util/oslib-posix.c

   1 /*
   2  * os-posix-lib.c
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  * Copyright (c) 2010 Red Hat, Inc.
   6  *
   7  * QEMU library functions on POSIX which are shared between QEMU and
   8  * the QEMU tools.
   9  *
  10  * Permission is hereby granted, free of charge, to any person obtaining a copy
  11  * of this software and associated documentation files (the "Software"), to deal
  12  * in the Software without restriction, including without limitation the rights
  13  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  14  * copies of the Software, and to permit persons to whom the Software is
  15  * furnished to do so, subject to the following conditions:
  16  *
  17  * The above copyright notice and this permission notice shall be included in
  18  * all copies or substantial portions of the Software.
  19  *
  20  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  21  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  23  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  24  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  25  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  26  * THE SOFTWARE.
  27  */
  28
  29 #include "qemu/osdep.h"
  30 #include <termios.h>
  31
  32 #include <glib/gprintf.h>
  33
  34 #include "sysemu/sysemu.h"
  35 #include "trace.h"
  36 #include "qapi/error.h"
  37 #include "qemu/error-report.h"
  38 #include "qemu/madvise.h"
  39 #include "qemu/sockets.h"
  40 #include "qemu/thread.h"
  41 #include <libgen.h>
  42 #include "qemu/cutils.h"
  43 #include "qemu/units.h"
  44 #include "qemu/thread-context.h"
  45
  46 #ifdef CONFIG_LINUX
  47 #include <sys/syscall.h>
  48 #endif
  49
  50 #ifdef __FreeBSD__
  51 #include <sys/thr.h>
  52 #include <sys/user.h>
  53 #include <libutil.h>
  54 #endif
  55
  56 #ifdef __NetBSD__
  57 #include <lwp.h>
  58 #endif
  59
  60 #include "qemu/mmap-alloc.h"
  61
  62 #ifdef CONFIG_DEBUG_STACK_USAGE
  63 #include "qemu/error-report.h"
  64 #endif
  65
  66 #define MAX_MEM_PREALLOC_THREAD_COUNT 16
  67
  68 struct MemsetThread;
  69
  70 typedef struct MemsetContext {
  71     bool all_threads_created;
  72     bool any_thread_failed;
  73     struct MemsetThread *threads;
  74     int num_threads;
  75 } MemsetContext;
  76
  77 struct MemsetThread {
  78     char *addr;
  79     size_t numpages;
  80     size_t hpagesize;
  81     QemuThread pgthread;
  82     sigjmp_buf env;
  83     MemsetContext *context;
  84 };
  85 typedef struct MemsetThread MemsetThread;
  86
  87 /* used by sigbus_handler() */
  88 static MemsetContext *sigbus_memset_context;
  89 struct sigaction sigbus_oldact;
  90 static QemuMutex sigbus_mutex;
  91
  92 static QemuMutex page_mutex;
  93 static QemuCond page_cond;
  94
  95 int qemu_get_thread_id(void)
  96 {
  97 #if defined(__linux__)
  98     return syscall(SYS_gettid);
  99 #elif defined(__FreeBSD__)
 100     /* thread id is up to INT_MAX */
 101     long tid;
 102     thr_self(&tid);
 103     return (int)tid;
 104 #elif defined(__NetBSD__)
 105     return _lwp_self();
 106 #elif defined(__OpenBSD__)
 107     return getthrid();
 108 #else
 109     return getpid();
 110 #endif
 111 }
 112
 113 int qemu_daemon(int nochdir, int noclose)
 114 {
 115     return daemon(nochdir, noclose);
 116 }
 117
 118 bool qemu_write_pidfile(const char *path, Error **errp)
 119 {
 120     int fd;
 121     char pidstr[32];
 122
 123     while (1) {
 124         struct stat a, b;
 125         struct flock lock = {
 126             .l_type = F_WRLCK,
 127             .l_whence = SEEK_SET,
 128             .l_len = 0,
 129         };
 130
 131         fd = qemu_create(path, O_WRONLY, S_IRUSR | S_IWUSR, errp);
 132         if (fd == -1) {
 133             return false;
 134         }
 135
 136         if (fstat(fd, &b) < 0) {
 137             error_setg_errno(errp, errno, "Cannot stat file");
 138             goto fail_close;
 139         }
 140
 141         if (fcntl(fd, F_SETLK, &lock)) {
 142             error_setg_errno(errp, errno, "Cannot lock pid file");
 143             goto fail_close;
 144         }
 145
 146         /*
 147          * Now make sure the path we locked is the same one that now
 148          * exists on the filesystem.
