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/cpus.h"
  37 #include "sysemu/replay.h"
  38
  39 /* -icount align implementation. */
  40
  41 typedef struct SyncClocks {
  42     int64_t diff_clk;
  43     int64_t last_cpu_icount;
  44     int64_t realtime_clock;
  45 } SyncClocks;
  46
  47 #if !defined(CONFIG_USER_ONLY)
  48 /* Allow the guest to have a max 3ms advance.
  49  * The difference between the 2 clocks could therefore
  50  * oscillate around 0.
  51  */
  52 #define VM_CLOCK_ADVANCE 3000000
  53 #define THRESHOLD_REDUCE 1.5
  54 #define MAX_DELAY_PRINT_RATE 2000000000LL
  55 #define MAX_NB_PRINTS 100
  56
  57 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
  58 {
  59     int64_t cpu_icount;
  60
  61     if (!icount_align_option) {
  62         return;
  63     }
  64
  65     cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
  66     sc->diff_clk += cpu_icount_to_ns(sc->last_cpu_icount - cpu_icount);
  67     sc->last_cpu_icount = cpu_icount;
  68
  69     if (sc->diff_clk > VM_CLOCK_ADVANCE) {
  70 #ifndef _WIN32
  71         struct timespec sleep_delay, rem_delay;
  72         sleep_delay.tv_sec = sc->diff_clk / 1000000000LL;
  73         sleep_delay.tv_nsec = sc->diff_clk % 1000000000LL;
  74         if (nanosleep(&sleep_delay, &rem_delay) < 0) {
  75             sc->diff_clk = rem_delay.tv_sec * 1000000000LL + rem_delay.tv_nsec;
  76         } else {
  77             sc->diff_clk = 0;
  78         }
  79 #else
  80         Sleep(sc->diff_clk / SCALE_MS);
  81         sc->diff_clk = 0;
  82 #endif
  83     }
  84 }
  85
  86 static void print_delay(const SyncClocks *sc)
  87 {
  88     static float threshold_delay;
  89     static int64_t last_realtime_clock;
  90     static int nb_prints;
  91
  92     if (icount_align_option &&
  93         sc->realtime_clock - last_realtime_clock >= MAX_DELAY_PRINT_RATE &&
  94         nb_prints < MAX_NB_PRINTS) {
  95         if ((-sc->diff_clk / (float)1000000000LL > threshold_delay) ||
  96             (-sc->diff_clk / (float)1000000000LL <
  97              (threshold_delay - THRESHOLD_REDUCE))) {
  98             threshold_delay = (-sc->diff_clk / 1000000000LL) + 1;
  99             printf("Warning: The guest is now late by %.1f to %.1f seconds\n",
 100                    threshold_delay - 1,
 101                    threshold_delay);
 102             nb_prints++;
 103             last_realtime_clock = sc->realtime_clock;
 104         }
 105     }
 106 }
 107
 108 static void init_delay_params(SyncClocks *sc,
 109                               const CPUState *cpu)
 110 {
 111     if (!icount_align_option) {
 112         return;
 113     }
 114     sc->realtime_clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT);
 115     sc->diff_clk = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) - sc->realtime_clock;
 116     sc->last_cpu_icount = cpu->icount_extra + cpu->icount_decr.u16.low;
 117     if (sc->diff_clk < max_delay) {
 118         max_delay = sc->diff_clk;
 119     }
 120     if (sc->diff_clk > max_advance) {
 121         max_advance = sc->diff_clk;
 122     }
 123
 124     /* Print every 2s max if the guest is late. We limit the number
 125        of printed messages to NB_PRINT_MAX(currently 100) */
 126     print_delay(sc);
 127 }
 128 #else
 129 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
 130 {
 131 }
 132
 133 static void init_delay_params(SyncClocks *sc, const CPUState *cpu)
 134 {
 135 }
 136 #endif /* CONFIG USER ONLY */
 137
 138 /* Execute a TB, and fix up the CPU state afterwards if necessary */
 139 static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
 140 {
 141     CPUArchState *env = cpu->env_ptr;
 142     uintptr_t ret;
 143     TranslationBlock *last_tb;
 144     int tb_exit;
 145     uint8_t *tb_ptr = itb->tc_ptr;
 146
 147     qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 148                            "Trace %p [%d: " TARGET_FMT_lx "] %s\n",
 149                            itb->tc_ptr, cpu->cpu_index, itb->pc,
 150                            lookup_symbol(itb->pc));
 151
 152 #if defined(DEBUG_DISAS)
 153     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)
 154         && qemu_log_in_addr_range(itb->pc)) {
 155         qemu_log_lock();
 156 #if defined(TARGET_I386)
 157         log_cpu_state(cpu, CPU_DUMP_CCOP);
 158 #else
 159         log_cpu_state(cpu, 0);
 160 #endif
 161         qemu_log_unlock();
 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     return ret;
 191 }
 192
 193 #ifndef CONFIG_USER_ONLY
 194 /* Execute the code without caching the generated code. An interpreter
 195    could be used if available. */
 196 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 197                              TranslationBlock *orig_tb, bool ignore_icount)
 198 {
 199     TranslationBlock *tb;
 200
 201     /* Should never happen.
 202        We only end up here when an existing TB is too long.  */
 203     if (max_cycles > CF_COUNT_MASK)
 204         max_cycles = CF_COUNT_MASK;
 205
 206     tb_lock();
 207     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base, orig_tb->flags,
 208                      max_cycles | CF_NOCACHE
 209                          | (ignore_icount ? CF_IGNORE_ICOUNT : 0));
 210     tb->orig_tb = orig_tb;
 211     tb_unlock();
 212
 213     /* execute the generated code */
 214     trace_exec_tb_nocache(tb, tb->pc);
 215     cpu_tb_exec(cpu, tb);
 216
 217     tb_lock();
 218     tb_phys_invalidate(tb, -1);
 219     tb_free(tb);
 220     tb_unlock();
 221 }
 222 #endif
 223
 224 static void cpu_exec_step(CPUState *cpu)
 225 {
 226     CPUClass *cc = CPU_GET_CLASS(cpu);
 227     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 228     TranslationBlock *tb;
 229     target_ulong cs_base, pc;
 230     uint32_t flags;
 231
 232     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 233     if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 234         mmap_lock();
 235         tb_lock();
 236         tb = tb_gen_code(cpu, pc, cs_base, flags,
 237                          1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
 238         tb->orig_tb = NULL;
 239         tb_unlock();
 240         mmap_unlock();
 241
 242         cc->cpu_exec_enter(cpu);
 243         /* execute the generated code */
 244         trace_exec_tb_nocache(tb, pc);
 245         cpu_tb_exec(cpu, tb);
 246         cc->cpu_exec_exit(cpu);
 247
 248         tb_lock();
 249         tb_phys_invalidate(tb, -1);
 250         tb_free(tb);
 251         tb_unlock();
 252     } else {
 253         /* We may have exited due to another problem here, so we need
 254          * to reset any tb_locks we may have taken but didn't release.
 255          * The mmap_lock is dropped by tb_gen_code if it runs out of
 256          * memory.
 257          */
 258 #ifndef CONFIG_SOFTMMU
 259         tcg_debug_assert(!have_mmap_lock());
 260 #endif
 261         tb_lock_reset();
 262     }
 263 }
 264
 265 void cpu_exec_step_atomic(CPUState *cpu)
 266 {
 267     start_exclusive();
 268
 269     /* Since we got here, we know that parallel_cpus must be true.  */
 270     parallel_cpus = false;
 271     cpu_exec_step(cpu);
 272     parallel_cpus = true;
 273
 274     end_exclusive();
 275 }
 276
 277 struct tb_desc {
 278     target_ulong pc;
 279     target_ulong cs_base;
 280     CPUArchState *env;
 281     tb_page_addr_t phys_page1;
 282     uint32_t flags;
 283 };
 284
 285 static bool tb_cmp(const void *p, const void *d)
 286 {
 287     const TranslationBlock *tb = p;
 288     const struct tb_desc *desc = d;
 289
 290     if (tb->pc == desc->pc &&
 291         tb->page_addr[0] == desc->phys_page1 &&
 292         tb->cs_base == desc->cs_base &&
 293         tb->flags == desc->flags &&
 294         !atomic_read(&tb->invalid)) {
 295         /* check next page if needed */
 296         if (tb->page_addr[1] == -1) {
 297             return true;
 298         } else {
 299             tb_page_addr_t phys_page2;
 300             target_ulong virt_page2;
 301
 302             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 303             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 304             if (tb->page_addr[1] == phys_page2) {
 305                 return true;
 306             }
 307         }
 308     }
 309     return false;
 310 }
 311
 312 static TranslationBlock *tb_htable_lookup(CPUState *cpu,
 313                                           target_ulong pc,
 314                                           target_ulong cs_base,
 315                                           uint32_t flags)
 316 {
 317     tb_page_addr_t phys_pc;
 318     struct tb_desc desc;
 319     uint32_t h;
 320
 321     desc.env = (CPUArchState *)cpu->env_ptr;
 322     desc.cs_base = cs_base;
 323     desc.flags = flags;
 324     desc.pc = pc;
 325     phys_pc = get_page_addr_code(desc.env, pc);
 326     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 327     h = tb_hash_func(phys_pc, pc, flags);
 328     return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h);
 329 }
 330
 331 static inline TranslationBlock *tb_find(CPUState *cpu,
 332                                         TranslationBlock *last_tb,
 333                                         int tb_exit)
 334 {
 335     CPUArchState *env = (CPUArchState *)cpu->env_ptr;
 336     TranslationBlock *tb;
 337     target_ulong cs_base, pc;
 338     uint32_t flags;
 339     bool have_tb_lock = false;
 340
 341     /* we record a subset of the CPU state. It will
 342        always be the same before a given translated block
 343        is executed. */
 344     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
 345     tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]);
 346     if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base ||
 347                  tb->flags != flags)) {
 348         tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 349         if (!tb) {
 350
 351             /* mmap_lock is needed by tb_gen_code, and mmap_lock must be
 352              * taken outside tb_lock. As system emulation is currently
 353              * single threaded the locks are NOPs.
 354              */
 355             mmap_lock();
 356             tb_lock();
 357             have_tb_lock = true;
 358
 359             /* There's a chance that our desired tb has been translated while
 360              * taking the locks so we check again inside the lock.
 361              */
 362             tb = tb_htable_lookup(cpu, pc, cs_base, flags);
 363             if (!tb) {
 364                 /* if no translated code available, then translate it now */
 365                 tb = tb_gen_code(cpu, pc, cs_base, flags, 0);
 366             }
 367
 368             mmap_unlock();
 369         }
 370
 371         /* We add the TB in the virtual pc hash table for the fast lookup */
 372         atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 373     }
 374 #ifndef CONFIG_USER_ONLY
 375     /* We don't take care of direct jumps when address mapping changes in
 376      * system emulation. So it's not safe to make a direct jump to a TB
 377      * spanning two pages because the mapping for the second page can change.
 378      */
 379     if (tb->page_addr[1] != -1) {
 380         last_tb = NULL;
 381     }
 382 #endif
 383     /* See if we can patch the calling TB. */
 384     if (last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
 385         if (!have_tb_lock) {
 386             tb_lock();
 387             have_tb_lock = true;
 388         }
 389         if (!tb->invalid) {
 390             tb_add_jump(last_tb, tb_exit, tb);
 391         }
 392     }
 393     if (have_tb_lock) {
 394         tb_unlock();
 395     }
 396     return tb;
 397 }
 398
 399 static inline bool cpu_handle_halt(CPUState *cpu)
 400 {
 401     if (cpu->halted) {
 402 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 403         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 404             && replay_interrupt()) {
 405             X86CPU *x86_cpu = X86_CPU(cpu);
 406             qemu_mutex_lock_iothread();
 407             apic_poll_irq(x86_cpu->apic_state);
 408             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 409             qemu_mutex_unlock_iothread();
 410         }
 411 #endif
 412         if (!cpu_has_work(cpu)) {
 413             return true;
 414         }
 415
 416         cpu->halted = 0;
 417     }
 418
 419     return false;
 420 }
 421
 422 static inline void cpu_handle_debug_exception(CPUState *cpu)
 423 {
 424     CPUClass *cc = CPU_GET_CLASS(cpu);
 425     CPUWatchpoint *wp;
 426
 427     if (!cpu->watchpoint_hit) {
 428         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 429             wp->flags &= ~BP_WATCHPOINT_HIT;
 430         }
 431     }
 432
 433     cc->debug_excp_handler(cpu);
 434 }
 435
 436 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 437 {
 438     if (cpu->exception_index >= 0) {
 439         if (cpu->exception_index >= EXCP_INTERRUPT) {
 440             /* exit request from the cpu execution loop */
 441             *ret = cpu->exception_index;
 442             if (*ret == EXCP_DEBUG) {
 443                 cpu_handle_debug_exception(cpu);
 444             }
 445             cpu->exception_index = -1;
 446             return true;
 447         } else {
 448 #if defined(CONFIG_USER_ONLY)
 449             /* if user mode only, we simulate a fake exception
 450                which will be handled outside the cpu execution
 451                loop */
 452 #if defined(TARGET_I386)
 453             CPUClass *cc = CPU_GET_CLASS(cpu);
 454             cc->do_interrupt(cpu);
 455 #endif
 456             *ret = cpu->exception_index;
 457             cpu->exception_index = -1;
 458             return true;
 459 #else
 460             if (replay_exception()) {
 461                 CPUClass *cc = CPU_GET_CLASS(cpu);
 462                 qemu_mutex_lock_iothread();
 463                 cc->do_interrupt(cpu);
 464                 qemu_mutex_unlock_iothread();
 465                 cpu->exception_index = -1;
 466             } else if (!replay_has_interrupt()) {
 467                 /* give a chance to iothread in replay mode */
 468                 *ret = EXCP_INTERRUPT;
 469                 return true;
 470             }
 471 #endif
 472         }
 473 #ifndef CONFIG_USER_ONLY
 474     } else if (replay_has_exception()
 475                && cpu->icount_decr.u16.low + cpu->icount_extra == 0) {
 476         /* try to cause an exception pending in the log */
 477         cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0), true);
 478         *ret = -1;
 479         return true;
 480 #endif
 481     }
 482
 483     return false;
 484 }
 485
 486 static inline bool cpu_handle_interrupt(CPUState *cpu,
 487                                         TranslationBlock **last_tb)
 488 {
 489     CPUClass *cc = CPU_GET_CLASS(cpu);
 490
 491     if (unlikely(atomic_read(&cpu->interrupt_request))) {
 492         int interrupt_request;
 493         qemu_mutex_lock_iothread();
 494         interrupt_request = cpu->interrupt_request;
 495         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 496             /* Mask out external interrupts for this step. */
 497             interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 498         }
 499         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 500             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 501             cpu->exception_index = EXCP_DEBUG;
 502             qemu_mutex_unlock_iothread();
 503             return true;
 504         }
 505         if (replay_mode == REPLAY_MODE_PLAY && !replay_has_interrupt()) {
 506             /* Do nothing */
 507         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 508             replay_interrupt();
 509             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 510             cpu->halted = 1;
 511             cpu->exception_index = EXCP_HLT;
 512             qemu_mutex_unlock_iothread();
 513             return true;
 514         }
 515 #if defined(TARGET_I386)
 516         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 517             X86CPU *x86_cpu = X86_CPU(cpu);
 518             CPUArchState *env = &x86_cpu->env;
 519             replay_interrupt();
 520             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0, 0);
 521             do_cpu_init(x86_cpu);
 522             cpu->exception_index = EXCP_HALTED;
 523             qemu_mutex_unlock_iothread();
 524             return true;
 525         }
 526 #else
 527         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 528             replay_interrupt();
 529             cpu_reset(cpu);
 530             qemu_mutex_unlock_iothread();
 531             return true;
 532         }
 533 #endif
 534         /* The target hook has 3 exit conditions:
 535            False when the interrupt isn't processed,
 536            True when it is, and we should restart on a new TB,
 537            and via longjmp via cpu_loop_exit.  */
 538         else {
 539             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 540                 replay_interrupt();
 541                 *last_tb = NULL;
 542             }
 543             /* The target hook may have updated the 'cpu->interrupt_request';
 544              * reload the 'interrupt_request' value */
 545             interrupt_request = cpu->interrupt_request;
 546         }
 547         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 548             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 549             /* ensure that no TB jump will be modified as
