diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 89061b6..2688626 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -72,6 +72,12 @@
 #define	__static_cast(x,y)	(x)y
 #endif
 
+#if defined(__cplusplus)
+#define __BIONIC_CAST(_k,_t,_v) (_k<_t>(_v))
+#else
+#define __BIONIC_CAST(_k,_t,_v) ((_t) (_v))
+#endif
+
 /*
  * The __CONCAT macro is used to concatenate parts of symbol names, e.g.
  * with "#define OLD(foo) __CONCAT(old,foo)", OLD(foo) produces oldfoo.
@@ -88,9 +94,6 @@
 #define	__CONCAT(x,y)	x ## y
 #define	__STRING(x)	#x
 
-#define	__const		const		/* define reserved names to standard */
-#define	__signed	signed
-#define	__volatile	volatile
 #if defined(__cplusplus)
 #define	__inline	inline		/* convert to C++ keyword */
 #endif /* !__cplusplus */
@@ -102,17 +105,6 @@
 
 #endif	/* !(__STDC__ || __cplusplus) */
 
-/*
- * The following macro is used to remove const cast-away warnings
- * from gcc -Wcast-qual; it should be used with caution because it
- * can hide valid errors; in particular most valid uses are in
- * situations where the API requires it, not to cast away string
- * constants. We don't use *intptr_t on purpose here and we are
- * explicit about unsigned long so that we don't have additional
- * dependencies.
- */
-#define __UNCONST(a)	((void *)(unsigned long)(const void *)(a))
-
 #define __always_inline __attribute__((__always_inline__))
 #define __dead __attribute__((__noreturn__))
 #define __noreturn __attribute__((__noreturn__))
@@ -154,6 +146,7 @@
  */
 #if !(defined(__clang__) && __has_feature(nullability))
 #define _Nonnull
+#define _Nullable
 #endif
 
 #define __printflike(x, y) __attribute__((__format__(printf, x, y)))
@@ -198,8 +191,6 @@
 #define __errorattr(msg) __attribute__((__error__(msg)))
 #endif
 
-#define __warnattr(msg) __attribute__((__warning__(msg)))
-
 #define __errordecl(name, msg) extern void name(void) __errorattr(msg)
 
 /*
@@ -274,9 +265,13 @@
 #    define __bos(s) __builtin_object_size((s), 0)
 #  endif
 #  define __bos0(s) __builtin_object_size((s), 0)
-#  define __BIONIC_FORTIFY_INLINE extern __inline__ __always_inline __attribute__((gnu_inline)) __attribute__((__artificial__))
+#  if defined(__clang__)
+#    define __BIONIC_FORTIFY_INLINE extern __inline__ __always_inline __attribute__((gnu_inline))
+#  else
+#    define __BIONIC_FORTIFY_INLINE extern __inline__ __always_inline __attribute__((gnu_inline)) __attribute__((__artificial__))
+#  endif
 #endif
-#define __BIONIC_FORTIFY_UNKNOWN_SIZE ((size_t) -1)
+#define __BIONIC_FORTIFY_UNKNOWN_SIZE __BIONIC_CAST(static_cast, size_t, -1)
 
 /* Used to tag non-static symbols that are private and never exposed by the shared library. */
 #define __LIBC_HIDDEN__ __attribute__((visibility("hidden")))
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index 7a8aa89..934963f 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -38,7 +38,7 @@
 #define MAP_ANON  MAP_ANONYMOUS
 #endif
 
-#define MAP_FAILED ((void *)-1)
+#define MAP_FAILED __BIONIC_CAST(reinterpret_cast, void*, -1)
 
 #define MREMAP_MAYMOVE  1
 #define MREMAP_FIXED    2
@@ -50,26 +50,26 @@
 #define POSIX_MADV_DONTNEED   MADV_DONTNEED
 
 #if defined(__USE_FILE_OFFSET64)
-extern void* mmap(void*, size_t, int, int, int, off_t) __RENAME(mmap64) __INTRODUCED_IN(21);
+void* mmap(void*, size_t, int, int, int, off_t) __RENAME(mmap64) __INTRODUCED_IN(21);
 #else
-extern void* mmap(void*, size_t, int, int, int, off_t);
+void* mmap(void*, size_t, int, int, int, off_t);
 #endif
-extern void* mmap64(void*, size_t, int, int, int, off64_t) __INTRODUCED_IN(21);
+void* mmap64(void*, size_t, int, int, int, off64_t) __INTRODUCED_IN(21);
 
-extern int munmap(void*, size_t);
-extern int msync(const void*, size_t, int);
-extern int mprotect(const void*, size_t, int);
-extern void* mremap(void*, size_t, size_t, int, ...);
+int munmap(void*, size_t);
+int msync(const void*, size_t, int);
+int mprotect(const void*, size_t, int);
+void* mremap(void*, size_t, size_t, int, ...);
 
