diff --git a/libc/include/nsswitch.h b/libc/dns/include/nsswitch.h
similarity index 100%
rename from libc/include/nsswitch.h
rename to libc/dns/include/nsswitch.h
diff --git a/libc/dns/nameser/ns_parse.c b/libc/dns/nameser/ns_parse.c
index 2d6d530..3a1901a 100644
--- a/libc/dns/nameser/ns_parse.c
+++ b/libc/dns/nameser/ns_parse.c
@@ -52,6 +52,8 @@
 
 /* Public. */
 
+struct _ns_flagdata {  int mask, shift;  };
+
 /* These need to be in the same order as the nres.h:ns_flag enum. */
 const struct _ns_flagdata _ns_flagdata[16] = {
 	{ 0x8000, 15 },		/* qr. */
diff --git a/libc/dns/net/getnameinfo.c b/libc/dns/net/getnameinfo.c
index 893e982..abd1a66 100644
--- a/libc/dns/net/getnameinfo.c
+++ b/libc/dns/net/getnameinfo.c
@@ -54,7 +54,6 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <net/if.h>
-#include <net/if_ieee1394.h>
 #include <net/if_types.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
diff --git a/libc/include/android/dlext.h b/libc/include/android/dlext.h
index 6e32b68..05a27f3 100644
--- a/libc/include/android/dlext.h
+++ b/libc/include/android/dlext.h
@@ -129,7 +129,8 @@
   struct android_namespace_t* library_namespace;
 } android_dlextinfo;
 
-extern void* android_dlopen_ext(const char* filename, int flag, const android_dlextinfo* extinfo);
+extern void* android_dlopen_ext(const char* filename, int flag, const android_dlextinfo* extinfo)
+  __INTRODUCED_IN(21);
 
 /*
  * Initializes public and anonymous namespaces. The public_ns_sonames is the list of sonames
diff --git a/libc/include/android/set_abort_message.h b/libc/include/android/set_abort_message.h
index 4b3d82b..aebedba 100644
--- a/libc/include/android/set_abort_message.h
+++ b/libc/include/android/set_abort_message.h
@@ -33,7 +33,7 @@
 
 __BEGIN_DECLS
 
-void android_set_abort_message(const char* msg);
+void android_set_abort_message(const char* msg) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/arpa/inet.h b/libc/include/arpa/inet.h
index 86265bf..e4f94ef 100644
--- a/libc/include/arpa/inet.h
+++ b/libc/include/arpa/inet.h
@@ -37,10 +37,10 @@
 
 in_addr_t inet_addr(const char*);
 int inet_aton(const char*, struct in_addr*);
-in_addr_t inet_lnaof(struct in_addr);
-struct in_addr inet_makeaddr(in_addr_t, in_addr_t);
-in_addr_t inet_netof(struct in_addr);
-in_addr_t inet_network(const char*);
+in_addr_t inet_lnaof(struct in_addr) __INTRODUCED_IN(21);
+struct in_addr inet_makeaddr(in_addr_t, in_addr_t) __INTRODUCED_IN(21);
+in_addr_t inet_netof(struct in_addr) __INTRODUCED_IN(21);
+in_addr_t inet_network(const char*) __INTRODUCED_IN(21);
 char* inet_ntoa(struct in_addr);
 const char* inet_ntop(int, const void*, char*, socklen_t);
 unsigned int inet_nsap_addr(const char*, unsigned char*, int);
diff --git a/libc/include/arpa/nameser.h b/libc/include/arpa/nameser.h
index 3690f9c..a207eab 100644
--- a/libc/include/arpa/nameser.h
+++ b/libc/include/arpa/nameser.h
@@ -141,10 +141,6 @@
 };
 typedef struct ns_newmsg ns_newmsg;
 
-/* Private data structure - do not use from outside library. */
-struct _ns_flagdata {  int mask, shift;  };
-extern const struct _ns_flagdata _ns_flagdata[];
-
 /* Accessor macros - this is part of the public interface. */
 
 #define ns_msg_id(handle) ((handle)._id + 0)
@@ -566,30 +562,34 @@
 #endif
 
 __BEGIN_DECLS
-int ns_msg_getflag(ns_msg, int);
-uint16_t ns_get16(const u_char*);
-uint32_t ns_get32(const u_char*);
-void ns_put16(uint16_t, u_char*);
-void ns_put32(uint32_t, u_char*);
-int ns_initparse(const u_char*, int, ns_msg*);
-int ns_skiprr(const u_char*, const u_char*, ns_sect, int);
-int ns_parserr(ns_msg*, ns_sect, int, ns_rr*);
-int ns_sprintrr(const ns_msg*, const ns_rr*, const char*, const char*, char*, size_t);
+int ns_msg_getflag(ns_msg, int) __INTRODUCED_IN_64(23);
+uint16_t ns_get16(const u_char*) __INTRODUCED_IN_64(23);
+uint32_t ns_get32(const u_char*) __INTRODUCED_IN_64(23);
+void ns_put16(uint16_t, u_char*) __INTRODUCED_IN_64(23);
+void ns_put32(uint32_t, u_char*) __INTRODUCED_IN_64(23);
+int ns_initparse(const u_char*, int, ns_msg*) __INTRODUCED_IN_64(23);
+int ns_skiprr(const u_char*, const u_char*, ns_sect, int) __INTRODUCED_IN_64(23);
+int ns_parserr(ns_msg*, ns_sect, int, ns_rr*) __INTRODUCED_IN_64(23);
+int ns_sprintrr(const ns_msg*, const ns_rr*, const char*, const char*, char*, size_t)
+  __INTRODUCED_IN_64(23);
 int ns_sprintrrf(const u_char*, size_t, const char*, ns_class, ns_type, u_long, const u_char*,
-                 size_t, const char*, const char*, char*, size_t);
-int ns_format_ttl(u_long, char*, size_t);
-int ns_name_ntol(const u_char*, u_char*, size_t);
-int ns_name_ntop(const u_char*, char*, size_t);
-int ns_name_pton(const char*, u_char*, size_t);
-int ns_name_unpack(const u_char*, const u_char*, const u_char*, u_char*, size_t);
-int ns_name_pack(const u_char*, u_char*, int, const u_char**, const u_char**);
-int ns_name_uncompress(const u_char*, const u_char*, const u_char*, char*, size_t);
-int ns_name_compress(const char*, u_char*, size_t, const u_char**, const u_char**);
-int ns_name_skip(const u_char**, const u_char*);
-void ns_name_rollback(const u_char*, const u_char**, const u_char**);
+                 size_t, const char*, const char*, char*, size_t) __INTRODUCED_IN_64(23);
+int ns_format_ttl(u_long, char*, size_t) __INTRODUCED_IN_64(23);
+int ns_name_ntol(const u_char*, u_char*, size_t) __INTRODUCED_IN_64(23);
+int ns_name_ntop(const u_char*, char*, size_t) __INTRODUCED_IN_64(23);
+int ns_name_pton(const char*, u_char*, size_t) __INTRODUCED_IN_64(23);
+int ns_name_unpack(const u_char*, const u_char*, const u_char*, u_char*, size_t)
+  __INTRODUCED_IN_64(23);
+int ns_name_pack(const u_char*, u_char*, int, const u_char**, const u_char**) __INTRODUCED_IN_64(23);
+int ns_name_uncompress(const u_char*, const u_char*, const u_char*, char*, size_t)
+  __INTRODUCED_IN_64(23);
+int ns_name_compress(const char*, u_char*, size_t, const u_char**, const u_char**)
+  __INTRODUCED_IN_64(23);
+int ns_name_skip(const u_char**, const u_char*) __INTRODUCED_IN_64(23);
+void ns_name_rollback(const u_char*, const u_char**, const u_char**) __INTRODUCED_IN_64(23);
 
-int ns_makecanon(const char*, char*, size_t);
-int ns_samename(const char*, const char*);
+int ns_makecanon(const char*, char*, size_t) __INTRODUCED_IN_64(23);
+int ns_samename(const char*, const char*) __INTRODUCED_IN_64(23);
 __END_DECLS
 
 #ifdef BIND_4_COMPAT
diff --git a/libc/include/bits/lockf.h b/libc/include/bits/lockf.h
index a0ba19d..655514d 100644
--- a/libc/include/bits/lockf.h
+++ b/libc/include/bits/lockf.h
@@ -42,9 +42,9 @@
 #if defined(__USE_FILE_OFFSET64)
 int lockf(int, int, off_t) __RENAME(lockf64);
 #else
-int lockf(int, int, off_t);
+int lockf(int, int, off_t) __INTRODUCED_IN(24);
 #endif
-int lockf64(int, int, off64_t);
+int lockf64(int, int, off64_t) __INTRODUCED_IN(24);
 
 __END_DECLS
 
diff --git a/libc/include/bits/strcasecmp.h b/libc/include/bits/strcasecmp.h
index 124f5cd..7cb713e 100644
--- a/libc/include/bits/strcasecmp.h
+++ b/libc/include/bits/strcasecmp.h
@@ -36,9 +36,9 @@
 __BEGIN_DECLS
 
 int strcasecmp(const char*, const char*) __purefunc;
-int strcasecmp_l(const char*, const char*, locale_t) __purefunc;
+int strcasecmp_l(const char*, const char*, locale_t) __purefunc __INTRODUCED_IN(23);
 int strncasecmp(const char*, const char*, size_t) __purefunc;
-int strncasecmp_l(const char*, const char*, size_t, locale_t) __purefunc;
+int strncasecmp_l(const char*, const char*, size_t, locale_t) __purefunc __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/bits/wctype.h b/libc/include/bits/wctype.h
index 8f32aba..fe7c80e 100644
--- a/libc/include/bits/wctype.h
+++ b/libc/include/bits/wctype.h
@@ -37,7 +37,7 @@
 
 int iswalnum(wint_t);
 int iswalpha(wint_t);
-int iswblank(wint_t);
+int iswblank(wint_t) __INTRODUCED_IN(21);
 int iswcntrl(wint_t);
 int iswdigit(wint_t);
 int iswgraph(wint_t);
@@ -56,8 +56,8 @@
 int iswctype(wint_t, wctype_t);
 
 typedef const void* wctrans_t;
-wint_t towctrans(wint_t, wctrans_t);
-wctrans_t wctrans(const char*);
+wint_t towctrans(wint_t, wctrans_t) __INTRODUCED_IN_FUTURE;
+wctrans_t wctrans(const char*) __INTRODUCED_IN_FUTURE;
 
 __END_DECLS
 
diff --git a/libc/include/complex.h b/libc/include/complex.h
index b54d2fc..66ea97e 100644
--- a/libc/include/complex.h
+++ b/libc/include/complex.h
@@ -60,101 +60,101 @@
 
 /* 7.3.5 Trigonometric functions */
 /* 7.3.5.1 The cacos functions */
-double complex cacos(double complex);
-float complex cacosf(float complex);
-long double complex cacosl(long double complex);
+double complex cacos(double complex) __INTRODUCED_IN(23);
+float complex cacosf(float complex) __INTRODUCED_IN(23);
+long double complex cacosl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.5.2 The casin functions */
-double complex casin(double complex);
-float complex casinf(float complex);
-long double complex casinl(long double complex);
+double complex casin(double complex) __INTRODUCED_IN(23);
+float complex casinf(float complex) __INTRODUCED_IN(23);
+long double complex casinl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.5.1 The catan functions */
-double complex catan(double complex);
-float complex catanf(float complex);
-long double complex catanl(long double complex);
+double complex catan(double complex) __INTRODUCED_IN(23);
+float complex catanf(float complex) __INTRODUCED_IN(23);
+long double complex catanl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.5.1 The ccos functions */
-double complex ccos(double complex);
-float complex ccosf(float complex);
-long double complex ccosl(long double complex);
+double complex ccos(double complex) __INTRODUCED_IN(23);
+float complex ccosf(float complex) __INTRODUCED_IN(23);
+long double complex ccosl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.5.1 The csin functions */
-double complex csin(double complex);
-float complex csinf(float complex);
-long double complex csinl(long double complex);
+double complex csin(double complex) __INTRODUCED_IN(23);
+float complex csinf(float complex) __INTRODUCED_IN(23);
+long double complex csinl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.5.1 The ctan functions */
-double complex ctan(double complex);
-float complex ctanf(float complex);
-long double complex ctanl(long double complex);
+double complex ctan(double complex) __INTRODUCED_IN(23);
+float complex ctanf(float complex) __INTRODUCED_IN(23);
+long double complex ctanl(long double complex) __INTRODUCED_IN_FUTURE;
 
