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 #include "sysemu/hax.h"
  37
  38 /* -icount align implementation. */
  39
  40 typedef struct SyncClocks {
  41     int64_t diff_clk;
  42     int64_t last_cpu_icount;
  43     int64_t realtime_clock;
  44 } SyncClocks;
  45
  46 #if !defined(CONFIG_USER_ONLY)
  47 /* Allow the guest to have a max 3ms advance.
  48  * The difference between the 2 clocks could therefore
  49  * oscillate around 0.
  50  */
  51 #define VM_CLOCK_ADVANCE 3000000
  52 #define THRESHOLD_REDUCE 1.5
  53 #define MAX_DELAY_PRINT_RATE 2000000000LL
  54 #define MAX_NB_PRINTS 100
  55
  56 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
  57 {
  58     int64_t cpu_icount;
  59
  60     if (!icount_align_option) {
  61         return;
  62     }
  63
  64     cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
  65     sc->diff_clk += cpu_icount_to_ns(sc->last_cpu_icount - cpu_icount);
  66     sc->last_cpu_icount = cpu_icount;
  67
  68     if (sc->diff_clk > VM_CLOCK_ADVANCE) {
  69 #ifndef _WIN32
  70         struct timespec sleep_delay, rem_delay;
  71         sleep_delay.tv_sec = sc->diff_clk / 1000000000LL;
  72         sleep_delay.tv_nsec = sc->diff_clk % 1000000000LL;
  73         if (nanosleep(&sleep_delay, &rem_delay) < 0) {
  74             sc->diff_clk = rem_delay.tv_sec * 1000000000LL + rem_delay.tv_nsec;
  75         } else {
  76             sc->diff_clk = 0;
  77         }
  78 #else
  79         Sleep(sc->diff_clk / SCALE_MS);
  80         sc->diff_clk = 0;
  81 #endif
  82     }
  83 }
  84
  85 static void print_delay(const SyncClocks *sc)
  86 {
  87     static float threshold_delay;
  88     static int64_t last_realtime_clock;
  89     static int nb_prints;
  90
  91     if (icount_align_option &&
  92         sc->realtime_clock - last_realtime_clock >= MAX_DELAY_PRINT_RATE &&
  93         nb_prints < MAX_NB_PRINTS) {
  94         if ((-sc->diff_clk / (float)1000000000LL > threshold_delay) ||
  95             (-sc->diff_clk / (float)1000000000LL <
  96              (threshold_delay - THRESHOLD_REDUCE))) {
  97             threshold_delay = (-sc->diff_clk / 1000000000LL) + 1;
  98             printf("Warning: The guest is now late by %.1f to %.1f seconds\n",
  99                    threshold_delay - 1,
 100                    threshold_delay);
 101             nb_prints++;
 102             last_realtime_clock = sc->realtime_clock;
 103         }
 104     }
 105 }
 106
 107 static void init_delay_params(SyncClocks *sc,
 108                               const CPUState *cpu)
 109 {
 110     if (!icount_align_option) {
 111         return;
 112     }
 113     sc->realtime_clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT);
 114     sc->diff_clk = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) - sc->realtime_clock;
 115     sc->last_cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
 116     if (sc->diff_clk < max_delay) {
 117         max_delay = sc->diff_clk;
 118     }
 119     if (sc->diff_clk > max_advance) {
 120         max_advance = sc->diff_clk;
 121     }
 122
 123     /* Print every 2s max if the guest is late. We limit the number
 124        of printed messages to NB_PRINT_MAX(currently 100) */
 125     print_delay(sc);
 126 }
 127 #else
 128 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
 129 {
 130 }
 131
 132 static void init_delay_params(SyncClocks *sc, const CPUState *cpu)
 133 {
 134 }
 135 #endif /* CONFIG USER ONLY */
 136
 137 /* Execute a TB, and fix up the CPU state afterwards if necessary */
 138 static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
 139 {
 140     CPUArchState *env = cpu->env_ptr;
 141     uintptr_t next_tb;
 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     next_tb = tcg_qemu_tb_exec(env, tb_ptr);
 166     cpu->can_do_io = 1;
 167     trace_exec_tb_exit((void *) (next_tb & ~TB_EXIT_MASK),
 168                        next_tb & TB_EXIT_MASK);
 169
 170     if ((next_tb & TB_EXIT_MASK) > TB_EXIT_IDX1) {
 171         /* We didn't start executing this TB (eg because the instruction
 172          * counter hit zero); we must restore the guest PC to the address
 173          * of the start of the TB.
