diff --git a/libc/async_safe/Android.bp b/libc/async_safe/Android.bp
new file mode 100644
index 0000000..9e36d97
--- /dev/null
+++ b/libc/async_safe/Android.bp
@@ -0,0 +1,15 @@
+// ========================================================
+// libasync_safe.a
+// ========================================================
+cc_library_static {
+    defaults: ["libc_defaults"],
+    srcs: [
+        "async_safe_log.cpp",
+    ],
+
+    name: "libasync_safe",
+
+    include_dirs: ["bionic/libc"],
+
+    export_include_dirs: ["include"],
+}
diff --git a/libc/async_safe/async_safe_log.cpp b/libc/async_safe/async_safe_log.cpp
new file mode 100644
index 0000000..372f385
--- /dev/null
+++ b/libc/async_safe/async_safe_log.cpp
@@ -0,0 +1,576 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <assert.h>
+#include <ctype.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/un.h>
+#include <time.h>
+#include <unistd.h>
+
+#include <android/set_abort_message.h>
+#include <async_safe/log.h>
+
+#include "private/CachedProperty.h"
+#include "private/ScopedPthreadMutexLocker.h"
+
+// Must be kept in sync with frameworks/base/core/java/android/util/EventLog.java.
+enum AndroidEventLogType {
+  EVENT_TYPE_INT = 0,
+  EVENT_TYPE_LONG = 1,
+  EVENT_TYPE_STRING = 2,
+  EVENT_TYPE_LIST = 3,
+  EVENT_TYPE_FLOAT = 4,
+};
+
+struct BufferOutputStream {
+ public:
+  BufferOutputStream(char* buffer, size_t size) : total(0) {
+    buffer_ = buffer;
+    end_ = buffer + size - 1;
+    pos_ = buffer_;
+    pos_[0] = '\0';
+  }
+
+  ~BufferOutputStream() {}
+
+  void Send(const char* data, int len) {
+    if (len < 0) {
+      len = strlen(data);
+    }
+
+    total += len;
+
+    while (len > 0) {
+      int avail = end_ - pos_;
+      if (avail == 0) {
+        return;
+      }
+      if (avail > len) {
+        avail = len;
+      }
+      memcpy(pos_, data, avail);
+      pos_ += avail;
+      pos_[0] = '\0';
+      len -= avail;
+    }
+  }
+
+  size_t total;
+
+ private:
+  char* buffer_;
+  char* pos_;
+  char* end_;
+};
+
+struct FdOutputStream {
+ public:
+  explicit FdOutputStream(int fd) : total(0), fd_(fd) {}
+
+  void Send(const char* data, int len) {
+    if (len < 0) {
+      len = strlen(data);
+    }
+
+    total += len;
+
+    while (len > 0) {
+      int rc = TEMP_FAILURE_RETRY(write(fd_, data, len));
+      if (rc == -1) {
+        return;
+      }
+      data += rc;
+      len -= rc;
+    }
+  }
+
+  size_t total;
+
+ private:
+  int fd_;
+};
+
+/*** formatted output implementation
+ ***/
+
+/* Parse a decimal string from 'format + *ppos',
+ * return the value, and writes the new position past
+ * the decimal string in '*ppos' on exit.
+ *
+ * NOTE: Does *not* handle a sign prefix.
+ */
+static unsigned parse_decimal(const char* format, int* ppos) {
+  const char* p = format + *ppos;
+  unsigned result = 0;
+
+  for (;;) {
+    int ch = *p;
+    unsigned d = static_cast<unsigned>(ch - '0');
+
+    if (d >= 10U) {
+      break;
+    }
+
+    result = result * 10 + d;
+    p++;
+  }
+  *ppos = p - format;
+  return result;
+}
+
+// Writes number 'value' in base 'base' into buffer 'buf' of size 'buf_size' bytes.
+// Assumes that buf_size > 0.
+static void format_unsigned(char* buf, size_t buf_size, uint64_t value, int base, bool caps) {
+  char* p = buf;
+  char* end = buf + buf_size - 1;
+
+  // Generate digit string in reverse order.
+  while (value) {
+    unsigned d = value % base;
+    value /= base;
+    if (p != end) {
+      char ch;
+      if (d < 10) {
+        ch = '0' + d;
+      } else {
+        ch = (caps ? 'A' : 'a') + (d - 10);
+      }
+      *p++ = ch;
+    }
+  }
+
+  // Special case for 0.
