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 "exec/exec-all.h"
  24 #include "tcg.h"
  25 #include "qemu/atomic.h"
  26 #include "sysemu/qtest.h"
  27 #include "qemu/timer.h"
  28 #include "exec/address-spaces.h"
  29 #include "qemu/rcu.h"
  30 #include "exec/tb-hash.h"
  31 #include "exec/log.h"
  32 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
  33 #include "hw/i386/apic.h"
  34 #endif
  35 #include "sysemu/replay.h"
  36
  37 /* -icount align implementation. */
  38
  39 typedef struct SyncClocks {
  40     int64_t diff_clk;
  41     int64_t last_cpu_icount;
  42     int64_t realtime_clock;
  43 } SyncClocks;
  44
  45 #if !defined(CONFIG_USER_ONLY)
  46 /* Allow the guest to have a max 3ms advance.
  47  * The difference between the 2 clocks could therefore
  48  * oscillate around 0.
  49  */
  50 #define VM_CLOCK_ADVANCE 3000000
  51 #define THRESHOLD_REDUCE 1.5
  52 #define MAX_DELAY_PRINT_RATE 2000000000LL
  53 #define MAX_NB_PRINTS 100
  54
  55 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
  56 {
  57     int64_t cpu_icount;
  58
  59     if (!icount_align_option) {
  60         return;
  61     }
  62
  63     cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
  64     sc->diff_clk += cpu_icount_to_ns(sc->last_cpu_icount - cpu_icount);
  65     sc->last_cpu_icount = cpu_icount;
  66
  67     if (sc->diff_clk > VM_CLOCK_ADVANCE) {
  68 #ifndef _WIN32
  69         struct timespec sleep_delay, rem_delay;
  70         sleep_delay.tv_sec = sc->diff_clk / 1000000000LL;
  71         sleep_delay.tv_nsec = sc->diff_clk % 1000000000LL;
  72         if (nanosleep(&sleep_delay, &rem_delay) < 0) {
  73             sc->diff_clk = rem_delay.tv_sec * 1000000000LL + rem_delay.tv_nsec;
  74         } else {
  75             sc->diff_clk = 0;
  76         }
  77 #else
  78         Sleep(sc->diff_clk / SCALE_MS);
  79         sc->diff_clk = 0;
  80 #endif
  81     }
  82 }
  83
  84 static void print_delay(const SyncClocks *sc)
  85 {
  86     static float threshold_delay;
  87     static int64_t last_realtime_clock;
  88     static int nb_prints;
  89
  90     if (icount_align_option &&
  91         sc->realtime_clock - last_realtime_clock >= MAX_DELAY_PRINT_RATE &&
  92         nb_prints < MAX_NB_PRINTS) {
  93         if ((-sc->diff_clk / (float)1000000000LL > threshold_delay) ||
  94             (-sc->diff_clk / (float)1000000000LL <
  95              (threshold_delay - THRESHOLD_REDUCE))) {
  96             threshold_delay = (-sc->diff_clk / 1000000000LL) + 1;
  97             printf("Warning: The guest is now late by %.1f to %.1f seconds\n",
  98                    threshold_delay - 1,
  99                    threshold_delay);
 100             nb_prints++;
 101             last_realtime_clock = sc->realtime_clock;
 102         }
 103     }
 104 }
 105
 106 static void init_delay_params(SyncClocks *sc,
 107                               const CPUState *cpu)
 108 {
 109     if (!icount_align_option) {
 110         return;
 111     }
 112     sc->realtime_clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT);
 113     sc->diff_clk = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) - sc->realtime_clock;
 114     sc->last_cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
 115     if (sc->diff_clk < max_delay) {
 116         max_delay = sc->diff_clk;
 117     }
 118     if (sc->diff_clk > max_advance) {
 119         max_advance = sc->diff_clk;
 120     }
 121
 122     /* Print every 2s max if the guest is late. We limit the number
 123        of printed messages to NB_PRINT_MAX(currently 100) */
 124     print_delay(sc);
 125 }
 126 #else
 127 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
 128 {
 129 }
 130
 131 static void init_delay_params(SyncClocks *sc, const CPUState *cpu)
 132 {
 133 }
 134 #endif /* CONFIG USER ONLY */
 135
 136 /* Execute a TB, and fix up the CPU state afterwards if necessary */
 137 static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
 138 {
 139     CPUArchState *env = cpu->env_ptr;
 140     uintptr_t ret;
 141     TranslationBlock *last_tb;
 142     int tb_exit;
 143     uint8_t *tb_ptr = itb->tc_ptr;
 144
 145     qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 146                            "Trace %p [" TARGET_FMT_lx "] %s\n",
 147                            itb->tc_ptr, itb->pc, lookup_symbol(itb->pc));
 148
 149 #if defined(DEBUG_DISAS)
 150     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)
 151         && qemu_log_in_addr_range(itb->pc)) {
 152 #if defined(TARGET_I386)
 153         log_cpu_state(cpu, CPU_DUMP_CCOP);
 154 #else
 155         log_cpu_state(cpu, 0);
 156 #endif
 157     }
 158 #endif /* DEBUG_DISAS */
 159
 160     cpu->can_do_io = !use_icount;
 161     ret = tcg_qemu_tb_exec(env, tb_ptr);
 162     cpu->can_do_io = 1;
 163     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 164     tb_exit = ret & TB_EXIT_MASK;
 165     trace_exec_tb_exit(last_tb, tb_exit);
 166
 167     if (tb_exit > TB_EXIT_IDX1) {
 168         /* We didn't start executing this TB (eg because the instruction
 169          * counter hit zero); we must restore the guest PC to the address
 170          * of the start of the TB.
 171          */
 172         CPUClass *cc = CPU_GET_CLASS(cpu);
 173         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 174                                "Stopped execution of TB chain before %p ["
 175                                TARGET_FMT_lx "] %s\n",
 176                                last_tb->tc_ptr, last_tb->pc,
 177                                lookup_symbol(last_tb->pc));
 178         if (cc->synchronize_from_tb) {
 179             cc->synchronize_from_tb(cpu, last_tb);
 180         } else {
 181             assert(cc->set_pc);
 182             cc->set_pc(cpu, last_tb->pc);
 183         }
 184     }
 185     if (tb_exit == TB_EXIT_REQUESTED) {
 186         /* We were asked to stop executing TBs (probably a pending
 187          * interrupt. We've now stopped, so clear the flag.
 188          */
 189         atomic_set(&cpu->tcg_exit_req, 0);
 190     }
 191     return ret;
 192 }
 193
 194 #ifndef CONFIG_USER_ONLY
 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 = orig_tb;
 211     /* execute the generated code */
 212     trace_exec_tb_nocache(tb, tb->pc);
 213     cpu_tb_exec(cpu, tb);
 214     tb_phys_invalidate(tb, -1);
 215     tb_free(tb);
 216 }
 217 #endif
 218
 219 struct tb_desc {
 220     target_ulong pc;
 221     target_ulong cs_base;
 222     CPUArchState *env;
 223     tb_page_addr_t phys_page1;
 224     uint32_t flags;
 225 };
 226
 227 static bool tb_cmp(const void *p, const void *d)
 228 {
 229     const TranslationBlock *tb = p;
 230     const struct tb_desc *desc = d;
 231
 232     if (tb->pc == desc->pc &&
 233         tb->page_addr[0] == desc->phys_page1 &&
 234         tb->cs_base == desc->cs_base &&
 235         tb->flags == desc->flags &&
 236         !atomic_read(&tb->invalid)) {
 237         /* check next page if needed */
 238         if (tb->page_addr[1] == -1) {
 239             return true;
 240         } else {
 241             tb_page_addr_t phys_page2;
 242             target_ulong virt_page2;
 243
 244             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 245             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 246             if (tb->page_addr[1] == phys_page2) {
 247                 return true;
 248             }
 249         }
 250     }
 251     return false;
 252 }
 253
 254 static TranslationBlock *tb_htable_lookup(CPUState *cpu,
 255                                           target_ulong pc,
 256                                           target_ulong cs_base,
 257                                           uint32_t flags)
 258 {
 259     tb_page_addr_t phys_pc;
 260     struct tb_desc desc;
 261     uint32_t h;
 262
 263     desc.env = (CPUArchState *)cpu->env_ptr;
 264     desc.cs_base = cs_base;
 265     desc.flags = flags;
 266     desc.pc = pc;
 267     phys_pc = get_page_addr_code(desc.env, pc);
 268     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 269     h = tb_hash_func(phys_pc, pc, flags);
 270     return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h);
 271 }
 272
 273 static inline TranslationBlock *tb_find(CPUState *cpu,
 274                                         TranslationBlock *last_tb,
 275                                         int tb_exit)
 276 {
 277     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 278     TranslationBlock *tb;
 279     target_ulong cs_base, pc;
 280     uint32_t flags;
 281     bool have_tb_lock = false;
 282
 283     /* we record a subset of the CPU state. It will
