source: mainline/kernel/generic/src/udebug/udebug.c@ 0dd0f71f

/*
 * Copyright (c) 2008 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup generic
 * @{
 */

/**
 * @file
 * @brief       Udebug hooks and data structure management.
 *
 * Udebug is an interface that makes userspace debuggers possible.
 *
 * Functions in this file are executed directly in each thread, which
 * may or may not be the subject of debugging. The udebug_stoppable_begin/end()
 * functions are also executed in the clock interrupt handler. To avoid
 * deadlock, functions in this file are protected from the interrupt
 * by locking the recursive lock THREAD->udebug.int_lock (just an atomic
 * variable). This prevents udebug_stoppable_begin/end() from being
 * executed in the interrupt handler (they are skipped).
 *
 * Functions in udebug_ops.c and udebug_ipc.c execute in different threads,
 * so they needn't be protected from the (preemptible) interrupt-initiated
 * code.
 */
 
#include <synch/waitq.h>
#include <debug.h>
#include <udebug/udebug.h>
#include <errno.h>
#include <arch.h>

static inline void udebug_int_lock(void)
{
        atomic_inc(&THREAD->udebug.int_lock);
}

static inline void udebug_int_unlock(void)
{
        atomic_dec(&THREAD->udebug.int_lock);
}

/** Initialize udebug part of task structure.
 *
 * Called as part of task structure initialization.
 * @param ut    Pointer to the structure to initialize.
 */
void udebug_task_init(udebug_task_t *ut)
{
        mutex_initialize(&ut->lock, MUTEX_PASSIVE);
        ut->dt_state = UDEBUG_TS_INACTIVE;
        ut->begin_call = NULL;
        ut->not_stoppable_count = 0;
        ut->evmask = 0;
}

/** Initialize udebug part of thread structure.
 *
 * Called as part of thread structure initialization.
 * @param ut    Pointer to the structure to initialize.
 */
void udebug_thread_initialize(udebug_thread_t *ut)
{
        mutex_initialize(&ut->lock, MUTEX_PASSIVE);
        waitq_initialize(&ut->go_wq);

        /*
         * At the beginning the thread is stoppable, so int_lock be set, too.
         */
        atomic_set(&ut->int_lock, 1);

        ut->go_call = NULL;
        ut->stop = true;
        ut->stoppable = true;
        ut->debug_active = false;
        ut->cur_event = 0; /* none */
}

/** Wait for a GO message.
 *
 * When a debugging event occurs in a thread or the thread is stopped,
 * this function is called to block the thread until a GO message
 * is received.
 *
 * @param wq    The wait queue used by the thread to wait for GO messages.
 */
static void udebug_wait_for_go(waitq_t *wq)
{
        int rc;
        ipl_t ipl;

        ipl = waitq_sleep_prepare(wq);

        wq->missed_wakeups = 0; /* Enforce blocking. */
        rc = waitq_sleep_timeout_unsafe(wq, SYNCH_NO_TIMEOUT, SYNCH_FLAGS_NONE);

        waitq_sleep_finish(wq, rc, ipl);
}

/** Do a preliminary check that a debugging session is in progress.
 * 
 * This only requires the THREAD->udebug.lock mutex (and not TASK->udebug.lock
 * mutex). For an undebugged task, this will never block (while there could be
 * collisions by different threads on the TASK mutex), thus improving SMP
 * perormance for undebugged tasks.
 *
 * @return      True if the thread was in a debugging session when the function
 *              checked, false otherwise.
 */
static bool udebug_thread_precheck(void)
{
        bool res;

        mutex_lock(&THREAD->udebug.lock);
        res = THREAD->udebug.debug_active;
        mutex_unlock(&THREAD->udebug.lock);

        return res;
}

/** Start of stoppable section.
 *
 * A stoppable section is a section of code where if the thread can be stoped. In other words,
 * if a STOP operation is issued, the thread is guaranteed not to execute
 * any userspace instructions until the thread is resumed.
 *
 * Having stoppable sections is better than having stopping points, since
 * a thread can be stopped even when it is blocked indefinitely in a system
 * call (whereas it would not reach any stopping point).
 */
void udebug_stoppable_begin(void)
{
        int nsc;
        call_t *db_call, *go_call;

        ASSERT(THREAD);
        ASSERT(TASK);

        udebug_int_lock();

