...

README.md

@@ -4,24 +4,15 @@
 
 ### Building the kernel
 
-- `make`
-- `i386-elf-gcc`
-- `i386-elf-ld`
-- `nasm`
-
-### Creating a disk image
-
 - `grub`
 - `mtools`
+- `make`
+- `x86_64-elf-gcc`
+- `x86_64-elf-ld`
+- `nasm`
 
 ## Building
 
-### Kernel
-
-```sh
-make kernel
-```
-
 ### Disk image
 
 ```sh
@@ -30,8 +21,15 @@ make iso
 
 ## Running
 
-After building, run the following:
+After building the iso, run the following:
 
 ```sh
-qemu-system-i386 -kernel .build/kernel
+qemu-system-x86_64 -cdrom .build/nub-os.iso
+```
+
+## Debugging
+
+```sh
+qemu-system-x86_64 -s -S -cdrom .build/nub-os.iso
+gdb -tui .build/kernel -ex "target remote localhost:1234"
 ```

grub.cfg

@@ -2,5 +2,5 @@ menuentry "nub-os" {
     multiboot /boot/kernel
 }
 
-set default=0
+set default="nub-os"
 set timeout=0

makefile

@@ -1,8 +1,10 @@
-CC = i386-elf-gcc
-LD = i386-elf-ld
+CC = x86_64-elf-gcc
+LD = x86_64-elf-ld
+AS = nasm
 
-CFLAGS 	= -m32 -ffreestanding -fno-builtin -Wall -Wextra -Wshadow -std=c23
-LDFLAGS = 
+CFLAGS 	= -m64 -ffreestanding -fno-builtin -Wall -Wextra -Wshadow -std=c23 -g
+LDFLAGS	= -g
+ASFLAGS	= -f elf64 -g -F dwarf
 
 SRC_C   := src/kernel.c src/string.c src/vga.c
 SRC_ASM := src/boot.asm
@@ -11,9 +13,6 @@ OBJ_C   := $(SRC_C:src/%.c=.build/%.o)
 OBJ_ASM := $(SRC_ASM:src/%.asm=.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'"
 
@@ -30,10 +29,10 @@ build-dir:
 	grub-mkrescue -o .build/nub-os.iso .build/nub-os/
 
 .build/kernel: $(OBJS) | linker.ld
-	$(LD) $(LDFLAGS) -m elf_i386 -T linker.ld -o $@ $^
+	$(LD) $(LDFLAGS) -T linker.ld -o $@ $^
 
 .build/%.o: src/%.c | build-dir
 	$(CC) $(CFLAGS) -c -o $@ $<
 
 .build/%.o: src/%.asm | build-dir
-	nasm -f elf32 -o $@ $<
+	$(AS) $(ASFLAGS) -o $@ $<

src/boot.asm

@@ -1,5 +1,4 @@
 global _start
-extern kernel_main
 
 %define FLAGS       0b10
 %define MAGIC       0x1BADB002
@@ -11,21 +10,20 @@ section .multiboot
     dd FLAGS
     dd CHECKSUM
 
-section .bss
-    align 4096
-    pml4_table:
-        resb 4096
-    pdpt_table:
-        resb 4096
-    pd_table:
-        resb 4096
-
 section .bss
     align 16
-    stack_bottom:
         resb 16384
     stack_top:
 
+section .bss
+    align 4096
+    pml4:
+        resb 4096
+    pdpt:
+        resb 4096
+    pd:
+        resb 4096
+
 section .data
     align 8
     gdt64:
@@ -48,7 +46,7 @@ section .text
         cmp eax, 0x2BADB002
         jne error
 
-        ; Check if cpuid is available by flipping the 22-nth youngest bit
+        ; Check if cpuid is available by flipping bit 21
         ; in the eflags register and checking if the cpu flipped it back
         pushfd
         pop eax
@@ -74,33 +72,51 @@ section .text
 
         ; Check if long mode is available by calling cpuid with 0x80000001
         ; this will place the extended features of the cpu in edx
-        ; The 30-nth youngest bit tells us if long mode is supported or not
+        ; Bit 29 tells us if long mode is supported or not
         mov eax, 0x80000001
         cpuid
         test edx, 1 << 29
         jz error
 
-        ; todo(nub31): setup paging
-        ; todo(nub31): enter long mode
+        ; Enable PAE by setting bit 5 in cr4 to 1
+        mov eax, cr4
+        or eax, 1 << 5
+        mov cr4, eax
+
+        ; todo(nub31): Set up page tables
+
+        ; Load cr3 with the address of pml4
+        mov eax, pml4
+        mov cr3, eax
 
-        ; Load global descriptor table which is set up for 64 bit
         lgdt [gdt64.descriptor]
 
-        call kernel_main
-        jmp error
+        ; Enable long mode by setting bit 8 to 1 in EFER (Extended Feature Enable Register)
+        mov ecx, 0xc0000080
+        rdmsr
+        or eax, 1 << 8
+        wrmsr
+
+        ; Enable paging bt setting bit 31 in cr0 to 1
+        mov eax, cr0
+        or eax, 1 << 31
+        mov cr0, eax
+
+        jmp 0x8:long_mode
 
     error:
         cli
-        mov byte [0xb8000], 'B'
-        mov byte [0xb8002], 'O'
-        mov byte [0xb8004], 'O'
-        mov byte [0xb8006], 'T'
-        mov byte [0xb8008], ' '
-        mov byte [0xb800a], 'E'
-        mov byte [0xb800c], 'R'
-        mov byte [0xb800e], 'R'
-        mov byte [0xb8010], 'O'
-        mov byte [0xb8012], 'R'
-    hang:
+        mov byte [0xb8000], 'E'
+        mov byte [0xb8002], 'R'
+        mov byte [0xb8004], 'R'
+    .hang:
         hlt
-        jmp hang
+        jmp .hang
+
+section .text
+    bits 64
+    long_mode:
+        cli
+    .hang:
+        hlt
+        jmp .hang