Initial commit: kernel source and build scripts

.gitignore

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+*.o
+*.bin
+*.elf
+*.map
+

boot.asm

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+; File: boot.asm
+global _start
+extern kmain
+
+section .multiboot
+    ; Multiboot header
+    dd 0x1BADB002           ; magic number
+    dd 0x00000003           ; flags
+    dd -(0x1BADB002 + 0x00000003) ; checksum
+
+
+section .text
+[bits 32]
+_start:
+    mov esp, kernel_stack_top 
+
+    ; Load the gdt_ptr
+    lgdt [gdt_ptr]
+
+    mov cr3, pml4_table
+
+    mov rax, cr4
+    or rax, 0x20            ; Enable PAE
+    mov cr4, rax
+
+    mov ecx, 0xC0000080   ; IA32_EFER MSR
+    rdmsr
+    or rax, 0x00000100     ; Set LME (Long Mode Enable) bit
+    wrmsr
+
+    ; Enable long mode
+    mov rax, cr0
+    or rax, 0x80000000      ; Set the Long Mode Enable (LME) bit
+    mov cr0, rax
+
+    ; Jump to 64-bit code Segment
+    jmp 0x08:long_mode_start
+
+section .bss
+; We define the stack size and labels in the uninitialized data section (.bss)
+kernel_stack_bottom:
+    ; Reserve 16 KB for the stack
+    resb 16 * 1024
+kernel_stack_top:
+
+gdt_ptr:
+    dw 0                 ; Limit (set by linker/code later)
+    dq 0                 ; Base Address (set by linker/code later)
+gdt_start:               ; Start of the actual GDT entries
+    ; Entry 0: Null Descriptor
+    dq 0x0000000000000000
+    ; Entry 1: 64-bit Code Segment Descriptor
+    ; Entry 2: 64-bit Data Segment Descriptor
+gdt_end:
+
+pml4_table:
+    ; Define a simple PML4 table here (identity mapping for simplicity)
+    ; In a real kernel, you would set up proper paging structures
+    resb 4096            ; Reserve 4 KB for the PML4 table 
+pml4_end:
+
+section .text
+[bits 64] ; Tell NASM to assemble in 64-bit mode
+
+long_mode_start:
+    ; 1. Pass GRUB's Multiboot info (in ebx) as the first C argument (in rdi)
+    ;    We must use the 64-bit register RDI, but the data is in the 32-bit EBX.
+    ;    Moving ebx to rdi automatically clears the upper 32 bits of rdi.
+    mov rdi, rbx 
+
+    ; 2. Call the C kernel's main function
+    call kmain
+
+    ; 3. If kmain ever returns, halt the CPU
+    hlt
+
+

build.sh

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+echo ">>> Compiling bootloader"
+nasm boot.asm -o boot.o -f elf64
+
+echo ">>> Compiling kernel"
+gcc kernel.c -o kernel.o -c -m64 -ffreestanding -nostdlib
+
+echo ">>> Linking kernel"
+ld -T linker.ld -o SoraOS boot.o kernel.o

kernel.c

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+// file: kerlnel.c
+
+void kmain(void) {
+  // Kernel main function
+  // Set VGA memory address
+  unsigned short *VGA_mem = (unsigned short *)0xB8000;
+
+  VGA_mem[0] = (0x07 << 8) | 'S';
+  VGA_mem[1] = (0x07 << 8) | 'O';
+  VGA_mem[2] = (0x07 << 8) | 'R';
+  VGA_mem[3] = (0x07 << 8) | 'A';
+  VGA_mem[4] = (0x07 << 8) | ' ';
+  VGA_mem[5] = (0x07 << 8) | 'O';
+  VGA_mem[6] = (0x07 << 8) | 'S';
+}

linker.ld

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+ENTRY(_start);
+FORMAT(elf64-x86-64);
+
+SECTIONS
+{
+/* Set the location counter to 0x100000 (1MB) */
+. = 0x100000;
+
+/* Define the .text section at the current location */
+.text :
+{
+    /* Put all .text sections from all input files here */
+    *(.text)
+}
+
+/* Define the .data section immediately after .text */ 
+.data :
+{
+    /* Put all .data sections from all input files here */
+    *(.data)
+}
+
+/* Define the .bss section immediately after .data */ 
+.bss :
+{
+    /* Put all .bss sections from all input files here */
+    *(.bss)
+}
+
+/* End of the linker script */
+}