        /* Early check for undebugged tasks */
        if (!udebug_thread_precheck()) {
                udebug_int_unlock();
                return;
        }

        mutex_lock(&TASK->udebug.lock);

        nsc = --TASK->udebug.not_stoppable_count;

        /* Lock order OK, THREAD->udebug.lock is after TASK->udebug.lock */
        mutex_lock(&THREAD->udebug.lock);
        ASSERT(THREAD->udebug.stoppable == false);
        THREAD->udebug.stoppable = true;

        if (TASK->udebug.dt_state == UDEBUG_TS_BEGINNING && nsc == 0) {
                /*
                 * This was the last non-stoppable thread. Reply to
                 * DEBUG_BEGIN call.
                 */

                db_call = TASK->udebug.begin_call;
                ASSERT(db_call);

                TASK->udebug.dt_state = UDEBUG_TS_ACTIVE;
                TASK->udebug.begin_call = NULL;

                IPC_SET_RETVAL(db_call->data, 0);
                ipc_answer(&TASK->answerbox, db_call);          

        } else if (TASK->udebug.dt_state == UDEBUG_TS_ACTIVE) {
                /*
                 * Active debugging session
                 */

                if (THREAD->udebug.debug_active && THREAD->udebug.stop) {
                        /*
                         * Thread was requested to stop - answer go call
                         */

                        /* Make sure nobody takes this call away from us */
                        go_call = THREAD->udebug.go_call;
                        THREAD->udebug.go_call = NULL;
                        ASSERT(go_call);

                        IPC_SET_RETVAL(go_call->data, 0);
                        IPC_SET_ARG1(go_call->data, UDEBUG_EVENT_STOP);

                        THREAD->udebug.cur_event = UDEBUG_EVENT_STOP;

                        ipc_answer(&TASK->answerbox, go_call);
                }
        }

        mutex_unlock(&THREAD->udebug.lock);
        mutex_unlock(&TASK->udebug.lock);
}

/** End of a stoppable section.
 *
 * This is the point where the thread will block if it is stopped.
 * (As, by definition, a stopped thread must not leave its stoppable section).
 */
void udebug_stoppable_end(void)
{
        /* Early check for undebugged tasks */
        if (!udebug_thread_precheck()) {
                udebug_int_unlock();
                return;
        }

restart:
        mutex_lock(&TASK->udebug.lock);
        mutex_lock(&THREAD->udebug.lock);

        if (THREAD->udebug.debug_active &&
            THREAD->udebug.stop == true) {
                TASK->udebug.begin_call = NULL;
                mutex_unlock(&THREAD->udebug.lock);
                mutex_unlock(&TASK->udebug.lock);

                udebug_wait_for_go(&THREAD->udebug.go_wq);

                goto restart;
                /* must try again - have to lose stoppability atomically */
        } else {
                ++TASK->udebug.not_stoppable_count;
                ASSERT(THREAD->udebug.stoppable == true);
                THREAD->udebug.stoppable = false;

                mutex_unlock(&THREAD->udebug.lock);
                mutex_unlock(&TASK->udebug.lock);
        }

        udebug_int_unlock();
}

/** Upon being scheduled to run, check if the current thread should stop.
 *
 * This function is called from clock(). Preemption is enabled.
 * interrupts are disabled, but since this is called after
 * being scheduled-in, we can enable them, if we're careful enough
 * not to allow arbitrary recursion or deadlock with the thread context.
 */
void udebug_before_thread_runs(void)
{
        ipl_t ipl;

        return;
        ASSERT(!PREEMPTION_DISABLED);

        /* 
         * Prevent agains re-entering, such as when preempted inside this
         * function.
         */
        if (atomic_get(&THREAD->udebug.int_lock) != 0)
                return;

        udebug_int_lock();

        ipl = interrupts_enable();

        /* Now we're free to do whatever we need (lock mutexes, sleep, etc.) */

        /* Check if we're supposed to stop */
        udebug_stoppable_begin();
        udebug_stoppable_end();

        interrupts_restore(ipl);

        udebug_int_unlock();
}

/** Syscall event hook.
 *
 * Must be called before and after servicing a system call. This generates
 * a SYSCALL_B or SYSCALL_E event, depending on the value of @a end_variant.
 */
void udebug_syscall_event(unative_t a1, unative_t a2, unative_t a3,
    unative_t a4, unative_t a5, unative_t a6, unative_t id, unative_t rc,
    bool end_variant)
{
        call_t *call;
        udebug_event_t etype;

        etype = end_variant ? UDEBUG_EVENT_SYSCALL_E : UDEBUG_EVENT_SYSCALL_B;

        udebug_int_lock();

