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 ret;
 140     TranslationBlock *last_tb;
 141     int tb_exit;
 142     uint8_t *tb_ptr = itb->tc_ptr;
 143
 144     qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 145                            "Trace %p [" TARGET_FMT_lx "] %s\n",
 146                            itb->tc_ptr, itb->pc, lookup_symbol(itb->pc));
 147
 148 #if defined(DEBUG_DISAS)
 149     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)) {
 150 #if defined(TARGET_I386)
 151         log_cpu_state(cpu, CPU_DUMP_CCOP);
 152 #elif defined(TARGET_M68K)
 153         /* ??? Should not modify env state for dumping.  */
 154         cpu_m68k_flush_flags(env, env->cc_op);
 155         env->cc_op = CC_OP_FLAGS;
 156         env->sr = (env->sr & 0xffe0) | env->cc_dest | (env->cc_x << 4);
 157         log_cpu_state(cpu, 0);
 158 #else
 159         log_cpu_state(cpu, 0);
 160 #endif
 161     }
 162 #endif /* DEBUG_DISAS */
 163
 164     cpu->can_do_io = !use_icount;
 165     ret = tcg_qemu_tb_exec(env, tb_ptr);
 166     cpu->can_do_io = 1;
 167     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 168     tb_exit = ret & TB_EXIT_MASK;
 169     trace_exec_tb_exit(last_tb, tb_exit);
 170
 171     if (tb_exit > TB_EXIT_IDX1) {
 172         /* We didn't start executing this TB (eg because the instruction
 173          * counter hit zero); we must restore the guest PC to the address
 174          * of the start of the TB.
 175          */
 176         CPUClass *cc = CPU_GET_CLASS(cpu);
 177         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 178                                "Stopped execution of TB chain before %p ["
 179                                TARGET_FMT_lx "] %s\n",
 180                                last_tb->tc_ptr, last_tb->pc,
 181                                lookup_symbol(last_tb->pc));
 182         if (cc->synchronize_from_tb) {
 183             cc->synchronize_from_tb(cpu, last_tb);
 184         } else {
 185             assert(cc->set_pc);
 186             cc->set_pc(cpu, last_tb->pc);
 187         }
 188     }
 189     if (tb_exit == TB_EXIT_REQUESTED) {
 190         /* We were asked to stop executing TBs (probably a pending
 191          * interrupt. We've now stopped, so clear the flag.
 192          */
 193         cpu->tcg_exit_req = 0;
 194     }
 195     return ret;
 196 }
 197
 198 #ifndef CONFIG_USER_ONLY
 199 /* Execute the code without caching the generated code. An interpreter
 200    could be used if available. */
 201 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 202                              TranslationBlock *orig_tb, bool ignore_icount)
 203 {
 204     TranslationBlock *tb;
 205     bool old_tb_flushed;
 206
 207     /* Should never happen.
 208        We only end up here when an existing TB is too long.  */
 209     if (max_cycles > CF_COUNT_MASK)
 210         max_cycles = CF_COUNT_MASK;
 211
 212     old_tb_flushed = cpu->tb_flushed;
 213     cpu->tb_flushed = false;
 214     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags,
 215                      max_cycles | CF_NOCACHE
 216                          | (ignore_icount ? CF_IGNORE_ICOUNT : 0));
 217     tb->orig_tb = cpu->tb_flushed ? NULL : orig_tb;
 218     cpu->tb_flushed |= old_tb_flushed;
 219     cpu->current_tb = tb;
 220     /* execute the generated code */
 221     trace_exec_tb_nocache(tb, tb->pc);
 222     cpu_tb_exec(cpu, tb);
 223     cpu->current_tb = NULL;
 224     tb_phys_invalidate(tb, -1);
 225     tb_free(tb);
 226 }
 227 #endif
 228
 229 static TranslationBlock *tb_find_physical(CPUState *cpu,
 230                                           target_ulong pc,
 231                                           target_ulong cs_base,
 232                                           uint32_t flags)
 233 {
 234     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 235     TranslationBlock *tb, **tb_hash_head, **ptb1;
 236     unsigned int h;
 237     tb_page_addr_t phys_pc, phys_page1;
 238
 239     /* find translated block using physical mappings */
 240     phys_pc = get_page_addr_code(env, pc);
 241     phys_page1 = phys_pc & TARGET_PAGE_MASK;
 242     h = tb_phys_hash_func(phys_pc);
 243
 244     /* Start at head of the hash entry */
 245     ptb1 = tb_hash_head = &tcg_ctx.tb_ctx.tb_phys_hash[h];
 246     tb = *ptb1;
 247
 248     while (tb) {
 249         if (tb->pc == pc &&
 250             tb->page_addr[0] == phys_page1 &&
 251             tb->cs_base == cs_base &&
 252             tb->flags == flags) {
 253
