libsanitizer/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc

   1 //===-- sanitizer_stoptheworld_linux_libcdep.cc ---------------------------===//
   2 //
   3 // This file is distributed under the University of Illinois Open Source
   4 // License. See LICENSE.TXT for details.
   5 //
   6 //===----------------------------------------------------------------------===//
   7 //
   8 // See sanitizer_stoptheworld.h for details.
   9 // This implementation was inspired by Markus Gutschke's linuxthreads.cc.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "sanitizer_platform.h"
  14
  15 #if SANITIZER_LINUX && (defined(__x86_64__) || defined(__mips__) || \
  16                         defined(__aarch64__) || defined(__powerpc64__) || \
  17                         defined(__s390__) || defined(__i386__) || \
  18                         defined(__arm__))
  19
  20 #include "sanitizer_stoptheworld.h"
  21
  22 #include "sanitizer_platform_limits_posix.h"
  23 #include "sanitizer_atomic.h"
  24
  25 #include <errno.h>
  26 #include <sched.h> // for CLONE_* definitions
  27 #include <stddef.h>
  28 #include <sys/prctl.h> // for PR_* definitions
  29 #include <sys/ptrace.h> // for PTRACE_* definitions
  30 #include <sys/types.h> // for pid_t
  31 #include <sys/uio.h> // for iovec
  32 #include <elf.h> // for NT_PRSTATUS
  33 #if defined(__aarch64__) && !SANITIZER_ANDROID
  34 // GLIBC 2.20+ sys/user does not include asm/ptrace.h
  35 # include <asm/ptrace.h>
  36 #endif
  37 #include <sys/user.h>  // for user_regs_struct
  38 #if SANITIZER_ANDROID && SANITIZER_MIPS
  39 # include <asm/reg.h>  // for mips SP register in sys/user.h
  40 #endif
  41 #include <sys/wait.h> // for signal-related stuff
  42
  43 #ifdef sa_handler
  44 # undef sa_handler
  45 #endif
  46
  47 #ifdef sa_sigaction
  48 # undef sa_sigaction
  49 #endif
  50
  51 #include "sanitizer_common.h"
  52 #include "sanitizer_flags.h"
  53 #include "sanitizer_libc.h"
  54 #include "sanitizer_linux.h"
  55 #include "sanitizer_mutex.h"
  56 #include "sanitizer_placement_new.h"
  57
  58 // This module works by spawning a Linux task which then attaches to every
  59 // thread in the caller process with ptrace. This suspends the threads, and
  60 // PTRACE_GETREGS can then be used to obtain their register state. The callback
  61 // supplied to StopTheWorld() is run in the tracer task while the threads are
  62 // suspended.
  63 // The tracer task must be placed in a different thread group for ptrace to
  64 // work, so it cannot be spawned as a pthread. Instead, we use the low-level
  65 // clone() interface (we want to share the address space with the caller
  66 // process, so we prefer clone() over fork()).
  67 //
  68 // We don't use any libc functions, relying instead on direct syscalls. There
  69 // are two reasons for this:
  70 // 1. calling a library function while threads are suspended could cause a
  71 // deadlock, if one of the treads happens to be holding a libc lock;
  72 // 2. it's generally not safe to call libc functions from the tracer task,
  73 // because clone() does not set up a thread-local storage for it. Any
  74 // thread-local variables used by libc will be shared between the tracer task
  75 // and the thread which spawned it.
  76
  77 namespace __sanitizer {
  78
  79 class SuspendedThreadsListLinux : public SuspendedThreadsList {
  80  public:
  81   SuspendedThreadsListLinux() : thread_ids_(1024) {}
  82
  83   tid_t GetThreadID(uptr index) const;
  84   uptr ThreadCount() const;
  85   bool ContainsTid(tid_t thread_id) const;
  86   void Append(tid_t tid);
  87
  88   PtraceRegistersStatus GetRegistersAndSP(uptr index, uptr *buffer,
  89                                           uptr *sp) const;
  90   uptr RegisterCount() const;
  91
  92  private:
  93   InternalMmapVector<tid_t> thread_ids_;
  94 };
  95
  96 // Structure for passing arguments into the tracer thread.
  97 struct TracerThreadArgument {
  98   StopTheWorldCallback callback;
  99   void *callback_argument;
 100   // The tracer thread waits on this mutex while the parent finishes its
 101   // preparations.
