diff options
Diffstat (limited to 'src/boot.s')
| -rw-r--r-- | src/boot.s | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/src/boot.s b/src/boot.s new file mode 100644 index 0000000..592ba46 --- /dev/null +++ b/src/boot.s @@ -0,0 +1,57 @@ +/* Multiboot header dark magic, do not touch */ +.set ALIGN, 1<<0 +.set MEMINFO, 1<<1 +.set FLAGS, ALIGN | MEMINFO +.set MAGIC, 0x1BADB002 +.set CHECKSUM, -(MAGIC + FLAGS) + +.section .multiboot +.align 4 +.long MAGIC +.long FLAGS +.long CHECKSUM + +/* Multiboot does not define the esp/stack, create the stack ourselves */ +.section bss +/* Stack on x86 must be 16-byte aligned by the System V ABI standard */ +.align 16 +/* Create a symbol at the bottom, allocate 16KiB, then finally create a symbol at the top */ +stack_bottom: +.skip 16384 +stack_top: + +/* _start is the entrypoint */ +.section text +.global _start +.type _start, @function +_start: + /* we are in 32bit protected mode + interrupts disabled, paging disabled + kernel has full control over cpu */ + + /* setup the stack, point to the top becausei t grows downwrad on x86 for som e reason */ + mov $stack_top, %esp + + /* here we need to init crucial processor state. + load the gdt, enable pages, init isa extensions/floating point instructions and stuff + for now just dont do anything we'll add that later */ + + /* enter the high level kernel + ABI says we need 16-byte alignment here, we aligned that before and pushed a multiple of 16 bits (zero) so we fine + but i will realign for good measure anyway */ + .align 16 + call kernel_main + + /* if nothing left then just infinite loop */ + /* + 1. disable interrupts with cli/clear interrupts + 2. wait for next interrupt with hlt. because they disabled this will just lockup the ocmputer + 3. justincase it wakes up just jmp back to the hlt instruction + */ + cli +1: hlt + jmp 1b + +/* set the size of the _start symbol to the current location (.) minus it's _start +for debugging stuff */ +.size _start, . - _start |