Implement exit syscall

src/drivers/nulldrv/main.s

@@ -20,6 +20,9 @@ _start:
 	mov rax, 1		; DEBUG syscall
 	syscall ; int 0xee
 
+	cmp r13, 0
+	je .doexit
+
 	cmp r12, 1
 	je .dosend
 	jne .doreceive
@@ -59,3 +62,7 @@ _start:
 	mov rdi, 1      ; source is pid 2
 	syscall ; int 0xee
 	jmp .preloop
+
+.doexit
+	mov rax, 9      ; EXIT syscall
+	syscall

src/kernel/process.cpp

@@ -4,6 +4,13 @@
 #include "scheduler.h"
 
 
+void
+process::exit(uint32_t code)
+{
+	return_code = code;
+	flags -= process_flags::running;
+}
+
 pid_t
 process::fork(uintptr_t in_rsp)
 {

src/kernel/process.h

@@ -57,6 +57,10 @@ struct process
 	uintptr_t kernel_stack;
 	size_t kernel_stack_size;
 
+	/// Terminate this process.
+	/// \arg code   The return code to exit with.
+	void exit(unsigned code);
+
 	/// Copy this process.
 	/// \arg in_rsp The RSP of the calling process
 	/// \returns    Returns the child's pid to the parent, and

src/kernel/syscall.cpp

@@ -127,12 +127,18 @@ syscall_dispatch(uintptr_t return_rsp, cpu_state &regs)
 			cons->set_color();
 
 			pid_t pid = p->fork(return_rsp);
-			if (pid == scheduler::get().current()->pid)
-				pid = 0;
 			regs.rax = pid;
 		}
 		break;
 
+	case syscall::exit:
+		cons->set_color(11);
+		cons->printf("\nProcess %u: Received EXIT syscall\n", p->pid);
+		cons->set_color();
+		p->exit(regs.rdi);
+		return_rsp = s.schedule(return_rsp);
+		break;
+
 	default:
 		cons->set_color(9);
 		cons->printf("\nReceived unknown syscall: %02x\n", call);

src/kernel/syscall.h

@@ -15,6 +15,7 @@ enum class syscall : uint64_t
 	send           = 0x0006,
 	receive        = 0x0007,
 	fork           = 0x0008,
+	exit           = 0x0009,
 
 	last_syscall
 };