 284        always be the same before a given translated block
 285        is executed. */
 286     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 287     tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
 288     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 289                  tb->flags != flags)) {
 290         tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 291         if (!tb) {
 292
 293             /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 294              * taken outside tb_lock. As system emulation is currently
 295              * single threaded the locks are NOPs.
 296              */
 297             mmap_lock();
 298             tb_lock();
 299             have_tb_lock = true;
 300
 301             /* There's a chance that our desired tb has been translated while
 302              * taking the locks so we check again inside the lock.
 303              */
 304             tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 305             if (!tb) {
 306                 /* if no translated code available, then translate it now */
 307                 tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 308             }
 309
 310             mmap_unlock();
 311         }
 312
 313         /* We add the TB in the virtual pc hash table for the fast lookup */
 314         atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 315     }
 316 #ifndef CONFIG_USER_ONLY
 317     /* We don't take care of direct jumps when address mapping changes in
 318      * system emulation. So it's not safe to make a direct jump to a TB
 319      * spanning two pages because the mapping for the second page can change.
 320      */
 321     if (tb->page_addr[1] != -1) {
 322         last_tb = NULL;
 323     }
 324 #endif
 325     /* See if we can patch the calling TB. */
 326     if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 327         if (!have_tb_lock) {
 328             tb_lock();
 329             have_tb_lock = true;
 330         }
 331         if (!tb->invalid) {
 332             tb_add_jump(last_tb, tb_exit, tb);
 333         }
 334     }
 335     if (have_tb_lock) {
 336         tb_unlock();
 337     }
 338     return tb;
 339 }
 340
 341 static inline bool cpu_handle_halt(CPUState *cpu)
 342 {
 343     if (cpu->halted) {
 344 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 345         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 346             && replay_interrupt()) {
 347             X86CPU *x86_cpu = X86_CPU(cpu);
 348             apic_poll_irq(x86_cpu->apic_state);
 349             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 350         }
 351 #endif
 352         if (!cpu_has_work(cpu)) {
 353             current_cpu = NULL;
 354             return true;
 355         }
 356
 357         cpu->halted = 0;
 358     }
 359
 360     return false;
 361 }
 362
 363 static inline void cpu_handle_debug_exception(CPUState *cpu)
 364 {
 365     CPUClass *cc = CPU_GET_CLASS(cpu);
 366     CPUWatchpoint *wp;
 367
 368     if (!cpu->watchpoint_hit) {
 369         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 370             wp->flags &= ~BP_WATCHPOINT_HIT;
 371         }
 372     }
 373
 374     cc->debug_excp_handler(cpu);
 375 }
 376
 377 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 378 {
 379     if (cpu->exception_index >= 0) {
 380         if (cpu->exception_index >= EXCP_INTERRUPT) {
 381             /* exit request from the cpu execution loop */
 382             *ret = cpu->exception_index;
 383             if (*ret == EXCP_DEBUG) {
 384                 cpu_handle_debug_exception(cpu);
 385             }
 386             cpu->exception_index = -1;
 387             return true;
 388         } else {
 389 #if defined(CONFIG_USER_ONLY)
 390             /* if user mode only, we simulate a fake exception
 391                which will be handled outside the cpu execution
 392                loop */
 393 #if defined(TARGET_I386)
 394             CPUClass *cc = CPU_GET_CLASS(cpu);
 395             cc->do_interrupt(cpu);
 396 #endif
 397             *ret = cpu->exception_index;
 398             cpu->exception_index = -1;
 399             return true;
 400 #else
 401             if (replay_exception()) {
 402                 CPUClass *cc = CPU_GET_CLASS(cpu);
