diff --git a/libc/include/bits/stdatomic.h b/libc/include/bits/stdatomic.h
new file mode 100644
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--- /dev/null
+++ b/libc/include/bits/stdatomic.h
@@ -0,0 +1,286 @@
+/*-
+ * Copyright (c) 2011 Ed Schouten <ed@FreeBSD.org>
+ *                    David Chisnall <theraven@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. 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 AUTHOR 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 AUTHOR 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.
+ *
+ * $FreeBSD$
+ */
+
+#pragma once
+
+#include <sys/cdefs.h>
+#include <sys/types.h>
+#include <stdbool.h>
+
+/*
+ * C: Do it ourselves.
+ * Note that the runtime representation defined here should be compatible
+ * with the C++ one, i.e. an _Atomic(T) needs to contain the same
+ * bits as a T.
+ */
+
+#include <stddef.h>  /* For ptrdiff_t. */
+#include <stdint.h>  /* TODO: don't drag in all the macros, just the types. */
+// Include uchar.h only when available.  Bionic's stdatomic.h is also used for
+// the host (via a copy in prebuilts/clang) and uchar.h is not available in the
+// glibc used for the host.
+#if defined(__BIONIC__)
+# include <uchar.h>  /* For char16_t and char32_t.              */
+#endif
+
+/*
+ * 7.17.1 Atomic lock-free macros.
+ */
+
+#ifdef __GCC_ATOMIC_BOOL_LOCK_FREE
+#define	ATOMIC_BOOL_LOCK_FREE		__GCC_ATOMIC_BOOL_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_CHAR_LOCK_FREE
+#define	ATOMIC_CHAR_LOCK_FREE		__GCC_ATOMIC_CHAR_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_CHAR16_T_LOCK_FREE
+#define	ATOMIC_CHAR16_T_LOCK_FREE	__GCC_ATOMIC_CHAR16_T_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_CHAR32_T_LOCK_FREE
+#define	ATOMIC_CHAR32_T_LOCK_FREE	__GCC_ATOMIC_CHAR32_T_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_WCHAR_T_LOCK_FREE
+#define	ATOMIC_WCHAR_T_LOCK_FREE	__GCC_ATOMIC_WCHAR_T_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_SHORT_LOCK_FREE
+#define	ATOMIC_SHORT_LOCK_FREE		__GCC_ATOMIC_SHORT_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_INT_LOCK_FREE
+#define	ATOMIC_INT_LOCK_FREE		__GCC_ATOMIC_INT_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_LONG_LOCK_FREE
+#define	ATOMIC_LONG_LOCK_FREE		__GCC_ATOMIC_LONG_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_LLONG_LOCK_FREE
+#define	ATOMIC_LLONG_LOCK_FREE		__GCC_ATOMIC_LLONG_LOCK_FREE
+#endif
+#ifdef __GCC_ATOMIC_POINTER_LOCK_FREE
+#define	ATOMIC_POINTER_LOCK_FREE	__GCC_ATOMIC_POINTER_LOCK_FREE
+#endif
+
+/*
+ * 7.17.2 Initialization.
+ */
+
+#define	ATOMIC_VAR_INIT(value)		(value)
+#define	atomic_init(obj, value)		__c11_atomic_init(obj, value)
+
+/*
+ * Clang and recent GCC both provide predefined macros for the memory
+ * orderings.  If we are using a compiler that doesn't define them, use the
+ * clang values - these will be ignored in the fallback path.
+ */
+
+#ifndef __ATOMIC_RELAXED
+#define __ATOMIC_RELAXED		0
+#endif
+#ifndef __ATOMIC_CONSUME
+#define __ATOMIC_CONSUME		1
+#endif
+#ifndef __ATOMIC_ACQUIRE
+#define __ATOMIC_ACQUIRE		2
+#endif
+#ifndef __ATOMIC_RELEASE
+#define __ATOMIC_RELEASE		3
+#endif
+#ifndef __ATOMIC_ACQ_REL
+#define __ATOMIC_ACQ_REL		4
+#endif
+#ifndef __ATOMIC_SEQ_CST
+#define __ATOMIC_SEQ_CST		5
+#endif
+
+/*
+ * 7.17.3 Order and consistency.