 /* 7.3.6 Hyperbolic functions */
 /* 7.3.6.1 The cacosh functions */
-double complex cacosh(double complex);
-float complex cacoshf(float complex);
-long double complex cacoshl(long double complex);
+double complex cacosh(double complex) __INTRODUCED_IN(23);
+float complex cacoshf(float complex) __INTRODUCED_IN(23);
+long double complex cacoshl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.6.2 The casinh functions */
-double complex casinh(double complex);
-float complex casinhf(float complex);
-long double complex casinhl(long double complex);
+double complex casinh(double complex) __INTRODUCED_IN(23);
+float complex casinhf(float complex) __INTRODUCED_IN(23);
+long double complex casinhl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.6.3 The catanh functions */
-double complex catanh(double complex);
-float complex catanhf(float complex);
-long double complex catanhl(long double complex);
+double complex catanh(double complex) __INTRODUCED_IN(23);
+float complex catanhf(float complex) __INTRODUCED_IN(23);
+long double complex catanhl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.6.4 The ccosh functions */
-double complex ccosh(double complex);
-float complex ccoshf(float complex);
-long double complex ccoshl(long double complex);
+double complex ccosh(double complex) __INTRODUCED_IN(23);
+float complex ccoshf(float complex) __INTRODUCED_IN(23);
+long double complex ccoshl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.6.5 The csinh functions */
-double complex csinh(double complex);
-float complex csinhf(float complex);
-long double complex csinhl(long double complex);
+double complex csinh(double complex) __INTRODUCED_IN(23);
+float complex csinhf(float complex) __INTRODUCED_IN(23);
+long double complex csinhl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.6.6 The ctanh functions */
-double complex ctanh(double complex);
-float complex ctanhf(float complex);
-long double complex ctanhl(long double complex);
+double complex ctanh(double complex) __INTRODUCED_IN(23);
+float complex ctanhf(float complex) __INTRODUCED_IN(23);
+long double complex ctanhl(long double complex) __INTRODUCED_IN_FUTURE;
 
 /* 7.3.7 Exponential and logarithmic functions */
 /* 7.3.7.1 The cexp functions */
-double complex cexp(double complex);
-float complex cexpf(float complex);
-long double complex cexpl(long double complex);
+double complex cexp(double complex) __INTRODUCED_IN(23);
+float complex cexpf(float complex) __INTRODUCED_IN(23);
+long double complex cexpl(long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.7.2 The clog functions */
-double complex clog(double complex);
-float complex clogf(float complex);
-long double complex clogl(long double complex);
+double complex clog(double complex) __INTRODUCED_IN_FUTURE;
+float complex clogf(float complex) __INTRODUCED_IN_FUTURE;
+long double complex clogl(long double complex) __INTRODUCED_IN_FUTURE;
 
 /* 7.3.8 Power and absolute-value functions */
 /* 7.3.8.1 The cabs functions */
-double cabs(double complex);
-float cabsf(float complex);
-long double cabsl(long double complex);
+double cabs(double complex) __INTRODUCED_IN(23);
+float cabsf(float complex) __INTRODUCED_IN(23);
+long double cabsl(long double complex) __INTRODUCED_IN_32(21) __INTRODUCED_IN_64(23);
 /* 7.3.8.2 The cpow functions */
-double complex cpow(double complex, double complex);
-float complex cpowf(float complex, float complex);
-long double complex cpowl(long double complex, long double complex);
+double complex cpow(double complex, double complex) __INTRODUCED_IN_FUTURE;
+float complex cpowf(float complex, float complex) __INTRODUCED_IN_FUTURE;
+long double complex cpowl(long double complex, long double complex) __INTRODUCED_IN_FUTURE;
 /* 7.3.8.3 The csqrt functions */
-double complex csqrt(double complex);
-float complex csqrtf(float complex);
-long double complex csqrtl(long double complex);
+double complex csqrt(double complex) __INTRODUCED_IN(23);
+float complex csqrtf(float complex) __INTRODUCED_IN(23);
+long double complex csqrtl(long double complex) __INTRODUCED_IN_32(21) __INTRODUCED_IN_64(23);
 
 /* 7.3.9 Manipulation functions */
 /* 7.3.9.1 The carg functions */
-double carg(double complex);
-float cargf(float complex);
-long double cargl(long double complex);
+double carg(double complex) __INTRODUCED_IN(23);
+float cargf(float complex) __INTRODUCED_IN(23);
+long double cargl(long double complex) __INTRODUCED_IN(23);
 /* 7.3.9.2 The cimag functions */
-double cimag(double complex);
-float cimagf(float complex);
-long double cimagl(long double complex);
+double cimag(double complex) __INTRODUCED_IN(23);
+float cimagf(float complex) __INTRODUCED_IN(23);
+long double cimagl(long double complex) __INTRODUCED_IN(23);
 /* 7.3.9.3 The conj functions */
-double complex conj(double complex);
-float complex conjf(float complex);
-long double complex conjl(long double complex);
+double complex conj(double complex) __INTRODUCED_IN(23);
+float complex conjf(float complex) __INTRODUCED_IN(23);
+long double complex conjl(long double complex) __INTRODUCED_IN(23);
 /* 7.3.9.4 The cproj functions */
-double complex cproj(double complex);
-float complex cprojf(float complex);
-long double complex cprojl(long double complex);
+double complex cproj(double complex) __INTRODUCED_IN(23);
+float complex cprojf(float complex) __INTRODUCED_IN(23);
+long double complex cprojl(long double complex) __INTRODUCED_IN_32(21) __INTRODUCED_IN_64(23);
 /* 7.3.9.5 The creal functions */
-double creal(double complex);
-float crealf(float complex);
-long double creall(long double complex);
+double creal(double complex) __INTRODUCED_IN(23);
+float crealf(float complex) __INTRODUCED_IN(23);
+long double creall(long double complex) __INTRODUCED_IN(23);
 
 #pragma GCC visibility pop
 __END_DECLS
diff --git a/libc/include/ctype.h b/libc/include/ctype.h
index 83b5ba7..199f810 100644
--- a/libc/include/ctype.h
+++ b/libc/include/ctype.h
@@ -73,22 +73,20 @@
 int tolower(int);
 int toupper(int);
 
-#if __ANDROID_API__ >= 21
-int isalnum_l(int, locale_t);
-int isalpha_l(int, locale_t);
-int isblank_l(int, locale_t);
-int iscntrl_l(int, locale_t);
-int isdigit_l(int, locale_t);
-int isgraph_l(int, locale_t);
-int islower_l(int, locale_t);
-int isprint_l(int, locale_t);
-int ispunct_l(int, locale_t);
-int isspace_l(int, locale_t);
-int isupper_l(int, locale_t);
-int isxdigit_l(int, locale_t);
-int tolower_l(int, locale_t);
-int toupper_l(int, locale_t);
-#endif /* __ANDROID_API__ >= 21 */
+int isalnum_l(int, locale_t) __INTRODUCED_IN(21);
+int isalpha_l(int, locale_t) __INTRODUCED_IN(21);
+int isblank_l(int, locale_t) __INTRODUCED_IN(21);
+int iscntrl_l(int, locale_t) __INTRODUCED_IN(21);
+int isdigit_l(int, locale_t) __INTRODUCED_IN(21);
+int isgraph_l(int, locale_t) __INTRODUCED_IN(21);
+int islower_l(int, locale_t) __INTRODUCED_IN(21);
+int isprint_l(int, locale_t) __INTRODUCED_IN(21);
+int ispunct_l(int, locale_t) __INTRODUCED_IN(21);
+int isspace_l(int, locale_t) __INTRODUCED_IN(21);
+int isupper_l(int, locale_t) __INTRODUCED_IN(21);
+int isxdigit_l(int, locale_t) __INTRODUCED_IN(21);
+int tolower_l(int, locale_t) __INTRODUCED_IN(21);
+int toupper_l(int, locale_t) __INTRODUCED_IN(21);
 
 #if __BSD_VISIBLE || __ISO_C_VISIBLE >= 1999 || __POSIX_VISIBLE > 200112 \
     || __XPG_VISIBLE > 600
@@ -98,8 +96,8 @@
 #if __BSD_VISIBLE || __XPG_VISIBLE
 int isascii(int);
 int toascii(int);
-int _tolower(int);
-int _toupper(int);
+int _tolower(int) __INTRODUCED_IN(21);
+int _toupper(int) __INTRODUCED_IN(21);
 #endif /* __BSD_VISIBLE || __XPG_VISIBLE */
 
 #endif /* __GNUC__ || _ANSI_LIBRARY || lint */
diff --git a/libc/include/dirent.h b/libc/include/dirent.h
index 3cdfa68..db8a520 100644
--- a/libc/include/dirent.h
+++ b/libc/include/dirent.h
@@ -71,22 +71,25 @@
 extern DIR* opendir(const char*);
 extern DIR* fdopendir(int);
 extern struct dirent* readdir(DIR*);
-extern struct dirent64* readdir64(DIR*);
+extern struct dirent64* readdir64(DIR*) __INTRODUCED_IN(21);
 extern int readdir_r(DIR*, struct dirent*, struct dirent**);
-extern int readdir64_r(DIR*, struct dirent64*, struct dirent64**);
+extern int readdir64_r(DIR*, struct dirent64*, struct dirent64**) __INTRODUCED_IN(21);
 extern int closedir(DIR*);
 extern void rewinddir(DIR*);
-extern void seekdir(DIR*, long);
-extern long telldir(DIR*);
+extern void seekdir(DIR*, long) __INTRODUCED_IN(23);
+extern long telldir(DIR*) __INTRODUCED_IN(23);
 extern int dirfd(DIR*);
 extern int alphasort(const struct dirent**, const struct dirent**);
-extern int alphasort64(const struct dirent64**, const struct dirent64**);
-extern int scandir64(const char*, struct dirent64***, int (*)(const struct dirent64*), int (*)(const struct dirent64**, const struct dirent64**));
+extern int alphasort64(const struct dirent64**, const struct dirent64**) __INTRODUCED_IN(21);
+extern int scandir64(const char*, struct dirent64***, int (*)(const struct dirent64*),
+                     int (*)(const struct dirent64**, const struct dirent64**)) __INTRODUCED_IN(21);
 extern int scandir(const char*, struct dirent***, int (*)(const struct dirent*), int (*)(const struct dirent**, const struct dirent**));
 
 #if defined(__USE_GNU)
-int scandirat64(int, const char*, struct dirent64***, int (*)(const struct dirent64*), int (*)(const struct dirent64**, const struct dirent64**));
-int scandirat(int, const char*, struct dirent***, int (*)(const struct dirent*), int (*)(const struct dirent**, const struct dirent**));
+int scandirat64(int, const char*, struct dirent64***, int (*)(const struct dirent64*),
+                int (*)(const struct dirent64**, const struct dirent64**)) __INTRODUCED_IN(24);
+int scandirat(int, const char*, struct dirent***, int (*)(const struct dirent*),
+              int (*)(const struct dirent**, const struct dirent**)) __INTRODUCED_IN(24);
 #endif
 
 __END_DECLS
diff --git a/libc/include/dlfcn.h b/libc/include/dlfcn.h
index c2e8980..25a302f 100644
--- a/libc/include/dlfcn.h
+++ b/libc/include/dlfcn.h
@@ -47,7 +47,8 @@
 extern int dlclose(void*  handle);
 extern const char* dlerror(void);
 extern void* dlsym(void* handle, const char* symbol) __nonnull((2));
-extern void* dlvsym(void* handle, const char* symbol, const char* version) __nonnull((2, 3));
+extern void* dlvsym(void* handle, const char* symbol, const char* version) __nonnull((2, 3))
+  __INTRODUCED_IN(24);
 extern int dladdr(const void* addr, Dl_info *info);
 
 enum {
diff --git a/libc/include/error.h b/libc/include/error.h
index dd12884..205890f 100644
--- a/libc/include/error.h
+++ b/libc/include/error.h
@@ -33,12 +33,13 @@
 
 __BEGIN_DECLS
 
-void error(int, int, const char*, ...) __printflike(3, 4);
-void error_at_line(int, int, const char*, unsigned int, const char*, ...) __printflike(5, 6);
+void error(int, int, const char*, ...) __printflike(3, 4) __INTRODUCED_IN(23);
+void error_at_line(int, int, const char*, unsigned int, const char*, ...) __printflike(5, 6)
+  __INTRODUCED_IN(23);
 
