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-root.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 #include "qemu/main-loop.h"
  33 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
  34 #include "hw/i386/apic.h"
  35 #endif
  36 #include "sysemu/replay.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 ret;
 142     TranslationBlock *last_tb;
 143     int tb_exit;
 144     uint8_t *tb_ptr = itb->tc_ptr;
 145
 146     qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 147                            "Trace %p [%d: " TARGET_FMT_lx "] %s\n",
 148                            itb->tc_ptr, cpu->cpu_index, itb->pc,
 149                            lookup_symbol(itb->pc));
 150
 151 #if defined(DEBUG_DISAS)
 152     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)
 153         && qemu_log_in_addr_range(itb->pc)) {
 154         qemu_log_lock();
 155 #if defined(TARGET_I386)
 156         log_cpu_state(cpu, CPU_DUMP_CCOP);
 157 #else
 158         log_cpu_state(cpu, 0);
 159 #endif
 160         qemu_log_unlock();
 161     }
 162 #endif /* DEBUG_DISAS */
 163
 164     cpu->can_do_io = !use_icount;
 165     ret = tcg_qemu_tb_exec(env, tb_ptr);
 166     cpu->can_do_io = 1;
 167     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 168     tb_exit = ret & TB_EXIT_MASK;
 169     trace_exec_tb_exit(last_tb, tb_exit);
 170
 171     if (tb_exit > TB_EXIT_IDX1) {
 172         /* We didn't start executing this TB (eg because the instruction
 173          * counter hit zero); we must restore the guest PC to the address
 174          * of the start of the TB.
 175          */
 176         CPUClass *cc = CPU_GET_CLASS(cpu);
 177         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 178                                "Stopped execution of TB chain before %p ["
 179                                TARGET_FMT_lx "] %s\n",
 180                                last_tb->tc_ptr, last_tb->pc,
 181                                lookup_symbol(last_tb->pc));
 182         if (cc->synchronize_from_tb) {
 183             cc->synchronize_from_tb(cpu, last_tb);
 184         } else {
 185             assert(cc->set_pc);
 186             cc->set_pc(cpu, last_tb->pc);
 187         }
 188     }
 189     if (tb_exit == TB_EXIT_REQUESTED) {
 190         /* We were asked to stop executing TBs (probably a pending
 191          * interrupt. We've now stopped, so clear the flag.
 192          */
 193         atomic_set(&cpu->tcg_exit_req, 0);
 194     }
 195     return ret;
 196 }
 197
 198 #ifndef CONFIG_USER_ONLY
 199 /* Execute the code without caching the generated code. An interpreter
 200    could be used if available. */
 201 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 202                              TranslationBlock *orig_tb, bool ignore_icount)
 203 {
 204     TranslationBlock *tb;
 205
 206     /* Should never happen.
 207        We only end up here when an existing TB is too long.  */
 208     if (max_cycles > CF_COUNT_MASK)
 209         max_cycles = CF_COUNT_MASK;
 210
 211     tb_lock();
 212     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags,
 213                      max_cycles | CF_NOCACHE
 214                          | (ignore_icount ? CF_IGNORE_ICOUNT : 0));
 215     tb->orig_tb = orig_tb;
 216     tb_unlock();
 217
 218     /* execute the generated code */
 219     trace_exec_tb_nocache(tb, tb->pc);
 220     cpu_tb_exec(cpu, tb);
 221
 222     tb_lock();
 223     tb_phys_invalidate(tb, -1);
 224     tb_free(tb);
 225     tb_unlock();
 226 }
 227 #endif
 228
 229 static void cpu_exec_step(CPUState *cpu)
 230 {
 231     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 232     TranslationBlock *tb;
 233     target_ulong cs_base, pc;
 234     uint32_t flags;
 235
 236     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 237     tb_lock();
 238     tb = tb_gen_code(cpu, pc, cs_base, flags,
 239                      1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
 240     tb->orig_tb = NULL;
 241     tb_unlock();
 242     /* execute the generated code */
 243     trace_exec_tb_nocache(tb, pc);
 244     cpu_tb_exec(cpu, tb);
 245     tb_lock();
 246     tb_phys_invalidate(tb, -1);
 247     tb_free(tb);
 248     tb_unlock();
 249 }
 250
 251 void cpu_exec_step_atomic(CPUState *cpu)
 252 {
 253     start_exclusive();
 254
 255     /* Since we got here, we know that parallel_cpus must be true.  */
 256     parallel_cpus = false;
 257     cpu_exec_step(cpu);
 258     parallel_cpus = true;
 259
 260     end_exclusive();
 261 }
 262
 263 struct tb_desc {
 264     target_ulong pc;
 265     target_ulong cs_base;
 266     CPUArchState *env;
 267     tb_page_addr_t phys_page1;
 268     uint32_t flags;
 269 };
 270
 271 static bool tb_cmp(const void *p, const void *d)
 272 {
 273     const TranslationBlock *tb = p;
 274     const struct tb_desc *desc = d;
 275
 276     if (tb->pc == desc->pc &&
 277         tb->page_addr[0] == desc->phys_page1 &&
 278         tb->cs_base == desc->cs_base &&
 279         tb->flags == desc->flags &&
 280         !atomic_read(&tb->invalid)) {
 281         /* check next page if needed */
 282         if (tb->page_addr[1] == -1) {
 283             return true;
 284         } else {
 285             tb_page_addr_t phys_page2;
 286             target_ulong virt_page2;
 287
 288             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 289             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 290             if (tb->page_addr[1] == phys_page2) {
 291                 return true;
 292             }
 293         }
 294     }
 295     return false;
 296 }
 297
 298 static TranslationBlock *tb_htable_lookup(CPUState *cpu,
 299                                           target_ulong pc,
 300                                           target_ulong cs_base,
 301                                           uint32_t flags)
 302 {
 303     tb_page_addr_t phys_pc;
 304     struct tb_desc desc;
 305     uint32_t h;
 306
 307     desc.env = (CPUArchState *)cpu->env_ptr;
 308     desc.cs_base = cs_base;
 309     desc.flags = flags;
 310     desc.pc = pc;
 311     phys_pc = get_page_addr_code(desc.env, pc);
 312     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 313     h = tb_hash_func(phys_pc, pc, flags);
 314     return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h);
 315 }
 316
 317 static inline TranslationBlock *tb_find(CPUState *cpu,
 318                                         TranslationBlock *last_tb,
 319                                         int tb_exit)
 320 {
 321     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 322     TranslationBlock *tb;
 323     target_ulong cs_base, pc;
 324     uint32_t flags;
 325     bool have_tb_lock = false;
 326
 327     /* we record a subset of the CPU state. It will
 328        always be the same before a given translated block
 329        is executed. */
 330     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 331     tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
 332     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 333                  tb->flags != flags)) {
 334         tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 335         if (!tb) {
 336
 337             /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 338              * taken outside tb_lock. As system emulation is currently
 339              * single threaded the locks are NOPs.
 340              */
 341             mmap_lock();
 342             tb_lock();
 343             have_tb_lock = true;
 344
 345             /* There's a chance that our desired tb has been translated while
 346              * taking the locks so we check again inside the lock.
 347              */
 348             tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 349             if (!tb) {
 350                 /* if no translated code available, then translate it now */
 351                 tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 352             }
 353
 354             mmap_unlock();
 355         }
 356
 357         /* We add the TB in the virtual pc hash table for the fast lookup */
 358         atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 359     }
 360 #ifndef CONFIG_USER_ONLY
 361     /* We don't take care of direct jumps when address mapping changes in
 362      * system emulation. So it's not safe to make a direct jump to a TB
 363      * spanning two pages because the mapping for the second page can change.
 364      */
 365     if (tb->page_addr[1] != -1) {
 366         last_tb = NULL;
 367     }
 368 #endif
 369     /* See if we can patch the calling TB. */
 370     if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 371         if (!have_tb_lock) {
 372             tb_lock();
 373             have_tb_lock = true;
 374         }
 375         if (!tb->invalid) {
 376             tb_add_jump(last_tb, tb_exit, tb);
 377         }
 378     }
 379     if (have_tb_lock) {
 380         tb_unlock();
 381     }
 382     return tb;
 383 }
 384
 385 static inline bool cpu_handle_halt(CPUState *cpu)
 386 {
 387     if (cpu->halted) {
 388 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 389         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 390             && replay_interrupt()) {
 391             X86CPU *x86_cpu = X86_CPU(cpu);
 392             qemu_mutex_lock_iothread();
 393             apic_poll_irq(x86_cpu->apic_state);
 394             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 395             qemu_mutex_unlock_iothread();
 396         }
 397 #endif
 398         if (!cpu_has_work(cpu)) {
 399             return true;
 400         }
 401
 402         cpu->halted = 0;
 403     }
 404
 405     return false;
 406 }
 407
 408 static inline void cpu_handle_debug_exception(CPUState *cpu)
 409 {
 410     CPUClass *cc = CPU_GET_CLASS(cpu);
 411     CPUWatchpoint *wp;
 412
 413     if (!cpu->watchpoint_hit) {
 414         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 415             wp->flags &= ~BP_WATCHPOINT_HIT;
 416         }
 417     }
 418
 419     cc->debug_excp_handler(cpu);
 420 }
 421
 422 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 423 {
 424     if (cpu->exception_index >= 0) {
 425         if (cpu->exception_index >= EXCP_INTERRUPT) {
 426             /* exit request from the cpu execution loop */
 427             *ret = cpu->exception_index;
 428             if (*ret == EXCP_DEBUG) {
 429                 cpu_handle_debug_exception(cpu);
 430             }
 431             cpu->exception_index = -1;
 432             return true;
 433         } else {
 434 #if defined(CONFIG_USER_ONLY)
 435             /* if user mode only, we simulate a fake exception
 436                which will be handled outside the cpu execution
 437                loop */
 438 #if defined(TARGET_I386)
 439             CPUClass *cc = CPU_GET_CLASS(cpu);
 440             cc->do_interrupt(cpu);
 441 #endif
 442             *ret = cpu->exception_index;
