cpu-exec.c

   1 /*
   2  *  emulator main execution loop
   3  *
   4  *  Copyright (c) 2003-2005 Fabrice Bellard
   5  *
   6  * This library is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2 of the License, or (at your option) any later version.
  10  *
  11  * This library is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  18  */
  19 #include "qemu/osdep.h"
  20 #include "cpu.h"
  21 #include "trace.h"
  22 #include "disas/disas.h"
  23 #include "tcg.h"
  24 #include "qemu/atomic.h"
  25 #include "sysemu/qtest.h"
  26 #include "qemu/timer.h"
  27 #include "exec/address-spaces.h"
  28 #include "qemu/rcu.h"
  29 #include "exec/tb-hash.h"
  30 #include "exec/log.h"
  31 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
  32 #include "hw/i386/apic.h"
  33 #endif
  34 #include "sysemu/replay.h"
  35
  36 /* -icount align implementation. */
  37
  38 typedef struct SyncClocks {
  39     int64_t diff_clk;
  40     int64_t last_cpu_icount;
  41     int64_t realtime_clock;
  42 } SyncClocks;
  43
  44 #if !defined(CONFIG_USER_ONLY)
  45 /* Allow the guest to have a max 3ms advance.
  46  * The difference between the 2 clocks could therefore
  47  * oscillate around 0.
  48  */
  49 #define VM_CLOCK_ADVANCE 3000000
  50 #define THRESHOLD_REDUCE 1.5
  51 #define MAX_DELAY_PRINT_RATE 2000000000LL
  52 #define MAX_NB_PRINTS 100
  53
  54 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
  55 {
  56     int64_t cpu_icount;
  57
  58     if (!icount_align_option) {
  59         return;
  60     }
  61
  62     cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
  63     sc->diff_clk += cpu_icount_to_ns(sc->last_cpu_icount - cpu_icount);
  64     sc->last_cpu_icount = cpu_icount;
  65
  66     if (sc->diff_clk > VM_CLOCK_ADVANCE) {
  67 #ifndef _WIN32
  68         struct timespec sleep_delay, rem_delay;
  69         sleep_delay.tv_sec = sc->diff_clk / 1000000000LL;
  70         sleep_delay.tv_nsec = sc->diff_clk % 1000000000LL;
  71         if (nanosleep(&sleep_delay, &rem_delay) < 0) {
  72             sc->diff_clk = rem_delay.tv_sec * 1000000000LL + rem_delay.tv_nsec;
  73         } else {
  74             sc->diff_clk = 0;
  75         }
  76 #else
  77         Sleep(sc->diff_clk / SCALE_MS);
  78         sc->diff_clk = 0;
  79 #endif
  80     }
  81 }
  82
  83 static void print_delay(const SyncClocks *sc)
  84 {
  85     static float threshold_delay;
  86     static int64_t last_realtime_clock;
  87     static int nb_prints;
  88
  89     if (icount_align_option &&
  90         sc->realtime_clock - last_realtime_clock >= MAX_DELAY_PRINT_RATE &&
  91         nb_prints < MAX_NB_PRINTS) {
  92         if ((-sc->diff_clk / (float)1000000000LL > threshold_delay) ||
  93             (-sc->diff_clk / (float)1000000000LL <
  94              (threshold_delay - THRESHOLD_REDUCE))) {
  95             threshold_delay = (-sc->diff_clk / 1000000000LL) + 1;
  96             printf("Warning: The guest is now late by %.1f to %.1f seconds\n",
  97                    threshold_delay - 1,
  98                    threshold_delay);
  99             nb_prints++;
 100             last_realtime_clock = sc->realtime_clock;
 101         }
 102     }
 103 }
 104
 105 static void init_delay_params(SyncClocks *sc,
 106                               const CPUState *cpu)
 107 {
 108     if (!icount_align_option) {
 109         return;
 110     }
 111     sc->realtime_clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT);
 112     sc->diff_clk = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) - sc->realtime_clock;
 113     sc->last_cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
 114     if (sc->diff_clk < max_delay) {
 115         max_delay = sc->diff_clk;
 116     }
 117     if (sc->diff_clk > max_advance) {
 118         max_advance = sc->diff_clk;
 119     }
 120
 121     /* Print every 2s max if the guest is late. We limit the number
 122        of printed messages to NB_PRINT_MAX(currently 100) */
 123     print_delay(sc);
 124 }
 125 #else
 126 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
 127 {
 128 }
 129
 130 static void init_delay_params(SyncClocks *sc, const CPUState *cpu)
 131 {
 132 }
 133 #endif /* CONFIG USER ONLY */
 134
 135 /* Execute a TB, and fix up the CPU state afterwards if necessary */
 136 static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
 137 {
 138     CPUArchState *env = cpu->env_ptr;
 139     uintptr_t next_tb;
