diff --git a/libc/include/sys/auxv.h b/libc/include/sys/auxv.h
index 4611fcc..2fa637e 100644
--- a/libc/include/sys/auxv.h
+++ b/libc/include/sys/auxv.h
@@ -33,7 +33,7 @@
 
 __BEGIN_DECLS
 
-unsigned long int getauxval(unsigned long int type) __INTRODUCED_IN(21);
+unsigned long int getauxval(unsigned long int type) __INTRODUCED_IN(18);
 
 __END_DECLS
 
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 7b06967..fa03207 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -501,6 +501,24 @@
 #define __INTRODUCED_IN_64(api_level)
 #endif
 
+#if defined(__arm__)
+#define __INTRODUCED_IN_ARM __INTRODUCED_IN
+#else
+#define __INTRODUCED_IN_ARM(x)
+#endif
+
+#if defined(__i386__)
+#define __INTRODUCED_IN_X86 __INTRODUCED_IN
+#else
+#define __INTRODUCED_IN_X86(x)
+#endif
+
+#if defined(__mips__)
+#define __INTRODUCED_IN_MIPS __INTRODUCED_IN
+#else
+#define __INTRODUCED_IN_MIPS(x)
+#endif
+
 #if __has_builtin(__builtin_umul_overflow) || __GNUC__ >= 5
 #if __LP64__
 #define __size_mul_overflow(a, b, result) __builtin_umull_overflow(a, b, result)
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index af96eff..7a8aa89 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -61,8 +61,8 @@
 extern int mprotect(const void*, size_t, int);
 extern void* mremap(void*, size_t, size_t, int, ...);
 
-extern int mlockall(int) __INTRODUCED_IN(21);
-extern int munlockall(void) __INTRODUCED_IN(21);
+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);
 
diff --git a/libc/include/sys/personality.h b/libc/include/sys/personality.h
index 68ae77c..15a5e68 100644
--- a/libc/include/sys/personality.h
+++ b/libc/include/sys/personality.h
@@ -34,7 +34,7 @@
 
 __BEGIN_DECLS
 
-extern int personality(unsigned int persona) __INTRODUCED_IN(21);
+extern int personality(unsigned int persona) __INTRODUCED_IN(15);
 
 __END_DECLS
 
diff --git a/libc/include/sys/signalfd.h b/libc/include/sys/signalfd.h
index 084a528..41036b0 100644
--- a/libc/include/sys/signalfd.h
+++ b/libc/include/sys/signalfd.h
@@ -35,7 +35,7 @@
 
 __BEGIN_DECLS
 
-extern int signalfd(int fd, const sigset_t* _Nonnull mask, int flags) __INTRODUCED_IN(21);
+extern int signalfd(int fd, const sigset_t* _Nonnull mask, int flags) __INTRODUCED_IN(18);
 
 __END_DECLS
 
diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index 46eec96..f26a492 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -157,7 +157,7 @@
 extern int mknod(const char*, mode_t, dev_t);
 extern mode_t umask(mode_t);
 
-extern mode_t __umask_chk(mode_t) __INTRODUCED_IN(21);
+extern mode_t __umask_chk(mode_t) __INTRODUCED_IN(18);
 extern mode_t __umask_real(mode_t) __RENAME(umask);
 __errordecl(__umask_invalid_mode, "umask called with invalid mode");
 
diff --git a/libc/include/sys/statvfs.h b/libc/include/sys/statvfs.h
index 1f00b9d..f6b9803 100644
--- a/libc/include/sys/statvfs.h
+++ b/libc/include/sys/statvfs.h
@@ -60,10 +60,10 @@
 #define ST_RELATIME    0x1000
 
 extern int statvfs(const char* __restrict _Nonnull, struct statvfs* __restrict _Nonnull)
-  __INTRODUCED_IN(21);
+  __INTRODUCED_IN(19);
 extern int statvfs64(const char* __restrict _Nonnull, struct statvfs64* __restrict _Nonnull)
   __INTRODUCED_IN(21);
-extern int fstatvfs(int, struct statvfs* _Nonnull) __INTRODUCED_IN(21);
+extern int fstatvfs(int, struct statvfs* _Nonnull) __INTRODUCED_IN(19);
 extern int fstatvfs64(int, struct statvfs64* _Nonnull) __INTRODUCED_IN(21);
 
 __END_DECLS
diff --git a/libc/include/sys/swap.h b/libc/include/sys/swap.h
index fe14a30..2d99df8 100644
--- a/libc/include/sys/swap.h
+++ b/libc/include/sys/swap.h
@@ -38,8 +38,8 @@
 #define SWAP_FLAG_PRIO_MASK 0x7fff
 #define SWAP_FLAG_PRIO_SHIFT 0
 
