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
 

grub.cfg

@@ -1,4 +1,3 @@
 menuentry "nub-os" {
-    multiboot /boot/kernel.bin
+    multiboot2 /boot/kernel.bin
-    boot
 }

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
 
@@ -17,17 +17,14 @@ build-dir:
 	cp .build/kernel.bin .build/iso/boot/
 	grub-mkrescue -o .build/nub-os.iso .build/iso/
 
-.build/kernel.bin: build-dir .build/entry.o .build/kernel.o .build/mem.o .build/print.o
+.build/kernel.bin: build-dir .build/boot.o .build/kernel.o .build/print.o
-	$(LD) -Ttext 0x100000 -o .build/kernel.bin .build/entry.o .build/kernel.o .build/mem.o .build/print.o
+	$(LD) -Ttext 0x100000 -o .build/kernel.bin .build/boot.o .build/kernel.o .build/print.o
 
 .build/kernel.o: build-dir src/kernel.c
 	$(CC) $(CFLAGS) -c -o .build/kernel.o src/kernel.c
 
-.build/mem.o: build-dir src/mem.c
-	$(CC) $(CFLAGS) -c -o .build/mem.o src/mem.c
-
 .build/print.o: build-dir src/print.c
 	$(CC) $(CFLAGS) -c -o .build/print.o src/print.c
 
-.build/entry.o: build-dir src/entry.asm
+.build/boot.o: build-dir src/boot.asm
-	nasm -f elf -o .build/entry.o src/entry.asm
+	nasm -f elf64 -o .build/boot.o src/boot.asm

src/boot.asm

@@ -0,0 +1,157 @@
+%define MAGIC       0xe85250d6
+%define ARCH        0
+%define LEN         (header_end - header_start)
+%define CHECKSUM    -(MAGIC + ARCH + LEN)
+
+header_start:
+align 4
+    dd MAGIC
+    dd ARCH
+    dd LEN
+    dd CHECKSUM
+    dw 0
+    dd 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:
+
+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

src/entry.asm

@@ -1,21 +0,0 @@
-extern kernel_init
-
-section .multiboot
-align 4
-    dd 0x1BADB002          ; multiboot magic number
-    dd 0x0                 ; flags
-    dd -(0x1BADB002+0x0)   ; checksum
-
-section .text
-global _start
-_start:
-    cli
-    mov esp, stack_top
-    call kernel_init
-.hang:
-    hlt
-    jmp .hang
-
-section .bss
-resb 8192
-stack_top:

src/kernel.c

@@ -1,6 +1,6 @@
 #include "print.h"
 
-void kernel_init(void)
+void kernel_main(void)
 {
     print("Starting nub-os\n");
 }

src/mem.c

@@ -1,26 +0,0 @@
-#include "mem.h"
-
-void* memcpy(void* dest, const void* src, long n)
-{
-    char* d = dest;
-    const char* s = src;
-    for (long i = 0; i < n; i++)
-        d[i] = s[i];
-    return dest;
-}
-
-void* memset(void* dest, int val, long n)
-{
-    char* d = dest;
-    for (long i = 0; i < n; i++)
-        d[i] = val;
-    return dest;
-}
-
-long strlen(const char* str)
-{
-    long len = 0;
-    while (str[len])
-        len++;
-    return len;
-}

src/mem.h

@@ -1,3 +0,0 @@
-void* memcpy(void* dest, const void* src, long n);
-void* memset(void* dest, int val, long n);
-long strlen(const char* str);