 403                 cc->do_interrupt(cpu);
 404                 cpu->exception_index = -1;
 405             } else if (!replay_has_interrupt()) {
 406                 /* give a chance to iothread in replay mode */
 407                 *ret = EXCP_INTERRUPT;
 408                 return true;
 409             }
 410 #endif
 411         }
 412 #ifndef CONFIG_USER_ONLY
 413     } else if (replay_has_exception()
 414                && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 415         /* try to cause an exception pending in the log */
 416         cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true);
 417         *ret = -1;
 418         return true;
 419 #endif
 420     }
 421
 422     return false;
 423 }
 424
 425 static inline void cpu_handle_interrupt(CPUState *cpu,
 426                                         TranslationBlock **last_tb)
 427 {
 428     CPUClass *cc = CPU_GET_CLASS(cpu);
 429     int interrupt_request = cpu->interrupt_request;
 430
 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 && !replay_has_interrupt()) {
 442             /* Do nothing */
 443         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 444             replay_interrupt();
 445             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 446             cpu->halted = 1;
 447             cpu->exception_index = EXCP_HLT;
 448             cpu_loop_exit(cpu);
 449         }
 450 #if defined(TARGET_I386)
 451         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 452             X86CPU *x86_cpu = X86_CPU(cpu);
 453             CPUArchState *env = &x86_cpu->env;
 454             replay_interrupt();
 455             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 456             do_cpu_init(x86_cpu);
 457             cpu->exception_index = EXCP_HALTED;
 458             cpu_loop_exit(cpu);
 459         }
 460 #else
 461         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 462             replay_interrupt();
 463             cpu_reset(cpu);
 464             cpu_loop_exit(cpu);
 465         }
 466 #endif
 467         /* The target hook has 3 exit conditions:
 468            False when the interrupt isn't processed,
 469            True when it is, and we should restart on a new TB,
 470            and via longjmp via cpu_loop_exit.  */
 471         else {
 472             replay_interrupt();
 473             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 474                 *last_tb = NULL;
 475             }
 476             /* The target hook may have updated the 'cpu->interrupt_request';
 477              * reload the 'interrupt_request' value */
 478             interrupt_request = cpu->interrupt_request;
 479         }
 480         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 481             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 482             /* ensure that no TB jump will be modified as
 483                the program flow was changed */
 484             *last_tb = NULL;
 485         }
 486     }
 487     if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt())) {
 488         atomic_set(&cpu->exit_request, 0);
 489         cpu->exception_index = EXCP_INTERRUPT;
 490         cpu_loop_exit(cpu);
 491     }
 492 }
 493
 494 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 495                                     TranslationBlock **last_tb, int *tb_exit,
 496                                     SyncClocks *sc)
 497 {
 498     uintptr_t ret;
 499
 500     if (unlikely(atomic_read(&cpu->exit_request))) {
 501         return;
 502     }
 503
 504     trace_exec_tb(tb, tb->pc);
 505     ret = cpu_tb_exec(cpu, tb);
 506     *last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 507     *tb_exit = ret & TB_EXIT_MASK;
 508     switch (*tb_exit) {
 509     case TB_EXIT_REQUESTED:
 510         /* Something asked us to stop executing
 511          * chained TBs; just continue round the main
 512          * loop. Whatever requested the exit will also
 513          * have set something else (eg exit_request or
 514          * interrupt_request) which we will handle
 515          * next time around the loop.  But we need to
 516          * ensure the tcg_exit_req read in generated code
 517          * comes before the next read of cpu->exit_request
 518          * or cpu->interrupt_request.
