Added string.h

kernel/include/gdt.h

@@ -0,0 +1,122 @@
+#ifndef _GDT_H
+#define _GDT_H
+
+#include <kernel.h>
+
+/*
+ * Entries:
+ * 0 Null desc.
+ * 1 Kernel code desc.
+ * 2 Kernel data desc.
+ * 3 SYSENTER
+ * 4 SYSEXIT
+ * 5 User code desc.
+ * 6 User data desc.
+ * 7 Task State Segment
+ */
+#define GDT_ENTRIES	8
+#define GDT_KERNEL_CODE	0x28
+#define GDT_KERNEL_DATA	0x30
+#define GDT_USER_CODE	0x50
+#define GDT_USER_DATA	0x48
+#define GDT_TSS		0x50
+
+/*
+ * Segment selector explanation (why kcode is 0x08?)
+ *
+ * Each segment selector must be 16 bits. These bits
+ * have the following layout: (example is 0x08)
+ *   0000000000001 0 00 (lsb)
+ *              |  | '- Privilege level
+ *              |  '--- Table indicator
+ *              '------ Index in table
+ *
+ * Bits 0-1 are the privilege level. x86 has four, 
+ * where 00 is the highest and 11 is the lowest. Only
+ * these two are widely used. 00 being kernel space &
+ * 11 being userspace. Bit 3 is the table indicator.
+ * 0 means the GDT and 1 means the LDT. This will most
+ * likely be 0. Bits 4-15 are the index. This is just
+ * which descriptor in the table is used.
+ *
+ * SO, for the kernel code segment:
+ * Privilege is 00 for kernel space, table indicator
+ * s 0 for the GDT and the index is one, because it
+ * is the second entry in our GDT (after null desc.)
+ */
+#define SEGMENT_SEL(_priv, _tab, _i)\
+	(uint16_t)(((_i) << 3) | ((_tab) << 2) | (_priv))
+
+struct gdt_entry {
+	uint16_t limit;
+	uint16_t baseLow;
+	uint8_t baseMid;
+	uint8_t access;
+	uint8_t granulatiry;
+	uint8_t baseHigh;
+} __packed;
+
+struct gdt_pointer {
+	uint16_t limit;
+	uint32_t base;
+} __packed;
+
+struct tss_entry {
+	uint16_t length;
+	uint16_t baseLow;
+	uint8_t baseMid;
+	uint8_t flags1;
+	uint8_t flags2;
+	uint8_t baseHigh;
+} __packed;
+
+struct tss_pointer {
+	uint16_t link;
+	uint16_t __reserved0;
+	uint32_t esp0;
+	uint16_t ss0;
+	uint16_t __reserved1;
+	uint32_t esp1;
+	uint16_t ss1;
+	uint16_t __reserved2;
+	uint32_t esp2;
+	uint16_t ss2;
+	uint16_t __reserved3;
+	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 ebs;
+	uint32_t ebp;
+	uint32_t esi;
+	uint32_t edi;
+	uint16_t es;
+	uint16_t __reserved4;
+	uint16_t cs;
+	uint16_t __reserved5;
+	uint16_t ss;
+	uint16_t __reserved6;
+	uint16_t ds;
+	uint16_t __reserved7;
+	uint16_t fs;
+	uint16_t __reserved8;
+	uint16_t gs;
+	uint16_t __reserved9;
+	uint16_t ldtr;
+	uint32_t __reserved10;
+	uint16_t iopb;
+	uint32_t ssp;
+} __packed;
+
+struct gdt_entries {
+	struct gdt_entry descriptors[GDT_ENTRIES - 1]; // Subtract one for TSS
+	struct tss_entry tss;
+};
+
+int gdt_init(void);
+
+#endif