gdbstub initial code, v11

gdbstub initial code, v11

[Oleg Nesterov]

[-- Attachment #1: Type: text/plain, Size: 681 bytes --]

Changes: syscall stepping + minor cleanups.

Seems to work, more or less, but surely there are some bugs.

Honestly, I don't really know how do the "right thing" here.
Anyway, most probably this code will be changed. Like ptrace,
ugdb uses ->report_syscall_exit() to synthesize a trap. Unlike
ptrace, ugdb_report_signal() doesn't send SIGTRAP to itself
but reports SIGTRAP using siginfo_t we have. In any case,
whatever we do, multiple tracers can confuse each other.

Next: fully implement g/G/p/P, currently I am a bit confused...

But what about features? What should I do next? all-stop,
thread-specific breakpoints (currently I have no idea what
this means), or what?

Oleg.


[-- Attachment #2: ugdb.c --]
[-- Type: text/plain, Size: 55451 bytes --]

#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/utrace.h>
#include <linux/poll.h>
#include <linux/mm.h>
#include <linux/regset.h>
#include <asm/uaccess.h>

static int o_remote_debug;
module_param_named(echo, o_remote_debug, bool, 0);

#define BUFFER_SIZE		1024
#define PACKET_SIZE		1024

struct pbuf {
	char	*cur, *pkt;
	char	buf[BUFFER_SIZE];
};

static inline void pb_init(struct pbuf *pb)
{
	pb->cur = pb->buf;
	pb->pkt = NULL;
}

enum {
	U_STOP_IDLE = 0,
	U_STOP_PENDING,
	U_STOP_SENT,
};

struct ugdb {
	struct list_head	u_processes;
	struct list_head	u_stopped;

	int			u_stop_state;

	struct mutex		u_mutex;
	spinlock_t		u_slock;

	struct ugdb_thread
				*u_cur_tinfo,
				*u_cur_hg,
				*u_cur_hc;

	wait_queue_head_t	u_wait;

	int			u_err;

	struct pbuf		u_pbuf;
	char			u_cbuf[PACKET_SIZE];
	int			u_clen;

	sigset_t		u_sig_ign;

	unsigned int
				u_no_ack:1,
				u_allstop:1;
};

static inline void ugdb_ck_stopped(struct ugdb *ugdb)
{
	spin_lock(&ugdb->u_slock);
	WARN_ON(!list_empty(&ugdb->u_stopped) &&
				ugdb->u_stop_state == U_STOP_IDLE);
	WARN_ON(list_empty(&ugdb->u_stopped) &&
				ugdb->u_stop_state == U_STOP_PENDING);
	spin_unlock(&ugdb->u_slock);
}

static struct ugdb *ugdb_create(void)
{
	struct ugdb *ugdb;
	int err;

	err = -ENODEV;
	// XXX: ugly. proc_reg_open() should take care.
	if (!try_module_get(THIS_MODULE))
		goto out;

	err = -ENOMEM;
	ugdb = kzalloc(sizeof(*ugdb), GFP_KERNEL);
	if (!ugdb)
		goto put_module;

	INIT_LIST_HEAD(&ugdb->u_processes);
	INIT_LIST_HEAD(&ugdb->u_stopped);

	mutex_init(&ugdb->u_mutex);
	spin_lock_init(&ugdb->u_slock);

	init_waitqueue_head(&ugdb->u_wait);

	pb_init(&ugdb->u_pbuf);

	return ugdb;

put_module:
	module_put(THIS_MODULE);
out:
	return ERR_PTR(err);
}

#define P_DETACHING	(1 << 1)
#define P_ZOMBIE	(1 << 2)

struct ugdb_process {
	int			p_pid;
	int			p_state;

	struct list_head	p_threads;

	struct ugdb		*p_ugdb;
	struct list_head	p_processes;
};

static inline bool process_alive(struct ugdb_process *process)
{
	return !(process->p_state & P_ZOMBIE);
}

static inline void mark_process_dead(struct ugdb_process *process)
{
	process->p_state |= P_ZOMBIE;
}

static struct ugdb_process *ugdb_create_process(struct ugdb *ugdb, int pid_nr)
{
	struct ugdb_process *process;

	process = kzalloc(sizeof(*process), GFP_KERNEL);
	if (!process)
		return NULL;

	process->p_pid = pid_nr;
	process->p_ugdb = ugdb;
	INIT_LIST_HEAD(&process->p_threads);
	list_add_tail(&process->p_processes, &ugdb->u_processes);

	return process;
}

#define T_STOP_RUN	0
#define T_STOP_REQ	(1 << 0)	/* requested by gdb */
#define T_STOP_ALL	(1 << 1)	/* vCont;c:pX.-1, for report_clone */
#define T_STOP_ACK	(1 << 2)	/* visible to vStopped */
#define T_STOP_STOPPED	(1 << 3)	/* reported as stopped to gdb */
					/* TASK_TRACED + deactivated ? */

#define T_EV_NONE		0
#define T_EV_EXIT		(1 << 24)
#define T_EV_SIGN		(2 << 24)

#define T_EV_TYPE(event)	((0xff << 24) & (event))
#define T_EV_DATA(event)	(~(0xff << 24) & (event))

struct ugdb_thread {
	int			t_tid;
	int			t_stop_state;
	int			t_stop_event;
	bool			t_step; 	// XXX: move me into t_stop_event

	siginfo_t		*t_siginfo;

	struct ugdb		*t_ugdb;
	struct ugdb_process	*t_process;

	struct list_head	t_threads;
	struct list_head	t_stopped;

	struct pid		*t_spid;

	struct utrace_engine	*t_engine;
};

static inline bool thread_alive(struct ugdb_thread *thread)
{
	WARN_ON((thread->t_tid != 0) != process_alive(thread->t_process));

	return thread->t_tid != 0;
}

static inline void mark_thread_dead(struct ugdb_thread *thread)
{
	mark_process_dead(thread->t_process);
	thread->t_tid = 0;
}

/*
 * The thread should be alive, and it can't pass ugdb_report_death()
 * if the caller holds ugdb->u_mutex. However the tracee can be
 * reaped anyway, pid_task() can return NULL after detach_pid().
 */
static inline struct task_struct *thread_to_task(struct ugdb_thread *thread)
{
	BUG_ON(!thread_alive(thread));

	return pid_task(thread->t_spid, PIDTYPE_PID);
}

static struct ugdb_thread *ugdb_create_thread(struct ugdb_process *process,
						struct pid *spid)
{
	struct ugdb_thread *thread;

	thread = kzalloc(sizeof(*thread), GFP_KERNEL);
	if (!thread)
		return NULL;

	thread->t_tid = pid_vnr(spid);
	thread->t_spid = get_pid(spid);
	thread->t_process = process;
	thread->t_ugdb = process->p_ugdb;
	INIT_LIST_HEAD(&thread->t_stopped);
	list_add_tail(&thread->t_threads, &process->p_threads);

	return thread;
}

static void ugdb_del_stopped(struct ugdb *ugdb, struct ugdb_thread *thread)
{
	if (!list_empty(&thread->t_stopped)) {
		WARN_ON(!(thread->t_stop_state & T_STOP_ACK));

		spin_lock(&ugdb->u_slock);
		list_del_init(&thread->t_stopped);

		if (!(thread->t_stop_state & T_STOP_STOPPED)) {
			if (ugdb->u_stop_state == U_STOP_PENDING &&
					list_empty(&ugdb->u_stopped))
				ugdb->u_stop_state = U_STOP_IDLE;
		}
		spin_unlock(&ugdb->u_slock);
	}

	thread->t_stop_state = T_STOP_RUN;
}

static void ugdb_destroy_thread(struct ugdb_thread *thread)
{
	struct ugdb *ugdb = thread->t_ugdb;

	ugdb_ck_stopped(ugdb);

	ugdb_del_stopped(ugdb, thread);

	/* NULL if attach fails */
	if (thread->t_engine)
		utrace_engine_put(thread->t_engine);

	list_del(&thread->t_threads);
	put_pid(thread->t_spid);
	kfree(thread);
}

static int ugdb_set_events(struct ugdb_thread *thread,
				unsigned long events)
{
	WARN_ON(!thread_alive(thread));

	events |= (UTRACE_EVENT(CLONE) | UTRACE_EVENT(DEATH) |
			UTRACE_EVENT_SIGNAL_ALL);

	//XXX: I think utrace_get_signal() is buggy !!!!!!!!!!!!
	events |= UTRACE_EVENT(QUIESCE);

	return utrace_set_events_pid(thread->t_spid, thread->t_engine,
					events);
}

static int ugdb_control(struct ugdb_thread *thread,
				enum utrace_resume_action action)
{
	// XXX: temporary racy check
	WARN_ON(!thread_alive(thread) && action != UTRACE_DETACH);

	return utrace_control_pid(thread->t_spid, thread->t_engine,
					action);
}

static const struct utrace_engine_ops ugdb_utrace_ops;

static void ugdb_detach_thread(struct ugdb_thread *thread, bool running)
{
	int ret;

	ret = ugdb_control(thread, UTRACE_DETACH);

	/* engine->flags == 0, it can't run a callback */
	if (!running)
		return;

	/* callbacks are no longer possible */
	if (!ret)
		return;

	if (ret == -EINPROGRESS) {
		/*
		 * We raced with a callback, it can't be ->report_death().
		 * However, we can not use utrace_barrier_pid(), it can
		 * hang "forever" until the next utrace_resume() if it
		 * sees ->ops == &utrace_detached_ops set by us, but the
		 * tracee is no longer running.
		 *
		 * But: we have no choice.
		 */
		do {
			ret = utrace_barrier_pid(thread->t_spid,
						thread->t_engine);
		} while (ret == -ERESTARTSYS);
	} else {
		/*
		 * Nothing can help us to synchronize with ->report_death.
		 * We do not know if it was already called or not, we can't
		 * know if it is running. utrace_barrier_pid() can't help,
		 * it can return zero and then later ->report_death() will
		 * be called. Or it can return -ESRCH just because the task
		 * was alredy released and pid_task() == NULL, but this
		 * doesn't mean ->report_death() can't be called later.
		 *
		 * Fortunately, we know that the tracee is dying or dead,
		 * engine->ops should be changed after ugdb_report_death()
		 * returns UTRACE_DETACH.
		 */
		 while (thread->t_engine->ops == &ugdb_utrace_ops) {
		 	schedule_timeout_uninterruptible(1);
		 }
	}
}

