util/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 "qemu/osdep.h"
  26 #include <ucontext.h>
  27 #include "qemu/coroutine_int.h"
  28
  29 #ifdef CONFIG_VALGRIND_H
  30 #include <valgrind/valgrind.h>
  31 #endif
  32
  33 #if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
  34 #ifdef CONFIG_ASAN_IFACE_FIBER
  35 #define CONFIG_ASAN 1
  36 #include <sanitizer/asan_interface.h>
  37 #endif
  38 #endif
  39
  40 #ifdef CONFIG_TSAN
  41 #include <sanitizer/tsan_interface.h>
  42 #endif
  43
  44 typedef struct {
  45     Coroutine base;
  46     void *stack;
  47     size_t stack_size;
  48     sigjmp_buf env;
  49
  50     void *tsan_co_fiber;
  51     void *tsan_caller_fiber;
  52
  53 #ifdef CONFIG_VALGRIND_H
  54     unsigned int valgrind_stack_id;
  55 #endif
  56
  57 } CoroutineUContext;
  58
  59 /**
  60  * Per-thread coroutine bookkeeping
  61  */
  62 static __thread CoroutineUContext leader;
  63 static __thread Coroutine *current;
  64
  65 /*
  66  * va_args to makecontext() must be type 'int', so passing
  67  * the pointer we need may require several int args. This
  68  * union is a quick hack to let us do that
  69  */
  70 union cc_arg {
  71     void *p;
  72     int i[2];
  73 };
  74
  75 /* QEMU_ALWAYS_INLINE only does so if __OPTIMIZE__, so we cannot use it. */
  76 static inline __attribute__((always_inline))
  77 void on_new_fiber(CoroutineUContext *co)
  78 {
  79 #ifdef CONFIG_TSAN
  80     co->tsan_co_fiber = __tsan_create_fiber(0); /* flags: sync on switch */
  81     co->tsan_caller_fiber = __tsan_get_current_fiber();
  82 #endif
  83 }
  84
  85 static inline __attribute__((always_inline))
  86 void finish_switch_fiber(void *fake_stack_save)
  87 {
  88 #ifdef CONFIG_ASAN
  89     const void *bottom_old;
  90     size_t size_old;
  91
  92     __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
  93
  94     if (!leader.stack) {
  95         leader.stack = (void *)bottom_old;
  96         leader.stack_size = size_old;
  97     }
  98 #endif
  99 #ifdef CONFIG_TSAN
 100     if (fake_stack_save) {
 101         __tsan_release(fake_stack_save);
 102         __tsan_switch_to_fiber(fake_stack_save, 0);  /* 0=synchronize */
 103     }
 104 #endif
 105 }
 106
 107 static inline __attribute__((always_inline)) void start_switch_fiber(
 108     CoroutineAction action, void **fake_stack_save,
 109     const void *bottom, size_t size, void *new_fiber)
 110 {
 111 #ifdef CONFIG_ASAN
 112     __sanitizer_start_switch_fiber(
 113             action == COROUTINE_TERMINATE ? NULL : fake_stack_save,
 114             bottom, size);
 115 #endif
 116 #ifdef CONFIG_TSAN
 117     void *curr_fiber =
 118         __tsan_get_current_fiber();
 119     __tsan_acquire(curr_fiber);
 120
 121     *fake_stack_save = curr_fiber;
 122     __tsan_switch_to_fiber(new_fiber, 0);  /* 0=synchronize */
 123 #endif
 124 }
 125
 126 static void coroutine_trampoline(int i0, int i1)
 127 {
 128     union cc_arg arg;
 129     CoroutineUContext *self;
 130     Coroutine *co;
 131     void *fake_stack_save = NULL;
 132
 133     finish_switch_fiber(NULL);
 134
 135     arg.i[0] = i0;
 136     arg.i[1] = i1;
 137     self = arg.p;
 138     co = &self->base;
 139
 140     /* Initialize longjmp environment and switch back the caller */
 141     if (!sigsetjmp(self->env, 0)) {
 142         start_switch_fiber(
 143             COROUTINE_YIELD,
 144             &fake_stack_save,
 145             leader.stack,
 146             leader.stack_size,
 147             self->tsan_caller_fiber);
 148         siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
 149     }
 150
 151     finish_switch_fiber(fake_stack_save);
 152
 153     while (true) {
 154         co->entry(co->entry_arg);
 155         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 156     }
 157 }
 158
 159 Coroutine *qemu_coroutine_new(void)
 160 {
 161     CoroutineUContext *co;
 162     ucontext_t old_uc, uc;
 163     sigjmp_buf old_env;
 164     union cc_arg arg = {0};
 165     void *fake_stack_save = NULL;
 166
 167     /* The ucontext functions preserve signal masks which incurs a
 168      * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not
 169      * preserve signal masks but only works on the current stack.
