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
  20 #include "qemu/osdep.h"
  21 #include "qemu-common.h"
  22 #include "cpu.h"
  23 #include "trace.h"
  24 #include "disas/disas.h"
  25 #include "exec/exec-all.h"
  26 #include "tcg.h"
  27 #include "qemu/atomic.h"
  28 #include "sysemu/qtest.h"
  29 #include "qemu/timer.h"
  30 #include "qemu/rcu.h"
  31 #include "exec/tb-hash.h"
  32 #include "exec/tb-lookup.h"
  33 #include "exec/log.h"
  34 #include "qemu/main-loop.h"
  35 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
  36 #include "hw/i386/apic.h"
  37 #endif
  38 #include "sysemu/cpus.h"
  39 #include "sysemu/replay.h"
  40
  41 /* -icount align implementation. */
  42
  43 typedef struct SyncClocks {
  44     int64_t diff_clk;
  45     int64_t last_cpu_icount;
  46     int64_t realtime_clock;
  47 } SyncClocks;
  48
  49 #if !defined(CONFIG_USER_ONLY)
  50 /* Allow the guest to have a max 3ms advance.
  51  * The difference between the 2 clocks could therefore
  52  * oscillate around 0.
  53  */
  54 #define VM_CLOCK_ADVANCE 3000000
  55 #define THRESHOLD_REDUCE 1.5
  56 #define MAX_DELAY_PRINT_RATE 2000000000LL
  57 #define MAX_NB_PRINTS 100
  58
  59 static void align_clocks(SyncClocks *sc, CPUState *cpu)
  60 {
  61     int64_t cpu_icount;
  62
  63     if (!icount_align_option) {
  64         return;
  65     }
  66
  67     cpu_icount = cpu->icount_extra + cpu_neg(cpu)->icount_decr.u16.low;
  68     sc->diff_clk += cpu_icount_to_ns(sc->last_cpu_icount - cpu_icount);
  69     sc->last_cpu_icount = cpu_icount;
  70
  71     if (sc->diff_clk > VM_CLOCK_ADVANCE) {
  72 #ifndef _WIN32
  73         struct timespec sleep_delay, rem_delay;
  74         sleep_delay.tv_sec = sc->diff_clk / 1000000000LL;
  75         sleep_delay.tv_nsec = sc->diff_clk % 1000000000LL;
  76         if (nanosleep(&sleep_delay, &rem_delay) < 0) {
  77             sc->diff_clk = rem_delay.tv_sec * 1000000000LL + rem_delay.tv_nsec;
  78         } else {
  79             sc->diff_clk = 0;
  80         }
  81 #else
  82         Sleep(sc->diff_clk / SCALE_MS);
  83         sc->diff_clk = 0;
  84 #endif
  85     }
  86 }
  87
  88 static void print_delay(const SyncClocks *sc)
  89 {
  90     static float threshold_delay;
  91     static int64_t last_realtime_clock;
  92     static int nb_prints;
  93
  94     if (icount_align_option &&
  95         sc->realtime_clock - last_realtime_clock >= MAX_DELAY_PRINT_RATE &&
  96         nb_prints < MAX_NB_PRINTS) {
  97         if ((-sc->diff_clk / (float)1000000000LL > threshold_delay) ||
  98             (-sc->diff_clk / (float)1000000000LL <
  99              (threshold_delay - THRESHOLD_REDUCE))) {
 100             threshold_delay = (-sc->diff_clk / 1000000000LL) + 1;
 101             printf("Warning: The guest is now late by %.1f to %.1f seconds\n",
 102                    threshold_delay - 1,
 103                    threshold_delay);
 104             nb_prints++;
 105             last_realtime_clock = sc->realtime_clock;
 106         }
 107     }
 108 }
 109
 110 static void init_delay_params(SyncClocks *sc, CPUState *cpu)
 111 {
 112     if (!icount_align_option) {
 113         return;
 114     }
 115     sc->realtime_clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL_RT);
 116     sc->diff_clk = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) - sc->realtime_clock;
 117     sc->last_cpu_icount
 118         = cpu->icount_extra + cpu_neg(cpu)->icount_decr.u16.low;
