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