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 [%d: " TARGET_FMT_lx "] %s\n",
 147                            itb->tc_ptr, cpu->cpu_index, itb->pc,
 148                            lookup_symbol(itb->pc));
 149
 150 #if defined(DEBUG_DISAS)
 151     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)
 152         && qemu_log_in_addr_range(itb->pc)) {
 153 #if defined(TARGET_I386)
 154         log_cpu_state(cpu, CPU_DUMP_CCOP);
 155 #else
 156         log_cpu_state(cpu, 0);
 157 #endif
 158     }
 159 #endif /* DEBUG_DISAS */
 160
 161     cpu->can_do_io = !use_icount;
 162     ret = tcg_qemu_tb_exec(env, tb_ptr);
 163     cpu->can_do_io = 1;
 164     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 165     tb_exit = ret & TB_EXIT_MASK;
 166     trace_exec_tb_exit(last_tb, tb_exit);
 167
 168     if (tb_exit > TB_EXIT_IDX1) {
 169         /* We didn't start executing this TB (eg because the instruction
 170          * counter hit zero); we must restore the guest PC to the address
 171          * of the start of the TB.
 172          */
 173         CPUClass *cc = CPU_GET_CLASS(cpu);
 174         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 175                                "Stopped execution of TB chain before %p ["
 176                                TARGET_FMT_lx "] %s\n",
 177                                last_tb->tc_ptr, last_tb->pc,
 178                                lookup_symbol(last_tb->pc));
 179         if (cc->synchronize_from_tb) {
 180             cc->synchronize_from_tb(cpu, last_tb);
 181         } else {
 182             assert(cc->set_pc);
 183             cc->set_pc(cpu, last_tb->pc);
 184         }
 185     }
 186     if (tb_exit == TB_EXIT_REQUESTED) {
 187         /* We were asked to stop executing TBs (probably a pending
 188          * interrupt. We've now stopped, so clear the flag.
 189          */
 190         atomic_set(&cpu->tcg_exit_req, 0);
 191     }
 192     return ret;
 193 }
 194
 195 #ifndef CONFIG_USER_ONLY
 196 /* Execute the code without caching the generated code. An interpreter
 197    could be used if available. */
 198 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 199                              TranslationBlock *orig_tb, bool ignore_icount)
 200 {
 201     TranslationBlock *tb;
 202
 203     /* Should never happen.
 204        We only end up here when an existing TB is too long.  */
 205     if (max_cycles > CF_COUNT_MASK)
 206         max_cycles = CF_COUNT_MASK;
 207
 208     tb_lock();
 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 = orig_tb;
 213     tb_unlock();
 214
 215     /* execute the generated code */
 216     trace_exec_tb_nocache(tb, tb->pc);
 217     cpu_tb_exec(cpu, tb);
 218
 219     tb_lock();
 220     tb_phys_invalidate(tb, -1);
 221     tb_free(tb);
 222     tb_unlock();
 223 }
 224 #endif
 225
 226 static void cpu_exec_step(CPUState *cpu)
 227 {
 228     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 229     TranslationBlock *tb;
 230     target_ulong cs_base, pc;
 231     uint32_t flags;
 232
 233     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 234     tb = tb_gen_code(cpu, pc, cs_base, flags,
 235                      1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
 236     tb->orig_tb = NULL;
 237     /* execute the generated code */
 238     trace_exec_tb_nocache(tb, pc);
 239     cpu_tb_exec(cpu, tb);
 240     tb_phys_invalidate(tb, -1);
 241     tb_free(tb);
 242 }
 243
 244 void cpu_exec_step_atomic(CPUState *cpu)
 245 {
 246     start_exclusive();
 247
 248     /* Since we got here, we know that parallel_cpus must be true.  */
 249     parallel_cpus = false;
 250     cpu_exec_step(cpu);
 251     parallel_cpus = true;
 252
 253     end_exclusive();
 254 }
 255
 256 struct tb_desc {
 257     target_ulong pc;
 258     target_ulong cs_base;
 259     CPUArchState *env;
 260     tb_page_addr_t phys_page1;
 261     uint32_t flags;
 262 };
 263
 264 static bool tb_cmp(const void *p, const void *d)
 265 {
 266     const TranslationBlock *tb = p;
 267     const struct tb_desc *desc = d;
 268
 269     if (tb->pc == desc->pc &&
 270         tb->page_addr[0] == desc->phys_page1 &&
 271         tb->cs_base == desc->cs_base &&
 272         tb->flags == desc->flags &&
 273         !atomic_read(&tb->invalid)) {
 274         /* check next page if needed */
 275         if (tb->page_addr[1] == -1) {
 276             return true;
 277         } else {
 278             tb_page_addr_t phys_page2;
 279             target_ulong virt_page2;
 280
 281             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 282             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 283             if (tb->page_addr[1] == phys_page2) {
 284                 return true;
 285             }
 286         }
 287     }
 288     return false;
 289 }
 290
 291 static TranslationBlock *tb_htable_lookup(CPUState *cpu,
 292                                           target_ulong pc,
 293                                           target_ulong cs_base,