 119     if (sc->diff_clk < max_delay) {
 120         max_delay = sc->diff_clk;
 121     }
 122     if (sc->diff_clk > max_advance) {
 123         max_advance = sc->diff_clk;
 124     }
 125
 126     /* Print every 2s max if the guest is late. We limit the number
 127        of printed messages to NB_PRINT_MAX(currently 100) */
 128     print_delay(sc);
 129 }
 130 #else
 131 static void align_clocks(SyncClocks *sc, const CPUState *cpu)
 132 {
 133 }
 134
 135 static void init_delay_params(SyncClocks *sc, const CPUState *cpu)
 136 {
 137 }
 138 #endif /* CONFIG USER ONLY */
 139
 140 /* Execute a TB, and fix up the CPU state afterwards if necessary */
 141 static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
 142 {
 143     CPUArchState *env = cpu->env_ptr;
 144     uintptr_t ret;
 145     TranslationBlock *last_tb;
 146     int tb_exit;
 147     uint8_t *tb_ptr = itb->tc.ptr;
 148
 149     qemu_log_mask_and_addr(CPU_LOG_EXEC, itb->pc,
 150                            "Trace %d: %p ["
 151                            TARGET_FMT_lx "/" TARGET_FMT_lx "/%#x] %s\n",
 152                            cpu->cpu_index, itb->tc.ptr,
 153                            itb->cs_base, itb->pc, itb->flags,
 154                            lookup_symbol(itb->pc));
 155
 156 #if defined(DEBUG_DISAS)
 157     if (qemu_loglevel_mask(CPU_LOG_TB_CPU)
 158         && qemu_log_in_addr_range(itb->pc)) {
 159         qemu_log_lock();
 160         int flags = 0;
 161         if (qemu_loglevel_mask(CPU_LOG_TB_FPU)) {
 162             flags |= CPU_DUMP_FPU;
 163         }
 164 #if defined(TARGET_I386)
 165         flags |= CPU_DUMP_CCOP;
 166 #endif
 167         log_cpu_state(cpu, flags);
 168         qemu_log_unlock();
 169     }
 170 #endif /* DEBUG_DISAS */
 171
 172     cpu->can_do_io = !use_icount;
 173     ret = tcg_qemu_tb_exec(env, tb_ptr);
 174     cpu->can_do_io = 1;
 175     last_tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 176     tb_exit = ret & TB_EXIT_MASK;
 177     trace_exec_tb_exit(last_tb, tb_exit);
 178
 179     if (tb_exit > TB_EXIT_IDX1) {
 180         /* We didn't start executing this TB (eg because the instruction
 181          * counter hit zero); we must restore the guest PC to the address
 182          * of the start of the TB.
 183          */
 184         CPUClass *cc = CPU_GET_CLASS(cpu);
 185         qemu_log_mask_and_addr(CPU_LOG_EXEC, last_tb->pc,
 186                                "Stopped execution of TB chain before %p ["
 187                                TARGET_FMT_lx "] %s\n",
 188                                last_tb->tc.ptr, last_tb->pc,
 189                                lookup_symbol(last_tb->pc));
 190         if (cc->synchronize_from_tb) {
 191             cc->synchronize_from_tb(cpu, last_tb);
 192         } else {
 193             assert(cc->set_pc);
 194             cc->set_pc(cpu, last_tb->pc);
 195         }
 196     }
 197     return ret;
 198 }
 199
 200 #ifndef CONFIG_USER_ONLY
 201 /* Execute the code without caching the generated code. An interpreter
 202    could be used if available. */
 203 static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
 204                              TranslationBlock *orig_tb, bool ignore_icount)
 205 {
 206     TranslationBlock *tb;
 207     uint32_t cflags = curr_cflags() | CF_NOCACHE;
 208
 209     if (ignore_icount) {
 210         cflags &= ~CF_USE_ICOUNT;
 211     }
 212
 213     /* Should never happen.
 214        We only end up here when an existing TB is too long.  */
 215     cflags |= MIN(max_cycles, CF_COUNT_MASK);
 216
 217     mmap_lock();
 218     tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base,
 219                      orig_tb->flags, cflags);
 220     tb->orig_tb = orig_tb;
 221     mmap_unlock();
 222
 223     /* execute the generated code */
 224     trace_exec_tb_nocache(tb, tb->pc);
 225     cpu_tb_exec(cpu, tb);
 226
 227     mmap_lock();
 228     tb_phys_invalidate(tb, -1);
 229     mmap_unlock();
 230     tcg_tb_remove(tb);
 231 }
 232 #endif
 233
 234 void cpu_exec_step_atomic(CPUState *cpu)
 235 {
 236     CPUClass *cc = CPU_GET_CLASS(cpu);
 237     TranslationBlock *tb;
 238     target_ulong cs_base, pc;
 239     uint32_t flags;
 240     uint32_t cflags = 1;
 241     uint32_t cf_mask = cflags & CF_HASH_MASK;
 242     /* volatile because we modify it between setjmp and longjmp */
 243     volatile bool in_exclusive_region = false;
 244
 245     if (sigsetjmp(cpu->jmp_env, 0) == 0) {
 246         tb = tb_lookup__cpu_state(cpu, &pc, &cs_base, &flags, cf_mask);
 247         if (tb == NULL) {
 248             mmap_lock();
 249             tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
 250             mmap_unlock();
 251         }
 252
 253         start_exclusive();
 254
 255         /* Since we got here, we know that parallel_cpus must be true.  */
 256         parallel_cpus = false;
 257         in_exclusive_region = true;
 258         cc->cpu_exec_enter(cpu);
 259         /* execute the generated code */
 260         trace_exec_tb(tb, pc);
 261         cpu_tb_exec(cpu, tb);
 262         cc->cpu_exec_exit(cpu);
 263     } else {
 264         /*
 265          * The mmap_lock is dropped by tb_gen_code if it runs out of
 266          * memory.
 267          */
 268 #ifndef CONFIG_SOFTMMU
 269         tcg_debug_assert(!have_mmap_lock());
 270 #endif
 271         if (qemu_mutex_iothread_locked()) {
 272             qemu_mutex_unlock_iothread();
 273         }
 274         assert_no_pages_locked();
 275     }
 276
 277     if (in_exclusive_region) {
 278         /* We might longjump out of either the codegen or the
 279          * execution, so must make sure we only end the exclusive
 280          * region if we started it.
 281          */
 282         parallel_cpus = true;
 283         end_exclusive();
 284     }
 285 }
 286
 287 struct tb_desc {
 288     target_ulong pc;
 289     target_ulong cs_base;
 290     CPUArchState *env;
 291     tb_page_addr_t phys_page1;
 292     uint32_t flags;
 293     uint32_t cf_mask;
 294     uint32_t trace_vcpu_dstate;
 295 };
 296
 297 static bool tb_lookup_cmp(const void *p, const void *d)
 298 {
 299     const TranslationBlock *tb = p;
 300     const struct tb_desc *desc = d;
 301
 302     if (tb->pc == desc->pc &&
 303         tb->page_addr[0] == desc->phys_page1 &&
 304         tb->cs_base == desc->cs_base &&
 305         tb->flags == desc->flags &&
 306         tb->trace_vcpu_dstate == desc->trace_vcpu_dstate &&
 307         (tb_cflags(tb) & (CF_HASH_MASK | CF_INVALID)) == desc->cf_mask) {
 308         /* check next page if needed */
 309         if (tb->page_addr[1] == -1) {
 310             return true;
 311         } else {
 312             tb_page_addr_t phys_page2;
 313             target_ulong virt_page2;
 314
 315             virt_page2 = (desc->pc & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE;
 316             phys_page2 = get_page_addr_code(desc->env, virt_page2);
 317             if (tb->page_addr[1] == phys_page2) {
 318                 return true;
 319             }
 320         }
 321     }