 149          */
 150         if (stat(path, &a) < 0) {
 151             /*
 152              * PID file disappeared, someone else must be racing with
 153              * us, so try again.
 154              */
 155             close(fd);
 156             continue;
 157         }
 158
 159         if (a.st_ino == b.st_ino) {
 160             break;
 161         }
 162
 163         /*
 164          * PID file was recreated, someone else must be racing with
 165          * us, so try again.
 166          */
 167         close(fd);
 168     }
 169
 170     if (ftruncate(fd, 0) < 0) {
 171         error_setg_errno(errp, errno, "Failed to truncate pid file");
 172         goto fail_unlink;
 173     }
 174
 175     snprintf(pidstr, sizeof(pidstr), FMT_pid "\n", getpid());
 176     if (qemu_write_full(fd, pidstr, strlen(pidstr)) != strlen(pidstr)) {
 177         error_setg(errp, "Failed to write pid file");
 178         goto fail_unlink;
 179     }
 180
 181     return true;
 182
 183 fail_unlink:
 184     unlink(path);
 185 fail_close:
 186     close(fd);
 187     return false;
 188 }
 189
 190 /* alloc shared memory pages */
 191 void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared,
 192                           bool noreserve)
 193 {
 194     const uint32_t qemu_map_flags = (shared ? QEMU_MAP_SHARED : 0) |
 195                                     (noreserve ? QEMU_MAP_NORESERVE : 0);
 196     size_t align = QEMU_VMALLOC_ALIGN;
 197     void *ptr = qemu_ram_mmap(-1, size, align, qemu_map_flags, 0);
 198
 199     if (ptr == MAP_FAILED) {
 200         return NULL;
 201     }
 202
 203     if (alignment) {
 204         *alignment = align;
 205     }
 206
 207     trace_qemu_anon_ram_alloc(size, ptr);
 208     return ptr;
 209 }
 210
 211 void qemu_anon_ram_free(void *ptr, size_t size)
 212 {
 213     trace_qemu_anon_ram_free(ptr, size);
 214     qemu_ram_munmap(-1, ptr, size);
 215 }
 216
 217 void qemu_socket_set_block(int fd)
 218 {
 219     g_unix_set_fd_nonblocking(fd, false, NULL);
 220 }
 221
 222 int qemu_socket_try_set_nonblock(int fd)
 223 {
 224     return g_unix_set_fd_nonblocking(fd, true, NULL) ? 0 : -errno;
 225 }
 226
 227 void qemu_socket_set_nonblock(int fd)
 228 {
 229     int f;
 230     f = qemu_socket_try_set_nonblock(fd);
 231     assert(f == 0);
 232 }
 233
 234 int socket_set_fast_reuse(int fd)
 235 {
 236     int val = 1, ret;
 237
 238     ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
 239                      (const char *)&val, sizeof(val));
 240
 241     assert(ret == 0);
 242
 243     return ret;
 244 }
 245
 246 void qemu_set_cloexec(int fd)
 247 {
 248     int f;
 249     f = fcntl(fd, F_GETFD);
 250     assert(f != -1);
 251     f = fcntl(fd, F_SETFD, f | FD_CLOEXEC);
 252     assert(f != -1);
 253 }
 254
 255 int qemu_socketpair(int domain, int type, int protocol, int sv[2])
 256 {
 257     int ret;
 258
 259 #ifdef SOCK_CLOEXEC
 260     ret = socketpair(domain, type | SOCK_CLOEXEC, protocol, sv);
 261     if (ret != -1 || errno != EINVAL) {
 262         return ret;
 263     }
 264 #endif
 265     ret = socketpair(domain, type, protocol, sv);;
 266     if (ret == 0) {
 267         qemu_set_cloexec(sv[0]);
 268         qemu_set_cloexec(sv[1]);
 269     }
 270
 271     return ret;
 272 }
 273
 274 char *