 174          */
 175         CPUClass *cc = CPU_GET_CLASS(cpu);
 176         TranslationBlock *tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
 177         qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 178                                "Stopped execution of TB chain before %p ["
 179                                TARGET_FMT_lx "] %s\n",
 180                                itb->tc_ptr, itb->pc, lookup_symbol(itb->pc));
 181         if (cc->synchronize_from_tb) {
 182             cc->synchronize_from_tb(cpu, tb);
 183         } else {
 184             assert(cc->set_pc);
 185             cc->set_pc(cpu, tb->pc);
 186         }
 187     }
 188     if ((next_tb & TB_EXIT_MASK) == TB_EXIT_REQUESTED) {
 189         /* We were asked to stop executing TBs (probably a pending
 190          * interrupt. We've now stopped, so clear the flag.
 191          */
 192         cpu->tcg_exit_req = 0;
 193     }
 194     return next_tb;
 195 }
 196
 197 /* Execute the code without caching the generated code. An interpreter
 198    could be used if available. */
 199 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 200                              TranslationBlock *orig_tb, bool ignore_icount)
 201 {
 202     TranslationBlock *tb;
 203
 204     /* Should never happen.
 205        We only end up here when an existing TB is too long.  */
 206     if (max_cycles > CF_COUNT_MASK)
 207         max_cycles = CF_COUNT_MASK;
 208
 209     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags,
 210                      max_cycles | CF_NOCACHE
 211                          | (ignore_icount ? CF_IGNORE_ICOUNT : 0));
 212     tb->orig_tb = tcg_ctx.tb_ctx.tb_invalidated_flag ? NULL : orig_tb;
 213     cpu->current_tb = tb;
 214     /* execute the generated code */
 215     trace_exec_tb_nocache(tb, tb->pc);
 216     cpu_tb_exec(cpu, tb);
 217     cpu->current_tb = NULL;
 218     tb_phys_invalidate(tb, -1);
 219     tb_free(tb);
 220 }
 221
 222 static TranslationBlock *tb_find_physical(CPUState *cpu,
 223                                           target_ulong pc,
 224                                           target_ulong cs_base,
 225                                           uint64_t flags)
 226 {
 227     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 228     TranslationBlock *tb, **ptb1;
 229     unsigned int h;
 230     tb_page_addr_t phys_pc, phys_page1;
 231     target_ulong virt_page2;
 232
 233     tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
 234
 235     /* find translated block using physical mappings */
 236     phys_pc = get_page_addr_code(env, pc);
 237     phys_page1 = phys_pc & TARGET_PAGE_MASK;
 238     h = tb_phys_hash_func(phys_pc);
 239     ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
 240     for(;;) {
 241         tb = *ptb1;
 242         if (!tb) {
 243             return NULL;
 244         }
 245         if (tb->pc == pc &&
 246             tb->page_addr[0] == phys_page1 &&
 247             tb->cs_base == cs_base &&
 248             tb->flags == flags) {
 249             /* check next page if needed */
 250             if (tb->page_addr[1] != -1) {
 251                 tb_page_addr_t phys_page2;
 252
 253                 virt_page2 = (pc & TARGET_PAGE_MASK) +
 254                     TARGET_PAGE_SIZE;
 255                 phys_page2 = get_page_addr_code(env, virt_page2);
 256                 if (tb->page_addr[1] == phys_page2) {
 257                     break;
 258                 }
 259             } else {
 260                 break;
 261             }
 262         }
 263         ptb1 = &tb->phys_hash_next;
 264     }
 265
 266     /* Move the TB to the head of the list */
 267     *ptb1 = tb->phys_hash_next;
 268     tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
 269     tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
 270     return tb;
 271 }
 272
 273 static TranslationBlock *tb_find_slow(CPUState *cpu,
 274                                       target_ulong pc,
 275                                       target_ulong cs_base,
 276                                       uint64_t flags)
 277 {
 278     TranslationBlock *tb;
 279
 280     tb = tb_find_physical(cpu, pc, cs_base, flags);
 281     if (tb) {
 282         goto found;
 283     }
 284
 285 #ifdef CONFIG_USER_ONLY
 286     /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 287      * taken outside tb_lock.  Since we're momentarily dropping
 288      * tb_lock, there's a chance that our desired tb has been
 289      * translated.
 290      */
 291     tb_unlock();
 292     mmap_lock();
 293     tb_lock();
 294     tb = tb_find_physical(cpu, pc, cs_base, flags);
 295     if (tb) {
 296         mmap_unlock();
 297         goto found;
 298     }
 299 #endif
 300
 301     /* if no translated code available, then translate it now */
 302     tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 303
 304 #ifdef CONFIG_USER_ONLY
 305     mmap_unlock();
 306 #endif
 307
 308 found:
 309     /* we add the TB in the virtual pc hash table */
 310     cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)] = tb;
 311     return tb;
 312 }
 313
 314 static inline TranslationBlock *tb_find_fast(CPUState *cpu)
 315 {
 316     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 317     TranslationBlock *tb;
 318     target_ulong cs_base, pc;
 319     int flags;
 320
 321     /* we record a subset of the CPU state. It will
 322        always be the same before a given translated block
 323        is executed. */
 324     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 325     tb = cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)];
 326     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 327                  tb->flags != flags)) {
 328         tb = tb_find_slow(cpu, pc, cs_base, flags);
 329     }
 330     return tb;
 331 }
 332
 333 static void cpu_handle_debug_exception(CPUState *cpu)
 334 {
 335     CPUClass *cc = CPU_GET_CLASS(cpu);
 336     CPUWatchpoint *wp;
 337
 338     if (!cpu->watchpoint_hit) {
 339         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 340             wp->flags &= ~BP_WATCHPOINT_HIT;
 341         }
 342     }
 343
 344     cc->debug_excp_handler(cpu);
 345 }
 346
 347 /* main execution loop */
 348
 349 int cpu_exec(CPUState *cpu)
 350 {
 351     CPUClass *cc = CPU_GET_CLASS(cpu);
 352 #ifdef TARGET_I386
 353     X86CPU *x86_cpu = X86_CPU(cpu);
 354     CPUArchState *env = &x86_cpu->env;
 355 #endif
 356     int ret, interrupt_request;
 357     TranslationBlock *tb;
 358     uintptr_t next_tb;
 359     SyncClocks sc;
 360
 361     /* replay_interrupt may need current_cpu */
 362     current_cpu = cpu;
 363
 364     if (cpu->halted) {
 365 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 366         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 367             && replay_interrupt()) {
 368             apic_poll_irq(x86_cpu->apic_state);
 369             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 370         }
 371 #endif
 372         if (!cpu_has_work(cpu)) {
 373             current_cpu = NULL;
 374             return EXCP_HALTED;
 375         }
 376
 377         cpu->halted = 0;
 378     }
 379
 380     atomic_mb_set(&tcg_current_cpu, cpu);
 381     rcu_read_lock();
 382
 383     if (unlikely(atomic_mb_read(&exit_request))) {
 384         cpu->exit_request = 1;
 385     }
 386
 387     cc->cpu_exec_enter(cpu);
 388
 389     /* Calculate difference between guest clock and host clock.
 390      * This delay includes the delay of the last cycle, so
 391      * what we have to do is sleep until it is 0. As for the
 392      * advance/delay we gain here, we try to fix it next time.
 393      */
 394     init_delay_params(&sc, cpu);
 395
 396     /* prepare setjmp context for exception handling */
 397     for(;;) {
 398         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 399             /* if an exception is pending, we execute it here */
 400             if (cpu->exception_index >= 0) {
 401                 if (cpu->exception_index >= EXCP_INTERRUPT) {
 402                     /* exit request from the cpu execution loop */
 403                     ret = cpu->exception_index;
 404                     if (ret == EXCP_DEBUG) {
 405                         cpu_handle_debug_exception(cpu);
 406                     }
 407                     cpu->exception_index = -1;
 408                     break;
 409                 } else {
 410 #if defined(CONFIG_USER_ONLY)
 411                     /* if user mode only, we simulate a fake exception
 412                        which will be handled outside the cpu execution
 413                        loop */
 414 #if defined(TARGET_I386)
 415                     cc->do_interrupt(cpu);
 416 #endif
 417                     ret = cpu->exception_index;
 418                     cpu->exception_index = -1;
 419                     break;
 420 #else
 421                     if (replay_exception()) {
 422                         cc->do_interrupt(cpu);
 423                         cpu->exception_index = -1;
 424                     } else if (!replay_has_interrupt()) {
 425                         /* give a chance to iothread in replay mode */
 426                         ret = EXCP_INTERRUPT;
 427                         break;
 428                     }
 429 #endif
 430                 }
 431             } else if (replay_has_exception()
 432                        && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 433                 /* try to cause an exception pending in the log */
 434                 cpu_exec_nocache(cpu, 1, tb_find_fast(cpu), true);
 435                 ret = -1;
 436                 break;
 437             }
 438
 439 #ifdef CONFIG_HAX
 440             if (hax_enabled() && !hax_vcpu_exec(cpu))
 441                 longjmp(cpu->jmp_env, 1);
 442 #endif
 443
 444             next_tb = 0; /* force lookup of first TB */
 445             for(;;) {
 446                 interrupt_request = cpu->interrupt_request;
 447                 if (unlikely(interrupt_request)) {
 448                     if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 449                         /* Mask out external interrupts for this step. */
 450                         interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 451                     }
 452                     if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 453                         cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 454                         cpu->exception_index = EXCP_DEBUG;
 455                         cpu_loop_exit(cpu);
 456                     }
 457                     if (replay_mode == REPLAY_MODE_PLAY
 458                         && !replay_has_interrupt()) {
 459                         /* Do nothing */
 460                     } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 461                         replay_interrupt();
 462                         cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 463                         cpu->halted = 1;
 464                         cpu->exception_index = EXCP_HLT;
 465                         cpu_loop_exit(cpu);
 466                     }
 467 #if defined(TARGET_I386)
 468                     else if (interrupt_request & CPU_INTERRUPT_INIT) {
 469                         replay_interrupt();
 470                         cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 471                         do_cpu_init(x86_cpu);
 472                         cpu->exception_index = EXCP_HALTED;
 473                         cpu_loop_exit(cpu);
 474                     }
 475 #else
 476                     else if (interrupt_request & CPU_INTERRUPT_RESET) {
 477                         replay_interrupt();
 478                         cpu_reset(cpu);
 479                         cpu_loop_exit(cpu);
 480                     }
 481 #endif
 482                     /* The target hook has 3 exit conditions:
 483                        False when the interrupt isn't processed,
 484                        True when it is, and we should restart on a new TB,
 485                        and via longjmp via cpu_loop_exit.  */
 486                     else {
 487                         replay_interrupt();
 488                         if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 489                             next_tb = 0;
 490                         }
 491                     }
 492                     /* Don't use the cached interrupt_request value,
 493                        do_interrupt may have updated the EXITTB flag. */
 494                     if (cpu->interrupt_request & CPU_INTERRUPT_EXITTB) {
 495                         cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 496                         /* ensure that no TB jump will be modified as
 497                            the program flow was changed */
 498                         next_tb = 0;
 499                     }
 500                 }
 501                 if (unlikely(cpu->exit_request
 502                              || replay_has_interrupt())) {
 503                     cpu->exit_request = 0;
 504                     cpu->exception_index = EXCP_INTERRUPT;
 505                     cpu_loop_exit(cpu);
 506                 }
 507                 tb_lock();
 508                 tb = tb_find_fast(cpu);
 509                 /* Note: we do it here to avoid a gcc bug on Mac OS X when
 510                    doing it in tb_find_slow */
 511                 if (tcg_ctx.tb_ctx.tb_invalidated_flag) {
 512                     /* as some TB could have been invalidated because
 513                        of memory exceptions while generating the code, we
 514                        must recompute the hash index here */
 515                     next_tb = 0;
 516                     tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
 517                 }
 518                 /* see if we can patch the calling TB. When the TB
 519                    spans two pages, we cannot safely do a direct
 520                    jump. */
 521                 if (next_tb != 0 && tb->page_addr[1] == -1
 522                     && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 523                     tb_add_jump((TranslationBlock *)(next_tb & ~TB_EXIT_MASK),
 524                                 next_tb & TB_EXIT_MASK, tb);
 525                 }
 526                 tb_unlock();
 527                 if (likely(!cpu->exit_request)) {
 528                     trace_exec_tb(tb, tb->pc);
 529                     /* execute the generated code */
 530                     cpu->current_tb = tb;
 531                     next_tb = cpu_tb_exec(cpu, tb);
 532                     cpu->current_tb = NULL;
 533                     switch (next_tb & TB_EXIT_MASK) {
 534                     case TB_EXIT_REQUESTED:
 535                         /* Something asked us to stop executing
 536                          * chained TBs; just continue round the main
 537                          * loop. Whatever requested the exit will also
 538                          * have set something else (eg exit_request or
 539                          * interrupt_request) which we will handle
 540                          * next time around the loop.  But we need to
 541                          * ensure the tcg_exit_req read in generated code
 542                          * comes before the next read of cpu->exit_request
 543                          * or cpu->interrupt_request.
 544                          */
 545                         smp_rmb();
 546                         next_tb = 0;
 547                         break;
 548                     case TB_EXIT_ICOUNT_EXPIRED:
 549                     {
 550                         /* Instruction counter expired.  */
 551                         int insns_left = cpu->icount_decr.u32;
 552                         if (cpu->icount_extra && insns_left >= 0) {
 553                             /* Refill decrementer and continue execution.  */
 554                             cpu->icount_extra += insns_left;
 555                             insns_left = MIN(0xffff, cpu->icount_extra);
 556                             cpu->icount_extra -= insns_left;
 557                             cpu->icount_decr.u16.low = insns_left;
 558                         } else {
 559                             if (insns_left > 0) {
 560                                 /* Execute remaining instructions.  */
 561                                 tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
 562                                 cpu_exec_nocache(cpu, insns_left, tb, false);
 563                                 align_clocks(&sc, cpu);
 564                             }
 565                             cpu->exception_index = EXCP_INTERRUPT;
 566                             next_tb = 0;
 567                             cpu_loop_exit(cpu);
 568                         }
 569                         break;
 570                     }
 571                     default:
 572                         break;
 573                     }
 574                 }
 575 #ifdef CONFIG_HAX
 576                 if (hax_enabled() && hax_stop_emulation(cpu))
 577                     cpu_loop_exit(cpu);
 578 #endif
 579                 /* Try to align the host and virtual clocks
 580                    if the guest is in advance */
 581                 align_clocks(&sc, cpu);
 582                 /* reset soft MMU for next block (it can currently
 583                    only be set by a memory fault) */
 584             } /* for(;;) */
 585         } else {
 586 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 587             /* Some compilers wrongly smash all local variables after
 588              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 589              * Reload essential local variables here for those compilers.
 590              * Newer versions of gcc would complain about this code (-Wclobbered). */
 591             cpu = current_cpu;
 592             cc = CPU_GET_CLASS(cpu);
 593 #ifdef TARGET_I386
 594             x86_cpu = X86_CPU(cpu);
 595             env = &x86_cpu->env;
 596 #endif
 597 #else /* buggy compiler */
 598             /* Assert that the compiler does not smash local variables. */
 599             g_assert(cpu == current_cpu);
 600             g_assert(cc == CPU_GET_CLASS(cpu));
 601 #ifdef TARGET_I386
 602             g_assert(x86_cpu == X86_CPU(cpu));
 603             g_assert(env == &x86_cpu->env);
 604 #endif
 605 #endif /* buggy compiler */
 606             cpu->can_do_io = 1;
 607             tb_lock_reset();
 608         }
 609     } /* for(;;) */
 610
 611     cc->cpu_exec_exit(cpu);
 612     rcu_read_unlock();
 613
 614     /* fail safe : never use current_cpu outside cpu_exec() */
 615     current_cpu = NULL;
 616
 617     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 618     atomic_set(&tcg_current_cpu, NULL);
 619     return ret;
 620 }