diff options
| -rw-r--r-- | kernel/src/boot.asm | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/kernel/src/boot.asm b/kernel/src/boot.asm index a10b14c..de832f8 100644 --- a/kernel/src/boot.asm +++ b/kernel/src/boot.asm @@ -5,10 +5,75 @@ bits 32 start: mov esp, stack_top + call check_multiboot + call check_cpuid + call check_long_mode + ; print 'OK' mov dword [0xb8000], 0x2f4b2f4f 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 + ; Prints 'ERR: ' and the given error code to the screen and halts ; parameter: error code letter (ascii) in al error: |