 275 qemu_get_local_state_dir(void)
 276 {
 277     return get_relocated_path(CONFIG_QEMU_LOCALSTATEDIR);
 278 }
 279
 280 void qemu_set_tty_echo(int fd, bool echo)
 281 {
 282     struct termios tty;
 283
 284     tcgetattr(fd, &tty);
 285
 286     if (echo) {
 287         tty.c_lflag |= ECHO | ECHONL | ICANON | IEXTEN;
 288     } else {
 289         tty.c_lflag &= ~(ECHO | ECHONL | ICANON | IEXTEN);
 290     }
 291
 292     tcsetattr(fd, TCSANOW, &tty);
 293 }
 294
 295 #ifdef CONFIG_LINUX
 296 static void sigbus_handler(int signal, siginfo_t *siginfo, void *ctx)
 297 #else /* CONFIG_LINUX */
 298 static void sigbus_handler(int signal)
 299 #endif /* CONFIG_LINUX */
 300 {
 301     int i;
 302
 303     if (sigbus_memset_context) {
 304         for (i = 0; i < sigbus_memset_context->num_threads; i++) {
 305             MemsetThread *thread = &sigbus_memset_context->threads[i];
 306
 307             if (qemu_thread_is_self(&thread->pgthread)) {
 308                 siglongjmp(thread->env, 1);
 309             }
 310         }
 311     }
 312
 313 #ifdef CONFIG_LINUX
 314     /*
 315      * We assume that the MCE SIGBUS handler could have been registered. We
 316      * should never receive BUS_MCEERR_AO on any of our threads, but only on
 317      * the main thread registered for PR_MCE_KILL_EARLY. Further, we should not
 318      * receive BUS_MCEERR_AR triggered by action of other threads on one of
 319      * our threads. So, no need to check for unrelated SIGBUS when seeing one
 320      * for our threads.
 321      *
 322      * We will forward to the MCE handler, which will either handle the SIGBUS
 323      * or reinstall the default SIGBUS handler and reraise the SIGBUS. The
 324      * default SIGBUS handler will crash the process, so we don't care.
 325      */
 326     if (sigbus_oldact.sa_flags & SA_SIGINFO) {
 327         sigbus_oldact.sa_sigaction(signal, siginfo, ctx);
 328         return;
 329     }
 330 #endif /* CONFIG_LINUX */
 331     warn_report("qemu_prealloc_mem: unrelated SIGBUS detected and ignored");
 332 }
 333
 334 static void *do_touch_pages(void *arg)
 335 {
 336     MemsetThread *memset_args = (MemsetThread *)arg;
 337     sigset_t set, oldset;
 338     int ret = 0;
 339
 340     /*
 341      * On Linux, the page faults from the loop below can cause mmap_sem
 342      * contention with allocation of the thread stacks.  Do not start
 343      * clearing until all threads have been created.
 344      */
 345     qemu_mutex_lock(&page_mutex);
 346     while (!memset_args->context->all_threads_created) {
 347         qemu_cond_wait(&page_cond, &page_mutex);
 348     }
 349     qemu_mutex_unlock(&page_mutex);
 350
 351     /* unblock SIGBUS */
 352     sigemptyset(&set);
 353     sigaddset(&set, SIGBUS);
 354     pthread_sigmask(SIG_UNBLOCK, &set, &oldset);
 355
 356     if (sigsetjmp(memset_args->env, 1)) {
 357         ret = -EFAULT;
 358     } else {
 359         char *addr = memset_args->addr;
 360         size_t numpages = memset_args->numpages;
 361         size_t hpagesize = memset_args->hpagesize;
 362         size_t i;
 363         for (i = 0; i < numpages; i++) {
 364             /*
 365              * Read & write back the same value, so we don't
 366              * corrupt existing user/app data that might be
 367              * stored.