 254             if (tb->page_addr[1] == -1) {
 255                 /* done, we have a match */
 256                 break;
 257             } else {
 258                 /* check next page if needed */
 259                 target_ulong virt_page2 = (pc & TARGET_PAGE_MASK) +
 260                                           TARGET_PAGE_SIZE;
 261                 tb_page_addr_t phys_page2 = get_page_addr_code(env, virt_page2);
 262
 263                 if (tb->page_addr[1] == phys_page2) {
 264                     break;
 265                 }
 266             }
 267         }
 268
 269         ptb1 = &tb->phys_hash_next;
 270         tb = *ptb1;
 271     }
 272
 273     if (tb) {
 274         /* Move the TB to the head of the list */
 275         *ptb1 = tb->phys_hash_next;
 276         tb->phys_hash_next = *tb_hash_head;
 277         *tb_hash_head = tb;
 278     }
 279     return tb;
 280 }
 281
 282 static TranslationBlock *tb_find_slow(CPUState *cpu,
 283                                       target_ulong pc,
 284                                       target_ulong cs_base,
 285                                       uint32_t flags)
 286 {
 287     TranslationBlock *tb;
 288
 289     tb = tb_find_physical(cpu, pc, cs_base, flags);
 290     if (tb) {
 291         goto found;
 292     }
 293
 294 #ifdef CONFIG_USER_ONLY
 295     /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 296      * taken outside tb_lock.  Since we're momentarily dropping
 297      * tb_lock, there's a chance that our desired tb has been
 298      * translated.
 299      */
 300     tb_unlock();
 301     mmap_lock();
 302     tb_lock();
 303     tb = tb_find_physical(cpu, pc, cs_base, flags);
 304     if (tb) {
 305         mmap_unlock();
 306         goto found;
 307     }
 308 #endif
 309
 310     /* if no translated code available, then translate it now */
 311     tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 312
 313 #ifdef CONFIG_USER_ONLY
 314     mmap_unlock();
 315 #endif
 316
 317 found:
 318     /* we add the TB in the virtual pc hash table */
 319     cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)] = tb;
 320     return tb;
 321 }
 322
 323 static inline TranslationBlock *tb_find_fast(CPUState *cpu)
 324 {
 325     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 326     TranslationBlock *tb;
 327     target_ulong cs_base, pc;
 328     uint32_t flags;
 329
 330     /* we record a subset of the CPU state. It will
 331        always be the same before a given translated block
 332        is executed. */
 333     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 334     tb = cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)];
 335     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 336                  tb->flags != flags)) {
 337         tb = tb_find_slow(cpu, pc, cs_base, flags);
 338     }
 339     return tb;
 340 }
 341
 342 static void cpu_handle_debug_exception(CPUState *cpu)
 343 {
 344     CPUClass *cc = CPU_GET_CLASS(cpu);
 345     CPUWatchpoint *wp;
 346
 347     if (!cpu->watchpoint_hit) {
 348         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 349             wp->flags &= ~BP_WATCHPOINT_HIT;
 350         }
 351     }
 352
 353     cc->debug_excp_handler(cpu);
 354 }
 355
 356 /* main execution loop */
 357
 358 int cpu_exec(CPUState *cpu)
 359 {
 360     CPUClass *cc = CPU_GET_CLASS(cpu);
 361 #ifdef TARGET_I386
 362     X86CPU *x86_cpu = X86_CPU(cpu);
 363     CPUArchState *env = &x86_cpu->env;
 364 #endif
 365     int ret, interrupt_request;
 366     TranslationBlock *tb, *last_tb;
 367     int tb_exit = 0;
 368     SyncClocks sc;
 369
 370     /* replay_interrupt may need current_cpu */
 371     current_cpu = cpu;
 372
 373     if (cpu->halted) {
 374 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 375         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 376             && replay_interrupt()) {
 377             apic_poll_irq(x86_cpu->apic_state);
 378             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 379         }
 380 #endif
 381         if (!cpu_has_work(cpu)) {
 382             current_cpu = NULL;
 383             return EXCP_HALTED;
 384         }
 385
 386         cpu->halted = 0;
 387     }
 388
 389     atomic_mb_set(&tcg_current_cpu, cpu);
 390     rcu_read_lock();
 391
 392     if (unlikely(atomic_mb_read(&exit_request))) {
 393         cpu->exit_request = 1;
 394     }
 395
 396     cc->cpu_exec_enter(cpu);
 397
 398     /* Calculate difference between guest clock and host clock.