 550                the program flow was changed */
 551             *last_tb = NULL;
 552         }
 553
 554         /* If we exit via cpu_loop_exit/longjmp it is reset in cpu_exec */
 555         qemu_mutex_unlock_iothread();
 556     }
 557
 558     /* Finally, check if we need to exit to the main loop.  */
 559     if (unlikely(atomic_read(&cpu->exit_request)
 560         || (use_icount && cpu->icount_decr.u16.low + cpu->icount_extra == 0))) {
 561         atomic_set(&cpu->exit_request, 0);
 562         cpu->exception_index = EXCP_INTERRUPT;
 563         return true;
 564     }
 565
 566     return false;
 567 }
 568
 569 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 570                                     TranslationBlock **last_tb, int *tb_exit)
 571 {
 572     uintptr_t ret;
 573     int32_t insns_left;
 574
 575     trace_exec_tb(tb, tb->pc);
 576     ret = cpu_tb_exec(cpu, tb);
 577     tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 578     *tb_exit = ret & TB_EXIT_MASK;
 579     if (*tb_exit != TB_EXIT_REQUESTED) {
 580         *last_tb = tb;
 581         return;
 582     }
 583
 584     *last_tb = NULL;
 585     insns_left = atomic_read(&cpu->icount_decr.u32);
 586     atomic_set(&cpu->icount_decr.u16.high, 0);
 587     if (insns_left < 0) {
 588         /* Something asked us to stop executing chained TBs; just
 589          * continue round the main loop. Whatever requested the exit
 590          * will also have set something else (eg exit_request or
 591          * interrupt_request) which we will handle next time around
 592          * the loop.  But we need to ensure the zeroing of icount_decr
 593          * comes before the next read of cpu->exit_request
 594          * or cpu->interrupt_request.
 595          */
 596         smp_mb();
 597         return;
 598     }
 599
 600     /* Instruction counter expired.  */
 601     assert(use_icount);
 602 #ifndef CONFIG_USER_ONLY
 603     /* Ensure global icount has gone forward */
 604     cpu_update_icount(cpu);
 605     /* Refill decrementer and continue execution.  */
 606     insns_left = MIN(0xffff, cpu->icount_budget);
 607     cpu->icount_decr.u16.low = insns_left;
 608     cpu->icount_extra = cpu->icount_budget - insns_left;
 609     if (!cpu->icount_extra) {
 610         /* Execute any remaining instructions, then let the main loop
 611          * handle the next event.
 612          */
 613         if (insns_left > 0) {
 614             cpu_exec_nocache(cpu, insns_left, tb, false);
 615         }
 616     }
 617 #endif
 618 }
 619
 620 /* main execution loop */
 621
 622 int cpu_exec(CPUState *cpu)
 623 {
 624     CPUClass *cc = CPU_GET_CLASS(cpu);
 625     int ret;
 626     SyncClocks sc = { 0 };
 627
 628     /* replay_interrupt may need current_cpu */
 629     current_cpu = cpu;
 630
 631     if (cpu_handle_halt(cpu)) {
 632         return EXCP_HALTED;
 633     }
 634
 635     rcu_read_lock();
 636
 637     cc->cpu_exec_enter(cpu);
 638
 639     /* Calculate difference between guest clock and host clock.
 640      * This delay includes the delay of the last cycle, so
 641      * what we have to do is sleep until it is 0. As for the
 642      * advance/delay we gain here, we try to fix it next time.
 643      */
 644     init_delay_params(&sc, cpu);
 645
 646     /* prepare setjmp context for exception handling */
 647     if (sigsetjmp(cpu->jmp_env, 0) != 0) {
 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         if (qemu_mutex_iothread_locked()) {
 663             qemu_mutex_unlock_iothread();
 664         }
 665     }
 666
 667     /* if an exception is pending, we execute it here */
 668     while (!cpu_handle_exception(cpu, &ret)) {
 669         TranslationBlock *last_tb = NULL;
 670         int tb_exit = 0;
 671
 672         while (!cpu_handle_interrupt(cpu, &last_tb)) {
 673             TranslationBlock *tb = tb_find(cpu, last_tb, tb_exit);
 674             cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit);
 675             /* Try to align the host and virtual clocks
 676                if the guest is in advance */
 677             align_clocks(&sc, cpu);
 678         }
 679     }
 680
 681     cc->cpu_exec_exit(cpu);
 682     rcu_read_unlock();
 683
 684     return ret;
 685 }