-extern void (*error_print_progname)(void);
-extern unsigned int error_message_count;
-extern int error_one_per_line;
+extern void (*error_print_progname)(void) __INTRODUCED_IN(23);
+extern unsigned int error_message_count __INTRODUCED_IN(23);
+extern int error_one_per_line __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/fcntl.h b/libc/include/fcntl.h
index 013d72c..c8030f1 100644
--- a/libc/include/fcntl.h
+++ b/libc/include/fcntl.h
@@ -64,36 +64,36 @@
 #define SYNC_FILE_RANGE_WAIT_AFTER 4
 
 extern int creat(const char*, mode_t);
-extern int creat64(const char*, mode_t);
+extern int creat64(const char*, mode_t) __INTRODUCED_IN(21);
 extern int openat(int, const char*, int, ...);
-extern int openat64(int, const char*, int, ...);
+extern int openat64(int, const char*, int, ...) __INTRODUCED_IN(21);
 extern int open(const char*, int, ...);
-extern int open64(const char*, int, ...);
-extern ssize_t splice(int, off64_t*, int, off64_t*, size_t, unsigned int);
-extern ssize_t tee(int, int, size_t, unsigned int);
-extern ssize_t vmsplice(int, const struct iovec*, size_t, unsigned int);
+extern int open64(const char*, int, ...) __INTRODUCED_IN(21);
+extern ssize_t splice(int, off64_t*, int, off64_t*, size_t, unsigned int) __INTRODUCED_IN(21);
+extern ssize_t tee(int, int, size_t, unsigned int) __INTRODUCED_IN(21);
+extern ssize_t vmsplice(int, const struct iovec*, size_t, unsigned int) __INTRODUCED_IN(21);
 
 #if defined(__USE_FILE_OFFSET64)
-extern int fallocate(int, int, off_t, off_t) __RENAME(fallocate64);
-extern int posix_fadvise(int, off_t, off_t, int) __RENAME(posix_fadvise64);
-extern int posix_fallocate(int, off_t, off_t) __RENAME(posix_fallocate);
+extern int fallocate(int, int, off_t, off_t) __RENAME(fallocate64) __INTRODUCED_IN(21);
+extern int posix_fadvise(int, off_t, off_t, int) __RENAME(posix_fadvise64) __INTRODUCED_IN(21);
+extern int posix_fallocate(int, off_t, off_t) __RENAME(posix_fallocate) __INTRODUCED_IN(21);
 #else
-extern int fallocate(int, int, off_t, off_t);
-extern int posix_fadvise(int, off_t, off_t, int);
-extern int posix_fallocate(int, off_t, off_t);
+extern int fallocate(int, int, off_t, off_t) __INTRODUCED_IN(21);
+extern int posix_fadvise(int, off_t, off_t, int) __INTRODUCED_IN(21);
+extern int posix_fallocate(int, off_t, off_t) __INTRODUCED_IN(21);
 #endif
-extern int fallocate64(int, int, off64_t, off64_t);
-extern int posix_fadvise64(int, off64_t, off64_t, int);
-extern int posix_fallocate64(int, off64_t, off64_t);
+extern int fallocate64(int, int, off64_t, off64_t) __INTRODUCED_IN(21);
+extern int posix_fadvise64(int, off64_t, off64_t, int) __INTRODUCED_IN(21);
+extern int posix_fallocate64(int, off64_t, off64_t) __INTRODUCED_IN(21);
 
 #if defined(__USE_GNU)
-ssize_t readahead(int, off64_t, size_t);
-int sync_file_range(int, off64_t, off64_t, unsigned int);
+ssize_t readahead(int, off64_t, size_t) __INTRODUCED_IN(21);
+int sync_file_range(int, off64_t, off64_t, unsigned int) __INTRODUCED_IN_FUTURE;
 #endif
 
-extern int __open_2(const char*, int);
+extern int __open_2(const char*, int) __INTRODUCED_IN(21);
 extern int __open_real(const char*, int, ...) __RENAME(open);
-extern int __openat_2(int, const char*, int);
+extern int __openat_2(int, const char*, int) __INTRODUCED_IN(21);
 extern int __openat_real(int, const char*, int, ...) __RENAME(openat);
 __errordecl(__creat_missing_mode, "called with O_CREAT, but missing mode");
 __errordecl(__creat_too_many_args, "too many arguments");
diff --git a/libc/include/fenv.h b/libc/include/fenv.h
index 73ecc80..e51f9b6 100644
--- a/libc/include/fenv.h
+++ b/libc/include/fenv.h
@@ -36,23 +36,23 @@
 __BEGIN_DECLS
 #pragma GCC visibility push(default)
 
-int feclearexcept(int);
-int fegetexceptflag(fexcept_t *, int);
-int feraiseexcept(int);
-int fesetexceptflag(const fexcept_t *, int);
-int fetestexcept(int);
+int feclearexcept(int) __INTRODUCED_IN(21);
+int fegetexceptflag(fexcept_t*, int) __INTRODUCED_IN(21);
+int feraiseexcept(int) __INTRODUCED_IN(21);
+int fesetexceptflag(const fexcept_t*, int) __INTRODUCED_IN(21);
+int fetestexcept(int) __INTRODUCED_IN(21);
 
-int fegetround(void);
-int fesetround(int);
+int fegetround(void) __INTRODUCED_IN(21);
+int fesetround(int) __INTRODUCED_IN(21);
 
-int fegetenv(fenv_t *);
-int feholdexcept(fenv_t *);
-int fesetenv(const fenv_t *);
-int feupdateenv(const fenv_t *);
+int fegetenv(fenv_t*) __INTRODUCED_IN(21);
+int feholdexcept(fenv_t*) __INTRODUCED_IN(21);
+int fesetenv(const fenv_t*) __INTRODUCED_IN(21);
+int feupdateenv(const fenv_t*) __INTRODUCED_IN(21);
 
-int feenableexcept(int);
-int fedisableexcept(int);
-int fegetexcept(void);
+int feenableexcept(int) __INTRODUCED_IN(21);
+int fedisableexcept(int) __INTRODUCED_IN(21);
+int fegetexcept(void) __INTRODUCED_IN(21);
 
 /*
  * The following constant represents the default floating-point environment
diff --git a/libc/include/ftw.h b/libc/include/ftw.h
index af524d0..ebd59f5 100644
--- a/libc/include/ftw.h
+++ b/libc/include/ftw.h
@@ -54,12 +54,12 @@
 };
 
 __BEGIN_DECLS
-int	ftw(const char *, int (*)(const char *, const struct stat *, int), int);
-int	nftw(const char *, int (*)(const char *, const struct stat *, int,
-	    struct FTW *), int, int);
-int	ftw64(const char *, int (*)(const char *, const struct stat64 *, int), int);
-int	nftw64(const char *, int (*)(const char *, const struct stat64 *, int,
-	    struct FTW *), int, int);
+int ftw(const char*, int (*)(const char*, const struct stat*, int), int) __INTRODUCED_IN(21);
+int nftw(const char*, int (*)(const char*, const struct stat*, int, struct FTW*), int, int)
+  __INTRODUCED_IN(21);
+int ftw64(const char*, int (*)(const char*, const struct stat64*, int), int) __INTRODUCED_IN(21);
+int nftw64(const char*, int (*)(const char*, const struct stat64*, int, struct FTW*), int, int)
+  __INTRODUCED_IN(21);
 __END_DECLS
 
 #endif	/* !_FTW_H */
diff --git a/libc/include/grp.h b/libc/include/grp.h
index 3ae0d6e..42cf223 100644
--- a/libc/include/grp.h
+++ b/libc/include/grp.h
@@ -55,11 +55,12 @@
 struct group* getgrnam(const char *);
 #if __POSIX_VISIBLE >= 200112 || __XPG_VISIBLE
 /* Android has thousands and thousands of ids to iterate through */
-struct group* getgrent(void) __attribute__((warning("getgrent is inefficient on Android")));
-void setgrent(void);
-void endgrent(void);
-int getgrgid_r(gid_t, struct group *, char *, size_t, struct group **);
-int getgrnam_r(const char *, struct group *, char *, size_t, struct group **);
+struct group* getgrent(void)
+  __attribute__((warning("getgrent is inefficient on Android"))) __INTRODUCED_IN_FUTURE;
+void setgrent(void) __INTRODUCED_IN_FUTURE;
+void endgrent(void) __INTRODUCED_IN_FUTURE;
+int getgrgid_r(gid_t, struct group*, char*, size_t, struct group**) __INTRODUCED_IN(24);
+int getgrnam_r(const char*, struct group*, char*, size_t, struct group**) __INTRODUCED_IN(24);
 #endif
 
 int getgrouplist (const char *user, gid_t group, gid_t *groups, int *ngroups);
diff --git a/libc/include/ifaddrs.h b/libc/include/ifaddrs.h
index 54a5a2c..083b27a 100644
--- a/libc/include/ifaddrs.h
+++ b/libc/include/ifaddrs.h
@@ -51,8 +51,8 @@
 #define ifa_broadaddr ifa_ifu.ifu_broadaddr
 #define ifa_dstaddr ifa_ifu.ifu_dstaddr
 
-void freeifaddrs(struct ifaddrs*);
-int getifaddrs(struct ifaddrs**);
+void freeifaddrs(struct ifaddrs*) __INTRODUCED_IN(24);
+int getifaddrs(struct ifaddrs**) __INTRODUCED_IN(24);
 
 __END_DECLS
 
diff --git a/libc/include/inttypes.h b/libc/include/inttypes.h
index 8853c08..4752c52 100644
--- a/libc/include/inttypes.h
+++ b/libc/include/inttypes.h
@@ -254,14 +254,12 @@
 } imaxdiv_t;
 
 __BEGIN_DECLS
-intmax_t	imaxabs(intmax_t) __pure2;
-imaxdiv_t	imaxdiv(intmax_t, intmax_t) __pure2;
+intmax_t imaxabs(intmax_t) __pure2 __INTRODUCED_IN(21);
+imaxdiv_t imaxdiv(intmax_t, intmax_t) __pure2 __INTRODUCED_IN(21);
 intmax_t	strtoimax(const char *, char **, int);
 uintmax_t	strtoumax(const char *, char **, int);
-intmax_t	wcstoimax(const wchar_t * __restrict,
-		    wchar_t ** __restrict, int);
-uintmax_t	wcstoumax(const wchar_t * __restrict,
-		    wchar_t ** __restrict, int);
+intmax_t wcstoimax(const wchar_t* __restrict, wchar_t** __restrict, int) __INTRODUCED_IN(21);
+uintmax_t wcstoumax(const wchar_t* __restrict, wchar_t** __restrict, int) __INTRODUCED_IN(21);
 __END_DECLS
 
 #endif /* _INTTYPES_H_ */
diff --git a/libc/include/link.h b/libc/include/link.h
index cb8e139..2d189f6 100644
--- a/libc/include/link.h
+++ b/libc/include/link.h
@@ -46,7 +46,11 @@
   ElfW(Half) dlpi_phnum;
 };
 
+#if defined(__arm__)
+int dl_iterate_phdr(int (*)(struct dl_phdr_info*, size_t, void*), void*) __INTRODUCED_IN(21);
+#else
 int dl_iterate_phdr(int (*)(struct dl_phdr_info*, size_t, void*), void*);
+#endif
 
 #ifdef __arm__
 typedef long unsigned int* _Unwind_Ptr;
diff --git a/libc/include/locale.h b/libc/include/locale.h
index 7fd8c2c..daef18f 100644
--- a/libc/include/locale.h
+++ b/libc/include/locale.h
@@ -92,13 +92,13 @@
     char  int_n_sign_posn;
 };
 
-struct lconv* localeconv(void);
+struct lconv* localeconv(void) __INTRODUCED_IN(21);
 
-locale_t duplocale(locale_t);
-void freelocale(locale_t);
-locale_t newlocale(int, const char*, locale_t);
+locale_t duplocale(locale_t) __INTRODUCED_IN(21);
+void freelocale(locale_t) __INTRODUCED_IN(21);
+locale_t newlocale(int, const char*, locale_t) __INTRODUCED_IN(21);
 char* setlocale(int, const char*);
-locale_t uselocale(locale_t);
+locale_t uselocale(locale_t) __INTRODUCED_IN(21);
 
 #define LC_GLOBAL_LOCALE ((locale_t) -1L)
 
diff --git a/libc/include/malloc.h b/libc/include/malloc.h
index 87555a9..02e2da7 100644
--- a/libc/include/malloc.h
+++ b/libc/include/malloc.h
@@ -29,7 +29,7 @@
 extern void free(void* p);
 
 extern void* memalign(size_t alignment, size_t byte_count) __mallocfunc __wur __attribute__((alloc_size(2)));
-extern size_t malloc_usable_size(const void* p);
+extern size_t malloc_usable_size(const void* p) __INTRODUCED_IN(21);
 