 443             cpu->exception_index = -1;
 444             return true;
 445 #else
 446             if (replay_exception()) {
 447                 CPUClass *cc = CPU_GET_CLASS(cpu);
 448                 qemu_mutex_lock_iothread();
 449                 cc->do_interrupt(cpu);
 450                 qemu_mutex_unlock_iothread();
 451                 cpu->exception_index = -1;
 452             } else if (!replay_has_interrupt()) {
 453                 /* give a chance to iothread in replay mode */
 454                 *ret = EXCP_INTERRUPT;
 455                 return true;
 456             }
 457 #endif
 458         }
 459 #ifndef CONFIG_USER_ONLY
 460     } else if (replay_has_exception()
 461                && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 462         /* try to cause an exception pending in the log */
 463         cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true);
 464         *ret = -1;
 465         return true;
 466 #endif
 467     }
 468
 469     return false;
 470 }
 471
 472 static inline bool cpu_handle_interrupt(CPUState *cpu,
 473                                         TranslationBlock **last_tb)
 474 {
 475     CPUClass *cc = CPU_GET_CLASS(cpu);
 476
 477     if (unlikely(atomic_read(&cpu->interrupt_request))) {
 478         int interrupt_request;
 479         qemu_mutex_lock_iothread();
 480         interrupt_request = cpu->interrupt_request;
 481         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 482             /* Mask out external interrupts for this step. */
 483             interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 484         }
 485         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 486             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 487             cpu->exception_index = EXCP_DEBUG;
 488             qemu_mutex_unlock_iothread();
 489             return true;
 490         }
 491         if (replay_mode == REPLAY_MODE_PLAY && !replay_has_interrupt()) {
 492             /* Do nothing */
 493         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 494             replay_interrupt();
 495             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 496             cpu->halted = 1;
 497             cpu->exception_index = EXCP_HLT;
 498             qemu_mutex_unlock_iothread();
 499             return true;
 500         }
 501 #if defined(TARGET_I386)
 502         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 503             X86CPU *x86_cpu = X86_CPU(cpu);
 504             CPUArchState *env = &x86_cpu->env;
 505             replay_interrupt();
 506             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0, 0);
 507             do_cpu_init(x86_cpu);
 508             cpu->exception_index = EXCP_HALTED;
 509             qemu_mutex_unlock_iothread();
 510             return true;
 511         }
 512 #else
 513         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 514             replay_interrupt();
 515             cpu_reset(cpu);
 516             qemu_mutex_unlock_iothread();
 517             return true;
 518         }
 519 #endif
 520         /* The target hook has 3 exit conditions:
 521            False when the interrupt isn't processed,
 522            True when it is, and we should restart on a new TB,
 523            and via longjmp via cpu_loop_exit.  */
 524         else {
 525             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 526                 replay_interrupt();
 527                 *last_tb = NULL;
 528             }
 529             /* The target hook may have updated the 'cpu->interrupt_request';
 530              * reload the 'interrupt_request' value */
 531             interrupt_request = cpu->interrupt_request;
 532         }
 533         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 534             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 535             /* ensure that no TB jump will be modified as
 536                the program flow was changed */
 537             *last_tb = NULL;
 538         }
 539
 540         /* If we exit via cpu_loop_exit/longjmp it is reset in cpu_exec */
 541         qemu_mutex_unlock_iothread();
 542     }
 543
 544
 545     if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt())) {
 546         atomic_set(&cpu->exit_request, 0);
 547         cpu->exception_index = EXCP_INTERRUPT;
 548         return true;
 549     }
 550
 551     return false;
 552 }
 553
 554 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 555                                     TranslationBlock **last_tb, int *tb_exit,
 556                                     SyncClocks *sc)
 557 {
 558     uintptr_t ret;
 559
 560     if (unlikely(atomic_read(&cpu->exit_request))) {
 561         return;
 562     }
 563
 564     trace_exec_tb(tb, tb->pc);
 565     ret = cpu_tb_exec(cpu, tb);
 566     tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 567     *tb_exit = ret & TB_EXIT_MASK;
 568     switch (*tb_exit) {
 569     case TB_EXIT_REQUESTED:
 570         /* Something asked us to stop executing chained TBs; just
 571          * continue round the main loop. Whatever requested the exit
 572          * will also have set something else (eg interrupt_request)
 573          * which we will handle next time around the loop.  But we
 574          * need to ensure the tcg_exit_req read in generated code
 575          * comes before the next read of cpu->exit_request or
 576          * cpu->interrupt_request.
