Merge branch 'master' of dennis:/var/repos/uff-os

2 files changed, 159 insertions, 2 deletions

diff --git a/kernel/src/boot.asm b/kernel/src/boot.asm
index a10b14c..e3484c1 100644
--- a/kernel/src/boot.asm
+++ b/kernel/src/boot.asm
@@ -1,14 +1,147 @@
 global start
+extern long_mode_start
 
 section .text
 bits 32
 start:
 	mov esp, stack_top
 
-	; print 'OK'
-	mov dword [0xb8000], 0x2f4b2f4f
+	call check_multiboot
+	call check_cpuid
+	call check_long_mode
+
+	call setup_page_tables
+	call enable_paging
+	; load the 64-bit GDT
+    lgdt [gdt64.pointer]
+	jmp gdt64.code:long_mode_start
+
 	hlt
 
+check_multiboot:
+	cmp eax, 0x36d76289
+	jne .no_multiboot
+	ret
+.no_multiboot
+	mov al, "0"
+	jmp error
+
+check_cpuid:
+	; Check if CPUID is supported by attempting to flip the ID bit (bit 21)
+    ; in the FLAGS register. If we can flip it, CPUID is available.
+
+    ; Copy EFLAGS in to EAX via stack
+	pushfd
+	pop eax
+
+	; Save the current flags
+	mov ecx, eax
+
+	; Flip the ID bit
+	xor eax, 1 << 21
+
+	; push eax to eflags
+	push eax
+	popfd
+
+	; Copy EAX to FLAGS via the Stack
+	pushfd
+	pop eax
+
+	; Restore FLAGS from the old version stored in ECX (i.e. flipping the
+    ; ID bit back if it was ever flipped).
+    push ecx
+    popfd
+
+	; Check if the ID was changed
+	cmp eax, ecx
+	je .no_cpuid
+	ret
+.no_cpuid:
+	mov al, "1"
+	jmp error
+
+check_long_mode:
+    ; test if extended processor info in available
+    mov eax, 0x80000000    ; implicit argument for cpuid
+    cpuid                  ; get highest supported argument
+    cmp eax, 0x80000001    ; it needs to be at least 0x80000001
+    jb .no_long_mode       ; if it's less, the CPU is too old for long mode
+	
+	; extended info about long mode
+    mov eax, 0x80000001    ; argument for the cpuid function
+    cpuid                  ; Cpu id
+	test edx, 1 << 29  	   ; check long mode availablity
+	jz .no_long_mode
+	ret
+
+.no_long_mode
+	mov al, "2"
+	jmp error
+
+setup_page_tables:
+	; map first P4 entry to P3 table
+    mov eax, p3_table
+    or eax, 0b11 ; present + writable
+    mov [p4_table], eax
+
+    ; map first P3 entry to P2 table
+    mov eax, p2_table
+    or eax, 0b11 ; present + writable
+    mov [p3_table], eax
+	
+	; map each P2 entry to a huge 2MiB page
+    mov ecx, 0         ; counter variable
+    mov eax, 0b10000011 ; present + writable + huge
+
+.map_p2_table:
+    ; map ecx-th P2 entry to a huge page that starts at address 2MiB*ecx
+    mov [p2_table + ecx     ], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+    mov [p2_table + ecx + 8 ], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+    mov [p2_table + ecx + 16], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+    mov [p2_table + ecx + 24], eax ; map ecx-th entry
+    add eax, 0x200000  ; 2MiB
+
+	add ecx, 32
+    cmp ecx, 4096      ; if counter == 512, the whole P2 table is mapped
+    jne .map_p2_table  ; else map the next entry
+
+	ret
+
+enable_paging:
+	mov eax, p4_table
+	mov cr3, eax
+
+    ; enable PAE-flag in cr4 (Physical Address Extension)
+    mov eax, cr4
+    or eax, 1 << 5
+    mov cr4, eax
+
+    ; set the long mode bit in the EFER MSR (model specific register)
+    mov ecx, 0xC0000080
+    rdmsr
+    or eax, 1 << 8
+    wrmsr
+
+    ; enable paging in the cr0 register
+    mov eax, cr0
+    or eax, 1 << 31
+    mov cr0, eax
+
+    ret
+
+section .rodata
+gdt64:
+    dq 0 ; zero entry
+.code: equ $ - gdt64
+    dq (1<<43) | (1<<44) | (1<<47) | (1<<53) ; code segment
+.pointer:
+    dw $ - gdt64 - 1
+    dq gdt64
+
 ; Prints 'ERR: ' and the given error code to the screen and halts
 ; parameter: error code letter (ascii) in al
 error:
@@ -19,6 +152,13 @@ error:
 	hlt
 
 section .bss
+align 4096
+p4_table:
+	resb 4096
+p3_table:
+	resb 4096
+p2_table:
+	resb 4096
 stack_bottom:
 	resb 64
 stack_top:
diff --git a/kernel/src/long_mode_init.asm b/kernel/src/long_mode_init.asm
new file mode 100644
index 0000000..f105388
--- /dev/null
+++ b/kernel/src/long_mode_init.asm
@@ -0,0 +1,17 @@
+global long_mode_start
+
+section .text
+bits 64
+long_mode_start:
+	; load 0 into all data segment registers
+    mov ax, 0
+    mov ss, ax
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+
+    ; print `Uff!` to screen
+    mov rax, 0x8521846683668255
+    mov qword [0xb8000], rax
+    hlt