diff options
Diffstat (limited to 'src/asm/boot.asm')
| -rw-r--r-- | src/asm/boot.asm | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/src/asm/boot.asm b/src/asm/boot.asm new file mode 100644 index 0000000..ae68761 --- /dev/null +++ b/src/asm/boot.asm @@ -0,0 +1,161 @@ +[BITS 32] + +; Declare constants for the multiboot header. +MBALIGN equ 1 << 0 ; align loaded modules on page boundaries +MEMINFO equ 1 << 1 ; provide memory map +MBFLAGS equ MBALIGN | MEMINFO ; this is the Multiboot 'flag' field +MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header +CHECKSUM equ -(MAGIC + MBFLAGS) ; checksum of above, to prove we are multiboot + +; Declare a multiboot header that marks the program as a kernel. These are magic +; values that are documented in the multiboot standard. The bootloader will +; search for this signature in the first 8 KiB of the kernel file, aligned at a +; 32-bit boundary. The signature is in its own section so the header can be +; forced to be within the first 8 KiB of the kernel file. +section .multiboot +align 4 + dd MAGIC + dd MBFLAGS + dd CHECKSUM + +section .bootstrap + +present equ 1 << 7 +not_sys equ 1 << 4 +exec equ 1 << 3 +cd equ 1 << 2 +rw equ 1 << 1 +access equ 1 << 0 + +gran_4k equ 1 << 7 +sz_32 equ 1 << 6 +long_m equ 1 << 5 + +global gdt.ptr +gdt: +.null: equ $ - gdt + dq 0 +.code: equ $ - gdt + dd 0xffff + db 0 + db present | not_sys | exec | rw + db gran_4k | long_m | 0xf + db 0 +.data: equ $ - gdt + dd 0xffff + db 0 + db present | not_sys | rw + db gran_4k | sz_32 | 0xf + db 0 +.ptr: + dw $ - gdt - 1 + dq gdt + +global bootstrap +bootstrap: + + mov dword [multiboot_magic], eax + mov dword [multiboot_header], ebx + + mov eax, cr0 + and eax, ~(1 << 31) + mov cr0, eax + + mov edi, pml4 ;0x1000 + mov cr3, edi + xor eax, eax + mov ecx, 1024 + rep stosd + + mov edi, 0x2000 + mov ecx, 4096 + rep stosd + + mov edi, cr3 + + mov dword [edi], 0x2003 + mov edi, 0x2000 + mov dword [edi], 0x3003 + add edi, 0x1000 + mov dword [edi], 0x4003 + mov dword [edi + 8], 0x5003 + add edi, 0x1000 + + mov ebx, 0x00000003 + mov ecx, 512 + +.set_entry: + mov dword [edi], ebx + add ebx, 0x1000 + add edi, 8 + loop .set_entry + + mov edi, 0x5000 + mov ecx, 512 + +.set_entry_2: + mov dword [edi], ebx + add ebx, 0x1000 + add edi, 8 + loop .set_entry_2 + + mov eax, cr4 + or eax, 1 << 5 + mov cr4, eax + + mov ecx, 0xc0000080 + rdmsr + or eax, 1 << 8 | 1 << 0 + wrmsr + + mov eax, cr0 + or eax, 1 << 31 + mov cr0, eax + + lgdt [gdt.ptr] + + mov ax, gdt.data + mov ds, ax + mov es, ax + mov fs, ax + mov gs, ax + mov ss, ax + + extern start + jmp gdt.code:start + +global set_pml4 +set_pml4: + mov ecx, 0xC000080 + rdmsr + and eax, ~(1 << 8) + wrmsr + + mov eax, cr0 + and eax, ~(1 << 31) + mov cr0, eax + + mov cr3, edi + + mov ecx, 0xC000080 + rdmsr + or eax, 1 << 8 + wrmsr + + mov eax, cr0 + or eax, 1 << 31 + mov cr0, eax + + retf + +section .data +align 16 +global multiboot_header +multiboot_header: dq 0 +global multiboot_magic +multiboot_magic: dq 0 + +section .bss +global pml4 +align 4096 +pml4: resq 512 |