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 #if defined(TARGET_I386)
 152         log_cpu_state(cpu, CPU_DUMP_CCOP);
 153 #elif defined(TARGET_M68K)
 154         /* ??? Should not modify env state for dumping.  */
 155         cpu_m68k_flush_flags(env, env->cc_op);
 156         env->cc_op = CC_OP_FLAGS;
 157         env->sr = (env->sr & 0xffe0) | env->cc_dest | (env->cc_x << 4);
 158         log_cpu_state(cpu, 0);
 159 #else
 160         log_cpu_state(cpu, 0);
 161 #endif
 162     }
 163 #endif /* DEBUG_DISAS */
 164
 165     cpu->can_do_io = !use_icount;
 166     ret = tcg_qemu_tb_exec(env, tb_ptr);
 167     cpu->can_do_io = 1;
 168     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 169     tb_exit = ret & TB_EXIT_MASK;
 170     trace_exec_tb_exit(last_tb, tb_exit);
 171
 172     if (tb_exit > TB_EXIT_IDX1) {
 173         /* We didn't start executing this TB (eg because the instruction
 174          * counter hit zero); we must restore the guest PC to the address
 175          * of the start of the TB.
 176          */
 177         CPUClass *cc = CPU_GET_CLASS(cpu);
 178         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 179                                "Stopped execution of TB chain before %p ["
 180                                TARGET_FMT_lx "] %s\n",
 181                                last_tb->tc_ptr, last_tb->pc,
 182                                lookup_symbol(last_tb->pc));
 183         if (cc->synchronize_from_tb) {
 184             cc->synchronize_from_tb(cpu, last_tb);
 185         } else {
 186             assert(cc->set_pc);
 187             cc->set_pc(cpu, last_tb->pc);
 188         }
 189     }
 190     if (tb_exit == TB_EXIT_REQUESTED) {
 191         /* We were asked to stop executing TBs (probably a pending
 192          * interrupt. We've now stopped, so clear the flag.
 193          */
 194         cpu->tcg_exit_req = 0;
 195     }
 196     return ret;
 197 }
 198
 199 #ifndef CONFIG_USER_ONLY
 200 /* Execute the code without caching the generated code. An interpreter
 201    could be used if available. */
 202 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 203                              TranslationBlock *orig_tb, bool ignore_icount)
 204 {
 205     TranslationBlock *tb;
 206     bool old_tb_flushed;
 207
 208     /* Should never happen.
 209        We only end up here when an existing TB is too long.  */
 210     if (max_cycles > CF_COUNT_MASK)
 211         max_cycles = CF_COUNT_MASK;
 212
 213     old_tb_flushed = cpu->tb_flushed;
 214     cpu->tb_flushed = false;
 215     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags,
 216                      max_cycles | CF_NOCACHE
 217                          | (ignore_icount ? CF_IGNORE_ICOUNT : 0));
 218     tb->orig_tb = cpu->tb_flushed ? NULL : orig_tb;
 219     cpu->tb_flushed |= old_tb_flushed;
 220     /* execute the generated code */
 221     trace_exec_tb_nocache(tb, tb->pc);
 222     cpu_tb_exec(cpu, tb);
 223     tb_phys_invalidate(tb, -1);
 224     tb_free(tb);
 225 }
 226 #endif
 227
 228 struct tb_desc {
 229     target_ulong pc;
 230     target_ulong cs_base;
 231     CPUArchState *env;
 232     tb_page_addr_t phys_page1;
 233     uint32_t flags;
 234 };
 235
 236 static bool tb_cmp(const void *p, const void *d)
 237 {
 238     const TranslationBlock *tb = p;
 239     const struct tb_desc *desc = d;
 240
 241     if (tb->pc == desc->pc &&
 242         tb->page_addr[0] == desc->phys_page1 &&
 243         tb->cs_base == desc->cs_base &&
 244         tb->flags == desc->flags &&
 245         !atomic_read(&tb->invalid)) {
 246         /* check next page if needed */
 247         if (tb->page_addr[1] == -1) {
 248             return true;
 249         } else {
 250             tb_page_addr_t phys_page2;
 251             target_ulong virt_page2;
 252
 253             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 254             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 255             if (tb->page_addr[1] == phys_page2) {
 256                 return true;
 257             }
 258         }
 259     }
 260     return false;
 261 }
 262
 263 static TranslationBlock *tb_find_physical(CPUState *cpu,
 264                                           target_ulong pc,
 265                                           target_ulong cs_base,
 266                                           uint32_t flags)
 267 {
 268     tb_page_addr_t phys_pc;
 269     struct tb_desc desc;
 270     uint32_t h;
 271
 272     desc.env = (CPUArchState *)cpu->env_ptr;
 273     desc.cs_base = cs_base;
 274     desc.flags = flags;
 275     desc.pc = pc;
 276     phys_pc = get_page_addr_code(desc.env, pc);
 277     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 278     h = tb_hash_func(phys_pc, pc, flags);
 279     return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h);
 280 }
 281
 282 static TranslationBlock *tb_find_slow(CPUState *cpu,
 283                                       target_ulong pc,
 284                                       target_ulong cs_base,
 285                                       uint32_t flags)
 286 {
 287     TranslationBlock *tb;
 288
 289     tb = tb_find_physical(cpu, pc, cs_base, flags);
 290     if (tb) {
 291         goto found;
 292     }
 293
 294 #ifdef CONFIG_USER_ONLY
 295     /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 296      * taken outside tb_lock.  Since we're momentarily dropping
 297      * tb_lock, there's a chance that our desired tb has been
 298      * translated.