 140     uint8_t *tb_ptr = itb->tc_ptr;
 141
 142     qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 143                            "Trace %p [" TARGET_FMT_lx "] %s\n",
 144                            itb->tc_ptr, itb->pc, lookup_symbol(itb->pc));
 145
 146 #if defined(DEBUG_DISAS)
 147     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)) {
 148 #if defined(TARGET_I386)
 149         log_cpu_state(cpu, CPU_DUMP_CCOP);
 150 #elif defined(TARGET_M68K)
 151         /* ??? Should not modify env state for dumping.  */
 152         cpu_m68k_flush_flags(env, env->cc_op);
 153         env->cc_op = CC_OP_FLAGS;
 154         env->sr = (env->sr & 0xffe0) | env->cc_dest | (env->cc_x << 4);
 155         log_cpu_state(cpu, 0);
 156 #else
 157         log_cpu_state(cpu, 0);
 158 #endif
 159     }
 160 #endif /* DEBUG_DISAS */
 161
 162     cpu->can_do_io = !use_icount;
 163     next_tb = tcg_qemu_tb_exec(env, tb_ptr);
 164     cpu->can_do_io = 1;
 165     trace_exec_tb_exit((void *) (next_tb & ~TB_EXIT_MASK),
 166                        next_tb & TB_EXIT_MASK);
 167
 168     if ((next_tb & TB_EXIT_MASK) > TB_EXIT_IDX1) {
 169         /* We didn't start executing this TB (eg because the instruction
 170          * counter hit zero); we must restore the guest PC to the address
 171          * of the start of the TB.
 172          */
 173         CPUClass *cc = CPU_GET_CLASS(cpu);
 174         TranslationBlock *tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
 175         qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 176                                "Stopped execution of TB chain before %p ["
 177                                TARGET_FMT_lx "] %s\n",
 178                                itb->tc_ptr, itb->pc, lookup_symbol(itb->pc));
 179         if (cc->synchronize_from_tb) {
 180             cc->synchronize_from_tb(cpu, tb);
 181         } else {
 182             assert(cc->set_pc);
 183             cc->set_pc(cpu, tb->pc);
 184         }
 185     }
 186     if ((next_tb & TB_EXIT_MASK) == TB_EXIT_REQUESTED) {
 187         /* We were asked to stop executing TBs (probably a pending
 188          * interrupt. We've now stopped, so clear the flag.
 189          */
 190         cpu->tcg_exit_req = 0;
 191     }
 192     return next_tb;
 193 }
 194
 195 /* Execute the code without caching the generated code. An interpreter
 196    could be used if available. */
 197 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 198                              TranslationBlock *orig_tb, bool ignore_icount)
 199 {
 200     TranslationBlock *tb;
 201
 202     /* Should never happen.
 203        We only end up here when an existing TB is too long.  */
 204     if (max_cycles > CF_COUNT_MASK)
 205         max_cycles = CF_COUNT_MASK;
 206
 207     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags,
 208                      max_cycles | CF_NOCACHE
 209                          | (ignore_icount ? CF_IGNORE_ICOUNT : 0));
 210     tb->orig_tb = tcg_ctx.tb_ctx.tb_invalidated_flag ? NULL : orig_tb;
 211     cpu->current_tb = tb;
 212     /* execute the generated code */
 213     trace_exec_tb_nocache(tb, tb->pc);
 214     cpu_tb_exec(cpu, tb);
 215     cpu->current_tb = NULL;
 216     tb_phys_invalidate(tb, -1);
 217     tb_free(tb);
 218 }
 219
 220 static TranslationBlock *tb_find_physical(CPUState *cpu,
 221                                           target_ulong pc,
 222                                           target_ulong cs_base,
 223                                           uint64_t flags)
 224 {
 225     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 226     TranslationBlock *tb, **ptb1;
 227     unsigned int h;
 228     tb_page_addr_t phys_pc, phys_page1;
 229     target_ulong virt_page2;
 230
 231     tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
 232
 233     /* find translated block using physical mappings */
 234     phys_pc = get_page_addr_code(env, pc);
 235     phys_page1 = phys_pc & TARGET_PAGE_MASK;
 236     h = tb_phys_hash_func(phys_pc);
 237     ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
 238     for(;;) {
 239         tb = *ptb1;
 240         if (!tb) {
 241             return NULL;
 242         }
 243         if (tb->pc == pc &&
 244             tb->page_addr[0] == phys_page1 &&
 245             tb->cs_base == cs_base &&
 246             tb->flags == flags) {
 247             /* check next page if needed */