 368              *
 369              * 'volatile' to stop compiler optimizing this away
 370              * to a no-op
 371              */
 372             *(volatile char *)addr = *addr;
 373             addr += hpagesize;
 374         }
 375     }
 376     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 377     return (void *)(uintptr_t)ret;
 378 }
 379
 380 static void *do_madv_populate_write_pages(void *arg)
 381 {
 382     MemsetThread *memset_args = (MemsetThread *)arg;
 383     const size_t size = memset_args->numpages * memset_args->hpagesize;
 384     char * const addr = memset_args->addr;
 385     int ret = 0;
 386
 387     /* See do_touch_pages(). */
 388     qemu_mutex_lock(&page_mutex);
 389     while (!memset_args->context->all_threads_created) {
 390         qemu_cond_wait(&page_cond, &page_mutex);
 391     }
 392     qemu_mutex_unlock(&page_mutex);
 393
 394     if (size && qemu_madvise(addr, size, QEMU_MADV_POPULATE_WRITE)) {
 395         ret = -errno;
 396     }
 397     return (void *)(uintptr_t)ret;
 398 }
 399
 400 static inline int get_memset_num_threads(size_t hpagesize, size_t numpages,
 401                                          int max_threads)
 402 {
 403     long host_procs = sysconf(_SC_NPROCESSORS_ONLN);
 404     int ret = 1;
 405
 406     if (host_procs > 0) {
 407         ret = MIN(MIN(host_procs, MAX_MEM_PREALLOC_THREAD_COUNT), max_threads);
 408     }
 409
 410     /* Especially with gigantic pages, don't create more threads than pages. */
 411     ret = MIN(ret, numpages);
 412     /* Don't start threads to prealloc comparatively little memory. */
 413     ret = MIN(ret, MAX(1, hpagesize * numpages / (64 * MiB)));
 414
 415     /* In case sysconf() fails, we fall back to single threaded */
 416     return ret;
 417 }
 418
 419 static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
 420                            int max_threads, ThreadContext *tc,
 421                            bool use_madv_populate_write)
 422 {
 423     static gsize initialized = 0;
 424     MemsetContext context = {
 425         .num_threads = get_memset_num_threads(hpagesize, numpages, max_threads),
 426     };
 427     size_t numpages_per_thread, leftover;
 428     void *(*touch_fn)(void *);
 429     int ret = 0, i = 0;
 430     char *addr = area;
 431
 432     if (g_once_init_enter(&initialized)) {
 433         qemu_mutex_init(&page_mutex);
 434         qemu_cond_init(&page_cond);
 435         g_once_init_leave(&initialized, 1);
 436     }
 437
 438     if (use_madv_populate_write) {
 439         /* Avoid creating a single thread for MADV_POPULATE_WRITE */
 440         if (context.num_threads == 1) {
 441             if (qemu_madvise(area, hpagesize * numpages,
 442                              QEMU_MADV_POPULATE_WRITE)) {
 443                 return -errno;
 444             }
 445             return 0;
 446         }
 447         touch_fn = do_madv_populate_write_pages;
 448     } else {
 449         touch_fn = do_touch_pages;
 450     }
 451
 452     context.threads = g_new0(MemsetThread, context.num_threads);
 453     numpages_per_thread = numpages / context.num_threads;
 454     leftover = numpages % context.num_threads;
 455     for (i = 0; i < context.num_threads; i++) {
 456         context.threads[i].addr = addr;
 457         context.threads[i].numpages = numpages_per_thread + (i < leftover);
 458         context.threads[i].hpagesize = hpagesize;
 459         context.threads[i].context = &context;
 460         if (tc) {
 461             thread_context_create_thread(tc, &context.threads[i].pgthread,
 462                                          "touch_pages",
 463                                          touch_fn, &context.threads[i],
 464                                          QEMU_THREAD_JOINABLE);
 465         } else {
 466             qemu_thread_create(&context.threads[i].pgthread, "touch_pages",
 467                                touch_fn, &context.threads[i],
 468                                QEMU_THREAD_JOINABLE);
 469         }
 470         addr += context.threads[i].numpages * hpagesize;
 471     }
 472
 473     if (!use_madv_populate_write) {
 474         sigbus_memset_context = &context;
 475     }
 476
 477     qemu_mutex_lock(&page_mutex);
 478     context.all_threads_created = true;
 479     qemu_cond_broadcast(&page_cond);
 480     qemu_mutex_unlock(&page_mutex);
 481
 482     for (i = 0; i < context.num_threads; i++) {
 483         int tmp = (uintptr_t)qemu_thread_join(&context.threads[i].pgthread);
 484
 485         if (tmp) {
 486             ret = tmp;
 487         }
 488     }
 489
 490     if (!use_madv_populate_write) {
 491         sigbus_memset_context = NULL;
 492     }
 493     g_free(context.threads);
 494
 495     return ret;
 496 }
 497
 498 static bool madv_populate_write_possible(char *area, size_t pagesize)
 499 {
 500     return !qemu_madvise(area, pagesize, QEMU_MADV_POPULATE_WRITE) ||
 501            errno != EINVAL;
 502 }
 503
 504 void qemu_prealloc_mem(int fd, char *area, size_t sz, int max_threads,
 505                        ThreadContext *tc, Error **errp)
 506 {
 507     static gsize initialized;
 508     int ret;
 509     size_t hpagesize = qemu_fd_getpagesize(fd);
 510     size_t numpages = DIV_ROUND_UP(sz, hpagesize);
 511     bool use_madv_populate_write;
 512     struct sigaction act;
 513
 514     /*
 515      * Sense on every invocation, as MADV_POPULATE_WRITE cannot be used for
 516      * some special mappings, such as mapping /dev/mem.