 399      * This delay includes the delay of the last cycle, so
 400      * what we have to do is sleep until it is 0. As for the
 401      * advance/delay we gain here, we try to fix it next time.
 402      */
 403     init_delay_params(&sc, cpu);
 404
 405     /* prepare setjmp context for exception handling */
 406     for(;;) {
 407         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 408             /* if an exception is pending, we execute it here */
 409             if (cpu->exception_index >= 0) {
 410                 if (cpu->exception_index >= EXCP_INTERRUPT) {
 411                     /* exit request from the cpu execution loop */
 412                     ret = cpu->exception_index;
 413                     if (ret == EXCP_DEBUG) {
 414                         cpu_handle_debug_exception(cpu);
 415                     }
 416                     cpu->exception_index = -1;
 417                     break;
 418                 } else {
 419 #if defined(CONFIG_USER_ONLY)
 420                     /* if user mode only, we simulate a fake exception
 421                        which will be handled outside the cpu execution
 422                        loop */
 423 #if defined(TARGET_I386)
 424                     cc->do_interrupt(cpu);
 425 #endif
 426                     ret = cpu->exception_index;
 427                     cpu->exception_index = -1;
 428                     break;
 429 #else
 430                     if (replay_exception()) {
 431                         cc->do_interrupt(cpu);
 432                         cpu->exception_index = -1;
 433                     } else if (!replay_has_interrupt()) {
 434                         /* give a chance to iothread in replay mode */
 435                         ret = EXCP_INTERRUPT;
 436                         break;
 437                     }
 438 #endif
 439                 }
 440 #ifndef CONFIG_USER_ONLY
 441             } else if (replay_has_exception()
 442                        && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 443                 /* try to cause an exception pending in the log */
 444                 cpu_exec_nocache(cpu, 1, tb_find_fast(cpu), true);
 445                 ret = -1;
 446                 break;
 447 #endif
 448             }
 449
 450             last_tb = NULL; /* forget the last executed TB after exception */
 451             cpu->tb_flushed = false; /* reset before first TB lookup */
 452             for(;;) {
 453                 interrupt_request = cpu->interrupt_request;
 454                 if (unlikely(interrupt_request)) {
 455                     if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 456                         /* Mask out external interrupts for this step. */
 457                         interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 458                     }
 459                     if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 460                         cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 461                         cpu->exception_index = EXCP_DEBUG;
 462                         cpu_loop_exit(cpu);
 463                     }
 464                     if (replay_mode == REPLAY_MODE_PLAY
 465                         && !replay_has_interrupt()) {
 466                         /* Do nothing */
 467                     } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 468                         replay_interrupt();
 469                         cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 470                         cpu->halted = 1;
 471                         cpu->exception_index = EXCP_HLT;
 472                         cpu_loop_exit(cpu);
 473                     }
 474 #if defined(TARGET_I386)
 475                     else if (interrupt_request & CPU_INTERRUPT_INIT) {
 476                         replay_interrupt();
 477                         cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 478                         do_cpu_init(x86_cpu);
 479                         cpu->exception_index = EXCP_HALTED;
 480                         cpu_loop_exit(cpu);
 481                     }
 482 #else
 483                     else if (interrupt_request & CPU_INTERRUPT_RESET) {
 484                         replay_interrupt();
 485                         cpu_reset(cpu);
 486                         cpu_loop_exit(cpu);
 487                     }
 488 #endif
 489                     /* The target hook has 3 exit conditions:
 490                        False when the interrupt isn't processed,
 491                        True when it is, and we should restart on a new TB,
 492                        and via longjmp via cpu_loop_exit.  */
 493                     else {
 494                         replay_interrupt();
 495                         if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 496                             last_tb = NULL;
 497                         }
 498                     }
 499                     /* Don't use the cached interrupt_request value,
 500                        do_interrupt may have updated the EXITTB flag. */
 501                     if (cpu->interrupt_request & CPU_INTERRUPT_EXITTB) {
 502                         cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 503                         /* ensure that no TB jump will be modified as
 504                            the program flow was changed */
 505                         last_tb = NULL;
 506                     }
 507                 }
 508                 if (unlikely(cpu->exit_request
 509                              || replay_has_interrupt())) {
 510                     cpu->exit_request = 0;
 511                     cpu->exception_index = EXCP_INTERRUPT;
 512                     cpu_loop_exit(cpu);
 513                 }
 514                 tb_lock();
 515                 tb = tb_find_fast(cpu);
 516                 if (cpu->tb_flushed) {
 517                     /* Ensure that no TB jump will be modified as the
 518                      * translation buffer has been flushed.
