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 #ifdef CONFIG_SAFESTACK
  49     /* Need an unsafe stack for each coroutine */
  50     void *unsafe_stack;
  51     size_t unsafe_stack_size;
  52 #endif
  53     sigjmp_buf env;
  54
  55 #ifdef CONFIG_TSAN
  56     void *tsan_co_fiber;
  57     void *tsan_caller_fiber;
  58 #endif
  59
  60 #ifdef CONFIG_VALGRIND_H
  61     unsigned int valgrind_stack_id;
  62 #endif
  63
  64 } CoroutineUContext;
  65
  66 /**
  67  * Per-thread coroutine bookkeeping
  68  */
  69 static __thread CoroutineUContext leader;
  70 static __thread Coroutine *current;
  71
  72 /*
  73  * va_args to makecontext() must be type 'int', so passing
  74  * the pointer we need may require several int args. This
  75  * union is a quick hack to let us do that
  76  */
  77 union cc_arg {
  78     void *p;
  79     int i[2];
  80 };
  81
  82 /*
  83  * QEMU_ALWAYS_INLINE only does so if __OPTIMIZE__, so we cannot use it.
  84  * always_inline is required to avoid TSan runtime fatal errors.
  85  */
  86 static inline __attribute__((always_inline))
  87 void on_new_fiber(CoroutineUContext *co)
  88 {
  89 #ifdef CONFIG_TSAN
  90     co->tsan_co_fiber = __tsan_create_fiber(0); /* flags: sync on switch */
  91     co->tsan_caller_fiber = __tsan_get_current_fiber();
  92 #endif
  93 }
  94
  95 /* always_inline is required to avoid TSan runtime fatal errors. */
  96 static inline __attribute__((always_inline))
  97 void finish_switch_fiber(void *fake_stack_save)
  98 {
  99 #ifdef CONFIG_ASAN
 100     const void *bottom_old;
 101     size_t size_old;
 102
 103     __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
 104
 105     if (!leader.stack) {
 106         leader.stack = (void *)bottom_old;
 107         leader.stack_size = size_old;
 108     }
 109 #endif
 110 #ifdef CONFIG_TSAN
 111     if (fake_stack_save) {
 112         __tsan_release(fake_stack_save);
 113         __tsan_switch_to_fiber(fake_stack_save, 0);  /* 0=synchronize */
 114     }
 115 #endif
 116 }
 117
 118 /* always_inline is required to avoid TSan runtime fatal errors. */
 119 static inline __attribute__((always_inline))
 120 void start_switch_fiber_asan(CoroutineAction action, void **fake_stack_save,
 121                              const void *bottom, size_t size)
 122 {
 123 #ifdef CONFIG_ASAN
 124     __sanitizer_start_switch_fiber(
 125             action == COROUTINE_TERMINATE ? NULL : fake_stack_save,
 126             bottom, size);
 127 #endif
 128 }
 129
 130 /* always_inline is required to avoid TSan runtime fatal errors. */
 131 static inline __attribute__((always_inline))
 132 void start_switch_fiber_tsan(void **fake_stack_save,
 133                              CoroutineUContext *co,
 134                              bool caller)
 135 {
 136 #ifdef CONFIG_TSAN
 137     void *new_fiber = caller ?
 138                       co->tsan_caller_fiber :
 139                       co->tsan_co_fiber;
 140     void *curr_fiber = __tsan_get_current_fiber();
 141     __tsan_acquire(curr_fiber);
 142
 143     *fake_stack_save = curr_fiber;
 144     __tsan_switch_to_fiber(new_fiber, 0);  /* 0=synchronize */
 145 #endif
 146 }
 147
 148 static void coroutine_trampoline(int i0, int i1)
 149 {
 150     union cc_arg arg;
 151     CoroutineUContext *self;
 152     Coroutine *co;
 153     void *fake_stack_save = NULL;
 154
 155     finish_switch_fiber(NULL);
 156
 157     arg.i[0] = i0;
 158     arg.i[1] = i1;
 159     self = arg.p;
 160     co = &self->base;
 161
 162     /* Initialize longjmp environment and switch back the caller */
 163     if (!sigsetjmp(self->env, 0)) {
 164         start_switch_fiber_asan(COROUTINE_YIELD, &fake_stack_save, leader.stack,
 165                                 leader.stack_size);
 166         start_switch_fiber_tsan(&fake_stack_save, self, true); /* true=caller */
 167         siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
 168     }
 169
 170     finish_switch_fiber(fake_stack_save);
 171
 172     while (true) {
 173         co->entry(co->entry_arg);
 174         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 175     }
 176 }
 177
 178 Coroutine *qemu_coroutine_new(void)
 179 {
 180     CoroutineUContext *co;
 181     ucontext_t old_uc, uc;
 182     sigjmp_buf old_env;
 183     union cc_arg arg = {0};
 184     void *fake_stack_save = NULL;
 185
 186     /* The ucontext functions preserve signal masks which incurs a
 187      * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not
 188      * preserve signal masks but only works on the current stack.