 102   BlockingMutex mutex;
 103   // Tracer thread signals its completion by setting done.
 104   atomic_uintptr_t done;
 105   uptr parent_pid;
 106 };
 107
 108 // This class handles thread suspending/unsuspending in the tracer thread.
 109 class ThreadSuspender {
 110  public:
 111   explicit ThreadSuspender(pid_t pid, TracerThreadArgument *arg)
 112     : arg(arg)
 113     , pid_(pid) {
 114       CHECK_GE(pid, 0);
 115     }
 116   bool SuspendAllThreads();
 117   void ResumeAllThreads();
 118   void KillAllThreads();
 119   SuspendedThreadsListLinux &suspended_threads_list() {
 120     return suspended_threads_list_;
 121   }
 122   TracerThreadArgument *arg;
 123  private:
 124   SuspendedThreadsListLinux suspended_threads_list_;
 125   pid_t pid_;
 126   bool SuspendThread(tid_t thread_id);
 127 };
 128
 129 bool ThreadSuspender::SuspendThread(tid_t tid) {
 130   // Are we already attached to this thread?
 131   // Currently this check takes linear time, however the number of threads is
 132   // usually small.
 133   if (suspended_threads_list_.ContainsTid(tid)) return false;
 134   int pterrno;
 135   if (internal_iserror(internal_ptrace(PTRACE_ATTACH, tid, nullptr, nullptr),
 136                        &pterrno)) {
 137     // Either the thread is dead, or something prevented us from attaching.
 138     // Log this event and move on.
 139     VReport(1, "Could not attach to thread %zu (errno %d).\n", (uptr)tid,
 140             pterrno);
 141     return false;
 142   } else {
 143     VReport(2, "Attached to thread %zu.\n", (uptr)tid);
 144     // The thread is not guaranteed to stop before ptrace returns, so we must
 145     // wait on it. Note: if the thread receives a signal concurrently,
 146     // we can get notification about the signal before notification about stop.
 147     // In such case we need to forward the signal to the thread, otherwise
 148     // the signal will be missed (as we do PTRACE_DETACH with arg=0) and
 149     // any logic relying on signals will break. After forwarding we need to
 150     // continue to wait for stopping, because the thread is not stopped yet.
 151     // We do ignore delivery of SIGSTOP, because we want to make stop-the-world
 152     // as invisible as possible.
 153     for (;;) {
 154       int status;
 155       uptr waitpid_status;
 156       HANDLE_EINTR(waitpid_status, internal_waitpid(tid, &status, __WALL));
 157       int wperrno;
 158       if (internal_iserror(waitpid_status, &wperrno)) {
 159         // Got a ECHILD error. I don't think this situation is possible, but it
 160         // doesn't hurt to report it.
 161         VReport(1, "Waiting on thread %zu failed, detaching (errno %d).\n",
 162                 (uptr)tid, wperrno);
 163         internal_ptrace(PTRACE_DETACH, tid, nullptr, nullptr);
 164         return false;
 165       }
 166       if (WIFSTOPPED(status) && WSTOPSIG(status) != SIGSTOP) {
 167         internal_ptrace(PTRACE_CONT, tid, nullptr,
 168                         (void*)(uptr)WSTOPSIG(status));
 169         continue;
 170       }
 171       break;
 172     }
 173     suspended_threads_list_.Append(tid);
 174     return true;
 175   }
 176 }
 177
 178 void ThreadSuspender::ResumeAllThreads() {
 179   for (uptr i = 0; i < suspended_threads_list_.ThreadCount(); i++) {
 180     pid_t tid = suspended_threads_list_.GetThreadID(i);
 181     int pterrno;
 182     if (!internal_iserror(internal_ptrace(PTRACE_DETACH, tid, nullptr, nullptr),
 183                           &pterrno)) {
 184       VReport(2, "Detached from thread %d.\n", tid);
 185     } else {
 186       // Either the thread is dead, or we are already detached.
 187       // The latter case is possible, for instance, if this function was called
 188       // from a signal handler.