 294                                           uint32_t flags)
 295 {
 296     tb_page_addr_t phys_pc;
 297     struct tb_desc desc;
 298     uint32_t h;
 299
 300     desc.env = (CPUArchState *)cpu->env_ptr;
 301     desc.cs_base = cs_base;
 302     desc.flags = flags;
 303     desc.pc = pc;
 304     phys_pc = get_page_addr_code(desc.env, pc);
 305     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 306     h = tb_hash_func(phys_pc, pc, flags);
 307     return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h);
 308 }
 309
 310 static inline TranslationBlock *tb_find(CPUState *cpu,
 311                                         TranslationBlock *last_tb,
 312                                         int tb_exit)
 313 {
 314     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 315     TranslationBlock *tb;
 316     target_ulong cs_base, pc;
 317     uint32_t flags;
 318     bool have_tb_lock = false;
 319
 320     /* we record a subset of the CPU state. It will
 321        always be the same before a given translated block
 322        is executed. */
 323     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 324     tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
 325     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 326                  tb->flags != flags)) {
 327         tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 328         if (!tb) {
 329
 330             /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 331              * taken outside tb_lock. As system emulation is currently
 332              * single threaded the locks are NOPs.
 333              */
 334             mmap_lock();
 335             tb_lock();
 336             have_tb_lock = true;
 337
 338             /* There's a chance that our desired tb has been translated while
 339              * taking the locks so we check again inside the lock.
 340              */
 341             tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 342             if (!tb) {
 343                 /* if no translated code available, then translate it now */
 344                 tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 345             }
 346
 347             mmap_unlock();
 348         }
 349
 350         /* We add the TB in the virtual pc hash table for the fast lookup */
 351         atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 352     }
 353 #ifndef CONFIG_USER_ONLY
 354     /* We don't take care of direct jumps when address mapping changes in
 355      * system emulation. So it's not safe to make a direct jump to a TB
 356      * spanning two pages because the mapping for the second page can change.
 357      */
 358     if (tb->page_addr[1] != -1) {
 359         last_tb = NULL;
 360     }
 361 #endif
 362     /* See if we can patch the calling TB. */
 363     if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 364         if (!have_tb_lock) {
 365             tb_lock();
 366             have_tb_lock = true;
 367         }
 368         if (!tb->invalid) {
 369             tb_add_jump(last_tb, tb_exit, tb);
 370         }
 371     }
 372     if (have_tb_lock) {
 373         tb_unlock();
 374     }
 375     return tb;
 376 }
 377
 378 static inline bool cpu_handle_halt(CPUState *cpu)
 379 {
 380     if (cpu->halted) {
 381 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 382         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 383             && replay_interrupt()) {
 384             X86CPU *x86_cpu = X86_CPU(cpu);
 385             apic_poll_irq(x86_cpu->apic_state);
 386             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 387         }
 388 #endif
 389         if (!cpu_has_work(cpu)) {
 390             current_cpu = NULL;
 391             return true;
 392         }
 393
 394         cpu->halted = 0;
 395     }
 396
 397     return false;
 398 }
 399
 400 static inline void cpu_handle_debug_exception(CPUState *cpu)
 401 {
 402     CPUClass *cc = CPU_GET_CLASS(cpu);
 403     CPUWatchpoint *wp;
 404
 405     if (!cpu->watchpoint_hit) {
 406         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 407             wp->flags &= ~BP_WATCHPOINT_HIT;
 408         }
 409     }
 410
 411     cc->debug_excp_handler(cpu);
 412 }
 413
 414 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 415 {
 416     if (cpu->exception_index >= 0) {
 417         if (cpu->exception_index >= EXCP_INTERRUPT) {
 418             /* exit request from the cpu execution loop */
 419             *ret = cpu->exception_index;
 420             if (*ret == EXCP_DEBUG) {
 421                 cpu_handle_debug_exception(cpu);
 422             }
 423             cpu->exception_index = -1;
 424             return true;
 425         } else {
 426 #if defined(CONFIG_USER_ONLY)
 427             /* if user mode only, we simulate a fake exception
 428                which will be handled outside the cpu execution
 429                loop */
 430 #if defined(TARGET_I386)
 431             CPUClass *cc = CPU_GET_CLASS(cpu);
 432             cc->do_interrupt(cpu);
 433 #endif
