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