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 #elif defined(TARGET_M68K)
 156         /* ??? Should not modify env state for dumping.  */
 157         cpu_m68k_flush_flags(env, env->cc_op);
 158         env->cc_op = CC_OP_FLAGS;
 159         env->sr = (env->sr & 0xffe0) | env->cc_dest | (env->cc_x << 4);
 160         log_cpu_state(cpu, 0);
 161 #else
 162         log_cpu_state(cpu, 0);
 163 #endif
 164     }
 165 #endif /* DEBUG_DISAS */
 166
 167     cpu->can_do_io = !use_icount;
 168     ret = tcg_qemu_tb_exec(env, tb_ptr);
 169     cpu->can_do_io = 1;
 170     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 171     tb_exit = ret & TB_EXIT_MASK;
 172     trace_exec_tb_exit(last_tb, tb_exit);
 173
 174     if (tb_exit > TB_EXIT_IDX1) {
 175         /* We didn't start executing this TB (eg because the instruction
 176          * counter hit zero); we must restore the guest PC to the address
 177          * of the start of the TB.
 178          */
 179         CPUClass *cc = CPU_GET_CLASS(cpu);
 180         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 181                                "Stopped execution of TB chain before %p ["
 182                                TARGET_FMT_lx "] %s\n",
 183                                last_tb->tc_ptr, last_tb->pc,
 184                                lookup_symbol(last_tb->pc));
 185         if (cc->synchronize_from_tb) {
 186             cc->synchronize_from_tb(cpu, last_tb);
 187         } else {
 188             assert(cc->set_pc);
 189             cc->set_pc(cpu, last_tb->pc);
 190         }
 191     }
 192     if (tb_exit == TB_EXIT_REQUESTED) {
 193         /* We were asked to stop executing TBs (probably a pending
 194          * interrupt. We've now stopped, so clear the flag.
 195          */
 196         atomic_set(&cpu->tcg_exit_req, 0);
 197     }
 198     return ret;
 199 }
 200
 201 #ifndef CONFIG_USER_ONLY
 202 /* Execute the code without caching the generated code. An interpreter
 203    could be used if available. */
 204 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 205                              TranslationBlock *orig_tb, bool ignore_icount)
 206 {
 207     TranslationBlock *tb;
 208
 209     /* Should never happen.
 210        We only end up here when an existing TB is too long.  */
 211     if (max_cycles > CF_COUNT_MASK)
 212         max_cycles = CF_COUNT_MASK;
 213
 214     tb_lock();
 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 = orig_tb;
 219     tb_unlock();
 220
 221     /* execute the generated code */
 222     trace_exec_tb_nocache(tb, tb->pc);
 223     cpu_tb_exec(cpu, tb);
 224
 225     tb_lock();
 226     tb_phys_invalidate(tb, -1);
 227     tb_free(tb);
 228     tb_unlock();
 229 }
 230 #endif
 231
 232 static void cpu_exec_step(CPUState *cpu)
 233 {
 234     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 235     TranslationBlock *tb;
 236     target_ulong cs_base, pc;
 237     uint32_t flags;
 238
 239     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 240     tb = tb_gen_code(cpu, pc, cs_base, flags,
 241                      1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
 242     tb->orig_tb = NULL;
 243     /* execute the generated code */
 244     trace_exec_tb_nocache(tb, pc);
 245     cpu_tb_exec(cpu, tb);
 246     tb_phys_invalidate(tb, -1);
 247     tb_free(tb);
 248 }
 249
 250 void cpu_exec_step_atomic(CPUState *cpu)
 251 {
 252     start_exclusive();
 253
 254     /* Since we got here, we know that parallel_cpus must be true.  */
 255     parallel_cpus = false;
 256     cpu_exec_step(cpu);
 257     parallel_cpus = true;
 258
 259     end_exclusive();
 260 }
 261
 262 struct tb_desc {
 263     target_ulong pc;
 264     target_ulong cs_base;
 265     CPUArchState *env;
 266     tb_page_addr_t phys_page1;
 267     uint32_t flags;
 268 };
 269
 270 static bool tb_cmp(const void *p, const void *d)
 271 {
 272     const TranslationBlock *tb = p;
 273     const struct tb_desc *desc = d;
 274
 275     if (tb->pc == desc->pc &&
 276         tb->page_addr[0] == desc->phys_page1 &&
 277         tb->cs_base == desc->cs_base &&
 278         tb->flags == desc->flags &&
 279         !atomic_read(&tb->invalid)) {
 280         /* check next page if needed */
 281         if (tb->page_addr[1] == -1) {
 282             return true;
 283         } else {
 284             tb_page_addr_t phys_page2;
 285             target_ulong virt_page2;
 286
 287             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 288             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 289             if (tb->page_addr[1] == phys_page2) {
 290                 return true;
 291             }
 292         }
 293     }
 294     return false;
 295 }
 296
 297 static TranslationBlock *tb_htable_lookup(CPUState *cpu,
 298                                           target_ulong pc,
 299                                           target_ulong cs_base,
 300                                           uint32_t flags)
 301 {
 302     tb_page_addr_t phys_pc;
 303     struct tb_desc desc;
 304     uint32_t h;
 305
 306     desc.env = (CPUArchState *)cpu->env_ptr;
 307     desc.cs_base = cs_base;
 308     desc.flags = flags;
 309     desc.pc = pc;
 310     phys_pc = get_page_addr_code(desc.env, pc);
 311     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 312     h = tb_hash_func(phys_pc, pc, flags);
 313     return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h);
 314 }
 315
 316 static inline TranslationBlock *tb_find(CPUState *cpu,
 317                                         TranslationBlock *last_tb,
 318                                         int tb_exit)
 319 {
 320     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 321     TranslationBlock *tb;
 322     target_ulong cs_base, pc;
 323     uint32_t flags;
 324     bool have_tb_lock = false;
 325
 326     /* we record a subset of the CPU state. It will
 327        always be the same before a given translated block
 328        is executed. */
 329     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 330     tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
 331     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 332                  tb->flags != flags)) {
 333         tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 334         if (!tb) {
 335
 336             /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 337              * taken outside tb_lock. As system emulation is currently
 338              * single threaded the locks are NOPs.
 339              */
 340             mmap_lock();
 341             tb_lock();
 342             have_tb_lock = true;
 343
 344             /* There's a chance that our desired tb has been translated while
 345              * taking the locks so we check again inside the lock.
 346              */
 347             tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 348             if (!tb) {
 349                 /* if no translated code available, then translate it now */
 350                 tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 351             }
 352
 353             mmap_unlock();
 354         }
 355
 356         /* We add the TB in the virtual pc hash table for the fast lookup */
 357         atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 358     }
 359 #ifndef CONFIG_USER_ONLY
 360     /* We don't take care of direct jumps when address mapping changes in
 361      * system emulation. So it's not safe to make a direct jump to a TB
 362      * spanning two pages because the mapping for the second page can change.
 363      */
 364     if (tb->page_addr[1] != -1) {
 365         last_tb = NULL;
 366     }
 367 #endif
 368     /* See if we can patch the calling TB. */
 369     if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 370         if (!have_tb_lock) {
 371             tb_lock();
 372             have_tb_lock = true;
 373         }
 374         if (!tb->invalid) {
 375             tb_add_jump(last_tb, tb_exit, tb);
 376         }
 377     }
 378     if (have_tb_lock) {
 379         tb_unlock();
 380     }
 381     return tb;
 382 }
 383
 384 static inline bool cpu_handle_halt(CPUState *cpu)
 385 {
 386     if (cpu->halted) {
 387 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 388         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 389             && replay_interrupt()) {
 390             X86CPU *x86_cpu = X86_CPU(cpu);
 391             apic_poll_irq(x86_cpu->apic_state);
 392             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 393         }
 394 #endif
 395         if (!cpu_has_work(cpu)) {
 396             current_cpu = NULL;
 397             return true;
 398         }
 399
 400         cpu->halted = 0;
 401     }
 402
 403     return false;
 404 }
 405
 406 static inline void cpu_handle_debug_exception(CPUState *cpu)
 407 {
 408     CPUClass *cc = CPU_GET_CLASS(cpu);
 409     CPUWatchpoint *wp;
 410
 411     if (!cpu->watchpoint_hit) {
 412         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 413             wp->flags &= ~BP_WATCHPOINT_HIT;
 414         }
 415     }
 416
 417     cc->debug_excp_handler(cpu);
 418 }
 419
 420 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 421 {
 422     if (cpu->exception_index >= 0) {
 423         if (cpu->exception_index >= EXCP_INTERRUPT) {
 424             /* exit request from the cpu execution loop */
 425             *ret = cpu->exception_index;
 426             if (*ret == EXCP_DEBUG) {
 427                 cpu_handle_debug_exception(cpu);
 428             }
 429             cpu->exception_index = -1;
 430             return true;
 431         } else {
 432 #if defined(CONFIG_USER_ONLY)
 433             /* if user mode only, we simulate a fake exception
 434                which will be handled outside the cpu execution
 435                loop */
 436 #if defined(TARGET_I386)
 437             CPUClass *cc = CPU_GET_CLASS(cpu);
 438             cc->do_interrupt(cpu);
 439 #endif
 440             *ret = cpu->exception_index;
