source: mainline/kernel/generic/src/udebug/udebug.c

/*
 * 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 kernel_generic
 * @{
 */

/**
 * @file
 * @brief Udebug hooks and data structure management.
 *
 * Udebug is an interface that makes userspace debuggers possible.
 */

#include <assert.h>
#include <debug.h>
#include <synch/waitq.h>
#include <udebug/udebug.h>
#include <errno.h>
#include <arch.h>
#include <proc/task.h>
#include <proc/thread.h>

/** 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);
        condvar_initialize(&ut->active_cv);

        ut->go_call = NULL;
        ut->uspace_state = NULL;
        ut->go = false;
        ut->stoppable = true;
        ut->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)
{
        waitq_sleep(wq);
}

/** 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)
{
        assert(THREAD);
        assert(TASK);

        mutex_lock(&TASK->udebug.lock);

        int 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.
                 *
                 */

                call_t *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.active == true &&
                    THREAD->udebug.go == false) {
                        /*
                         * Thread was requested to stop - answer go call
                         *
                         */

                        /* Make sure nobody takes this call away from us */
                        call_t *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)
{
restart:
        mutex_lock(&TASK->udebug.lock);
        mutex_lock(&THREAD->udebug.lock);

        if ((THREAD->udebug.active) && (THREAD->udebug.go == false)) {
                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);
        }
}

/** Upon being scheduled to run, check if the current thread should stop.
 *
 * This function is called from clock().
 *
 */
void udebug_before_thread_runs(void)
{
        /* Check if we're supposed to stop */
        udebug_stoppable_begin();
        udebug_stoppable_end();
}

/** 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(sysarg_t a1, sysarg_t a2, sysarg_t a3,
    sysarg_t a4, sysarg_t a5, sysarg_t a6, sysarg_t id, sysarg_t rc,
    bool end_variant)
{
        udebug_event_t etype =
            end_variant ? UDEBUG_EVENT_SYSCALL_E : UDEBUG_EVENT_SYSCALL_B;

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

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

        /* Fill in the GO response. */
        call_t *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);

        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.go is false 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.go = false;
        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);
}

/** Thread-creation event hook combined with attaching the thread.
 *
 * Must be called when a new userspace thread is created in the debugged
 * task. Generates a THREAD_B event. Also attaches the thread @a t
 * to the task @a ta.
 *
 * This is necessary to avoid a race condition where the BEGIN and THREAD_READ
 * requests would be handled inbetween attaching the thread and checking it
 * for being in a debugging session to send the THREAD_B event. We could then
 * either miss threads or get some threads both in the thread list
 * and get a THREAD_B event for them.
 *
 * @param thread Structure of the thread being created. Not locked, as the
 *               thread is not executing yet.
 * @param task   Task to which the thread should be attached.
 *
 */
void udebug_thread_b_event_attach(struct thread *thread, struct task *task)
{
        mutex_lock(&TASK->udebug.lock);
        mutex_lock(&THREAD->udebug.lock);

        thread_attach(thread, task);

        LOG("Check state");

        /* Must only generate events when in debugging session */
        if (THREAD->udebug.active != true) {
                LOG("udebug.active: %s, udebug.go: %s",
                    THREAD->udebug.active ? "Yes(+)" : "No",
                    THREAD->udebug.go ? "Yes(-)" : "No");

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

        LOG("Trigger event");

        call_t *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, (sysarg_t) thread);

        /*
         * Make sure udebug.go is false 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.go = false;
        THREAD->udebug.cur_event = UDEBUG_EVENT_THREAD_B;

        ipc_answer(&TASK->answerbox, call);

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

        LOG("Wait for Go");
        udebug_wait_for_go(&THREAD->udebug.go_wq);
}

/** Thread-termination event hook.
 *
 * Must be called when the current thread is terminating.
 * Generates a THREAD_E event.
 *
 */
void udebug_thread_e_event(void)
{
        mutex_lock(&TASK->udebug.lock);
        mutex_lock(&THREAD->udebug.lock);

        LOG("Check state");

        /* Must only generate events when in debugging session. */
        if (THREAD->udebug.active != true) {
                LOG("udebug.active: %s, udebug.go: %s",
                    THREAD->udebug.active ? "Yes" : "No",
                    THREAD->udebug.go ? "Yes" : "No");

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

        LOG("Trigger event");

        call_t *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.active = false;
        THREAD->udebug.cur_event = 0;   /* None */
        THREAD->udebug.go = false;      /* Set to initial value */

        ipc_answer(&TASK->answerbox, call);

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

        /*
         * This event does not sleep - debugging has finished
         * in this thread.
         *
         */
}

/** Terminate task debugging session.
 *
 * Gracefully terminate 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 task Task structure. task->udebug.lock must be already locked.
 *
 * @return Zero on success or an error code.
 *
 */
errno_t udebug_task_cleanup(struct task *task)
{
        assert(mutex_locked(&task->udebug.lock));

        if ((task->udebug.dt_state != UDEBUG_TS_BEGINNING) &&
            (task->udebug.dt_state != UDEBUG_TS_ACTIVE)) {
                return EINVAL;
        }

        LOG("Task %" PRIu64, task->taskid);

        /* Finish debugging of all userspace threads */
        list_foreach(task->threads, th_link, thread_t, thread) {
                mutex_lock(&thread->udebug.lock);

                /* Only process userspace threads. */
                if (thread->uspace) {
                        /* Prevent any further debug activity in thread. */
                        thread->udebug.active = false;
                        thread->udebug.cur_event = 0;   /* None */

                        /* Is the thread still go? */
                        if (thread->udebug.go == true) {
                                /*
                                 * Yes, so clear go. As active == false,
                                 * this doesn't affect anything.
                                 */
                                thread->udebug.go = false;

                                /* Answer GO call */
                                LOG("Answer GO call with EVENT_FINISHED.");

                                ipc_set_retval(&thread->udebug.go_call->data, 0);
                                ipc_set_arg1(&thread->udebug.go_call->data,
                                    UDEBUG_EVENT_FINISHED);

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

                                /*
                                 * thread's lock must not be held when calling
                                 * waitq_close.
                                 *
                                 */
                                waitq_close(&thread->udebug.go_wq);
                        }

                        mutex_unlock(&thread->udebug.lock);
                        condvar_broadcast(&thread->udebug.active_cv);
                } else
                        mutex_unlock(&thread->udebug.lock);
        }

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

        return 0;
}

/** Wait for debugger to handle a fault in this thread.
 *
 * When a thread faults and someone is subscribed to the FAULT kernel event,
 * this function is called to wait for a debugging session to give userspace
 * a chance to examine the faulting thead/task. When the debugging session
 * is over, this function returns (so that thread/task cleanup can continue).
 *
 */
void udebug_thread_fault(void)
{
        udebug_stoppable_begin();

        /* Wait until a debugger attends to us. */
        mutex_lock(&THREAD->udebug.lock);
        while (!THREAD->udebug.active)
                condvar_wait(&THREAD->udebug.active_cv, &THREAD->udebug.lock);
        mutex_unlock(&THREAD->udebug.lock);

        /*
         * This is where we will typically block until a post-mortem debugger
         * terminates the debugging session.
         */
        udebug_stoppable_end();
}

/** @}
 */