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 #include "sysemu/hax.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, uint8_t *tb_ptr)
 137 {
 138     CPUArchState *env = cpu->env_ptr;
 139     uintptr_t next_tb;
 140
 141 #if defined(DEBUG_DISAS)
 142     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)) {
 143 #if defined(TARGET_I386)
 144         log_cpu_state(cpu, CPU_DUMP_CCOP);
 145 #elif defined(TARGET_M68K)
 146         /* ??? Should not modify env state for dumping.  */
 147         cpu_m68k_flush_flags(env, env->cc_op);
 148         env->cc_op = CC_OP_FLAGS;
 149         env->sr = (env->sr & 0xffe0) | env->cc_dest | (env->cc_x << 4);
 150         log_cpu_state(cpu, 0);
 151 #else
 152         log_cpu_state(cpu, 0);
 153 #endif
 154     }
 155 #endif /* DEBUG_DISAS */
 156
 157     cpu->can_do_io = !use_icount;
 158     next_tb = tcg_qemu_tb_exec(env, tb_ptr);
 159     cpu->can_do_io = 1;
 160     trace_exec_tb_exit((void *) (next_tb & ~TB_EXIT_MASK),
 161                        next_tb & TB_EXIT_MASK);
 162
 163     if ((next_tb & TB_EXIT_MASK) > TB_EXIT_IDX1) {
 164         /* We didn't start executing this TB (eg because the instruction
 165          * counter hit zero); we must restore the guest PC to the address
 166          * of the start of the TB.
 167          */
 168         CPUClass *cc = CPU_GET_CLASS(cpu);
 169         TranslationBlock *tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
 170         if (cc->synchronize_from_tb) {
 171             cc->synchronize_from_tb(cpu, tb);
 172         } else {
 173             assert(cc->set_pc);
 174             cc->set_pc(cpu, tb->pc);
 175         }
 176     }
 177     if ((next_tb & TB_EXIT_MASK) == TB_EXIT_REQUESTED) {
 178         /* We were asked to stop executing TBs (probably a pending
 179          * interrupt. We've now stopped, so clear the flag.
 180          */
 181         cpu->tcg_exit_req = 0;
 182     }
 183     return next_tb;
 184 }
 185
 186 /* Execute the code without caching the generated code. An interpreter
 187    could be used if available. */
 188 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 189                              TranslationBlock *orig_tb, bool ignore_icount)
 190 {
 191     TranslationBlock *tb;
 192
 193     /* Should never happen.
 194        We only end up here when an existing TB is too long.  */
 195     if (max_cycles > CF_COUNT_MASK)
 196         max_cycles = CF_COUNT_MASK;
 197
 198     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags,
 199                      max_cycles | CF_NOCACHE
 200                          | (ignore_icount ? CF_IGNORE_ICOUNT : 0));
 201     tb->orig_tb = tcg_ctx.tb_ctx.tb_invalidated_flag ? NULL : orig_tb;
 202     cpu->current_tb = tb;
 203     /* execute the generated code */
 204     trace_exec_tb_nocache(tb, tb->pc);
 205     cpu_tb_exec(cpu, tb->tc_ptr);
 206     cpu->current_tb = NULL;
 207     tb_phys_invalidate(tb, -1);
 208     tb_free(tb);
 209 }
 210
 211 static TranslationBlock *tb_find_physical(CPUState *cpu,
 212                                           target_ulong pc,
 213                                           target_ulong cs_base,
 214                                           uint64_t flags)
 215 {
 216     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 217     TranslationBlock *tb, **ptb1;
 218     unsigned int h;
 219     tb_page_addr_t phys_pc, phys_page1;
 220     target_ulong virt_page2;
 221
 222     tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
 223
 224     /* find translated block using physical mappings */
 225     phys_pc = get_page_addr_code(env, pc);
 226     phys_page1 = phys_pc & TARGET_PAGE_MASK;
 227     h = tb_phys_hash_func(phys_pc);
 228     ptb1 = &tcg_ctx.tb_ctx.tb_phys_hash[h];
 229     for(;;) {
 230         tb = *ptb1;
 231         if (!tb) {
 232             return NULL;
 233         }
 234         if (tb->pc == pc &&
 235             tb->page_addr[0] == phys_page1 &&
 236             tb->cs_base == cs_base &&
 237             tb->flags == flags) {
 238             /* check next page if needed */
 239             if (tb->page_addr[1] != -1) {
 240                 tb_page_addr_t phys_page2;
 241
 242                 virt_page2 = (pc & TARGET_PAGE_MASK) +
 243                     TARGET_PAGE_SIZE;
 244                 phys_page2 = get_page_addr_code(env, virt_page2);
 245                 if (tb->page_addr[1] == phys_page2) {
 246                     break;
 247                 }
 248             } else {
 249                 break;
 250             }
 251         }
 252         ptb1 = &tb->phys_hash_next;
 253     }
 254
 255     /* Move the TB to the head of the list */
 256     *ptb1 = tb->phys_hash_next;
 257     tb->phys_hash_next = tcg_ctx.tb_ctx.tb_phys_hash[h];
 258     tcg_ctx.tb_ctx.tb_phys_hash[h] = tb;
 259     return tb;
 260 }
 261
 262 static TranslationBlock *tb_find_slow(CPUState *cpu,
 263                                       target_ulong pc,
 264                                       target_ulong cs_base,
 265                                       uint64_t flags)
 266 {
 267     TranslationBlock *tb;
 268
 269     tb = tb_find_physical(cpu, pc, cs_base, flags);
 270     if (tb) {
 271         goto found;
 272     }
 273
 274 #ifdef CONFIG_USER_ONLY
 275     /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 276      * taken outside tb_lock.  Since we're momentarily dropping
 277      * tb_lock, there's a chance that our desired tb has been
 278      * translated.
 279      */
 280     tb_unlock();
 281     mmap_lock();
 282     tb_lock();
 283     tb = tb_find_physical(cpu, pc, cs_base, flags);
 284     if (tb) {
 285         mmap_unlock();
 286         goto found;
 287     }
 288 #endif
 289
 290     /* if no translated code available, then translate it now */
 291     tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 292
 293 #ifdef CONFIG_USER_ONLY
 294     mmap_unlock();
 295 #endif
 296
 297 found:
 298     /* we add the TB in the virtual pc hash table */
 299     cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)] = tb;
 300     return tb;
 301 }
 302
 303 static inline TranslationBlock *tb_find_fast(CPUState *cpu)
 304 {
 305     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 306     TranslationBlock *tb;
 307     target_ulong cs_base, pc;
 308     int flags;
 309
 310     /* we record a subset of the CPU state. It will
 311        always be the same before a given translated block
 312        is executed. */
 313     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 314     tb = cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)];
 315     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 316                  tb->flags != flags)) {
 317         tb = tb_find_slow(cpu, pc, cs_base, flags);
 318     }
 319     return tb;
 320 }
 321
 322 static void cpu_handle_debug_exception(CPUState *cpu)
 323 {
 324     CPUClass *cc = CPU_GET_CLASS(cpu);
 325     CPUWatchpoint *wp;
 326
 327     if (!cpu->watchpoint_hit) {
 328         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 329             wp->flags &= ~BP_WATCHPOINT_HIT;
 330         }
 331     }
 332
 333     cc->debug_excp_handler(cpu);
 334 }
 335
 336 /* main execution loop */
 337
 338 int cpu_exec(CPUState *cpu)
 339 {
 340     CPUClass *cc = CPU_GET_CLASS(cpu);
 341 #ifdef TARGET_I386
 342     X86CPU *x86_cpu = X86_CPU(cpu);
 343     CPUArchState *env = &x86_cpu->env;
 344 #endif
 345     int ret, interrupt_request;
 346     TranslationBlock *tb;
 347     uint8_t *tc_ptr;
 348     uintptr_t next_tb;
 349     SyncClocks sc;
 350
 351     /* replay_interrupt may need current_cpu */
 352     current_cpu = cpu;
 353
 354     if (cpu->halted) {
 355 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 356         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 357             && replay_interrupt()) {
 358             apic_poll_irq(x86_cpu->apic_state);
 359             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 360         }
 361 #endif
 362         if (!cpu_has_work(cpu)) {
 363             current_cpu = NULL;
 364             return EXCP_HALTED;
 365         }
 366
 367         cpu->halted = 0;
 368     }
 369
 370     atomic_mb_set(&tcg_current_cpu, cpu);
 371     rcu_read_lock();
 372
 373     if (unlikely(atomic_mb_read(&exit_request))) {
 374         cpu->exit_request = 1;
 375     }
 376
 377     cc->cpu_exec_enter(cpu);
 378
 379     /* Calculate difference between guest clock and host clock.
 380      * This delay includes the delay of the last cycle, so
 381      * what we have to do is sleep until it is 0. As for the
 382      * advance/delay we gain here, we try to fix it next time.
 383      */
 384     init_delay_params(&sc, cpu);
 385
 386     /* prepare setjmp context for exception handling */
 387     for(;;) {
 388         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 389             /* if an exception is pending, we execute it here */
 390             if (cpu->exception_index >= 0) {
 391                 if (cpu->exception_index >= EXCP_INTERRUPT) {
 392                     /* exit request from the cpu execution loop */
 393                     ret = cpu->exception_index;
 394                     if (ret == EXCP_DEBUG) {
 395                         cpu_handle_debug_exception(cpu);
 396                     }
 397                     cpu->exception_index = -1;
 398                     break;
 399                 } else {
 400 #if defined(CONFIG_USER_ONLY)
 401                     /* if user mode only, we simulate a fake exception
 402                        which will be handled outside the cpu execution
 403                        loop */
 404 #if defined(TARGET_I386)
 405                     cc->do_interrupt(cpu);
 406 #endif
 407                     ret = cpu->exception_index;
 408                     cpu->exception_index = -1;
 409                     break;
 410 #else
 411                     if (replay_exception()) {
 412                         cc->do_interrupt(cpu);
 413                         cpu->exception_index = -1;
 414                     } else if (!replay_has_interrupt()) {
 415                         /* give a chance to iothread in replay mode */
 416                         ret = EXCP_INTERRUPT;
 417                         break;
 418                     }
 419 #endif
 420                 }
 421             } else if (replay_has_exception()
 422                        && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 423                 /* try to cause an exception pending in the log */
 424                 cpu_exec_nocache(cpu, 1, tb_find_fast(cpu), true);
 425                 ret = -1;
 426                 break;
 427             }
 428
 429 #ifdef CONFIG_HAX
 430             if (hax_enabled() && !hax_vcpu_exec(cpu))
 431                 longjmp(cpu->jmp_env, 1);
 432 #endif
 433
 434             next_tb = 0; /* force lookup of first TB */
 435             for(;;) {
 436                 interrupt_request = cpu->interrupt_request;
 437                 if (unlikely(interrupt_request)) {
 438                     if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 439                         /* Mask out external interrupts for this step. */
 440                         interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 441                     }
 442                     if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 443                         cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 444                         cpu->exception_index = EXCP_DEBUG;
 445                         cpu_loop_exit(cpu);
 446                     }
 447                     if (replay_mode == REPLAY_MODE_PLAY
 448                         && !replay_has_interrupt()) {
 449                         /* Do nothing */
 450                     } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 451                         replay_interrupt();
 452                         cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 453                         cpu->halted = 1;
 454                         cpu->exception_index = EXCP_HLT;
 455                         cpu_loop_exit(cpu);
 456                     }
 457 #if defined(TARGET_I386)
 458                     else if (interrupt_request & CPU_INTERRUPT_INIT) {
 459                         replay_interrupt();
 460                         cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 461                         do_cpu_init(x86_cpu);
 462                         cpu->exception_index = EXCP_HALTED;
 463                         cpu_loop_exit(cpu);
 464                     }
 465 #else
 466                     else if (interrupt_request & CPU_INTERRUPT_RESET) {
 467                         replay_interrupt();
 468                         cpu_reset(cpu);
 469                         cpu_loop_exit(cpu);
 470                     }
 471 #endif
 472                     /* The target hook has 3 exit conditions:
 473                        False when the interrupt isn't processed,
 474                        True when it is, and we should restart on a new TB,
 475                        and via longjmp via cpu_loop_exit.  */
 476                     else {
 477                         replay_interrupt();
 478                         if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 479                             next_tb = 0;
 480                         }
 481                     }
 482                     /* Don't use the cached interrupt_request value,
 483                        do_interrupt may have updated the EXITTB flag. */
 484                     if (cpu->interrupt_request & CPU_INTERRUPT_EXITTB) {
 485                         cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 486                         /* ensure that no TB jump will be modified as
 487                            the program flow was changed */
 488                         next_tb = 0;
 489                     }
 490                 }
 491                 if (unlikely(cpu->exit_request
 492                              || replay_has_interrupt())) {
 493                     cpu->exit_request = 0;
 494                     cpu->exception_index = EXCP_INTERRUPT;
 495                     cpu_loop_exit(cpu);
 496                 }
 497                 tb_lock();
 498                 tb = tb_find_fast(cpu);
 499                 /* Note: we do it here to avoid a gcc bug on Mac OS X when
 500                    doing it in tb_find_slow */
 501                 if (tcg_ctx.tb_ctx.tb_invalidated_flag) {
 502                     /* as some TB could have been invalidated because
 503                        of memory exceptions while generating the code, we
 504                        must recompute the hash index here */
 505                     next_tb = 0;
 506                     tcg_ctx.tb_ctx.tb_invalidated_flag = 0;
 507                 }
 508                 if (qemu_loglevel_mask(CPU_LOG_EXEC)) {
 509                     qemu_log("Trace %p [" TARGET_FMT_lx "] %s\n",
 510                              tb->tc_ptr, tb->pc, lookup_symbol(tb->pc));
 511                 }
 512                 /* see if we can patch the calling TB. When the TB
 513                    spans two pages, we cannot safely do a direct
 514                    jump. */
 515                 if (next_tb != 0 && tb->page_addr[1] == -1
 516                     && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 517                     tb_add_jump((TranslationBlock *)(next_tb & ~TB_EXIT_MASK),
 518                                 next_tb & TB_EXIT_MASK, tb);
 519                 }
 520                 tb_unlock();
 521                 if (likely(!cpu->exit_request)) {
 522                     trace_exec_tb(tb, tb->pc);
 523                     tc_ptr = tb->tc_ptr;
 524                     /* execute the generated code */
 525                     cpu->current_tb = tb;
 526                     next_tb = cpu_tb_exec(cpu, tc_ptr);
 527                     cpu->current_tb = NULL;
 528                     switch (next_tb & TB_EXIT_MASK) {
 529                     case TB_EXIT_REQUESTED:
 530                         /* Something asked us to stop executing
 531                          * chained TBs; just continue round the main
 532                          * loop. Whatever requested the exit will also
 533                          * have set something else (eg exit_request or
 534                          * interrupt_request) which we will handle
 535                          * next time around the loop.  But we need to
 536                          * ensure the tcg_exit_req read in generated code
 537                          * comes before the next read of cpu->exit_request
 538                          * or cpu->interrupt_request.
 539                          */
 540                         smp_rmb();
 541                         next_tb = 0;
 542                         break;
 543                     case TB_EXIT_ICOUNT_EXPIRED:
 544                     {
 545                         /* Instruction counter expired.  */
 546                         int insns_left = cpu->icount_decr.u32;
 547                         if (cpu->icount_extra && insns_left >= 0) {
 548                             /* Refill decrementer and continue execution.  */
 549                             cpu->icount_extra += insns_left;
 550                             insns_left = MIN(0xffff, cpu->icount_extra);
 551                             cpu->icount_extra -= insns_left;
 552                             cpu->icount_decr.u16.low = insns_left;
 553                         } else {
 554                             if (insns_left > 0) {
 555                                 /* Execute remaining instructions.  */
 556                                 tb = (TranslationBlock *)(next_tb & ~TB_EXIT_MASK);
 557                                 cpu_exec_nocache(cpu, insns_left, tb, false);
 558                                 align_clocks(&sc, cpu);
 559                             }
 560                             cpu->exception_index = EXCP_INTERRUPT;
 561                             next_tb = 0;
 562                             cpu_loop_exit(cpu);
 563                         }
 564                         break;
 565                     }
 566                     default:
 567                         break;
 568                     }
 569                 }
 570 #ifdef CONFIG_HAX
 571                 if (hax_enabled() && hax_stop_emulation(cpu))
 572                     cpu_loop_exit(cpu);
 573 #endif
 574                 /* Try to align the host and virtual clocks
 575                    if the guest is in advance */
 576                 align_clocks(&sc, cpu);
 577                 /* reset soft MMU for next block (it can currently
 578                    only be set by a memory fault) */
 579             } /* for(;;) */
 580         } else {
 581 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 582             /* Some compilers wrongly smash all local variables after
 583              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 584              * Reload essential local variables here for those compilers.
 585              * Newer versions of gcc would complain about this code (-Wclobbered). */
 586             cpu = current_cpu;
 587             cc = CPU_GET_CLASS(cpu);
 588 #ifdef TARGET_I386
 589             x86_cpu = X86_CPU(cpu);
 590             env = &x86_cpu->env;
 591 #endif
 592 #else /* buggy compiler */
 593             /* Assert that the compiler does not smash local variables. */
 594             g_assert(cpu == current_cpu);
 595             g_assert(cc == CPU_GET_CLASS(cpu));
 596 #ifdef TARGET_I386
 597             g_assert(x86_cpu == X86_CPU(cpu));
 598             g_assert(env == &x86_cpu->env);
 599 #endif
 600 #endif /* buggy compiler */
 601             cpu->can_do_io = 1;
 602             tb_lock_reset();
 603         }
 604     } /* for(;;) */
 605
 606     cc->cpu_exec_exit(cpu);
 607     rcu_read_unlock();
 608
 609     /* fail safe : never use current_cpu outside cpu_exec() */
 610     current_cpu = NULL;
 611
 612     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 613     atomic_set(&tcg_current_cpu, NULL);
 614     return ret;
 615 }