 441             cpu->exception_index = -1;
 442             return true;
 443 #else
 444             if (replay_exception()) {
 445                 CPUClass *cc = CPU_GET_CLASS(cpu);
 446                 cc->do_interrupt(cpu);
 447                 cpu->exception_index = -1;
 448             } else if (!replay_has_interrupt()) {
 449                 /* give a chance to iothread in replay mode */
 450                 *ret = EXCP_INTERRUPT;
 451                 return true;
 452             }
 453 #endif
 454         }
 455 #ifndef CONFIG_USER_ONLY
 456     } else if (replay_has_exception()
 457                && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 458         /* try to cause an exception pending in the log */
 459         cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true);
 460         *ret = -1;
 461         return true;
 462 #endif
 463     }
 464
 465     return false;
 466 }
 467
 468 static inline void cpu_handle_interrupt(CPUState *cpu,
 469                                         TranslationBlock **last_tb)
 470 {
 471     CPUClass *cc = CPU_GET_CLASS(cpu);
 472     int interrupt_request = cpu->interrupt_request;
 473
 474     if (unlikely(interrupt_request)) {
 475         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 476             /* Mask out external interrupts for this step. */
 477             interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 478         }
 479         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 480             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 481             cpu->exception_index = EXCP_DEBUG;
 482             cpu_loop_exit(cpu);
 483         }
 484         if (replay_mode == REPLAY_MODE_PLAY && !replay_has_interrupt()) {
 485             /* Do nothing */
 486         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 487             replay_interrupt();
 488             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 489             cpu->halted = 1;
 490             cpu->exception_index = EXCP_HLT;
 491             cpu_loop_exit(cpu);
 492         }
 493 #if defined(TARGET_I386)
 494         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 495             X86CPU *x86_cpu = X86_CPU(cpu);
 496             CPUArchState *env = &x86_cpu->env;
 497             replay_interrupt();
 498             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0);
 499             do_cpu_init(x86_cpu);
 500             cpu->exception_index = EXCP_HALTED;
 501             cpu_loop_exit(cpu);
 502         }
 503 #else
 504         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 505             replay_interrupt();
 506             cpu_reset(cpu);
 507             cpu_loop_exit(cpu);
 508         }
 509 #endif
 510         /* The target hook has 3 exit conditions:
 511            False when the interrupt isn't processed,
 512            True when it is, and we should restart on a new TB,
 513            and via longjmp via cpu_loop_exit.  */
 514         else {
 515             replay_interrupt();
 516             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 517                 *last_tb = NULL;
 518             }
 519             /* The target hook may have updated the 'cpu->interrupt_request';
 520              * reload the 'interrupt_request' value */
 521             interrupt_request = cpu->interrupt_request;
 522         }
 523         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 524             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 525             /* ensure that no TB jump will be modified as
 526                the program flow was changed */
 527             *last_tb = NULL;
 528         }
 529     }
 530     if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt())) {
 531         atomic_set(&cpu->exit_request, 0);
 532         cpu->exception_index = EXCP_INTERRUPT;
 533         cpu_loop_exit(cpu);
 534     }
 535 }
 536
 537 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 538                                     TranslationBlock **last_tb, int *tb_exit,
 539                                     SyncClocks *sc)
 540 {
 541     uintptr_t ret;
 542
 543     if (unlikely(atomic_read(&cpu->exit_request))) {
 544         return;
 545     }
 546
 547     trace_exec_tb(tb, tb->pc);
 548     ret = cpu_tb_exec(cpu, tb);
 549     *last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 550     *tb_exit = ret & TB_EXIT_MASK;
 551     switch (*tb_exit) {
 552     case TB_EXIT_REQUESTED:
 553         /* Something asked us to stop executing
 554          * chained TBs; just continue round the main
 555          * loop. Whatever requested the exit will also
 556          * have set something else (eg exit_request or
 557          * interrupt_request) which we will handle
 558          * next time around the loop.  But we need to
 559          * ensure the tcg_exit_req read in generated code
 560          * comes before the next read of cpu->exit_request
 561          * or cpu->interrupt_request.
