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

userspace/init/src/main.c

@@ -6,7 +6,9 @@
 #include <malloc.h>
 
 int main() {
-    printf("Launching debug\n");
-    spawn("debug");
-    while (1) {}
+    wait(spawn("debug"));
+    printf("\nStill here?\n");
+    while (1) {
+        printf("1");
+    }
 }

userspace/libterm/inc/process.h

@@ -4,4 +4,5 @@
 #pragma once
 #include <types.h>
 
-u64 spawn(const char* path);
+u64 spawn(const char* path);
+u64 wait(u64 pid);

userspace/libterm/src/process.c

@@ -4,7 +4,12 @@
 #include <process.h>
 
 extern u64 sys_spawn(const char* path);
+extern u64 sys_wait(u64 pid);
 
 u64 spawn(const char* path) {
     return sys_spawn(path);
+}
+
+u64 wait(u64 pid) {
+    return sys_wait(pid);
 }

userspace/libterm/src/syscalls.asm

@@ -10,6 +10,7 @@ global sys_spawn
 global sys_mem
 global sys_write
 global sys_read
+global sys_wait
 
 sys_exit:
     mov rax, 0
@@ -35,3 +36,8 @@ sys_read:
     mov rax, 4
     syscall
     ret
+
+sys_wait:
+    mov rax, 5
+    syscall
+    ret