Meta: Move kernel and userland to their own folders.

This is to allow both the kernel and the userland to share certain
header files and to make the folder structure a bit more clear.

1 files changed, 76 insertions, 0 deletions

diff --git a/kernel/cpu/gdt.h b/kernel/cpu/gdt.h
new file mode 100644
index 0000000..a490dea
--- /dev/null
+++ b/kernel/cpu/gdt.h
@@ -0,0 +1,76 @@
+#ifndef GDT_H
+#define GDT_H
+#include <stdint.h>
+#include <string.h>
+
+#define GDT_ENTRY_SIZE 0x8
+#define GDT_NULL_SEGMENT 0x0
+#define GDT_KERNEL_CODE_SEGMENT 0x1
+#define GDT_KERNEL_DATA_SEGMENT 0x2
+#define GDT_USERMODE_CODE_SEGMENT 0x3
+#define GDT_USERMODE_DATA_SEGMENT 0x4
+#define GDT_TSS_SEGMENT 0x5
+
+struct GDT_Entry
+{
+	uint16_t limit_low;
+	uint32_t base_low               : 24;
+	uint32_t accessed               :  1;
+	uint32_t read_write             :  1; // readable for code, writable for data
+	uint32_t conforming_expand_down :  1; // conforming for code, expand down for data
+	uint32_t code                   :  1; // 1 for code, 0 for data
+	uint32_t code_data_segment      :  1; // should be 1 for everything but TSS and LDT
+	uint32_t DPL                    :  2; // privilege level
+	uint32_t present                :  1;
+	uint32_t limit_high             :  4;
+	uint32_t available              :  1; // only used in software; has no effect on hardware
+	uint32_t long_mode              :  1;
+	uint32_t big                    :  1; // 32-bit opcodes for code, uint32_t stack for data
+	uint32_t gran                   :  1; // 1 to use 4k page addressing, 0 for byte addressing
+	uint8_t base_high;
+}__attribute__((packed));
+
+typedef struct GDT_Pointer
+{
+	uint16_t size;
+	uint32_t offset;
+}__attribute__((packed)) GDT_Pointer;
+
+struct tss_entry_struct
+{
+	uint32_t prev_tss; // The previous TSS - with hardware task switching these form a kind of backward linked list.
+	uint32_t esp0;     // The stack pointer to load when changing to kernel mode.
+	uint32_t ss0;      // The stack segment to load when changing to kernel mode.
+	// Everything below here is unused.
+	uint32_t esp1; // esp and ss 1 and 2 would be used when switching to rings 1 or 2.
+	uint32_t ss1;
+	uint32_t esp2;
+	uint32_t ss2;
+	uint32_t cr3;
+	uint32_t eip;
+	uint32_t eflags;
+	uint32_t eax;
+	uint32_t ecx;
+	uint32_t edx;
+	uint32_t ebx;
+	uint32_t esp;
+	uint32_t ebp;
+	uint32_t esi;
+	uint32_t edi;
+	uint32_t es;
+	uint32_t cs;
+	uint32_t ss;
+	uint32_t ds;
+	uint32_t fs;
+	uint32_t gs;
+	uint32_t ldt;
+	uint16_t trap;
+	uint16_t iomap_base;
+} __attribute__((packed));
+
+void gdt_init();
+
+uint8_t gen_access_byte(uint8_t priv, uint8_t s, uint8_t ex, uint8_t dc, uint8_t rw);
+uint64_t gen_gdt_entry(uint32_t base, uint32_t limit, uint8_t access_byte, uint8_t flag);
+uint8_t gen_flag(uint8_t gr, uint8_t sz);
+#endif