 562          */
 563         smp_rmb();
 564         *last_tb = NULL;
 565         break;
 566     case TB_EXIT_ICOUNT_EXPIRED:
 567     {
 568         /* Instruction counter expired.  */
 569 #ifdef CONFIG_USER_ONLY
 570         abort();
 571 #else
 572         int insns_left = cpu->icount_decr.u32;
 573         if (cpu->icount_extra && insns_left >= 0) {
 574             /* Refill decrementer and continue execution.  */
 575             cpu->icount_extra += insns_left;
 576             insns_left = MIN(0xffff, cpu->icount_extra);
 577             cpu->icount_extra -= insns_left;
 578             cpu->icount_decr.u16.low = insns_left;
 579         } else {
 580             if (insns_left > 0) {
 581                 /* Execute remaining instructions.  */
 582                 cpu_exec_nocache(cpu, insns_left, *last_tb, false);
 583                 align_clocks(sc, cpu);
 584             }
 585             cpu->exception_index = EXCP_INTERRUPT;
 586             *last_tb = NULL;
 587             cpu_loop_exit(cpu);
 588         }
 589         break;
 590 #endif
 591     }
 592     default:
 593         break;
 594     }
 595 }
 596
 597 /* main execution loop */
 598
 599 int cpu_exec(CPUState *cpu)
 600 {
 601     CPUClass *cc = CPU_GET_CLASS(cpu);
 602     int ret;
 603     SyncClocks sc;
 604
 605     /* replay_interrupt may need current_cpu */
 606     current_cpu = cpu;
 607
 608     if (cpu_handle_halt(cpu)) {
 609         return EXCP_HALTED;
 610     }
 611
 612     atomic_mb_set(&tcg_current_cpu, cpu);
 613     rcu_read_lock();
 614
 615     if (unlikely(atomic_mb_read(&exit_request))) {
 616         cpu->exit_request = 1;
 617     }
 618
 619     cc->cpu_exec_enter(cpu);
 620
 621     /* Calculate difference between guest clock and host clock.
 622      * This delay includes the delay of the last cycle, so
 623      * what we have to do is sleep until it is 0. As for the
 624      * advance/delay we gain here, we try to fix it next time.
 625      */
 626     init_delay_params(&sc, cpu);
 627
 628     for(;;) {
 629         /* prepare setjmp context for exception handling */
 630         if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 631             TranslationBlock *tb, *last_tb = NULL;
 632             int tb_exit = 0;
 633
 634             /* if an exception is pending, we execute it here */
 635             if (cpu_handle_exception(cpu, &ret)) {
 636                 break;
 637             }
 638
 639             for(;;) {
 640                 cpu_handle_interrupt(cpu, &last_tb);
 641                 tb = tb_find(cpu, last_tb, tb_exit);
 642                 cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
 643                 /* Try to align the host and virtual clocks
 644                    if the guest is in advance */
 645                 align_clocks(&sc, cpu);
 646             } /* for(;;) */
 647         } else {
 648 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 649             /* Some compilers wrongly smash all local variables after
 650              * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 651              * Reload essential local variables here for those compilers.
 652              * Newer versions of gcc would complain about this code (-Wclobbered). */
 653             cpu = current_cpu;
 654             cc = CPU_GET_CLASS(cpu);
 655 #else /* buggy compiler */
 656             /* Assert that the compiler does not smash local variables. */
 657             g_assert(cpu == current_cpu);
 658             g_assert(cc == CPU_GET_CLASS(cpu));
 659 #endif /* buggy compiler */
 660             cpu->can_do_io = 1;
 661             tb_lock_reset();
 662         }
 663     } /* for(;;) */
 664
 665     cc->cpu_exec_exit(cpu);
 666     rcu_read_unlock();
 667
 668     /* fail safe : never use current_cpu outside cpu_exec() */
 669     current_cpu = NULL;
 670
 671     /* Does not need atomic_mb_set because a spurious wakeup is okay.  */
 672     atomic_set(&tcg_current_cpu, NULL);
 673     return ret;
 674 }