64 bit mode

README.md

@@ -5,8 +5,8 @@
 - `make`
 - `grub`
 - `mtools`
-- `i386-elf-gcc`
+- `x86_64-elf-gcc`
-- `i386-elf-ld`
+- `x86_64-elf-ld`
 
 ## Building
 

makefile

@@ -1,7 +1,7 @@
-CC = i386-elf-gcc
+CC = x86_64-elf-gcc
-LD = i386-elf-ld
+LD = x86_64-elf-ld
 
-CFLAGS = -ffreestanding -m32
+CFLAGS = -ffreestanding -m64
 
 all: .build/nub-os.iso
 
@@ -27,4 +27,4 @@ build-dir:
 	$(CC) $(CFLAGS) -c -o .build/print.o src/print.c
 
 .build/boot.o: build-dir src/boot.asm
-	nasm -f elf32 -o .build/boot.o src/boot.asm
+	nasm -f elf64 -o .build/boot.o src/boot.asm

src/boot.asm

@@ -4,7 +4,7 @@
 %define CHECKSUM    -(MAGIC + ARCH + LEN)
 
 header_start:
-align 8
+align 4
     dd MAGIC
     dd ARCH
     dd LEN
@@ -14,6 +14,14 @@ align 8
 header_end:
 
 section .bss
+align 4096
+page_table_l4:
+    resb 4096
+page_table_l3:
+    resb 4096
+page_table_l2:
+    resb 4096
+
 align 16
     resb 16384
 stack_top:
@@ -21,11 +29,129 @@ stack_top:
 extern kernel_main
 
 section .text
+bits 32
 global _start
 _start:
     mov esp, stack_top
+
+    call check_cpuid
+    call check_long_mode
+
+    call setup_page_tables
+    call enable_paging
+
+    lgdt [gdt64.pointer]
+
+    jmp gdt64.kernel_code:long_mode_start
+
+check_cpuid:
+    pushfd
+    pop eax
+    mov ecx, eax
+    xor eax, 1 << 21
+    push eax
+    popfd
+    pushfd
+    pop eax
+    push ecx
+    popfd
+    xor eax, ecx
+    jz .no_cpuid
+    ret
+.no_cpuid:
+    mov al, 'I'
+    jmp error
+
+check_long_mode:
+    mov eax, 0x80000000
+    cpuid
+    cmp eax, 0x80000001
+    jb .no_long_mode
+
+    mov eax, 0x80000001
+    cpuid
+    test edx, 1 << 29
+    jz .no_long_mode
+    ret
+.no_long_mode:
+    mov al, 'L'
+    jmp error
+
+setup_page_tables:
+    mov edi, page_table_l4
+    mov ecx, 4096 * 3 / 4
+    xor eax, eax
+    rep stosd
+
+    mov eax, page_table_l3
+    or eax, 0b11
+    mov [page_table_l4], eax
+
+    mov eax, page_table_l2
+    or eax, 0b11
+    mov [page_table_l3], eax
+
+    mov ecx, 0
+.map_p2_table:
+    mov eax, 0x200000
+    mul ecx
+    or eax, 0b10000011
+    mov [page_table_l2 + ecx * 8], eax
+    inc ecx
+    cmp ecx, 512
+    jne .map_p2_table
+    ret
+
+enable_paging:
+    mov eax, page_table_l4
+    mov cr3, eax
+
+    mov eax, cr4
+    or eax, 1 << 5
+    mov cr4, eax
+
+    mov ecx, 0xC0000080
+    rdmsr
+    or eax, 1 << 8
+    wrmsr
+
+    mov eax, cr0
+    or eax, 1 << 31
+    mov cr0, eax
+    ret
+
+bits 64
+long_mode_start:
+    mov ax, gdt64.kernel_data
+    mov ss, ax
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+
+    mov rsp, stack_top
+
     call kernel_main
+
     cli
 hang:
     hlt
     jmp hang
+
+error:
+    mov dword [0xb8000], 0x4f524f45
+    mov dword [0xb8004], 0x4f3a4f52
+    mov dword [0xb8008], 0x4f204f20
+    mov byte  [0xb800a], al
+    hlt
+
+section .rodata
+gdt64:
+    dq 0
+.kernel_code: equ $ - gdt64
+    dq (1<<44) | (1<<47) | (1<<41) | (1<<43) | (1<<53)
+.kernel_data: equ $ - gdt64
+    dq (1<<44) | (1<<47) | (1<<41)
+.pointer:
+    dw $ - gdt64 - 1
+    dq gdt64