Archipelago » qemu

/*

 * ucontext coroutine initialization code

 *

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

 * Copyright (C) 2011  Kevin Wolf <kwolf@redhat.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 2.0 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 <ucontext.h>

#include "qemu-common.h"

#include "block/coroutine_int.h"

#ifdef CONFIG_VALGRIND_H

#include <valgrind/valgrind.h>

#endif

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;

    sigjmp_buf env;

#ifdef CONFIG_VALGRIND_H

    unsigned int valgrind_stack_id;

#endif

} CoroutineUContext;

/**

 * Per-thread coroutine bookkeeping

 */

typedef struct {

    /** Currently executing coroutine */

    Coroutine *current;

    /** The default coroutine */

    CoroutineUContext leader;

} CoroutineThreadState;

static pthread_key_t thread_state_key;

/*

 * va_args to makecontext() must be type 'int', so passing

 * the pointer we need may require several int args. This

 * union is a quick hack to let us do that

 */

union cc_arg {

    void *p;

    int i[2];

};

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();

    }

}

static void coroutine_trampoline(int i0, int i1)

{

    union cc_arg arg;

    CoroutineUContext *self;

    Coroutine *co;

    arg.i[0] = i0;

    arg.i[1] = i1;

    self = arg.p;

    co = &self->base;

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

    if (!sigsetjmp(self->env, 0)) {

        siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);

    }

    while (true) {

        co->entry(co->entry_arg);

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

    }

}

static Coroutine *coroutine_new(void)

{

    const size_t stack_size = 1 << 20;

    CoroutineUContext *co;

    ucontext_t old_uc, uc;

    sigjmp_buf old_env;

    union cc_arg arg = {0};

    /* The ucontext functions preserve signal masks which incurs a

     * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not

     * preserve signal masks but only works on the current stack.

     * Since we need a way to create and switch to a new stack, use

     * the ucontext functions for that but sigsetjmp()/siglongjmp() for

     * everything else.

     */

    if (getcontext(&uc) == -1) {

        abort();

    }

    co = g_malloc0(sizeof(*co));

    co->stack = g_malloc(stack_size);

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

    uc.uc_link = &old_uc;

    uc.uc_stack.ss_sp = co->stack;

    uc.uc_stack.ss_size = stack_size;

    uc.uc_stack.ss_flags = 0;

#ifdef CONFIG_VALGRIND_H

    co->valgrind_stack_id =

        VALGRIND_STACK_REGISTER(co->stack, co->stack + stack_size);

#endif

    arg.p = co;

    makecontext(&uc, (void (*)(void))coroutine_trampoline,

                2, arg.i[0], arg.i[1]);

    /* swapcontext() in, siglongjmp() back out */

    if (!sigsetjmp(old_env, 0)) {

        swapcontext(&old_uc, &uc);

    }

    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;

}

#ifdef CONFIG_VALGRIND_H

#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE

/* Work around an unused variable in the valgrind.h macro... */

#pragma GCC diagnostic ignored "-Wunused-but-set-variable"

#endif

static inline void valgrind_stack_deregister(CoroutineUContext *co)

{

    VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);

}

#ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE

#pragma GCC diagnostic error "-Wunused-but-set-variable"

#endif

#endif

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;

    }

#ifdef CONFIG_VALGRIND_H

    valgrind_stack_deregister(co);

#endif

    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 = sigsetjmp(from->env, 0);

    if (ret == 0) {

        siglongjmp(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;

}