        /* Early check for undebugged tasks */
        if (!udebug_thread_precheck()) {
                udebug_int_unlock();
                return;
        }

        mutex_lock(&TASK->udebug.lock);
        mutex_lock(&THREAD->udebug.lock);

        /* Must only generate events when in debugging session and have go */
        if (THREAD->udebug.debug_active != true ||
            THREAD->udebug.stop == true ||
            (TASK->udebug.evmask & UDEBUG_EVMASK(etype)) == 0) {
                mutex_unlock(&THREAD->udebug.lock);
                mutex_unlock(&TASK->udebug.lock);
                return;
        }

        //printf("udebug_syscall_event\n");
        call = THREAD->udebug.go_call;
        THREAD->udebug.go_call = NULL;

        IPC_SET_RETVAL(call->data, 0);
        IPC_SET_ARG1(call->data, etype);
        IPC_SET_ARG2(call->data, id);
        IPC_SET_ARG3(call->data, rc);
        //printf("udebug_syscall_event/ipc_answer\n");

        THREAD->udebug.syscall_args[0] = a1;
        THREAD->udebug.syscall_args[1] = a2;
        THREAD->udebug.syscall_args[2] = a3;
        THREAD->udebug.syscall_args[3] = a4;
        THREAD->udebug.syscall_args[4] = a5;
        THREAD->udebug.syscall_args[5] = a6;

        /*
         * Make sure udebug.stop is true when going to sleep
         * in case we get woken up by DEBUG_END. (At which
         * point it must be back to the initial true value).
         */
        THREAD->udebug.stop = true;
        THREAD->udebug.cur_event = etype;

        ipc_answer(&TASK->answerbox, call);

        mutex_unlock(&THREAD->udebug.lock);
        mutex_unlock(&TASK->udebug.lock);

        udebug_wait_for_go(&THREAD->udebug.go_wq);

        udebug_int_unlock();
}

/** Thread-creation event hook.
 *
 * Must be called when a new userspace thread is created in the debugged
 * task. Generates a THREAD_B event.
 *
 * @param t     Structure of the thread being created. Not locked, as the
 *              thread is not executing yet.
 */
void udebug_thread_b_event(struct thread *t)
{
        call_t *call;

        udebug_int_lock();

        mutex_lock(&TASK->udebug.lock);
        mutex_lock(&THREAD->udebug.lock);

        LOG("udebug_thread_b_event\n");
        LOG("- check state\n");

        /* Must only generate events when in debugging session */
        if (THREAD->udebug.debug_active != true) {
                LOG("- debug_active: %s, udebug.stop: %s\n",
                        THREAD->udebug.debug_active ? "yes(+)" : "no(-)",
                        THREAD->udebug.stop ? "yes(-)" : "no(+)");
                mutex_unlock(&THREAD->udebug.lock);
                mutex_unlock(&TASK->udebug.lock);
                return;
        }

        LOG("- trigger event\n");

        call = THREAD->udebug.go_call;
        THREAD->udebug.go_call = NULL;
        IPC_SET_RETVAL(call->data, 0);
        IPC_SET_ARG1(call->data, UDEBUG_EVENT_THREAD_B);
        IPC_SET_ARG2(call->data, (unative_t)t);

        /*
         * Make sure udebug.stop is true when going to sleep
         * in case we get woken up by DEBUG_END. (At which
         * point it must be back to the initial true value).
         */
        THREAD->udebug.stop = true;
        THREAD->udebug.cur_event = UDEBUG_EVENT_THREAD_B;

        ipc_answer(&TASK->answerbox, call);

        mutex_unlock(&THREAD->udebug.lock);
        mutex_unlock(&TASK->udebug.lock);