/*
 * returns NULL if raced with exit(), or ERR_PTR().
 */
static struct ugdb_thread *ugdb_attach_thread(struct ugdb_process *process,
						struct pid *spid)
{
	struct ugdb_thread *thread;
	struct utrace_engine *engine;
	struct task_struct *task;

	thread = ugdb_create_thread(process, spid);
	if (!thread)
		goto err;

	engine = utrace_attach_pid(thread->t_spid, UTRACE_ATTACH_CREATE,
					&ugdb_utrace_ops, thread);
	if (IS_ERR(engine))
		goto free_thread;

	thread->t_engine = engine;

	if (ugdb_set_events(thread, 0))
		goto detach_thread;

	return thread;

detach_thread:
	ugdb_detach_thread(thread, false);
free_thread:
	ugdb_destroy_thread(thread);
err:
	rcu_read_lock();
	task = pid_task(spid, PIDTYPE_PID);
	if (task && task->exit_state)
		task = NULL;
	rcu_read_unlock();

	return task ? ERR_PTR(-ENOMEM) : NULL;
}

static inline bool is_subthread(struct ugdb_process *process,
				struct ugdb_thread *thread)
{
	return thread && thread->t_process == process;
}

static inline void ugdb_reset_tinfo(struct ugdb *ugdb)
{
	ugdb->u_cur_tinfo = NULL;
}

static void ugdb_destroy_process(struct ugdb_process *process)
{
	struct ugdb *ugdb = process->p_ugdb;
	struct ugdb_thread *thread;

	mutex_lock(&ugdb->u_mutex);
	process->p_state |= P_DETACHING;
	list_del(&process->p_processes);

	if (is_subthread(process, ugdb->u_cur_hg))
		ugdb->u_cur_hg = NULL;
	if (is_subthread(process, ugdb->u_cur_hc))
		ugdb->u_cur_hc = NULL;

	/* I hope gdb won't do detach from under qfThreadInfo */
	if (ugdb->u_cur_tinfo) {
		printk(KERN_WARNING "ugdb: detach from under qfThreadInfo\n");
		ugdb_reset_tinfo(ugdb);
	}
	mutex_unlock(&ugdb->u_mutex);

	while (!list_empty(&process->p_threads)) {
		thread = list_first_entry(&process->p_threads,
				struct ugdb_thread, t_threads);
		ugdb_detach_thread(thread, true);
		ugdb_destroy_thread(thread);
	}

	BUG_ON(!list_empty(&process->p_threads));

	kfree(process);
}

static void ugdb_destroy(struct ugdb *ugdb)
{
	struct ugdb_process *process;

	while (!list_empty(&ugdb->u_processes)) {
		process = list_first_entry(&ugdb->u_processes,
				struct ugdb_process, p_processes);
		ugdb_destroy_process(process);
	}

	BUG_ON(!list_empty(&ugdb->u_processes));
	BUG_ON(!list_empty(&ugdb->u_stopped));

	module_put(THIS_MODULE);
	kfree(ugdb);
}

static struct pid *get_next_pid(struct pid *main, struct pid *curr)
{
	struct task_struct *task;
	struct sighand_struct *sighand;
	struct pid *next = NULL;

	rcu_read_lock();
	/*
	 * If task/sighand is NULL we return NULL. This is fine if
	 * the caller is get_first_pid(), we should abort attaching.
	 *
	 * But this can also happen if curr was already attached,
	 * and this is wrong. Fortunately, this is very unlikely
	 * case. The attached sub-thread can't pass ->report_death,
	 * if it was reaped the caller of release_task() must be
	 * ptracer who re-parented this thread.
	 */
	task = pid_task(curr, PIDTYPE_PID);
	if (!task)
		goto unlock_rcu;

	// XXX: we need lock_task_sighand() but it is not exported,
	// so we ran race with de_thread().
	sighand = rcu_dereference(task->sighand);
	if (!sighand)
		goto unlock_rcu;

	spin_lock_irq(&sighand->siglock);
	for (;;) {
		task = next_thread(task);

		// XXX: if main is not leader we can race with exec.
		if (task_pid(task) == main)
			break;

		if (!task->exit_state) {
			next = get_pid(task_pid(task));
			break;
		}
	}
	spin_unlock_irq(&sighand->siglock);
unlock_rcu:
	rcu_read_unlock();

	return next;
}

static struct pid *get_first_pid(struct pid *main)
{
	struct task_struct *leader;

	rcu_read_lock();
	leader = pid_task(main, PIDTYPE_PID);
	if (leader && leader->exit_state)
		leader = NULL;
	rcu_read_unlock();

	/*
	 * The group-leader is alive, try to attach. If it exits
	 * before utrace_set_events(), get_first_pid() will be
	 * called again and it will notice ->exit_state != 0.
	 */
	if (leader)
		return get_pid(main);

	/*
	 * Try to find the live sub-thread. If the whole group
	 * is dead it returns NULL and the caller aborts.
	 */
	return get_next_pid(main, main);
}

static int ugdb_attach_all_threads(struct ugdb *ugdb,
				struct ugdb_process *process,
				struct pid *main_pid)
{
	struct ugdb_thread *thread;
	struct pid *curr_pid;

	mutex_lock(&ugdb->u_mutex);

	for (;;) {
		curr_pid = get_first_pid(main_pid);
		if (!curr_pid)
			goto abort;

		thread = ugdb_attach_thread(process, curr_pid);
		put_pid(curr_pid);

		if (IS_ERR(thread))
			goto abort;

		if (thread)
			break;
	}

	for (;;) {
		struct pid *next_pid;

		next_pid = get_next_pid(main_pid, curr_pid);
		if (!next_pid)
			break;

		thread = ugdb_attach_thread(process, next_pid);
		put_pid(next_pid);

		if (IS_ERR(thread))
			goto abort;

		if (!thread)
			continue;

		curr_pid = next_pid;
	}

	mutex_unlock(&ugdb->u_mutex);
	return 0;

abort:
	mutex_unlock(&ugdb->u_mutex);
	return -1;
}

static int ugdb_attach(struct ugdb *ugdb, int pid_nr)
{
	struct pid *main_pid;
	struct ugdb_process *process;
	int err;

	// XXX: check if exists
	// XXX: check if group leader ?

	err = -ESRCH;
	main_pid = find_get_pid(pid_nr);
	if (!main_pid)
		goto out;

	err = -ENOMEM;
	process = ugdb_create_process(ugdb, pid_nr);
	if (!process)
		goto free_pid;

	err = ugdb_attach_all_threads(ugdb, process, main_pid);
	if (err)
		ugdb_destroy_process(process);

free_pid:
	put_pid(main_pid);
out:
	return err;
}

static struct ugdb_process *ugdb_find_process(struct ugdb *ugdb, int pid)
{
	struct ugdb_process *process;

	list_for_each_entry(process, &ugdb->u_processes, p_processes) {
		if (process->p_pid == pid)
			return process;
	}

	return NULL;
}

static struct ugdb_thread *ugdb_find_thread(struct ugdb *ugdb, int pid, int tid)
{
	struct ugdb_process *process;
	struct ugdb_thread *thread;

	list_for_each_entry(process, &ugdb->u_processes, p_processes) {
		if (unlikely(!process_alive(process)))
			continue;
		if (pid && process->p_pid != pid)
			continue;

		list_for_each_entry(thread, &process->p_threads, t_threads) {
			if (WARN_ON(!thread_alive(thread)))
				continue;
			if (!tid || thread->t_tid == tid)
				return thread;
		}

		if (pid)
			break;
	}

	return NULL;
}

static int ugdb_detach(struct ugdb *ugdb, int pid)
{
	struct ugdb_process *process = ugdb_find_process(ugdb, pid);

	if (!process)
		return -1;

	ugdb_destroy_process(process);
	return 0;
}

#define CUR_TINFO_END	((struct ugdb_thread *)1)

static struct ugdb_thread *ugdb_advance_tinfo(struct ugdb *ugdb)
{
	struct ugdb_thread *cur, *nxt;
	struct ugdb_process *process;

	cur = ugdb->u_cur_tinfo;

	if (cur == CUR_TINFO_END) {
		ugdb->u_cur_tinfo = NULL;
		return NULL;
	}

	if (!cur) {
		list_for_each_entry(process, &ugdb->u_processes, p_processes) {
			if (unlikely(!process_alive(process)))
				continue;

			if (!list_empty(&process->p_threads)) {
				cur = list_first_entry(&process->p_threads,
						struct ugdb_thread, t_threads);
				break;
			}
		}

		if (!cur)
			return NULL;
	}

	process = cur->t_process;

	if (list_is_last(&cur->t_threads, &process->p_threads)) {
		nxt = CUR_TINFO_END;

		list_for_each_entry_continue(process, &ugdb->u_processes, p_processes) {
			if (unlikely(!process_alive(process)))
				continue;

			if (!list_empty(&process->p_threads)) {
				nxt = list_first_entry(&process->p_threads,
						struct ugdb_thread, t_threads);
				break;
			}
		}
	} else {
		nxt = list_first_entry(&cur->t_threads,
				struct ugdb_thread, t_threads);
	}

	ugdb->u_cur_tinfo = nxt;
	return cur;
}

// -----------------------------------------------------------------------------
static bool ugdb_add_stopped(struct ugdb_thread *thread, int stop_event)
{
	struct ugdb *ugdb = thread->t_ugdb;
	bool ret = false;

	ugdb_ck_stopped(ugdb);

	spin_lock(&ugdb->u_slock);
	if (stop_event == T_EV_NONE) {
		if (WARN_ON(thread->t_stop_state & T_STOP_ACK))
			goto unlock;
		if (WARN_ON(!list_empty(&thread->t_stopped)))
			goto unlock;

		/* raced with ugdb_cont_thread() */
		if (!(thread->t_stop_state & T_STOP_REQ))
			goto unlock;
	}

	if (thread->t_stop_state & T_STOP_ACK) {
		if (thread->t_stop_state & T_STOP_STOPPED)
			/*
			 * Alas, we can't report this event. We already
			 * reported T00 and there is no way to inform gdb
			 * the state of tracee was changed.
			 */
			goto unlock;
	} else {
		WARN_ON(thread->t_stop_state & T_STOP_STOPPED);

		thread->t_stop_state |= T_STOP_ACK;
		list_add_tail(&thread->t_stopped, &ugdb->u_stopped);

		if (ugdb->u_stop_state == U_STOP_IDLE) {
			ugdb->u_stop_state = U_STOP_PENDING;
			wake_up_all(&ugdb->u_wait);
		}
	}

	thread->t_stop_event = stop_event;
	ret = true;
unlock:
	spin_unlock(&ugdb->u_slock);

	return ret;
}

static void ugdb_process_exit(struct ugdb_thread *thread)
{
	struct ugdb *ugdb = thread->t_ugdb;
	int status;

	BUG_ON(!thread_alive(thread));

	ugdb_del_stopped(ugdb, thread);
	mark_thread_dead(thread);

	// XXX: OOPS, we can't read ->signal->group_exit_code !!!
	status = current->exit_code;
	if (ugdb_add_stopped(thread, T_EV_EXIT | status))
		return;

	WARN_ON(1);
}

static int ugdb_stop_thread(struct ugdb_thread *thread, bool all)
{
	struct ugdb *ugdb = thread->t_ugdb;
	int err;

	WARN_ON(!thread_alive(thread));

	ugdb_ck_stopped(ugdb);

	if (thread->t_stop_state != T_STOP_RUN) {
		if (!all || (thread->t_stop_state & T_STOP_ALL))
			return 0;
		/*
		 * Otherwise we should set T_STOP_ALL anyway,
		 *
		 *	(gdb) interrupt &
		 *	(gbd) interrupt -a &
		 *
		 * to ensure -a actually works if it races with clone.
		 */
	}

	err = -EALREADY;
	spin_lock(&ugdb->u_slock);
	if (thread->t_stop_state == T_STOP_RUN) {
		thread->t_stop_state = T_STOP_REQ;
		err = 0;
	}

	/*
	 * We hold ugdb->u_mutex, we can't race with ugdb_report_clone().
	 * ugdb->u_slock protects us against ugdb_add_stopped(). We can
	 * change ->t_stop_state even if we did not initiate this stop.
	 */
	if (all)
		thread->t_stop_state |= T_STOP_ALL;
	spin_unlock(&ugdb->u_slock);

	if (err)
		return 0;

	// XXX: we don't do UTRACE_STOP! this means we can't
	// stop TASK_STOPEED task. Need to discuss jctl issues.
	// if we do UTRACE_STOP we should call ugdb_add_stopped().

	ugdb_set_events(thread, UTRACE_EVENT(QUIESCE));
	err = ugdb_control(thread, UTRACE_INTERRUPT);
	if (err && err != -EINPROGRESS)
		return err;
	return 1;
}

static int ugdb_cont_thread(struct ugdb_thread *thread, bool all, bool step)
{
	struct ugdb *ugdb = thread->t_ugdb;
	int ret;

	WARN_ON(!thread_alive(thread));

	ugdb_ck_stopped(ugdb);

	// XXX: gdb shouldn't explicitly cont an unreported thread
	WARN_ON(!all && !(thread->t_stop_state & T_STOP_STOPPED));

	if (thread->t_stop_state == T_STOP_RUN)
		return 0;

	spin_lock(&ugdb->u_slock);
	/*
	 * Nothing to do except clear the pending T_STOP_REQ.
	 */
	ret = 0;
	if (!(thread->t_stop_state & T_STOP_ACK))
		goto set_run;

	/*
	 * Alas. Thanks to remote protocol, we can't cont this
	 * thread. We probably already sent the notification, we
	 * can do nothing except ack that %Stop later in response
	 * to vStopped.
	 *
	 * OTOH, gdb shouldn't send 'c' if this thread was not
	 * reported as stopped. However, this means that gdb can
	 * see the new %Stop:T00 notification after vCont;c:pX.-1,
	 * it should handle this case correctly anyway. I hope.
	 *
	 * If this stop was not initiated by gdb we should not
	 * cancel it too, this event should be reported first.
	 */
	ret = -1;
	if (!(thread->t_stop_state & T_STOP_STOPPED))
		goto unlock;

	ret = 1;
	list_del_init(&thread->t_stopped);
set_run:
	thread->t_stop_state = T_STOP_RUN;
unlock:
	spin_unlock(&ugdb->u_slock);

	if (ret >= 0) {
		unsigned long events = 0;
		enum utrace_resume_action action = UTRACE_RESUME;

		thread->t_step = step;
		if (step) {
			/* to correctly step over syscall insn */
			events |= UTRACE_EVENT(SYSCALL_EXIT);
			action = UTRACE_SINGLESTEP;
		}

		// XXX: OK, this all is racy, and I do not see any
		// solution except: implement UTRACE_STOP_STICKY and
		// move this code up under the lock, or add
		// utrace_engine_ops->notify_stopped().

		// 1. UTRACE_RESUME is racy, this is fixeable.
		// 2. we need utrace_barrier() to close the race
		//    with the callback which is going to return
		//    UTRACE_STOP, but:
		//    	a) we can deadlock (solveable)
		//	b) in this case UTRACE_RESUME can race with
		//	   another stop initiated by tracee itself.

		ugdb_set_events(thread, events);
		ugdb_control(thread, action);
	}

	return ret;
}

static struct ugdb_thread *ugdb_next_stopped(struct ugdb *ugdb)
{
	struct ugdb_thread *thread = NULL;

	// XXX: temporary racy check
	WARN_ON(ugdb->u_stop_state == U_STOP_IDLE);

	spin_lock(&ugdb->u_slock);
	if (list_empty(&ugdb->u_stopped)) {
		ugdb->u_stop_state = U_STOP_IDLE;
	} else {
		ugdb->u_stop_state = U_STOP_SENT;

		thread = list_first_entry(&ugdb->u_stopped,
					struct ugdb_thread, t_stopped);

		thread->t_stop_state |= T_STOP_STOPPED;
		list_del_init(&thread->t_stopped);
	}
	spin_unlock(&ugdb->u_slock);

	return thread;
}

// -----------------------------------------------------------------------------
static bool ugdb_stop_pending(struct ugdb_thread *thread)
{
	if (!(thread->t_stop_state & T_STOP_REQ))
		return false;

	if (!(thread->t_stop_state & T_STOP_ACK))
		return ugdb_add_stopped(thread, T_EV_NONE);

	return true;
}

static u32 ugdb_report_quiesce(u32 action, struct utrace_engine *engine,
					unsigned long event)
{
	struct ugdb_thread *thread = engine->data;

	WARN_ON(!thread_alive(thread));

	/* ensure SIGKILL can't race with stop/cont in progress */
	if (event != UTRACE_EVENT(DEATH)) {
		if (ugdb_stop_pending(thread))
			return UTRACE_STOP;
	}

	return utrace_resume_action(action);
}

static int cont_signal(struct ugdb_thread *thread,
				struct k_sigaction *return_ka)
{
	int signr = T_EV_DATA(thread->t_stop_event);
	siginfo_t *info = thread->t_siginfo;

	thread->t_siginfo = NULL;

	if (WARN_ON(!valid_signal(signr)))
		return 0;

	if (!signr)
		return signr;
	/*
	 * Update the siginfo structure if the signal has changed.
	 */
	if (info->si_signo != signr) {
		info->si_signo = signr;
		info->si_errno = 0;
		info->si_code = SI_USER;
		info->si_pid = 0;
		info->si_uid = 0;
	}

	/* If the (new) signal is now blocked, requeue it. */
	if (sigismember(&current->blocked, signr)) {
		send_sig_info(signr, info, current);
		signr = 0;
	} else {
		spin_lock_irq(&current->sighand->siglock);
		*return_ka = current->sighand->action[signr - 1];
		spin_unlock_irq(&current->sighand->siglock);
	}

	return signr;
}

static u32 ugdb_report_signal(u32 action, struct utrace_engine *engine,
				struct pt_regs *regs,
				siginfo_t *info,
				const struct k_sigaction *orig_ka,
				struct k_sigaction *return_ka)
{
	struct ugdb_thread *thread = engine->data;
	struct ugdb *ugdb = thread->t_ugdb;
	int signr;

	WARN_ON(!thread_alive(thread));

	switch (utrace_signal_action(action)) {
	case UTRACE_SIGNAL_HANDLER:
		if (WARN_ON(thread->t_siginfo))
			thread->t_siginfo = NULL;

		if (thread->t_step) {
			WARN_ON(orig_ka);
			// user_single_step_siginfo(current, regs, info);
			memset(info, 0, sizeof(*info));
			info->si_signo = SIGTRAP;
			break;
		}

		/* Fall through */

	default:
		if (orig_ka)
			break;

		/*
		 * It was UTRACE_SIGNAL_REPORT, but another tracer has
		 * changed utrace_report->result to deliver or stop.
		 * Fall through.
		 */

	case UTRACE_SIGNAL_REPORT:
		if (!thread->t_siginfo) {
			/* UTRACE_INTERRUPT from ugdb_report_syscall_exit() */
			if (thread->t_step) {
				WARN_ON(orig_ka);
				// user_single_step_siginfo(current, regs, info);
				memset(info, 0, sizeof(*info));
				info->si_signo = SIGTRAP;
				break;
			}
		} else {
			if (WARN_ON(thread->t_siginfo != info))
				return action;
			WARN_ON(T_EV_TYPE(thread->t_stop_event) != T_EV_SIGN);

			signr = cont_signal(thread, return_ka);
			if (signr) {
				/*
				 * Consider:
				 *
				 *	(gdb) signal SIG &
				 *	(gdb) interrupt
				 *
				 * We shouldn't miss the new stop request, so
				 * we do not return from here.
				 */
				action = UTRACE_RESUME | UTRACE_SIGNAL_DELIVER;
			}
		}

		if (ugdb_stop_pending(thread))
			return UTRACE_STOP | utrace_signal_action(action);

		if (thread->t_step)
			return UTRACE_SINGLESTEP | utrace_signal_action(action);
		return action;
	}

	WARN_ON(thread->t_siginfo);

	signr = info->si_signo;
	if (WARN_ON(!signr || !valid_signal(signr)))
		return action;

	if (sigismember(&ugdb->u_sig_ign, signr))
		return action;

	if (ugdb_add_stopped(thread, T_EV_SIGN | signr)) {
		thread->t_siginfo = info;
		/*
		 * Make sure the subsequent UTRACE_SIGNAL_REPORT clears
		 * ->t_siginfo before return from get_signal_to_deliver().
		 */
		if (utrace_control(current, engine, UTRACE_INTERRUPT))
			WARN_ON(1);
		return UTRACE_STOP | UTRACE_SIGNAL_IGN;
	}

	/*
	 * We already reported T00 to gdb. We can't change our state,
	 * we are already stopped from gdb pov. Push back this signal
	 * to report it later, after "continue".
	 *
	 * Not multitrace-friendly.
	 */
	return UTRACE_STOP | UTRACE_SIGNAL_REPORT | UTRACE_SIGNAL_HOLD;
}

static u32 ugdb_report_syscall_exit(u32 action, struct utrace_engine *engine,
					struct pt_regs *regs)
{
	struct ugdb_thread *thread = engine->data;

	if (thread->t_step)
		return UTRACE_INTERRUPT;

	printk(KERN_INFO "ugdb: unexpected SYSCALL_EXIT\n");
	return action;
}

static bool is_already_attached(struct ugdb_process *process,
				struct task_struct *task)
{
	struct ugdb_thread *thread;

	if (likely(!task_utrace_flags(task)))
		return false;

	/*
	 * Currently there is no way to know if it was attached by us.
	 * We can't trust utrace_attach_task(UTRACE_ATTACH_MATCH_OPS),
	 * ugdb attaches without UTRACE_ATTACH_EXCLUSIVE. We have to
	 * check every attached thread.
	 *
	 * This is really bad, but without multitracing this can only
	 * happen in unlikely case right after ugdb_attach_all_threads().
	 */
	list_for_each_entry(thread, &process->p_threads, t_threads) {
		if (thread->t_spid == task_pid(task))
			return true;
	}

	return false;
}

static u32 ugdb_report_clone(u32 action, struct utrace_engine *engine,
			       unsigned long clone_flags,
			       struct task_struct *task)
{
	struct ugdb_thread *thread = engine->data;
	struct ugdb_process *process = thread->t_process;
	struct ugdb *ugdb = thread->t_ugdb;
	struct ugdb_thread *new_thread;

	WARN_ON(!thread_alive(thread));

	if (!(clone_flags & CLONE_THREAD))
		goto out;

	mutex_lock(&ugdb->u_mutex);
	if (process->p_state & P_DETACHING)
		goto unlock;
	/*
	 * This can only happen if we raced with ugdb_attach() which
	 * could attach both current and the new PF_STARTING child.
	 */
	if (unlikely(is_already_attached(process, task)))
		goto unlock;

	new_thread = ugdb_attach_thread(process, task_pid(task));
	BUG_ON(!new_thread);

	if (WARN_ON(IS_ERR(new_thread)))
		goto unlock;

	if (thread->t_stop_state & T_STOP_ALL)
		ugdb_stop_thread(new_thread, false);

unlock:
	mutex_unlock(&ugdb->u_mutex);
out:
	return utrace_resume_action(action);
}

static u32 ugdb_report_death(struct utrace_engine *engine,
				bool group_dead, int signal)
{
	struct ugdb_thread *thread = engine->data;
	struct ugdb_process *process = thread->t_process;
	struct ugdb *ugdb = thread->t_ugdb;

	WARN_ON(!thread_alive(thread));

	mutex_lock(&ugdb->u_mutex);
	if (process->p_state & P_DETACHING)
		goto unlock;

	if (ugdb->u_cur_hg == thread)
		ugdb->u_cur_hg = NULL;
	if (ugdb->u_cur_hc == thread)
		ugdb->u_cur_hc = NULL;

	if (ugdb->u_cur_tinfo == thread)
		ugdb_advance_tinfo(ugdb);

	if (list_is_singular(&process->p_threads))
		ugdb_process_exit(thread);
	else
		ugdb_destroy_thread(thread);

unlock:
	mutex_unlock(&ugdb->u_mutex);

	return UTRACE_DETACH;
}

static const struct utrace_engine_ops ugdb_utrace_ops = {
	.report_quiesce		= ugdb_report_quiesce,
	.report_signal		= ugdb_report_signal,
	.report_syscall_exit	= ugdb_report_syscall_exit,
	.report_clone		= ugdb_report_clone,
	.report_death		= ugdb_report_death,
};

// -----------------------------------------------------------------------------
static inline int pb_size(struct pbuf *pb)
{
	return pb->cur - pb->buf;
}

static inline int pb_room(struct pbuf *pb)
{
	return pb->buf + BUFFER_SIZE - pb->cur;
}

static inline void pb_putc(struct pbuf *pb, char c)
{
	if (WARN_ON(pb->cur >= pb->buf + BUFFER_SIZE-1))
		return;
	*pb->cur++ = c;
}

static void pb_memcpy(struct pbuf *pb, const void *data, int size)
{
	if (WARN_ON(size > pb_room(pb)))
		return;
	memcpy(pb->cur, data, size);
	pb->cur += size;
}

static inline void pb_puts(struct pbuf *pb, const char *s)
{
	pb_memcpy(pb, s, strlen(s));
}

static inline void pb_putb(struct pbuf *pb, unsigned char val)
{
	static char hex[] = "0123456789abcdef";
	pb_putc(pb, hex[(val & 0xf0) >> 4]);
	pb_putc(pb, hex[(val & 0x0f) >> 0]);
}

static void pb_putbs(struct pbuf *pb, const char *data, int size)
{
	while (size--)
		pb_putb(pb, *data++);
}

static inline void __pb_start(struct pbuf *pb, char pref)
{
	WARN_ON(pb->pkt);
	pb_putc(pb, pref);
	pb->pkt = pb->cur;
}

static inline void pb_start(struct pbuf *pb)
{
	return __pb_start(pb, '$');
}

static inline void pb_cancel(struct pbuf *pb)
{
	if (WARN_ON(!pb->pkt))
		return;

	pb->cur = pb->pkt - 1;
	pb->pkt = NULL;
}

static void pb_end(struct pbuf *pb)
{
	unsigned char csm = 0;
	char *pkt = pb->pkt;

	pb->pkt = NULL;
	if (WARN_ON(!pkt))
		return;

	while (pkt < pb->cur) {
		/* pb_qfer() can write '%' */
		WARN_ON(*pkt == '$' || *pkt == '#');
		csm += (unsigned char)*pkt++;
	}

	pb_putc(pb, '#');
	pb_putb(pb, csm);
}

static inline void pb_packs(struct pbuf *pb, const char *s)
{
	pb_start(pb);
	pb_puts(pb, s);
	pb_end(pb);
}

static void __attribute__ ((format(printf, 3, 4)))
__pb_format(struct pbuf *pb, bool whole_pkt, const char *fmt, ...)
{
	int room = pb_room(pb), size;
	va_list args;

	if (whole_pkt)
		pb_start(pb);

	va_start(args, fmt);
	size = vsnprintf(pb->cur, room, fmt, args);
	va_end(args);

	if (WARN_ON(size > room))
		return;

	pb->cur += size;

	if (whole_pkt)
		pb_end(pb);
}

#define pb_printf(pb, args...)	__pb_format((pb), false, args)
#define pb_packf(pb, args...)	__pb_format((pb), true,  args)

static int pb_qfer(struct pbuf *pb, const void *_data, int len, bool more)
{
	const unsigned char *data = _data;
	int i;

	if (pb_room(pb) < 3 + len * 2) {
		WARN_ON(1);
		return -EOVERFLOW;
	}

	pb_start(pb);
	pb_putc(pb, more ? 'm' : 'l');

	for (i = 0; i < len; ++i) {
		unsigned char c = data[i];

		if (c == '$' || c == '#' || c == '}' || c == '*') {
			pb_putc(pb, '}');
			c ^= 0x20;
		}

		pb_putc(pb, c);
	}

	pb_end(pb);

	return 0;
}

static inline void *pb_alloc_bs(struct pbuf *pb, int size)
{
	if (unlikely(pb_room(pb) < 2 * size + 4))
		return NULL;
	return pb->cur + size + 1;
}

static inline void *pb_alloc_tmp(struct pbuf *pb, int size)
{
	if (unlikely(pb_room(pb) < size))
		return NULL;
	return pb->cur + BUFFER_SIZE - size;
}

static inline void pb_flush(struct pbuf *pb, int size)
{
	int keep = pb_size(pb) - size;
	if (keep)
		memmove(pb->buf, pb->buf + size, keep);
	pb->cur -= size;
}

static int pb_copy_to_user(struct pbuf *pb, char __user *ubuf, int size)
{
	int copy = min(size, pb_size(pb));

	if (!copy)
		return -EAGAIN;

	if (o_remote_debug)
		printk(KERN_INFO "<= %.*s\n", min(copy, 64), pb->buf);

	if (copy_to_user(ubuf, pb->buf, copy))
		return -EFAULT;

	pb_flush(pb, copy);
	return copy;
}

// -----------------------------------------------------------------------------
// XXX: include/gdb/signals.h:target_signal
// incomplete: 7, 29, rt?
static int to_gdb_sigmap[] = {
	[SIGHUP]	= 1,
	[SIGINT]	= 2,
	[SIGQUIT]	= 3,
	[SIGILL]	= 4,
	[SIGTRAP]	= 5,
	[SIGABRT]	= 6,
	[SIGIOT]	= 0,	/* ??? */
	[SIGBUS]	= 10,
	[SIGFPE]	= 8,
	[SIGKILL]	= 9,
	[SIGUSR1]	= 30,
	[SIGSEGV]	= 11,
	[SIGUSR2]	= 31,
	[SIGPIPE]	= 13,
	[SIGALRM]	= 14,
	[SIGTERM]	= 15,
	[SIGSTKFLT]	= 0,	/* ??? */
	[SIGCHLD]	= 20,
	[SIGCONT]	= 19,
	[SIGSTOP]	= 17,
	[SIGTSTP]	= 18,
	[SIGTTIN]	= 21,
	[SIGTTOU]	= 22,
	[SIGURG]	= 16,
	[SIGXCPU]	= 24,
	[SIGXFSZ]	= 25,
	[SIGVTALRM]	= 26,
	[SIGPROF]	= 27,
	[SIGWINCH]	= 28,
	[SIGIO]		= 23,
	[SIGPWR]	= 32,
	[SIGSYS]	= 12,
};

static int sig_to_gdb(unsigned sig)
{
	if (sig < ARRAY_SIZE(to_gdb_sigmap) && to_gdb_sigmap[sig])
		return to_gdb_sigmap[sig];
	return sig;