+  if (p == buf) {
+    if (p != end) {
+      *p++ = '0';
+    }
+  }
+  *p = '\0';
+
+  // Reverse digit string in-place.
+  size_t length = p - buf;
+  for (size_t i = 0, j = length - 1; i < j; ++i, --j) {
+    char ch = buf[i];
+    buf[i] = buf[j];
+    buf[j] = ch;
+  }
+}
+
+static void format_integer(char* buf, size_t buf_size, uint64_t value, char conversion) {
+  // Decode the conversion specifier.
+  int is_signed = (conversion == 'd' || conversion == 'i' || conversion == 'o');
+  int base = 10;
+  if (conversion == 'x' || conversion == 'X') {
+    base = 16;
+  } else if (conversion == 'o') {
+    base = 8;
+  }
+  bool caps = (conversion == 'X');
+
+  if (is_signed && static_cast<int64_t>(value) < 0) {
+    buf[0] = '-';
+    buf += 1;
+    buf_size -= 1;
+    value = static_cast<uint64_t>(-static_cast<int64_t>(value));
+  }
+  format_unsigned(buf, buf_size, value, base, caps);
+}
+
+template <typename Out>
+static void SendRepeat(Out& o, char ch, int count) {
+  char pad[8];
+  memset(pad, ch, sizeof(pad));
+
+  const int pad_size = static_cast<int>(sizeof(pad));
+  while (count > 0) {
+    int avail = count;
+    if (avail > pad_size) {
+      avail = pad_size;
+    }
+    o.Send(pad, avail);
+    count -= avail;
+  }
+}
+
+/* Perform formatted output to an output target 'o' */
+template <typename Out>
+static void out_vformat(Out& o, const char* format, va_list args) {
+  int nn = 0;
+
+  for (;;) {
+    int mm;
+    int padZero = 0;
+    int padLeft = 0;
+    char sign = '\0';
+    int width = -1;
+    int prec = -1;
+    size_t bytelen = sizeof(int);
+    int slen;
+    char buffer[32]; /* temporary buffer used to format numbers */
+
+    char c;
+
+    /* first, find all characters that are not 0 or '%' */
+    /* then send them to the output directly */
+    mm = nn;
+    do {
+      c = format[mm];
+      if (c == '\0' || c == '%') break;
+      mm++;
+    } while (1);
+
+    if (mm > nn) {
+      o.Send(format + nn, mm - nn);
+      nn = mm;
+    }
+
+    /* is this it ? then exit */
+    if (c == '\0') break;
+
+    /* nope, we are at a '%' modifier */
+    nn++;  // skip it
+
+    /* parse flags */
+    for (;;) {
+      c = format[nn++];
+      if (c == '\0') { /* single trailing '%' ? */
+        c = '%';
+        o.Send(&c, 1);
+        return;
+      } else if (c == '0') {
+        padZero = 1;
+        continue;
+      } else if (c == '-') {
+        padLeft = 1;
+        continue;
+      } else if (c == ' ' || c == '+') {
+        sign = c;
+        continue;
+      }
+      break;
+    }
+
+    /* parse field width */
+    if ((c >= '0' && c <= '9')) {
+      nn--;
+      width = static_cast<int>(parse_decimal(format, &nn));
+      c = format[nn++];
+    }
+
+    /* parse precision */
+    if (c == '.') {
+      prec = static_cast<int>(parse_decimal(format, &nn));
+      c = format[nn++];
+    }
+
+    /* length modifier */
+    switch (c) {
+      case 'h':
+        bytelen = sizeof(short);
+        if (format[nn] == 'h') {
+          bytelen = sizeof(char);
+          nn += 1;
+        }
+        c = format[nn++];
+        break;
+      case 'l':
+        bytelen = sizeof(long);
+        if (format[nn] == 'l') {
+          bytelen = sizeof(long long);
+          nn += 1;
+        }
+        c = format[nn++];
+        break;
+      case 'z':
+        bytelen = sizeof(size_t);
+        c = format[nn++];
+        break;
+      case 't':
+        bytelen = sizeof(ptrdiff_t);
+        c = format[nn++];
+        break;
+      default:;
+    }
+
+    /* conversion specifier */
+    const char* str = buffer;
+    if (c == 's') {
+      /* string */
+      str = va_arg(args, const char*);
+      if (str == NULL) {
+        str = "(null)";
+      }
+    } else if (c == 'c') {
