v0.5.3: syscalls, minilibc.

- fix(gs): was a nightmare. now its solved. Both MSR_GS_BASE and MSR_KERNEL_GS_BASE are now initialized to , preventing null GS_BASE when interrupt occurs during the first kernel task run
- chore(syscall.asm): stability improvements. User RSP is now saved via kernel stack instead of global g_cpu, preventing stack theft when task switch occurs during a syscall
- feat(interrupts): all irq and isr handlers now conditionally perform swapgs based on the CS selector (checkin if comfing from ring 3)
- upgrade(scheduler): big update: 1) added TASK_BLOCKED state from process sync; 2) syncronized PID and Task ID to fix wakeup logic; 3) implemented sched_block and sched_exit() for proper wait/exit syscalls

kernel/inc/arch/x86_64/syscall.h

@@ -3,10 +3,11 @@
 
 #pragma once
 
-#define MSR_EFER         0xC0000080
-#define MSR_STAR         0xC0000081
-#define MSR_LSTAR        0xC0000082
-#define MSR_FMASK        0xC0000084
+#define MSR_EFER           0xC0000080
+#define MSR_STAR           0xC0000081
+#define MSR_LSTAR          0xC0000082
+#define MSR_FMASK          0xC0000084
+#define MSR_GS_BASE        0xC0000101
 #define MSR_KERNEL_GS_BASE 0xC0000102
 
 #define EFER_SCE         0x01 // System Call Enable
@@ -17,6 +18,7 @@ typedef enum {
     SYS_MEM,
     SYS_WRITE,
     SYS_READ,
+    SYS_WAIT,
 } syscalls;
 
 void syscall_init();

kernel/inc/core/scheduler.h

@@ -7,6 +7,9 @@
 typedef enum process_state {
     DEAD,
     RUNNING,
+    READY,
+    BLOCKED,
+    SLEEPING,
 } process_state;
 
 typedef struct process {
@@ -27,9 +30,13 @@ typedef struct task {
     process_state task_state; // reusing process_state cuz wn
     u64 kernel_stack_top;
     process* proc;
+    i32 waiting_on_pid;
 } task;
 
 void sched_init();
 task* sched_spawn(void(*entry)(), process* owner, bool is_user, u64 fixed_user_stack);
 u64 sched_next(u64 curr_rsp);
-void yield(u64 ticks);
+void yield(u64 ticks);
+void sched_block(u32 pid);
+void sched_wakeup(u32 pid);
+void sched_exit(); // suicide

kernel/inc/drivers/timer.h

@@ -7,4 +7,4 @@
 void timer_init(u32 freq);
 u64 timer_handler(Registers *regs);
 void sleep(u64 ms);
-u64 get_uptime();
+u64 get_uptime();

kernel/inc/syscalls/proc.h

@@ -6,4 +6,5 @@
 #include <types.h>
 
 u64 sys_exit(i32 code);
-u64 sys_spawn(const char* path);
+u64 sys_spawn(const char* path);
+u64 sys_wait(u64 pid);