 434             *ret = cpu->exception_index;
 435             cpu->exception_index = -1;
 436             return true;
 437 #else
 438             if (replay_exception()) {
 439                 CPUClass *cc = CPU_GET_CLASS(cpu);
 440                 cc->do_interrupt(cpu);
 441                 cpu->exception_index = -1;
 442             } else if (!replay_has_interrupt()) {
 443                 /* give a chance to iothread in replay mode */
 444                 *ret = EXCP_INTERRUPT;
 445                 return true;
 446             }
 447 #endif
 448         }
 449 #ifndef CONFIG_USER_ONLY
 450     } else if (replay_has_exception()
 451                && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 452         /* try to cause an exception pending in the log */
 453         cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true);
 454         *ret = -1;
 455         return true;
 456 #endif
 457     }
 458
 459     return false;
 460 }
 461
 462 static inline void cpu_handle_interrupt(CPUState *cpu,
 463                                         TranslationBlock **last_tb)
 464 {
 465     CPUClass *cc = CPU_GET_CLASS(cpu);
 466     int interrupt_request = cpu->interrupt_request;
 467
 468     if (unlikely(interrupt_request)) {
 469         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 470             /* Mask out external interrupts for this step. */
 471             interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 472         }
 473         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 474             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 475             cpu->exception_index = EXCP_DEBUG;
 476             cpu_loop_exit(cpu);
 477         }
 478         if (replay_mode == REPLAY_MODE_PLAY && !replay_has_interrupt()) {
 479             /* Do nothing */
 480         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 481             replay_interrupt();
 482             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 483             cpu->halted = 1;
 484             cpu->exception_index = EXCP_HLT;
 485             cpu_loop_exit(cpu);
 486         }
 487 #if defined(TARGET_I386)
 488         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 489             X86CPU *x86_cpu = X86_CPU(cpu);
 490             CPUArchState *env = &x86_cpu->env;
 491             replay_interrupt();
 492             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 493             do_cpu_init(x86_cpu);
 494             cpu->exception_index = EXCP_HALTED;
 495             cpu_loop_exit(cpu);
 496         }
 497 #else
 498         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 499             replay_interrupt();
 500             cpu_reset(cpu);
 501             cpu_loop_exit(cpu);
 502         }
 503 #endif
 504         /* The target hook has 3 exit conditions:
 505            False when the interrupt isn't processed,
 506            True when it is, and we should restart on a new TB,
 507            and via longjmp via cpu_loop_exit.  */
 508         else {
 509             replay_interrupt();
 510             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 511                 *last_tb = NULL;
 512             }
 513             /* The target hook may have updated the 'cpu->interrupt_request';
 514              * reload the 'interrupt_request' value */
 515             interrupt_request = cpu->interrupt_request;
 516         }
 517         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 518             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 519             /* ensure that no TB jump will be modified as
 520                the program flow was changed */
 521             *last_tb = NULL;
 522         }
 523     }
 524     if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt())) {
 525         atomic_set(&cpu->exit_request, 0);
 526         cpu->exception_index = EXCP_INTERRUPT;
 527         cpu_loop_exit(cpu);
 528     }
 529 }
 530
 531 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 532                                     TranslationBlock **last_tb, int *tb_exit,
 533                                     SyncClocks *sc)
 534 {
 535     uintptr_t ret;
 536
 537     if (unlikely(atomic_read(&cpu->exit_request))) {
 538         return;
 539     }
 540
 541     trace_exec_tb(tb, tb->pc);
 542     ret = cpu_tb_exec(cpu, tb);
 543     *last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 544     *tb_exit = ret & TB_EXIT_MASK;
 545     switch (*tb_exit) {
 546     case TB_EXIT_REQUESTED:
 547         /* Something asked us to stop executing
 548          * chained TBs; just continue round the main
 549          * loop. Whatever requested the exit will also
 550          * have set something else (eg exit_request or
 551          * interrupt_request) which we will handle
 552          * next time around the loop.  But we need to
 553          * ensure the tcg_exit_req read in generated code
 554          * comes before the next read of cpu->exit_request
 555          * or cpu->interrupt_request.