        LOG("- sleep\n");
        udebug_wait_for_go(&THREAD->udebug.go_wq);

        udebug_int_unlock();
}

/** Thread-termination event hook.
 *
 * Must be called when the current thread is terminating.
 * Generates a THREAD_E event.
 */
void udebug_thread_e_event(void)
{
        call_t *call;

        udebug_int_lock();

        mutex_lock(&TASK->udebug.lock);
        mutex_lock(&THREAD->udebug.lock);

        LOG("udebug_thread_e_event\n");
        LOG("- check state\n");

        /* Must only generate events when in debugging session */
        if (THREAD->udebug.debug_active != true) {
/*              printf("- debug_active: %s, udebug.stop: %s\n",
                        THREAD->udebug.debug_active ? "yes(+)" : "no(-)",
                        THREAD->udebug.stop ? "yes(-)" : "no(+)");*/
                mutex_unlock(&THREAD->udebug.lock);
                mutex_unlock(&TASK->udebug.lock);
                return;
        }

        LOG("- trigger event\n");

        call = THREAD->udebug.go_call;
        THREAD->udebug.go_call = NULL;
        IPC_SET_RETVAL(call->data, 0);
        IPC_SET_ARG1(call->data, UDEBUG_EVENT_THREAD_E);

        /* Prevent any further debug activity in thread */
        THREAD->udebug.debug_active = false;
        THREAD->udebug.cur_event = 0;           /* none */
        THREAD->udebug.stop = true;     /* set to initial value */

        ipc_answer(&TASK->answerbox, call);

        mutex_unlock(&THREAD->udebug.lock);
        mutex_unlock(&TASK->udebug.lock);

        /* Leave int_lock enabled */
        /* This event does not sleep - debugging has finished in this thread */
}

/**
 * Terminate task debugging session.
 *
 * Gracefully terminates the debugging session for a task. If the debugger
 * is still waiting for events on some threads, it will receive a
 * FINISHED event for each of them.
 *
 * @param ta    Task structure. ta->udebug.lock must be already locked.
 * @return      Zero on success or negative error code.
 */
int udebug_task_cleanup(struct task *ta)
{
        thread_t *t;
        link_t *cur;
        int flags;
        ipl_t ipl;

        LOG("udebug_task_cleanup()\n");
        LOG("task %" PRIu64 "\n", ta->taskid);

        udebug_int_lock();

        if (ta->udebug.dt_state != UDEBUG_TS_BEGINNING &&
            ta->udebug.dt_state != UDEBUG_TS_ACTIVE) {
                LOG("udebug_task_cleanup(): task not being debugged\n");
                return EINVAL;
        }

        /* Finish debugging of all userspace threads */
        for (cur = ta->th_head.next; cur != &ta->th_head; cur = cur->next) {
                t = list_get_instance(cur, thread_t, th_link);

                mutex_lock(&t->udebug.lock);

                ipl = interrupts_disable();
                spinlock_lock(&t->lock);

                flags = t->flags;

                spinlock_unlock(&t->lock);
                interrupts_restore(ipl);

                /* Only process userspace threads */
                if ((flags & THREAD_FLAG_USPACE) != 0) {
                        /* Prevent any further debug activity in thread */
                        t->udebug.debug_active = false;
                        t->udebug.cur_event = 0;        /* none */

                        /* Still has go? */
                        if (t->udebug.stop == false) {
                                /*
                                * Yes, so clear go. As debug_active == false,
                                 * this doesn't affect anything.
                                 */
                                t->udebug.stop = true;  

                                /* Answer GO call */
                                LOG("answer GO call with EVENT_FINISHED\n");
                                IPC_SET_RETVAL(t->udebug.go_call->data, 0);
                                IPC_SET_ARG1(t->udebug.go_call->data, UDEBUG_EVENT_FINISHED);

                                ipc_answer(&ta->answerbox, t->udebug.go_call);
                                t->udebug.go_call = NULL;
                        } else {
                                /*
                                 * Debug_stop is already at initial value.
                                 * Yet this means the thread needs waking up.
                                 */

                                /*
                                 * t's lock must not be held when calling
                                 * waitq_wakeup.
                                 */
                                waitq_wakeup(&t->udebug.go_wq, WAKEUP_FIRST);
                        }
                }
                mutex_unlock(&t->udebug.lock);
        }

        ta->udebug.dt_state = UDEBUG_TS_INACTIVE;
        ta->udebug.debugger = NULL;

        udebug_int_unlock();

        return 0;
}


/** @}
 */