 189       VReport(1, "Could not detach from thread %d (errno %d).\n", tid, pterrno);
 190     }
 191   }
 192 }
 193
 194 void ThreadSuspender::KillAllThreads() {
 195   for (uptr i = 0; i < suspended_threads_list_.ThreadCount(); i++)
 196     internal_ptrace(PTRACE_KILL, suspended_threads_list_.GetThreadID(i),
 197                     nullptr, nullptr);
 198 }
 199
 200 bool ThreadSuspender::SuspendAllThreads() {
 201   ThreadLister thread_lister(pid_);
 202   bool added_threads;
 203   bool first_iteration = true;
 204   do {
 205     // Run through the directory entries once.
 206     added_threads = false;
 207     pid_t tid = thread_lister.GetNextTID();
 208     while (tid >= 0) {
 209       if (SuspendThread(tid))
 210         added_threads = true;
 211       tid = thread_lister.GetNextTID();
 212     }
 213     if (thread_lister.error() || (first_iteration && !added_threads)) {
 214       // Detach threads and fail.
 215       ResumeAllThreads();
 216       return false;
 217     }
 218     thread_lister.Reset();
 219     first_iteration = false;
 220   } while (added_threads);
 221   return true;
 222 }
 223
 224 // Pointer to the ThreadSuspender instance for use in signal handler.
 225 static ThreadSuspender *thread_suspender_instance = nullptr;
 226
 227 // Synchronous signals that should not be blocked.
 228 static const int kSyncSignals[] = { SIGABRT, SIGILL, SIGFPE, SIGSEGV, SIGBUS,
 229                                     SIGXCPU, SIGXFSZ };
 230
 231 static void TracerThreadDieCallback() {
 232   // Generally a call to Die() in the tracer thread should be fatal to the
 233   // parent process as well, because they share the address space.
 234   // This really only works correctly if all the threads are suspended at this
 235   // point. So we correctly handle calls to Die() from within the callback, but
 236   // not those that happen before or after the callback. Hopefully there aren't
 237   // a lot of opportunities for that to happen...
 238   ThreadSuspender *inst = thread_suspender_instance;
 239   if (inst && stoptheworld_tracer_pid == internal_getpid()) {
 240     inst->KillAllThreads();
 241     thread_suspender_instance = nullptr;
 242   }
 243 }
 244
 245 // Signal handler to wake up suspended threads when the tracer thread dies.
 246 static void TracerThreadSignalHandler(int signum, void *siginfo, void *uctx) {
 247   SignalContext ctx(siginfo, uctx);
 248   Printf("Tracer caught signal %d: addr=0x%zx pc=0x%zx sp=0x%zx\n", signum,
 249          ctx.addr, ctx.pc, ctx.sp);
 250   ThreadSuspender *inst = thread_suspender_instance;
 251   if (inst) {
 252     if (signum == SIGABRT)
 253       inst->KillAllThreads();
 254     else
 255       inst->ResumeAllThreads();
 256     RAW_CHECK(RemoveDieCallback(TracerThreadDieCallback));
 257     thread_suspender_instance = nullptr;
 258     atomic_store(&inst->arg->done, 1, memory_order_relaxed);
 259   }
 260   internal__exit((signum == SIGABRT) ? 1 : 2);
 261 }
 262
 263 // Size of alternative stack for signal handlers in the tracer thread.
 264 static const int kHandlerStackSize = 8192;
 265
 266 // This function will be run as a cloned task.
 267 static int TracerThread(void* argument) {
 268   TracerThreadArgument *tracer_thread_argument =
 269       (TracerThreadArgument *)argument;
 270
 271   internal_prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
 272   // Check if parent is already dead.
 273   if (internal_getppid() != tracer_thread_argument->parent_pid)
 274     internal__exit(4);
 275
 276   // Wait for the parent thread to finish preparations.
 277   tracer_thread_argument->mutex.Lock();
 278   tracer_thread_argument->mutex.Unlock();
 279
 280   RAW_CHECK(AddDieCallback(TracerThreadDieCallback));
 281
 282   ThreadSuspender thread_suspender(internal_getppid(), tracer_thread_argument);
 283   // Global pointer for the signal handler.
 284   thread_suspender_instance = &thread_suspender;
 285
 286   // Alternate stack for signal handling.
 287   InternalScopedBuffer<char> handler_stack_memory(kHandlerStackSize);
 288   stack_t handler_stack;
 289   internal_memset(&handler_stack, 0, sizeof(handler_stack));
 290   handler_stack.ss_sp = handler_stack_memory.data();
 291   handler_stack.ss_size = kHandlerStackSize;
 292   internal_sigaltstack(&handler_stack, nullptr);
 293
 294   // Install our handler for synchronous signals. Other signals should be
 295   // blocked by the mask we inherited from the parent thread.
