// ============================================================================
// arch/x86_64/entry.S - Kernel entry point (x86_64)
//
// Called by the UEFI loader after ExitBootServices.
//   - Long mode active, paging on (identity map from UEFI)
//   - RDI = pointer to BootInfo structure
//   - Interrupts disabled
// ============================================================================

.section .text
.global _start
.extern kernel_main

_start:
    // Disable interrupts
    cli

    // Set up kernel stack
    // Load Effective Address quadword
    // the address RIP (current exec instruction) + offset_to_stack_top
    // to the Stack pointer register (rsp)
    //(AT&T syntax: lea symbol(%rip), %reg)
    leaq    _stack_top(%rip), %rsp

    // Align stack to 16 bytes (System V ABI)
    // Because ABI mandates that rsp must be 16-byte aligned at the point of a call instruction
    andq    $-16, %rsp

    // The UEFI boot loader (PE/MS x64 ABI) passes BootInfo* in RCX.
    // kernel_main uses System V ABI and expects it in RDI.
    movq    %rcx, %rdi
    call    kernel_main

    // Should never return
.Lhalt:
    cli
    hlt
    jmp     .Lhalt

// ============================================================================
// Kernel stack (16 KiB)
// ============================================================================

.section .bss
.align 4096
_stack_bottom:
    .space CONFIG_KERNEL_STACK_SIZE
_stack_top: