Archipelago » qemu

/*

 * sigaltstack coroutine initialization code

 *

 * Copyright (C) 2006  Anthony Liguori <anthony@codemonkey.ws>

 * Copyright (C) 2011  Kevin Wolf <kwolf@redhat.com>

 * Copyright (C) 2012  Alex Barcelo <abarcelo@ac.upc.edu>

** This file is partly based on pth_mctx.c, from the GNU Portable Threads

**  Copyright (c) 1999-2006 Ralf S. Engelschall <rse@engelschall.com>

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with this library; if not, see <http://www.gnu.org/licenses/>.

 */

/* XXX Is there a nicer way to disable glibc's stack check for longjmp? */

#ifdef _FORTIFY_SOURCE

#undef _FORTIFY_SOURCE

#endif

#include <stdlib.h>

#include <setjmp.h>

#include <stdint.h>

#include <pthread.h>

#include <signal.h>

#include "qemu-common.h"

#include "block/coroutine_int.h"

enum {

    /* Maximum free pool size prevents holding too many freed coroutines */

    POOL_MAX_SIZE = 64,

};

/** Free list to speed up creation */

static QSLIST_HEAD(, Coroutine) pool = QSLIST_HEAD_INITIALIZER(pool);

static unsigned int pool_size;

typedef struct {

    Coroutine base;

    void *stack;

    jmp_buf env;

} CoroutineUContext;

/**

 * Per-thread coroutine bookkeeping

 */

typedef struct {

    /** Currently executing coroutine */

    Coroutine *current;

    /** The default coroutine */

    CoroutineUContext leader;

    /** Information for the signal handler (trampoline) */

    jmp_buf tr_reenter;

    volatile sig_atomic_t tr_called;

    void *tr_handler;

} CoroutineThreadState;

static pthread_key_t thread_state_key;

static CoroutineThreadState *coroutine_get_thread_state(void)

{

    CoroutineThreadState *s = pthread_getspecific(thread_state_key);

    if (!s) {

        s = g_malloc0(sizeof(*s));

        s->current = &s->leader.base;

        pthread_setspecific(thread_state_key, s);

    }

    return s;

}

static void qemu_coroutine_thread_cleanup(void *opaque)

{

    CoroutineThreadState *s = opaque;

    g_free(s);

}

static void __attribute__((destructor)) coroutine_cleanup(void)

{

    Coroutine *co;

    Coroutine *tmp;

    QSLIST_FOREACH_SAFE(co, &pool, pool_next, tmp) {

        g_free(DO_UPCAST(CoroutineUContext, base, co)->stack);

        g_free(co);

    }

}

static void __attribute__((constructor)) coroutine_init(void)

{

    int ret;

    ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);

    if (ret != 0) {

        fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));

        abort();

    }

}

/* "boot" function

 * This is what starts the coroutine, is called from the trampoline

 * (from the signal handler when it is not signal handling, read ahead

 * for more information).

 */

static void coroutine_bootstrap(CoroutineUContext *self, Coroutine *co)

{

    /* Initialize longjmp environment and switch back the caller */

    if (!setjmp(self->env)) {

        longjmp(*(jmp_buf *)co->entry_arg, 1);

    }

    while (true) {

        co->entry(co->entry_arg);

        qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);

    }

}

/*

 * This is used as the signal handler. This is called with the brand new stack

 * (thanks to sigaltstack). We have to return, given that this is a signal

 * handler and the sigmask and some other things are changed.

 */

static void coroutine_trampoline(int signal)

{

    CoroutineUContext *self;

    Coroutine *co;

    CoroutineThreadState *coTS;

    /* Get the thread specific information */

    coTS = coroutine_get_thread_state();

    self = coTS->tr_handler;

    coTS->tr_called = 1;

    co = &self->base;

    /*

     * Here we have to do a bit of a ping pong between the caller, given that

     * this is a signal handler and we have to do a return "soon". Then the

     * caller can reestablish everything and do a longjmp here again.

     */

    if (!setjmp(coTS->tr_reenter)) {

        return;

    }

    /*

     * Ok, the caller has longjmp'ed back to us, so now prepare

     * us for the real machine state switching. We have to jump

     * into another function here to get a new stack context for

     * the auto variables (which have to be auto-variables

     * because the start of the thread happens later). Else with

     * PIC (i.e. Position Independent Code which is used when PTH

     * is built as a shared library) most platforms would

     * horrible core dump as experience showed.

