diff options
Diffstat (limited to 'boot/boot.asm')
| -rw-r--r-- | boot/boot.asm | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/boot/boot.asm b/boot/boot.asm new file mode 100644 index 0000000..645061c --- /dev/null +++ b/boot/boot.asm @@ -0,0 +1,55 @@ +; Cheers to wiki.osdev.org for this quick starter. It really helped me +; get a prototype off the ground quickly without pissing around + +; Declare constants used for creating a multiboot header. +MBALIGN equ 1<<0 ; align loaded modules on page boundaries +MEMINFO equ 1<<1 ; provide memory map +FLAGS equ MBALIGN | MEMINFO ; this is the Multiboot 'flag' field +MAGIC equ 0x1BADB002 ; 'magic number' lets bootloader find the header +CHECKSUM equ -(MAGIC + FLAGS) ; checksum of above, to prove we are multiboot + +; Declare a header as in the Multiboot Standard. We put this into a special +; section so we can force the header to be in the start of the final program. +; You don't need to understand all these details as it is just magic values that +; is documented in the multiboot standard. The bootloader will search for this +; magic sequence and recognize us as a multiboot kernel. +section .multiboot +align 4 + dd MAGIC + dd FLAGS + dd CHECKSUM + +; Currently the stack pointer register (esp) points at anything and using it may +; cause massive harm. Instead, we'll provide our own stack. We will allocate +; room for a small temporary stack by creating a symbol at the bottom of it, +; then allocating 16384 bytes for it, and finally creating a symbol at the top. +section .bootstrap_stack +align 4 +stack_bottom: +times 16384 db 0 +stack_top: + +; The linker script specifies _start as the entry point to the kernel and the +; bootloader will jump to this position once the kernel has been loaded. It +; doesn't make sense to return from this function as the bootloader is gone. +section .text +global _start +_start: + extern kernel_main + extern console_print + extern console_set_colors + + mov esp, stack_top + call kernel_main + + ; Let the user know that kernel_main() exited + push word 0x0007 + call console_set_colors + push mainexit + call console_print + cli +.hang: + hlt + jmp .hang + +mainexit db 10,"asm: kernel_main() exited",0 |