 322     return false;
 323 }
 324
 325 TranslationBlock *tb_htable_lookup(CPUState *cpu, target_ulong pc,
 326                                    target_ulong cs_base, uint32_t flags,
 327                                    uint32_t cf_mask)
 328 {
 329     tb_page_addr_t phys_pc;
 330     struct tb_desc desc;
 331     uint32_t h;
 332
 333     desc.env = (CPUArchState *)cpu->env_ptr;
 334     desc.cs_base = cs_base;
 335     desc.flags = flags;
 336     desc.cf_mask = cf_mask;
 337     desc.trace_vcpu_dstate = *cpu->trace_dstate;
 338     desc.pc = pc;
 339     phys_pc = get_page_addr_code(desc.env, pc);
 340     if (phys_pc == -1) {
 341         return NULL;
 342     }
 343     desc.phys_page1 = phys_pc & TARGET_PAGE_MASK;
 344     h = tb_hash_func(phys_pc, pc, flags, cf_mask, *cpu->trace_dstate);
 345     return qht_lookup_custom(&tb_ctx.htable, &desc, h, tb_lookup_cmp);
 346 }
 347
 348 void tb_set_jmp_target(TranslationBlock *tb, int n, uintptr_t addr)
 349 {
 350     if (TCG_TARGET_HAS_direct_jump) {
 351         uintptr_t offset = tb->jmp_target_arg[n];
 352         uintptr_t tc_ptr = (uintptr_t)tb->tc.ptr;
 353         tb_target_set_jmp_target(tc_ptr, tc_ptr + offset, addr);
 354     } else {
 355         tb->jmp_target_arg[n] = addr;
 356     }
 357 }
 358
 359 static inline void tb_add_jump(TranslationBlock *tb, int n,
 360                                TranslationBlock *tb_next)
 361 {
 362     uintptr_t old;
 363
 364     assert(n < ARRAY_SIZE(tb->jmp_list_next));
 365     qemu_spin_lock(&tb_next->jmp_lock);
 366
 367     /* make sure the destination TB is valid */
 368     if (tb_next->cflags & CF_INVALID) {
 369         goto out_unlock_next;
 370     }
 371     /* Atomically claim the jump destination slot only if it was NULL */
 372     old = atomic_cmpxchg(&tb->jmp_dest[n], (uintptr_t)NULL, (uintptr_t)tb_next);
 373     if (old) {
 374         goto out_unlock_next;
 375     }
 376
 377     /* patch the native jump address */
 378     tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc.ptr);
 379
 380     /* add in TB jmp list */
 381     tb->jmp_list_next[n] = tb_next->jmp_list_head;
 382     tb_next->jmp_list_head = (uintptr_t)tb | n;
 383
 384     qemu_spin_unlock(&tb_next->jmp_lock);
 385
 386     qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc,
 387                            "Linking TBs %p [" TARGET_FMT_lx
 388                            "] index %d -> %p [" TARGET_FMT_lx "]\n",
 389                            tb->tc.ptr, tb->pc, n,
 390                            tb_next->tc.ptr, tb_next->pc);
 391     return;
 392
 393  out_unlock_next:
 394     qemu_spin_unlock(&tb_next->jmp_lock);
 395     return;
 396 }
 397
 398 static inline TranslationBlock *tb_find(CPUState *cpu,
 399                                         TranslationBlock *last_tb,
 400                                         int tb_exit, uint32_t cf_mask)
 401 {
 402     TranslationBlock *tb;
 403     target_ulong cs_base, pc;
 404     uint32_t flags;
 405
 406     tb = tb_lookup__cpu_state(cpu, &pc, &cs_base, &flags, cf_mask);
 407     if (tb == NULL) {
 408         mmap_lock();
 409         tb = tb_gen_code(cpu, pc, cs_base, flags, cf_mask);
 410         mmap_unlock();
 411         /* We add the TB in the virtual pc hash table for the fast lookup */
 412         atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb);
 413     }
 414 #ifndef CONFIG_USER_ONLY
 415     /* We don't take care of direct jumps when address mapping changes in
 416      * system emulation. So it's not safe to make a direct jump to a TB
 417      * spanning two pages because the mapping for the second page can change.