 517      */
 518     use_madv_populate_write = madv_populate_write_possible(area, hpagesize);
 519
 520     if (!use_madv_populate_write) {
 521         if (g_once_init_enter(&initialized)) {
 522             qemu_mutex_init(&sigbus_mutex);
 523             g_once_init_leave(&initialized, 1);
 524         }
 525
 526         qemu_mutex_lock(&sigbus_mutex);
 527         memset(&act, 0, sizeof(act));
 528 #ifdef CONFIG_LINUX
 529         act.sa_sigaction = &sigbus_handler;
 530         act.sa_flags = SA_SIGINFO;
 531 #else /* CONFIG_LINUX */
 532         act.sa_handler = &sigbus_handler;
 533         act.sa_flags = 0;
 534 #endif /* CONFIG_LINUX */
 535
 536         ret = sigaction(SIGBUS, &act, &sigbus_oldact);
 537         if (ret) {
 538             qemu_mutex_unlock(&sigbus_mutex);
 539             error_setg_errno(errp, errno,
 540                 "qemu_prealloc_mem: failed to install signal handler");
 541             return;
 542         }
 543     }
 544
 545     /* touch pages simultaneously */
 546     ret = touch_all_pages(area, hpagesize, numpages, max_threads, tc,
 547                           use_madv_populate_write);
 548     if (ret) {
 549         error_setg_errno(errp, -ret,
 550                          "qemu_prealloc_mem: preallocating memory failed");
 551     }
 552
 553     if (!use_madv_populate_write) {
 554         ret = sigaction(SIGBUS, &sigbus_oldact, NULL);
 555         if (ret) {
 556             /* Terminate QEMU since it can't recover from error */
 557             perror("qemu_prealloc_mem: failed to reinstall signal handler");
 558             exit(1);
 559         }
 560         qemu_mutex_unlock(&sigbus_mutex);
 561     }
 562 }
 563
 564 char *qemu_get_pid_name(pid_t pid)
 565 {
 566     char *name = NULL;
 567
 568 #if defined(__FreeBSD__)
 569     /* BSDs don't have /proc, but they provide a nice substitute */
 570     struct kinfo_proc *proc = kinfo_getproc(pid);
 571
 572     if (proc) {
 573         name = g_strdup(proc->ki_comm);
 574         free(proc);
 575     }
 576 #else
 577     /* Assume a system with reasonable procfs */
 578     char *pid_path;
 579     size_t len;
 580
 581     pid_path = g_strdup_printf("/proc/%d/cmdline", pid);
 582     g_file_get_contents(pid_path, &name, &len, NULL);
 583     g_free(pid_path);
 584 #endif
 585
 586     return name;
 587 }
 588
 589
 590 pid_t qemu_fork(Error **errp)
 591 {
 592     sigset_t oldmask, newmask;
 593     struct sigaction sig_action;
 594     int saved_errno;
 595     pid_t pid;
 596
 597     /*
 598      * Need to block signals now, so that child process can safely
 599      * kill off caller's signal handlers without a race.
