kernel: Add core dump facility

* Add function core_dump_write_core_file(). It writes a core file for
  the current thread's team. The file format is similar to that of
  other OSs (i.e. ELF with PT_LOAD segments and a PT_NOTE segment), but
  most of the notes are Haiku specific (infos for team, areas, images,
  threads). More data will probably need to be added.
* Add team flag TEAM_FLAG_DUMP_CORE, thread flag
  THREAD_FLAGS_TRAP_FOR_CORE_DUMP, and Team property coreDumpCondition,
  a condition variable available while a core dump is progress. A
  thread that finds its flag THREAD_FLAGS_TRAP_FOR_CORE_DUMP set before
  exiting the kernel to userland calls core_dump_trap_thread(), which
  blocks on the condition variable until the core dump has finished. We
  need the team's threads to stop so we can get their CPU state (and
  have a generally unchanging team state while writing the core file).
* Add user debugger message B_DEBUG_WRITE_CORE_FILE. It causes
  core_dump_write_core_file() to be called for the team.
* Dumping core as an immediate effect of a terminal signal has not been
  implemented yet, but that should be fairly straight forward.

headers/os/kernel/debugger.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2005, Ingo Weinhold, [email protected].
+ * Copyright 2005-2016 Haiku, Inc. All rights reserved.
  * Distributed under the terms of the MIT License.
  */
 #ifndef _DEBUGGER_H
@@ -163,7 +163,9 @@ typedef enum {
 										// install_team_debugger()
 
 	B_DEBUG_START_PROFILER,				// start/stop sampling
-	B_DEBUG_STOP_PROFILER				//
+	B_DEBUG_STOP_PROFILER,				//
+
+	B_DEBUG_WRITE_CORE_FILE				// write a core file
 } debug_nub_message;
 
 // messages sent to the debugger
@@ -412,6 +414,20 @@ typedef struct {
 	thread_id			thread;			// thread to profile
 } debug_nub_stop_profiler;
 
+// B_DEBUG_WRITE_CORE_FILE
+
+typedef struct {
+	port_id				reply_port;		// port to send the reply to
+	char				path[B_PATH_NAME_LENGTH];
+										// path of the core file; must not exist
+										// yet; must be absolute
+} debug_nub_write_core_file;
+
+typedef struct {
+	status_t	error;					// B_OK on success
+} debug_nub_write_core_file_reply;
+
+
 // reply is debug_profiler_update
 
 // union of all messages structures sent to the debug nub thread
@@ -433,6 +449,7 @@ typedef union {
 	debug_nub_get_signal_handler	get_signal_handler;
 	debug_nub_start_profiler		start_profiler;
 	debug_nub_stop_profiler			stop_profiler;
+	debug_nub_write_core_file		write_core_file;
 } debug_nub_message_data;