 #ifndef STRUCT_MALLINFO_DECLARED
 #define STRUCT_MALLINFO_DECLARED 1
@@ -68,7 +68,7 @@
  *   <!-- more heaps -->
  * </malloc>
  */
-extern int malloc_info(int, FILE *);
+extern int malloc_info(int, FILE*) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/math.h b/libc/include/math.h
index 203968a..97539d7 100644
--- a/libc/include/math.h
+++ b/libc/include/math.h
@@ -127,6 +127,13 @@
 #endif
 #endif /* __BSD_VISIBLE */
 
+/* scalbln, scalbnf, and scalblnl were unavailable on x86 until API level 18 */
+#if defined(__i386__)
+#define __INTRODUCED_IN_X86 __INTRODUCED_IN
+#else
+#define __INTRODUCED_IN_X86(x)
+#endif
+
 /*
  * Most of these functions depend on the rounding mode and have the side
  * effect of raising floating-point exceptions, so they are not declared
@@ -144,7 +151,7 @@
 int	__isfinitel(long double) __pure2;
 int	__isinff(float) __pure2;
 int	__isinfl(long double) __pure2;
-int	__isnanf(float) __pure2;
+int __isnanf(float) __pure2 __INTRODUCED_IN(21);
 int	__isnanl(long double) __pure2;
 int	__isnormalf(float) __pure2;
 int	__isnormal(double) __pure2;
@@ -195,17 +202,17 @@
 double	fma(double, double, double);
 double	hypot(double, double);
 int	ilogb(double) __pure2;
-int	(isinf)(double) __pure2;
+int(isinf)(double) __pure2 __INTRODUCED_IN(21);
 int	(isnan)(double) __pure2;
 double	lgamma(double);
 long long llrint(double);
 long long llround(double);
 double	log1p(double);
-double	log2(double);
+double log2(double) __INTRODUCED_IN(18);
 double	logb(double);
 long	lrint(double);
 long	lround(double);
-double	nan(const char *) __pure2;
+double nan(const char*) __pure2 __INTRODUCED_IN(13);
 double	nextafter(double, double);
 double	remainder(double, double);
 double	remquo(double, double, int *);
@@ -237,7 +244,7 @@
 double	nearbyint(double);
 double	round(double);
 double	scalbln(double, long);
-double	scalbn(double, int);
+double scalbn(double, int) __INTRODUCED_IN_X86(18);
 double	tgamma(double);
 double	trunc(double);
 #endif
@@ -249,7 +256,7 @@
 double	drem(double, double);
 int	finite(double) __pure2;
 int	isnanf(float) __pure2;
-long double significandl(long double);
+long double significandl(long double) __INTRODUCED_IN(21);
 
 /*
  * Reentrant version of gamma & lgamma; passes signgam back by reference
@@ -286,7 +293,7 @@
 float	ldexpf(float, int);
 float	log10f(float);
 float	log1pf(float);
-float	log2f(float);
+float log2f(float) __INTRODUCED_IN(18);
 float	logf(float);
 float	modff(float, float *);	/* fundamentally !__pure2 */
 
@@ -303,7 +310,7 @@
 float	erfcf(float);
 float	hypotf(float, float);
 float	lgammaf(float);
-float	tgammaf(float);
+float tgammaf(float) __INTRODUCED_IN(13);
 
 float	acoshf(float);
 float	asinhf(float);
@@ -315,14 +322,14 @@
 long long llroundf(float);
 long	lrintf(float);
 long	lroundf(float);
-float	nanf(const char *) __pure2;
+float nanf(const char*) __pure2 __INTRODUCED_IN(13);
 float	nearbyintf(float);
 float	nextafterf(float, float);
 float	remainderf(float, float);
 float	remquof(float, float, int *);
 float	rintf(float);
 float	scalblnf(float, long);
-float	scalbnf(float, int);
+float scalbnf(float, int) __INTRODUCED_IN_X86(18);
 float	truncf(float);
 
 float	fdimf(float, float);
@@ -364,69 +371,69 @@
  * long double versions of ISO/POSIX math functions
  */
 #if __ISO_C_VISIBLE >= 1999
-long double	acoshl(long double);
-long double	acosl(long double);
-long double	asinhl(long double);
-long double	asinl(long double);
-long double	atan2l(long double, long double);
-long double	atanhl(long double);
-long double	atanl(long double);
-long double	cbrtl(long double);
+long double acoshl(long double) __INTRODUCED_IN(21);
+long double acosl(long double) __INTRODUCED_IN(21);
+long double asinhl(long double) __INTRODUCED_IN(21);
+long double asinl(long double) __INTRODUCED_IN(21);
+long double atan2l(long double, long double) __INTRODUCED_IN(21);
+long double atanhl(long double) __INTRODUCED_IN(21);
+long double atanl(long double) __INTRODUCED_IN(21);
+long double cbrtl(long double) __INTRODUCED_IN(21);
 long double	ceill(long double);
 long double	copysignl(long double, long double) __pure2;
-long double	coshl(long double);
-long double	cosl(long double);
-long double	erfcl(long double);
-long double	erfl(long double);
-long double	exp2l(long double);
-long double	expl(long double);
-long double	expm1l(long double);
+long double coshl(long double) __INTRODUCED_IN(21);
+long double cosl(long double) __INTRODUCED_IN(21);
+long double erfcl(long double) __INTRODUCED_IN(21);
+long double erfl(long double) __INTRODUCED_IN(21);
+long double exp2l(long double) __INTRODUCED_IN(21);
+long double expl(long double) __INTRODUCED_IN(21);
+long double expm1l(long double) __INTRODUCED_IN(21);
 long double	fabsl(long double) __pure2;
 long double	fdiml(long double, long double);
 long double	floorl(long double);
-long double	fmal(long double, long double, long double);
+long double fmal(long double, long double, long double) __INTRODUCED_IN(21);
 long double	fmaxl(long double, long double) __pure2;
 long double	fminl(long double, long double) __pure2;
-long double	fmodl(long double, long double);
-long double	frexpl(long double value, int *); /* fundamentally !__pure2 */
-long double	hypotl(long double, long double);
+long double fmodl(long double, long double) __INTRODUCED_IN(21);
+long double frexpl(long double value, int*) __INTRODUCED_IN(21); /* fundamentally !__pure2 */
+long double hypotl(long double, long double) __INTRODUCED_IN(21);
 int		ilogbl(long double) __pure2;
 long double	ldexpl(long double, int);
-long double	lgammal(long double);
-long long	llrintl(long double);
+long double lgammal(long double) __INTRODUCED_IN(21);
+long long llrintl(long double) __INTRODUCED_IN(21);
 long long	llroundl(long double);
-long double	log10l(long double);
-long double	log1pl(long double);
-long double	log2l(long double);
-long double	logbl(long double);
-long double	logl(long double);
-long		lrintl(long double);
+long double log10l(long double) __INTRODUCED_IN(21);
+long double log1pl(long double) __INTRODUCED_IN(21);
+long double log2l(long double) __INTRODUCED_IN(18);
+long double logbl(long double) __INTRODUCED_IN(18);
+long double logl(long double) __INTRODUCED_IN(21);
+long lrintl(long double) __INTRODUCED_IN(21);
 long		lroundl(long double);
-long double	modfl(long double, long double *); /* fundamentally !__pure2 */
-long double	nanl(const char *) __pure2;
-long double	nearbyintl(long double);
-long double	nextafterl(long double, long double);
-double		nexttoward(double, long double);
+long double modfl(long double, long double*) __INTRODUCED_IN(21); /* fundamentally !__pure2 */
+long double nanl(const char*) __pure2 __INTRODUCED_IN(13);
+long double nearbyintl(long double) __INTRODUCED_IN(21);
+long double nextafterl(long double, long double) __INTRODUCED_IN(21);
+double nexttoward(double, long double) __INTRODUCED_IN(18);
 float		nexttowardf(float, long double);
-long double	nexttowardl(long double, long double);
-long double	powl(long double, long double);
-long double	remainderl(long double, long double);
-long double	remquol(long double, long double, int *);
-long double	rintl(long double);
+long double nexttowardl(long double, long double) __INTRODUCED_IN(18);
+long double powl(long double, long double) __INTRODUCED_IN(21);
+long double remainderl(long double, long double) __INTRODUCED_IN(21);
+long double remquol(long double, long double, int*) __INTRODUCED_IN(21);
+long double rintl(long double) __INTRODUCED_IN(21);
 long double	roundl(long double);
 long double	scalblnl(long double, long);
-long double	scalbnl(long double, int);
-long double	sinhl(long double);
-long double	sinl(long double);
-long double	sqrtl(long double);
-long double	tanhl(long double);
-long double	tanl(long double);
-long double	tgammal(long double);
+long double scalbnl(long double, int) __INTRODUCED_IN_X86(18);
+long double sinhl(long double) __INTRODUCED_IN(21);
+long double sinl(long double) __INTRODUCED_IN(21);
+long double sqrtl(long double) __INTRODUCED_IN(21);
+long double tanhl(long double) __INTRODUCED_IN(21);
+long double tanl(long double) __INTRODUCED_IN(21);
+long double tgammal(long double) __INTRODUCED_IN(21);
 long double	truncl(long double);
 #endif /* __ISO_C_VISIBLE >= 1999 */
 
 #if __BSD_VISIBLE
-long double	lgammal_r(long double, int *);
+long double lgammal_r(long double, int*) __INTRODUCED_IN(23);
 #endif
 
 #if defined(__USE_GNU)
diff --git a/libc/include/mntent.h b/libc/include/mntent.h
index ab40079..ad9d72f 100644
--- a/libc/include/mntent.h
+++ b/libc/include/mntent.h
@@ -57,11 +57,11 @@
 
 __BEGIN_DECLS
 
-int endmntent(FILE*);
+int endmntent(FILE*) __INTRODUCED_IN(21);
 struct mntent* getmntent(FILE*);
-struct mntent* getmntent_r(FILE*, struct mntent*, char*, int);
-FILE* setmntent(const char*, const char*);
-char* hasmntopt(const struct mntent*, const char*);
+struct mntent* getmntent_r(FILE*, struct mntent*, char*, int) __INTRODUCED_IN(21);
+FILE* setmntent(const char*, const char*) __INTRODUCED_IN(21);
+char* hasmntopt(const struct mntent*, const char*) __INTRODUCED_IN_FUTURE;
 
 __END_DECLS
 
diff --git a/libc/include/net/if.h b/libc/include/net/if.h
index aa4c19e..eac7699 100644
--- a/libc/include/net/if.h
+++ b/libc/include/net/if.h
@@ -46,8 +46,8 @@
 
 char* if_indextoname(unsigned, char*);
 unsigned if_nametoindex(const char*);
-struct if_nameindex* if_nameindex(void);
-void if_freenameindex(struct if_nameindex*);
+struct if_nameindex* if_nameindex(void) __INTRODUCED_IN(24);
+void if_freenameindex(struct if_nameindex*) __INTRODUCED_IN(24);
 