 299      */
 300     tb_unlock();
 301     mmap_lock();
 302     tb_lock();
 303     tb = tb_find_physical(cpu, pc, cs_base, flags);
 304     if (tb) {
 305         mmap_unlock();
 306         goto found;
 307     }
 308 #endif
 309
 310     /* if no translated code available, then translate it now */
 311     tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 312
 313 #ifdef CONFIG_USER_ONLY
 314     mmap_unlock();
 315 #endif
 316
 317 found:
 318     /* we add the TB in the virtual pc hash table */
 319     atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 320     return tb;
 321 }
 322
 323 static inline TranslationBlock *tb_find_fast(CPUState *cpu,
 324                                              TranslationBlock *last_tb,
 325                                              int tb_exit)
 326 {
 327     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 328     TranslationBlock *tb;
 329     target_ulong cs_base, pc;
 330     uint32_t flags;
 331
 332     /* we record a subset of the CPU state. It will
 333        always be the same before a given translated block
 334        is executed. */
 335     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 336     tb_lock();
 337     tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
 338     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 339                  tb->flags != flags)) {
 340         tb = tb_find_slow(cpu, pc, cs_base, flags);
 341     }
 342 #ifndef CONFIG_USER_ONLY
 343     /* We don't take care of direct jumps when address mapping changes in
 344      * system emulation. So it's not safe to make a direct jump to a TB
 345      * spanning two pages because the mapping for the second page can change.
 346      */
 347     if (tb->page_addr[1] != -1) {
 348         last_tb = NULL;
 349     }
 350 #endif
 351     /* See if we can patch the calling TB. */
 352     if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 353         /* Check if translation buffer has been flushed */
 354         if (cpu->tb_flushed) {
 355             cpu->tb_flushed = false;
 356         } else if (!tb->invalid) {
 357             tb_add_jump(last_tb, tb_exit, tb);
 358         }
 359     }
 360     tb_unlock();
 361     return tb;
 362 }
 363
 364 static inline bool cpu_handle_halt(CPUState *cpu)
 365 {
 366     if (cpu->halted) {
 367 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 368         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 369             && replay_interrupt()) {
 370             X86CPU *x86_cpu = X86_CPU(cpu);
 371             apic_poll_irq(x86_cpu->apic_state);
 372             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 373         }
 374 #endif
 375         if (!cpu_has_work(cpu)) {
 376             current_cpu = NULL;
 377             return true;
 378         }
 379
 380         cpu->halted = 0;
 381     }
 382
 383     return false;
 384 }
 385
 386 static inline void cpu_handle_debug_exception(CPUState *cpu)
 387 {
 388     CPUClass *cc = CPU_GET_CLASS(cpu);
 389     CPUWatchpoint *wp;
 390
 391     if (!cpu->watchpoint_hit) {
 392         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 393             wp->flags &= ~BP_WATCHPOINT_HIT;
 394         }
 395     }
 396
 397     cc->debug_excp_handler(cpu);
 398 }
 399
 400 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 401 {
 402     if (cpu->exception_index >= 0) {
 403         if (cpu->exception_index >= EXCP_INTERRUPT) {
 404             /* exit request from the cpu execution loop */
 405             *ret = cpu->exception_index;
 406             if (*ret == EXCP_DEBUG) {
 407                 cpu_handle_debug_exception(cpu);
 408             }
 409             cpu->exception_index = -1;
 410             return true;
 411         } else {
 412 #if defined(CONFIG_USER_ONLY)
 413             /* if user mode only, we simulate a fake exception
 414                which will be handled outside the cpu execution
 415                loop */
 416 #if defined(TARGET_I386)
 417             CPUClass *cc = CPU_GET_CLASS(cpu);
 418             cc->do_interrupt(cpu);
 419 #endif
 420             *ret = cpu->exception_index;
 421             cpu->exception_index = -1;
 422             return true;
 423 #else
 424             if (replay_exception()) {
 425                 CPUClass *cc = CPU_GET_CLASS(cpu);
 426                 cc->do_interrupt(cpu);
 427                 cpu->exception_index = -1;
 428             } else if (!replay_has_interrupt()) {
 429                 /* give a chance to iothread in replay mode */
 430                 *ret = EXCP_INTERRUPT;
 431                 return true;
 432             }
 433 #endif
 434         }
 435 #ifndef CONFIG_USER_ONLY
 436     } else if (replay_has_exception()
 437                && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 438         /* try to cause an exception pending in the log */
 439         cpu_exec_nocache(cpu, 1, tb_find_fast(cpu, NULL, 0), true);
 440         *ret = -1;
 441         return true;
 442 #endif
 443     }
 444
 445     return false;
 446 }
 447
 448 static inline void cpu_handle_interrupt(CPUState *cpu,
 449                                         TranslationBlock **last_tb)
 450 {
 451     CPUClass *cc = CPU_GET_CLASS(cpu);
 452     int interrupt_request = cpu->interrupt_request;
 453
 454     if (unlikely(interrupt_request)) {
 455         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 456             /* Mask out external interrupts for this step. */
 457             interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 458         }
 459         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 460             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 461             cpu->exception_index = EXCP_DEBUG;
 462             cpu_loop_exit(cpu);
 463         }
 464         if (replay_mode == REPLAY_MODE_PLAY && !replay_has_interrupt()) {
 465             /* Do nothing */
 466         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 467             replay_interrupt();
 468             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 469             cpu->halted = 1;
 470             cpu->exception_index = EXCP_HLT;
 471             cpu_loop_exit(cpu);
 472         }
 473 #if defined(TARGET_I386)
 474         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 475             X86CPU *x86_cpu = X86_CPU(cpu);
 476             CPUArchState *env = &x86_cpu->env;
 477             replay_interrupt();
 478             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 479             do_cpu_init(x86_cpu);
 480             cpu->exception_index = EXCP_HALTED;
 481             cpu_loop_exit(cpu);
 482         }
 483 #else
 484         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 485             replay_interrupt();
 486             cpu_reset(cpu);
 487             cpu_loop_exit(cpu);
 488         }
 489 #endif
 490         /* The target hook has 3 exit conditions:
 491            False when the interrupt isn't processed,
 492            True when it is, and we should restart on a new TB,
 493            and via longjmp via cpu_loop_exit.  */
 494         else {
 495             replay_interrupt();
 496             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 497                 *last_tb = NULL;
 498             }
 499             /* The target hook may have updated the 'cpu->interrupt_request';
 500              * reload the 'interrupt_request' value */
 501             interrupt_request = cpu->interrupt_request;
 502         }
 503         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 504             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 505             /* ensure that no TB jump will be modified as
 506                the program flow was changed */
 507             *last_tb = NULL;
 508         }
 509     }
 510     if (unlikely(cpu->exit_request || replay_has_interrupt())) {
 511         cpu->exit_request = 0;
 512         cpu->exception_index = EXCP_INTERRUPT;
 513         cpu_loop_exit(cpu);
 514     }
 515 }
 516
 517 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 518                                     TranslationBlock **last_tb, int *tb_exit,
 519                                     SyncClocks *sc)
 520 {
 521     uintptr_t ret;
 522
 523     if (unlikely(cpu->exit_request)) {
 524         return;
 525     }
 526
 527     trace_exec_tb(tb, tb->pc);
 528     ret = cpu_tb_exec(cpu, tb);
 529     *last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 530     *tb_exit = ret & TB_EXIT_MASK;
 531     switch (*tb_exit) {
 532     case TB_EXIT_REQUESTED:
 533         /* Something asked us to stop executing
 534          * chained TBs; just continue round the main
 535          * loop. Whatever requested the exit will also
 536          * have set something else (eg exit_request or
 537          * interrupt_request) which we will handle
 538          * next time around the loop.  But we need to
 539          * ensure the tcg_exit_req read in generated code
 540          * comes before the next read of cpu->exit_request
 541          * or cpu->interrupt_request.
 542          */
 543         smp_rmb();
 544         *last_tb = NULL;
 545         break;
 546     case TB_EXIT_ICOUNT_EXPIRED:
 547     {
 548         /* Instruction counter expired.  */
 549 #ifdef CONFIG_USER_ONLY
 550         abort();
 551 #else
 552         int insns_left = cpu->icount_decr.u32;
 553         if (cpu->icount_extra && insns_left >= 0) {
 554             /* Refill decrementer and continue execution.  */
 555             cpu->icount_extra += insns_left;
 556             insns_left = MIN(0xffff, cpu->icount_extra);
 557             cpu->icount_extra -= insns_left;
 558             cpu->icount_decr.u16.low = insns_left;
 559         } else {
 560             if (insns_left > 0) {
 561                 /* Execute remaining instructions.  */
 562                 cpu_exec_nocache(cpu, insns_left, *last_tb, false);
 563                 align_clocks(sc, cpu);
 564             }
 565             cpu->exception_index = EXCP_INTERRUPT;
 566             *last_tb = NULL;
 567             cpu_loop_exit(cpu);
 568         }
 569         break;
 570 #endif
 571     }
 572     default:
 573         break;
 574     }
 575 }
 576
 577 /* main execution loop */
 578
 579 int cpu_exec(CPUState *cpu)
 580 {
 581     CPUClass *cc = CPU_GET_CLASS(cpu);
 582     int ret;
 583     SyncClocks sc;
 584
 585     /* replay_interrupt may need current_cpu */
 586     current_cpu = cpu;
 587
 588     if (cpu_handle_halt(cpu)) {
 589         return EXCP_HALTED;
 590     }
 591
 592     atomic_mb_set(&tcg_current_cpu, cpu);
 593     rcu_read_lock();
 594
 595     if (unlikely(atomic_mb_read(&exit_request))) {
 596         cpu->exit_request = 1;
 597     }
 598
 599     cc->cpu_exec_enter(cpu);
 600
 601     /* Calculate difference between guest clock and host clock.
 602      * This delay includes the delay of the last cycle, so
 603      * what we have to do is sleep until it is 0. As for the
 604      * advance/delay we gain here, we try to fix it next time.
 605      */
 606     init_delay_params(&sc, cpu);
 607
 608     for(;;) {
 609         /* prepare setjmp context for exception handling */
 610         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 611             TranslationBlock *tb, *last_tb = NULL;
 612             int tb_exit = 0;
 613
 614             /* if an exception is pending, we execute it here */
 615             if (cpu_handle_exception(cpu, &ret)) {
 616                 break;
 617             }
 618
 619             atomic_mb_set(&cpu->tb_flushed, false); /* reset before first TB lookup */
 620             for(;;) {
 621                 cpu_handle_interrupt(cpu, &last_tb);
 622                 tb = tb_find_fast(cpu, last_tb, tb_exit);
 623                 cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
 624                 /* Try to align the host and virtual clocks
 625                    if the guest is in advance */
 626                 align_clocks(&sc, cpu);
 627             } /* for(;;) */
 628         } else {
 629 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 630             /* Some compilers wrongly smash all local variables after
 631              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 632              * Reload essential local variables here for those compilers.
 633              * Newer versions of gcc would complain about this code (-Wclobbered). */
 634             cpu = current_cpu;
 635             cc = CPU_GET_CLASS(cpu);
 636 #else /* buggy compiler */
 637             /* Assert that the compiler does not smash local variables. */
 638             g_assert(cpu == current_cpu);
 639             g_assert(cc == CPU_GET_CLASS(cpu));
 640 #endif /* buggy compiler */
 641             cpu->can_do_io = 1;
 642             tb_lock_reset();
 643         }
 644     } /* for(;;) */
 645
 646     cc->cpu_exec_exit(cpu);
 647     rcu_read_unlock();
 648
 649     /* fail safe : never use current_cpu outside cpu_exec() */
 650     current_cpu = NULL;
 651
 652     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 653     atomic_set(&tcg_current_cpu, NULL);
 654     return ret;
 655 }