-extern int swapon(const char* _Nonnull, int) __INTRODUCED_IN(21);
-extern int swapoff(const char* _Nonnull) __INTRODUCED_IN(21);
+extern int swapon(const char* _Nonnull, int) __INTRODUCED_IN(19);
+extern int swapoff(const char* _Nonnull) __INTRODUCED_IN(19);
 
 __END_DECLS
 
diff --git a/libc/include/sys/system_properties.h b/libc/include/sys/system_properties.h
index 99a6e59..d3e0d8d 100644
--- a/libc/include/sys/system_properties.h
+++ b/libc/include/sys/system_properties.h
@@ -48,7 +48,7 @@
 
 /* Set a system property by name.
 **/
-int __system_property_set(const char* key, const char* value) __INTRODUCED_IN(21);
+int __system_property_set(const char* key, const char* value) __INTRODUCED_IN(12);
 
 /* Return a pointer to the system property named name, if it
 ** exists, or NULL if there is no such property.  Use 
@@ -94,7 +94,7 @@
 ** not a bug.
 */
 int __system_property_foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie)
-  __INTRODUCED_IN(21);
+  __INTRODUCED_IN(19);
 
 __END_DECLS
 
diff --git a/libc/include/sys/timerfd.h b/libc/include/sys/timerfd.h
index a189742..8311f08 100644
--- a/libc/include/sys/timerfd.h
+++ b/libc/include/sys/timerfd.h
@@ -41,10 +41,10 @@
 #define TFD_CLOEXEC O_CLOEXEC
 #define TFD_NONBLOCK O_NONBLOCK
 
-extern int timerfd_create(clockid_t, int) __INTRODUCED_IN(21);
+extern int timerfd_create(clockid_t, int) __INTRODUCED_IN(19);
 extern int timerfd_settime(int, int, const struct itimerspec*, struct itimerspec*)
-  __INTRODUCED_IN(21);
-extern int timerfd_gettime(int, struct itimerspec*) __INTRODUCED_IN(21);
+  __INTRODUCED_IN(19);
+extern int timerfd_gettime(int, struct itimerspec*) __INTRODUCED_IN(19);
 
 __END_DECLS
 
diff --git a/libc/include/sys/wait.h b/libc/include/sys/wait.h
index aba20e5..e0afabc 100644
--- a/libc/include/sys/wait.h
+++ b/libc/include/sys/wait.h
@@ -51,7 +51,7 @@
 
 extern pid_t  wait(int *);
 extern pid_t  waitpid(pid_t, int *, int);
-extern pid_t wait4(pid_t, int*, int, struct rusage*) __INTRODUCED_IN(19);
+extern pid_t wait4(pid_t, int*, int, struct rusage*) __INTRODUCED_IN(18);
 
 /* Posix states that idtype_t should be an enumeration type, but
  * the kernel headers define P_ALL, P_PID and P_PGID as constant macros
diff --git a/libc/include/sys/xattr.h b/libc/include/sys/xattr.h
index 070913f..63605c5 100644
--- a/libc/include/sys/xattr.h
+++ b/libc/include/sys/xattr.h
@@ -36,25 +36,25 @@
 #define XATTR_REPLACE 2
 
 extern int fsetxattr(int fd, const char* name, const void* value, size_t size, int flags)
-  __INTRODUCED_IN(21);
+  __INTRODUCED_IN(16);
 extern int setxattr(const char* path, const char* name, const void* value, size_t size, int flags)
-  __INTRODUCED_IN(21);
+  __INTRODUCED_IN(16);
 extern int lsetxattr(const char* path, const char* name, const void* value, size_t size, int flags)
-  __INTRODUCED_IN(21);
+  __INTRODUCED_IN(16);
 
-extern ssize_t fgetxattr(int fd, const char* name, void* value, size_t size) __INTRODUCED_IN(21);
+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(21);
+  __INTRODUCED_IN(16);
 extern ssize_t lgetxattr(const char* path, const char* name, void* value, size_t size)
-  __INTRODUCED_IN(21);
+  __INTRODUCED_IN(16);
 
-extern ssize_t listxattr(const char* path, char* list, size_t size) __INTRODUCED_IN(21);
-extern ssize_t llistxattr(const char* path, char* list, size_t size) __INTRODUCED_IN(21);
-extern ssize_t flistxattr(int fd, char* list, size_t size) __INTRODUCED_IN(21);
+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);
 
-extern int removexattr(const char* path, const char* name) __INTRODUCED_IN(21);
-extern int lremovexattr(const char* path, const char* name) __INTRODUCED_IN(21);
-extern int fremovexattr(int fd, const char* name) __INTRODUCED_IN(21);
+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);
 
 __END_DECLS