/* Copyright (C) 2021,2022 fef <owo@fef.moe>.  All rights reserved. */

#pragma once

#include <gay/config.h>

#define X86_32_KERN_CS	0x10
#define X86_32_USER_CS	0x18
#define X86_64_KERN_CS	0x20
#define X86_64_USER_CS	0x28
#define X86_KERN_DS	0x30
#define X86_USER_DS	0x38
#define X86_KERN_TSS	0x40
#define X86_USER_TSS	0x50

#ifndef _ASM_SOURCE

/*
 * This code is mostly obsolete (until we need to actually manipulate the GDT
 * when there is long mode support and we want to enable 32-bit compatibility
 * mode).  I wrote this because i initially wanted to use it for an encoder that
 * would dynamically initialize the GDT entries at runtime, but fuck that.
 * I've lost way more than enough time on the utterly useless GDT, so we'll just
 * leave this here as it is until we actually need it.  See arch/mm/segment.S
 * for the actual GDT entries and how the GDT is loaded.
 */

#include <arch/page.h>

#include <gay/cdefs.h>
#include <gay/types.h>

/** @brief x86 Global Descriptor Table entry as used by the kernel. */
struct x86_gdt_entry {
	u32 base;
	unsigned limit:20;
	unsigned flags:4;
#define X86_GDT_SIZE		(1u << 2)
#define X86_GDT_GRANULARITY	(1u << 3)
	u8 access;
#define X86_GDT_ACCESSED	(1u << 0)
#define X86_GDT_RW		(1u << 1)
#define X86_GDT_DIRECTION	(1u << 2) /* for data selectors (executable not set) */
#define X86_GDT_CONFORMING	(1u << 2) /* for code selectors (executable set) */
#define X86_GDT_EXEC		(1u << 3)
#define X86_GDT_TYPE		(1u << 4) /* 1 for code/data, 0 for system (e.g. TSS) */
#define X86_GDT_PRIVL_SHIFT	(5)
#define X86_GDT_PRIVL_MASK	(3u << X86_GDT_PRIVL_SHIFT)
#define X86_GDT_PRIVL(n)	(((n) << X86_GDT_PRIVL_SHIFT) & X86_GDT_PRIVL_MASK)
#define X86_GDT_PRESENT		(1u << 7)
};

/** @brief x86 Global Descriptor Table entry as laid out in hardware. */
struct x86_insane_gdt_entry {
	u16 limit0;
	u16 base0;
	u8 base1;
	u8 access;
	unsigned limit1:4;
	unsigned flags:4;
	u8 base2;
} __packed;

/** @brief The main GDT (defined in `arch/mm/segment.S`) */
extern struct x86_insane_gdt_entry x86_gdt[5];

struct x86_tss {
	u16 link;	u16 _reserved0;
	u32 esp0;
	u16 ss0;	u16 _reserved1;
	u32 esp1;
	u16 ss1;	u16 _reserved2;
	u32 esp2;
	u16 ss2;	u16 _reserved3;
	u32 cr3;
	u32 eip;
	u32 eflags;
	u32 eax;
	u32 ecx;
	u32 edx;
	u32 ebx;
	u32 esp;
	u32 ebp;
	u32 esi;
	u32 edi;
	u16 es;		u16 _reserved4;
	u16 cs;		u16 _reserved5;
	u16 ss;		u16 _reserved6;
	u16 ds;		u16 _reserved7;
	u16 fs;		u16 _reserved8;
	u16 gs;		u16 _reserved9;
	u16 ldtr;	u16 _reserved10;
	u16 _reserved11; u16 iopb_offset;
};

#endif /* not _ASM_SOURCE */