 519                      */
 520                     last_tb = NULL;
 521                     cpu->tb_flushed = false;
 522                 }
 523                 /* See if we can patch the calling TB. */
 524                 if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 525                     tb_add_jump(last_tb, tb_exit, tb);
 526                 }
 527                 tb_unlock();
 528                 if (likely(!cpu->exit_request)) {
 529                     uintptr_t ret;
 530                     trace_exec_tb(tb, tb->pc);
 531                     /* execute the generated code */
 532                     cpu->current_tb = tb;
 533                     ret = cpu_tb_exec(cpu, tb);
 534                     cpu->current_tb = NULL;
 535                     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 536                     tb_exit = ret & TB_EXIT_MASK;
 537                     switch (tb_exit) {
 538                     case TB_EXIT_REQUESTED:
 539                         /* Something asked us to stop executing
 540                          * chained TBs; just continue round the main
 541                          * loop. Whatever requested the exit will also
 542                          * have set something else (eg exit_request or
 543                          * interrupt_request) which we will handle
 544                          * next time around the loop.  But we need to
 545                          * ensure the tcg_exit_req read in generated code
 546                          * comes before the next read of cpu->exit_request
 547                          * or cpu->interrupt_request.
 548                          */
 549                         smp_rmb();
 550                         last_tb = NULL;
 551                         break;
 552                     case TB_EXIT_ICOUNT_EXPIRED:
 553                     {
 554                         /* Instruction counter expired.  */
 555 #ifdef CONFIG_USER_ONLY
 556                         abort();
 557 #else
 558                         int insns_left = cpu->icount_decr.u32;
 559                         if (cpu->icount_extra && insns_left >= 0) {
 560                             /* Refill decrementer and continue execution.  */
 561                             cpu->icount_extra += insns_left;
 562                             insns_left = MIN(0xffff, cpu->icount_extra);
 563                             cpu->icount_extra -= insns_left;
 564                             cpu->icount_decr.u16.low = insns_left;
 565                         } else {
 566                             if (insns_left > 0) {
 567                                 /* Execute remaining instructions.  */
 568                                 cpu_exec_nocache(cpu, insns_left,
 569                                                  last_tb, false);
 570                                 align_clocks(&sc, cpu);
 571                             }
 572                             cpu->exception_index = EXCP_INTERRUPT;
 573                             last_tb = NULL;
 574                             cpu_loop_exit(cpu);
 575                         }
 576                         break;
 577 #endif
 578                     }
 579                     default:
 580                         break;
 581                     }
 582                 }
 583                 /* Try to align the host and virtual clocks
 584                    if the guest is in advance */
 585                 align_clocks(&sc, cpu);
 586                 /* reset soft MMU for next block (it can currently
 587                    only be set by a memory fault) */
 588             } /* for(;;) */
 589         } else {
 590 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 591             /* Some compilers wrongly smash all local variables after
 592              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 593              * Reload essential local variables here for those compilers.
 594              * Newer versions of gcc would complain about this code (-Wclobbered). */
 595             cpu = current_cpu;
 596             cc = CPU_GET_CLASS(cpu);
 597 #ifdef TARGET_I386
 598             x86_cpu = X86_CPU(cpu);
 599             env = &x86_cpu->env;
 600 #endif
 601 #else /* buggy compiler */
 602             /* Assert that the compiler does not smash local variables. */
 603             g_assert(cpu == current_cpu);
 604             g_assert(cc == CPU_GET_CLASS(cpu));
 605 #ifdef TARGET_I386
 606             g_assert(x86_cpu == X86_CPU(cpu));
 607             g_assert(env == &x86_cpu->env);
 608 #endif
 609 #endif /* buggy compiler */
 610             cpu->can_do_io = 1;
 611             tb_lock_reset();
 612         }
 613     } /* for(;;) */
 614
 615     cc->cpu_exec_exit(cpu);
 616     rcu_read_unlock();
 617
 618     /* fail safe : never use current_cpu outside cpu_exec() */
 619     current_cpu = NULL;
 620
 621     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 622     atomic_set(&tcg_current_cpu, NULL);
 623     return ret;
 624 }