accel/tcg/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 2.1 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 "qemu/rcu.h"
  29 #include "exec/tb-hash.h"
  30 #include "exec/tb-lookup.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, 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_neg(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, 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
 116         = cpu->icount_extra + cpu_neg(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 %d: %p ["
 149                            TARGET_FMT_lx "/" TARGET_FMT_lx "/%#x] %s\n",
 150                            cpu->cpu_index, itb->tc.ptr,
 151                            itb->cs_base, itb->pc, itb->flags,
 152                            lookup_symbol(itb->pc));
 153
 154 #if defined(DEBUG_DISAS)
 155     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)
 156         && qemu_log_in_addr_range(itb->pc)) {
 157         qemu_log_lock();
 158         int flags = 0;
 159         if (qemu_loglevel_mask(CPU_LOG_TB_FPU)) {
 160             flags |= CPU_DUMP_FPU;
 161         }
 162 #if defined(TARGET_I386)
 163         flags |= CPU_DUMP_CCOP;
 164 #endif
 165         log_cpu_state(cpu, flags);
 166         qemu_log_unlock();
 167     }
 168 #endif /* DEBUG_DISAS */
 169
 170     cpu->can_do_io = !use_icount;
 171     ret = tcg_qemu_tb_exec(env, tb_ptr);
 172     cpu->can_do_io = 1;
 173     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 174     tb_exit = ret & TB_EXIT_MASK;
 175     trace_exec_tb_exit(last_tb, tb_exit);
 176
 177     if (tb_exit > TB_EXIT_IDX1) {
 178         /* We didn't start executing this TB (eg because the instruction
 179          * counter hit zero); we must restore the guest PC to the address
 180          * of the start of the TB.
 181          */
 182         CPUClass *cc = CPU_GET_CLASS(cpu);
 183         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 184                                "Stopped execution of TB chain before %p ["
 185                                TARGET_FMT_lx "] %s\n",
 186                                last_tb->tc.ptr, last_tb->pc,
 187                                lookup_symbol(last_tb->pc));
 188         if (cc->synchronize_from_tb) {
 189             cc->synchronize_from_tb(cpu, last_tb);
 190         } else {
 191             assert(cc->set_pc);
 192             cc->set_pc(cpu, last_tb->pc);
 193         }
 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     uint32_t cflags = curr_cflags() | CF_NOCACHE;
 206
 207     if (ignore_icount) {
 208         cflags &= ~CF_USE_ICOUNT;
 209     }
 210
 211     /* Should never happen.
 212        We only end up here when an existing TB is too long.  */
 213     cflags |= MIN(max_cycles, CF_COUNT_MASK);
 214
 215     mmap_lock();
 216     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base,
 217                      orig_tb->flags, cflags);
 218     tb->orig_tb = orig_tb;
 219     mmap_unlock();
 220
 221     /* execute the generated code */
 222     trace_exec_tb_nocache(tb, tb->pc);
 223     cpu_tb_exec(cpu, tb);
 224
 225     mmap_lock();
 226     tb_phys_invalidate(tb, -1);
 227     mmap_unlock();
 228     tcg_tb_remove(tb);
 229 }
 230 #endif
 231
 232 void cpu_exec_step_atomic(CPUState *cpu)
 233 {
 234     CPUClass *cc = CPU_GET_CLASS(cpu);
 235     TranslationBlock *tb;
 236     target_ulong cs_base, pc;
 237     uint32_t flags;
 238     uint32_t cflags = 1;
 239     uint32_t cf_mask = cflags & CF_HASH_MASK;
 240     /* volatile because we modify it between setjmp and longjmp */
 241     volatile bool in_exclusive_region = false;
 242
 243     if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 244         tb = tb_lookup__cpu_state(cpu, &pc, &cs_base, &flags, cf_mask);
 245         if (tb == NULL) {
 246             mmap_lock();
 247             tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
 248             mmap_unlock();
 249         }
 250
 251         start_exclusive();
 252
 253         /* Since we got here, we know that parallel_cpus must be true.  */
 254         parallel_cpus = false;
 255         in_exclusive_region = true;
 256         cc->cpu_exec_enter(cpu);
 257         /* execute the generated code */
 258         trace_exec_tb(tb, pc);
 259         cpu_tb_exec(cpu, tb);
 260         cc->cpu_exec_exit(cpu);
 261     } else {
 262         /*
 263          * The mmap_lock is dropped by tb_gen_code if it runs out of
 264          * memory.
