[kernel] Added the process_kill syscall

Added process_kill, and also cleaned up all the disparate types being
used for thread/process exit codes. (Now all int32_t.)

src/kernel/objects/process.cpp

@@ -52,7 +52,7 @@ process::create_kernel_process(page_table *pml4)
 }
 
 void
-process::exit(unsigned code)
+process::exit(int32_t code)
 {
 	// TODO: make this thread-safe
 	m_state = state::exited;

src/kernel/objects/process.h

@@ -34,7 +34,7 @@ public:
 
 	/// Terminate this process.
 	/// \arg code   The return code to exit with.
-	void exit(unsigned code);
+	void exit(int32_t code);
 
 	/// Update internal bookkeeping about threads.
 	void update();
@@ -84,7 +84,7 @@ private:
 	// This constructor is called by create_kernel_process
 	process(page_table *kpml4);
 
-	uint32_t m_return_code;
+	int32_t m_return_code;
 
 	vm_space m_space;
 

src/kernel/objects/thread.cpp

@@ -136,7 +136,7 @@ thread::wake_on_result(kobject *obj, j6_status_t result)
 }
 
 void
-thread::exit(uint32_t code)
+thread::exit(int32_t code)
 {
 	m_return_code = code;
 	set_state(state::exited);

src/kernel/objects/thread.h

@@ -131,7 +131,7 @@ public:
 
 	/// Terminate this thread.
 	/// \arg code   The return code to exit with.
-	void exit(unsigned code);
+	void exit(int32_t code);
 
 	/// Add a stack header that returns to the given address in kernel space.
 	/// \arg rip  The address to return to, must be kernel space
@@ -173,7 +173,7 @@ private:
 	wait_type m_wait_type;
 	// There should be 1 byte of padding here
 
-	uint32_t m_return_code;
+	int32_t m_return_code;
 
 	uint64_t m_wait_data;
 	j6_status_t m_wait_result;