 248             if (tb->page_addr[1] != -1) {
 249                 tb_page_addr_t phys_page2;
 250
 251                 virt_page2 = (pc & TARGET_PAGE_MASK) +
 252                     TARGET_PAGE_SIZE;
 253                 phys_page2 = get_page_addr_code(env, virt_page2);
 254                 if (tb->page_addr[1] == phys_page2) {
 255                     break;
 256                 }
 257             } else {
 258                 break;
 259             }
 260         }
 261         ptb1 = &tb->phys_hash_next;
 262     }
 263
 264     /* Move the TB to the head of the list */
 265     *ptb1 = tb->phys_hash_next;
 266     tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
 267     tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
 268     return tb;
 269 }
 270
 271 static TranslationBlock *tb_find_slow(CPUState *cpu,
 272                                       target_ulong pc,
 273                                       target_ulong cs_base,
 274                                       uint64_t flags)
 275 {
 276     TranslationBlock *tb;
 277
 278     tb = tb_find_physical(cpu, pc, cs_base, flags);
 279     if (tb) {
 280         goto found;
 281     }
 282
 283 #ifdef CONFIG_USER_ONLY
 284     /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 285      * taken outside tb_lock.  Since we're momentarily dropping
 286      * tb_lock, there's a chance that our desired tb has been
 287      * translated.
 288      */
 289     tb_unlock();
 290     mmap_lock();
 291     tb_lock();
 292     tb = tb_find_physical(cpu, pc, cs_base, flags);
 293     if (tb) {
 294         mmap_unlock();
 295         goto found;
 296     }
 297 #endif
 298
 299     /* if no translated code available, then translate it now */
 300     tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 301
 302 #ifdef CONFIG_USER_ONLY
 303     mmap_unlock();
 304 #endif
 305
 306 found:
 307     /* we add the TB in the virtual pc hash table */
 308     cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)] = tb;
 309     return tb;
 310 }
 311
 312 static inline TranslationBlock *tb_find_fast(CPUState *cpu)
 313 {
 314     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 315     TranslationBlock *tb;
 316     target_ulong cs_base, pc;
 317     int flags;
 318
 319     /* we record a subset of the CPU state. It will
 320        always be the same before a given translated block
 321        is executed. */
 322     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 323     tb = cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)];
 324     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 325                  tb->flags != flags)) {
 326         tb = tb_find_slow(cpu, pc, cs_base, flags);
 327     }
 328     return tb;
 329 }
 330
 331 static void cpu_handle_debug_exception(CPUState *cpu)
 332 {
 333     CPUClass *cc = CPU_GET_CLASS(cpu);
 334     CPUWatchpoint *wp;
 335
 336     if (!cpu->watchpoint_hit) {
 337         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 338             wp->flags &= ~BP_WATCHPOINT_HIT;
 339         }
 340     }
 341
 342     cc->debug_excp_handler(cpu);
 343 }
 344
 345 /* main execution loop */
 346
 347 int cpu_exec(CPUState *cpu)
 348 {
 349     CPUClass *cc = CPU_GET_CLASS(cpu);
 350 #ifdef TARGET_I386
 351     X86CPU *x86_cpu = X86_CPU(cpu);
 352     CPUArchState *env = &x86_cpu->env;
 353 #endif
 354     int ret, interrupt_request;
 355     TranslationBlock *tb;
 356     uintptr_t next_tb;
 357     SyncClocks sc;
 358
 359     /* replay_interrupt may need current_cpu */
 360     current_cpu = cpu;
 361
 362     if (cpu->halted) {
 363 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 364         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 365             && replay_interrupt()) {
 366             apic_poll_irq(x86_cpu->apic_state);
 367             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 368         }
 369 #endif
 370         if (!cpu_has_work(cpu)) {
 371             current_cpu = NULL;
 372             return EXCP_HALTED;
 373         }
 374
 375         cpu->halted = 0;
 376     }
 377
 378     atomic_mb_set(&tcg_current_cpu, cpu);
 379     rcu_read_lock();
 380
 381     if (unlikely(atomic_mb_read(&exit_request))) {
 382         cpu->exit_request = 1;
 383     }
 384
 385     cc->cpu_exec_enter(cpu);
 386
 387     /* Calculate difference between guest clock and host clock.
