first commit

src/bootload/GDT.asm

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+gdt_start:
+    dd 0x0 ; 4 byte
+    dd 0x0 ; 4 byte
+	
+gdt_code: 
+    dw 0xffff    ; segment length, bits 0-15
+    dw 0x0       ; segment base, bits 0-15
+    db 0x0       ; segment base, bits 16-23
+    db 10011010b ; flags (8 bits)
+    db 11001111b ; flags (4 bits) + segment length, bits 16-19
+    db 0x0       ; segment base, bits 24-31
+
+gdt_data:
+    dw 0xffff
+    dw 0x0
+    db 0x0
+    db 10010010b
+    db 11001111b
+    db 0x0
+
+gdt_end:
+
+gdt_descriptor:
+    dw gdt_end - gdt_start - 1
+    dd gdt_start
+
+CODE_SEG equ gdt_code - gdt_start
+DATA_SEG equ gdt_data - gdt_start

src/bootload/boot.asm

@@ -0,0 +1,69 @@
+; constants for multiboot
+MAGIC equ 0xE85250D6
+ARCH equ 0 ; 0 for i386, 4 for MIPS
+HDRLEN equ 24 ; Total length: 4 fields + end tag
+CHECKSUM equ -(MAGIC + ARCH + HDRLEN)
+
+section .multiboot_header
+align 8
+header_start:
+    dd 0xE85250D6                ; Magic
+    dd 0                         ; Architecture (i386)
+    dd header_end - header_start ; Length
+    dd -(0xE85250D6 + 0 + (header_end - header_start)) ; Checksum
+
+    ; End tag
+    dw 0    ; Type
+    dw 0    ; Flags
+    dd 8    ; Size
+header_end:
+
+
+section .bss
+align 16
+stack_bottom:
+resb 16384 ; 16 KiB is reserved for stack
+stack_top:
+
+section .rodata
+%include "src/bootload/GDT.asm"
+
+section .text ; entrypoint for bootloader
+[BITS 32]
+global _start:function (_start.end - _start)
+_start:
+	; To set up a stack, we set the esp register to point to the top of our
+	; stack (as it grows downwards on x86 systems). This is necessarily done
+	; in assembly as languages such as C cannot function without a stack.
+	mov esp, stack_top
+	mov ebp, esp
+	
+	mov ecx, eax ; move multiboot magic number to ecx
+
+	; TODO:
+	; load GDT 		[x]
+	; enter long m. [ ]
+	; init FPU		[ ]
+
+	; load GDT
+	cli
+	lgdt [gdt_descriptor]
+	jmp   CODE_SEG:.final ; if I get problems, check this line here, future me!
+.final:
+	mov   AX, DATA_SEG ; data segment selectors
+	mov   DS, AX
+	mov   ES, AX
+	mov   FS, AX
+	mov   GS, AX
+	mov   SS, AX
+
+	push ecx ; magic number
+	push ebx ; info structure
+	extern kernel_main
+	call kernel_main
+	add esp, 8 ; remove arguments
+	cli ; the infamous infinite loop
+.hang:	hlt
+	jmp .hang
+.end:
+	

src/bootload/longm.asm

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+; DEPRECATED!
+
+CPUID_EXTENSIONS equ 0x80000000
+CPUID_EXT_FEATURES equ 0x80000001
+EFLAGS_ID equ 1 << 21
+CPUID_EDX_EXT_FEAT_LM equ 1 << 29
+
+enterlong:
+	call .queryLongMode
+	
+
+.NoLongMode
+	cli
+	hlt
+	jmp .NoLongMode
+
+.checkCPUID:
+    pushfd
+    pop eax
+
+    ; The original value should be saved for comparison and restoration later
+    mov ecx, eax
+    xor eax, EFLAGS_ID
+
+    ; storing the eflags and then retrieving it again will show whether or not
+    ; the bit could successfully be flipped
+    push eax                    ; save to eflags
+    popfd
+    pushfd                      ; restore from eflags
+    pop eax
+
+    ; Restore EFLAGS to its original value
+    push ecx
+    popfd
+
+    ; if the bit in eax was successfully flipped (eax != ecx), CPUID is supported.
+    xor eax, ecx
+    jnz .NoLongMode
+	ret
+
+.queryLongMode:
+	call .checkCPUID
+
+    mov eax, CPUID_EXTENSIONS
+    cpuid
+    cmp eax, CPUID_FEATURES
+    jb .NoLongMode
+
+	mov eax, CPUID_EXT_FEATURES
+    cpuid
+    test edx, CPUID_EDX_EXT_FEAT_LM
+    jz .NoLongMode
+	
+	ret
+