+ *
+ * The memory_order_* constants that denote the barrier behaviour of the
+ * atomic operations.
+ * The enum values must be identical to those used by the
+ * C++ <atomic> header.
+ */
+
+typedef enum {
+	memory_order_relaxed = __ATOMIC_RELAXED,
+	memory_order_consume = __ATOMIC_CONSUME,
+	memory_order_acquire = __ATOMIC_ACQUIRE,
+	memory_order_release = __ATOMIC_RELEASE,
+	memory_order_acq_rel = __ATOMIC_ACQ_REL,
+	memory_order_seq_cst = __ATOMIC_SEQ_CST
+} memory_order;
+
+/*
+ * 7.17.4 Fences.
+ */
+
+static __inline void atomic_thread_fence(memory_order __order __attribute__((unused))) {
+	__c11_atomic_thread_fence(__order);
+}
+
+static __inline void atomic_signal_fence(memory_order __order __attribute__((unused))) {
+	__c11_atomic_signal_fence(__order);
+}
+
+/*
+ * 7.17.5 Lock-free property.
+ */
+
+#define	atomic_is_lock_free(obj) __c11_atomic_is_lock_free(sizeof(*(obj)))
+
+/*
+ * 7.17.6 Atomic integer types.
+ */
+
+typedef _Atomic(bool)			atomic_bool;
+typedef _Atomic(char)			atomic_char;
+typedef _Atomic(signed char)		atomic_schar;
+typedef _Atomic(unsigned char)		atomic_uchar;
+typedef _Atomic(short)			atomic_short;
+typedef _Atomic(unsigned short)		atomic_ushort;
+typedef _Atomic(int)			atomic_int;
+typedef _Atomic(unsigned int)		atomic_uint;
+typedef _Atomic(long)			atomic_long;
+typedef _Atomic(unsigned long)		atomic_ulong;
+typedef _Atomic(long long)		atomic_llong;
+typedef _Atomic(unsigned long long)	atomic_ullong;
+#if defined(__BIONIC__) || (defined(__cplusplus) && __cplusplus >= 201103L)
+  typedef _Atomic(char16_t)		atomic_char16_t;
+  typedef _Atomic(char32_t)		atomic_char32_t;
+#endif
+typedef _Atomic(wchar_t)		atomic_wchar_t;
+typedef _Atomic(int_least8_t)		atomic_int_least8_t;
+typedef _Atomic(uint_least8_t)	atomic_uint_least8_t;
+typedef _Atomic(int_least16_t)	atomic_int_least16_t;
+typedef _Atomic(uint_least16_t)	atomic_uint_least16_t;
+typedef _Atomic(int_least32_t)	atomic_int_least32_t;
+typedef _Atomic(uint_least32_t)	atomic_uint_least32_t;
+typedef _Atomic(int_least64_t)	atomic_int_least64_t;
+typedef _Atomic(uint_least64_t)	atomic_uint_least64_t;
+typedef _Atomic(int_fast8_t)		atomic_int_fast8_t;
+typedef _Atomic(uint_fast8_t)		atomic_uint_fast8_t;
+typedef _Atomic(int_fast16_t)		atomic_int_fast16_t;
+typedef _Atomic(uint_fast16_t)	atomic_uint_fast16_t;
+typedef _Atomic(int_fast32_t)		atomic_int_fast32_t;
+typedef _Atomic(uint_fast32_t)	atomic_uint_fast32_t;
+typedef _Atomic(int_fast64_t)		atomic_int_fast64_t;
+typedef _Atomic(uint_fast64_t)	atomic_uint_fast64_t;
+typedef _Atomic(intptr_t)		atomic_intptr_t;
+typedef _Atomic(uintptr_t)		atomic_uintptr_t;
+typedef _Atomic(size_t)		atomic_size_t;
+typedef _Atomic(ptrdiff_t)		atomic_ptrdiff_t;
+typedef _Atomic(intmax_t)		atomic_intmax_t;
+typedef _Atomic(uintmax_t)		atomic_uintmax_t;
+
+/*
+ * 7.17.7 Operations on atomic types.