 418      */
 419     if (tb->page_addr[1] != -1) {
 420         last_tb = NULL;
 421     }
 422 #endif
 423     /* See if we can patch the calling TB. */
 424     if (last_tb) {
 425         tb_add_jump(last_tb, tb_exit, tb);
 426     }
 427     return tb;
 428 }
 429
 430 static inline bool cpu_handle_halt(CPUState *cpu)
 431 {
 432     if (cpu->halted) {
 433 #if defined(TARGET_I386) && !defined(CONFIG_USER_ONLY)
 434         if ((cpu->interrupt_request & CPU_INTERRUPT_POLL)
 435             && replay_interrupt()) {
 436             X86CPU *x86_cpu = X86_CPU(cpu);
 437             qemu_mutex_lock_iothread();
 438             apic_poll_irq(x86_cpu->apic_state);
 439             cpu_reset_interrupt(cpu, CPU_INTERRUPT_POLL);
 440             qemu_mutex_unlock_iothread();
 441         }
 442 #endif
 443         if (!cpu_has_work(cpu)) {
 444             return true;
 445         }
 446
 447         cpu->halted = 0;
 448     }
 449
 450     return false;
 451 }
 452
 453 static inline void cpu_handle_debug_exception(CPUState *cpu)
 454 {
 455     CPUClass *cc = CPU_GET_CLASS(cpu);
 456     CPUWatchpoint *wp;
 457
 458     if (!cpu->watchpoint_hit) {
 459         QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
 460             wp->flags &= ~BP_WATCHPOINT_HIT;
 461         }
 462     }
 463
 464     cc->debug_excp_handler(cpu);
 465 }
 466
 467 static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 468 {
 469     if (cpu->exception_index < 0) {
 470 #ifndef CONFIG_USER_ONLY
 471         if (replay_has_exception()
 472             && cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra == 0) {
 473             /* try to cause an exception pending in the log */
 474             cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0, curr_cflags()), true);
 475         }
 476 #endif
 477         if (cpu->exception_index < 0) {
 478             return false;
 479         }
 480     }
 481
 482     if (cpu->exception_index >= EXCP_INTERRUPT) {
 483         /* exit request from the cpu execution loop */
 484         *ret = cpu->exception_index;
 485         if (*ret == EXCP_DEBUG) {
 486             cpu_handle_debug_exception(cpu);
 487         }
 488         cpu->exception_index = -1;
 489         return true;
 490     } else {
 491 #if defined(CONFIG_USER_ONLY)
 492         /* if user mode only, we simulate a fake exception
 493            which will be handled outside the cpu execution
 494            loop */
 495 #if defined(TARGET_I386)
 496         CPUClass *cc = CPU_GET_CLASS(cpu);
 497         cc->do_interrupt(cpu);
 498 #endif
 499         *ret = cpu->exception_index;
 500         cpu->exception_index = -1;
 501         return true;
 502 #else
 503         if (replay_exception()) {
 504             CPUClass *cc = CPU_GET_CLASS(cpu);
 505             qemu_mutex_lock_iothread();
 506             cc->do_interrupt(cpu);
 507             qemu_mutex_unlock_iothread();
 508             cpu->exception_index = -1;
 509         } else if (!replay_has_interrupt()) {
 510             /* give a chance to iothread in replay mode */
 511             *ret = EXCP_INTERRUPT;
 512             return true;
 513         }
 514 #endif
 515     }
 516
 517     return false;
 518 }
 519
 520 static inline bool cpu_handle_interrupt(CPUState *cpu,
 521                                         TranslationBlock **last_tb)
 522 {
 523     CPUClass *cc = CPU_GET_CLASS(cpu);
 524
 525     /* Clear the interrupt flag now since we're processing
 526      * cpu->interrupt_request and cpu->exit_request.
