diff options
Diffstat (limited to 'src/header/boot.s')
| -rw-r--r-- | src/header/boot.s | 156 |
1 files changed, 47 insertions, 109 deletions
diff --git a/src/header/boot.s b/src/header/boot.s index 2276e3d..5eaa794 100644 --- a/src/header/boot.s +++ b/src/header/boot.s @@ -1,117 +1,55 @@ -/* multiboot header constants */ -.set ALIGN, 1<<0 /* Align loaded modules on page boundries */ -.set MEMINFO, 1<<1 /* Provide memory map*/ -.set FLAGS, ALIGN | MEMINFO /* Multiboot flag field*/ -.set MAGIC, 0x1BADB002 /*Lets bootloader find header*/ -.set CHECKSUM, -(MAGIC + FLAGS) /* Proves we are multiboot via checksum*/ - -/* - * Declare a multiboot header that marks the program as a kernel. - * These are magic values that are docymented in the multiboot standard. - * The bootloader will search fot this signature in the first 8KiB of - * the kernel file, aligned at a 32-bit boundry. - * The signature is in its own section so the header can be forced to be - * within the first 8KiB of the kernel file. - */ -.section .multiboot -.align 4 -.long MAGIC -.long FLAGS -.long CHECKSUM - -/* - * The multiboot standard doesn't define the value of the "stack pointer register," - * or esp, as it is up to the kernel to provide a stack. - * This allocates room for a small stack through a few steps: - * 1. Create a symbol at the bottom of the stack - * 2. Allocate 16 KiB for the stack - * 3. Create a symbol at the top of the stack. - * The stack grows DOWN on x86. - * Since the stack is in its own section*, it can be marked "nobits" - * which means the kernel file is smaller since it doesn't contain - * an uninitialized stack. - * On x86, the stack must be 16-byte aligned** according to System V ABI standard - * and de-facto extentions. - * The compiler assumes the stack is properly aligned, so failure to align will - * result in UB. - */ -.section bss -.align 16 -.stack_bottom: -.skip 16384 -stack_top: - -/* - * Our linker script specifies _start as te entry point to the kernel. - * The bootloader will jump here once the kernel is loaded. - * We won't return, since the bootloader would be gone at that point - */ -.section .text -.global _start -.type _start, @function +MBALIGN equ 1<<0 ; Align loaded modules on page boundries */ +MBMEMINFO equ 1<<1 ; Provide memory map*/ +MBFLAGS equ MBALIGN | MBMEMINFO ; Multiboot flag field*/ +MAGIC equ 0x1BADB002 ;Lets bootloader find header*/ +CHECKSUM equ -(MAGIC + MBFLAGS) ; Proves we are multiboot via checksum*/ + + +section .multiboot +align 4 + dd MAGIC + dd MBFLAGS + dd CHECKSUM + +section .bss +align 16 +stack_bottom: +resb 16384 +stack_top: + +section .text +global _start:function (_start.end - _start) _start: - /* - * The bootloader loads us into 32-bit mode on x86 machines. - * Interrupts and paging are disabled. - * The multiboot standard defines our current processor state. - * The kernel has full control over the CPU - * The kernel can only use two things - * 1. hardware features - * 2. its own code - * No printing is available (Unless we make it). - * No security restrictions, safeguards, or debugging mechanisms. - * We only have what the kernel provides. - * ABSOLUTE POWER OVER THE MACHINE!! - */ + mov esp, stack_top - /* - * To setup a stack, make the esp register point to the top of the stack. - * We have to do this in assembly since C wont even function without the stack. - */ - mov $stack_top, %esp + extern get_gdtr + call get_gdtr + extern gdtr + mov [gdtr], eax + cli + lgdt [gdtr] - /* - * This is a good point to initialize crucial processor state before our - * high level kernel is entered. - * It's best to minize early environment where crucial features are offline. - * The processor is not fully initialized yet, therefore - * features such as floating point instructions and instruction set extentions - * are ALSO not initialized. - * The GDT (global descriptor table) should be loaded here. - * Paging should be enabled here. - */ - /* - * Enter our high level kernel. - * the ABI (?) requres the stack is 16-byte aligned at the time of - * the call instruction (which afterward will push the return pointer - * of size 4 bytes). - * The stack was 16-byte aligned above, and we have pushed a multiple of - * 16 bytes to the stack (we have pushed zero bytes so far), so - * the alignment is preserved, and the call is well defined. - */ + call reloadSegments ; this motherfucker is what is causing so many issues + + [bits 32] + extern kernel_main call kernel_main - /* - * If the system has nothing else to do, we will infinitely loop. - * To do this, we must: - * 1. Disable interrupts with `cli` - * (clear interrupt enable in eflags.) - * They are already disabled by the bootloader, so we can skip this. - * Keep in mind, we may have to do this later AND return from main - * (for some nonsensical reason) - * 2. wait for the next interrupt to arrive with `hlt` (halt instruction) - * Since interrupts are disabled, this locks up the computer (yay!) - * 3. jump to the `hlt` instruction if it ever wakes up due to a - * non-maskable interrupt occuring or due to a system management mode. - */ - cli -1: hlt - jmp 1 -/* - * Set the size of _start to { current_location - (start of _start) } - * This is useful for debugging or for call tracing later on. - */ -.size _start, . - _start + cli +.hang: hlt + jmp .hang +.end: + + reloadSegments: + JMP 0x0008:.reload_CS ; should def define a CODESEG +.reload_CS: + MOV AX, 0x0010 + MOV DS, AX + MOV ES, AX + MOV FS, AX + MOV GS, AX + MOV SS, AX + RET |