Hardware Discovery

Read RSDP address from BootInfo. Why it matters: The RSDP is the entry point into the ACPI table chain; without it, no hardware can be discovered dynamically. Focus on `boot_info.rsdp_addr` and `kernel_main` in `kernel/src/main.rs` while you trace the snippet.

fn kernel_main(boot_info: &'static mut BootInfo) -> ! {
    serial::init();
    serial::init_logger();

    serial_println!("[m3os] Hello from kernel!");
    log::info!("Kernel initialized");

    // Load GDT/IDT — no IRQs yet.
    arch::init();

    // P9-T001: parse framebuffer info before mm::init consumes boot_info.
    // `mm::init` takes `&'static mut BootInfo` which borrows the whole struct
    // for 'static, so we must extract the raw pointer + layout first.
    let fb_parts: Option<(*mut u8, bootloader_api::info::FrameBufferInfo)> =
        boot_info.framebuffer.as_mut().map(|fb| {
            let info = fb.info();
            // SAFETY: boot_info is &'static mut so the framebuffer memory is
            // valid for the kernel lifetime.  We extract a raw pointer here
            // and hand it to fb::init_from_parts after mm::init returns;
            // no other code accesses the framebuffer between these two points.
            let ptr: *mut u8 = fb.buffer_mut().as_mut_ptr();
            (ptr, info)
        });

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Define RSDP structures. Why it matters: The RSDP v1/v2 structures must be correctly defined to locate the root system descriptor table. Focus on `RsdpDescriptor` and `RsdpDescriptorV2` in `kernel/src/acpi/mod.rs` while you trace the snippet.

/// ACPI 1.0 RSDP (Root System Description Pointer), 20 bytes.
#[repr(C, packed)]
#[derive(Clone, Copy)]
struct RsdpDescriptor {
    signature: [u8; 8],
    checksum: u8,
    oem_id: [u8; 6],
    revision: u8,
    rsdt_address: u32,
}

/// ACPI 2.0+ RSDP extension, 36 bytes total.
#[repr(C, packed)]
#[derive(Clone, Copy)]
struct RsdpDescriptorV2 {

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Read Local APIC base address. Why it matters: The LAPIC base address is needed to memory-map its control registers. Focus on `IA32_APIC_BASE` in `kernel/src/arch/x86_64/apic.rs` while you trace the snippet.

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