}

static int sig_from_gdb(unsigned sig)
{
	int i;

	// XXX: valid_signal() is wrong, gdb has its own idea
	// about signals. fix to_gdb_sigmap[].
	if (!sig || !valid_signal(sig))
		return 0;

	for (i = 0; i < ARRAY_SIZE(to_gdb_sigmap); i++) {
		if (to_gdb_sigmap[i] == sig)
			return i;
	}

	return sig;
}

static int ugdb_report_stopped(struct ugdb *ugdb, bool async)
{
	struct ugdb_thread *thread;
	int pid, tid, event, data;
	struct pbuf *pb;
	char ex_r;

	mutex_lock(&ugdb->u_mutex);
	thread = ugdb_next_stopped(ugdb);
	if (!thread)
		goto unlock;

	event = thread->t_stop_event;

	WARN_ON(thread_alive(thread) != (T_EV_TYPE(event) != T_EV_EXIT));

	pid = thread->t_process->p_pid;
	tid = thread->t_tid;
unlock:
	mutex_unlock(&ugdb->u_mutex);

	if (!thread)
		return false;

	pb = &ugdb->u_pbuf;

	// XXX: damn, cleanup me...
	if (async) {
		__pb_start(pb, '%');
		pb_puts(pb, "Stop:");
	} else {
		pb_start(pb);
	}

	data = T_EV_DATA(event);
	switch (T_EV_TYPE(event)) {
	case T_EV_EXIT:
		if (data & 0xff) {
			data = sig_to_gdb(data & 0xff);
			ex_r = 'X';
		} else {
			data >>= 8;
			ex_r = 'W';
		}

		pb_printf(pb, "%c%x;process:%x", ex_r, data, pid);
		ugdb_destroy_process(thread->t_process);
		break;

	case T_EV_SIGN:
	case T_EV_NONE:
		pb_printf(pb, "T%02xthread:p%x.%x;",
					sig_to_gdb(data), pid, tid);
		break;

	default:
		printk(KERN_INFO "ugdb: bad stop event %x\n", event);
	}

	pb_end(pb);

	return true;
}

const char *handle_vstopped(struct ugdb *ugdb)
{
	if (ugdb->u_stop_state != U_STOP_SENT)
		return "E01";

	if (ugdb_report_stopped(ugdb, false))
		return NULL;

	return "OK";
}

static const char *handle_thread_info(struct ugdb *ugdb, bool start)
{
	struct ugdb_thread *thread;
	int pid = 0, tid;

	mutex_lock(&ugdb->u_mutex);
	if (start)
		ugdb_reset_tinfo(ugdb);
	else if (!ugdb->u_cur_tinfo)
		printk(KERN_INFO "ugdb: unexpected qsThreadInfo\n");

	thread = ugdb_advance_tinfo(ugdb);
	if (thread) {
		pid = thread->t_process->p_pid;
		tid = thread->t_tid;
	}
	mutex_unlock(&ugdb->u_mutex);

	if (!pid)
		return start ? "E01" : "l";

	pb_packf(&ugdb->u_pbuf, "mp%x.%x", pid, tid);
	return NULL;
}

static char *parse_xid(char *str, int *ppid, bool multi)
{
	if (*str == '-') {
		str++;

		if (multi && *str++ == '1')
			*ppid = -1;
		else
			str = NULL;
	} else {
		char *cur = str;

		*ppid = simple_strtoul(cur, &str, 16);
		if (str == cur)
			str = NULL;
	}

	return str;
}

static char *parse_pid_tid(char *str, int *ppid, int *ptid, bool multi)
{
	if (*str++ != 'p')
		return NULL;

	str = parse_xid(str, ppid, multi);
	if (!str)
		return NULL;

	if (*str++ != '.')
		return NULL;

	str = parse_xid(str, ptid, multi);
	if (!str)
		return NULL;

	return str;
}

static const char *handle_set_cur(struct ugdb *ugdb, char *cmd)
{

	struct ugdb_thread **pthread;
	int pid, tid;

	switch (*cmd++) {
	case 'g':
		pthread = &ugdb->u_cur_hg;
		break;

	case 'c':
		pthread = &ugdb->u_cur_hc;
		break;

	default:
		goto err;
	}

	if (!parse_pid_tid(cmd, &pid, &tid, false))
		goto err;

	mutex_lock(&ugdb->u_mutex);
	*pthread = ugdb_find_thread(ugdb, pid, tid);
	mutex_unlock(&ugdb->u_mutex);

	if (*pthread)
		return "OK";

err:
	return "E01";
}

static const char *handle_ck_alive(struct ugdb *ugdb, char *cmd)
{
	struct ugdb_thread *thread;
	int pid = 0, tid;

	if (!parse_pid_tid(cmd, &pid, &tid, false))
		goto err;

	mutex_lock(&ugdb->u_mutex);
	thread = ugdb_find_thread(ugdb, pid, tid);
	mutex_unlock(&ugdb->u_mutex);

	if (thread)
		return "OK";

err:
	return "E01";
}

static int parse_pid(char *str)
{
	int pid;

	if (!parse_xid(str, &pid, false))
		return 0;

	return pid;
}

static const char *handle_vattach(struct ugdb *ugdb, char *cmd)
{
	int pid = parse_pid(cmd);

	if (pid && !ugdb_attach(ugdb, pid))
		return "OK";

	return "E01";
}

static const char *handle_detach(struct ugdb *ugdb, char *cmd)
{
	int pid;

	if (*cmd++ != ';')
		goto err;

	pid = parse_pid(cmd);
	if (pid && !ugdb_detach(ugdb, pid))
		return "OK";

err:
	return "E01";
}

typedef int (*each_func_t)(struct ugdb_thread *, void *);

static int ugdb_do_each_thread(struct ugdb *ugdb, int pid, int tid,
				each_func_t func, void *arg)
{
	struct ugdb_process *process;
	struct ugdb_thread *thread;
	int ret = -ESRCH;

	list_for_each_entry(process, &ugdb->u_processes, p_processes) {
		if (unlikely(!process_alive(process)))
			continue;
		if (pid > 0 && process->p_pid != pid)
			continue;

		list_for_each_entry(thread, &process->p_threads, t_threads) {
			if (WARN_ON(!thread_alive(thread)))
				continue;
			if (tid > 0 && thread->t_tid != tid)
				continue;

			ret = func(thread, arg);
			if (ret)
				goto out;

			if (tid >= 0)
				break;
		}

		if (pid >= 0)
			break;
	}

out:
	return ret;
}

static int do_stop_thread(struct ugdb_thread *thread, void *arg)
{
	ugdb_stop_thread(thread, arg != NULL);
	return 0;
}

static int do_cont_thread(struct ugdb_thread *thread, void *arg)
{
	ugdb_cont_thread(thread, arg != NULL, false);
	return 0;
}

static const char *handle_vcont(struct ugdb *ugdb, char *cmd)
{
	int pid, tid;
	void *arg;
	int ret;

	switch (*cmd ++) {
	default:
		return "E01";
	case '?':
		return "vCont;t";
	case ';':
		break;
	}

	// XXX: Discuss the generic case! currently trivial.

	if (*cmd++ != 't')
		return "E01";

	pid = tid = -1;
	if (*cmd++ == ':') {
		if (!parse_pid_tid(cmd, &pid, &tid, true))
			return "E01";
	}
	arg = (tid >= 0) ? NULL : (void*)1;

	mutex_lock(&ugdb->u_mutex);
	// XXX: currently we only report -ESRCH
	ret = ugdb_do_each_thread(ugdb, pid, tid, do_stop_thread, arg);
	mutex_unlock(&ugdb->u_mutex);

	return ret < 0 ? "E01" : "OK";
}

static int thread_cont_signal(struct ugdb_thread *thread, int signr)
{
	/*
	 * T_STOP_STOPPED was set under ->u_slock so we can't race
	 * with ugdb_add_stopped() and get the wrong t_stop_event.
	 * And, the tracee never changes it after T_STOP_STOPPED.
	 */

	switch (T_EV_TYPE(thread->t_stop_event)) {
	case T_EV_SIGN:
		WARN_ON(!T_EV_DATA(thread->t_stop_event));
		thread->t_stop_event = T_EV_SIGN | signr;
		break;

	default:
		if (!signr)
			break;

		// XXX: temporary hack, will be reported.
		// but perhaps this is what we want ???
		kill_pid(thread->t_spid, signr, 0);
		break;
	}

	return 0;
}

static const char *handle_c(struct ugdb *ugdb, char *cmd)
{
	struct ugdb_thread *thread;
	const char *rc = "E01";
	int gdbsig, signr = 0;
	bool step;

	step = (*cmd == 'S' || *cmd == 's');

	switch (*cmd++) {
	case 'C':
	case 'S':
		gdbsig = simple_strtoul(cmd, &cmd, 16);
		if (!gdbsig)
			return rc;

		signr = sig_from_gdb(gdbsig);
		if (!signr)
			printk(KERN_INFO "ugdb: sorry, can't map signal %d\n",
					gdbsig);

		if (*cmd == ';')
			++cmd;
		/* fall */

	case 'c':
	case 's':
		if (!*cmd)
			break;

		printk(KERN_INFO "ugdb: $c ADDR not implemented\n");
		return rc;

		break;
	}

	mutex_lock(&ugdb->u_mutex);
	thread = ugdb->u_cur_hc;
	if (!thread)
		goto unlock;

	/*
	 * Otherwise I do not know what to do if sig/step, and anyway
	 * I don't think gdb can try to cont a thread which was not
	 * reported as stopped.
	 */
	if (!(thread->t_stop_state & T_STOP_STOPPED))
		goto unlock;

	if (thread_cont_signal(thread, signr))
		goto unlock;

	if (ugdb_cont_thread(thread, false, step) <= 0)
		goto unlock;

	rc = "OK";
unlock:
	mutex_unlock(&ugdb->u_mutex);

	return rc;
}

static const char *handle_qpass_signals(struct ugdb *ugdb, char *cmd)
{
	sigset_t *set = &ugdb->u_sig_ign;

	sigemptyset(set);
	while (*cmd) {
		char *end;
		int sig = simple_strtoul(cmd, &end, 16);

		if (cmd == end || *end != ';')
			return "E01";
		cmd = end + 1;

		sig = sig_from_gdb(sig);
		if (!sig)
			// XXX: to_gdb_sigmap[] incomplete...
			// return "E01";
			continue;

		sigaddset(set, sig);
	}

	return "OK";
}

// -----------------------------------------------------------------------------
static struct task_struct *
ugdb_prepare_examine(struct ugdb *ugdb, struct utrace_examiner *exam)
{
	struct ugdb_thread *thread;
	struct task_struct *task;
	int err;

	mutex_lock(&ugdb->u_mutex);
	thread = ugdb->u_cur_hg;
	if (!thread || !(thread->t_stop_state & T_STOP_STOPPED))
		goto err;

	// XXX: u_cur_hg can't exit, we hold the mutex
	task = thread_to_task(thread);
	if (!task)
		goto err;

	for (;;) {
		if (fatal_signal_pending(current))
			goto err;

		err = utrace_prepare_examine(task, thread->t_engine, exam);
		if (!err)
			break;

		if (err == -ESRCH)
			goto err;

		schedule_timeout_interruptible(1);
	}

	return task;
err:
	mutex_unlock(&ugdb->u_mutex);
	return NULL;
}

// XXX: we hold the mutex in between, but only because we can't
// use get_task_struct/put_task_struct.

static int
ugdb_finish_examine(struct ugdb *ugdb, struct utrace_examiner *exam)
{
	// XXX: u_cur_hg can't exit, we hold the mutex
	struct ugdb_thread *thread = ugdb->u_cur_hg;
	struct task_struct *task = thread_to_task(thread);
	int ret = -ESRCH;

	if (task)
		ret = utrace_finish_examine(task, thread->t_engine, exam);

	mutex_unlock(&ugdb->u_mutex);
	return ret;
}

#define REGSET_GENERAL	0
// stolen from gdb-7.1/gdb/gdbserver/linux-x86-low.c
static int x86_64_regmap[] = {
	80, 40, 88, 96, 104, 112, 32, 152, 72, 64, 56, 48, 24, 16,
	8, 0, 128, 144, 136, 160, 184, 192, 200, 208, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 120,
};

static char *handle_getregs(struct ugdb *ugdb)
{
	struct utrace_examiner exam;
	struct task_struct *task;
	const struct user_regset_view *view;
	const struct user_regset *rset;
	struct user_regs_struct *pregs;
	int rn;

	static int pkt_size;
	if (!pkt_size) {
		int sz = 0;
		for (rn = 0; rn < ARRAY_SIZE(x86_64_regmap); ++rn) {
			int offs = x86_64_regmap[rn];
			if (offs < 0)
				continue;
			if (offs > (sizeof(*pregs) - sizeof(long))) {
				printk(KERN_INFO "XXX: x86_64_regmap is wrong!\n");
				ugdb->u_err = -EINVAL;
				goto err;
			}
			sz += sizeof(long) * 2;
		}
		pkt_size = sz;
	}

	if (pb_room(&ugdb->u_pbuf) < 4 + pkt_size + sizeof(*pregs)) {
		printk(KERN_INFO "XXX: getregs ENOMEM %d %ld\n",
					pkt_size, sizeof(*pregs));
		goto err;
	}

	pregs = pb_alloc_tmp(&ugdb->u_pbuf, sizeof(*pregs));
	BUG_ON(pregs + 1 != (void*)ugdb->u_pbuf.cur + BUFFER_SIZE);

	task = ugdb_prepare_examine(ugdb, &exam);
	if (!task)
		goto err;

	view = task_user_regset_view(task);
	rset = view->regsets + REGSET_GENERAL;

	rset->get(task, rset, 0, sizeof(*pregs), pregs, NULL);

	if (ugdb_finish_examine(ugdb, &exam))
		goto err;

	pb_start(&ugdb->u_pbuf);
	for (rn = 0; rn < ARRAY_SIZE(x86_64_regmap); ++rn) {
		int offs = x86_64_regmap[rn];
		if (offs >= 0)
			pb_putbs(&ugdb->u_pbuf, (void*)pregs + offs,
					sizeof(long));
	}

	WARN_ON(pb_room(&ugdb->u_pbuf) < sizeof(*pregs));
	pb_end(&ugdb->u_pbuf);
	return NULL;
err:
	return "E01";
}

static const char *handle_setregs(struct ugdb *ugdb, char *cmd)
{
	printk(KERN_INFO "ugdb: unexpected $G packet.\n");
	return "";
}

static const char *handle_set_one_reg(struct ugdb *ugdb, char *cmd)
{
	unsigned int reg;
	long val;
	struct utrace_examiner exam;
	struct task_struct *task;

	if (sscanf(cmd, "%x=%lx", &reg, &val) != 2)
		goto err;

	if (reg != 0x10 && reg != 0x39) {
		printk(KERN_INFO "ugdb: unknown reg %x\n", reg);
		goto err;
	}

	// XXX: Hmm.
	val = be64_to_cpu(val);

	// DO NOT LOOK AT THIS TEMPORARY CODE
	task = ugdb_prepare_examine(ugdb, &exam);
	if (!task)
		goto err;

	if (reg == 0x10)
		task_pt_regs(task)->ip = val;
	else if (reg == 0x39)
		task_pt_regs(task)->orig_ax = val;

	ugdb_finish_examine(ugdb, &exam);

	return "OK";
err:
	return "E01";
}

static typeof(access_process_vm) *u_access_process_vm;

static const char *handle_readmem(struct ugdb *ugdb, char *cmd)
{
	struct utrace_examiner exam;
	struct task_struct *task;
	unsigned long addr, size;
	unsigned char *mbuf;
	int copied;

	if (sscanf(cmd, "m%lx,%lx", &addr, &size) != 2)
		goto err;

	mbuf = pb_alloc_bs(&ugdb->u_pbuf, size);
	if (!mbuf) {
		printk(KERN_INFO "XXX: apvm(%ld) ENOMEM\n", size);
		goto err;
	}

	task = ugdb_prepare_examine(ugdb, &exam);
	if (!task)
		goto err;

	copied = u_access_process_vm(task, addr, mbuf, size, 0);

	if (ugdb_finish_examine(ugdb, &exam))
		goto err;

	if (copied > 0 ) {
		pb_start(&ugdb->u_pbuf);
		pb_putbs(&ugdb->u_pbuf, mbuf, size);
		pb_end(&ugdb->u_pbuf);

		return NULL;
	}
err:
	return "E01";
}

// XXX: hex_to_bin() after 90378889 commit
#include <linux/ctype.h>
static int cap_hex_to_bin(char ch)
{
	if ((ch >= '0') && (ch <= '9'))
		return ch - '0';
	ch = tolower(ch);
	if ((ch >= 'a') && (ch <= 'f'))
		return ch - 'a' + 10;
	return -1;
}

static int unhex(char *cmd, int size)
{
	char *bytes = cmd;

	while (size--) {
		int lo, hi;

		hi = cap_hex_to_bin(*cmd++);
		lo = cap_hex_to_bin(*cmd++);
		if (lo < 0 || hi < 0)
			return -EINVAL;

		*bytes++ = (hi << 4) | lo;
	}

	return 0;
}

static const char *handle_writemem(struct ugdb *ugdb, char *cmd, int len)
{
	unsigned long addr, size;
	unsigned int skip, written;
	struct utrace_examiner exam;
	struct task_struct *task;

	if (sscanf(cmd, "M%lx,%lx:%n", &addr, &size, &skip) != 2)
		goto err;

	cmd += skip;
	len -= skip;
	if (len != 2*size || !size)
		goto err;

	if (unhex(cmd, size))
		goto err;

	task = ugdb_prepare_examine(ugdb, &exam);
	if (!task)
		goto err;

	written = u_access_process_vm(task, addr, cmd, size, 1);

	if (ugdb_finish_examine(ugdb, &exam))
		goto err;

	if (written == size)
		return "OK";
err:
	return "E01";
}

static int ugdb_siginfo_rw(struct ugdb *ugdb, siginfo_t *info, bool write)
{
	struct task_struct *task;
	struct utrace_examiner exam;
	struct sighand_struct *sighand;
	siginfo_t *t_siginfo;
	int ret = -EINVAL;

	/*
	 * ugdb_prepare_examine() is overkill, but otherwise we can't
	 * assume task_is_traced(), and this is what ensures we can
	 * safely read/write ->t_siginfo which points to task's stack.
	 */
	task = ugdb_prepare_examine(ugdb, &exam);
	if (!task)
		goto out;

