- made improvements to memory code (refactored)

- started on improvements to the page frame allocator. it should be able to provide a usable page for any given virtual memory address requested.

kernel/src/arch/x86_64/memory/mapping.rs

@@ -0,0 +1,55 @@
+//! Sets up a memory map using Limine.
+
+use limine::{
+    request::{HhdmRequest, KernelAddressRequest, MemoryMapRequest},
+    response::MemoryMapResponse,
+};
+use spin::Lazy;
+
+#[used]
+#[unsafe(link_section = ".requests")]
+static MEMORY_MAP_REQUEST: MemoryMapRequest = MemoryMapRequest::new();
+
+#[used]
+#[unsafe(link_section = ".requests")]
+static HIGHER_HALF_DIRECT_MAP_REQUEST: HhdmRequest = HhdmRequest::new();
+
+#[used]
+#[unsafe(link_section = ".requests")]
+static KERNEL_ADDRESS_REQUEST: KernelAddressRequest = KernelAddressRequest::new();
+
+/// ```rs
+/// let virt_addr = phys_addr + offset;
+/// let phys_addr = virt_addr - offset; // (given VA is in the HHDM). Do not use for executable code.
+/// ```
+pub static PHYSICAL_MEMORY_OFFSET: Lazy<u64> = Lazy::new(|| {
+    HIGHER_HALF_DIRECT_MAP_REQUEST
+        .get_response()
+        .unwrap()
+        .offset()
+});
+
+/// Converts virtual addresses in the kernel to a physical address like this:
+/// ```rs
+/// let phys_addr = virt_addr - virtual_base + physical_base;
+/// ```
+///
+/// Returns (virtual_base, physical_base)
+pub static _KERNEL_PHYSICAL_MEMORY_OFFSET: Lazy<(u64, u64)> = Lazy::new(|| {
+    let resp = KERNEL_ADDRESS_REQUEST.get_response().unwrap();
+
+    // These are base addresses, using Limine's built in page table.
+    (resp.virtual_base(), resp.physical_base())
+});
+
+/// Fetches the memory map from Limine.
+///
+/// # Panics
+///
+/// Panics if the memory map was not found in MEMORY_MAP_REQUEST.
+pub fn get_memory_map() -> &'static MemoryMapResponse {
+    MEMORY_MAP_REQUEST.get_response().map_or_else(
+        || unreachable!("Could not fetch memory map from Limine."),
+        |memory_map| memory_map,
+    )
+}