 388      * This delay includes the delay of the last cycle, so
 389      * what we have to do is sleep until it is 0. As for the
 390      * advance/delay we gain here, we try to fix it next time.
 391      */
 392     init_delay_params(&sc, cpu);
 393
 394     /* prepare setjmp context for exception handling */
 395     for(;;) {
 396         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 397             /* if an exception is pending, we execute it here */
 398             if (cpu->exception_index >= 0) {
 399                 if (cpu->exception_index >= EXCP_INTERRUPT) {
 400                     /* exit request from the cpu execution loop */
 401                     ret = cpu->exception_index;
 402                     if (ret == EXCP_DEBUG) {
 403                         cpu_handle_debug_exception(cpu);
 404                     }
 405                     cpu->exception_index = -1;
 406                     break;
 407                 } else {
 408 #if defined(CONFIG_USER_ONLY)
 409                     /* if user mode only, we simulate a fake exception
 410                        which will be handled outside the cpu execution
 411                        loop */
 412 #if defined(TARGET_I386)
 413                     cc->do_interrupt(cpu);
 414 #endif
 415                     ret = cpu->exception_index;
 416                     cpu->exception_index = -1;
 417                     break;
 418 #else
 419                     if (replay_exception()) {
 420                         cc->do_interrupt(cpu);
 421                         cpu->exception_index = -1;
 422                     } else if (!replay_has_interrupt()) {
 423                         /* give a chance to iothread in replay mode */
 424                         ret = EXCP_INTERRUPT;
 425                         break;
 426                     }
 427 #endif
 428                 }
 429             } else if (replay_has_exception()
 430                        && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 431                 /* try to cause an exception pending in the log */
 432                 cpu_exec_nocache(cpu, 1, tb_find_fast(cpu), true);
 433                 ret = -1;
 434                 break;
 435             }
 436
 437             next_tb = 0; /* force lookup of first TB */
 438             for(;;) {
 439                 interrupt_request = cpu->interrupt_request;
 440                 if (unlikely(interrupt_request)) {
 441                     if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 442                         /* Mask out external interrupts for this step. */
 443                         interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 444                     }
 445                     if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 446                         cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 447                         cpu->exception_index = EXCP_DEBUG;
 448                         cpu_loop_exit(cpu);
 449                     }
 450                     if (replay_mode == REPLAY_MODE_PLAY
 451                         && !replay_has_interrupt()) {
 452                         /* Do nothing */
 453                     } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 454                         replay_interrupt();
 455                         cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 456                         cpu->halted = 1;
 457                         cpu->exception_index = EXCP_HLT;
 458                         cpu_loop_exit(cpu);
 459                     }
 460 #if defined(TARGET_I386)
 461                     else if (interrupt_request & CPU_INTERRUPT_INIT) {
 462                         replay_interrupt();
 463                         cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 464                         do_cpu_init(x86_cpu);
 465                         cpu->exception_index = EXCP_HALTED;
 466                         cpu_loop_exit(cpu);
 467                     }
 468 #else
 469                     else if (interrupt_request & CPU_INTERRUPT_RESET) {
 470                         replay_interrupt();
 471                         cpu_reset(cpu);
 472                         cpu_loop_exit(cpu);
 473                     }
 474 #endif
 475                     /* The target hook has 3 exit conditions:
 476                        False when the interrupt isn't processed,
 477                        True when it is, and we should restart on a new TB,
 478                        and via longjmp via cpu_loop_exit.  */
 479                     else {
 480                         replay_interrupt();
 481                         if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 482                             next_tb = 0;
 483                         }
 484                     }
 485                     /* Don't use the cached interrupt_request value,
 486                        do_interrupt may have updated the EXITTB flag. */
 487                     if (cpu->interrupt_request & CPU_INTERRUPT_EXITTB) {
 488                         cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 489                         /* ensure that no TB jump will be modified as
 490                            the program flow was changed */
 491                         next_tb = 0;
 492                     }
 493                 }
 494                 if (unlikely(cpu->exit_request
 495                              || replay_has_interrupt())) {
 496                     cpu->exit_request = 0;
 497                     cpu->exception_index = EXCP_INTERRUPT;
 498                     cpu_loop_exit(cpu);