 265          */
 266 #ifndef CONFIG_SOFTMMU
 267         tcg_debug_assert(!have_mmap_lock());
 268 #endif
 269         if (qemu_mutex_iothread_locked()) {
 270             qemu_mutex_unlock_iothread();
 271         }
 272         assert_no_pages_locked();
 273     }
 274
 275     if (in_exclusive_region) {
 276         /* We might longjump out of either the codegen or the
 277          * execution, so must make sure we only end the exclusive
 278          * region if we started it.
 279          */
 280         parallel_cpus = true;
 281         end_exclusive();
 282     }
 283 }
 284
 285 struct tb_desc {
 286     target_ulong pc;
 287     target_ulong cs_base;
 288     CPUArchState *env;
 289     tb_page_addr_t phys_page1;
 290     uint32_t flags;
 291     uint32_t cf_mask;
 292     uint32_t trace_vcpu_dstate;
 293 };
 294
 295 static bool tb_lookup_cmp(const void *p, const void *d)
 296 {
 297     const TranslationBlock *tb = p;
 298     const struct tb_desc *desc = d;
 299
 300     if (tb->pc == desc->pc &&
 301         tb->page_addr[0] == desc->phys_page1 &&
 302         tb->cs_base == desc->cs_base &&
 303         tb->flags == desc->flags &&
 304         tb->trace_vcpu_dstate == desc->trace_vcpu_dstate &&
 305         (tb_cflags(tb) & (CF_HASH_MASK | CF_INVALID)) == desc->cf_mask) {
 306         /* check next page if needed */
 307         if (tb->page_addr[1] == -1) {
 308             return true;
 309         } else {
 310             tb_page_addr_t phys_page2;
 311             target_ulong virt_page2;
 312
 313             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 314             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 315             if (tb->page_addr[1] == phys_page2) {
 316                 return true;
 317             }
 318         }
 319     }
 320     return false;
 321 }
 322
 323 TranslationBlock *tb_htable_lookup(CPUState *cpu, target_ulong pc,
 324                                    target_ulong cs_base, uint32_t flags,
 325                                    uint32_t cf_mask)
 326 {
 327     tb_page_addr_t phys_pc;
 328     struct tb_desc desc;
 329     uint32_t h;
 330
 331     desc.env = (CPUArchState *)cpu->env_ptr;
 332     desc.cs_base = cs_base;
 333     desc.flags = flags;
 334     desc.cf_mask = cf_mask;
 335     desc.trace_vcpu_dstate = *cpu->trace_dstate;
 336     desc.pc = pc;
 337     phys_pc = get_page_addr_code(desc.env, pc);
 338     if (phys_pc == -1) {
 339         return NULL;
 340     }
 341     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 342     h = tb_hash_func(phys_pc, pc, flags, cf_mask, *cpu->trace_dstate);
 343     return qht_lookup_custom(&tb_ctx.htable, &desc, h, tb_lookup_cmp);
 344 }
 345
 346 void tb_set_jmp_target(TranslationBlock *tb, int n, uintptr_t addr)
 347 {
 348     if (TCG_TARGET_HAS_direct_jump) {
 349         uintptr_t offset = tb->jmp_target_arg[n];
 350         uintptr_t tc_ptr = (uintptr_t)tb->tc.ptr;
 351         tb_target_set_jmp_target(tc_ptr, tc_ptr + offset, addr);
 352     } else {
 353         tb->jmp_target_arg[n] = addr;
 354     }
 355 }
 356
 357 static inline void tb_add_jump(TranslationBlock *tb, int n,
 358                                TranslationBlock *tb_next)
 359 {
 360     uintptr_t old;
 361
 362     assert(n < ARRAY_SIZE(tb->jmp_list_next));
 363     qemu_spin_lock(&tb_next->jmp_lock);
 364
 365     /* make sure the destination TB is valid */
 366     if (tb_next->cflags & CF_INVALID) {
 367         goto out_unlock_next;
 368     }
 369     /* Atomically claim the jump destination slot only if it was NULL */
 370     old = atomic_cmpxchg(&tb->jmp_dest[n], (uintptr_t)NULL, (uintptr_t)tb_next);
 371     if (old) {
 372         goto out_unlock_next;
 373     }
 374
 375     /* patch the native jump address */
 376     tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc.ptr);
 377
 378     /* add in TB jmp list */
 379     tb->jmp_list_next[n] = tb_next->jmp_list_head;
 380     tb_next->jmp_list_head = (uintptr_t)tb | n;
 381
 382     qemu_spin_unlock(&tb_next->jmp_lock);
 383
 384     qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc,
 385                            "Linking TBs %p [" TARGET_FMT_lx
 386                            "] index %d -> %p [" TARGET_FMT_lx "]\n",
 387                            tb->tc.ptr, tb->pc, n,
 388                            tb_next->tc.ptr, tb_next->pc);
 389     return;
 390
 391  out_unlock_next:
 392     qemu_spin_unlock(&tb_next->jmp_lock);
 393     return;
 394 }
