Start writing the kernel and add a linker script

Move the code unders [BITS 32] label to its own file to be loaded as a
kernel by the boot loader.

Add a linker script to link the bootloader and the kernel in a single
binary file.

Add a build script to make it easier to use the cross compiler

Update the Makefile to build everything and pack it into the os.bin

Signed-off-by: Carlos Maiolino <[email protected]>

3 files changed, 58 insertions, 25 deletions

diff --git a/src/boot/bootloader.asm b/src/boot/bootloader.asm
index fc17af8..eb226a6 100644
--- a/src/boot/bootloader.asm
+++ b/src/boot/bootloader.asm
@@ -3,6 +3,7 @@ BITS	16
 
 CODE_SEG equ	gdt_code - gdt_start	; 0x8
 DATA_SEG equ	gdt_data - gdt_start	; 0x10
+
 _start:
 	jmp short start
 	nop
@@ -34,7 +35,9 @@ step2:
 	mov eax, cr0
 	or eax, 0x1
 	mov cr0, eax
-	jmp CODE_SEG:start_32
+
+	jmp $
+;	jmp CODE_SEG:start_32
 
 ; GDT table description
 gdt_start:
@@ -71,30 +74,6 @@ gdt_table:
 	dw gdt_end - gdt_start - 1
 	dd gdt_start
 
-
-[BITS 32]
-
-; No access to BIOS from now on....
-start_32:
-	; Set all segments to the same as the DATA_SEG
-	mov ax, DATA_SEG
-	mov ds, ax
-	mov es, ax
-	mov fs, ax
-	mov gs, ax
-	mov ss, ax
-
-	; Set the stack pointer and base pointer further in mem
-	mov ebp, 0x00200000
-	mov esp, ebp
-
-	; Enable A20 line
-	in al, 0x92
-	or al, 2
-	out 0x92, al
-
-	jmp $
-
 ; Fill in to the end and add bootloader signature
 	times 510 - ($ - $$) db 0
 	dw 0xAA55
diff --git a/src/kernel.asm b/src/kernel.asm
new file mode 100644
index 0000000..93afff7
--- /dev/null
+++ b/src/kernel.asm
@@ -0,0 +1,27 @@
+[BITS 32]
+global _start
+
+CODE_SEG equ 0x08
+DATA_SEG equ 0x10
+
+; No access to BIOS from now on....
+_start:
+	; Set all segments to the same as the DATA_SEG
+	mov ax, DATA_SEG
+	mov ds, ax
+	mov es, ax
+	mov fs, ax
+	mov gs, ax
+	mov ss, ax
+
+	; Set the stack pointer and base pointer further in mem
+	mov ebp, 0x00200000
+	mov esp, ebp
+
+	; Enable A20 line
+	in al, 0x92
+	or al, 2
+	out 0x92, al
+
+	jmp $
+
diff --git a/src/linker.ld b/src/linker.ld
new file mode 100644
index 0000000..9ea0171
--- /dev/null
+++ b/src/linker.ld
@@ -0,0 +1,27 @@
+ENTRY(_start)
+OUTPUT_FORMAT(binary)
+
+SECTIONS {
+	. = 1M;
+
+	.text :
+	{
+		*(.text)
+	}
+
+	.rodata :
+	{
+		*(.rodata)
+	}
+
+	.data :
+	{
+		*(.data)
+	}
+
+	.bss :
+	{
+		*(COMMON)
+		*(.bss)
+	}
+}