     */

    coroutine_bootstrap(self, co);

}

static Coroutine *coroutine_new(void)

{

    const size_t stack_size = 1 << 20;

    CoroutineUContext *co;

    CoroutineThreadState *coTS;

    struct sigaction sa;

    struct sigaction osa;

    stack_t ss;

    stack_t oss;

    sigset_t sigs;

    sigset_t osigs;

    jmp_buf old_env;

    /* The way to manipulate stack is with the sigaltstack function. We

     * prepare a stack, with it delivering a signal to ourselves and then

     * put setjmp/longjmp where needed.

     * This has been done keeping coroutine-ucontext as a model and with the

     * pth ideas (GNU Portable Threads). See coroutine-ucontext for the basics

     * of the coroutines and see pth_mctx.c (from the pth project) for the

     * sigaltstack way of manipulating stacks.

     */

    co = g_malloc0(sizeof(*co));

    co->stack = g_malloc(stack_size);

    co->base.entry_arg = &old_env; /* stash away our jmp_buf */

    coTS = coroutine_get_thread_state();

    coTS->tr_handler = co;

    /*

     * Preserve the SIGUSR2 signal state, block SIGUSR2,

     * and establish our signal handler. The signal will

     * later transfer control onto the signal stack.

     */

    sigemptyset(&sigs);

    sigaddset(&sigs, SIGUSR2);

    pthread_sigmask(SIG_BLOCK, &sigs, &osigs);

    sa.sa_handler = coroutine_trampoline;

    sigfillset(&sa.sa_mask);

    sa.sa_flags = SA_ONSTACK;

    if (sigaction(SIGUSR2, &sa, &osa) != 0) {

        abort();

    }

    /*

     * Set the new stack.

     */

    ss.ss_sp = co->stack;

    ss.ss_size = stack_size;

    ss.ss_flags = 0;

    if (sigaltstack(&ss, &oss) < 0) {

        abort();

    }

    /*

     * Now transfer control onto the signal stack and set it up.

     * It will return immediately via "return" after the setjmp()

     * was performed. Be careful here with race conditions.  The

     * signal can be delivered the first time sigsuspend() is

     * called.

     */

    coTS->tr_called = 0;

    pthread_kill(pthread_self(), SIGUSR2);

    sigfillset(&sigs);

    sigdelset(&sigs, SIGUSR2);

    while (!coTS->tr_called) {

        sigsuspend(&sigs);

    }

    /*

     * Inform the system that we are back off the signal stack by

     * removing the alternative signal stack. Be careful here: It

     * first has to be disabled, before it can be removed.

     */

    sigaltstack(NULL, &ss);

    ss.ss_flags = SS_DISABLE;

    if (sigaltstack(&ss, NULL) < 0) {

        abort();

    }

    sigaltstack(NULL, &ss);

    if (!(oss.ss_flags & SS_DISABLE)) {

        sigaltstack(&oss, NULL);

    }

    /*

     * Restore the old SIGUSR2 signal handler and mask

     */

    sigaction(SIGUSR2, &osa, NULL);

    pthread_sigmask(SIG_SETMASK, &osigs, NULL);

    /*

     * Now enter the trampoline again, but this time not as a signal

     * handler. Instead we jump into it directly. The functionally

     * redundant ping-pong pointer arithmetic is necessary to avoid

     * type-conversion warnings related to the `volatile' qualifier and

     * the fact that `jmp_buf' usually is an array type.

     */

    if (!setjmp(old_env)) {

        longjmp(coTS->tr_reenter, 1);

    }

    /*

     * Ok, we returned again, so now we're finished

     */

    return &co->base;

}

Coroutine *qemu_coroutine_new(void)

{

    Coroutine *co;

    co = QSLIST_FIRST(&pool);

    if (co) {

        QSLIST_REMOVE_HEAD(&pool, pool_next);

        pool_size--;

    } else {

        co = coroutine_new();

    }

    return co;

}

void qemu_coroutine_delete(Coroutine *co_)

{

    CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);

    if (pool_size < POOL_MAX_SIZE) {

        QSLIST_INSERT_HEAD(&pool, &co->base, pool_next);

        co->base.caller = NULL;

        pool_size++;

        return;

    }

    g_free(co->stack);

    g_free(co);

}

CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,

                                      CoroutineAction action)

{

    CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);

    CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);

    CoroutineThreadState *s = coroutine_get_thread_state();

    int ret;

    s->current = to_;

    ret = setjmp(from->env);

    if (ret == 0) {

        longjmp(to->env, action);

    }

    return ret;

}

Coroutine *qemu_coroutine_self(void)

{

    CoroutineThreadState *s = coroutine_get_thread_state();

    return s->current;

}

bool qemu_in_coroutine(void)

{

    CoroutineThreadState *s = pthread_getspecific(thread_state_key);

    return s && s->current->caller;

}