[boot] Set up initial page tables

Set up initial page tables for both the offset-mapped area and the
loaded kernel code and data.

* Got rid of the `loaded_elf` struct - the loader now runs after the
  initial PML4 is created and maps the ELF sections itself.
* Copied in the `page_table` and `page_table_indices` from the kernel,
  still need to clean this up and extract it into shared code.
* Added `page_table_cache` to the kernel args to pass along free pages
  that can be used for initial page tables.

Tags: paging

src/boot/loader.h

@@ -2,22 +2,22 @@
 /// Definitions for loading the kernel into memory
 #pragma once
 
+#include <uefi/boot_services.h>
+
+#include "kernel_args.h"
+
 namespace boot {
 namespace loader {
 
-/// Structure to hold information about loaded binary image.
-struct loaded_elf
-{
-	void *data;           ///< Start of the kernel in memory
-	uintptr_t vaddr;      ///< Virtual address to map to
-	uintptr_t entrypoint; ///< (Virtual) address of the kernel entrypoint
-};
-
 /// Parse and load an ELF file in memory into a loaded image.
 /// \arg data  The start of the ELF file in memory
 /// \arg size  The size of the ELF file in memory
-/// \returns   A `loaded_elf` structure defining the loaded image
-loaded_elf load(const void *data, size_t size, uefi::boot_services *bs);
+/// \arg args  The kernel args, used for modifying page tables
+/// \returns   A descriptor defining the loaded image
+kernel::entrypoint load(
+	const void *data, size_t size,
+	kernel::args::header *args,
+	uefi::boot_services *bs);
 
 } // namespace loader
 } // namespace boot