coroutine-ucontext.c

   1 /*
   2  * ucontext coroutine initialization code
   3  *
   4  * Copyright (C) 2006  Anthony Liguori <anthony@codemonkey.ws>
   5  * Copyright (C) 2011  Kevin Wolf <kwolf@redhat.com>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.0 of the License, or (at your option) any later version.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 /* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
  22 #ifdef _FORTIFY_SOURCE
  23 #undef _FORTIFY_SOURCE
  24 #endif
  25 #include <stdlib.h>
  26 #include <setjmp.h>
  27 #include <stdint.h>
  28 #include <pthread.h>
  29 #include <ucontext.h>
  30 #include "qemu-common.h"
  31 #include "block/coroutine_int.h"
  32
  33 #ifdef CONFIG_VALGRIND_H
  34 #include <valgrind/valgrind.h>
  35 #endif
  36
  37 typedef struct {
  38     Coroutine base;
  39     void *stack;
  40     sigjmp_buf env;
  41
  42 #ifdef CONFIG_VALGRIND_H
  43     unsigned int valgrind_stack_id;
  44 #endif
  45
  46 } CoroutineUContext;
  47
  48 /**
  49  * Per-thread coroutine bookkeeping
  50  */
  51 typedef struct {
  52     /** Currently executing coroutine */
  53     Coroutine *current;
  54
  55     /** The default coroutine */
  56     CoroutineUContext leader;
  57 } CoroutineThreadState;
  58
  59 static pthread_key_t thread_state_key;
  60
  61 /*
  62  * va_args to makecontext() must be type 'int', so passing
  63  * the pointer we need may require several int args. This
  64  * union is a quick hack to let us do that
  65  */
  66 union cc_arg {
  67     void *p;
  68     int i[2];
  69 };
  70
  71 static CoroutineThreadState *coroutine_get_thread_state(void)
  72 {
  73     CoroutineThreadState *s = pthread_getspecific(thread_state_key);
  74
  75     if (!s) {
  76         s = g_malloc0(sizeof(*s));
  77         s->current = &s->leader.base;
  78         pthread_setspecific(thread_state_key, s);
  79     }
  80     return s;
  81 }
  82
  83 static void qemu_coroutine_thread_cleanup(void *opaque)
  84 {
  85     CoroutineThreadState *s = opaque;
  86
  87     g_free(s);
  88 }
  89
  90 static void __attribute__((constructor)) coroutine_init(void)
  91 {
  92     int ret;
  93
  94     ret = pthread_key_create(&thread_state_key, qemu_coroutine_thread_cleanup);
  95     if (ret != 0) {
  96         fprintf(stderr, "unable to create leader key: %s\n", strerror(errno));
  97         abort();
  98     }
  99 }
 100
 101 static void coroutine_trampoline(int i0, int i1)
 102 {
 103     union cc_arg arg;
 104     CoroutineUContext *self;
 105     Coroutine *co;
 106
 107     arg.i[0] = i0;
 108     arg.i[1] = i1;
 109     self = arg.p;
 110     co = &self->base;
 111
 112     /* Initialize longjmp environment and switch back the caller */
 113     if (!sigsetjmp(self->env, 0)) {
 114         siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
 115     }
 116
 117     while (true) {
 118         co->entry(co->entry_arg);
 119         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 120     }
 121 }
 122
 123 Coroutine *qemu_coroutine_new(void)
 124 {
 125     const size_t stack_size = 1 << 20;
 126     CoroutineUContext *co;
 127     ucontext_t old_uc, uc;
 128     sigjmp_buf old_env;
 129     union cc_arg arg = {0};
 130
 131     /* The ucontext functions preserve signal masks which incurs a
 132      * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not
 133      * preserve signal masks but only works on the current stack.
 134      * Since we need a way to create and switch to a new stack, use
 135      * the ucontext functions for that but sigsetjmp()/siglongjmp() for
 136      * everything else.
 137      */
 138
 139     if (getcontext(&uc) == -1) {
 140         abort();
 141     }
 142
 143     co = g_malloc0(sizeof(*co));
 144     co->stack = g_malloc(stack_size);
 145     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 146
 147     uc.uc_link = &old_uc;
 148     uc.uc_stack.ss_sp = co->stack;
 149     uc.uc_stack.ss_size = stack_size;
 150     uc.uc_stack.ss_flags = 0;
 151
 152 #ifdef CONFIG_VALGRIND_H
 153     co->valgrind_stack_id =
 154         VALGRIND_STACK_REGISTER(co->stack, co->stack + stack_size);
 155 #endif
 156
 157     arg.p = co;
 158
 159     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 160                 2, arg.i[0], arg.i[1]);
 161
 162     /* swapcontext() in, siglongjmp() back out */
 163     if (!sigsetjmp(old_env, 0)) {
 164         swapcontext(&old_uc, &uc);
 165     }
 166     return &co->base;
 167 }
 168
 169 #ifdef CONFIG_VALGRIND_H
 170 #ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE
 171 /* Work around an unused variable in the valgrind.h macro... */
 172 #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 173 #endif
 174 static inline void valgrind_stack_deregister(CoroutineUContext *co)
 175 {
 176     VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
 177 }
 178 #ifdef CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE
 179 #pragma GCC diagnostic error "-Wunused-but-set-variable"
 180 #endif
 181 #endif
 182
 183 void qemu_coroutine_delete(Coroutine *co_)
 184 {
 185     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 186
 187 #ifdef CONFIG_VALGRIND_H
 188     valgrind_stack_deregister(co);
 189 #endif
 190
 191     g_free(co->stack);
 192     g_free(co);
 193 }
 194
 195 CoroutineAction qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 196                                       CoroutineAction action)
 197 {
 198     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 199     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 200     CoroutineThreadState *s = coroutine_get_thread_state();
 201     int ret;
 202
 203     s->current = to_;
 204
 205     ret = sigsetjmp(from->env, 0);
 206     if (ret == 0) {
 207         siglongjmp(to->env, action);
 208     }
 209     return ret;
 210 }
 211
 212 Coroutine *qemu_coroutine_self(void)
 213 {
 214     CoroutineThreadState *s = coroutine_get_thread_state();
 215
 216     return s->current;
 217 }
 218
 219 bool qemu_in_coroutine(void)
 220 {
 221     CoroutineThreadState *s = pthread_getspecific(thread_state_key);
 222
 223     return s && s->current->caller;
 224 }