 __END_DECLS
 
diff --git a/libc/include/net/if_ether.h b/libc/include/net/if_ether.h
index 6da96e4..06cceb1 100644
--- a/libc/include/net/if_ether.h
+++ b/libc/include/net/if_ether.h
@@ -205,8 +205,8 @@
  */
 #include <sys/cdefs.h>
 __BEGIN_DECLS
-char* ether_ntoa __P((const struct ether_addr*));
-struct ether_addr* ether_aton __P((const char*));
+char* ether_ntoa __P((const struct ether_addr*)) __INTRODUCED_IN(21);
+struct ether_addr* ether_aton __P((const char*)) __INTRODUCED_IN(21);
 __END_DECLS
 #endif
 
diff --git a/libc/include/net/if_ieee1394.h b/libc/include/net/if_ieee1394.h
deleted file mode 100644
index 2f8a7c3..0000000
--- a/libc/include/net/if_ieee1394.h
+++ /dev/null
@@ -1,129 +0,0 @@
-/*	$NetBSD: if_ieee1394.h,v 1.6 2005/12/10 23:21:38 elad Exp $	*/
-
-/*
- * Copyright (c) 2000 The NetBSD Foundation, Inc.
- * All rights reserved.
- *
- * This code is derived from software contributed to The NetBSD Foundation
- * by Atsushi Onoe.
- *
- * 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.
- * 3. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *	This product includes software developed by the NetBSD
- *	Foundation, Inc. and its contributors.
- * 4. Neither the name of The NetBSD Foundation nor the names of its
- *    contributors may be used to endorse or promote products derived
- *    from this software without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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 _NET_IF_IEEE1394_H_
-#define _NET_IF_IEEE1394_H_
-
-#include <sys/types.h>
-
-/* hardware address information for arp / nd */
-struct ieee1394_hwaddr {
-	u_int8_t	iha_uid[8];		/* node unique ID */
-	u_int8_t	iha_maxrec;		/* max_rec in the config ROM */
-	u_int8_t	iha_speed;		/* min of link/PHY speed */
-	u_int8_t	iha_offset[6];		/* unicast FIFO address */
-};
-
-/*
- * BPF wants to see one of these.
- */
-struct ieee1394_bpfhdr {
-	uint8_t		ibh_dhost[8];
-	uint8_t		ibh_shost[8];
-	uint16_t	ibh_type;
-};
-
-#ifdef _KERNEL
-
-/* pseudo header */
-struct ieee1394_header {
-	u_int8_t	ih_uid[8];		/* dst/src uid */
-	u_int8_t	ih_maxrec;		/* dst maxrec for tx */
-	u_int8_t	ih_speed;		/* speed */
-	u_int8_t	ih_offset[6];		/* dst offset */
-};
-
-/* unfragment encapsulation header */
-struct ieee1394_unfraghdr {
-	u_int16_t	iuh_ft;			/* fragment type == 0 */
-	u_int16_t	iuh_etype;		/* ether_type */
-};
-
-/* fragmented encapsulation header */
-struct ieee1394_fraghdr {
-	u_int16_t	ifh_ft_size;		/* fragment type, data size-1 */
-	u_int16_t	ifh_etype_off;		/* etype for first fragment */
-						/* offset for subseq frag */
-	u_int16_t	ifh_dgl;		/* datagram label */
-	u_int16_t	ifh_reserved;
-};
-
-#define	IEEE1394_FT_SUBSEQ	0x8000
-#define	IEEE1394_FT_MORE	0x4000
-
-#define	IEEE1394MTU		1500
-
-#define	IEEE1394_GASP_LEN	8		/* GASP header for Stream */
-#define	IEEE1394_ADDR_LEN	8
-#define	IEEE1394_CRC_LEN	4
-
-struct ieee1394_reass_pkt {
-	LIST_ENTRY(ieee1394_reass_pkt) rp_next;
-	struct mbuf	*rp_m;
-	u_int16_t	rp_size;
-	u_int16_t	rp_etype;
-	u_int16_t	rp_off;
-	u_int16_t	rp_dgl;
-	u_int16_t	rp_len;
-	u_int16_t	rp_ttl;
-};
-
-struct ieee1394_reassq {
-	LIST_ENTRY(ieee1394_reassq) rq_node;
-	LIST_HEAD(, ieee1394_reass_pkt) rq_pkt;
-	u_int32_t	fr_id;
-};
-
-struct ieee1394com {
-	struct ifnet	fc_if;
-	struct ieee1394_hwaddr ic_hwaddr;
-	u_int16_t	ic_dgl;
-	LIST_HEAD(, ieee1394_reassq) ic_reassq;
-};
-
-const char *ieee1394_sprintf(const u_int8_t *);
-void ieee1394_input(struct ifnet *, struct mbuf *, u_int16_t);
-void ieee1394_ifattach(struct ifnet *, const struct ieee1394_hwaddr *);
-void ieee1394_ifdetach(struct ifnet *);
-int  ieee1394_ioctl(struct ifnet *, u_long, caddr_t);
-struct mbuf * ieee1394_fragment(struct ifnet *, struct mbuf *, int, u_int16_t);
-void ieee1394_drain(struct ifnet *);
-void ieee1394_watchdog(struct ifnet *);
-#endif /* _KERNEL */
-
-#endif /* !_NET_IF_IEEE1394_H_ */
diff --git a/libc/include/netdb.h b/libc/include/netdb.h
index 339bac2..6bcfdcd 100644
--- a/libc/include/netdb.h
+++ b/libc/include/netdb.h
@@ -202,11 +202,12 @@
 void endservent(void);
 struct hostent* gethostbyaddr(const void*, socklen_t, int);
 int gethostbyaddr_r(const void*, socklen_t, int, struct hostent*, char*, size_t, struct hostent**,
-                    int*);
+                    int*) __INTRODUCED_IN(23);
 struct hostent* gethostbyname(const char*);
 int gethostbyname_r(const char*, struct hostent*, char*, size_t, struct hostent**, int*);
 struct hostent* gethostbyname2(const char*, int);
-int gethostbyname2_r(const char*, int, struct hostent*, char*, size_t, struct hostent**, int*);
+int gethostbyname2_r(const char*, int, struct hostent*, char*, size_t, struct hostent**, int*)
+  __INTRODUCED_IN(23);
 struct hostent* gethostent(void);
 struct netent* getnetbyaddr(uint32_t, int);
 struct netent* getnetbyname(const char*);
diff --git a/libc/include/netinet/in.h b/libc/include/netinet/in.h
index 5f3d11f..b524b05 100644
--- a/libc/include/netinet/in.h
+++ b/libc/include/netinet/in.h
@@ -49,8 +49,8 @@
 
 int bindresvport(int, struct sockaddr_in*);
 
-extern const struct in6_addr in6addr_any;
-extern const struct in6_addr in6addr_loopback;
+extern const struct in6_addr in6addr_any __INTRODUCED_IN(24);
+extern const struct in6_addr in6addr_loopback __INTRODUCED_IN(24);
 
 __END_DECLS
 
diff --git a/libc/include/nl_types.h b/libc/include/nl_types.h
index 84227bd..bcaab06 100644
--- a/libc/include/nl_types.h
+++ b/libc/include/nl_types.h
@@ -39,9 +39,9 @@
 typedef void* nl_catd;
 typedef int nl_item;
 
-nl_catd catopen(const char*, int);
-char* catgets(nl_catd, int, int, const char*);
-int catclose(nl_catd);
+nl_catd catopen(const char*, int) __INTRODUCED_IN_FUTURE;
+char* catgets(nl_catd, int, int, const char*) __INTRODUCED_IN_FUTURE;
+int catclose(nl_catd) __INTRODUCED_IN_FUTURE;
 
 __END_DECLS
 
diff --git a/libc/include/poll.h b/libc/include/poll.h
index 7c16d81..d75c2d0 100644
--- a/libc/include/poll.h
+++ b/libc/include/poll.h
@@ -39,14 +39,16 @@
 typedef unsigned int nfds_t;
 
 int poll(struct pollfd*, nfds_t, int);
-int ppoll(struct pollfd*, nfds_t, const struct timespec*, const sigset_t*);
+int ppoll(struct pollfd*, nfds_t, const struct timespec*, const sigset_t*) __INTRODUCED_IN(21);
 
-int __poll_chk(struct pollfd*, nfds_t, int, size_t);
+int __poll_chk(struct pollfd*, nfds_t, int, size_t) __INTRODUCED_IN(23);
 int __poll_real(struct pollfd*, nfds_t, int) __RENAME(poll);
 __errordecl(__poll_too_small_error, "poll: pollfd array smaller than fd count");
 
-int __ppoll_chk(struct pollfd*, nfds_t, const struct timespec*, const sigset_t*, size_t);
-int __ppoll_real(struct pollfd*, nfds_t, const struct timespec*, const sigset_t*) __RENAME(ppoll);
+int __ppoll_chk(struct pollfd*, nfds_t, const struct timespec*, const sigset_t*, size_t)
+  __INTRODUCED_IN(23);
+int __ppoll_real(struct pollfd*, nfds_t, const struct timespec*, const sigset_t*) __RENAME(ppoll)
+  __INTRODUCED_IN(21);
 __errordecl(__ppoll_too_small_error, "ppoll: pollfd array smaller than fd count");
 
 #if defined(__BIONIC_FORTIFY)
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index a0fcc88..2df9b74 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -133,7 +133,7 @@
 
 __BEGIN_DECLS
 
-int pthread_atfork(void (*)(void), void (*)(void), void(*)(void));
+int pthread_atfork(void (*)(void), void (*)(void), void (*)(void)) __INTRODUCED_IN(21);
 
 int pthread_attr_destroy(pthread_attr_t*) __nonnull((1));
 int pthread_attr_getdetachstate(const pthread_attr_t*, int*) __nonnull((1, 2));
@@ -153,10 +153,11 @@
 int pthread_attr_setstacksize(pthread_attr_t*, size_t) __nonnull((1));
 
 int pthread_condattr_destroy(pthread_condattr_t*) __nonnull((1));
-int pthread_condattr_getclock(const pthread_condattr_t*, clockid_t*) __nonnull((1, 2));
+int pthread_condattr_getclock(const pthread_condattr_t*, clockid_t*) __nonnull((1, 2))
+  __INTRODUCED_IN(21);
 int pthread_condattr_getpshared(const pthread_condattr_t*, int*) __nonnull((1, 2));
 int pthread_condattr_init(pthread_condattr_t*) __nonnull((1));
-int pthread_condattr_setclock(pthread_condattr_t*, clockid_t) __nonnull((1));
+int pthread_condattr_setclock(pthread_condattr_t*, clockid_t) __nonnull((1)) __INTRODUCED_IN(21);
 int pthread_condattr_setpshared(pthread_condattr_t*, int) __nonnull((1));
 
 int pthread_cond_broadcast(pthread_cond_t*) __nonnull((1));
@@ -180,7 +181,7 @@
 
 void* pthread_getspecific(pthread_key_t);
 
-pid_t pthread_gettid_np(pthread_t);
+pid_t pthread_gettid_np(pthread_t) __INTRODUCED_IN(21);
 
 int pthread_join(pthread_t, void**);
 
@@ -201,7 +202,8 @@
 #else
 int pthread_mutex_lock(pthread_mutex_t*) __nonnull((1));
 #endif
-int pthread_mutex_timedlock(pthread_mutex_t*, const struct timespec*) __nonnull((1, 2));
+int pthread_mutex_timedlock(pthread_mutex_t*, const struct timespec*) __nonnull((1, 2))
+  __INTRODUCED_IN(21);
 int pthread_mutex_trylock(pthread_mutex_t*) __nonnull((1));
 #if !defined(__LP4__)
 int pthread_mutex_unlock(pthread_mutex_t*) /* __nonnull((1)) */;
@@ -215,8 +217,9 @@
 int pthread_rwlockattr_destroy(pthread_rwlockattr_t*) __nonnull((1));
 int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t*, int*) __nonnull((1, 2));
 int pthread_rwlockattr_setpshared(pthread_rwlockattr_t*, int) __nonnull((1));
-int pthread_rwlockattr_getkind_np(const pthread_rwlockattr_t*, int*) __nonnull((1, 2));
-int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t*, int) __nonnull((1));
+int pthread_rwlockattr_getkind_np(const pthread_rwlockattr_t*, int*) __nonnull((1, 2))
+  __INTRODUCED_IN(23);
+int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t*, int) __nonnull((1)) __INTRODUCED_IN(23);
 
 int pthread_rwlock_destroy(pthread_rwlock_t*) __nonnull((1));
 int pthread_rwlock_init(pthread_rwlock_t*, const pthread_rwlockattr_t*) __nonnull((1));
@@ -228,25 +231,28 @@
 int pthread_rwlock_unlock(pthread_rwlock_t *) __nonnull((1));
 int pthread_rwlock_wrlock(pthread_rwlock_t*) __nonnull((1));
 
-int pthread_barrierattr_init(pthread_barrierattr_t* attr) __nonnull((1));
-int pthread_barrierattr_destroy(pthread_barrierattr_t* attr) __nonnull((1));
-int pthread_barrierattr_getpshared(pthread_barrierattr_t* attr, int* pshared) __nonnull((1, 2));
-int pthread_barrierattr_setpshared(pthread_barrierattr_t* attr, int pshared) __nonnull((1));
+int pthread_barrierattr_init(pthread_barrierattr_t* attr) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_barrierattr_destroy(pthread_barrierattr_t* attr) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_barrierattr_getpshared(pthread_barrierattr_t* attr, int* pshared) __nonnull((1, 2))
+  __INTRODUCED_IN(24);
+int pthread_barrierattr_setpshared(pthread_barrierattr_t* attr, int pshared) __nonnull((1))
+  __INTRODUCED_IN(24);
 
-int pthread_barrier_init(pthread_barrier_t*, const pthread_barrierattr_t*, unsigned) __nonnull((1));
-int pthread_barrier_destroy(pthread_barrier_t*) __nonnull((1));
-int pthread_barrier_wait(pthread_barrier_t*) __nonnull((1));
+int pthread_barrier_init(pthread_barrier_t*, const pthread_barrierattr_t*, unsigned) __nonnull((1))
+  __INTRODUCED_IN(24);
+int pthread_barrier_destroy(pthread_barrier_t*) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_barrier_wait(pthread_barrier_t*) __nonnull((1)) __INTRODUCED_IN(24);
 
