...

makefile

@@ -1,16 +1,16 @@
-CC = i686-elf-gcc
+CC = x86_64-elf-gcc
-LD = i686-elf-ld
+LD = x86_64-elf-ld
 AS = nasm
 
 # Modify these settings here for defines and debug info
-CFLAGS  = -g -D DEBUG
+CFLAGS  =
-LDFLAGS	= -g
+LDFLAGS	=
-ASFLAGS = -g -F dwarf
+ASFLAGS =
 
 # Do not modify
-CFLAGS += -m32 -ffreestanding -fno-stack-protector -nostdlib -nostdinc -Wall -Wextra -std=c23 -Isrc/shared
+CFLAGS += -m64 -ffreestanding -fno-stack-protector -nostdlib -nostdinc -Wall -Wextra -std=c23 -Isrc/shared
 LDFLAGS	+=
-ASFLAGS	+= -f elf32
+ASFLAGS	+= -f elf64
 
 SRC_C   := $(shell find src -name '*.c')
 SRC_ASM := $(shell find src -name '*.asm')

src/boot/main.c

@@ -1,3 +1,6 @@
+#include "console.h"
+#include "multiboot2.h"
+
 #include <def.h>
 #include "console.h"
 #include "multiboot2.h"
@@ -58,3 +61,7 @@ static void find_memory_regions(uptr multiboot_info) {
         entry_ptr += tag->entry_size;
     }
 }
+
+void kmain(uptr multiboot_info) {
+    find_memory_regions(multiboot_info);
+}

src/boot/start.asm

@@ -1,4 +1,7 @@
 global _start
+extern kernel_start
+extern kernel_end
+extern kmain
 
 %define MAGIC   0xe85250d6
 %define ARCH    0x0
@@ -20,10 +23,42 @@ header:
 
 section .data
 align 8
-multiboot_info: dd 0
+multiboot_info: dq 0
+
+%define PRESENT     1 << 7
+%define NOT_SYS     1 << 4
+%define EXEC        1 << 3
+%define DC          1 << 2
+%define RW          1 << 1
+%define ACCESSED    1 << 0
+
+%define GRAN_4K     1 << 7
+%define SZ_32       1 << 6
+%define LONG_MODE   1 << 5
+
+gdt:
+    .null: equ $ - gdt
+        dq 0
+    .code: equ $ - gdt
+        .code.limit_lo: dw 0xffff
+        .code.base_lo: dw 0
+        .code.base_mid: db 0
+        .code.access: db PRESENT | NOT_SYS | EXEC | RW
+        .code.flags: db GRAN_4K | LONG_MODE | 0xF
+        .code.base_hi: db 0
+    .data: equ $ - gdt
+        .data.limit_lo: dw 0xffff
+        .data.base_lo: dw 0
+        .data.base_mid: db 0
+        .data.access: db PRESENT | NOT_SYS | RW
+        .data.Flags: db GRAN_4K | SZ_32 | 0xF
+        .data.base_hi: db 0
+    .pointer:
+        dw $ - gdt - 1
+        dq gdt
 
 section .bss
-align 4096
+align 16
 stack:
     .bottom:
         resb 1024 * 16
@@ -36,9 +71,8 @@ pdt:    resb 4096
 pt:     resb 4096
 
 section .text
+bits 32
 _start:
-    mov esp, stack.top
-
     %define BOOTLOADER_MAGIC    0x36d76289
 
     ; Make sure we booted with multiboot 2
@@ -75,10 +109,17 @@ _start:
     %define PAGE_SIZE       0x1000
     %define START_ADDRESS   0x0
 
-    ; Identity map first 2mb of memory
+    ; Identity map kernel pages
     mov edi, pt
-    mov ebx, START_ADDRESS | PT_PRESENT | PT_READABLE
+    mov ebx, kernel_start
-    mov ecx, ENTRIES_PER_PT
+    and ebx, 0xfffff000
+    or ebx, PT_PRESENT | PT_READABLE
+
+    mov eax, kernel_end
+    sub eax, kernel_start
+    add eax, PAGE_SIZE-1
+    shr eax, 12
+    mov ecx, eax
 
 .set_pt_entry:
     mov [edi], ebx
@@ -108,6 +149,28 @@ _start:
     mov eax, cr0
     or eax, CR0_PG_ENABLE
     mov cr0, eax
+
+    ; Load gdt
+    lgdt [gdt.pointer]
+    jmp gdt.code:start64
+.halt:
+    cli
+    hlt
+    jmp .halt
+
+section .text
+bits 64
+start64:
+    mov ax, gdt.data
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+
+    mov rsp, stack.top
+    mov rdi, [multiboot_info]
+    call kmain
 .halt:
     cli
     hlt

src/boot/start.c

@@ -1,8 +0,0 @@
-#include <def.h>
-#include "console.h"
-#include "multiboot2.h"
-#include "panic.h"
-
-void c_start() {
-    console_clear();
-}