-extern int mlockall(int) __INTRODUCED_IN(17);
-extern int munlockall(void) __INTRODUCED_IN(17);
-extern int mlock(const void*, size_t);
-extern int munlock(const void*, size_t);
+int mlockall(int) __INTRODUCED_IN(17);
+int munlockall(void) __INTRODUCED_IN(17);
+int mlock(const void*, size_t);
+int munlock(const void*, size_t);
 
-extern int mincore(void*, size_t, unsigned char*);
+int mincore(void*, size_t, unsigned char*);
 
-extern int madvise(void*, size_t, int);
-extern int posix_madvise(void*, size_t, int) __INTRODUCED_IN(23);
+int madvise(void*, size_t, int);
+int posix_madvise(void*, size_t, int) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/sys/select.h b/libc/include/sys/select.h
index 06c1c72..96d735e 100644
--- a/libc/include/sys/select.h
+++ b/libc/include/sys/select.h
@@ -46,7 +46,7 @@
 
 #define __FDELT(fd) ((fd) / NFDBITS)
 #define __FDMASK(fd) (1UL << ((fd) % NFDBITS))
-#define __FDS_BITS(set) (((fd_set*)(set))->fds_bits)
+#define __FDS_BITS(set) (__BIONIC_CAST(static_cast, fd_set*, set)->fds_bits)
 
 /* Inline loop so we don't have to declare memset. */
 #define FD_ZERO(set) \
diff --git a/libc/include/sys/xattr.h b/libc/include/sys/xattr.h
index 63605c5..7e437e9 100644
--- a/libc/include/sys/xattr.h
+++ b/libc/include/sys/xattr.h
@@ -25,36 +25,33 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
 #ifndef _SYS_XATTR_H_
 #define _SYS_XATTR_H_
 
+#include <linux/xattr.h>
 #include <sys/types.h>
 
 __BEGIN_DECLS
 
-#define XATTR_CREATE 1
-#define XATTR_REPLACE 2
-
-extern int fsetxattr(int fd, const char* name, const void* value, size_t size, int flags)
+int fsetxattr(int fd, const char* name, const void* value, size_t size, int flags)
   __INTRODUCED_IN(16);
-extern int setxattr(const char* path, const char* name, const void* value, size_t size, int flags)
+int setxattr(const char* path, const char* name, const void* value, size_t size, int flags)
   __INTRODUCED_IN(16);
-extern int lsetxattr(const char* path, const char* name, const void* value, size_t size, int flags)
+int lsetxattr(const char* path, const char* name, const void* value, size_t size, int flags)
   __INTRODUCED_IN(16);
 
-extern ssize_t fgetxattr(int fd, const char* name, void* value, size_t size) __INTRODUCED_IN(16);
-extern ssize_t getxattr(const char* path, const char* name, void* value, size_t size)
-  __INTRODUCED_IN(16);
-extern ssize_t lgetxattr(const char* path, const char* name, void* value, size_t size)
-  __INTRODUCED_IN(16);
+ssize_t fgetxattr(int fd, const char* name, void* value, size_t size) __INTRODUCED_IN(16);
+ssize_t getxattr(const char* path, const char* name, void* value, size_t size) __INTRODUCED_IN(16);
+ssize_t lgetxattr(const char* path, const char* name, void* value, size_t size) __INTRODUCED_IN(16);
 
-extern ssize_t listxattr(const char* path, char* list, size_t size) __INTRODUCED_IN(16);
-extern ssize_t llistxattr(const char* path, char* list, size_t size) __INTRODUCED_IN(16);
-extern ssize_t flistxattr(int fd, char* list, size_t size) __INTRODUCED_IN(16);
+ssize_t listxattr(const char* path, char* list, size_t size) __INTRODUCED_IN(16);
+ssize_t llistxattr(const char* path, char* list, size_t size) __INTRODUCED_IN(16);
+ssize_t flistxattr(int fd, char* list, size_t size) __INTRODUCED_IN(16);
 
-extern int removexattr(const char* path, const char* name) __INTRODUCED_IN(16);
-extern int lremovexattr(const char* path, const char* name) __INTRODUCED_IN(16);
-extern int fremovexattr(int fd, const char* name) __INTRODUCED_IN(16);
+int removexattr(const char* path, const char* name) __INTRODUCED_IN(16);
+int lremovexattr(const char* path, const char* name) __INTRODUCED_IN(16);
+int fremovexattr(int fd, const char* name) __INTRODUCED_IN(16);
 
 __END_DECLS