 296   for (uptr i = 0; i < ARRAY_SIZE(kSyncSignals); i++) {
 297     __sanitizer_sigaction act;
 298     internal_memset(&act, 0, sizeof(act));
 299     act.sigaction = TracerThreadSignalHandler;
 300     act.sa_flags = SA_ONSTACK | SA_SIGINFO;
 301     internal_sigaction_norestorer(kSyncSignals[i], &act, 0);
 302   }
 303
 304   int exit_code = 0;
 305   if (!thread_suspender.SuspendAllThreads()) {
 306     VReport(1, "Failed suspending threads.\n");
 307     exit_code = 3;
 308   } else {
 309     tracer_thread_argument->callback(thread_suspender.suspended_threads_list(),
 310                                      tracer_thread_argument->callback_argument);
 311     thread_suspender.ResumeAllThreads();
 312     exit_code = 0;
 313   }
 314   RAW_CHECK(RemoveDieCallback(TracerThreadDieCallback));
 315   thread_suspender_instance = nullptr;
 316   atomic_store(&tracer_thread_argument->done, 1, memory_order_relaxed);
 317   return exit_code;
 318 }
 319
 320 class ScopedStackSpaceWithGuard {
 321  public:
 322   explicit ScopedStackSpaceWithGuard(uptr stack_size) {
 323     stack_size_ = stack_size;
 324     guard_size_ = GetPageSizeCached();
 325     // FIXME: Omitting MAP_STACK here works in current kernels but might break
 326     // in the future.
 327     guard_start_ = (uptr)MmapOrDie(stack_size_ + guard_size_,
 328                                    "ScopedStackWithGuard");
 329     CHECK(MprotectNoAccess((uptr)guard_start_, guard_size_));
 330   }
 331   ~ScopedStackSpaceWithGuard() {
 332     UnmapOrDie((void *)guard_start_, stack_size_ + guard_size_);
 333   }
 334   void *Bottom() const {
 335     return (void *)(guard_start_ + stack_size_ + guard_size_);
 336   }
 337
 338  private:
 339   uptr stack_size_;
 340   uptr guard_size_;
 341   uptr guard_start_;
 342 };
 343
 344 // We have a limitation on the stack frame size, so some stuff had to be moved
 345 // into globals.
 346 static __sanitizer_sigset_t blocked_sigset;
 347 static __sanitizer_sigset_t old_sigset;
 348
 349 class StopTheWorldScope {
 350  public:
 351   StopTheWorldScope() {
 352     // Make this process dumpable. Processes that are not dumpable cannot be
 353     // attached to.
 354     process_was_dumpable_ = internal_prctl(PR_GET_DUMPABLE, 0, 0, 0, 0);
 355     if (!process_was_dumpable_)
 356       internal_prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);
 357   }
 358
 359   ~StopTheWorldScope() {
 360     // Restore the dumpable flag.
 361     if (!process_was_dumpable_)
 362       internal_prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
 363   }
 364
 365  private:
 366   int process_was_dumpable_;
 367 };
 368
 369 // When sanitizer output is being redirected to file (i.e. by using log_path),
 370 // the tracer should write to the parent's log instead of trying to open a new
 371 // file. Alert the logging code to the fact that we have a tracer.
 372 struct ScopedSetTracerPID {
 373   explicit ScopedSetTracerPID(uptr tracer_pid) {
 374     stoptheworld_tracer_pid = tracer_pid;
 375     stoptheworld_tracer_ppid = internal_getpid();
 376   }
 377   ~ScopedSetTracerPID() {
 378     stoptheworld_tracer_pid = 0;
 379     stoptheworld_tracer_ppid = 0;
 380   }
 381 };
 382
 383 void StopTheWorld(StopTheWorldCallback callback, void *argument) {
 384   StopTheWorldScope in_stoptheworld;
 385   // Prepare the arguments for TracerThread.