 189      * Since we need a way to create and switch to a new stack, use
 190      * the ucontext functions for that but sigsetjmp()/siglongjmp() for
 191      * everything else.
 192      */
 193
 194     if (getcontext(&uc) == -1) {
 195         abort();
 196     }
 197
 198     co = g_malloc0(sizeof(*co));
 199     co->stack_size = COROUTINE_STACK_SIZE;
 200     co->stack = qemu_alloc_stack(&co->stack_size);
 201 #ifdef CONFIG_SAFESTACK
 202     co->unsafe_stack_size = COROUTINE_STACK_SIZE;
 203     co->unsafe_stack = qemu_alloc_stack(&co->unsafe_stack_size);
 204 #endif
 205     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 206
 207     uc.uc_link = &old_uc;
 208     uc.uc_stack.ss_sp = co->stack;
 209     uc.uc_stack.ss_size = co->stack_size;
 210     uc.uc_stack.ss_flags = 0;
 211
 212 #ifdef CONFIG_VALGRIND_H
 213     co->valgrind_stack_id =
 214         VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
 215 #endif
 216
 217     arg.p = co;
 218
 219     on_new_fiber(co);
 220     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 221                 2, arg.i[0], arg.i[1]);
 222
 223     /* swapcontext() in, siglongjmp() back out */
 224     if (!sigsetjmp(old_env, 0)) {
 225         start_switch_fiber_asan(COROUTINE_YIELD, &fake_stack_save, co->stack,
 226                                 co->stack_size);
 227         start_switch_fiber_tsan(&fake_stack_save,
 228                                 co, false); /* false=not caller */
 229
 230 #ifdef CONFIG_SAFESTACK
 231         /*
 232          * Before we swap the context, set the new unsafe stack
 233          * The unsafe stack grows just like the normal stack, so start from
 234          * the last usable location of the memory area.
 235          * NOTE: we don't have to re-set the usp afterwards because we are
 236          * coming back to this context through a siglongjmp.
 237          * The compiler already wrapped the corresponding sigsetjmp call with
 238          * code that saves the usp on the (safe) stack before the call, and
 239          * restores it right after (which is where we return with siglongjmp).
 240          */
 241         void *usp = co->unsafe_stack + co->unsafe_stack_size;
 242         __safestack_unsafe_stack_ptr = usp;
 243 #endif
 244
 245         swapcontext(&old_uc, &uc);
 246     }
 247
 248     finish_switch_fiber(fake_stack_save);
 249
 250     return &co->base;
 251 }
 252
 253 #ifdef CONFIG_VALGRIND_H
 254 /* Work around an unused variable in the valgrind.h macro... */
 255 #if !defined(__clang__)
 256 #pragma GCC diagnostic push
 257 #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 258 #endif
 259 static inline void valgrind_stack_deregister(CoroutineUContext *co)
 260 {
 261     VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
 262 }
 263 #if !defined(__clang__)
 264 #pragma GCC diagnostic pop
 265 #endif
 266 #endif
 267
 268 void qemu_coroutine_delete(Coroutine *co_)
 269 {
 270     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 271
 272 #ifdef CONFIG_VALGRIND_H
 273     valgrind_stack_deregister(co);
 274 #endif
 275
 276     qemu_free_stack(co->stack, co->stack_size);
 277 #ifdef CONFIG_SAFESTACK
 278     qemu_free_stack(co->unsafe_stack, co->unsafe_stack_size);
 279 #endif
 280     g_free(co);
 281 }
 282
 283 /* This function is marked noinline to prevent GCC from inlining it
 284  * into coroutine_trampoline(). If we allow it to do that then it
 285  * hoists the code to get the address of the TLS variable "current"
 286  * out of the while() loop. This is an invalid transformation because
 287  * the sigsetjmp() call may be called when running thread A but
 288  * return in thread B, and so we might be in a different thread
 289  * context each time round the loop.
 290  */
 291 CoroutineAction __attribute__((noinline))
 292 qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 293                       CoroutineAction action)
 294 {
 295     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 296     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 297     int ret;
 298     void *fake_stack_save = NULL;
 299
 300     current = to_;
 301
 302     ret = sigsetjmp(from->env, 0);
 303     if (ret == 0) {
 304         start_switch_fiber_asan(action, &fake_stack_save, to->stack,
 305                                 to->stack_size);
 306         start_switch_fiber_tsan(&fake_stack_save,
 307                                 to, false); /* false=not caller */
 308         siglongjmp(to->env, action);
 309     }
 310
 311     finish_switch_fiber(fake_stack_save);
 312
 313     return ret;
 314 }
 315
 316 Coroutine *qemu_coroutine_self(void)
 317 {
 318     if (!current) {
 319         current = &leader.base;
 320     }
 321 #ifdef CONFIG_TSAN
 322     if (!leader.tsan_co_fiber) {
 323         leader.tsan_co_fiber = __tsan_get_current_fiber();
 324     }
 325 #endif
 326     return current;
 327 }
 328
 329 bool qemu_in_coroutine(void)
 330 {
 331     return current && current->caller;
 332 }