 519          */
 520         smp_rmb();
 521         *last_tb = NULL;
 522         break;
 523     case TB_EXIT_ICOUNT_EXPIRED:
 524     {
 525         /* Instruction counter expired.  */
 526 #ifdef CONFIG_USER_ONLY
 527         abort();
 528 #else
 529         int insns_left = cpu->icount_decr.u32;
 530         if (cpu->icount_extra && insns_left >= 0) {
 531             /* Refill decrementer and continue execution.  */
 532             cpu->icount_extra += insns_left;
 533             insns_left = MIN(0xffff, cpu->icount_extra);
 534             cpu->icount_extra -= insns_left;
 535             cpu->icount_decr.u16.low = insns_left;
 536         } else {
 537             if (insns_left > 0) {
 538                 /* Execute remaining instructions.  */
 539                 cpu_exec_nocache(cpu, insns_left, *last_tb, false);
 540                 align_clocks(sc, cpu);
 541             }
 542             cpu->exception_index = EXCP_INTERRUPT;
 543             *last_tb = NULL;
 544             cpu_loop_exit(cpu);
 545         }
 546         break;
 547 #endif
 548     }
 549     default:
 550         break;
 551     }
 552 }
 553
 554 /* main execution loop */
 555
 556 int cpu_exec(CPUState *cpu)
 557 {
 558     CPUClass *cc = CPU_GET_CLASS(cpu);
 559     int ret;
 560     SyncClocks sc;
 561
 562     /* replay_interrupt may need current_cpu */
 563     current_cpu = cpu;
 564
 565     if (cpu_handle_halt(cpu)) {
 566         return EXCP_HALTED;
 567     }
 568
 569     atomic_mb_set(&tcg_current_cpu, cpu);
 570     rcu_read_lock();
 571
 572     if (unlikely(atomic_mb_read(&exit_request))) {
 573         cpu->exit_request = 1;
 574     }
 575
 576     cc->cpu_exec_enter(cpu);
 577
 578     /* Calculate difference between guest clock and host clock.
 579      * This delay includes the delay of the last cycle, so
 580      * what we have to do is sleep until it is 0. As for the
 581      * advance/delay we gain here, we try to fix it next time.
 582      */
 583     init_delay_params(&sc, cpu);
 584
 585     for(;;) {
 586         /* prepare setjmp context for exception handling */
 587         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 588             TranslationBlock *tb, *last_tb = NULL;
 589             int tb_exit = 0;
 590
 591             /* if an exception is pending, we execute it here */
 592             if (cpu_handle_exception(cpu, &ret)) {
 593                 break;
 594             }
 595
 596             for(;;) {
 597                 cpu_handle_interrupt(cpu, &last_tb);
 598                 tb = tb_find(cpu, last_tb, tb_exit);
 599                 cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
 600                 /* Try to align the host and virtual clocks
 601                    if the guest is in advance */
 602                 align_clocks(&sc, cpu);
 603             } /* for(;;) */
 604         } else {
 605 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 606             /* Some compilers wrongly smash all local variables after
 607              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 608              * Reload essential local variables here for those compilers.
 609              * Newer versions of gcc would complain about this code (-Wclobbered). */
 610             cpu = current_cpu;
 611             cc = CPU_GET_CLASS(cpu);
 612 #else /* buggy compiler */
 613             /* Assert that the compiler does not smash local variables. */
 614             g_assert(cpu == current_cpu);
 615             g_assert(cc == CPU_GET_CLASS(cpu));
 616 #endif /* buggy compiler */
 617             cpu->can_do_io = 1;
 618             tb_lock_reset();
 619         }
 620     } /* for(;;) */
 621
 622     cc->cpu_exec_exit(cpu);
 623     rcu_read_unlock();
 624
 625     /* fail safe : never use current_cpu outside cpu_exec() */
 626     current_cpu = NULL;
 627
 628     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 629     atomic_set(&tcg_current_cpu, NULL);
 630     return ret;
 631 }