-int pthread_spin_destroy(pthread_spinlock_t*) __nonnull((1));
-int pthread_spin_init(pthread_spinlock_t*, int) __nonnull((1));
-int pthread_spin_lock(pthread_spinlock_t*) __nonnull((1));
-int pthread_spin_trylock(pthread_spinlock_t*) __nonnull((1));
-int pthread_spin_unlock(pthread_spinlock_t*) __nonnull((1));
+int pthread_spin_destroy(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_spin_init(pthread_spinlock_t*, int) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_spin_lock(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_spin_trylock(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
+int pthread_spin_unlock(pthread_spinlock_t*) __nonnull((1)) __INTRODUCED_IN(24);
 
 pthread_t pthread_self(void) __pure2;
 
 #if defined(__USE_GNU)
-int pthread_getname_np(pthread_t, char*, size_t) __nonnull((2));
+int pthread_getname_np(pthread_t, char*, size_t) __nonnull((2)) __INTRODUCED_IN_FUTURE;
 #endif
 /* TODO: this should be __USE_GNU too. */
 int pthread_setname_np(pthread_t, const char*) __nonnull((2));
diff --git a/libc/include/pty.h b/libc/include/pty.h
index bca1137..ec257a5 100644
--- a/libc/include/pty.h
+++ b/libc/include/pty.h
@@ -36,8 +36,8 @@
 
 __BEGIN_DECLS
 
-int openpty(int*, int*, char*, const struct termios*, const struct winsize*);
-int forkpty(int*, char*, const struct termios*, const struct winsize*);
+int openpty(int*, int*, char*, const struct termios*, const struct winsize*) __INTRODUCED_IN(23);
+int forkpty(int*, char*, const struct termios*, const struct winsize*) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/pwd.h b/libc/include/pwd.h
index e32825e..96a1cd4 100644
--- a/libc/include/pwd.h
+++ b/libc/include/pwd.h
@@ -119,12 +119,13 @@
 struct passwd* getpwnam(const char*);
 struct passwd* getpwuid(uid_t);
 /* Android has thousands and thousands of ids to iterate through */
-struct passwd* getpwent(void) __attribute__((warning("getpwent is inefficient on Android")));
-void setpwent(void);
-void endpwent(void);
+struct passwd* getpwent(void)
+  __attribute__((warning("getpwent is inefficient on Android"))) __INTRODUCED_IN_FUTURE;
+void setpwent(void) __INTRODUCED_IN_FUTURE;
+void endpwent(void) __INTRODUCED_IN_FUTURE;
 
-int getpwnam_r(const char*, struct passwd*, char*, size_t, struct passwd**);
-int getpwuid_r(uid_t, struct passwd*, char*, size_t, struct passwd**);
+int getpwnam_r(const char*, struct passwd*, char*, size_t, struct passwd**) __INTRODUCED_IN(21);
+int getpwuid_r(uid_t, struct passwd*, char*, size_t, struct passwd**) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sched.h b/libc/include/sched.h
index 0b9235b..a1f1dfa 100644
--- a/libc/include/sched.h
+++ b/libc/include/sched.h
@@ -53,9 +53,9 @@
 #if defined(__USE_GNU)
 
 extern int clone(int (*)(void*), void*, int, void*, ...);
-extern int unshare(int);
-extern int sched_getcpu(void);
-extern int setns(int, int);
+extern int unshare(int) __INTRODUCED_IN(21);
+extern int sched_getcpu(void) __INTRODUCED_IN(21);
+extern int setns(int, int) __INTRODUCED_IN(21);
 
 #ifdef __LP64__
 #define CPU_SETSIZE 1024
@@ -72,9 +72,9 @@
   __CPU_BITTYPE  __bits[ CPU_SETSIZE / __CPU_BITS ];
 } cpu_set_t;
 
-extern int sched_setaffinity(pid_t pid, size_t setsize, const cpu_set_t* set);
+extern int sched_setaffinity(pid_t pid, size_t setsize, const cpu_set_t* set) __INTRODUCED_IN(21);
 
-extern int sched_getaffinity(pid_t pid, size_t setsize, cpu_set_t* set);
+extern int sched_getaffinity(pid_t pid, size_t setsize, cpu_set_t* set) __INTRODUCED_IN(21);
 
 #define CPU_ZERO(set)          CPU_ZERO_S(sizeof(cpu_set_t), set)
 #define CPU_SET(cpu, set)      CPU_SET_S(cpu, sizeof(cpu_set_t), set)
@@ -97,8 +97,8 @@
 #define CPU_ALLOC(count)  __sched_cpualloc((count))
 #define CPU_FREE(set)     __sched_cpufree((set))
 
-extern cpu_set_t* __sched_cpualloc(size_t count);
-extern void       __sched_cpufree(cpu_set_t* set);
+extern cpu_set_t* __sched_cpualloc(size_t count) __INTRODUCED_IN(21);
+extern void __sched_cpufree(cpu_set_t* set) __INTRODUCED_IN(21);
 
 #define CPU_ZERO_S(setsize, set)  __builtin_memset(set, 0, setsize)
 
@@ -142,7 +142,7 @@
 
 #define CPU_COUNT_S(setsize, set)  __sched_cpucount((setsize), (set))
 
-extern int __sched_cpucount(size_t setsize, cpu_set_t* set);
+extern int __sched_cpucount(size_t setsize, cpu_set_t* set) __INTRODUCED_IN(21);
 
 #endif /* __USE_GNU */
 
diff --git a/libc/include/search.h b/libc/include/search.h
index 9b01e12..1ac6d21 100644
--- a/libc/include/search.h
+++ b/libc/include/search.h
@@ -29,17 +29,20 @@
 
 __BEGIN_DECLS
 
-void insque(void*, void*);
-void remque(void*);
+void insque(void*, void*) __INTRODUCED_IN(21);
+void remque(void*) __INTRODUCED_IN(21);
 
-void* lfind(const void*, const void*, size_t*, size_t, int (*)(const void*, const void*));
-void* lsearch(const void*, void*, size_t*, size_t, int (*)(const void*, const void*));
+void* lfind(const void*, const void*, size_t*, size_t, int (*)(const void*, const void*))
+  __INTRODUCED_IN(21);
+void* lsearch(const void*, void*, size_t*, size_t, int (*)(const void*, const void*))
+  __INTRODUCED_IN(21);
 
-void* tdelete(const void* __restrict, void** __restrict, int (*)(const void*, const void*));
-void tdestroy(void*, void (*)(void*));
-void* tfind(const void*, void* const*, int (*)(const void*, const void*));
-void* tsearch(const void*, void**, int (*)(const void*, const void*));
-void twalk(const void*, void (*)(const void*, VISIT, int));
+void* tdelete(const void* __restrict, void** __restrict, int (*)(const void*, const void*))
+  __INTRODUCED_IN(21);
+void tdestroy(void*, void (*)(void*)) __INTRODUCED_IN(21);
+void* tfind(const void*, void* const*, int (*)(const void*, const void*)) __INTRODUCED_IN(21);
+void* tsearch(const void*, void**, int (*)(const void*, const void*)) __INTRODUCED_IN(21);
+void twalk(const void*, void (*)(const void*, VISIT, int)) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/signal.h b/libc/include/signal.h
index 5679402..4b5e4ac 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -72,8 +72,8 @@
 /* We take a few real-time signals for ourselves. May as well use the same names as glibc. */
 #define SIGRTMIN (__libc_current_sigrtmin())
 #define SIGRTMAX (__libc_current_sigrtmax())
-extern int __libc_current_sigrtmin(void);
-extern int __libc_current_sigrtmax(void);
+extern int __libc_current_sigrtmin(void) __INTRODUCED_IN(21);
+extern int __libc_current_sigrtmax(void) __INTRODUCED_IN(21);
 
 extern const char* const sys_siglist[];
 extern const char* const sys_signame[]; /* BSD compatibility. */
@@ -125,11 +125,18 @@
 extern int sigsuspend(const sigset_t*) __nonnull((1));
 extern int sigwait(const sigset_t*, int*) __nonnull((1, 2));
 
-extern int sighold(int) __attribute__((deprecated("use sigprocmask() or pthread_sigmask() instead")));
-extern int sigignore(int) __attribute__((deprecated("use sigaction() instead")));
-extern int sigpause(int) __attribute__((deprecated("use sigsuspend() instead")));
-extern int sigrelse(int) __attribute__((deprecated("use sigprocmask() or pthread_sigmask() instead")));
-extern sighandler_t sigset(int, sighandler_t) __attribute__((deprecated("use sigaction() instead")));
+extern int sighold(int)
+  __attribute__((deprecated("use sigprocmask() or pthread_sigmask() instead")))
+  __INTRODUCED_IN_FUTURE;
+extern int sigignore(int)
+  __attribute__((deprecated("use sigaction() instead"))) __INTRODUCED_IN_FUTURE;
+extern int sigpause(int)
+  __attribute__((deprecated("use sigsuspend() instead"))) __INTRODUCED_IN_FUTURE;
+extern int sigrelse(int)
+  __attribute__((deprecated("use sigprocmask() or pthread_sigmask() instead")))
+  __INTRODUCED_IN_FUTURE;
+extern sighandler_t sigset(int, sighandler_t)
+  __attribute__((deprecated("use sigaction() instead"))) __INTRODUCED_IN_FUTURE;
 
 extern int raise(int);
 extern int kill(pid_t, int);
@@ -137,15 +144,15 @@
 
 extern int sigaltstack(const stack_t*, stack_t*);
 
-extern void psiginfo(const siginfo_t*, const char*);
-extern void psignal(int, const char*);
+extern void psiginfo(const siginfo_t*, const char*) __INTRODUCED_IN(21);
+extern void psignal(int, const char*) __INTRODUCED_IN(21);
 
 extern int pthread_kill(pthread_t, int);
 extern int pthread_sigmask(int, const sigset_t*, sigset_t*);
 
-extern int sigqueue(pid_t, int, const union sigval);
-extern int sigtimedwait(const sigset_t*, siginfo_t*, const struct timespec*);
-extern int sigwaitinfo(const sigset_t*, siginfo_t*);
+extern int sigqueue(pid_t, int, const union sigval) __INTRODUCED_IN(23);
+extern int sigtimedwait(const sigset_t*, siginfo_t*, const struct timespec*) __INTRODUCED_IN(23);
+extern int sigwaitinfo(const sigset_t*, siginfo_t*) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index 623995b..05f2d98 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -55,9 +55,9 @@
 struct __sFILE;
 typedef struct __sFILE FILE;
 
-extern FILE* stdin;
-extern FILE* stdout;
-extern FILE* stderr;
+extern FILE* stdin __INTRODUCED_IN(23);
+extern FILE* stdout __INTRODUCED_IN(23);
+extern FILE* stderr __INTRODUCED_IN(23);
 /* C99 and earlier plus current C++ standards say these must be macros. */
 #define stdin stdin
 #define stdout stdout
@@ -119,9 +119,8 @@
 size_t	 fwrite(const void * __restrict, size_t, size_t, FILE * __restrict);
 int	 getc(FILE *);
 int	 getchar(void);
-ssize_t	 getdelim(char ** __restrict, size_t * __restrict, int,
-	    FILE * __restrict);
-ssize_t	 getline(char ** __restrict, size_t * __restrict, FILE * __restrict);
+ssize_t getdelim(char** __restrict, size_t* __restrict, int, FILE* __restrict) __INTRODUCED_IN(21);
+ssize_t getline(char** __restrict, size_t* __restrict, FILE* __restrict) __INTRODUCED_IN(21);
 
 void	 perror(const char *);
 int	 printf(const char * __restrict, ...)
@@ -143,8 +142,8 @@
 int	 vprintf(const char * __restrict, __va_list)
 		__printflike(1, 0);
 
-int dprintf(int, const char * __restrict, ...) __printflike(2, 3);
-int vdprintf(int, const char * __restrict, __va_list) __printflike(2, 0);
+int dprintf(int, const char* __restrict, ...) __printflike(2, 3) __INTRODUCED_IN(21);
+int vdprintf(int, const char* __restrict, __va_list) __printflike(2, 0) __INTRODUCED_IN(21);
 
 #ifndef __AUDIT__
 #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L
@@ -192,24 +191,22 @@
               int (*)(void*));
 #  endif
 #endif
-int fgetpos64(FILE*, fpos64_t*);
-int fsetpos64(FILE*, const fpos64_t*);
-int fseeko64(FILE*, off64_t, int);
-off64_t ftello64(FILE*);
+int fgetpos64(FILE*, fpos64_t*) __INTRODUCED_IN(24);
+int fsetpos64(FILE*, const fpos64_t*) __INTRODUCED_IN(24);
+int fseeko64(FILE*, off64_t, int) __INTRODUCED_IN(24);
+off64_t ftello64(FILE*) __INTRODUCED_IN(24);
 #if defined(__USE_BSD)
-FILE* funopen64(const void*,
-                int (*)(void*, char*, int),
-                int (*)(void*, const char*, int),
-                fpos64_t (*)(void*, fpos64_t, int),
-                int (*)(void*));
+FILE* funopen64(const void*, int (*)(void*, char*, int), int (*)(void*, const char*, int),
+                fpos64_t (*)(void*, fpos64_t, int), int (*)(void*)) __INTRODUCED_IN(24);
 #endif
 