 386   struct TracerThreadArgument tracer_thread_argument;
 387   tracer_thread_argument.callback = callback;
 388   tracer_thread_argument.callback_argument = argument;
 389   tracer_thread_argument.parent_pid = internal_getpid();
 390   atomic_store(&tracer_thread_argument.done, 0, memory_order_relaxed);
 391   const uptr kTracerStackSize = 2 * 1024 * 1024;
 392   ScopedStackSpaceWithGuard tracer_stack(kTracerStackSize);
 393   // Block the execution of TracerThread until after we have set ptrace
 394   // permissions.
 395   tracer_thread_argument.mutex.Lock();
 396   // Signal handling story.
 397   // We don't want async signals to be delivered to the tracer thread,
 398   // so we block all async signals before creating the thread. An async signal
 399   // handler can temporary modify errno, which is shared with this thread.
 400   // We ought to use pthread_sigmask here, because sigprocmask has undefined
 401   // behavior in multithreaded programs. However, on linux sigprocmask is
 402   // equivalent to pthread_sigmask with the exception that pthread_sigmask
 403   // does not allow to block some signals used internally in pthread
 404   // implementation. We are fine with blocking them here, we are really not
 405   // going to pthread_cancel the thread.
 406   // The tracer thread should not raise any synchronous signals. But in case it
 407   // does, we setup a special handler for sync signals that properly kills the
 408   // parent as well. Note: we don't pass CLONE_SIGHAND to clone, so handlers
 409   // in the tracer thread won't interfere with user program. Double note: if a
 410   // user does something along the lines of 'kill -11 pid', that can kill the
 411   // process even if user setup own handler for SEGV.
 412   // Thing to watch out for: this code should not change behavior of user code
 413   // in any observable way. In particular it should not override user signal
 414   // handlers.
 415   internal_sigfillset(&blocked_sigset);
 416   for (uptr i = 0; i < ARRAY_SIZE(kSyncSignals); i++)
 417     internal_sigdelset(&blocked_sigset, kSyncSignals[i]);
 418   int rv = internal_sigprocmask(SIG_BLOCK, &blocked_sigset, &old_sigset);
 419   CHECK_EQ(rv, 0);
 420   uptr tracer_pid = internal_clone(
 421       TracerThread, tracer_stack.Bottom(),
 422       CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_UNTRACED,
 423       &tracer_thread_argument, nullptr /* parent_tidptr */,
 424       nullptr /* newtls */, nullptr /* child_tidptr */);
 425   internal_sigprocmask(SIG_SETMASK, &old_sigset, 0);
 426   int local_errno = 0;
 427   if (internal_iserror(tracer_pid, &local_errno)) {
 428     VReport(1, "Failed spawning a tracer thread (errno %d).\n", local_errno);
 429     tracer_thread_argument.mutex.Unlock();
 430   } else {
 431     ScopedSetTracerPID scoped_set_tracer_pid(tracer_pid);
 432     // On some systems we have to explicitly declare that we want to be traced
 433     // by the tracer thread.
 434 #ifdef PR_SET_PTRACER
 435     internal_prctl(PR_SET_PTRACER, tracer_pid, 0, 0, 0);
 436 #endif
 437     // Allow the tracer thread to start.
 438     tracer_thread_argument.mutex.Unlock();
 439     // NOTE: errno is shared between this thread and the tracer thread.
 440     // internal_waitpid() may call syscall() which can access/spoil errno,
 441     // so we can't call it now. Instead we for the tracer thread to finish using
 442     // the spin loop below. Man page for sched_yield() says "In the Linux
 443     // implementation, sched_yield() always succeeds", so let's hope it does not
 444     // spoil errno. Note that this spin loop runs only for brief periods before
 445     // the tracer thread has suspended us and when it starts unblocking threads.
 446     while (atomic_load(&tracer_thread_argument.done, memory_order_relaxed) == 0)
 447       sched_yield();
 448     // Now the tracer thread is about to exit and does not touch errno,
 449     // wait for it.
 450     for (;;) {
 451       uptr waitpid_status = internal_waitpid(tracer_pid, nullptr, __WALL);
 452       if (!internal_iserror(waitpid_status, &local_errno))
 453         break;
 454       if (local_errno == EINTR)
 455         continue;
 456       VReport(1, "Waiting on the tracer thread failed (errno %d).\n",
 457               local_errno);
 458       break;
 459     }
 460   }
 461 }
 462
 463 // Platform-specific methods from SuspendedThreadsList.
 464 #if SANITIZER_ANDROID && defined(__arm__)
 465 typedef pt_regs regs_struct;
 466 #define REG_SP ARM_sp
 467
 468 #elif SANITIZER_LINUX && defined(__arm__)
 469 typedef user_regs regs_struct;
 470 #define REG_SP uregs[13]
 471
 472 #elif defined(__i386__) || defined(__x86_64__)
 473 typedef user_regs_struct regs_struct;
 474 #if defined(__i386__)
 475 #define REG_SP esp
 476 #else
 477 #define REG_SP rsp
 478 #endif
 479
 480 #elif defined(__powerpc__) || defined(__powerpc64__)
 481 typedef pt_regs regs_struct;
 482 #define REG_SP gpr[PT_R1]
 483
 484 #elif defined(__mips__)
 485 typedef struct user regs_struct;
 486 # if SANITIZER_ANDROID
 487 #  define REG_SP regs[EF_R29]
 488 # else
 489 #  define REG_SP regs[EF_REG29]
 490 # endif
 491
 492 #elif defined(__aarch64__)
 493 typedef struct user_pt_regs regs_struct;
 494 #define REG_SP sp
 495 #define ARCH_IOVEC_FOR_GETREGSET
 496
 497 #elif defined(__s390__)
 498 typedef _user_regs_struct regs_struct;
 499 #define REG_SP gprs[15]
 500 #define ARCH_IOVEC_FOR_GETREGSET
 501
 502 #else
 503 #error "Unsupported architecture"
 504 #endif // SANITIZER_ANDROID && defined(__arm__)
 505
 506 tid_t SuspendedThreadsListLinux::GetThreadID(uptr index) const {
 507   CHECK_LT(index, thread_ids_.size());
 508   return thread_ids_[index];
 509 }
 510
 511 uptr SuspendedThreadsListLinux::ThreadCount() const {
 512   return thread_ids_.size();
 513 }
 514
 515 bool SuspendedThreadsListLinux::ContainsTid(tid_t thread_id) const {
 516   for (uptr i = 0; i < thread_ids_.size(); i++) {
 517     if (thread_ids_[i] == thread_id) return true;
 518   }
 519   return false;
 520 }
 521
 522 void SuspendedThreadsListLinux::Append(tid_t tid) {
 523   thread_ids_.push_back(tid);
 524 }
 525
 526 PtraceRegistersStatus SuspendedThreadsListLinux::GetRegistersAndSP(
 527     uptr index, uptr *buffer, uptr *sp) const {
 528   pid_t tid = GetThreadID(index);
 529   regs_struct regs;
 530   int pterrno;
 531 #ifdef ARCH_IOVEC_FOR_GETREGSET
 532   struct iovec regset_io;
 533   regset_io.iov_base = &regs;
 534   regset_io.iov_len = sizeof(regs_struct);
 535   bool isErr = internal_iserror(internal_ptrace(PTRACE_GETREGSET, tid,
 536                                 (void*)NT_PRSTATUS, (void*)&regset_io),
 537                                 &pterrno);
 538 #else
 539   bool isErr = internal_iserror(internal_ptrace(PTRACE_GETREGS, tid, nullptr,
 540                                 &regs), &pterrno);
 541 #endif
 542   if (isErr) {
 543     VReport(1, "Could not get registers from thread %d (errno %d).\n", tid,
 544             pterrno);
 545     // ESRCH means that the given thread is not suspended or already dead.
 546     // Therefore it's unsafe to inspect its data (e.g. walk through stack) and
 547     // we should notify caller about this.
 548     return pterrno == ESRCH ? REGISTERS_UNAVAILABLE_FATAL
 549                             : REGISTERS_UNAVAILABLE;
 550   }
 551
 552   *sp = regs.REG_SP;
 553   internal_memcpy(buffer, &regs, sizeof(regs));
 554   return REGISTERS_AVAILABLE;
 555 }
 556
 557 uptr SuspendedThreadsListLinux::RegisterCount() const {
 558   return sizeof(regs_struct) / sizeof(uptr);
 559 }
 560 } // namespace __sanitizer
 561
 562 #endif  // SANITIZER_LINUX && (defined(__x86_64__) || defined(__mips__)
 563         // || defined(__aarch64__) || defined(__powerpc64__)
 564         // || defined(__s390__) || defined(__i386__) || defined(__arm__)