 395
 396 static inline TranslationBlock *tb_find(CPUState *cpu,
 397                                         TranslationBlock *last_tb,
 398                                         int tb_exit, uint32_t cf_mask)
 399 {
 400     TranslationBlock *tb;
 401     target_ulong cs_base, pc;
 402     uint32_t flags;
 403
 404     tb = tb_lookup__cpu_state(cpu, &pc, &cs_base, &flags, cf_mask);
 405     if (tb == NULL) {
 406         mmap_lock();
 407         tb = tb_gen_code(cpu, pc, cs_base, flags, cf_mask);
 408         mmap_unlock();
 409         /* We add the TB in the virtual pc hash table for the fast lookup */
 410         atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 411     }
 412 #ifndef CONFIG_USER_ONLY
 413     /* We don't take care of direct jumps when address mapping changes in
 414      * system emulation. So it's not safe to make a direct jump to a TB
 415      * spanning two pages because the mapping for the second page can change.
 416      */
 417     if (tb->page_addr[1] != -1) {
 418         last_tb = NULL;
 419     }
 420 #endif
 421     /* See if we can patch the calling TB. */
 422     if (last_tb) {
 423         tb_add_jump(last_tb, tb_exit, tb);
 424     }
 425     return tb;
 426 }
 427
 428 static inline bool cpu_handle_halt(CPUState *cpu)
 429 {
 430     if (cpu->halted) {
 431 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 432         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 433             && replay_interrupt()) {
 434             X86CPU *x86_cpu = X86_CPU(cpu);
 435             qemu_mutex_lock_iothread();
 436             apic_poll_irq(x86_cpu->apic_state);
 437             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 438             qemu_mutex_unlock_iothread();
 439         }
 440 #endif
 441         if (!cpu_has_work(cpu)) {
 442             return true;
 443         }
 444
 445         cpu->halted = 0;
 446     }
 447
 448     return false;
 449 }
 450
 451 static inline void cpu_handle_debug_exception(CPUState *cpu)
 452 {
 453     CPUClass *cc = CPU_GET_CLASS(cpu);
 454     CPUWatchpoint *wp;
 455
 456     if (!cpu->watchpoint_hit) {
 457         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 458             wp->flags &= ~BP_WATCHPOINT_HIT;
 459         }
 460     }
 461
 462     cc->debug_excp_handler(cpu);
 463 }
 464
 465 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 466 {
 467     if (cpu->exception_index < 0) {
 468 #ifndef CONFIG_USER_ONLY
 469         if (replay_has_exception()
 470             && cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra == 0) {
 471             /* try to cause an exception pending in the log */
 472             cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0, curr_cflags()), true);
 473         }
 474 #endif
 475         if (cpu->exception_index < 0) {
 476             return false;
 477         }
 478     }
 479
 480     if (cpu->exception_index >= EXCP_INTERRUPT) {
 481         /* exit request from the cpu execution loop */
 482         *ret = cpu->exception_index;
 483         if (*ret == EXCP_DEBUG) {
 484             cpu_handle_debug_exception(cpu);
 485         }
 486         cpu->exception_index = -1;
 487         return true;
 488     } else {
 489 #if defined(CONFIG_USER_ONLY)
 490         /* if user mode only, we simulate a fake exception
 491            which will be handled outside the cpu execution
 492            loop */
 493 #if defined(TARGET_I386)
 494         CPUClass *cc = CPU_GET_CLASS(cpu);
 495         cc->do_interrupt(cpu);
 496 #endif
 497         *ret = cpu->exception_index;
 498         cpu->exception_index = -1;
 499         return true;
 500 #else
 501         if (replay_exception()) {
 502             CPUClass *cc = CPU_GET_CLASS(cpu);
 503             qemu_mutex_lock_iothread();
 504             cc->do_interrupt(cpu);
 505             qemu_mutex_unlock_iothread();
 506             cpu->exception_index = -1;
 507         } else if (!replay_has_interrupt()) {
 508             /* give a chance to iothread in replay mode */
 509             *ret = EXCP_INTERRUPT;
 510             return true;
 511         }
 512 #endif
 513     }
 514
 515     return false;
 516 }
 517
 518 static inline bool cpu_handle_interrupt(CPUState *cpu,
 519                                         TranslationBlock **last_tb)
 520 {
 521     CPUClass *cc = CPU_GET_CLASS(cpu);
 522
 523     /* Clear the interrupt flag now since we're processing
 524      * cpu->interrupt_request and cpu->exit_request.
 525      * Ensure zeroing happens before reading cpu->exit_request or
 526      * cpu->interrupt_request (see also smp_wmb in cpu_exit())
 527      */
 528     atomic_mb_set(&cpu_neg(cpu)->icount_decr.u16.high, 0);
 529
 530     if (unlikely(atomic_read(&cpu->interrupt_request))) {
 531         int interrupt_request;
 532         qemu_mutex_lock_iothread();
 533         interrupt_request = cpu->interrupt_request;
 534         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 535             /* Mask out external interrupts for this step. */
 536             interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 537         }
 538         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 539             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 540             cpu->exception_index = EXCP_DEBUG;
 541             qemu_mutex_unlock_iothread();
 542             return true;
 543         }
 544         if (replay_mode == REPLAY_MODE_PLAY && !replay_has_interrupt()) {
 545             /* Do nothing */
 546         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 547             replay_interrupt();
 548             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 549             cpu->halted = 1;
 550             cpu->exception_index = EXCP_HLT;
 551             qemu_mutex_unlock_iothread();
 552             return true;
 553         }
 554 #if defined(TARGET_I386)
 555         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 556             X86CPU *x86_cpu = X86_CPU(cpu);
 557             CPUArchState *env = &x86_cpu->env;
 558             replay_interrupt();
 559             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0, 0);
 560             do_cpu_init(x86_cpu);
 561             cpu->exception_index = EXCP_HALTED;
 562             qemu_mutex_unlock_iothread();
 563             return true;
 564         }
 565 #else
 566         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 567             replay_interrupt();
 568             cpu_reset(cpu);
 569             qemu_mutex_unlock_iothread();
 570             return true;
 571         }
 572 #endif
 573         /* The target hook has 3 exit conditions:
 574            False when the interrupt isn't processed,
 575            True when it is, and we should restart on a new TB,
 576            and via longjmp via cpu_loop_exit.  */
 577         else {
 578             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 579                 replay_interrupt();
 580                 cpu->exception_index = -1;
 581                 *last_tb = NULL;
 582             }
 583             /* The target hook may have updated the 'cpu->interrupt_request';
 584              * reload the 'interrupt_request' value */
 585             interrupt_request = cpu->interrupt_request;
 586         }
 587         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 588             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 589             /* ensure that no TB jump will be modified as
 590                the program flow was changed */
 591             *last_tb = NULL;
 592         }
 593
 594         /* If we exit via cpu_loop_exit/longjmp it is reset in cpu_exec */
 595         qemu_mutex_unlock_iothread();
 596     }
 597
 598     /* Finally, check if we need to exit to the main loop.  */
 599     if (unlikely(atomic_read(&cpu->exit_request))
 600         || (use_icount
 601             && cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra == 0)) {
 602         atomic_set(&cpu->exit_request, 0);
 603         if (cpu->exception_index == -1) {
 604             cpu->exception_index = EXCP_INTERRUPT;
 605         }
 606         return true;
 607     }
 608
 609     return false;
 610 }
 611
 612 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 613                                     TranslationBlock **last_tb, int *tb_exit)
 614 {
 615     uintptr_t ret;
 616     int32_t insns_left;
 617
 618     trace_exec_tb(tb, tb->pc);
 619     ret = cpu_tb_exec(cpu, tb);
 620     tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 621     *tb_exit = ret & TB_EXIT_MASK;
 622     if (*tb_exit != TB_EXIT_REQUESTED) {
 623         *last_tb = tb;
 624         return;
 625     }
 626
 627     *last_tb = NULL;
 628     insns_left = atomic_read(&cpu_neg(cpu)->icount_decr.u32);
 629     if (insns_left < 0) {
 630         /* Something asked us to stop executing chained TBs; just
 631          * continue round the main loop. Whatever requested the exit
 632          * will also have set something else (eg exit_request or
 633          * interrupt_request) which will be handled by
 634          * cpu_handle_interrupt.  cpu_handle_interrupt will also
 635          * clear cpu->icount_decr.u16.high.