 FILE* fopen(const char* __restrict, const char* __restrict);
-FILE* fopen64(const char* __restrict, const char* __restrict);
+FILE* fopen64(const char* __restrict, const char* __restrict) __INTRODUCED_IN(24);
 FILE* freopen(const char* __restrict, const char* __restrict, FILE* __restrict);
-FILE* freopen64(const char* __restrict, const char* __restrict, FILE* __restrict);
+FILE* freopen64(const char* __restrict, const char* __restrict, FILE* __restrict)
+  __INTRODUCED_IN(24);
 FILE* tmpfile(void);
-FILE* tmpfile64(void);
+FILE* tmpfile64(void) __INTRODUCED_IN(24);
 
 #if __ISO_C_VISIBLE >= 1999 || __BSD_VISIBLE
 int	 snprintf(char * __restrict, size_t, const char * __restrict, ...)
@@ -254,8 +251,8 @@
 #endif /* __POSIX_VISIBLE >= 199506 */
 
 #if __POSIX_VISIBLE >= 200809
-FILE* fmemopen(void*, size_t, const char*);
-FILE* open_memstream(char**, size_t*);
+FILE* fmemopen(void*, size_t, const char*) __INTRODUCED_IN(23);
+FILE* open_memstream(char**, size_t*) __INTRODUCED_IN(23);
 #endif /* __POSIX_VISIBLE >= 200809 */
 
 #endif /* __BSD_VISIBLE || __POSIX_VISIBLE || __XPG_VISIBLE */
@@ -274,26 +271,28 @@
     __va_list)
 		__printflike(2, 0);
 
-void clearerr_unlocked(FILE*);
-int feof_unlocked(FILE*);
-int ferror_unlocked(FILE*);
-int fileno_unlocked(FILE*);
+void clearerr_unlocked(FILE*) __INTRODUCED_IN(23);
+int feof_unlocked(FILE*) __INTRODUCED_IN(23);
+int ferror_unlocked(FILE*) __INTRODUCED_IN(23);
+int fileno_unlocked(FILE*) __INTRODUCED_IN(24);
 
 #define fropen(cookie, fn) funopen(cookie, fn, 0, 0, 0)
 #define fwopen(cookie, fn) funopen(cookie, 0, fn, 0, 0)
 #endif /* __BSD_VISIBLE */
 
-extern char* __fgets_chk(char*, int, FILE*, size_t);
+extern char* __fgets_chk(char*, int, FILE*, size_t) __INTRODUCED_IN(21);
 extern char* __fgets_real(char*, int, FILE*) __RENAME(fgets);
 __errordecl(__fgets_too_big_error, "fgets called with size bigger than buffer");
 __errordecl(__fgets_too_small_error, "fgets called with size less than zero");
 
-extern size_t __fread_chk(void * __restrict, size_t, size_t, FILE * __restrict, size_t);
+extern size_t __fread_chk(void* __restrict, size_t, size_t, FILE* __restrict, size_t)
+  __INTRODUCED_IN(24);
 extern size_t __fread_real(void * __restrict, size_t, size_t, FILE * __restrict) __RENAME(fread);
 __errordecl(__fread_too_big_error, "fread called with size * count bigger than buffer");
 __errordecl(__fread_overflow, "fread called with overflowing size * count");
 
-extern size_t __fwrite_chk(const void * __restrict, size_t, size_t, FILE * __restrict, size_t);
+extern size_t __fwrite_chk(const void* __restrict, size_t, size_t, FILE* __restrict, size_t)
+  __INTRODUCED_IN(24);
 extern size_t __fwrite_real(const void * __restrict, size_t, size_t, FILE * __restrict) __RENAME(fwrite);
 __errordecl(__fwrite_too_big_error, "fwrite called with size * count bigger than buffer");
 __errordecl(__fwrite_overflow, "fwrite called with overflowing size * count");
diff --git a/libc/include/stdio_ext.h b/libc/include/stdio_ext.h
index de5d715..fdf6772 100644
--- a/libc/include/stdio_ext.h
+++ b/libc/include/stdio_ext.h
@@ -38,14 +38,14 @@
 
 __BEGIN_DECLS
 
-size_t __fbufsize(FILE*);
-int __freadable(FILE*);
-int __fwritable(FILE*);
-int __flbf(FILE*);
-void __fpurge(FILE*);
-size_t __fpending(FILE*);
-void _flushlbf(void);
-int __fsetlocking(FILE*, int);
+size_t __fbufsize(FILE*) __INTRODUCED_IN(23);
+int __freadable(FILE*) __INTRODUCED_IN(23);
+int __fwritable(FILE*) __INTRODUCED_IN(23);
+int __flbf(FILE*) __INTRODUCED_IN(23);
+void __fpurge(FILE*) __INTRODUCED_IN(23);
+size_t __fpending(FILE*) __INTRODUCED_IN(23);
+void _flushlbf(void) __INTRODUCED_IN(23);
+int __fsetlocking(FILE*, int) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index ba4b149..b3e52d5 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -43,7 +43,7 @@
 
 extern __noreturn void abort(void);
 extern __noreturn void exit(int);
-extern __noreturn void _Exit(int);
+extern __noreturn void _Exit(int) __INTRODUCED_IN(21);
 extern int atexit(void (*)(void));
 
 #if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L
@@ -60,13 +60,13 @@
 extern char* mkdtemp(char*);
 extern char* mktemp(char*) __attribute__((deprecated("mktemp is unsafe, use mkstemp or tmpfile instead")));
 
-extern int mkostemp64(char*, int);
-extern int mkostemp(char*, int);
-extern int mkostemps64(char*, int, int);
-extern int mkostemps(char*, int, int);
-extern int mkstemp64(char*);
+extern int mkostemp64(char*, int) __INTRODUCED_IN(23);
+extern int mkostemp(char*, int) __INTRODUCED_IN(23);
+extern int mkostemps64(char*, int, int) __INTRODUCED_IN(23);
+extern int mkostemps(char*, int, int) __INTRODUCED_IN(23);
+extern int mkstemp64(char*) __INTRODUCED_IN(21);
 extern int mkstemp(char*);
-extern int mkstemps64(char*, int);
+extern int mkstemps64(char*, int) __INTRODUCED_IN(23);
 extern int mkstemps(char*, int);
 
 extern long strtol(const char *, char **, int);
@@ -74,17 +74,19 @@
 extern unsigned long strtoul(const char *, char **, int);
 extern unsigned long long strtoull(const char *, char **, int);
 
-extern int posix_memalign(void **memptr, size_t alignment, size_t size);
+extern int posix_memalign(void** memptr, size_t alignment, size_t size) __INTRODUCED_IN(16);
 
 __BIONIC_LEGACY_INLINE double atof(const char*);
 
 extern double strtod(const char*, char**) __LIBC_ABI_PUBLIC__;
 __BIONIC_LEGACY_INLINE float strtof(const char*, char**) __LIBC_ABI_PUBLIC__;
-extern long double strtold(const char*, char**) __LIBC_ABI_PUBLIC__;
+extern long double strtold(const char*, char**) __LIBC_ABI_PUBLIC__ __INTRODUCED_IN(21);
 
-extern long double strtold_l(const char *, char **, locale_t) __LIBC_ABI_PUBLIC__;
-extern long long strtoll_l(const char *, char **, int, locale_t) __LIBC_ABI_PUBLIC__;
-extern unsigned long long strtoull_l(const char *, char **, int, locale_t) __LIBC_ABI_PUBLIC__;
+extern long double strtold_l(const char*, char**, locale_t) __LIBC_ABI_PUBLIC__ __INTRODUCED_IN(21);
+extern long long strtoll_l(const char*, char**, int, locale_t) __LIBC_ABI_PUBLIC__
+  __INTRODUCED_IN(21);
+extern unsigned long long strtoull_l(const char*, char**, int, locale_t) __LIBC_ABI_PUBLIC__
+  __INTRODUCED_IN(21);
 
 extern int atoi(const char*) __purefunc;
 extern long atol(const char*) __purefunc;
@@ -110,32 +112,32 @@
 #define RAND_MAX 0x7fffffff
 
 __BIONIC_LEGACY_INLINE int rand(void);
-int rand_r(unsigned int*);
+int rand_r(unsigned int*) __INTRODUCED_IN(21);
 __BIONIC_LEGACY_INLINE void srand(unsigned int);
 
 double drand48(void);
 double erand48(unsigned short[3]);
 long jrand48(unsigned short[3]);
-void lcong48(unsigned short[7]);
+void lcong48(unsigned short[7]) __INTRODUCED_IN(23);
 long lrand48(void);
 long mrand48(void);
 long nrand48(unsigned short[3]);
 unsigned short* seed48(unsigned short[3]);
 void srand48(long);
 
-char* initstate(unsigned int, char*, size_t);
+char* initstate(unsigned int, char*, size_t) __INTRODUCED_IN(21);
 __BIONIC_LEGACY_INLINE long random(void);
-char* setstate(char*);
+char* setstate(char*) __INTRODUCED_IN(21);
 __BIONIC_LEGACY_INLINE void srandom(unsigned int);
 
 int getpt(void);
 __BIONIC_LEGACY_INLINE int grantpt(int);
-int posix_openpt(int);
+int posix_openpt(int) __INTRODUCED_IN(21);
 char* ptsname(int);
 int ptsname_r(int, char*, size_t);
 int unlockpt(int);
 
-int getsubopt(char**, char* const*, char**);
+int getsubopt(char**, char* const*, char**) __INTRODUCED_IN_FUTURE;
 
 typedef struct {
     int  quot;
@@ -159,16 +161,16 @@
 extern lldiv_t   lldiv(long long, long long) __pure2;
 
 /* BSD compatibility. */
-extern const char* getprogname(void);
-extern void setprogname(const char*);
+extern const char* getprogname(void) __INTRODUCED_IN(21);
+extern void setprogname(const char*) __INTRODUCED_IN(21);
 
-int mblen(const char*, size_t);
+int mblen(const char*, size_t) __INTRODUCED_IN_FUTURE;
 size_t mbstowcs(wchar_t*, const char*, size_t);
-int mbtowc(wchar_t*, const char*, size_t);
-int wctomb(char*, wchar_t);
+int mbtowc(wchar_t*, const char*, size_t) __INTRODUCED_IN(21);
+int wctomb(char*, wchar_t) __INTRODUCED_IN(21);
 size_t wcstombs(char*, const wchar_t*, size_t);
 
-extern size_t __ctype_get_mb_cur_max(void);
+extern size_t __ctype_get_mb_cur_max(void) __INTRODUCED_IN(21);
 #define MB_CUR_MAX __ctype_get_mb_cur_max()
 
 #if defined(__BIONIC_FORTIFY)
diff --git a/libc/include/string.h b/libc/include/string.h
index dada52b..3f98af1 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -47,30 +47,30 @@
 extern int    memcmp(const void *, const void *, size_t) __purefunc;
 extern void*  memcpy(void* __restrict, const void* __restrict, size_t);
 #if defined(__USE_GNU)
-extern void*  mempcpy(void* __restrict, const void* __restrict, size_t);
+extern void* mempcpy(void* __restrict, const void* __restrict, size_t) __INTRODUCED_IN(23);
 #endif
 extern void*  memmove(void *, const void *, size_t);
 extern void*  memset(void *, int, size_t);
 extern void*  memmem(const void *, size_t, const void *, size_t) __purefunc;
 
 extern char*  strchr(const char *, int) __purefunc;
-extern char* __strchr_chk(const char *, int, size_t);
+extern char* __strchr_chk(const char*, int, size_t) __INTRODUCED_IN(21);
 #if defined(__USE_GNU)
 #if defined(__cplusplus)
 extern "C++" char* strchrnul(char*, int) __RENAME(strchrnul) __purefunc;
 extern "C++" const char* strchrnul(const char*, int) __RENAME(strchrnul) __purefunc;
 #else
-char* strchrnul(const char*, int) __purefunc;
+char* strchrnul(const char*, int) __purefunc __INTRODUCED_IN(24);
 #endif
 #endif
 
 extern char*  strrchr(const char *, int) __purefunc;
-extern char* __strrchr_chk(const char *, int, size_t);
+extern char* __strrchr_chk(const char*, int, size_t) __INTRODUCED_IN(21);
 
 extern size_t strlen(const char *) __purefunc;
-extern size_t __strlen_chk(const char *, size_t);
+extern size_t __strlen_chk(const char*, size_t) __INTRODUCED_IN(21);
 extern int    strcmp(const char *, const char *) __purefunc;
-extern char*  stpcpy(char* __restrict, const char* __restrict);
+extern char* stpcpy(char* __restrict, const char* __restrict) __INTRODUCED_IN(21);
 extern char*  strcpy(char* __restrict, const char* __restrict);
 extern char*  strcat(char* __restrict, const char* __restrict);
 