 600      */
 601     sigfillset(&newmask);
 602     if (pthread_sigmask(SIG_SETMASK, &newmask, &oldmask) != 0) {
 603         error_setg_errno(errp, errno,
 604                          "cannot block signals");
 605         return -1;
 606     }
 607
 608     pid = fork();
 609     saved_errno = errno;
 610
 611     if (pid < 0) {
 612         /* attempt to restore signal mask, but ignore failure, to
 613          * avoid obscuring the fork failure */
 614         (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 615         error_setg_errno(errp, saved_errno,
 616                          "cannot fork child process");
 617         errno = saved_errno;
 618         return -1;
 619     } else if (pid) {
 620         /* parent process */
 621
 622         /* Restore our original signal mask now that the child is
 623          * safely running. Only documented failures are EFAULT (not
 624          * possible, since we are using just-grabbed mask) or EINVAL
 625          * (not possible, since we are using correct arguments).  */
 626         (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 627     } else {
 628         /* child process */
 629         size_t i;
 630
 631         /* Clear out all signal handlers from parent so nothing
 632          * unexpected can happen in our child once we unblock
 633          * signals */
 634         sig_action.sa_handler = SIG_DFL;
 635         sig_action.sa_flags = 0;
 636         sigemptyset(&sig_action.sa_mask);
 637
 638         for (i = 1; i < NSIG; i++) {
 639             /* Only possible errors are EFAULT or EINVAL The former
 640              * won't happen, the latter we expect, so no need to check
 641              * return value */
 642             (void)sigaction(i, &sig_action, NULL);
 643         }
 644
 645         /* Unmask all signals in child, since we've no idea what the
 646          * caller's done with their signal mask and don't want to
 647          * propagate that to children */
 648         sigemptyset(&newmask);
 649         if (pthread_sigmask(SIG_SETMASK, &newmask, NULL) != 0) {
 650             Error *local_err = NULL;
 651             error_setg_errno(&local_err, errno,
 652                              "cannot unblock signals");
 653             error_report_err(local_err);
 654             _exit(1);
 655         }
 656     }
 657     return pid;
 658 }
 659
 660 void *qemu_alloc_stack(size_t *sz)
 661 {
 662     void *ptr, *guardpage;
 663     int flags;
 664 #ifdef CONFIG_DEBUG_STACK_USAGE
 665     void *ptr2;
 666 #endif
 667     size_t pagesz = qemu_real_host_page_size();
 668 #ifdef _SC_THREAD_STACK_MIN
 669     /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
 670     long min_stack_sz = sysconf(_SC_THREAD_STACK_MIN);
 671     *sz = MAX(MAX(min_stack_sz, 0), *sz);
 672 #endif
 673     /* adjust stack size to a multiple of the page size */
 674     *sz = ROUND_UP(*sz, pagesz);
 675     /* allocate one extra page for the guard page */
 676     *sz += pagesz;
 677
 678     flags = MAP_PRIVATE | MAP_ANONYMOUS;
 679 #if defined(MAP_STACK) && defined(__OpenBSD__)
 680     /* Only enable MAP_STACK on OpenBSD. Other OS's such as
 681      * Linux/FreeBSD/NetBSD have a flag with the same name
 682      * but have differing functionality. OpenBSD will SEGV
 683      * if it spots execution with a stack pointer pointing
 684      * at memory that was not allocated with MAP_STACK.
 685      */
 686     flags |= MAP_STACK;
 687 #endif
 688
 689     ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE, flags, -1, 0);
 690     if (ptr == MAP_FAILED) {
 691         perror("failed to allocate memory for stack");
 692         abort();
 693     }
 694
 695 #if defined(HOST_IA64)
 696     /* separate register stack */
 697     guardpage = ptr + (((*sz - pagesz) / 2) & ~pagesz);
 698 #elif defined(HOST_HPPA)
 699     /* stack grows up */
 700     guardpage = ptr + *sz - pagesz;
 701 #else
 702     /* stack grows down */
 703     guardpage = ptr;
 704 #endif
 705     if (mprotect(guardpage, pagesz, PROT_NONE) != 0) {
 706         perror("failed to set up stack guard page");
 707         abort();
 708     }
 709
 710 #ifdef CONFIG_DEBUG_STACK_USAGE
 711     for (ptr2 = ptr + pagesz; ptr2 < ptr + *sz; ptr2 += sizeof(uint32_t)) {
 712         *(uint32_t *)ptr2 = 0xdeadbeaf;
 713     }
 714 #endif
 715
 716     return ptr;
 717 }
 718
 719 #ifdef CONFIG_DEBUG_STACK_USAGE
 720 static __thread unsigned int max_stack_usage;
 721 #endif
 722
 723 void qemu_free_stack(void *stack, size_t sz)
 724 {
 725 #ifdef CONFIG_DEBUG_STACK_USAGE
 726     unsigned int usage;
 727     void *ptr;
 728
 729     for (ptr = stack + qemu_real_host_page_size(); ptr < stack + sz;
 730          ptr += sizeof(uint32_t)) {
 731         if (*(uint32_t *)ptr != 0xdeadbeaf) {
 732             break;
 733         }
 734     }
 735     usage = sz - (uintptr_t) (ptr - stack);
 736     if (usage > max_stack_usage) {
 737         error_report("thread %d max stack usage increased from %u to %u",
 738                      qemu_get_thread_id(), max_stack_usage, usage);
 739         max_stack_usage = usage;
 740     }
 741 #endif
 742
 743     munmap(stack, sz);
 744 }
 745
 746 /*
 747  * Disable CFI checks.