+      /* character */
+      /* NOTE: char is promoted to int when passed through the stack */
+      buffer[0] = static_cast<char>(va_arg(args, int));
+      buffer[1] = '\0';
+    } else if (c == 'p') {
+      uint64_t value = reinterpret_cast<uintptr_t>(va_arg(args, void*));
+      buffer[0] = '0';
+      buffer[1] = 'x';
+      format_integer(buffer + 2, sizeof(buffer) - 2, value, 'x');
+    } else if (c == 'd' || c == 'i' || c == 'o' || c == 'u' || c == 'x' || c == 'X') {
+      /* integers - first read value from stack */
+      uint64_t value;
+      int is_signed = (c == 'd' || c == 'i' || c == 'o');
+
+      /* NOTE: int8_t and int16_t are promoted to int when passed
+       *       through the stack
+       */
+      switch (bytelen) {
+        case 1:
+          value = static_cast<uint8_t>(va_arg(args, int));
+          break;
+        case 2:
+          value = static_cast<uint16_t>(va_arg(args, int));
+          break;
+        case 4:
+          value = va_arg(args, uint32_t);
+          break;
+        case 8:
+          value = va_arg(args, uint64_t);
+          break;
+        default:
+          return; /* should not happen */
+      }
+
+      /* sign extension, if needed */
+      if (is_signed) {
+        int shift = 64 - 8 * bytelen;
+        value = static_cast<uint64_t>((static_cast<int64_t>(value << shift)) >> shift);
+      }
+
+      /* format the number properly into our buffer */
+      format_integer(buffer, sizeof(buffer), value, c);
+    } else if (c == '%') {
+      buffer[0] = '%';
+      buffer[1] = '\0';
+    } else {
+      __assert(__FILE__, __LINE__, "conversion specifier unsupported");
+    }
+
+    /* if we are here, 'str' points to the content that must be
+     * outputted. handle padding and alignment now */
+
+    slen = strlen(str);
+
+    if (sign != '\0' || prec != -1) {
+      __assert(__FILE__, __LINE__, "sign/precision unsupported");
+    }
+
+    if (slen < width && !padLeft) {
+      char padChar = padZero ? '0' : ' ';
+      SendRepeat(o, padChar, width - slen);
+    }
+
+    o.Send(str, slen);
+
+    if (slen < width && padLeft) {
+      char padChar = padZero ? '0' : ' ';
+      SendRepeat(o, padChar, width - slen);
+    }
+  }
+}
+
+int async_safe_format_buffer(char* buffer, size_t buffer_size, const char* format, ...) {
+  BufferOutputStream os(buffer, buffer_size);
+  va_list args;
+  va_start(args, format);
+  out_vformat(os, format, args);
+  va_end(args);
+  return os.total;
+}
+
+int async_safe_format_buffer_va_list(char* buffer, size_t buffer_size, const char* format,
+                                     va_list args) {
+  BufferOutputStream os(buffer, buffer_size);
+  out_vformat(os, format, args);
+  return os.total;
+}
+
+int async_safe_format_fd(int fd, const char* format, ...) {
+  FdOutputStream os(fd);
+  va_list args;
+  va_start(args, format);
+  out_vformat(os, format, args);
+  va_end(args);
+  return os.total;
+}
+
+static int write_stderr(const char* tag, const char* msg) {
+  iovec vec[4];
+  vec[0].iov_base = const_cast<char*>(tag);
+  vec[0].iov_len = strlen(tag);
+  vec[1].iov_base = const_cast<char*>(": ");
+  vec[1].iov_len = 2;
+  vec[2].iov_base = const_cast<char*>(msg);
+  vec[2].iov_len = strlen(msg);
+  vec[3].iov_base = const_cast<char*>("\n");
+  vec[3].iov_len = 1;
+
+  int result = TEMP_FAILURE_RETRY(writev(STDERR_FILENO, vec, 4));
+  return result;
+}
+
+static int open_log_socket() {
+  // ToDo: Ideally we want this to fail if the gid of the current
+  // process is AID_LOGD, but will have to wait until we have
+  // registered this in private/android_filesystem_config.h. We have
+  // found that all logd crashes thus far have had no problem stuffing
+  // the UNIX domain socket and moving on so not critical *today*.