 577          */
 578         smp_mb();
 579         *last_tb = NULL;
 580         break;
 581     case TB_EXIT_ICOUNT_EXPIRED:
 582     {
 583         /* Instruction counter expired.  */
 584 #ifdef CONFIG_USER_ONLY
 585         abort();
 586 #else
 587         int insns_left = cpu->icount_decr.u32;
 588         *last_tb = NULL;
 589         if (cpu->icount_extra && insns_left >= 0) {
 590             /* Refill decrementer and continue execution.  */
 591             cpu->icount_extra += insns_left;
 592             insns_left = MIN(0xffff, cpu->icount_extra);
 593             cpu->icount_extra -= insns_left;
 594             cpu->icount_decr.u16.low = insns_left;
 595         } else {
 596             if (insns_left > 0) {
 597                 /* Execute remaining instructions.  */
 598                 cpu_exec_nocache(cpu, insns_left, tb, false);
 599                 align_clocks(sc, cpu);
 600             }
 601             cpu->exception_index = EXCP_INTERRUPT;
 602             cpu_loop_exit(cpu);
 603         }
 604         break;
 605 #endif
 606     }
 607     default:
 608         *last_tb = tb;
 609         break;
 610     }
 611 }
 612
 613 /* main execution loop */
 614
 615 int cpu_exec(CPUState *cpu)
 616 {
 617     CPUClass *cc = CPU_GET_CLASS(cpu);
 618     int ret;
 619     SyncClocks sc;
 620
 621     /* replay_interrupt may need current_cpu */
 622     current_cpu = cpu;
 623
 624     if (cpu_handle_halt(cpu)) {
 625         return EXCP_HALTED;
 626     }
 627
 628     rcu_read_lock();
 629
 630     cc->cpu_exec_enter(cpu);
 631
 632     /* Calculate difference between guest clock and host clock.
 633      * This delay includes the delay of the last cycle, so
 634      * what we have to do is sleep until it is 0. As for the
 635      * advance/delay we gain here, we try to fix it next time.
 636      */
 637     init_delay_params(&sc, cpu);
 638
 639     /* prepare setjmp context for exception handling */
 640     if (sigsetjmp(cpu->jmp_env, 0) != 0) {
 641 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 642         /* Some compilers wrongly smash all local variables after
 643          * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 644          * Reload essential local variables here for those compilers.
 645          * Newer versions of gcc would complain about this code (-Wclobbered). */
 646         cpu = current_cpu;
 647         cc = CPU_GET_CLASS(cpu);
 648 #else /* buggy compiler */
 649         /* Assert that the compiler does not smash local variables. */
 650         g_assert(cpu == current_cpu);
 651         g_assert(cc == CPU_GET_CLASS(cpu));
 652 #endif /* buggy compiler */
 653         cpu->can_do_io = 1;
 654         tb_lock_reset();
 655         if (qemu_mutex_iothread_locked()) {
 656             qemu_mutex_unlock_iothread();
 657         }
 658     }
 659
 660     /* if an exception is pending, we execute it here */
 661     while (!cpu_handle_exception(cpu, &ret)) {
 662         TranslationBlock *last_tb = NULL;
 663         int tb_exit = 0;
 664
 665         while (!cpu_handle_interrupt(cpu, &last_tb)) {
 666             TranslationBlock *tb = tb_find(cpu, last_tb, tb_exit);
 667             cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
 668             /* Try to align the host and virtual clocks
 669                if the guest is in advance */
 670             align_clocks(&sc, cpu);
 671         }
 672     }
 673
 674     cc->cpu_exec_exit(cpu);
 675     rcu_read_unlock();
 676
 677     return ret;
 678 }