 556          */
 557         smp_rmb();
 558         *last_tb = NULL;
 559         break;
 560     case TB_EXIT_ICOUNT_EXPIRED:
 561     {
 562         /* Instruction counter expired.  */
 563 #ifdef CONFIG_USER_ONLY
 564         abort();
 565 #else
 566         int insns_left = cpu->icount_decr.u32;
 567         if (cpu->icount_extra && insns_left >= 0) {
 568             /* Refill decrementer and continue execution.  */
 569             cpu->icount_extra += insns_left;
 570             insns_left = MIN(0xffff, cpu->icount_extra);
 571             cpu->icount_extra -= insns_left;
 572             cpu->icount_decr.u16.low = insns_left;
 573         } else {
 574             if (insns_left > 0) {
 575                 /* Execute remaining instructions.  */
 576                 cpu_exec_nocache(cpu, insns_left, *last_tb, false);
 577                 align_clocks(sc, cpu);
 578             }
 579             cpu->exception_index = EXCP_INTERRUPT;
 580             *last_tb = NULL;
 581             cpu_loop_exit(cpu);
 582         }
 583         break;
 584 #endif
 585     }
 586     default:
 587         break;
 588     }
 589 }
 590
 591 /* main execution loop */
 592
 593 int cpu_exec(CPUState *cpu)
 594 {
 595     CPUClass *cc = CPU_GET_CLASS(cpu);
 596     int ret;
 597     SyncClocks sc;
 598
 599     /* replay_interrupt may need current_cpu */
 600     current_cpu = cpu;
 601
 602     if (cpu_handle_halt(cpu)) {
 603         return EXCP_HALTED;
 604     }
 605
 606     atomic_mb_set(&tcg_current_cpu, cpu);
 607     rcu_read_lock();
 608
 609     if (unlikely(atomic_mb_read(&exit_request))) {
 610         cpu->exit_request = 1;
 611     }
 612
 613     cc->cpu_exec_enter(cpu);
 614
 615     /* Calculate difference between guest clock and host clock.
 616      * This delay includes the delay of the last cycle, so
 617      * what we have to do is sleep until it is 0. As for the
 618      * advance/delay we gain here, we try to fix it next time.
 619      */
 620     init_delay_params(&sc, cpu);
 621
 622     for(;;) {
 623         /* prepare setjmp context for exception handling */
 624         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 625             TranslationBlock *tb, *last_tb = NULL;
 626             int tb_exit = 0;
 627
 628             /* if an exception is pending, we execute it here */
 629             if (cpu_handle_exception(cpu, &ret)) {
 630                 break;
 631             }
 632
 633             for(;;) {
 634                 cpu_handle_interrupt(cpu, &last_tb);
 635                 tb = tb_find(cpu, last_tb, tb_exit);
 636                 cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
 637                 /* Try to align the host and virtual clocks
 638                    if the guest is in advance */
 639                 align_clocks(&sc, cpu);
 640             } /* for(;;) */
 641         } else {
 642 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 643             /* Some compilers wrongly smash all local variables after
 644              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 645              * Reload essential local variables here for those compilers.
 646              * Newer versions of gcc would complain about this code (-Wclobbered). */
 647             cpu = current_cpu;
 648             cc = CPU_GET_CLASS(cpu);
 649 #else /* buggy compiler */
 650             /* Assert that the compiler does not smash local variables. */
 651             g_assert(cpu == current_cpu);
 652             g_assert(cc == CPU_GET_CLASS(cpu));
 653 #endif /* buggy compiler */
 654             cpu->can_do_io = 1;
 655             tb_lock_reset();
 656         }
 657     } /* for(;;) */
 658
 659     cc->cpu_exec_exit(cpu);
 660     rcu_read_unlock();
 661
 662     /* fail safe : never use current_cpu outside cpu_exec() */
 663     current_cpu = NULL;
 664
 665     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 666     atomic_set(&tcg_current_cpu, NULL);
 667     return ret;
 668 }