[kernel] Start all other processors in the system

This very large commit is mainly focused on getting the APs started and
to a state where they're waiting to have work scheduled. (Actually
scheduling on them is for another commit.)

To do this, a bunch of major changes were needed:

- Moving a lot of the CPU initialization (including for the BSP) to
  init_cpu(). This includes setting up IST stacks, writing MSRs, and
  creating the cpu_data structure. For the APs, this also creates and
  installs the GDT and TSS, and installs the global IDT.

- Creating the AP startup code, which tries to be as position
  independent as possible. It's copied from its location to 0x8000 for
  AP startup, and some of it is fixed at that address. The AP startup
  code jumps from real mode to long mode with paging in one swell foop.

- Adding limited IPI capability to the lapic class. This will need to
  improve.

- Renaming cpu/cpu.* to cpu/cpu_id.* because it was just annoying in GDB
  and really isn't anything but cpu_id anymore.

- Moved all the GDT, TSS, and IDT code into their own files and made
  them classes instead of a mess of free functions.

- Got rid of bsp_cpu_data everywhere. Now always call the new
  current_cpu() to get the current CPU's cpu_data.

- Device manager keeps a list of APIC ids now. This should go somewhere
  else eventually, device_manager needs to be refactored away.

- Moved some more things (notably the g_kernel_stacks vma) to the
  pre-constructor setup in memory_bootstrap. That whole file is in bad
  need of a refactor.

src/kernel/gdt.h

@@ -1,58 +1,66 @@
 #pragma once
 /// \file gdt.h
-/// Definitions relating to system descriptor tables: GDT, IDT, TSS
+/// Definitions relating to a CPU's GDT table
 #include <stdint.h>
 
-/// Set up the GDT and TSS, and switch segment registers to point
-/// to them.
-void gdt_init();
+#include "kutil/enum_bitfields.h"
 
-/// Set an entry in the IDT
-/// \arg i         Index in the IDT (vector of the interrupt this handles)
-/// \arg addr      Address of the handler
-/// \arg selector  GDT selector to set when invoking this handler
-/// \arg flags     Descriptor flags to set
-void idt_set_entry(uint8_t i, uint64_t addr, uint16_t selector, uint8_t flags);
+class TSS;
 
-/// Set the stack pointer for a given ring in the TSS
-/// \arg ring  Ring to set for (0-2)
-/// \arg rsp   Stack pointer to set
-void tss_set_stack(unsigned ring, uintptr_t rsp);
+enum class gdt_type : uint8_t
+{
+	accessed	= 0x01,
+	read_write	= 0x02,
+	conforming	= 0x04,
+	execute		= 0x08,
+	system		= 0x10,
+	ring1		= 0x20,
+	ring2		= 0x40,
+	ring3		= 0x60,
+	present		= 0x80
+};
+IS_BITFIELD(gdt_type);
 
-/// Get the stack pointer for a given ring in the TSS
-/// \arg ring  Ring to get (0-2)
-/// \returns   Stack pointers for that ring
-uintptr_t tss_get_stack(unsigned ring);
+class GDT
+{
+public:
+	GDT(TSS *tss);
 
-/// Set the given IDT entry to use the given IST entry
-/// \arg i     Which IDT entry to set
-/// \arg ist   Which IST entry to set (1-7)
-void idt_set_ist(unsigned i, unsigned ist);
+	/// Get the currently running CPU's GDT
+	static GDT & current();
 
-/// Set the stack pointer for a given IST in the TSS
-/// \arg ist   Which IST entry to set (1-7)
-/// \arg rsp   Stack pointer to set
-void tss_set_ist(unsigned ist, uintptr_t rsp);
+	/// Install this GDT to the current CPU
+	void install() const;
 
-/// Increment the stack pointer for the given vector,
-/// if it's using an IST entry
-/// \arg i     Which IDT entry to use
-void ist_increment(unsigned i);
+	/// Get the addrss of the pointer
+	inline const void * pointer() const { return static_cast<const void*>(&m_ptr); }
 
-/// Decrement the stack pointer for the given vector,
-/// if it's using an IST entry
-/// \arg i     Which IDT entry to use
-void ist_decrement(unsigned i);
+	/// Dump debug information about the GDT to the console.
+	/// \arg index  Which entry to print, or -1 for all entries
+	void dump(unsigned index = -1) const;
 
-/// Get the stack pointer for a given IST in the TSS
-/// \arg ring  Which IST entry to get (1-7)
-/// \returns   Stack pointers for that IST entry
-uintptr_t tss_get_ist(unsigned ist);
+private:
+	void set(uint8_t i, uint32_t base, uint64_t limit, bool is64, gdt_type type);
+	void set_tss(TSS *tss);
 
-/// Dump information about the current GDT to the screen
-/// \arg index  Which entry to print, or -1 for all entries
-void gdt_dump(unsigned index = -1);
+	struct descriptor
+	{
+		uint16_t limit_low;
+		uint16_t base_low;
+		uint8_t base_mid;
+		gdt_type type;
+		uint8_t size;
+		uint8_t base_high;
+	} __attribute__ ((packed, align(8)));
 
-/// Dump information about the current IDT to the screen
-/// \arg index  Which entry to print, or -1 for all entries
-void idt_dump(unsigned index = -1);
+	struct ptr
+	{
+		uint16_t limit;
+		descriptor *base;
+	} __attribute__ ((packed, align(4)));
+
+	descriptor m_entries[8];
+	TSS *m_tss;
+
+	ptr m_ptr;
+};