diff options
Diffstat (limited to 'src/arch/x86_64/boot.asm')
| -rw-r--r-- | src/arch/x86_64/boot.asm | 163 |
1 files changed, 0 insertions, 163 deletions
diff --git a/src/arch/x86_64/boot.asm b/src/arch/x86_64/boot.asm deleted file mode 100644 index 2e334a8..0000000 --- a/src/arch/x86_64/boot.asm +++ /dev/null @@ -1,163 +0,0 @@ -global start -extern long_mode_start - -section .text -bits 32 -start: - mov esp, stack_top - - call check_multiboot - call check_cpuid - call check_long_mode - - call set_up_page_tables - call enable_paging - - ; load the 64-bit GDT - lgdt [gdt64.pointer] - - jmp gdt64.code:long_mode_start - - ; print `OK` to screen - 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 FLAGS in to EAX via stack - pushfd - pop eax - - ; Copy to ECX as well for comparing later on - mov ecx, eax - - ; Flip the ID bit - xor eax, 1 << 21 - - ; Copy EAX to FLAGS via the stack - push eax - popfd - - ; Copy FLAGS back to EAX (with the flipped bit if CPUID is supported) - 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 - - ; Compare EAX and ECX. If they are equal then that means the bit - ; wasn't flipped, and CPUID isn't supported. - 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 - - ; use extended info to test if long mode is available - mov eax, 0x80000001 ; argument for extended processor info - cpuid ; returns various feature bits in ecx and edx - test edx, 1 << 29 ; test if the LM-bit is set in the D-register - jz .no_long_mode ; If it's not set, there is no long mode - ret -.no_long_mode: - mov al, "2" - jmp error - -; Prints `ERR: ` and the given error code to screen and hangs. -; parameter: error code (in ascii) in al -error: - mov dword [0xb8000], 0x4f524f45 - mov dword [0xb8004], 0x4f3a4f52 - mov dword [0xb8008], 0x4f204f20 - mov byte [0xb800a], al - hlt - -set_up_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 -.map_p2_table: - ; map ecx-th P2 entry to a huge page that starts at address 2MiB*ecx - mov eax, 0x200000 ; 2MiB - mul ecx ; start address of ecx-th page - or eax, 0b10000011 ; present + writable + huge - mov [p2_table + ecx * 8], eax ; map ecx-th entry - - inc ecx ; increase counter - cmp ecx, 512 ; if counter == 512, the whole P2 table is mapped - jne .map_p2_table ; else map the next entry - - ret - -enable_paging: - ; load P4 to cr3 register (cpu uses this to access the P4 table) - 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 .bss -align 4096 -p4_table: - resb 4096 -p3_table: - resb 4096 -p2_table: - resb 4096 -stack_bottom: - resb 64 -stack_top: - -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 |