	/* OK, task_struct can't go away, but ->sighand can. */
	rcu_read_lock();
	sighand = rcu_dereference(task->sighand);
	if (!sighand)
		goto unlock_rcu;

	spin_lock_irq(&sighand->siglock);
	if (!task_is_traced(task))
		goto unlock_siglock;

	t_siginfo = ugdb->u_cur_hg->t_siginfo;
	if (!t_siginfo)
		goto unlock_siglock;

	if (write)
		*t_siginfo = *info;
	else
		*info = *t_siginfo;

	ret = 0;
unlock_siglock:
	spin_unlock_irq(&sighand->siglock);
unlock_rcu:
	rcu_read_unlock();

	ugdb_finish_examine(ugdb, &exam);
out:
	return ret;
}

static const char *handle_siginfo_read(struct ugdb *ugdb, char *cmd)
{
	unsigned int off, len;
	siginfo_t info;

	if (sscanf(cmd, "%x,%x", &off, &len) != 2)
		goto err;

	if (off >= sizeof(info))
		goto err;

	if (len > sizeof(info) || off + len > sizeof(info))
		len = sizeof(info) - off;

	if (ugdb_siginfo_rw(ugdb, &info, false))
		goto err;

	if (pb_qfer(&ugdb->u_pbuf, &info + off, len,
				(off + len < sizeof(info))))
		goto err;

	// XXX: Oh. we also need x86_siginfo_fixup(). how ugly.

	return NULL;
err:
	return "E01";
}

// -----------------------------------------------------------------------------
#define EQ(cmd, str)					\
	(strncmp((cmd), (str), sizeof(str)-1) ?	false :	\
		((cmd) += sizeof(str)-1, true))

static const char *handle_qfer(struct ugdb *ugdb, char *cmd)
{
	const char *rc = "E01";

	if (EQ(cmd, "siginfo:")) {
		if (EQ(cmd, "read::"))
			rc = handle_siginfo_read(ugdb, cmd);
	}

	return rc;
}

static void handle_command(struct ugdb *ugdb, char *cmd, int len)
{
	struct pbuf *pb = &ugdb->u_pbuf;
	const char *rc = "";

	switch (cmd[0]) {
	case '!':
	case '?':
		rc = "OK";
		break;

	case 'H':
		rc = handle_set_cur(ugdb, cmd + 1);
		break;

	case 'T':
		rc = handle_ck_alive(ugdb, cmd + 1);
		break;

	case 'D':
		rc = handle_detach(ugdb, cmd + 1);
		break;

	case 'g':
		rc = handle_getregs(ugdb);
		break;

	case 'G':
		rc = handle_setregs(ugdb, cmd + 1);
		break;

	case 'P':
		rc = handle_set_one_reg(ugdb, cmd + 1);
		break;

	case 'm':
		rc = handle_readmem(ugdb, cmd);
		break;

	case 'M':
		rc = handle_writemem(ugdb, cmd, len);
		break;

	case 'C':
	case 'c':
	case 'S':
	case 's':
		rc = handle_c(ugdb, cmd);
		break;

	case 'q':
		if (EQ(cmd, "qSupported")) {
			if (!strstr(cmd, "multiprocess+")) {
				printk(KERN_INFO "ugdb: can't work without multiprocess\n");
				ugdb->u_err = -EPROTONOSUPPORT;
			}

			pb_packf(&ugdb->u_pbuf, "PacketSize=%x;%s",
				PACKET_SIZE,
				"QStartNoAckMode+;QNonStop+;multiprocess+;"
				"QPassSignals+;qXfer:siginfo:read+");
			rc = NULL;
		}
		else if (EQ(cmd, "qfThreadInfo")) {
			rc = handle_thread_info(ugdb, true);
		}
		else if (EQ(cmd, "qsThreadInfo")) {
			rc = handle_thread_info(ugdb, false);
		}
		else if (EQ(cmd, "qXfer:")) {
			rc = handle_qfer(ugdb, cmd);
		}
		else if (EQ(cmd, "qTStatus")) {
			rc = "T0";
		}

		break;

	case 'Q':
		if (EQ(cmd, "QStartNoAckMode")) {
			ugdb->u_no_ack = true;
			rc = "OK";
		}
		else if (EQ(cmd, "QNonStop:")) {
			if (*cmd != '1') {
				printk(KERN_INFO "ugdb: all-stop is not implemented.\n");
				ugdb->u_err = -EPROTONOSUPPORT;
			}

			rc = "OK";
		}
		else if (EQ(cmd, "QPassSignals:")) {
			rc = handle_qpass_signals(ugdb, cmd);
		}

		break;

	case 'v':
		if (EQ(cmd, "vAttach;")) {
			rc = handle_vattach(ugdb, cmd);
		}
		else if (EQ(cmd, "vStopped")) {
			rc = handle_vstopped(ugdb);
		}
		else if (EQ(cmd, "vCont")) {
			rc = handle_vcont(ugdb, cmd);
		}

		break;

	default:
		;
	}

	if (rc)
		pb_packs(pb, rc);
}

static void process_commands(struct ugdb *ugdb)
{
	char *cmds = ugdb->u_cbuf;
	int todo = ugdb->u_clen;

	if (o_remote_debug)
		printk(KERN_INFO "=> %.*s\n", ugdb->u_clen, ugdb->u_cbuf);

	while (todo) {
		char first;
		char *c_cmd, *c_end;
		int c_len;

		first = *cmds++;
		todo--;

		switch (first) {
		default:
			printk(KERN_INFO "XXX: unknown chr %02x\n", first);
			pb_putc(&ugdb->u_pbuf, '-');
			break;

		case '-':
			printk(KERN_INFO "XXX: got NACK!\n");
			ugdb->u_err = -EPROTO;
		case '+':
			break;

		case 0x3:
			printk(KERN_INFO "XXX: unexpected CTRL-C\n");
			break;

		case '$':
			c_cmd = cmds;
			c_end = strnchr(c_cmd, todo, '#');
			c_len = c_end ? c_end - cmds : -1;

			if (c_len < 0 || todo < c_len + 3) {
				printk(KERN_INFO "XXX: can't find '#cs'\n");
				++todo;
				--cmds;
				goto out;
			}

			// XXX: verify checksum ?
			todo -= c_len + 3;
			cmds += c_len + 3;
			*c_end = 0;

			if (!ugdb->u_no_ack)
				pb_putc(&ugdb->u_pbuf, '+');

			handle_command(ugdb, c_cmd, c_len);
		}
	}
out:
	ugdb->u_clen = todo;
	if (todo && cmds > ugdb->u_cbuf)
		memmove(ugdb->u_cbuf, cmds, todo);
}

// -----------------------------------------------------------------------------
static int xxx_tinfo(struct ugdb *ugdb)
{
	struct ugdb_thread *thread;
	int tid = 0;

	mutex_lock(&ugdb->u_mutex);
	thread = ugdb_advance_tinfo(ugdb);
	if (thread)
		tid = thread->t_tid;
	mutex_unlock(&ugdb->u_mutex);

	return tid;
}

static int xxx_sc_threads(struct ugdb *ugdb, int tid, bool sc)
{
	void *arg = NULL;
	int pid = 0;
	int ret;

	if (tid < 0) {
		pid = -tid;
		tid = -1;
		arg = (void*)1;
	}

	mutex_lock(&ugdb->u_mutex);
	ret = ugdb_do_each_thread(ugdb, pid, tid,
				sc ? do_stop_thread : do_cont_thread,
				arg);
	mutex_unlock(&ugdb->u_mutex);

	return ret;
}

static int xxx_stop(struct ugdb *ugdb, int tid)
{
	return xxx_sc_threads(ugdb, tid, true);
}

static int xxx_cont(struct ugdb *ugdb, int tid)
{
	return xxx_sc_threads(ugdb, tid, false);
}

static int xxx_get_stopped(struct ugdb *ugdb)
{
	struct ugdb_thread *thread;
	int tid = 1;

	if (ugdb->u_stop_state == U_STOP_IDLE)
		return -1;

	if (ugdb->u_stop_state == U_STOP_PENDING)
		tid = 1000;

	thread = ugdb_next_stopped(ugdb);
	if (!thread)
		return 0;
	return tid * thread->t_tid;
}

static int xxx_show_all(struct ugdb *ugdb)
{
	struct ugdb_process *process;
	struct ugdb_thread *thread;

	printk(KERN_INFO "SHOW start ----------------------------------------\n");

	mutex_lock(&ugdb->u_mutex);
	list_for_each_entry(process, &ugdb->u_processes, p_processes) {
		printk(KERN_INFO "PROC: %x\n", process->p_pid);

		list_for_each_entry(thread, &process->p_threads, t_threads) {
			printk(KERN_INFO "    T: %x %p; %p %p\n",
					thread->t_tid, thread,
					thread->t_spid, pid_task(thread->t_spid, PIDTYPE_PID));
		}

	}
	mutex_unlock(&ugdb->u_mutex);

	printk(KERN_INFO "SHOW end ----------------------------------------\n");
	return 0;
}

static long ugdb_f_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct ugdb *ugdb = file->private_data;
	// XXX: otherwise gdb->get_tty_state(TCGETS, TCSETS, TCFLSH) complains
	int ret = 0;

