/**
 * @file tss.h
 * @brief Task State Segment (TSS) definitions.
 *
 * The TSS is required by x86 for ring transitions. When a user-mode process
 * triggers an interrupt, the CPU loads the kernel stack pointer (SS0:ESP0)
 * from the TSS before pushing the interrupt frame.
 */

#ifndef TSS_H
#define TSS_H

#include <stdint.h>

/**
 * x86 Task State Segment structure.
 * Only SS0 and ESP0 are actively used for ring 3 -> ring 0 transitions.
 */
typedef struct tss_entry {
    uint32_t prev_tss;
    uint32_t esp0;      /**< Kernel stack pointer (loaded on ring transition). */
    uint32_t ss0;       /**< Kernel stack segment (loaded on ring transition). */
    uint32_t esp1;
    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)) tss_entry_t;

/**
 * Initialize the TSS and install it as GDT entry 5 (selector 0x28).
 * Must be called after init_gdt().
 */
void init_tss(void);

/**
 * Update the kernel stack pointer in the TSS.
 * Called during context switches to set the stack for the next process.
 *
 * @param esp0 The new kernel stack pointer.
 */
void tss_set_kernel_stack(uint32_t esp0);

#endif /* TSS_H */