 499                 }
 500                 tb_lock();
 501                 tb = tb_find_fast(cpu);
 502                 /* Note: we do it here to avoid a gcc bug on Mac OS X when
 503                    doing it in tb_find_slow */
 504                 if (tcg_ctx.tb_ctx.tb_invalidated_flag) {
 505                     /* as some TB could have been invalidated because
 506                        of memory exceptions while generating the code, we
 507                        must recompute the hash index here */
 508                     next_tb = 0;
 509                     tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
 510                 }
 511                 /* see if we can patch the calling TB. When the TB
 512                    spans two pages, we cannot safely do a direct
 513                    jump. */
 514                 if (next_tb != 0 && tb->page_addr[1] == -1
 515                     && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 516                     tb_add_jump((TranslationBlock *)(next_tb & ~TB_EXIT_MASK),
 517                                 next_tb & TB_EXIT_MASK, tb);
 518                 }
 519                 tb_unlock();
 520                 if (likely(!cpu->exit_request)) {
 521                     trace_exec_tb(tb, tb->pc);
 522                     /* execute the generated code */
 523                     cpu->current_tb = tb;
 524                     next_tb = cpu_tb_exec(cpu, tb);
 525                     cpu->current_tb = NULL;
 526                     switch (next_tb & TB_EXIT_MASK) {
 527                     case TB_EXIT_REQUESTED:
 528                         /* Something asked us to stop executing
 529                          * chained TBs; just continue round the main
 530                          * loop. Whatever requested the exit will also
 531                          * have set something else (eg exit_request or
 532                          * interrupt_request) which we will handle
 533                          * next time around the loop.  But we need to
 534                          * ensure the tcg_exit_req read in generated code
 535                          * comes before the next read of cpu->exit_request
 536                          * or cpu->interrupt_request.
 537                          */
 538                         smp_rmb();
 539                         next_tb = 0;
 540                         break;
 541                     case TB_EXIT_ICOUNT_EXPIRED:
 542                     {
 543                         /* Instruction counter expired.  */
 544                         int insns_left = cpu->icount_decr.u32;
 545                         if (cpu->icount_extra && insns_left >= 0) {
 546                             /* Refill decrementer and continue execution.  */
 547                             cpu->icount_extra += insns_left;
 548                             insns_left = MIN(0xffff, cpu->icount_extra);
 549                             cpu->icount_extra -= insns_left;
 550                             cpu->icount_decr.u16.low = insns_left;
 551                         } else {
 552                             if (insns_left > 0) {
 553                                 /* Execute remaining instructions.  */
 554                                 tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
 555                                 cpu_exec_nocache(cpu, insns_left, tb, false);
 556                                 align_clocks(&sc, cpu);
 557                             }
 558                             cpu->exception_index = EXCP_INTERRUPT;
 559                             next_tb = 0;
 560                             cpu_loop_exit(cpu);
 561                         }
 562                         break;
 563                     }
 564                     default:
 565                         break;
 566                     }
 567                 }
 568                 /* Try to align the host and virtual clocks
 569                    if the guest is in advance */
 570                 align_clocks(&sc, cpu);
 571                 /* reset soft MMU for next block (it can currently
 572                    only be set by a memory fault) */
 573             } /* for(;;) */
 574         } else {
 575 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 576             /* Some compilers wrongly smash all local variables after
 577              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 578              * Reload essential local variables here for those compilers.
 579              * Newer versions of gcc would complain about this code (-Wclobbered). */
 580             cpu = current_cpu;
 581             cc = CPU_GET_CLASS(cpu);
 582 #ifdef TARGET_I386
 583             x86_cpu = X86_CPU(cpu);
 584             env = &x86_cpu->env;
 585 #endif
 586 #else /* buggy compiler */
 587             /* Assert that the compiler does not smash local variables. */
 588             g_assert(cpu == current_cpu);
 589             g_assert(cc == CPU_GET_CLASS(cpu));
 590 #ifdef TARGET_I386
 591             g_assert(x86_cpu == X86_CPU(cpu));
 592             g_assert(env == &x86_cpu->env);
 593 #endif
 594 #endif /* buggy compiler */
 595             cpu->can_do_io = 1;
 596             tb_lock_reset();
 597         }
 598     } /* for(;;) */
 599
 600     cc->cpu_exec_exit(cpu);
 601     rcu_read_unlock();
 602
 603     /* fail safe : never use current_cpu outside cpu_exec() */
 604     current_cpu = NULL;
 605
 606     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 607     atomic_set(&tcg_current_cpu, NULL);
 608     return ret;
 609 }