summaryrefslogtreecommitdiff
path: root/kernel/src/asm
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/src/asm')
-rw-r--r--kernel/src/asm/boot.asm172
-rw-r--r--kernel/src/asm/long_mode_init.asm19
-rw-r--r--kernel/src/asm/multiboot_header.asm15
3 files changed, 206 insertions, 0 deletions
diff --git a/kernel/src/asm/boot.asm b/kernel/src/asm/boot.asm
new file mode 100644
index 0000000..2ecaba8
--- /dev/null
+++ b/kernel/src/asm/boot.asm
@@ -0,0 +1,172 @@
+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 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 ; huge + writable + present
+
+.map_p2_table:
+ cmp eax, 0b10000011 + stack_bottom
+ jne .valid_mem
+ mov ebx, 0b10000010
+ mov [p2_table + ecx], ebx
+ add ecx, 8
+ cmp ecx, 4096
+ jne .valid_mem
+ ret
+.valid_mem:
+ mov [p2_table + ecx], eax
+ add eax, 0x200000 ; 2MiB
+
+ add ecx, 8
+ cmp ecx, 4096
+ jne .map_p2_table
+
+ 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
+
+ ; move stack pointer to accommodate for the guard page
+ add esp, 0x200000
+
+ 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:
+ mov dword [0xb8000], 0x4f524f45
+ mov dword [0xb8004], 0x4f3a4f52
+ mov dword [0xb8008], 0x4f504f20
+ mov byte [0xb800a], al
+ hlt
+
+section .bss
+align 4096
+p4_table:
+ resb 4096
+p3_table:
+ resb 4096
+p2_table:
+ resb 4096
+alignb 4096 * 512 ; align memory into huge memory page
+stack_bottom:
+ resb 4096 * 512
+stack_top:
diff --git a/kernel/src/asm/long_mode_init.asm b/kernel/src/asm/long_mode_init.asm
new file mode 100644
index 0000000..8c1b1e7
--- /dev/null
+++ b/kernel/src/asm/long_mode_init.asm
@@ -0,0 +1,19 @@
+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
+
+ extern _start
+ jmp _start
diff --git a/kernel/src/asm/multiboot_header.asm b/kernel/src/asm/multiboot_header.asm
new file mode 100644
index 0000000..9c9d859
--- /dev/null
+++ b/kernel/src/asm/multiboot_header.asm
@@ -0,0 +1,15 @@
+section .multiboot_header
+header_start:
+ dd 0xe85250d6 ; magic number (multiboot 2)
+ dd 0 ; architecture 0
+ dd header_end - header_start ; header length
+ ; checksum
+ dd 0x100000000 - (0xe85250d6 + 0 + (header_end - header_start))
+
+ ; insert optional multiboot tags here
+
+ ; required end tag
+ dw 0 ; type
+ dw 0 ; flags
+ dd 8 ; size
+header_end: