text: //===-- sanitizer_linux.cpp -----------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This file is shared between AddressSanitizer and ThreadSanitizer
  // run-time libraries and implements linux-specific functions from
  // sanitizer_libc.h.
  //===----------------------------------------------------------------------===//
  
  #include "sanitizer_platform.h"
  
  #if SANITIZER_FREEBSD || SANITIZER_LINUX || SANITIZER_NETBSD || \
      SANITIZER_OPENBSD || SANITIZER_SOLARIS
  
  #include "sanitizer_common.h"
  #include "sanitizer_flags.h"
  #include "sanitizer_getauxval.h"
  #include "sanitizer_internal_defs.h"
  #include "sanitizer_libc.h"
  #include "sanitizer_linux.h"
  #include "sanitizer_mutex.h"
  #include "sanitizer_placement_new.h"
  #include "sanitizer_procmaps.h"
  
  #if SANITIZER_LINUX
  #include <asm/param.h>
  #endif
  
  // For mips64, syscall(__NR_stat) fills the buffer in the 'struct kernel_stat'
  // format. Struct kernel_stat is defined as 'struct stat' in asm/stat.h. To
  // access stat from asm/stat.h, without conflicting with definition in
  // sys/stat.h, we use this trick.
  #if defined(__mips64)
  #include <asm/unistd.h>
  #include <sys/types.h>
  #define stat kernel_stat
  #include <asm/stat.h>
  #undef stat
  #endif
  
  #include <dlfcn.h>
  #include <errno.h>
  #include <fcntl.h>
  #include <link.h>
  #include <pthread.h>
  #include <sched.h>
  #include <signal.h>
  #include <sys/mman.h>
  #include <sys/param.h>
  #if !SANITIZER_SOLARIS
  #include <sys/ptrace.h>
  #endif
  #include <sys/resource.h>
  #include <sys/stat.h>
  #include <sys/syscall.h>
  #include <sys/time.h>
  #include <sys/types.h>
  #if !SANITIZER_OPENBSD
  #include <ucontext.h>
  #endif
  #if SANITIZER_OPENBSD
  #include <sys/futex.h>
  #include <sys/sysctl.h>
  #endif
  #include <unistd.h>
  
  #if SANITIZER_LINUX
  #include <sys/utsname.h>
  #endif
  
  #if SANITIZER_LINUX && !SANITIZER_ANDROID
  #include <sys/personality.h>
  #endif
  
  #if SANITIZER_FREEBSD
  #include <sys/exec.h>
  #include <sys/sysctl.h>
  #include <machine/atomic.h>
  extern "C" {
  // <sys/umtx.h> must be included after <errno.h> and <sys/types.h> on
  // FreeBSD 9.2 and 10.0.
  #include <sys/umtx.h>
  }
  #include <sys/thr.h>
  #endif  // SANITIZER_FREEBSD
  
  #if SANITIZER_NETBSD
  #include <limits.h>  // For NAME_MAX
  #include <sys/sysctl.h>
  #include <sys/exec.h>
  extern struct ps_strings *__ps_strings;
  #endif  // SANITIZER_NETBSD
  
  #if SANITIZER_SOLARIS
  #include <stdlib.h>
  #include <thread.h>
  #define environ _environ
  #endif
  
  extern char **environ;
  
  #if SANITIZER_LINUX
  // <linux/time.h>
  struct kernel_timeval {
    long tv_sec;
    long tv_usec;
  };
  
  // <linux/futex.h> is broken on some linux distributions.
  const int FUTEX_WAIT = 0;
  const int FUTEX_WAKE = 1;
  const int FUTEX_PRIVATE_FLAG = 128;
  const int FUTEX_WAIT_PRIVATE = FUTEX_WAIT | FUTEX_PRIVATE_FLAG;
  const int FUTEX_WAKE_PRIVATE = FUTEX_WAKE | FUTEX_PRIVATE_FLAG;
  #endif  // SANITIZER_LINUX
  
  // Are we using 32-bit or 64-bit Linux syscalls?
  // x32 (which defines __x86_64__) has SANITIZER_WORDSIZE == 32
  // but it still needs to use 64-bit syscalls.
  #if SANITIZER_LINUX && (defined(__x86_64__) || defined(__powerpc64__) ||       \
                          SANITIZER_WORDSIZE == 64)
  # define SANITIZER_LINUX_USES_64BIT_SYSCALLS 1
  #else
  # define SANITIZER_LINUX_USES_64BIT_SYSCALLS 0
  #endif
  
  // Note : FreeBSD had implemented both
  // Linux and OpenBSD apis, available from
  // future 12.x version most likely
  #if SANITIZER_LINUX && defined(__NR_getrandom)
  # if !defined(GRND_NONBLOCK)
  #  define GRND_NONBLOCK 1
  # endif
  # define SANITIZER_USE_GETRANDOM 1
  #else
  # define SANITIZER_USE_GETRANDOM 0
  #endif  // SANITIZER_LINUX && defined(__NR_getrandom)
  
  #if SANITIZER_OPENBSD
  # define SANITIZER_USE_GETENTROPY 1
  #else
  # if SANITIZER_FREEBSD && __FreeBSD_version >= 1200000
  #   define SANITIZER_USE_GETENTROPY 1
  # else
  #   define SANITIZER_USE_GETENTROPY 0
  # endif
  #endif // SANITIZER_USE_GETENTROPY
  
  namespace __sanitizer {
  
  #if SANITIZER_LINUX && defined(__x86_64__)
  #include "sanitizer_syscall_linux_x86_64.inc"
  #elif SANITIZER_LINUX && defined(__aarch64__)
  #include "sanitizer_syscall_linux_aarch64.inc"
  #elif SANITIZER_LINUX && defined(__arm__)
  #include "sanitizer_syscall_linux_arm.inc"
  #else
  #include "sanitizer_syscall_generic.inc"
  #endif
  
  // --------------- sanitizer_libc.h
  #if !SANITIZER_SOLARIS && !SANITIZER_NETBSD
  #if !SANITIZER_S390 && !SANITIZER_OPENBSD
  uptr internal_mmap(void *addr, uptr length, int prot, int flags, int fd,
                     OFF_T offset) {
  #if SANITIZER_FREEBSD || SANITIZER_LINUX_USES_64BIT_SYSCALLS
    return internal_syscall(SYSCALL(mmap), (uptr)addr, length, prot, flags, fd,
                            offset);
  #else
    // mmap2 specifies file offset in 4096-byte units.
    CHECK(IsAligned(offset, 4096));
    return internal_syscall(SYSCALL(mmap2), addr, length, prot, flags, fd,
                            offset / 4096);
  #endif
  }
  #endif // !SANITIZER_S390 && !SANITIZER_OPENBSD
  
  #if !SANITIZER_OPENBSD
  uptr internal_munmap(void *addr, uptr length) {
    return internal_syscall(SYSCALL(munmap), (uptr)addr, length);
  }
  
  int internal_mprotect(void *addr, uptr length, int prot) {
    return internal_syscall(SYSCALL(mprotect), (uptr)addr, length, prot);
  }
  #endif
  
  uptr internal_close(fd_t fd) {
    return internal_syscall(SYSCALL(close), fd);
  }
  
  uptr internal_open(const char *filename, int flags) {
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(openat), AT_FDCWD, (uptr)filename, flags);
  #else
    return internal_syscall(SYSCALL(open), (uptr)filename, flags);
  #endif
  }
  
  uptr internal_open(const char *filename, int flags, u32 mode) {
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(openat), AT_FDCWD, (uptr)filename, flags,
                            mode);
  #else
    return internal_syscall(SYSCALL(open), (uptr)filename, flags, mode);
  #endif
  }
  
  uptr internal_read(fd_t fd, void *buf, uptr count) {
    sptr res;
    HANDLE_EINTR(res,
                 (sptr)internal_syscall(SYSCALL(read), fd, (uptr)buf, count));
    return res;
  }
  
  uptr internal_write(fd_t fd, const void *buf, uptr count) {
    sptr res;
    HANDLE_EINTR(res,
                 (sptr)internal_syscall(SYSCALL(write), fd, (uptr)buf, count));
    return res;
  }
  
  uptr internal_ftruncate(fd_t fd, uptr size) {
    sptr res;
    HANDLE_EINTR(res, (sptr)internal_syscall(SYSCALL(ftruncate), fd,
                 (OFF_T)size));
    return res;
  }
  
  #if !SANITIZER_LINUX_USES_64BIT_SYSCALLS && SANITIZER_LINUX
  static void stat64_to_stat(struct stat64 *in, struct stat *out) {
    internal_memset(out, 0, sizeof(*out));
    out->st_dev = in->st_dev;
    out->st_ino = in->st_ino;
    out->st_mode = in->st_mode;
    out->st_nlink = in->st_nlink;
    out->st_uid = in->st_uid;
    out->st_gid = in->st_gid;
    out->st_rdev = in->st_rdev;
    out->st_size = in->st_size;
    out->st_blksize = in->st_blksize;
    out->st_blocks = in->st_blocks;
    out->st_atime = in->st_atime;
    out->st_mtime = in->st_mtime;
    out->st_ctime = in->st_ctime;
  }
  #endif
  
  #if defined(__mips64)
  // Undefine compatibility macros from <sys/stat.h>
  // so that they would not clash with the kernel_stat
  // st_[a|m|c]time fields
  #undef st_atime
  #undef st_mtime
  #undef st_ctime
  #if defined(SANITIZER_ANDROID)
  // Bionic sys/stat.h defines additional macros
  // for compatibility with the old NDKs and
  // they clash with the kernel_stat structure
  // st_[a|m|c]time_nsec fields.
  #undef st_atime_nsec
  #undef st_mtime_nsec
  #undef st_ctime_nsec
  #endif
  static void kernel_stat_to_stat(struct kernel_stat *in, struct stat *out) {
    internal_memset(out, 0, sizeof(*out));
    out->st_dev = in->st_dev;
    out->st_ino = in->st_ino;
    out->st_mode = in->st_mode;
    out->st_nlink = in->st_nlink;
    out->st_uid = in->st_uid;
    out->st_gid = in->st_gid;
    out->st_rdev = in->st_rdev;
    out->st_size = in->st_size;
    out->st_blksize = in->st_blksize;
    out->st_blocks = in->st_blocks;
  #if defined(__USE_MISC)     || \
      defined(__USE_XOPEN2K8) || \
      defined(SANITIZER_ANDROID)
    out->st_atim.tv_sec = in->st_atime;
    out->st_atim.tv_nsec = in->st_atime_nsec;
    out->st_mtim.tv_sec = in->st_mtime;
    out->st_mtim.tv_nsec = in->st_mtime_nsec;
    out->st_ctim.tv_sec = in->st_ctime;
    out->st_ctim.tv_nsec = in->st_ctime_nsec;
  #else
    out->st_atime = in->st_atime;
    out->st_atimensec = in->st_atime_nsec;
    out->st_mtime = in->st_mtime;
    out->st_mtimensec = in->st_mtime_nsec;
    out->st_ctime = in->st_ctime;
    out->st_atimensec = in->st_ctime_nsec;
  #endif
  }
  #endif
  
  uptr internal_stat(const char *path, void *buf) {
  #if SANITIZER_FREEBSD || SANITIZER_OPENBSD
    return internal_syscall(SYSCALL(fstatat), AT_FDCWD, (uptr)path, (uptr)buf, 0);
  #elif SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(newfstatat), AT_FDCWD, (uptr)path, (uptr)buf,
                            0);
  #elif SANITIZER_LINUX_USES_64BIT_SYSCALLS
  # if defined(__mips64)
    // For mips64, stat syscall fills buffer in the format of kernel_stat
    struct kernel_stat kbuf;
    int res = internal_syscall(SYSCALL(stat), path, &kbuf);
    kernel_stat_to_stat(&kbuf, (struct stat *)buf);
    return res;
  # else
    return internal_syscall(SYSCALL(stat), (uptr)path, (uptr)buf);
  # endif
  #else
    struct stat64 buf64;
    int res = internal_syscall(SYSCALL(stat64), path, &buf64);
    stat64_to_stat(&buf64, (struct stat *)buf);
    return res;
  #endif
  }
  
  uptr internal_lstat(const char *path, void *buf) {
  #if SANITIZER_FREEBSD || SANITIZER_OPENBSD
    return internal_syscall(SYSCALL(fstatat), AT_FDCWD, (uptr)path, (uptr)buf,
                            AT_SYMLINK_NOFOLLOW);
  #elif SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(newfstatat), AT_FDCWD, (uptr)path, (uptr)buf,
                            AT_SYMLINK_NOFOLLOW);
  #elif SANITIZER_LINUX_USES_64BIT_SYSCALLS
  # if SANITIZER_MIPS64
    // For mips64, lstat syscall fills buffer in the format of kernel_stat
    struct kernel_stat kbuf;
    int res = internal_syscall(SYSCALL(lstat), path, &kbuf);
    kernel_stat_to_stat(&kbuf, (struct stat *)buf);
    return res;
  # else
    return internal_syscall(SYSCALL(lstat), (uptr)path, (uptr)buf);
  # endif
  #else
    struct stat64 buf64;
    int res = internal_syscall(SYSCALL(lstat64), path, &buf64);
    stat64_to_stat(&buf64, (struct stat *)buf);
    return res;
  #endif
  }
  
  uptr internal_fstat(fd_t fd, void *buf) {
  #if SANITIZER_FREEBSD || SANITIZER_OPENBSD || \
      SANITIZER_LINUX_USES_64BIT_SYSCALLS
  #if SANITIZER_MIPS64 && !SANITIZER_OPENBSD
    // For mips64, fstat syscall fills buffer in the format of kernel_stat
    struct kernel_stat kbuf;
    int res = internal_syscall(SYSCALL(fstat), fd, &kbuf);
    kernel_stat_to_stat(&kbuf, (struct stat *)buf);
    return res;
  # else
    return internal_syscall(SYSCALL(fstat), fd, (uptr)buf);
  # endif
  #else
    struct stat64 buf64;
    int res = internal_syscall(SYSCALL(fstat64), fd, &buf64);
    stat64_to_stat(&buf64, (struct stat *)buf);
    return res;
  #endif
  }
  
  uptr internal_filesize(fd_t fd) {
    struct stat st;
    if (internal_fstat(fd, &st))
      return -1;
    return (uptr)st.st_size;
  }
  
  uptr internal_dup(int oldfd) {
    return internal_syscall(SYSCALL(dup), oldfd);
  }
  
  uptr internal_dup2(int oldfd, int newfd) {
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(dup3), oldfd, newfd, 0);
  #else
    return internal_syscall(SYSCALL(dup2), oldfd, newfd);
  #endif
  }
  
  uptr internal_readlink(const char *path, char *buf, uptr bufsize) {
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(readlinkat), AT_FDCWD, (uptr)path, (uptr)buf,
                            bufsize);
  #elif SANITIZER_OPENBSD
    return internal_syscall(SYSCALL(readlinkat), AT_FDCWD, (uptr)path, (uptr)buf,
                            bufsize);
  #else
    return internal_syscall(SYSCALL(readlink), (uptr)path, (uptr)buf, bufsize);
  #endif
  }
  
  uptr internal_unlink(const char *path) {
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS || SANITIZER_OPENBSD
    return internal_syscall(SYSCALL(unlinkat), AT_FDCWD, (uptr)path, 0);
  #else
    return internal_syscall(SYSCALL(unlink), (uptr)path);
  #endif
  }
  
  uptr internal_rename(const char *oldpath, const char *newpath) {
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS || SANITIZER_OPENBSD
    return internal_syscall(SYSCALL(renameat), AT_FDCWD, (uptr)oldpath, AT_FDCWD,
                            (uptr)newpath);
  #else
    return internal_syscall(SYSCALL(rename), (uptr)oldpath, (uptr)newpath);
  #endif
  }
  
  uptr internal_sched_yield() {
    return internal_syscall(SYSCALL(sched_yield));
  }
  
  void internal__exit(int exitcode) {
  #if SANITIZER_FREEBSD || SANITIZER_OPENBSD
    internal_syscall(SYSCALL(exit), exitcode);
  #else
    internal_syscall(SYSCALL(exit_group), exitcode);
  #endif
    Die();  // Unreachable.
  }
  
  unsigned int internal_sleep(unsigned int seconds) {
    struct timespec ts;
    ts.tv_sec = seconds;
    ts.tv_nsec = 0;
    int res = internal_syscall(SYSCALL(nanosleep), &ts, &ts);
    if (res) return ts.tv_sec;
    return 0;
  }
  
  uptr internal_execve(const char *filename, char *const argv[],
                       char *const envp[]) {
    return internal_syscall(SYSCALL(execve), (uptr)filename, (uptr)argv,
                            (uptr)envp);
  }
  #endif  // !SANITIZER_SOLARIS && !SANITIZER_NETBSD
  
  // ----------------- sanitizer_common.h
  bool FileExists(const char *filename) {
    if (ShouldMockFailureToOpen(filename))
      return false;
    struct stat st;
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    if (internal_syscall(SYSCALL(newfstatat), AT_FDCWD, filename, &st, 0))
  #else
    if (internal_stat(filename, &st))
  #endif
      return false;
    // Sanity check: filename is a regular file.
    return S_ISREG(st.st_mode);
  }
  
  #if !SANITIZER_NETBSD
  tid_t GetTid() {
  #if SANITIZER_FREEBSD
    long Tid;
    thr_self(&Tid);
    return Tid;
  #elif SANITIZER_OPENBSD
    return internal_syscall(SYSCALL(getthrid));
  #elif SANITIZER_SOLARIS
    return thr_self();
  #else
    return internal_syscall(SYSCALL(gettid));
  #endif
  }
  
  int TgKill(pid_t pid, tid_t tid, int sig) {
  #if SANITIZER_LINUX
    return internal_syscall(SYSCALL(tgkill), pid, tid, sig);
  #elif SANITIZER_FREEBSD
    return internal_syscall(SYSCALL(thr_kill2), pid, tid, sig);
  #elif SANITIZER_OPENBSD
    (void)pid;
    return internal_syscall(SYSCALL(thrkill), tid, sig, nullptr);
  #elif SANITIZER_SOLARIS
    (void)pid;
    return thr_kill(tid, sig);
  #endif
  }
  #endif
  
  #if !SANITIZER_SOLARIS && !SANITIZER_NETBSD
  u64 NanoTime() {
  #if SANITIZER_FREEBSD || SANITIZER_OPENBSD
    timeval tv;
  #else
    kernel_timeval tv;
  #endif
    internal_memset(&tv, 0, sizeof(tv));
    internal_syscall(SYSCALL(gettimeofday), &tv, 0);
    return (u64)tv.tv_sec * 1000*1000*1000 + tv.tv_usec * 1000;
  }
  
  uptr internal_clock_gettime(__sanitizer_clockid_t clk_id, void *tp) {
    return internal_syscall(SYSCALL(clock_gettime), clk_id, tp);
  }
  #endif  // !SANITIZER_SOLARIS && !SANITIZER_NETBSD
  
  // Like getenv, but reads env directly from /proc (on Linux) or parses the
  // 'environ' array (on some others) and does not use libc. This function
  // should be called first inside __asan_init.
  const char *GetEnv(const char *name) {
  #if SANITIZER_FREEBSD || SANITIZER_NETBSD || SANITIZER_OPENBSD || \
      SANITIZER_SOLARIS
    if (::environ != 0) {
      uptr NameLen = internal_strlen(name);
      for (char **Env = ::environ; *Env != 0; Env++) {
        if (internal_strncmp(*Env, name, NameLen) == 0 && (*Env)[NameLen] == '=')
          return (*Env) + NameLen + 1;
      }
    }
    return 0;  // Not found.
  #elif SANITIZER_LINUX
    static char *environ;
    static uptr len;
    static bool inited;
    if (!inited) {
      inited = true;
      uptr environ_size;
      if (!ReadFileToBuffer("/proc/self/environ", &environ, &environ_size, &len))
        environ = nullptr;
    }
    if (!environ || len == 0) return nullptr;
    uptr namelen = internal_strlen(name);
    const char *p = environ;
    while (*p != '\0') {  // will happen at the \0\0 that terminates the buffer
      // proc file has the format NAME=value\0NAME=value\0NAME=value\0...
      const char* endp =
          (char*)internal_memchr(p, '\0', len - (p - environ));
      if (!endp)  // this entry isn't NUL terminated
        return nullptr;
      else if (!internal_memcmp(p, name, namelen) && p[namelen] == '=')  // Match.
        return p + namelen + 1;  // point after =
      p = endp + 1;
    }
    return nullptr;  // Not found.
  #else
  #error "Unsupported platform"
  #endif
  }
  
  #if !SANITIZER_FREEBSD && !SANITIZER_NETBSD && !SANITIZER_OPENBSD
  extern "C" {
  SANITIZER_WEAK_ATTRIBUTE extern void *__libc_stack_end;
  }
  #endif
  
  #if !SANITIZER_GO && !SANITIZER_FREEBSD && !SANITIZER_NETBSD &&                \
      !SANITIZER_OPENBSD
  static void ReadNullSepFileToArray(const char *path, char ***arr,
                                     int arr_size) {
    char *buff;
    uptr buff_size;
    uptr buff_len;
    *arr = (char **)MmapOrDie(arr_size * sizeof(char *), "NullSepFileArray");
    if (!ReadFileToBuffer(path, &buff, &buff_size, &buff_len, 1024 * 1024)) {
      (*arr)[0] = nullptr;
      return;
    }
    (*arr)[0] = buff;
    int count, i;
    for (count = 1, i = 1; ; i++) {
      if (buff[i] == 0) {
        if (buff[i+1] == 0) break;
        (*arr)[count] = &buff[i+1];
        CHECK_LE(count, arr_size - 1);  // FIXME: make this more flexible.
        count++;
      }
    }
    (*arr)[count] = nullptr;
  }
  #endif
  
  #if !SANITIZER_OPENBSD
  static void GetArgsAndEnv(char ***argv, char ***envp) {
  #if SANITIZER_FREEBSD
    // On FreeBSD, retrieving the argument and environment arrays is done via the
    // kern.ps_strings sysctl, which returns a pointer to a structure containing
    // this information. See also <sys/exec.h>.
    ps_strings *pss;
    uptr sz = sizeof(pss);
    if (internal_sysctlbyname("kern.ps_strings", &pss, &sz, NULL, 0) == -1) {
      Printf("sysctl kern.ps_strings failed\n");
      Die();
    }
    *argv = pss->ps_argvstr;
    *envp = pss->ps_envstr;
  #elif SANITIZER_NETBSD
    *argv = __ps_strings->ps_argvstr;
    *envp = __ps_strings->ps_envstr;
  #else // SANITIZER_FREEBSD
  #if !SANITIZER_GO
    if (&__libc_stack_end) {
  #endif // !SANITIZER_GO
      uptr* stack_end = (uptr*)__libc_stack_end;
      int argc = *stack_end;
      *argv = (char**)(stack_end + 1);
      *envp = (char**)(stack_end + argc + 2);
  #if !SANITIZER_GO
    } else {
      static const int kMaxArgv = 2000, kMaxEnvp = 2000;
      ReadNullSepFileToArray("/proc/self/cmdline", argv, kMaxArgv);
      ReadNullSepFileToArray("/proc/self/environ", envp, kMaxEnvp);
    }
  #endif // !SANITIZER_GO
  #endif // SANITIZER_FREEBSD
  }
  
  char **GetArgv() {
    char **argv, **envp;
    GetArgsAndEnv(&argv, &envp);
    return argv;
  }
  
  char **GetEnviron() {
    char **argv, **envp;
    GetArgsAndEnv(&argv, &envp);
    return envp;
  }
  
  #endif  // !SANITIZER_OPENBSD
  
  #if !SANITIZER_SOLARIS
  enum MutexState {
    MtxUnlocked = 0,
    MtxLocked = 1,
    MtxSleeping = 2
  };
  
  BlockingMutex::BlockingMutex() {
    internal_memset(this, 0, sizeof(*this));
  }
  
  void BlockingMutex::Lock() {
    CHECK_EQ(owner_, 0);
    atomic_uint32_t *m = reinterpret_cast<atomic_uint32_t *>(&opaque_storage_);
    if (atomic_exchange(m, MtxLocked, memory_order_acquire) == MtxUnlocked)
      return;
    while (atomic_exchange(m, MtxSleeping, memory_order_acquire) != MtxUnlocked) {
  #if SANITIZER_FREEBSD
      _umtx_op(m, UMTX_OP_WAIT_UINT, MtxSleeping, 0, 0);
  #elif SANITIZER_NETBSD
      sched_yield(); /* No userspace futex-like synchronization */
  #else
      internal_syscall(SYSCALL(futex), (uptr)m, FUTEX_WAIT_PRIVATE, MtxSleeping,
                       0, 0, 0);
  #endif
    }
  }
  
  void BlockingMutex::Unlock() {
    atomic_uint32_t *m = reinterpret_cast<atomic_uint32_t *>(&opaque_storage_);
    u32 v = atomic_exchange(m, MtxUnlocked, memory_order_release);
    CHECK_NE(v, MtxUnlocked);
    if (v == MtxSleeping) {
  #if SANITIZER_FREEBSD
      _umtx_op(m, UMTX_OP_WAKE, 1, 0, 0);
  #elif SANITIZER_NETBSD
                     /* No userspace futex-like synchronization */
  #else
      internal_syscall(SYSCALL(futex), (uptr)m, FUTEX_WAKE_PRIVATE, 1, 0, 0, 0);
  #endif
    }
  }
  
  void BlockingMutex::CheckLocked() {
    atomic_uint32_t *m = reinterpret_cast<atomic_uint32_t *>(&opaque_storage_);
    CHECK_NE(MtxUnlocked, atomic_load(m, memory_order_relaxed));
  }
  #endif // !SANITIZER_SOLARIS
  
  // ----------------- sanitizer_linux.h
  // The actual size of this structure is specified by d_reclen.
  // Note that getdents64 uses a different structure format. We only provide the
  // 32-bit syscall here.
  #if SANITIZER_NETBSD
  // Not used
  #elif SANITIZER_OPENBSD
  // struct dirent is different for Linux and us. At this moment, we use only
  // d_fileno (Linux call this d_ino), d_reclen, and d_name.
  struct linux_dirent {
    u64 d_ino;  // d_fileno
    u16 d_reclen;
    u16 d_namlen;  // not used
    u8 d_type;     // not used
    char d_name[NAME_MAX + 1];
  };
  #else
  struct linux_dirent {
  #if SANITIZER_X32 || defined(__aarch64__)
    u64 d_ino;
    u64 d_off;
  #else
    unsigned long      d_ino;
    unsigned long      d_off;
  #endif
    unsigned short     d_reclen;
  #ifdef __aarch64__
    unsigned char      d_type;
  #endif
    char               d_name[256];
  };
  #endif
  
  #if !SANITIZER_SOLARIS && !SANITIZER_NETBSD
  // Syscall wrappers.
  uptr internal_ptrace(int request, int pid, void *addr, void *data) {
    return internal_syscall(SYSCALL(ptrace), request, pid, (uptr)addr,
                            (uptr)data);
  }
  
  uptr internal_waitpid(int pid, int *status, int options) {
    return internal_syscall(SYSCALL(wait4), pid, (uptr)status, options,
                            0 /* rusage */);
  }
  
  uptr internal_getpid() {
    return internal_syscall(SYSCALL(getpid));
  }
  
  uptr internal_getppid() {
    return internal_syscall(SYSCALL(getppid));
  }
  
  uptr internal_getdents(fd_t fd, struct linux_dirent *dirp, unsigned int count) {
  #if SANITIZER_FREEBSD
    return internal_syscall(SYSCALL(getdirentries), fd, (uptr)dirp, count, NULL);
  #elif SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(getdents64), fd, (uptr)dirp, count);
  #else
    return internal_syscall(SYSCALL(getdents), fd, (uptr)dirp, count);
  #endif
  }
  
  uptr internal_lseek(fd_t fd, OFF_T offset, int whence) {
    return internal_syscall(SYSCALL(lseek), fd, offset, whence);
  }
  
  #if SANITIZER_LINUX
  uptr internal_prctl(int option, uptr arg2, uptr arg3, uptr arg4, uptr arg5) {
    return internal_syscall(SYSCALL(prctl), option, arg2, arg3, arg4, arg5);
  }
  #endif
  
  uptr internal_sigaltstack(const void *ss, void *oss) {
    return internal_syscall(SYSCALL(sigaltstack), (uptr)ss, (uptr)oss);
  }
  
  int internal_fork() {
  #if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
    return internal_syscall(SYSCALL(clone), SIGCHLD, 0);
  #else
    return internal_syscall(SYSCALL(fork));
  #endif
  }
  
  #if SANITIZER_FREEBSD || SANITIZER_OPENBSD
  int internal_sysctl(const int *name, unsigned int namelen, void *oldp,
                      uptr *oldlenp, const void *newp, uptr newlen) {
  #if SANITIZER_OPENBSD
    return sysctl(name, namelen, oldp, (size_t *)oldlenp, (void *)newp,
                  (size_t)newlen);
  #else
    return internal_syscall(SYSCALL(__sysctl), name, namelen, oldp,
                            (size_t *)oldlenp, newp, (size_t)newlen);
  #endif
  }
  
  #if SANITIZER_FREEBSD
  int internal_sysctlbyname(const char *sname, void *oldp, uptr *oldlenp,
                            const void *newp, uptr newlen) {
    static decltype(sysctlbyname) *real = nullptr;
    if (!real)
      real = (decltype(sysctlbyname) *)dlsym(RTLD_NEXT, "sysctlbyname");
    CHECK(real);
    return real(sname, oldp, (size_t *)oldlenp, newp, (size_t)newlen);
  }
  #endif
  #endif
  
  #if SANITIZER_LINUX
  #define SA_RESTORER 0x04000000
  // Doesn't set sa_restorer if the caller did not set it, so use with caution
  //(see below).
  int internal_sigaction_norestorer(int signum, const void *act, void *oldact) {
    __sanitizer_kernel_sigaction_t k_act, k_oldact;
    internal_memset(&k_act, 0, sizeof(__sanitizer_kernel_sigaction_t));
    internal_memset(&k_oldact, 0, sizeof(__sanitizer_kernel_sigaction_t));
    const __sanitizer_sigaction *u_act = (const __sanitizer_sigaction *)act;
    __sanitizer_sigaction *u_oldact = (__sanitizer_sigaction *)oldact;
    if (u_act) {
      k_act.handler = u_act->handler;
      k_act.sigaction = u_act->sigaction;
      internal_memcpy(&k_act.sa_mask, &u_act->sa_mask,
                      sizeof(__sanitizer_kernel_sigset_t));
      // Without SA_RESTORER kernel ignores the calls (probably returns EINVAL).
      k_act.sa_flags = u_act->sa_flags | SA_RESTORER;
      // FIXME: most often sa_restorer is unset, however the kernel requires it
      // to point to a valid signal restorer that calls the rt_sigreturn syscall.
      // If sa_restorer passed to the kernel is NULL, the program may crash upon
      // signal delivery or fail to unwind the stack in the signal handler.
      // libc implementation of sigaction() passes its own restorer to
      // rt_sigaction, so we need to do the same (we'll need to reimplement the
      // restorers; for x86_64 the restorer address can be obtained from
      // oldact->sa_restorer upon a call to sigaction(xxx, NULL, oldact).
  #if !SANITIZER_ANDROID || !SANITIZER_MIPS32
      k_act.sa_restorer = u_act->sa_restorer;
  #endif
    }
  
    uptr result = internal_syscall(SYSCALL(rt_sigaction), (uptr)signum,
        (uptr)(u_act ? &k_act : nullptr),
        (uptr)(u_oldact ? &k_oldact : nullptr),
        (uptr)sizeof(__sanitizer_kernel_sigset_t));
  
    if ((result == 0) && u_oldact) {
      u_oldact->handler = k_oldact.handler;
      u_oldact->sigaction = k_oldact.sigaction;
      internal_memcpy(&u_oldact->sa_mask, &k_oldact.sa_mask,
                      sizeof(__sanitizer_kernel_sigset_t));
      u_oldact->sa_flags = k_oldact.sa_flags;
  #if !SANITIZER_ANDROID || !SANITIZER_MIPS32
      u_oldact->sa_restorer = k_oldact.sa_restorer;
  #endif
    }
    return result;
  }
  #endif  // SANITIZER_LINUX
  
  uptr internal_sigprocmask(int how, __sanitizer_sigset_t *set,
                            __sanitizer_sigset_t *oldset) {
  #if SANITIZER_FREEBSD || SANITIZER_OPENBSD
    return internal_syscall(SYSCALL(sigprocmask), how, set, oldset);
  #else
    __sanitizer_kernel_sigset_t *k_set = (__sanitizer_kernel_sigset_t *)set;
    __sanitizer_kernel_sigset_t *k_oldset = (__sanitizer_kernel_sigset_t *)oldset;
    return internal_syscall(SYSCALL(rt_sigprocmask), (uptr)how,
                            (uptr)&k_set->sig[0], (uptr)&k_oldset->sig[0],
                            sizeof(__sanitizer_kernel_sigset_t));
  #endif
  }
  
  void internal_sigfillset(__sanitizer_sigset_t *set) {
    internal_memset(set, 0xff, sizeof(*set));
  }
  
  void internal_sigemptyset(__sanitizer_sigset_t *set) {
    internal_memset(set, 0, sizeof(*set));
  }
  
  #if SANITIZER_LINUX
  void internal_sigdelset(__sanitizer_sigset_t *set, int signum) {
    signum -= 1;
    CHECK_GE(signum, 0);
    CHECK_LT(signum, sizeof(*set) * 8);
    __sanitizer_kernel_sigset_t *k_set = (__sanitizer_kernel_sigset_t *)set;
    const uptr idx = signum / (sizeof(k_set->sig[0]) * 8);
    const uptr bit = signum % (sizeof(k_set->sig[0]) * 8);
    k_set->sig[idx] &= ~(1 << bit);
  }
  
  bool internal_sigismember(__sanitizer_sigset_t *set, int signum) {
    signum -= 1;
    CHECK_GE(signum, 0);
    CHECK_LT(signum, sizeof(*set) * 8);
    __sanitizer_kernel_sigset_t *k_set = (__sanitizer_kernel_sigset_t *)set;
    const uptr idx = signum / (sizeof(k_set->sig[0]) * 8);
    const uptr bit = signum % (sizeof(k_set->sig[0]) * 8);
    return k_set->sig[idx] & (1 << bit);
  }
  #elif SANITIZER_FREEBSD
  void internal_sigdelset(__sanitizer_sigset_t *set, int signum) {
    sigset_t *rset = reinterpret_cast<sigset_t *>(set);
    sigdelset(rset, signum);
  }
  
  bool internal_sigismember(__sanitizer_sigset_t *set, int signum) {
    sigset_t *rset = reinterpret_cast<sigset_t *>(set);
    return sigismember(rset, signum);
  }
  #endif
  #endif // !SANITIZER_SOLARIS
  
  #if !SANITIZER_NETBSD
  // ThreadLister implementation.
  ThreadLister::ThreadLister(pid_t pid) : pid_(pid), buffer_(4096) {
    char task_directory_path[80];
    internal_snprintf(task_directory_path, sizeof(task_directory_path),
                      "/proc/%d/task/", pid);
    descriptor_ = internal_open(task_directory_path, O_RDONLY | O_DIRECTORY);
    if (internal_iserror(descriptor_)) {
      Report("Can't open /proc/%d/task for reading.\n", pid);
    }
  }
  
  ThreadLister::Result ThreadLister::ListThreads(
      InternalMmapVector<tid_t> *threads) {
    if (internal_iserror(descriptor_))
      return Error;
    internal_lseek(descriptor_, 0, SEEK_SET);
    threads->clear();
  
    Result result = Ok;
    for (bool first_read = true;; first_read = false) {
      // Resize to max capacity if it was downsized by IsAlive.
      buffer_.resize(buffer_.capacity());
      CHECK_GE(buffer_.size(), 4096);
      uptr read = internal_getdents(
          descriptor_, (struct linux_dirent *)buffer_.data(), buffer_.size());
      if (!read)
        return result;
      if (internal_iserror(read)) {
        Report("Can't read directory entries from /proc/%d/task.\n", pid_);
        return Error;
      }
  
      for (uptr begin = (uptr)buffer_.data(), end = begin + read; begin < end;) {
        struct linux_dirent *entry = (struct linux_dirent *)begin;
        begin += entry->d_reclen;
        if (entry->d_ino == 1) {
          // Inode 1 is for bad blocks and also can be a reason for early return.
          // Should be emitted if kernel tried to output terminating thread.
          // See proc_task_readdir implementation in Linux.
          result = Incomplete;
        }
        if (entry->d_ino && *entry->d_name >= '0' && *entry->d_name <= '9')
          threads->push_back(internal_atoll(entry->d_name));
      }
  
      // Now we are going to detect short-read or early EOF. In such cases Linux
      // can return inconsistent list with missing alive threads.
      // Code will just remember that the list can be incomplete but it will
      // continue reads to return as much as possible.
      if (!first_read) {
        // The first one was a short-read by definition.
        result = Incomplete;
      } else if (read > buffer_.size() - 1024) {
        // Read was close to the buffer size. So double the size and assume the
        // worst.
        buffer_.resize(buffer_.size() * 2);
        result = Incomplete;
      } else if (!threads->empty() && !IsAlive(threads->back())) {
        // Maybe Linux early returned from read on terminated thread (!pid_alive)
        // and failed to restore read position.
        // See next_tid and proc_task_instantiate in Linux.
        result = Incomplete;
      }
    }
  }
  
  bool ThreadLister::IsAlive(int tid) {
    // /proc/%d/task/%d/status uses same call to detect alive threads as
    // proc_task_readdir. See task_state implementation in Linux.
    char path[80];
    internal_snprintf(path, sizeof(path), "/proc/%d/task/%d/status", pid_, tid);
    if (!ReadFileToVector(path, &buffer_) || buffer_.empty())
      return false;
    buffer_.push_back(0);
    static const char kPrefix[] = "\nPPid:";
    const char *field = internal_strstr(buffer_.data(), kPrefix);
    if (!field)
      return false;
    field += internal_strlen(kPrefix);
    return (int)internal_atoll(field) != 0;
  }
  
  ThreadLister::~ThreadLister() {
    if (!internal_iserror(descriptor_))
      internal_close(descriptor_);
  }
  #endif
  
  #if SANITIZER_WORDSIZE == 32
  // Take care of unusable kernel area in top gigabyte.
  static uptr GetKernelAreaSize() {
  #if SANITIZER_LINUX && !SANITIZER_X32
    const uptr gbyte = 1UL << 30;
  
    // Firstly check if there are writable segments
    // mapped to top gigabyte (e.g. stack).
    MemoryMappingLayout proc_maps(/*cache_enabled*/true);
    if (proc_maps.Error())
      return 0;
    MemoryMappedSegment segment;
    while (proc_maps.Next(&segment)) {
      if ((segment.end >= 3 * gbyte) && segment.IsWritable()) return 0;
    }
  
  #if !SANITIZER_ANDROID
    // Even if nothing is mapped, top Gb may still be accessible
    // if we are running on 64-bit kernel.
    // Uname may report misleading results if personality type
    // is modified (e.g. under schroot) so check this as well.
    struct utsname uname_info;
    int pers = personality(0xffffffffUL);
    if (!(pers & PER_MASK)
        && uname(&uname_info) == 0
        && internal_strstr(uname_info.machine, "64"))
      return 0;
  #endif  // SANITIZER_ANDROID
  
    // Top gigabyte is reserved for kernel.
    return gbyte;
  #else
    return 0;
  #endif  // SANITIZER_LINUX && !SANITIZER_X32
  }
  #endif  // SANITIZER_WORDSIZE == 32
  
  uptr GetMaxVirtualAddress() {
  #if (SANITIZER_NETBSD || SANITIZER_OPENBSD) && defined(__x86_64__)
    return 0x7f7ffffff000ULL;  // (0x00007f8000000000 - PAGE_SIZE)
  #elif SANITIZER_WORDSIZE == 64
  # if defined(__powerpc64__) || defined(__aarch64__)
    // On PowerPC64 we have two different address space layouts: 44- and 46-bit.
    // We somehow need to figure out which one we are using now and choose
    // one of 0x00000fffffffffffUL and 0x00003fffffffffffUL.
    // Note that with 'ulimit -s unlimited' the stack is moved away from the top
    // of the address space, so simply checking the stack address is not enough.
    // This should (does) work for both PowerPC64 Endian modes.
    // Similarly, aarch64 has multiple address space layouts: 39, 42 and 47-bit.
    return (1ULL << (MostSignificantSetBitIndex(GET_CURRENT_FRAME()) + 1)) - 1;
  # elif defined(__mips64)
    return (1ULL << 40) - 1;  // 0x000000ffffffffffUL;
  # elif defined(__s390x__)
    return (1ULL << 53) - 1;  // 0x001fffffffffffffUL;
  #elif defined(__sparc__)
    return ~(uptr)0;
  # else
    return (1ULL << 47) - 1;  // 0x00007fffffffffffUL;
  # endif
  #else  // SANITIZER_WORDSIZE == 32
  # if defined(__s390__)
    return (1ULL << 31) - 1;  // 0x7fffffff;
  # else
    return (1ULL << 32) - 1;  // 0xffffffff;
  # endif
  #endif  // SANITIZER_WORDSIZE
  }
  
  uptr GetMaxUserVirtualAddress() {
    uptr addr = GetMaxVirtualAddress();
  #if SANITIZER_WORDSIZE == 32 && !defined(__s390__)
    if (!common_flags()->full_address_space)
      addr -= GetKernelAreaSize();
    CHECK_LT(reinterpret_cast<uptr>(&addr), addr);
  #endif
    return addr;
  }
  
  #if !SANITIZER_ANDROID
  uptr GetPageSize() {
  #if SANITIZER_LINUX && (defined(__x86_64__) || defined(__i386__))
    return EXEC_PAGESIZE;
  #elif SANITIZER_FREEBSD || SANITIZER_NETBSD
  // Use sysctl as sysconf can trigger interceptors internally.
    int pz = 0;
    uptr pzl = sizeof(pz);
    int mib[2] = {CTL_HW, HW_PAGESIZE};
    int rv = internal_sysctl(mib, 2, &pz, &pzl, nullptr, 0);
    CHECK_EQ(rv, 0);
    return (uptr)pz;
  #elif SANITIZER_USE_GETAUXVAL
    return getauxval(AT_PAGESZ);
  #else
    return sysconf(_SC_PAGESIZE);  // EXEC_PAGESIZE may not be trustworthy.
  #endif
  }
  #endif // !SANITIZER_ANDROID
  
  #if !SANITIZER_OPENBSD
  uptr ReadBinaryName(/*out*/char *buf, uptr buf_len) {
  #if SANITIZER_SOLARIS
    const char *default_module_name = getexecname();
    CHECK_NE(default_module_name, NULL);
    return internal_snprintf(buf, buf_len, "%s", default_module_name);
  #else
  #if SANITIZER_FREEBSD || SANITIZER_NETBSD
  #if SANITIZER_FREEBSD
    const int Mib[4] = {CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1};
  #else
    const int Mib[4] = {CTL_KERN, KERN_PROC_ARGS, -1, KERN_PROC_PATHNAME};
  #endif
    const char *default_module_name = "kern.proc.pathname";
    uptr Size = buf_len;
    bool IsErr =
        (internal_sysctl(Mib, ARRAY_SIZE(Mib), buf, &Size, NULL, 0) != 0);
    int readlink_error = IsErr ? errno : 0;
    uptr module_name_len = Size;
  #else
    const char *default_module_name = "/proc/self/exe";
    uptr module_name_len = internal_readlink(
        default_module_name, buf, buf_len);
    int readlink_error;
    bool IsErr = internal_iserror(module_name_len, &readlink_error);
  #endif  // SANITIZER_SOLARIS
    if (IsErr) {
      // We can't read binary name for some reason, assume it's unknown.
      Report("WARNING: reading executable name failed with errno %d, "
             "some stack frames may not be symbolized\n", readlink_error);
      module_name_len = internal_snprintf(buf, buf_len, "%s",
                                          default_module_name);
      CHECK_LT(module_name_len, buf_len);
    }
    return module_name_len;
  #endif
  }
  #endif // !SANITIZER_OPENBSD
  
  uptr ReadLongProcessName(/*out*/ char *buf, uptr buf_len) {
  #if SANITIZER_LINUX
    char *tmpbuf;
    uptr tmpsize;
    uptr tmplen;
    if (ReadFileToBuffer("/proc/self/cmdline", &tmpbuf, &tmpsize, &tmplen,
                         1024 * 1024)) {
      internal_strncpy(buf, tmpbuf, buf_len);
      UnmapOrDie(tmpbuf, tmpsize);
      return internal_strlen(buf);
    }
  #endif
    return ReadBinaryName(buf, buf_len);
  }
  
  // Match full names of the form /path/to/base_name{-,.}*
  bool LibraryNameIs(const char *full_name, const char *base_name) {
    const char *name = full_name;
    // Strip path.
    while (*name != '\0') name++;
    while (name > full_name && *name != '/') name--;
    if (*name == '/') name++;
    uptr base_name_length = internal_strlen(base_name);
    if (internal_strncmp(name, base_name, base_name_length)) return false;
    return (name[base_name_length] == '-' || name[base_name_length] == '.');
  }
  
  #if !SANITIZER_ANDROID
  // Call cb for each region mapped by map.
  void ForEachMappedRegion(link_map *map, void (*cb)(const void *, uptr)) {
    CHECK_NE(map, nullptr);
  #if !SANITIZER_FREEBSD && !SANITIZER_OPENBSD
    typedef ElfW(Phdr) Elf_Phdr;
    typedef ElfW(Ehdr) Elf_Ehdr;
  #endif // !SANITIZER_FREEBSD && !SANITIZER_OPENBSD
    char *base = (char *)map->l_addr;
    Elf_Ehdr *ehdr = (Elf_Ehdr *)base;
    char *phdrs = base + ehdr->e_phoff;
    char *phdrs_end = phdrs + ehdr->e_phnum * ehdr->e_phentsize;
  
    // Find the segment with the minimum base so we can "relocate" the p_vaddr
    // fields.  Typically ET_DYN objects (DSOs) have base of zero and ET_EXEC
    // objects have a non-zero base.
    uptr preferred_base = (uptr)-1;
    for (char *iter = phdrs; iter != phdrs_end; iter += ehdr->e_phentsize) {
      Elf_Phdr *phdr = (Elf_Phdr *)iter;
      if (phdr->p_type == PT_LOAD && preferred_base > (uptr)phdr->p_vaddr)
        preferred_base = (uptr)phdr->p_vaddr;
    }
  
    // Compute the delta from the real base to get a relocation delta.
    sptr delta = (uptr)base - preferred_base;
    // Now we can figure out what the loader really mapped.
    for (char *iter = phdrs; iter != phdrs_end; iter += ehdr->e_phentsize) {
      Elf_Phdr *phdr = (Elf_Phdr *)iter;
      if (phdr->p_type == PT_LOAD) {
        uptr seg_start = phdr->p_vaddr + delta;
        uptr seg_end = seg_start + phdr->p_memsz;
        // None of these values are aligned.  We consider the ragged edges of the
        // load command as defined, since they are mapped from the file.
        seg_start = RoundDownTo(seg_start, GetPageSizeCached());
        seg_end = RoundUpTo(seg_end, GetPageSizeCached());
        cb((void *)seg_start, seg_end - seg_start);
      }
    }
  }
  #endif
  
  #if defined(__x86_64__) && SANITIZER_LINUX
  // We cannot use glibc's clone wrapper, because it messes with the child
  // task's TLS. It writes the PID and TID of the child task to its thread
  // descriptor, but in our case the child task shares the thread descriptor with
  // the parent (because we don't know how to allocate a new thread
  // descriptor to keep glibc happy). So the stock version of clone(), when
  // used with CLONE_VM, would end up corrupting the parent's thread descriptor.
  uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
                      int *parent_tidptr, void *newtls, int *child_tidptr) {
    long long res;
    if (!fn || !child_stack)
      return -EINVAL;
    CHECK_EQ(0, (uptr)child_stack % 16);
    child_stack = (char *)child_stack - 2 * sizeof(unsigned long long);
    ((unsigned long long *)child_stack)[0] = (uptr)fn;
    ((unsigned long long *)child_stack)[1] = (uptr)arg;
    register void *r8 __asm__("r8") = newtls;
    register int *r10 __asm__("r10") = child_tidptr;
    __asm__ __volatile__(
                         /* %rax = syscall(%rax = SYSCALL(clone),
                          *                %rdi = flags,
                          *                %rsi = child_stack,
                          *                %rdx = parent_tidptr,
                          *                %r8  = new_tls,
                          *                %r10 = child_tidptr)
                          */
                         "syscall\n"
  
                         /* if (%rax != 0)
                          *   return;
                          */
                         "testq  %%rax,%%rax\n"
                         "jnz    1f\n"
  
                         /* In the child. Terminate unwind chain. */
                         // XXX: We should also terminate the CFI unwind chain
                         // here. Unfortunately clang 3.2 doesn't support the
                         // necessary CFI directives, so we skip that part.
                         "xorq   %%rbp,%%rbp\n"
  
                         /* Call "fn(arg)". */
                         "popq   %%rax\n"
                         "popq   %%rdi\n"
                         "call   *%%rax\n"
  
                         /* Call _exit(%rax). */
                         "movq   %%rax,%%rdi\n"
                         "movq   %2,%%rax\n"
                         "syscall\n"
  
                         /* Return to parent. */
                       "1:\n"
                         : "=a" (res)
                         : "a"(SYSCALL(clone)), "i"(SYSCALL(exit)),
                           "S"(child_stack),
                           "D"(flags),
                           "d"(parent_tidptr),
                           "r"(r8),
                           "r"(r10)
                         : "memory", "r11", "rcx");
    return res;
  }
  #elif defined(__mips__)
  uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
                      int *parent_tidptr, void *newtls, int *child_tidptr) {
    long long res;
    if (!fn || !child_stack)
      return -EINVAL;
    CHECK_EQ(0, (uptr)child_stack % 16);
    child_stack = (char *)child_stack - 2 * sizeof(unsigned long long);
    ((unsigned long long *)child_stack)[0] = (uptr)fn;
    ((unsigned long long *)child_stack)[1] = (uptr)arg;
    register void *a3 __asm__("$7") = newtls;
    register int *a4 __asm__("$8") = child_tidptr;
    // We don't have proper CFI directives here because it requires alot of code
    // for very marginal benefits.
    __asm__ __volatile__(
                         /* $v0 = syscall($v0 = __NR_clone,
                          * $a0 = flags,
                          * $a1 = child_stack,
                          * $a2 = parent_tidptr,
                          * $a3 = new_tls,
                          * $a4 = child_tidptr)
                          */
                         ".cprestore 16;\n"
                         "move $4,%1;\n"
                         "move $5,%2;\n"
                         "move $6,%3;\n"
                         "move $7,%4;\n"
                         /* Store the fifth argument on stack
                          * if we are using 32-bit abi.
                          */
  #if SANITIZER_WORDSIZE == 32
                         "lw %5,16($29);\n"
  #else
                         "move $8,%5;\n"
  #endif
                         "li $2,%6;\n"
                         "syscall;\n"
  
                         /* if ($v0 != 0)
                          * return;
                          */
                         "bnez $2,1f;\n"
  
                         /* Call "fn(arg)". */
  #if SANITIZER_WORDSIZE == 32
  #ifdef __BIG_ENDIAN__
                         "lw $25,4($29);\n"
                         "lw $4,12($29);\n"
  #else
                         "lw $25,0($29);\n"
                         "lw $4,8($29);\n"
  #endif
  #else
                         "ld $25,0($29);\n"
                         "ld $4,8($29);\n"
  #endif
                         "jal $25;\n"
  
                         /* Call _exit($v0). */
                         "move $4,$2;\n"
                         "li $2,%7;\n"
                         "syscall;\n"
  
                         /* Return to parent. */
                       "1:\n"
                         : "=r" (res)
                         : "r"(flags),
                           "r"(child_stack),
                           "r"(parent_tidptr),
                           "r"(a3),
                           "r"(a4),
                           "i"(__NR_clone),
                           "i"(__NR_exit)
                         : "memory", "$29" );
    return res;
  }
  #elif defined(__aarch64__)
  uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
                      int *parent_tidptr, void *newtls, int *child_tidptr) {
    long long res;
    if (!fn || !child_stack)
      return -EINVAL;
    CHECK_EQ(0, (uptr)child_stack % 16);
    child_stack = (char *)child_stack - 2 * sizeof(unsigned long long);
    ((unsigned long long *)child_stack)[0] = (uptr)fn;
    ((unsigned long long *)child_stack)[1] = (uptr)arg;
  
    register int (*__fn)(void *)  __asm__("x0") = fn;
    register void *__stack __asm__("x1") = child_stack;
    register int   __flags __asm__("x2") = flags;
    register void *__arg   __asm__("x3") = arg;
    register int  *__ptid  __asm__("x4") = parent_tidptr;
    register void *__tls   __asm__("x5") = newtls;
    register int  *__ctid  __asm__("x6") = child_tidptr;
  
    __asm__ __volatile__(
                         "mov x0,x2\n" /* flags  */
                         "mov x2,x4\n" /* ptid  */
                         "mov x3,x5\n" /* tls  */
                         "mov x4,x6\n" /* ctid  */
                         "mov x8,%9\n" /* clone  */
  
                         "svc 0x0\n"
  
                         /* if (%r0 != 0)
                          *   return %r0;
                          */
                         "cmp x0, #0\n"
                         "bne 1f\n"
  
                         /* In the child, now. Call "fn(arg)". */
                         "ldp x1, x0, [sp], #16\n"
                         "blr x1\n"
  
                         /* Call _exit(%r0).  */
                         "mov x8, %10\n"
                         "svc 0x0\n"
                       "1:\n"
  
                         : "=r" (res)
                         : "i"(-EINVAL),
                           "r"(__fn), "r"(__stack), "r"(__flags), "r"(__arg),
                           "r"(__ptid), "r"(__tls), "r"(__ctid),
                           "i"(__NR_clone), "i"(__NR_exit)
                         : "x30", "memory");
    return res;
  }
  #elif defined(__powerpc64__)
  uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
                     int *parent_tidptr, void *newtls, int *child_tidptr) {
    long long res;
  // Stack frame structure.
  #if SANITIZER_PPC64V1
  //   Back chain == 0        (SP + 112)
  // Frame (112 bytes):
  //   Parameter save area    (SP + 48), 8 doublewords
  //   TOC save area          (SP + 40)
  //   Link editor doubleword (SP + 32)
  //   Compiler doubleword    (SP + 24)
  //   LR save area           (SP + 16)
  //   CR save area           (SP + 8)
  //   Back chain             (SP + 0)
  # define FRAME_SIZE 112
  # define FRAME_TOC_SAVE_OFFSET 40
  #elif SANITIZER_PPC64V2
  //   Back chain == 0        (SP + 32)
  // Frame (32 bytes):
  //   TOC save area          (SP + 24)
  //   LR save area           (SP + 16)
  //   CR save area           (SP + 8)
  //   Back chain             (SP + 0)
  # define FRAME_SIZE 32
  # define FRAME_TOC_SAVE_OFFSET 24
  #else
  # error "Unsupported PPC64 ABI"
  #endif
    if (!fn || !child_stack)
      return -EINVAL;
    CHECK_EQ(0, (uptr)child_stack % 16);
  
    register int (*__fn)(void *) __asm__("r3") = fn;
    register void *__cstack      __asm__("r4") = child_stack;
    register int __flags         __asm__("r5") = flags;
    register void *__arg         __asm__("r6") = arg;
    register int *__ptidptr      __asm__("r7") = parent_tidptr;
    register void *__newtls      __asm__("r8") = newtls;
    register int *__ctidptr      __asm__("r9") = child_tidptr;
  
   __asm__ __volatile__(
             /* fn and arg are saved across the syscall */
             "mr 28, %5\n\t"
             "mr 27, %8\n\t"
  
             /* syscall
               r0 == __NR_clone
               r3 == flags
               r4 == child_stack
               r5 == parent_tidptr
               r6 == newtls
               r7 == child_tidptr */
             "mr 3, %7\n\t"
             "mr 5, %9\n\t"
             "mr 6, %10\n\t"
             "mr 7, %11\n\t"
             "li 0, %3\n\t"
             "sc\n\t"
  
             /* Test if syscall was successful */
             "cmpdi  cr1, 3, 0\n\t"
             "crandc cr1*4+eq, cr1*4+eq, cr0*4+so\n\t"
             "bne-   cr1, 1f\n\t"
  
             /* Set up stack frame */
             "li    29, 0\n\t"
             "stdu  29, -8(1)\n\t"
             "stdu  1, -%12(1)\n\t"
             /* Do the function call */
             "std   2, %13(1)\n\t"
  #if SANITIZER_PPC64V1
             "ld    0, 0(28)\n\t"
             "ld    2, 8(28)\n\t"
             "mtctr 0\n\t"
  #elif SANITIZER_PPC64V2
             "mr    12, 28\n\t"
             "mtctr 12\n\t"
  #else
  # error "Unsupported PPC64 ABI"
  #endif
             "mr    3, 27\n\t"
             "bctrl\n\t"
             "ld    2, %13(1)\n\t"
  
             /* Call _exit(r3) */
             "li 0, %4\n\t"
             "sc\n\t"
  
             /* Return to parent */
             "1:\n\t"
             "mr %0, 3\n\t"
               : "=r" (res)
               : "0" (-1),
                 "i" (EINVAL),
                 "i" (__NR_clone),
                 "i" (__NR_exit),
                 "r" (__fn),
                 "r" (__cstack),
                 "r" (__flags),
                 "r" (__arg),
                 "r" (__ptidptr),
                 "r" (__newtls),
                 "r" (__ctidptr),
                 "i" (FRAME_SIZE),
                 "i" (FRAME_TOC_SAVE_OFFSET)
               : "cr0", "cr1", "memory", "ctr", "r0", "r27", "r28", "r29");
    return res;
  }
  #elif defined(__i386__) && SANITIZER_LINUX
  uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
                      int *parent_tidptr, void *newtls, int *child_tidptr) {
    int res;
    if (!fn || !child_stack)
      return -EINVAL;
    CHECK_EQ(0, (uptr)child_stack % 16);
    child_stack = (char *)child_stack - 7 * sizeof(unsigned int);
    ((unsigned int *)child_stack)[0] = (uptr)flags;
    ((unsigned int *)child_stack)[1] = (uptr)0;
    ((unsigned int *)child_stack)[2] = (uptr)fn;
    ((unsigned int *)child_stack)[3] = (uptr)arg;
    __asm__ __volatile__(
                         /* %eax = syscall(%eax = SYSCALL(clone),
                          *                %ebx = flags,
                          *                %ecx = child_stack,
                          *                %edx = parent_tidptr,
                          *                %esi  = new_tls,
                          *                %edi = child_tidptr)
                          */
  
                          /* Obtain flags */
                          "movl    (%%ecx), %%ebx\n"
                          /* Do the system call */
                          "pushl   %%ebx\n"
                          "pushl   %%esi\n"
                          "pushl   %%edi\n"
                          /* Remember the flag value.  */
                          "movl    %%ebx, (%%ecx)\n"
                          "int     $0x80\n"
                          "popl    %%edi\n"
                          "popl    %%esi\n"
                          "popl    %%ebx\n"
  
                          /* if (%eax != 0)
                           *   return;
                           */
  
                          "test    %%eax,%%eax\n"
                          "jnz    1f\n"
  
                          /* terminate the stack frame */
                          "xorl   %%ebp,%%ebp\n"
                          /* Call FN. */
                          "call    *%%ebx\n"
  #ifdef PIC
                          "call    here\n"
                          "here:\n"
                          "popl    %%ebx\n"
                          "addl    $_GLOBAL_OFFSET_TABLE_+[.-here], %%ebx\n"
  #endif
                          /* Call exit */
                          "movl    %%eax, %%ebx\n"
                          "movl    %2, %%eax\n"
                          "int     $0x80\n"
                          "1:\n"
                         : "=a" (res)
                         : "a"(SYSCALL(clone)), "i"(SYSCALL(exit)),
                           "c"(child_stack),
                           "d"(parent_tidptr),
                           "S"(newtls),
                           "D"(child_tidptr)
                         : "memory");
    return res;
  }
  #elif defined(__arm__) && SANITIZER_LINUX
  uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
                      int *parent_tidptr, void *newtls, int *child_tidptr) {
    unsigned int res;
    if (!fn || !child_stack)
      return -EINVAL;
    child_stack = (char *)child_stack - 2 * sizeof(unsigned int);
    ((unsigned int *)child_stack)[0] = (uptr)fn;
    ((unsigned int *)child_stack)[1] = (uptr)arg;
    register int r0 __asm__("r0") = flags;
    register void *r1 __asm__("r1") = child_stack;
    register int *r2 __asm__("r2") = parent_tidptr;
    register void *r3 __asm__("r3") = newtls;
    register int *r4 __asm__("r4") = child_tidptr;
    register int r7 __asm__("r7") = __NR_clone;
  
  #if __ARM_ARCH > 4 || defined (__ARM_ARCH_4T__)
  # define ARCH_HAS_BX
  #endif
  #if __ARM_ARCH > 4
  # define ARCH_HAS_BLX
  #endif
  
  #ifdef ARCH_HAS_BX
  # ifdef ARCH_HAS_BLX
  #  define BLX(R) "blx "  #R "\n"
  # else
  #  define BLX(R) "mov lr, pc; bx " #R "\n"
  # endif
  #else
  # define BLX(R)  "mov lr, pc; mov pc," #R "\n"
  #endif
  
    __asm__ __volatile__(
                         /* %r0 = syscall(%r7 = SYSCALL(clone),
                          *               %r0 = flags,
                          *               %r1 = child_stack,
                          *               %r2 = parent_tidptr,
                          *               %r3  = new_tls,
                          *               %r4 = child_tidptr)
                          */
  
                         /* Do the system call */
                         "swi 0x0\n"
  
                         /* if (%r0 != 0)
                          *   return %r0;
                          */
                         "cmp r0, #0\n"
                         "bne 1f\n"
  
                         /* In the child, now. Call "fn(arg)". */
                         "ldr r0, [sp, #4]\n"
                         "ldr ip, [sp], #8\n"
                         BLX(ip)
                         /* Call _exit(%r0). */
                         "mov r7, %7\n"
                         "swi 0x0\n"
                         "1:\n"
                         "mov %0, r0\n"
                         : "=r"(res)
                         : "r"(r0), "r"(r1), "r"(r2), "r"(r3), "r"(r4), "r"(r7),
                           "i"(__NR_exit)
                         : "memory");
    return res;
  }
  #endif  // defined(__x86_64__) && SANITIZER_LINUX
  
  #if SANITIZER_ANDROID
  #if __ANDROID_API__ < 21
  extern "C" __attribute__((weak)) int dl_iterate_phdr(
      int (*)(struct dl_phdr_info *, size_t, void *), void *);
  #endif
  
  static int dl_iterate_phdr_test_cb(struct dl_phdr_info *info, size_t size,
                                     void *data) {
    // Any name starting with "lib" indicates a bug in L where library base names
    // are returned instead of paths.
    if (info->dlpi_name && info->dlpi_name[0] == 'l' &&
        info->dlpi_name[1] == 'i' && info->dlpi_name[2] == 'b') {
      *(bool *)data = true;
      return 1;
    }
    return 0;
  }
  
  static atomic_uint32_t android_api_level;
  
  static AndroidApiLevel AndroidDetectApiLevelStatic() {
  #if __ANDROID_API__ <= 19
    return ANDROID_KITKAT;
  #elif __ANDROID_API__ <= 22
    return ANDROID_LOLLIPOP_MR1;
  #else
    return ANDROID_POST_LOLLIPOP;
  #endif
  }
  
  static AndroidApiLevel AndroidDetectApiLevel() {
    if (!&dl_iterate_phdr)
      return ANDROID_KITKAT; // K or lower
    bool base_name_seen = false;
    dl_iterate_phdr(dl_iterate_phdr_test_cb, &base_name_seen);
    if (base_name_seen)
      return ANDROID_LOLLIPOP_MR1; // L MR1
    return ANDROID_POST_LOLLIPOP;   // post-L
    // Plain L (API level 21) is completely broken wrt ASan and not very
    // interesting to detect.
  }
  
  extern "C" __attribute__((weak)) void* _DYNAMIC;
  
  AndroidApiLevel AndroidGetApiLevel() {
    AndroidApiLevel level =
        (AndroidApiLevel)atomic_load(&android_api_level, memory_order_relaxed);
    if (level) return level;
    level = &_DYNAMIC == nullptr ? AndroidDetectApiLevelStatic()
                                 : AndroidDetectApiLevel();
    atomic_store(&android_api_level, level, memory_order_relaxed);
    return level;
  }
  
  #endif
  
  static HandleSignalMode GetHandleSignalModeImpl(int signum) {
    switch (signum) {
      case SIGABRT:
        return common_flags()->handle_abort;
      case SIGILL:
        return common_flags()->handle_sigill;
      case SIGTRAP:
        return common_flags()->handle_sigtrap;
      case SIGFPE:
        return common_flags()->handle_sigfpe;
      case SIGSEGV:
        return common_flags()->handle_segv;
      case SIGBUS:
        return common_flags()->handle_sigbus;
    }
    return kHandleSignalNo;
  }
  
  HandleSignalMode GetHandleSignalMode(int signum) {
    HandleSignalMode result = GetHandleSignalModeImpl(signum);
    if (result == kHandleSignalYes && !common_flags()->allow_user_segv_handler)
      return kHandleSignalExclusive;
    return result;
  }
  
  #if !SANITIZER_GO
  void *internal_start_thread(void(*func)(void *arg), void *arg) {
    // Start the thread with signals blocked, otherwise it can steal user signals.
    __sanitizer_sigset_t set, old;
    internal_sigfillset(&set);
  #if SANITIZER_LINUX && !SANITIZER_ANDROID
    // Glibc uses SIGSETXID signal during setuid call. If this signal is blocked
    // on any thread, setuid call hangs (see test/tsan/setuid.c).
    internal_sigdelset(&set, 33);
  #endif
    internal_sigprocmask(SIG_SETMASK, &set, &old);
    void *th;
    real_pthread_create(&th, nullptr, (void*(*)(void *arg))func, arg);
    internal_sigprocmask(SIG_SETMASK, &old, nullptr);
    return th;
  }
  
  void internal_join_thread(void *th) {
    real_pthread_join(th, nullptr);
  }
  #else
  void *internal_start_thread(void (*func)(void *), void *arg) { return 0; }
  
  void internal_join_thread(void *th) {}
  #endif
  
  #if defined(__aarch64__)
  // Android headers in the older NDK releases miss this definition.
  struct __sanitizer_esr_context {
    struct _aarch64_ctx head;
    uint64_t esr;
  };
  
  static bool Aarch64GetESR(ucontext_t *ucontext, u64 *esr) {
    static const u32 kEsrMagic = 0x45535201;
    u8 *aux = ucontext->uc_mcontext.__reserved;
    while (true) {
      _aarch64_ctx *ctx = (_aarch64_ctx *)aux;
      if (ctx->size == 0) break;
      if (ctx->magic == kEsrMagic) {
        *esr = ((__sanitizer_esr_context *)ctx)->esr;
        return true;
      }
      aux += ctx->size;
    }
    return false;
  }
  #endif
  
  #if SANITIZER_OPENBSD
  using Context = sigcontext;
  #else
  using Context = ucontext_t;
  #endif
  
  SignalContext::WriteFlag SignalContext::GetWriteFlag() const {
    Context *ucontext = (Context *)context;
  #if defined(__x86_64__) || defined(__i386__)
    static const uptr PF_WRITE = 1U << 1;
  #if SANITIZER_FREEBSD
    uptr err = ucontext->uc_mcontext.mc_err;
  #elif SANITIZER_NETBSD
    uptr err = ucontext->uc_mcontext.__gregs[_REG_ERR];
  #elif SANITIZER_OPENBSD
    uptr err = ucontext->sc_err;
  #elif SANITIZER_SOLARIS && defined(__i386__)
    const int Err = 13;
    uptr err = ucontext->uc_mcontext.gregs[Err];
  #else
    uptr err = ucontext->uc_mcontext.gregs[REG_ERR];
  #endif // SANITIZER_FREEBSD
    return err & PF_WRITE ? WRITE : READ;
  #elif defined(__mips__)
    uint32_t *exception_source;
    uint32_t faulty_instruction;
    uint32_t op_code;
  
    exception_source = (uint32_t *)ucontext->uc_mcontext.pc;
    faulty_instruction = (uint32_t)(*exception_source);
  
    op_code = (faulty_instruction >> 26) & 0x3f;
  
    // FIXME: Add support for FPU, microMIPS, DSP, MSA memory instructions.
    switch (op_code) {
      case 0x28:  // sb
      case 0x29:  // sh
      case 0x2b:  // sw
      case 0x3f:  // sd
  #if __mips_isa_rev < 6
      case 0x2c:  // sdl
      case 0x2d:  // sdr
      case 0x2a:  // swl
      case 0x2e:  // swr
  #endif
        return SignalContext::WRITE;
  
      case 0x20:  // lb
      case 0x24:  // lbu
      case 0x21:  // lh
      case 0x25:  // lhu
      case 0x23:  // lw
      case 0x27:  // lwu
      case 0x37:  // ld
  #if __mips_isa_rev < 6
      case 0x1a:  // ldl
      case 0x1b:  // ldr
      case 0x22:  // lwl
      case 0x26:  // lwr
  #endif
        return SignalContext::READ;
  #if __mips_isa_rev == 6
      case 0x3b:  // pcrel
        op_code = (faulty_instruction >> 19) & 0x3;
        switch (op_code) {
          case 0x1:  // lwpc
          case 0x2:  // lwupc
            return SignalContext::READ;
        }
  #endif
    }
    return SignalContext::UNKNOWN;
  #elif defined(__arm__)
    static const uptr FSR_WRITE = 1U << 11;
    uptr fsr = ucontext->uc_mcontext.error_code;
    return fsr & FSR_WRITE ? WRITE : READ;
  #elif defined(__aarch64__)
    static const u64 ESR_ELx_WNR = 1U << 6;
    u64 esr;
    if (!Aarch64GetESR(ucontext, &esr)) return UNKNOWN;
    return esr & ESR_ELx_WNR ? WRITE : READ;
  #elif defined(__sparc__)
    // Decode the instruction to determine the access type.
    // From OpenSolaris $SRC/uts/sun4/os/trap.c (get_accesstype).
  #if SANITIZER_SOLARIS
    uptr pc = ucontext->uc_mcontext.gregs[REG_PC];
  #else
    // Historical BSDism here.
    struct sigcontext *scontext = (struct sigcontext *)context;
  #if defined(__arch64__)
    uptr pc = scontext->sigc_regs.tpc;
  #else
    uptr pc = scontext->si_regs.pc;
  #endif
  #endif
    u32 instr = *(u32 *)pc;
    return (instr >> 21) & 1 ? WRITE: READ;
  #else
    (void)ucontext;
    return UNKNOWN;  // FIXME: Implement.
  #endif
  }
  
  void SignalContext::DumpAllRegisters(void *context) {
    // FIXME: Implement this.
  }
  
  static void GetPcSpBp(void *context, uptr *pc, uptr *sp, uptr *bp) {
  #if SANITIZER_NETBSD
    // This covers all NetBSD architectures
    ucontext_t *ucontext = (ucontext_t *)context;
    *pc = _UC_MACHINE_PC(ucontext);
    *bp = _UC_MACHINE_FP(ucontext);
    *sp = _UC_MACHINE_SP(ucontext);
  #elif defined(__arm__)
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.arm_pc;
    *bp = ucontext->uc_mcontext.arm_fp;
    *sp = ucontext->uc_mcontext.arm_sp;
  #elif defined(__aarch64__)
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.pc;
    *bp = ucontext->uc_mcontext.regs[29];
    *sp = ucontext->uc_mcontext.sp;
  #elif defined(__hppa__)
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.sc_iaoq[0];
    /* GCC uses %r3 whenever a frame pointer is needed.  */
    *bp = ucontext->uc_mcontext.sc_gr[3];
    *sp = ucontext->uc_mcontext.sc_gr[30];
  #elif defined(__x86_64__)
  # if SANITIZER_FREEBSD
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.mc_rip;
    *bp = ucontext->uc_mcontext.mc_rbp;
    *sp = ucontext->uc_mcontext.mc_rsp;
  #elif SANITIZER_OPENBSD
    sigcontext *ucontext = (sigcontext *)context;
    *pc = ucontext->sc_rip;
    *bp = ucontext->sc_rbp;
    *sp = ucontext->sc_rsp;
  # else
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.gregs[REG_RIP];
    *bp = ucontext->uc_mcontext.gregs[REG_RBP];
    *sp = ucontext->uc_mcontext.gregs[REG_RSP];
  # endif
  #elif defined(__i386__)
  # if SANITIZER_FREEBSD
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.mc_eip;
    *bp = ucontext->uc_mcontext.mc_ebp;
    *sp = ucontext->uc_mcontext.mc_esp;
  #elif SANITIZER_OPENBSD
    sigcontext *ucontext = (sigcontext *)context;
    *pc = ucontext->sc_eip;
    *bp = ucontext->sc_ebp;
    *sp = ucontext->sc_esp;
  # else
    ucontext_t *ucontext = (ucontext_t*)context;
  # if SANITIZER_SOLARIS
    /* Use the numeric values: the symbolic ones are undefined by llvm
       include/llvm/Support/Solaris.h.  */
  # ifndef REG_EIP
  #  define REG_EIP 14 // REG_PC
  # endif
  # ifndef REG_EBP
  #  define REG_EBP  6 // REG_FP
  # endif
  # ifndef REG_ESP
  #  define REG_ESP 17 // REG_SP
  # endif
  # endif
    *pc = ucontext->uc_mcontext.gregs[REG_EIP];
    *bp = ucontext->uc_mcontext.gregs[REG_EBP];
    *sp = ucontext->uc_mcontext.gregs[REG_ESP];
  # endif
  #elif defined(__powerpc__) || defined(__powerpc64__)
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.regs->nip;
    *sp = ucontext->uc_mcontext.regs->gpr[PT_R1];
    // The powerpc{,64}-linux ABIs do not specify r31 as the frame
    // pointer, but GCC always uses r31 when we need a frame pointer.
    *bp = ucontext->uc_mcontext.regs->gpr[PT_R31];
  #elif defined(__sparc__)
  #if defined(__arch64__) || defined(__sparcv9)
  #define STACK_BIAS 2047
  #else
  #define STACK_BIAS 0
  # endif
  # if SANITIZER_SOLARIS
    ucontext_t *ucontext = (ucontext_t *)context;
    *pc = ucontext->uc_mcontext.gregs[REG_PC];
    *sp = ucontext->uc_mcontext.gregs[REG_O6] + STACK_BIAS;
  #else
    // Historical BSDism here.
    struct sigcontext *scontext = (struct sigcontext *)context;
  #if defined(__arch64__)
    *pc = scontext->sigc_regs.tpc;
    *sp = scontext->sigc_regs.u_regs[14] + STACK_BIAS;
  #else
    *pc = scontext->si_regs.pc;
    *sp = scontext->si_regs.u_regs[14];
  #endif
  # endif
    *bp = (uptr)((uhwptr *)*sp)[14] + STACK_BIAS;
  #elif defined(__mips__)
    ucontext_t *ucontext = (ucontext_t*)context;
    *pc = ucontext->uc_mcontext.pc;
    *bp = ucontext->uc_mcontext.gregs[30];
    *sp = ucontext->uc_mcontext.gregs[29];
  #elif defined(__s390__)
    ucontext_t *ucontext = (ucontext_t*)context;
  # if defined(__s390x__)
    *pc = ucontext->uc_mcontext.psw.addr;
  # else
    *pc = ucontext->uc_mcontext.psw.addr & 0x7fffffff;
  # endif
    *bp = ucontext->uc_mcontext.gregs[11];
    *sp = ucontext->uc_mcontext.gregs[15];
  #else
  # error "Unsupported arch"
  #endif
  }
  
  void SignalContext::InitPcSpBp() { GetPcSpBp(context, &pc, &sp, &bp); }
  
  void InitializePlatformEarly() {
    // Do nothing.
  }
  
  void MaybeReexec() {
    // No need to re-exec on Linux.
  }
  
  void CheckASLR() {
  #if SANITIZER_NETBSD
    int mib[3];
    int paxflags;
    uptr len = sizeof(paxflags);
  
    mib[0] = CTL_PROC;
    mib[1] = internal_getpid();
    mib[2] = PROC_PID_PAXFLAGS;
  
    if (UNLIKELY(internal_sysctl(mib, 3, &paxflags, &len, NULL, 0) == -1)) {
      Printf("sysctl failed\n");
      Die();
    }
  
    if (UNLIKELY(paxflags & CTL_PROC_PAXFLAGS_ASLR)) {
      Printf("This sanitizer is not compatible with enabled ASLR\n");
      Die();
    }
  #elif SANITIZER_PPC64V2
    // Disable ASLR for Linux PPC64LE.
    int old_personality = personality(0xffffffff);
    if (old_personality != -1 && (old_personality & ADDR_NO_RANDOMIZE) == 0) {
      VReport(1, "WARNING: Program is being run with address space layout "
                 "randomization (ASLR) enabled which prevents the thread and "
                 "memory sanitizers from working on powerpc64le.\n"
                 "ASLR will be disabled and the program re-executed.\n");
      CHECK_NE(personality(old_personality | ADDR_NO_RANDOMIZE), -1);
      ReExec();
    }
  #elif SANITIZER_FREEBSD
    int aslr_pie;
    uptr len = sizeof(aslr_pie);
  #if SANITIZER_WORDSIZE == 64
    if (UNLIKELY(internal_sysctlbyname("kern.elf64.aslr.pie_enable",
        &aslr_pie, &len, NULL, 0) == -1)) {
      // We're making things less 'dramatic' here since
      // the OID is not necessarily guaranteed to be here
      // just yet regarding FreeBSD release
      return;
    }
  
    if (aslr_pie > 0) {
      Printf("This sanitizer is not compatible with enabled ASLR "
             "and binaries compiled with PIE\n");
      Die();
    }
  #endif
    // there might be 32 bits compat for 64 bits
    if (UNLIKELY(internal_sysctlbyname("kern.elf32.aslr.pie_enable",
        &aslr_pie, &len, NULL, 0) == -1)) {
      return;
    }
  
    if (aslr_pie > 0) {
      Printf("This sanitizer is not compatible with enabled ASLR "
             "and binaries compiled with PIE\n");
      Die();
    }
  #else
    // Do nothing
  #endif
  }
  
  void CheckMPROTECT() {
  #if SANITIZER_NETBSD
    int mib[3];
    int paxflags;
    uptr len = sizeof(paxflags);
  
    mib[0] = CTL_PROC;
    mib[1] = internal_getpid();
    mib[2] = PROC_PID_PAXFLAGS;
  
    if (UNLIKELY(internal_sysctl(mib, 3, &paxflags, &len, NULL, 0) == -1)) {
      Printf("sysctl failed\n");
      Die();
    }
  
    if (UNLIKELY(paxflags & CTL_PROC_PAXFLAGS_MPROTECT)) {
      Printf("This sanitizer is not compatible with enabled MPROTECT\n");
      Die();
    }
  #else
    // Do nothing
  #endif
  }
  
  void PrintModuleMap() { }
  
  void CheckNoDeepBind(const char *filename, int flag) {
  #ifdef RTLD_DEEPBIND
    if (flag & RTLD_DEEPBIND) {
      Report(
          "You are trying to dlopen a %s shared library with RTLD_DEEPBIND flag"
          " which is incompatibe with sanitizer runtime "
          "(see https://github.com/google/sanitizers/issues/611 for details"
          "). If you want to run %s library under sanitizers please remove "
          "RTLD_DEEPBIND from dlopen flags.\n",
          filename, filename);
      Die();
    }
  #endif
  }
  
  uptr FindAvailableMemoryRange(uptr size, uptr alignment, uptr left_padding,
                                uptr *largest_gap_found,
                                uptr *max_occupied_addr) {
    UNREACHABLE("FindAvailableMemoryRange is not available");
    return 0;
  }
  
  bool GetRandom(void *buffer, uptr length, bool blocking) {
    if (!buffer || !length || length > 256)
      return false;
  #if SANITIZER_USE_GETENTROPY
    uptr rnd = getentropy(buffer, length);
    int rverrno = 0;
    if (internal_iserror(rnd, &rverrno) && rverrno == EFAULT)
      return false;
    else if (rnd == 0)
      return true;
  #endif // SANITIZER_USE_GETENTROPY
  
  #if SANITIZER_USE_GETRANDOM
    static atomic_uint8_t skip_getrandom_syscall;
    if (!atomic_load_relaxed(&skip_getrandom_syscall)) {
      // Up to 256 bytes, getrandom will not be interrupted.
      uptr res = internal_syscall(SYSCALL(getrandom), buffer, length,
                                  blocking ? 0 : GRND_NONBLOCK);
      int rverrno = 0;
      if (internal_iserror(res, &rverrno) && rverrno == ENOSYS)
        atomic_store_relaxed(&skip_getrandom_syscall, 1);
      else if (res == length)
        return true;
    }
  #endif // SANITIZER_USE_GETRANDOM
    // Up to 256 bytes, a read off /dev/urandom will not be interrupted.
    // blocking is moot here, O_NONBLOCK has no effect when opening /dev/urandom.
    uptr fd = internal_open("/dev/urandom", O_RDONLY);
    if (internal_iserror(fd))
      return false;
    uptr res = internal_read(fd, buffer, length);
    if (internal_iserror(res))
      return false;
    internal_close(fd);
    return true;
  }
  
  } // namespace __sanitizer
  
  #endif
  