 170      * Since we need a way to create and switch to a new stack, use
 171      * the ucontext functions for that but sigsetjmp()/siglongjmp() for
 172      * everything else.
 173      */
 174
 175     if (getcontext(&uc) == -1) {
 176         abort();
 177     }
 178
 179     co = g_malloc0(sizeof(*co));
 180     co->stack_size = COROUTINE_STACK_SIZE;
 181     co->stack = qemu_alloc_stack(&co->stack_size);
 182     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 183
 184     uc.uc_link = &old_uc;
 185     uc.uc_stack.ss_sp = co->stack;
 186     uc.uc_stack.ss_size = co->stack_size;
 187     uc.uc_stack.ss_flags = 0;
 188
 189 #ifdef CONFIG_VALGRIND_H
 190     co->valgrind_stack_id =
 191         VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
 192 #endif
 193
 194     arg.p = co;
 195
 196     on_new_fiber(co);
 197     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 198                 2, arg.i[0], arg.i[1]);
 199
 200     /* swapcontext() in, siglongjmp() back out */
 201     if (!sigsetjmp(old_env, 0)) {
 202         start_switch_fiber(
 203             COROUTINE_YIELD,
 204             &fake_stack_save,
 205             co->stack, co->stack_size, co->tsan_co_fiber);
 206         swapcontext(&old_uc, &uc);
 207     }
 208
 209     finish_switch_fiber(fake_stack_save);
 210
 211     return &co->base;
 212 }
 213
 214 #ifdef CONFIG_VALGRIND_H
 215 #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
 216 /* Work around an unused variable in the valgrind.h macro... */
 217 #pragma GCC diagnostic push
 218 #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 219 #endif
 220 static inline void valgrind_stack_deregister(CoroutineUContext *co)
 221 {
 222     VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
 223 }
 224 #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
 225 #pragma GCC diagnostic pop
 226 #endif
 227 #endif
 228
 229 void qemu_coroutine_delete(Coroutine *co_)
 230 {
 231     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 232
 233 #ifdef CONFIG_VALGRIND_H
 234     valgrind_stack_deregister(co);
 235 #endif
 236
 237     qemu_free_stack(co->stack, co->stack_size);
 238     g_free(co);
 239 }
 240
 241 /* This function is marked noinline to prevent GCC from inlining it
 242  * into coroutine_trampoline(). If we allow it to do that then it
 243  * hoists the code to get the address of the TLS variable "current"
 244  * out of the while() loop. This is an invalid transformation because
 245  * the sigsetjmp() call may be called when running thread A but
 246  * return in thread B, and so we might be in a different thread
 247  * context each time round the loop.
 248  */
 249 CoroutineAction __attribute__((noinline))
 250 qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 251                       CoroutineAction action)
 252 {
 253     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 254     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 255     int ret;
 256     void *fake_stack_save = NULL;
 257
 258     current = to_;
 259
 260     ret = sigsetjmp(from->env, 0);
 261     if (ret == 0) {
 262         start_switch_fiber(action, &fake_stack_save,
 263                            to->stack, to->stack_size, to->tsan_co_fiber);
 264         siglongjmp(to->env, action);
 265     }
 266
 267     finish_switch_fiber(fake_stack_save);
 268
 269     return ret;
 270 }
 271
 272 Coroutine *qemu_coroutine_self(void)
 273 {
 274     if (!current) {
 275         current = &leader.base;
 276     }
 277 #ifdef CONFIG_TSAN
 278     if (!leader.tsan_co_fiber) {
 279         leader.tsan_co_fiber = __tsan_get_current_fiber();
 280     }
 281 #endif
 282     return current;
 283 }
 284
 285 bool qemu_in_coroutine(void)
 286 {
 287     return current && current->caller;
 288 }