+
+  int log_fd = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0));
+  if (log_fd == -1) {
+    return -1;
+  }
+
+  union {
+    struct sockaddr addr;
+    struct sockaddr_un addrUn;
+  } u;
+  memset(&u, 0, sizeof(u));
+  u.addrUn.sun_family = AF_UNIX;
+  strlcpy(u.addrUn.sun_path, "/dev/socket/logdw", sizeof(u.addrUn.sun_path));
+
+  if (TEMP_FAILURE_RETRY(connect(log_fd, &u.addr, sizeof(u.addrUn))) != 0) {
+    close(log_fd);
+    return -1;
+  }
+
+  return log_fd;
+}
+
+static clockid_t log_clockid() {
+  static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+  ScopedPthreadMutexLocker locker(&mutex);
+
+  static CachedProperty ro_logd_timestamp("ro.logd.timestamp");
+  static CachedProperty persist_logd_timestamp("persist.logd.timestamp");
+
+  char ch = persist_logd_timestamp.Get()[0];
+  if (ch == '\0') ch = ro_logd_timestamp.Get()[0];
+
+  return (tolower(ch) == 'm') ? CLOCK_MONOTONIC : CLOCK_REALTIME;
+}
+
+struct log_time {  // Wire format
+  uint32_t tv_sec;
+  uint32_t tv_nsec;
+};
+
+int async_safe_write_log(int priority, const char* tag, const char* msg) {
+  int main_log_fd = open_log_socket();
+  if (main_log_fd == -1) {
+    // Try stderr instead.
+    return write_stderr(tag, msg);
+  }
+
+  iovec vec[6];
+  char log_id = (priority == ANDROID_LOG_FATAL) ? LOG_ID_CRASH : LOG_ID_MAIN;
+  vec[0].iov_base = &log_id;
+  vec[0].iov_len = sizeof(log_id);
+  uint16_t tid = gettid();
+  vec[1].iov_base = &tid;
+  vec[1].iov_len = sizeof(tid);
+  timespec ts;
+  clock_gettime(log_clockid(), &ts);
+  log_time realtime_ts;
+  realtime_ts.tv_sec = ts.tv_sec;
+  realtime_ts.tv_nsec = ts.tv_nsec;
+  vec[2].iov_base = &realtime_ts;
+  vec[2].iov_len = sizeof(realtime_ts);
+
+  vec[3].iov_base = &priority;
+  vec[3].iov_len = 1;
+  vec[4].iov_base = const_cast<char*>(tag);
+  vec[4].iov_len = strlen(tag) + 1;
+  vec[5].iov_base = const_cast<char*>(msg);
+  vec[5].iov_len = strlen(msg) + 1;
+
+  int result = TEMP_FAILURE_RETRY(writev(main_log_fd, vec, sizeof(vec) / sizeof(vec[0])));
+  close(main_log_fd);
+  return result;
+}
+
+int async_safe_format_log_va_list(int priority, const char* tag, const char* format, va_list args) {
+  char buffer[1024];
+  BufferOutputStream os(buffer, sizeof(buffer));
+  out_vformat(os, format, args);
+  return async_safe_write_log(priority, tag, buffer);
+}
+
+int async_safe_format_log(int priority, const char* tag, const char* format, ...) {
+  va_list args;
+  va_start(args, format);
+  int result = async_safe_format_log_va_list(priority, tag, format, args);
+  va_end(args);
+  return result;
+}
+
+void async_safe_fatal_va_list(const char* prefix, const char* format, va_list args) {
+  char msg[1024];
+  BufferOutputStream os(msg, sizeof(msg));
+
+  if (prefix) {
+    os.Send(prefix, strlen(prefix));
+    os.Send(": ", 2);
+  }
+
+  out_vformat(os, format, args);
+
+  // Log to stderr for the benefit of "adb shell" users and gtests.
+  struct iovec iov[2] = {
+      {msg, os.total}, {const_cast<char*>("\n"), 1},
+  };
+  TEMP_FAILURE_RETRY(writev(2, iov, 2));
+
+  // Log to the log for the benefit of regular app developers (whose stdout and stderr are closed).
