080
-    rdmsr
-    or eax, 1 << 8
-    wrmsr
-
-    ; Enable paging in the cr0 register
-    mov eax, cr0
-    or eax, 1 << 31
-    mov cr0, eax
-
-    ret
-
-error:
-    mov byte [0xb8000], '['
-    mov byte [0xb8002], ' '
-    mov byte [0xb8004], 'E'
-    mov byte [0xb8005],  4
-    mov byte [0xb8006], 'R'
-    mov byte [0xb8007],  4
-    mov byte [0xb8008], 'R'
-    mov byte [0xb8009],  4
-    mov byte [0xb800a], ' '
-    mov byte [0xb800c], ']'
-    mov byte [0xb800e], ':'
-    mov byte [0xb8010], ' '
-    mov byte [0xb8012], al
-    cli
-.hang:
-    hlt
-    jmp .hang
-
-section .rodata
-gdt64:
-    dq 0
-.code: equ $ - gdt64
-    dq (1<<43) | (1<<44) | (1<<47) | (1<<53)
-.pointer:
-    dw $ - gdt64 - 1
-    dq gdt64
-
-section .text
-bits 64
-long_mode_start:
-    mov ax, 0
-    mov ss, ax
-    mov ds, ax
-    mov es, ax
-    mov fs, ax
-    mov gs, ax
-
-    extern kernel_main
-    call kernel_main
-
-    cli
-.hang:
-    hlt
-    jmp .hang

src/boot.s

@@ -0,0 +1,37 @@
+.intel_syntax noprefix
+
+.set ALIGN,    1<<0
+.set MEMINFO,  1<<1
+.set FLAGS,    ALIGN | MEMINFO
+.set MAGIC,    0x1BADB002
+.set CHECKSUM, -(MAGIC + FLAGS)
+
+.section .multiboot
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
+
+.section .bss
+.align 16
+stack_bottom:
+.skip 16384
+stack_top:
+
+.set BOOTLOADER_MAGIC, 0x2BADB002
+
+.section .text
+.global _start
+_start:
+	mov stack_top, esp
+
+	cmp eax, BOOTLOADER_MAGIC
+	jne hang
+
+	push ebx
+	call kernel_main
+	add esp, 4
+hang:
+	cli
+	hlt
+	jmp hang

src/kernel.c

@@ -1,35 +1,17 @@
 #include "kernel.h"
-#include "idt.h"
-#include "keyboard.h"
+#include "multiboot.h"
 #include "vga.h"
 #include <stdbool.h>
+#include <stdint.h>
 
-void keyboard_handler(const keyboard_event_t* event)
-{
-    if (event->pressed && event->ascii)
-    {
-        vga_print_char(event->ascii);
-    }
-}
-
-void kernel_main(void)
+void kernel_main(multiboot_info_t* multiboot_info)
 {
     vga_clear();
     vga_print_success();
     vga_print(" VGA intialzied\n");
 
-    init_idt();
-    vga_print_success();
-    vga_print(" IDT intialzied\n");
-
-    init_keyboard();
-    vga_print_success();
-    vga_print(" Keyboard driver intialzied\n");
-
     vga_print("\nWelcome to nub OS\n");
 
-    register_keypress_handler(keyboard_handler);
-
     while (true)
     {
     }

src/multiboot.h

@@ -0,0 +1,58 @@
+#pragma once
+#include <stdint.h>
+
+typedef struct multiboot_info
+{
+    uint32_t flags; // required
+
+    // Available if flags[0] is set
+    uint32_t mem_lower;
+    uint32_t mem_upper;
+
+    // Available if flags[1] is set
+    uint32_t boot_device;
+
+    // Available if flags[2] is set
+    uint32_t cmdline;
+
+    // Available if flags[3] is set
+    uint32_t mods_count;
+    uint32_t mods_addr;
+
+    // Available if flags[4] or flags[5] is set
+    uint8_t syms[16]; // 28 - 40 bytes, exact layout may differ depending on a.out or ELF
+
+    // Available if flags[6] is set
+    uint32_t mmap_length;
+    uint32_t mmap_addr;
+
+    // Available if flags[7] is set
+    uint32_t drives_length;
+    uint32_t drives_addr;
+
+    // Available if flags[8] is set
+    uint32_t config_table;
+
+    // Available if flags[9] is set
+    uint32_t boot_loader_name;
+
+    // Available if flags[10] is set
+    uint32_t apm_table;
+
+    // Available if flags[11] is set
+    uint32_t vbe_control_info;
+    uint32_t vbe_mode_info;
+    uint16_t vbe_mode;
+    uint16_t vbe_interface_seg;
+    uint16_t vbe_interface_off;
+    uint16_t vbe_interface_len;
+
+    // Available if flags[12] is set
+    uint64_t framebuffer_addr; // 64-bit for large memory addresses
+    uint32_t framebuffer_pitch;
+    uint32_t framebuffer_width;
+    uint32_t framebuffer_height;
+    uint8_t framebuffer_bpp;
+    uint8_t framebuffer_type;
+    uint8_t color_info[6]; // 110-115 bytes
+} __attribute__((packed)) multiboot_info_t;

src/string.c

@@ -26,7 +26,7 @@ void reverse(char* str, size_t length)
     }
 }
 
-int uitoa(uint64_t value, char* buffer)
+int uitoa(uint32_t value, char* buffer)
 {
     int i = 0;
     if (value == 0)
@@ -47,7 +47,7 @@ int uitoa(uint64_t value, char* buffer)
     return i;
 }
 
-int itoa(int64_t value, char* buffer)
+int itoa(int32_t value, char* buffer)
 {
     int i = 0;
 
@@ -59,16 +59,16 @@ int itoa(int64_t value, char* buffer)
     }
 
     bool negative = false;
-    uint64_t v;
+    uint32_t v;
 
     if (value < 0)
     {
         negative = true;
-        v = (uint64_t)(-value);
+        v = (uint32_t)(-value);
     }
     else
     {
-        v = (uint64_t)value;
+        v = (uint32_t)value;
     }
 
     while (v > 0)

src/string.h

@@ -5,5 +5,5 @@
 
 int strcmp(const char* a, const char* b);
 void reverse(char* str, size_t length);
-int uitoa(uint64_t value, char* buffer);
-int itoa(int64_t value, char* buffer);
+int uitoa(uint32_t value, char* buffer);
+int itoa(int32_t value, char* buffer);

src/vga.c

@@ -138,14 +138,14 @@ void vga_print_error(void)
     vga_print(" ]");
 }
 
-void vga_print_uint(uint64_t value)
+void vga_print_uint(uint32_t value)
 {
     char buffer[11];
     uitoa(value, buffer);
     vga_print(buffer);
 }
 
-void vga_print_int(int64_t value)
+void vga_print_int(int32_t value)
 {
     char buffer[12];
     itoa(value, buffer);

src/vga.h

@@ -30,8 +30,8 @@ void vga_print_colored(const char* string, vga_color_t color);
 void vga_print_success(void);
 void vga_print_error(void);
 
-void vga_print_uint(uint64_t value);
-void vga_print_int(int64_t value);
+void vga_print_uint(uint32_t value);
+void vga_print_int(int32_t value);
 
 static inline vga_color_t vga_color(vga_color_t fg_color, vga_color_t bg_color)
 {