kernel: Add support for exit codes and start preparing for waitpid()

kernel/src/sys/exit.cpp

@@ -1,7 +1,14 @@
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
 
-Result<u64> sys_exit(Registers*, SyscallArgs)
+Result<u64> sys_exit(Registers*, SyscallArgs args)
 {
-    kernel_exit();
+    u8 status = (u8)args[0];
+
+    Thread* current = Scheduler::current();
+
+    current->status = status;
+    current->state = ThreadState::Exited;
+
+    kernel_yield();
 }

kernel/src/thread/Thread.h

@@ -19,6 +19,7 @@ enum class ThreadState
     Idle,
     Runnable,
     Sleeping,
+    Exited,
     Dying
 };
 
@@ -64,6 +65,8 @@ struct Thread : public LinkedListNode<Thread>
 
     bool is_kernel { true };
 
+    u8 status { 0 };
+
     PageDirectory* directory;
 
     bool is_idle()

libc/include/stdlib.h

@@ -95,10 +95,10 @@ extern "C"
     void srand(int);
 
     /* Exit the program normally, performing any registered cleanup actions. */
-    __noreturn void exit(int);
+    __noreturn void exit(int status);
 
     /* Exit the program abnormally, without performing any registered cleanup actions. */
-    __noreturn void _Exit(int);
+    __noreturn void _Exit(int status);
 
     int system(const char*);
 

libc/src/stdlib.cpp

@@ -94,13 +94,13 @@ extern "C"
 
     __noreturn void abort()
     {
-        syscall(SYS_exit);
+        syscall(SYS_exit, 255);
         __builtin_unreachable();
     }
 
-    __noreturn void _Exit(int)
+    __noreturn void _Exit(int status)
     {
-        syscall(SYS_exit);
+        syscall(SYS_exit, status);
         __builtin_unreachable();
     }