+  async_safe_write_log(ANDROID_LOG_FATAL, "libc", msg);
+
+  android_set_abort_message(msg);
+}
+
+void async_safe_fatal(const char* fmt, ...) {
+  va_list args;
+  va_start(args, fmt);
+  async_safe_fatal_va_list(nullptr, fmt, args);
+  va_end(args);
+  abort();
+}
diff --git a/libc/async_safe/include/async_safe/log.h b/libc/async_safe/include/async_safe/log.h
new file mode 100644
index 0000000..f93f672
--- /dev/null
+++ b/libc/async_safe/include/async_safe/log.h
@@ -0,0 +1,116 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef _ASYNC_SAFE_LOG_LOG_H
+#define _ASYNC_SAFE_LOG_LOG_H
+
+#include <sys/cdefs.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdint.h>
+
+// These functions do not allocate memory to send data to the log.
+
+__BEGIN_DECLS
+
+enum {
+  ANDROID_LOG_UNKNOWN = 0,
+  ANDROID_LOG_DEFAULT,    /* only for SetMinPriority() */
+
+  ANDROID_LOG_VERBOSE,
+  ANDROID_LOG_DEBUG,
+  ANDROID_LOG_INFO,
+  ANDROID_LOG_WARN,
+  ANDROID_LOG_ERROR,
+  ANDROID_LOG_FATAL,
+
+  ANDROID_LOG_SILENT,     /* only for SetMinPriority(); must be last */
+};
+
+enum {
+  LOG_ID_MIN = 0,
+
+  LOG_ID_MAIN = 0,
+  LOG_ID_RADIO = 1,
+  LOG_ID_EVENTS = 2,
+  LOG_ID_SYSTEM = 3,
+  LOG_ID_CRASH = 4,
+
+  LOG_ID_MAX
+};
+
+// Formats a message to the log (priority 'fatal'), then aborts.
+__noreturn void async_safe_fatal(const char* _Nonnull fmt, ...) __printflike(1, 2);
+
+// This function does return, so callers that want to abort, must do so themselves.
+#if defined(__arm__) || defined(__aarch64__) || defined(__x86_64__)
+void async_safe_fatal_va_list(
+    const char* _Nullable prefix, const char* _Nonnull fmt, va_list);
+#else // defined(__mips__) || defined(__i386__)
+void async_safe_fatal_va_list(
+    const char* _Nullable prefix, const char* _Nonnull fmt, va_list _Nonnull);
+#endif
+
+//
+// Formatting routines for the C library's internal debugging.
+// Unlike the usual alternatives, these don't allocate, and they don't drag in all of stdio.
+// These are async signal safe, so they can be called from signal handlers.
+//
+
+int async_safe_format_buffer(char* _Nonnull buf, size_t size, const char* _Nonnull fmt, ...) __printflike(3, 4);
+
+#if defined(__arm__) || defined(__aarch64__) || defined(__x86_64__)
+int async_safe_format_buffer_va_list(
+    char* _Nonnull buffer, size_t buffer_size, const char* _Nonnull format, va_list args);
+#else // defined(__mips__) || defined(__i386__)
+int async_safe_format_buffer_va_list(
+    char* _Nonnull buffer, size_t buffer_size, const char* _Nonnull format, va_list _Nonnull args);
+#endif
+
+int async_safe_format_fd(int fd, const char* _Nonnull format , ...) __printflike(2, 3);
+int async_safe_format_log(int pri, const char* _Nonnull tag, const char* _Nonnull fmt, ...) __printflike(3, 4);
+#if defined(__arm__) || defined(__aarch64__) || defined(__x86_64__)
+int async_safe_format_log_va_list(
+    int pri, const char* _Nonnull tag, const char* _Nonnull fmt, va_list ap);
+#else // defined(__mips__) || defined(__i386__)
+int async_safe_format_log_va_list(
+    int pri, const char* _Nonnull tag, const char* _Nonnull fmt, va_list _Nonnull ap);
+#endif
+int async_safe_write_log(int pri, const char* _Nonnull tag, const char* _Nonnull msg);
+
+#define CHECK(predicate) \
+  do { \
+    if (!(predicate)) { \
+      async_safe_fatal("%s:%d: %s CHECK '" #predicate "' failed", \
+          __FILE__, __LINE__, __FUNCTION__); \
+    } \
+  } while(0)
+
+__END_DECLS
+
+#endif