	// XXX: temporary debugging hooks, ignore.
	switch (cmd) {
		case 0x666 + 0:
			ret = ugdb_attach(ugdb, arg);
			break;

		case 0x666 + 1:
			ret = ugdb_detach(ugdb, arg);
			break;

		case 0x666 + 2:
			ret = xxx_tinfo(ugdb);
			break;

		case 0x666 + 3:
			ret = xxx_stop(ugdb, arg);
			break;

		case 0x666 + 4:
			ret = xxx_cont(ugdb, arg);
			break;

		case 0x666 + 5:
			ret = xxx_get_stopped(ugdb);
			break;

		case 0x666 + 6:
			ret = xxx_show_all(ugdb);
			break;
	}

	return ret;
}

static unsigned int ugdb_f_poll(struct file *file, poll_table *wait)
{
	struct ugdb *ugdb = file->private_data;
	unsigned int mask;

	poll_wait(file, &ugdb->u_wait, wait);

	mask = (POLLOUT | POLLWRNORM);

	if (pb_size(&ugdb->u_pbuf) || ugdb->u_stop_state == U_STOP_PENDING)
		mask |= (POLLIN | POLLRDNORM);

	if (ugdb->u_err)
		mask |= POLLERR;

	return mask;
}

static ssize_t ugdb_f_read(struct file *file, char __user *ubuf,
				size_t count, loff_t *ppos)
{
	struct ugdb *ugdb = file->private_data;
	struct pbuf *pb = &ugdb->u_pbuf;

	if (ugdb->u_err)
		return ugdb->u_err;

	if (ugdb->u_stop_state == U_STOP_PENDING)
		ugdb_report_stopped(ugdb, true);

	if (pb_size(pb) > count) {
		printk(KERN_INFO "XXX: short read %d %ld\n",
					pb_size(pb), count);
	}

	return pb_copy_to_user(pb, ubuf, count);
}

static ssize_t ugdb_f_write(struct file *file, const char __user *ubuf,
				size_t count, loff_t *ppos)
{
	struct ugdb *ugdb = file->private_data;

	if (ugdb->u_err)
		return ugdb->u_err;

	if (count > PACKET_SIZE - ugdb->u_clen) {
		count = PACKET_SIZE - ugdb->u_clen;
		printk("XXX: write(%ld,%d) enospc\n", count, ugdb->u_clen);
	}

	if (copy_from_user(ugdb->u_cbuf + ugdb->u_clen, ubuf, count))
		return -EFAULT;

	ugdb->u_clen += count;
	process_commands(ugdb);

	return count;
}

static int ugdb_f_open(struct inode *inode, struct file *file)
{
	nonseekable_open(inode, file);

	file->private_data = ugdb_create();

	return	IS_ERR(file->private_data) ?
		PTR_ERR(file->private_data) : 0;
}

static int ugdb_f_release(struct inode *inode, struct file *file)
{
	ugdb_destroy(file->private_data);

	return 0;
}

static const struct file_operations ugdb_f_ops = {
	.open			= ugdb_f_open,
	.unlocked_ioctl		= ugdb_f_ioctl,
	.poll			= ugdb_f_poll,
	.read			= ugdb_f_read,
	.write			= ugdb_f_write,
	.release		= ugdb_f_release,
};

#include <linux/kallsyms.h>

struct kallsyms_sym {
	const char	*name;
	unsigned long	addr;
};

static int kallsyms_on_each_symbol_cb(void *data, const char *name,
				struct module *mod, unsigned long addr)
{
	struct kallsyms_sym *sym = data;

	if (strcmp(name, sym->name))
		return 0;

	sym->addr = addr;
	return 1;
}

// XXX: kallsyms_lookup_name() is not exported in 2.6.32
static bool lookup_unexported(void)
{
	struct kallsyms_sym sym;

	sym.name = "access_process_vm";
	if (!kallsyms_on_each_symbol(kallsyms_on_each_symbol_cb, &sym))
		goto err;
	u_access_process_vm = (void*)sym.addr;

	return true;
err:
	printk(KERN_ERR "ugdb: can't lookup %s\n", sym.name);
	return false;
}

#define PROC_NAME	"ugdb"
struct proc_dir_entry *ugdb_pde;

static int __init ugdb_init(void)
{
	if (!lookup_unexported())
		return -ESRCH;

	ugdb_pde = proc_create(PROC_NAME, S_IFREG|S_IRUGO|S_IWUGO,
				NULL, &ugdb_f_ops);
	if (!ugdb_pde)
		return -EBADF;

	return 0;
}

static void __exit ugdb_exit(void)
{
	remove_proc_entry(PROC_NAME, NULL);
}

MODULE_LICENSE("GPL");
module_init(ugdb_init);
module_exit(ugdb_exit);

Re: gdbstub initial code, v11

[Tom Tromey]

Oleg> But what about features? What should I do next? all-stop,
Oleg> thread-specific breakpoints (currently I have no idea what
Oleg> this means), or what?

I think it would be good to implement a feature that shows how this
approach is an improvement over the current state of gdb+ptrace or
gdb+gdbserver.

Exactly what feature this should be... I don't know :-)
I would imagine something performance-related.

There was previously some discussion about some watchpoint-related
thing, I forget the details of that.

I don't think thread-specific breakpoints are exposed outside of gdb
yet.  If that is true, then implementing that would mean adding remote
protocol features and also other stuff inside gdb.  So, I would suggest
not tackling this yet.

Tom

Re: gdbstub initial code, v11

[Jan Kratochvil]

On Wed, 22 Sep 2010 21:09:12 +0200, Tom Tromey wrote:
> I think it would be good to implement a feature that shows how this
> approach is an improvement over the current state of gdb+ptrace or
> gdb+gdbserver.
> 
> Exactly what feature this should be... I don't know :-)
> I would imagine something performance-related.

I would bet on a massive threads creating/deleting testcase signalling tasks
around, together with watchpoints.  There are races in the linux-nat code and
IIRC even gdbserver code.

OTOH if one tries hard one can probably manage one day to fix all the corner
cases in the ptrace based linux-nat and gdbserver.


Regards,
Jan

Re: gdbstub initial code, v11

[Frank Ch. Eigler]

 
oleg wrote:

> [...]  Honestly, I don't really know how do the "right thing" here.
> Anyway, most probably this code will be changed. Like ptrace, ugdb
> uses ->report_syscall_exit() to synthesize a trap. Unlike ptrace,
> ugdb_report_signal() doesn't send SIGTRAP to itself but reports
> SIGTRAP using siginfo_t we have. In any case, whatever we do,
> multiple tracers can confuse each other.

(It seems to me that a pure gdb report, without a synthetic
self-injected SIGTRAP, should be fine.)

> Next: fully implement g/G/p/P, currently I am a bit confused...
> But what about features? [...]

You could dig out the old "fishing plan".  One demonstrated
improvement was from simulating (software) watchpoints within the
gdb stub, instead of having gdb fall back to issing countless
single-steps with memory-fetch inquiries in between.

- FChE

Re: gdbstub initial code, v11

[Oleg Nesterov]

On 09/22, Frank Ch. Eigler wrote:
>
> oleg wrote:
>
> > [...]  Honestly, I don't really know how do the "right thing" here.
> > Anyway, most probably this code will be changed. Like ptrace, ugdb
> > uses ->report_syscall_exit() to synthesize a trap. Unlike ptrace,
> > ugdb_report_signal() doesn't send SIGTRAP to itself but reports
> > SIGTRAP using siginfo_t we have. In any case, whatever we do,
> > multiple tracers can confuse each other.
>
> (It seems to me that a pure gdb report, without a synthetic
> self-injected SIGTRAP, should be fine.)

What do you mean?

> > Next: fully implement g/G/p/P, currently I am a bit confused...
> > But what about features? [...]
>
> You could dig out the old "fishing plan".  One demonstrated
> improvement was from simulating (software) watchpoints within the
> gdb stub, instead of having gdb fall back to issing countless
> single-steps with memory-fetch inquiries in between.

When I do 'watch', gdb sends '$Z2'. I am a bit confused, iirc it
was decided I shouldn't play with Z packets now. But I won't
argue.

Oleg.

Re: gdbstub initial code, v11

[Frank Ch. Eigler]

Hi -

On Thu, Sep 23, 2010 at 01:14:51AM +0200, Oleg Nesterov wrote:
> > (It seems to me that a pure gdb report, without a synthetic
> > self-injected SIGTRAP, should be fine.)
> 
> What do you mean?

(Never mind, I'm probably just confused about what you were asking.)


> > > Next: fully implement g/G/p/P, currently I am a bit confused...
> > > But what about features? [...]
> >
> > You could dig out the old "fishing plan".  One demonstrated
> > improvement was from simulating (software) watchpoints within the
> > gdb stub, instead of having gdb fall back to issing countless
> > single-steps with memory-fetch inquiries in between.
> 
> When I do 'watch', gdb sends '$Z2'. I am a bit confused, iirc it
> was decided I shouldn't play with Z packets now. But I won't
> argue.

There are Z packets and then there are Z packets.  The ones Roland
told you not to worry about are Z0/Z1 related to (code) breakpoints,
which should be implemented via uprobes at some point.

The ones I'm talking about are Z2/Z3 for (data) watchpoints.

- FChE

Re: gdbstub initial code, v11

[Oleg Nesterov]

On 09/22, Frank Ch. Eigler wrote:
>
> On Thu, Sep 23, 2010 at 01:14:51AM +0200, Oleg Nesterov wrote:
> >
> > When I do 'watch', gdb sends '$Z2'. I am a bit confused, iirc it
> > was decided I shouldn't play with Z packets now. But I won't
> > argue.
>
> There are Z packets and then there are Z packets.  The ones Roland
> told you not to worry about are Z0/Z1 related to (code) breakpoints,
> which should be implemented via uprobes at some point.
>
> The ones I'm talking about are Z2/Z3 for (data) watchpoints.

Ah, OK, thanks. I'll try to understand how this works.

Oleg.

Re: gdbstub initial code, v11

[Roland McGrath]

> > The ones I'm talking about are Z2/Z3 for (data) watchpoints.
> 
> Ah, OK, thanks. I'll try to understand how this works.

In theory these will map to uses of the hw_breakpoint interface.


Thanks,
Roland

Re: gdbstub initial code, v11

[Roland McGrath]

> I think it would be good to implement a feature that shows how this
> approach is an improvement over the current state of gdb+ptrace or
> gdb+gdbserver.
> 
> Exactly what feature this should be... I don't know :-)
> I would imagine something performance-related.

My vague notion was that we'd get it working well enough to have basic
parity with native or gdbserver on some realish test cases, and then just
look at the protocol interaction log to see cases where we could reduce
round-trips between gdb and the stub.  Some of those are bound to entail
protocol extensions and gdb changes to exploit them.  Off hand, the Z cases
might be the only things that won't need that.


Thanks,
Roland

Re: gdbstub initial code, v11

[Frank Ch. Eigler]

Hi -

On Thu, Sep 23, 2010 at 02:21:38PM -0700, Roland McGrath wrote:
> > > The ones I'm talking about are Z2/Z3 for (data) watchpoints.
> > Ah, OK, thanks. I'll try to understand how this works.
> 
> In theory these will map to uses of the hw_breakpoint interface.

Not quite.  The hw_breakpoint widget is only useful for the first few
active watchpoints.  The rest, which gdb calls software watchpoints,
can be implemented in ugdb by local singlestep + polling, without
gdb's live involvement.

- FChE