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#ifndef _AMD64_GDT_H_
#define _AMD64_GDT_H_
#include <sys/types.h>
#include <sys/cdefs.h>
#define GDT_TSS_INDEX 5
#define GDT_ENTRY_COUNT 7
/* Segment selectors */
#define KERNEL_CS 0x08
#define KERNEL_DS 0x10
#define USER_CS 0x18
#define USER_DS 0x20
/*
* Bit definitions for regular segment descriptors
*
* See Intel SPG 3/25 Section 3.4.5 - Segment Descriptors
*/
#define GDT_ATTRIBUTE_ACCESSED BIT(0) /* Accessed */
#define GDT_ATTRIBUTE_EXECUTABLE BIT(3) /* Executable */
#define GDT_ATTRIBUTE_NONSYSTEM BIT(4) /* Code/data */
#define GDT_ATTRIBUTE_PRESENT BIT(7) /* Present */
#define GDT_ATTRIBUTE_64BIT_CODE BIT(13) /* 64-bit code */
#define GDT_ATTRIBUTE_32BIT BIT(14) /* 32-bit code/data */
#define GDT_ATTRIBUTE_GRANULARITY BIT(15) /* 4KiB limit granularity */
/* Attributes for executable segments */
#define GDT_ATTRIBUTE_READABLE BIT(1) /* Readable */
#define GDT_ATTRIBUTE_CONFORMING BIT(2) /* Conforming */
/* Attributes for non-executable segments */
#define GDT_ATTRIBUTE_WRITABLE BIT(1) /* Writable */
#define GDT_ATTRIBUTE_EXPANDS_DOWN BIT(2) /* See SPG 3/25 Section 6.8.1 */
/* DPL (Descriptor Privilege Level) specifier */
#define GDT_ATTRIBUTE_DPL0 0
#define GDT_ATTRIBUTE_DPL1 (1 << 5)
#define GDT_ATTRIBUTE_DPL2 (2 << 5)
#define GDT_ATTRIBUTE_DPL3 (3 << 5)
struct __packed gdt_entry {
uint16_t limit;
uint16_t base_low;
uint8_t base_mid;
uint16_t attributes;
uint8_t base_hi;
};
struct __packed gdtr {
uint16_t limit;
uintptr_t offset;
};
extern struct gdt_entry g_gdt_data[GDT_ENTRY_COUNT];
extern const struct gdtr g_gdtr;
__always_inline static inline void
gdt_load(void)
{
__ASMV("lgdt %0\n"
"push %1\n" /* Push code segment selector */
"lea 1f(%%rip), %%rax\n" /* Load label 1 address into RAX */
"push %%rax\n" /* Push return address (label 1) */
"lretq\n" /* Far return to update CS */
"1:\n"
" mov %2, %%ax\n" /* Load data segment selectors */
" mov %%ax, %%ds\n"
" mov %%ax, %%es\n"
" mov %%ax, %%fs\n"
" mov %%ax, %%gs\n"
" mov %%ax, %%ss\n"
:
: "m" (g_gdtr), "i"(KERNEL_CS), "i"(KERNEL_DS)
: "rax", "memory"
);
}
#endif /* !AMD64_GDT_H_ */
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