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]>

6 files changed, 77 insertions, 26 deletions

diff --git a/.gitignore b/.gitignore
index a8a0dce..f6cf5af 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 *.bin
+build/cemOS.o build/kernel.asm.o
diff --git a/Makefile b/Makefile
index 4df65dd..8f4b284 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,24 @@
+FILLES = ./build/kernel.asm.o
+
 BOOTLOADER=./src/boot/bootloader.asm
 TARGET=./bin/boot.bin
 
-all:
+all: ./bin/boot.bin ./bin/kernel.bin
+	rm -rf ./bin/os.bin
+	dd if=./bin/boot.bin >> ./bin/os.bin
+	dd if=./bin/kernel.bin >> ./bin/os.bin
+	dd if=/dev/zero bs=512 count=100 >> ./bin/os.bin
+./bin/kernel.bin: ./build/kernel.asm.o
+	i686-elf-ld -g -relocatable ./build/kernel.asm.o -o ./build/cemOS.o
+	i686-elf-gcc -T ./src/linker.ld -o ./bin/kernel.bin -ffreestanding -O0 -nostdlib ./build/cemOS.o
+
+./bin/boot.bin: ./src/boot/bootloader.asm
 	nasm -f bin $(BOOTLOADER) -o $(TARGET)
+
+./build/kernel.asm.o: ./src/kernel.asm
+	nasm -f elf -g ./src/kernel.asm -o ./build/kernel.asm.o
+
 clean:
 	rm -f $(TARGET)
+	rm -f build/cemOS.o
+	rm -f build/kernel.asm.o
diff --git a/build.sh b/build.sh
index ff9b513..ff9b513 100644..100755
--- a/build.sh
+++ b/build.sh
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)
+	}
+}