+ */
+
+/*
+ * Compiler-specific operations.
+ */
+
+#define	atomic_compare_exchange_strong_explicit(object, expected,	\
+    desired, success, failure)						\
+	__c11_atomic_compare_exchange_strong(object, expected, desired,	\
+	    success, failure)
+#define	atomic_compare_exchange_weak_explicit(object, expected,		\
+    desired, success, failure)						\
+	__c11_atomic_compare_exchange_weak(object, expected, desired,	\
+	    success, failure)
+#define	atomic_exchange_explicit(object, desired, order)		\
+	__c11_atomic_exchange(object, desired, order)
+#define	atomic_fetch_add_explicit(object, operand, order)		\
+	__c11_atomic_fetch_add(object, operand, order)
+#define	atomic_fetch_and_explicit(object, operand, order)		\
+	__c11_atomic_fetch_and(object, operand, order)
+#define	atomic_fetch_or_explicit(object, operand, order)		\
+	__c11_atomic_fetch_or(object, operand, order)
+#define	atomic_fetch_sub_explicit(object, operand, order)		\
+	__c11_atomic_fetch_sub(object, operand, order)
+#define	atomic_fetch_xor_explicit(object, operand, order)		\
+	__c11_atomic_fetch_xor(object, operand, order)
+#define	atomic_load_explicit(object, order)				\
+	__c11_atomic_load(object, order)
+#define	atomic_store_explicit(object, desired, order)			\
+	__c11_atomic_store(object, desired, order)
+
+/*
+ * Convenience functions.
+ */
+
+#define	atomic_compare_exchange_strong(object, expected, desired)	\
+	atomic_compare_exchange_strong_explicit(object, expected,	\
+	    desired, memory_order_seq_cst, memory_order_seq_cst)
+#define	atomic_compare_exchange_weak(object, expected, desired)		\
+	atomic_compare_exchange_weak_explicit(object, expected,		\
+	    desired, memory_order_seq_cst, memory_order_seq_cst)
+#define	atomic_exchange(object, desired)				\
+	atomic_exchange_explicit(object, desired, memory_order_seq_cst)
+#define	atomic_fetch_add(object, operand)				\
+	atomic_fetch_add_explicit(object, operand, memory_order_seq_cst)
+#define	atomic_fetch_and(object, operand)				\
+	atomic_fetch_and_explicit(object, operand, memory_order_seq_cst)
+#define	atomic_fetch_or(object, operand)				\
+	atomic_fetch_or_explicit(object, operand, memory_order_seq_cst)
+#define	atomic_fetch_sub(object, operand)				\
+	atomic_fetch_sub_explicit(object, operand, memory_order_seq_cst)
+#define	atomic_fetch_xor(object, operand)				\
+	atomic_fetch_xor_explicit(object, operand, memory_order_seq_cst)
+#define	atomic_load(object)						\
+	atomic_load_explicit(object, memory_order_seq_cst)
+#define	atomic_store(object, desired)					\
+	atomic_store_explicit(object, desired, memory_order_seq_cst)
+
+/*
+ * 7.17.8 Atomic flag type and operations.
+ *
+ * XXX: Assume atomic_bool can be used as an atomic_flag. Is there some
+ * kind of compiler built-in type we could use?
+ */
+
+typedef struct {
+	atomic_bool	__flag;
+} atomic_flag;
+
+#define	ATOMIC_FLAG_INIT		{ ATOMIC_VAR_INIT(false) }
+
+static __inline bool atomic_flag_test_and_set_explicit(volatile atomic_flag *__object, memory_order __order) {
+	return (atomic_exchange_explicit(&__object->__flag, 1, __order));
+}
+
+static __inline void atomic_flag_clear_explicit(volatile atomic_flag *__object, memory_order __order) {
+	atomic_store_explicit(&__object->__flag, 0, __order);
+}
+
+static __inline bool atomic_flag_test_and_set(volatile atomic_flag *__object) {
+	return (atomic_flag_test_and_set_explicit(__object, memory_order_seq_cst));
+}
+
+static __inline void atomic_flag_clear(volatile atomic_flag *__object) {
+	atomic_flag_clear_explicit(__object, memory_order_seq_cst);
+}