 527      * Ensure zeroing happens before reading cpu->exit_request or
 528      * cpu->interrupt_request (see also smp_wmb in cpu_exit())
 529      */
 530     atomic_mb_set(&cpu_neg(cpu)->icount_decr.u16.high, 0);
 531
 532     if (unlikely(atomic_read(&cpu->interrupt_request))) {
 533         int interrupt_request;
 534         qemu_mutex_lock_iothread();
 535         interrupt_request = cpu->interrupt_request;
 536         if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
 537             /* Mask out external interrupts for this step. */
 538             interrupt_request &= ~CPU_INTERRUPT_SSTEP_MASK;
 539         }
 540         if (interrupt_request & CPU_INTERRUPT_DEBUG) {
 541             cpu->interrupt_request &= ~CPU_INTERRUPT_DEBUG;
 542             cpu->exception_index = EXCP_DEBUG;
 543             qemu_mutex_unlock_iothread();
 544             return true;
 545         }
 546         if (replay_mode == REPLAY_MODE_PLAY && !replay_has_interrupt()) {
 547             /* Do nothing */
 548         } else if (interrupt_request & CPU_INTERRUPT_HALT) {
 549             replay_interrupt();
 550             cpu->interrupt_request &= ~CPU_INTERRUPT_HALT;
 551             cpu->halted = 1;
 552             cpu->exception_index = EXCP_HLT;
 553             qemu_mutex_unlock_iothread();
 554             return true;
 555         }
 556 #if defined(TARGET_I386)
 557         else if (interrupt_request & CPU_INTERRUPT_INIT) {
 558             X86CPU *x86_cpu = X86_CPU(cpu);
 559             CPUArchState *env = &x86_cpu->env;
 560             replay_interrupt();
 561             cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0, 0);
 562             do_cpu_init(x86_cpu);
 563             cpu->exception_index = EXCP_HALTED;
 564             qemu_mutex_unlock_iothread();
 565             return true;
 566         }
 567 #else
 568         else if (interrupt_request & CPU_INTERRUPT_RESET) {
 569             replay_interrupt();
 570             cpu_reset(cpu);
 571             qemu_mutex_unlock_iothread();
 572             return true;
 573         }
 574 #endif
 575         /* The target hook has 3 exit conditions:
 576            False when the interrupt isn't processed,
 577            True when it is, and we should restart on a new TB,
 578            and via longjmp via cpu_loop_exit.  */
 579         else {
 580             if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
 581                 replay_interrupt();
 582                 cpu->exception_index = -1;
 583                 *last_tb = NULL;
 584             }
 585             /* The target hook may have updated the 'cpu->interrupt_request';
 586              * reload the 'interrupt_request' value */
 587             interrupt_request = cpu->interrupt_request;
 588         }
 589         if (interrupt_request & CPU_INTERRUPT_EXITTB) {
 590             cpu->interrupt_request &= ~CPU_INTERRUPT_EXITTB;
 591             /* ensure that no TB jump will be modified as
 592                the program flow was changed */
 593             *last_tb = NULL;
 594         }
 595
 596         /* If we exit via cpu_loop_exit/longjmp it is reset in cpu_exec */
 597         qemu_mutex_unlock_iothread();
 598     }
 599
 600     /* Finally, check if we need to exit to the main loop.  */
 601     if (unlikely(atomic_read(&cpu->exit_request))
 602         || (use_icount
 603             && cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra == 0)) {
 604         atomic_set(&cpu->exit_request, 0);
 605         if (cpu->exception_index == -1) {
 606             cpu->exception_index = EXCP_INTERRUPT;
 607         }
 608         return true;
 609     }
 610
 611     return false;
 612 }
 613
 614 static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 615                                     TranslationBlock **last_tb, int *tb_exit)
 616 {
 617     uintptr_t ret;
 618     int32_t insns_left;
 619
 620     trace_exec_tb(tb, tb->pc);
 621     ret = cpu_tb_exec(cpu, tb);
 622     tb = (TranslationBlock *)(ret & ~TB_EXIT_MASK);
 623     *tb_exit = ret & TB_EXIT_MASK;
 624     if (*tb_exit != TB_EXIT_REQUESTED) {
 625         *last_tb = tb;
 626         return;
 627     }
 628
 629     *last_tb = NULL;
 630     insns_left = atomic_read(&cpu_neg(cpu)->icount_decr.u32);
 631     if (insns_left < 0) {
 632         /* Something asked us to stop executing chained TBs; just
 633          * continue round the main loop. Whatever requested the exit
 634          * will also have set something else (eg exit_request or
 635          * interrupt_request) which will be handled by
 636          * cpu_handle_interrupt.  cpu_handle_interrupt will also
 637          * clear cpu->icount_decr.u16.high.