 636          */
 637         return;
 638     }
 639
 640     /* Instruction counter expired.  */
 641     assert(use_icount);
 642 #ifndef CONFIG_USER_ONLY
 643     /* Ensure global icount has gone forward */
 644     cpu_update_icount(cpu);
 645     /* Refill decrementer and continue execution.  */
 646     insns_left = MIN(0xffff, cpu->icount_budget);
 647     cpu_neg(cpu)->icount_decr.u16.low = insns_left;
 648     cpu->icount_extra = cpu->icount_budget - insns_left;
 649     if (!cpu->icount_extra) {
 650         /* Execute any remaining instructions, then let the main loop
 651          * handle the next event.
 652          */
 653         if (insns_left > 0) {
 654             cpu_exec_nocache(cpu, insns_left, tb, false);
 655         }
 656     }
 657 #endif
 658 }
 659
 660 /* main execution loop */
 661
 662 int cpu_exec(CPUState *cpu)
 663 {
 664     CPUClass *cc = CPU_GET_CLASS(cpu);
 665     int ret;
 666     SyncClocks sc = { 0 };
 667
 668     /* replay_interrupt may need current_cpu */
 669     current_cpu = cpu;
 670
 671     if (cpu_handle_halt(cpu)) {
 672         return EXCP_HALTED;
 673     }
 674
 675     rcu_read_lock();
 676
 677     cc->cpu_exec_enter(cpu);
 678
 679     /* Calculate difference between guest clock and host clock.
 680      * This delay includes the delay of the last cycle, so
 681      * what we have to do is sleep until it is 0. As for the
 682      * advance/delay we gain here, we try to fix it next time.
 683      */
 684     init_delay_params(&sc, cpu);
 685
 686     /* prepare setjmp context for exception handling */
 687     if (sigsetjmp(cpu->jmp_env, 0) != 0) {
 688 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 689         /* Some compilers wrongly smash all local variables after
 690          * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 691          * Reload essential local variables here for those compilers.
 692          * Newer versions of gcc would complain about this code (-Wclobbered). */
 693         cpu = current_cpu;
 694         cc = CPU_GET_CLASS(cpu);
 695 #else /* buggy compiler */
 696         /* Assert that the compiler does not smash local variables. */
 697         g_assert(cpu == current_cpu);
 698         g_assert(cc == CPU_GET_CLASS(cpu));
 699 #endif /* buggy compiler */
 700 #ifndef CONFIG_SOFTMMU
 701         tcg_debug_assert(!have_mmap_lock());
 702 #endif
 703         if (qemu_mutex_iothread_locked()) {
 704             qemu_mutex_unlock_iothread();
 705         }
 706         assert_no_pages_locked();
 707     }
 708
 709     /* if an exception is pending, we execute it here */
 710     while (!cpu_handle_exception(cpu, &ret)) {
 711         TranslationBlock *last_tb = NULL;
 712         int tb_exit = 0;
 713
 714         while (!cpu_handle_interrupt(cpu, &last_tb)) {
 715             uint32_t cflags = cpu->cflags_next_tb;
 716             TranslationBlock *tb;
 717
 718             /* When requested, use an exact setting for cflags for the next
 719                execution.  This is used for icount, precise smc, and stop-
 720                after-access watchpoints.  Since this request should never
 721                have CF_INVALID set, -1 is a convenient invalid value that
 722                does not require tcg headers for cpu_common_reset.  */
 723             if (cflags == -1) {
 724                 cflags = curr_cflags();
 725             } else {
 726                 cpu->cflags_next_tb = -1;
 727             }
 728
 729             tb = tb_find(cpu, last_tb, tb_exit, cflags);
 730             cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit);
 731             /* Try to align the host and virtual clocks
 732                if the guest is in advance */
 733             align_clocks(&sc, cpu);
 734         }
 735     }
 736
 737     cc->cpu_exec_exit(cpu);
 738     rcu_read_unlock();
 739
 740     return ret;
 741 }