 748  * We are going to call a signal hander directly. Such handler may or may not
 749  * have been defined in our binary, so there's no guarantee that the pointer
 750  * used to set the handler is a cfi-valid pointer. Since the handlers are
 751  * stored in kernel memory, changing the handler to an attacker-defined
 752  * function requires being able to call a sigaction() syscall,
 753  * which is not as easy as overwriting a pointer in memory.
 754  */
 755 QEMU_DISABLE_CFI
 756 void sigaction_invoke(struct sigaction *action,
 757                       struct qemu_signalfd_siginfo *info)
 758 {
 759     siginfo_t si = {};
 760     si.si_signo = info->ssi_signo;
 761     si.si_errno = info->ssi_errno;
 762     si.si_code = info->ssi_code;
 763
 764     /* Convert the minimal set of fields defined by POSIX.
 765      * Positive si_code values are reserved for kernel-generated
 766      * signals, where the valid siginfo fields are determined by
 767      * the signal number.  But according to POSIX, it is unspecified
 768      * whether SI_USER and SI_QUEUE have values less than or equal to
 769      * zero.
 770      */
 771     if (info->ssi_code == SI_USER || info->ssi_code == SI_QUEUE ||
 772         info->ssi_code <= 0) {
 773         /* SIGTERM, etc.  */
 774         si.si_pid = info->ssi_pid;
 775         si.si_uid = info->ssi_uid;
 776     } else if (info->ssi_signo == SIGILL || info->ssi_signo == SIGFPE ||
 777                info->ssi_signo == SIGSEGV || info->ssi_signo == SIGBUS) {
 778         si.si_addr = (void *)(uintptr_t)info->ssi_addr;
 779     } else if (info->ssi_signo == SIGCHLD) {
 780         si.si_pid = info->ssi_pid;
 781         si.si_status = info->ssi_status;
 782         si.si_uid = info->ssi_uid;
 783     }
 784     action->sa_sigaction(info->ssi_signo, &si, NULL);
 785 }
 786
 787 size_t qemu_get_host_physmem(void)
 788 {
 789 #ifdef _SC_PHYS_PAGES
 790     long pages = sysconf(_SC_PHYS_PAGES);
 791     if (pages > 0) {
 792         if (pages > SIZE_MAX / qemu_real_host_page_size()) {
 793             return SIZE_MAX;
 794         } else {
 795             return pages * qemu_real_host_page_size();
 796         }
 797     }
 798 #endif
 799     return 0;
 800 }
 801
 802 int qemu_msync(void *addr, size_t length, int fd)
 803 {
 804     size_t align_mask = ~(qemu_real_host_page_size() - 1);
 805
 806     /**
 807      * There are no strict reqs as per the length of mapping
 808      * to be synced. Still the length needs to follow the address
 809      * alignment changes. Additionally - round the size to the multiple
 810      * of PAGE_SIZE
 811      */
 812     length += ((uintptr_t)addr & (qemu_real_host_page_size() - 1));
 813     length = (length + ~align_mask) & align_mask;
 814
 815     addr = (void *)((uintptr_t)addr & align_mask);
 816
 817     return msync(addr, length, MS_SYNC);
 818 }