71e2ae482a
Add complete user-mode process support: - TSS (tss.c/h): Task State Segment for Ring 3->0 transitions, installed as GDT entry 5 (selector 0x28). ESP0 updated per-process for kernel stack switching. - Process management (process.c/h): Process table with up to 64 processes. process_create() clones kernel page directory, maps user code at 0x08048000 and user stack at 0xBFFFF000, copies flat binary code. Round-robin scheduler via schedule_tick() modifies the interrupt frame in-place for zero-copy context switching. - System calls (syscall.c/h): INT 0x80 dispatcher with 8 syscalls: SYS_EXIT, SYS_WRITE (to debug port + VGA), SYS_READ, SYS_FORK, SYS_GETPID, SYS_YIELD, SYS_WAITPID, SYS_EXEC. IDT gate at 0x80 uses DPL=3 (flags 0xEE) so user code can invoke it. - Assembly stubs (interrupts.S): isr128 for INT 0x80, tss_flush for loading the Task Register, enter_usermode for initial iret to Ring 3. - Paging extensions (paging.c/h): paging_clone_directory() to create per-process page directories, paging_map_page_in() for mapping into non-active directories, paging_switch_directory() for CR3 switching. - GDT expanded from 5 to 6 entries to accommodate TSS descriptor. gdt_set_gate() exposed in header for TSS initialization. - ISR handler routes timer IRQ (32) to scheduler and INT 0x80 to syscall dispatcher. Exception handler now prints EIP/CS/ERR for debugging. - Kernel boots a test user program that writes 'Hello from Ring 3!' via SYS_WRITE and exits with code 42 via SYS_EXIT. Verified working in QEMU. Context switching approach: Timer/syscall interrupts save all registers via the ISR stub. schedule_tick() copies saved_regs between PCBs and overwrites the interrupt frame, so the existing iret restores the next process's state without separate switch assembly.
29 lines
590 B
C
29 lines
590 B
C
#ifndef GDT_H
|
|
#define GDT_H
|
|
|
|
#include <stdint.h>
|
|
|
|
/* GDT Entry Structure */
|
|
struct gdt_entry {
|
|
uint16_t limit_low;
|
|
uint16_t base_low;
|
|
uint8_t base_middle;
|
|
uint8_t access;
|
|
uint8_t granularity;
|
|
uint8_t base_high;
|
|
} __attribute__((packed));
|
|
|
|
/* GDT Pointer Structure */
|
|
struct gdt_ptr {
|
|
uint16_t limit;
|
|
uint32_t base;
|
|
} __attribute__((packed, aligned(1)));
|
|
|
|
/* Initialize GDT */
|
|
void init_gdt(void);
|
|
|
|
/* Set a GDT gate (also used by TSS setup) */
|
|
void gdt_set_gate(int32_t num, uint32_t base, uint32_t limit, uint8_t access, uint8_t gran);
|
|
|
|
#endif // GDT_H
|