 638          */
 639         return;
 640     }
 641
 642     /* Instruction counter expired.  */
 643     assert(use_icount);
 644 #ifndef CONFIG_USER_ONLY
 645     /* Ensure global icount has gone forward */
 646     cpu_update_icount(cpu);
 647     /* Refill decrementer and continue execution.  */
 648     insns_left = MIN(0xffff, cpu->icount_budget);
 649     cpu_neg(cpu)->icount_decr.u16.low = insns_left;
 650     cpu->icount_extra = cpu->icount_budget - insns_left;
 651     if (!cpu->icount_extra) {
 652         /* Execute any remaining instructions, then let the main loop
 653          * handle the next event.
 654          */
 655         if (insns_left > 0) {
 656             cpu_exec_nocache(cpu, insns_left, tb, false);
 657         }
 658     }
 659 #endif
 660 }
 661
 662 /* main execution loop */
 663
 664 int cpu_exec(CPUState *cpu)
 665 {
 666     CPUClass *cc = CPU_GET_CLASS(cpu);
 667     int ret;
 668     SyncClocks sc = { 0 };
 669
 670     /* replay_interrupt may need current_cpu */
 671     current_cpu = cpu;
 672
 673     if (cpu_handle_halt(cpu)) {
 674         return EXCP_HALTED;
 675     }
 676
 677     rcu_read_lock();
 678
 679     cc->cpu_exec_enter(cpu);
 680
 681     /* Calculate difference between guest clock and host clock.
 682      * This delay includes the delay of the last cycle, so
 683      * what we have to do is sleep until it is 0. As for the
 684      * advance/delay we gain here, we try to fix it next time.
 685      */
 686     init_delay_params(&sc, cpu);
 687
 688     /* prepare setjmp context for exception handling */
 689     if (sigsetjmp(cpu->jmp_env, 0) != 0) {
 690 #if defined(__clang__) || !QEMU_GNUC_PREREQ(4, 6)
 691         /* Some compilers wrongly smash all local variables after
 692          * siglongjmp. There were bug reports for gcc 4.5.0 and clang.
 693          * Reload essential local variables here for those compilers.
 694          * Newer versions of gcc would complain about this code (-Wclobbered). */
 695         cpu = current_cpu;
 696         cc = CPU_GET_CLASS(cpu);
 697 #else /* buggy compiler */
 698         /* Assert that the compiler does not smash local variables. */
 699         g_assert(cpu == current_cpu);
 700         g_assert(cc == CPU_GET_CLASS(cpu));
 701 #endif /* buggy compiler */
 702 #ifndef CONFIG_SOFTMMU
 703         tcg_debug_assert(!have_mmap_lock());
 704 #endif
 705         if (qemu_mutex_iothread_locked()) {
 706             qemu_mutex_unlock_iothread();
 707         }
 708         assert_no_pages_locked();
 709     }
 710
 711     /* if an exception is pending, we execute it here */
 712     while (!cpu_handle_exception(cpu, &ret)) {
 713         TranslationBlock *last_tb = NULL;
 714         int tb_exit = 0;
 715
 716         while (!cpu_handle_interrupt(cpu, &last_tb)) {
 717             uint32_t cflags = cpu->cflags_next_tb;
 718             TranslationBlock *tb;
 719
 720             /* When requested, use an exact setting for cflags for the next
 721                execution.  This is used for icount, precise smc, and stop-
 722                after-access watchpoints.  Since this request should never
 723                have CF_INVALID set, -1 is a convenient invalid value that
 724                does not require tcg headers for cpu_common_reset.  */
 725             if (cflags == -1) {
 726                 cflags = curr_cflags();
 727             } else {
 728                 cpu->cflags_next_tb = -1;
 729             }
 730
 731             tb = tb_find(cpu, last_tb, tb_exit, cflags);
 732             cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit);
 733             /* Try to align the host and virtual clocks
 734                if the guest is in advance */
 735             align_clocks(&sc, cpu);
 736         }
 737     }
 738
 739     cc->cpu_exec_exit(cpu);
 740     rcu_read_unlock();
 741
 742     return ret;
 743 }