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Check for Multiboot, CPUID, and Long Mode

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Philipp Oppermann
2015-08-13 13:09:13 +02:00
parent 49f8c3c810
commit bd11ed9a6f
1 changed files with 47 additions and 0 deletions
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47
src/arch/x86_64/boot.asm
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@@ -19,6 +19,10 @@ bits 32
start:
mov esp, stack_top
call check_multiboot
call check_cpuid
call check_long_mode
; print `OK` to screen
mov dword [0xb8000], 0x2f4b2f4f
hlt
@@ -32,6 +36,49 @@ error:
mov byte [0xb800a], al
hlt
; Throw error 0 if eax doesn't contain the Multiboot 2 magic value (0x36d76289).
check_multiboot:
cmp eax, 0x36d76289
jne .no_multiboot
ret
.no_multiboot:
mov al, "0"
jmp error
; Throw error 1 if the CPU doesn't support the CPUID command.
check_cpuid:
pushfd ; Store the FLAGS-register.
pop eax ; Restore the A-register.
mov ecx, eax ; Set the C-register to the A-register.
xor eax, 1 << 21 ; Flip the ID-bit, which is bit 21.
push eax ; Store the A-register.
popfd ; Restore the FLAGS-register.
pushfd ; Store the FLAGS-register.
pop eax ; Restore the A-register.
push ecx ; Store the C-register.
popfd ; Restore the FLAGS-register.
xor eax, ecx ; Do a XOR-operation on the A-register and the C-register.
jz .no_cpuid ; The zero flag is set, no CPUID.
ret ; CPUID is available for use.
.no_cpuid:
mov al, "1"
jmp error
; Throw error 2 if the CPU doesn't support Long Mode.
check_long_mode:
mov eax, 0x80000000 ; Set the A-register to 0x80000000.
cpuid ; CPU identification.
cmp eax, 0x80000001 ; Compare the A-register with 0x80000001.
jb .no_long_mode ; It is less, there is no long mode.
mov eax, 0x80000000 ; Set the A-register to 0x80000000.
cpuid ; CPU identification.
cmp eax, 0x80000001 ; Compare the A-register with 0x80000001.
jb .no_long_mode ; It is less, there is no long mode.
ret
.no_long_mode:
mov al, "2"
jmp error
section .bss
stack_bottom:
resb 64