@@ -82,9 +82,9 @@
 extern char*  strtok_r(char* __restrict, const char* __restrict, char** __restrict);
 
 extern char* strerror(int);
-extern char* strerror_l(int, locale_t);
+extern char* strerror_l(int, locale_t) __INTRODUCED_IN(23);
 #if defined(__USE_GNU)
-extern char* strerror_r(int, char*, size_t) __RENAME(__gnu_strerror_r);
+extern char* strerror_r(int, char*, size_t) __RENAME(__gnu_strerror_r) __INTRODUCED_IN(23);
 #else /* POSIX */
 extern int strerror_r(int, char*, size_t);
 #endif
@@ -93,7 +93,7 @@
 extern char*  strncat(char* __restrict, const char* __restrict, size_t);
 extern char*  strndup(const char *, size_t);
 extern int    strncmp(const char *, const char *, size_t) __purefunc;
-extern char*  stpncpy(char* __restrict, const char* __restrict, size_t);
+extern char* stpncpy(char* __restrict, const char* __restrict, size_t) __INTRODUCED_IN(21);
 extern char*  strncpy(char* __restrict, const char* __restrict, size_t);
 
 extern size_t strlcat(char* __restrict, const char* __restrict, size_t);
@@ -109,8 +109,9 @@
 extern int    strcoll(const char *, const char *) __purefunc;
 extern size_t strxfrm(char* __restrict, const char* __restrict, size_t);
 
-extern int    strcoll_l(const char *, const char *, locale_t) __purefunc;
-extern size_t strxfrm_l(char* __restrict, const char* __restrict, size_t, locale_t);
+extern int strcoll_l(const char*, const char*, locale_t) __purefunc __INTRODUCED_IN(21);
+extern size_t strxfrm_l(char* __restrict, const char* __restrict, size_t, locale_t)
+  __INTRODUCED_IN(21);
 
 #if defined(__USE_GNU) && !defined(basename)
 /*
@@ -122,23 +123,26 @@
 extern "C++" char* basename(char*) __RENAME(__gnu_basename) __nonnull((1));
 extern "C++" const char* basename(const char*) __RENAME(__gnu_basename) __nonnull((1));
 #else
-extern char* basename(const char*) __RENAME(__gnu_basename) __nonnull((1));
+extern char* basename(const char*) __RENAME(__gnu_basename) __nonnull((1)) __INTRODUCED_IN(23);
 #endif
 #endif
 
-extern void* __memchr_chk(const void*, int, size_t, size_t);
+extern void* __memchr_chk(const void*, int, size_t, size_t) __INTRODUCED_IN(23);
 __errordecl(__memchr_buf_size_error, "memchr called with size bigger than buffer");
 
-extern void* __memrchr_chk(const void*, int, size_t, size_t);
+extern void* __memrchr_chk(const void*, int, size_t, size_t) __INTRODUCED_IN(23);
 __errordecl(__memrchr_buf_size_error, "memrchr called with size bigger than buffer");
 extern void* __memrchr_real(const void*, int, size_t) __RENAME(memrchr);
 
-extern char* __stpncpy_chk2(char* __restrict, const char* __restrict, size_t, size_t, size_t);
-extern char* __strncpy_chk2(char* __restrict, const char* __restrict, size_t, size_t, size_t);
+extern char* __stpncpy_chk2(char* __restrict, const char* __restrict, size_t, size_t, size_t)
+  __INTRODUCED_IN(21);
+extern char* __strncpy_chk2(char* __restrict, const char* __restrict, size_t, size_t, size_t)
+  __INTRODUCED_IN(21);
 extern size_t __strlcpy_real(char* __restrict, const char* __restrict, size_t) __RENAME(strlcpy);
-extern size_t __strlcpy_chk(char *, const char *, size_t, size_t);
+extern size_t __strlcpy_chk(char*, const char*, size_t, size_t) __INTRODUCED_IN(21);
 extern size_t __strlcat_real(char* __restrict, const char* __restrict, size_t) __RENAME(strlcat);
-extern size_t __strlcat_chk(char* __restrict, const char* __restrict, size_t, size_t);
+extern size_t __strlcat_chk(char* __restrict, const char* __restrict, size_t, size_t)
+  __INTRODUCED_IN(21);
 
 #if defined(__BIONIC_FORTIFY)
 
diff --git a/libc/include/strings.h b/libc/include/strings.h
index 1200e77..ca9f658 100644
--- a/libc/include/strings.h
+++ b/libc/include/strings.h
@@ -54,7 +54,11 @@
 #define bzero(b, len) (void)(__builtin_memset((b), '\0', (len)))
 #endif
 
+#if defined(__i386__)
+int ffs(int) __INTRODUCED_IN(21);
+#else
 int ffs(int);
+#endif
 
 __END_DECLS
 
diff --git a/libc/include/sys/auxv.h b/libc/include/sys/auxv.h
index 0d753c3..4611fcc 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);
+unsigned long int getauxval(unsigned long int type) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 24b341e..3fcf163 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -459,6 +459,8 @@
 #define __DEPRECATED_IN(api_level) __AVAILABILITY(deprecated=api_level)
 #define __REMOVED_IN(api_level) __AVAILABILITY(obsoleted=api_level)
 
+#define __INTRODUCED_IN_FUTURE __INTRODUCED_IN(10000)
+
 #if __LP64__
 #define __INTRODUCED_IN_32(api_level)
 #define __INTRODUCED_IN_64 __INTRODUCED_IN
diff --git a/libc/include/sys/endian.h b/libc/include/sys/endian.h
index 60cc030..449e0d7 100644
--- a/libc/include/sys/endian.h
+++ b/libc/include/sys/endian.h
@@ -49,10 +49,10 @@
 
 /* glibc compatibility. */
 __BEGIN_DECLS
-uint32_t htonl(uint32_t) __pure2;
-uint16_t htons(uint16_t) __pure2;
-uint32_t ntohl(uint32_t) __pure2;
-uint16_t ntohs(uint16_t) __pure2;
+uint32_t htonl(uint32_t) __pure2 __INTRODUCED_IN(21);
+uint16_t htons(uint16_t) __pure2 __INTRODUCED_IN(21);
+uint32_t ntohl(uint32_t) __pure2 __INTRODUCED_IN(21);
+uint16_t ntohs(uint16_t) __pure2 __INTRODUCED_IN(21);
 __END_DECLS
 
 #define htonl(x) __swap32(x)
diff --git a/libc/include/sys/epoll.h b/libc/include/sys/epoll.h
index 4a5a37c..4ec8969 100644
--- a/libc/include/sys/epoll.h
+++ b/libc/include/sys/epoll.h
@@ -74,10 +74,10 @@
 ;
 
 int epoll_create(int);
-int epoll_create1(int);
+int epoll_create1(int) __INTRODUCED_IN(21);
 int epoll_ctl(int, int, int, struct epoll_event*);
 int epoll_wait(int, struct epoll_event*, int, int);
-int epoll_pwait(int, struct epoll_event*, int, int, const sigset_t*);
+int epoll_pwait(int, struct epoll_event*, int, int, const sigset_t*) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/fsuid.h b/libc/include/sys/fsuid.h
index 03355b7..223db90 100644
--- a/libc/include/sys/fsuid.h
+++ b/libc/include/sys/fsuid.h
@@ -34,8 +34,8 @@
 
 __BEGIN_DECLS
 
-extern int setfsuid(uid_t);
-extern int setfsgid(gid_t);
+extern int setfsuid(uid_t) __INTRODUCED_IN(21);
+extern int setfsgid(gid_t) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/inotify.h b/libc/include/sys/inotify.h
index dcdd29a..dcf0e1d 100644
--- a/libc/include/sys/inotify.h
+++ b/libc/include/sys/inotify.h
@@ -41,7 +41,7 @@
 #define IN_NONBLOCK O_NONBLOCK
 
 extern int inotify_init(void);
-extern int inotify_init1(int);
+extern int inotify_init1(int) __INTRODUCED_IN(21);
 extern int inotify_add_watch(int, const char*, uint32_t);
 extern int inotify_rm_watch(int, uint32_t);
 
diff --git a/libc/include/sys/ioctl.h b/libc/include/sys/ioctl.h
index ed261f2..efbcb0c 100644
--- a/libc/include/sys/ioctl.h
+++ b/libc/include/sys/ioctl.h
@@ -37,7 +37,6 @@
 #include <linux/termios.h>
 #include <asm/ioctls.h>
 #include <asm/termbits.h>
-#include <sys/ioctl_compat.h>
 #include <linux/tty.h>
 
 #include <bits/ioctl.h>
diff --git a/libc/include/sys/ioctl_compat.h b/libc/include/sys/ioctl_compat.h
deleted file mode 100644
index d9ba4c7..0000000
--- a/libc/include/sys/ioctl_compat.h
+++ /dev/null
@@ -1,174 +0,0 @@
-/*	$NetBSD: ioctl_compat.h,v 1.15 2005/12/03 17:10:46 christos Exp $	*/
-
-/*
- * Copyright (c) 1990, 1993
- *	The Regents of the University of California.  All rights reserved.
- * (c) UNIX System Laboratories, Inc.
- * All or some portions of this file are derived from material licensed
- * to the University of California by American Telephone and Telegraph
- * Co. or Unix System Laboratories, Inc. and are reproduced herein with
- * the permission of UNIX System Laboratories, Inc.
- *
- * 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.
- * 3. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
- *
- *	@(#)ioctl_compat.h	8.4 (Berkeley) 1/21/94
- */
-
-#ifndef _SYS_IOCTL_COMPAT_H_
-#define	_SYS_IOCTL_COMPAT_H_
-
-/*#include <sys/ttychars.h>*/
-/*#include <sys/ttydev.h>*/
-
-#if !defined(__mips__)
-struct tchars {
-	char	t_intrc;	/* interrupt */
-	char	t_quitc;	/* quit */
-	char	t_startc;	/* start output */
-	char	t_stopc;	/* stop output */
-	char	t_eofc;		/* end-of-file */
-	char	t_brkc;		/* input delimiter (like nl) */
-};
-
-struct ltchars {
-	char	t_suspc;	/* stop process signal */
-	char	t_dsuspc;	/* delayed stop process signal */
-	char	t_rprntc;	/* reprint line */
-	char	t_flushc;	/* flush output (toggles) */
-	char	t_werasc;	/* word erase */
-	char	t_lnextc;	/* literal next character */
-};
-
-/*
- * Structure for TIOCGETP and TIOCSETP ioctls.
- */
-#ifndef _SGTTYB_
-#define	_SGTTYB_
-struct sgttyb {
-	char	sg_ispeed;		/* input speed */
-	char	sg_ospeed;		/* output speed */
-	char	sg_erase;		/* erase character */
-	char	sg_kill;		/* kill character */
-	short	sg_flags;		/* mode flags */
-};
-#endif
-#endif
-
-#ifdef USE_OLD_TTY
-# undef  TIOCGETD
-# define TIOCGETD	_IOR('t', 0, int)	/* get line discipline */
-# undef  TIOCSETD
-# define TIOCSETD	_IOW('t', 1, int)	/* set line discipline */
-#else
-# define OTIOCGETD	_IOR('t', 0, int)	/* get line discipline */
-# define OTIOCSETD	_IOW('t', 1, int)	/* set line discipline */
-#endif
-#define	TIOCHPCL	_IO('t', 2)		/* hang up on last close */
-#if !defined(__mips__)
-#define	TIOCGETP	_IOR('t', 8,struct sgttyb)/* get parameters -- gtty */
-#define	TIOCSETP	_IOW('t', 9,struct sgttyb)/* set parameters -- stty */
-#define	TIOCSETN	_IOW('t',10,struct sgttyb)/* as above, but no flushtty*/
-#endif
-#define	TIOCSETC	_IOW('t',17,struct tchars)/* set special characters */
-#define	TIOCGETC	_IOR('t',18,struct tchars)/* get special characters */
-#if 0
-/* BUG: a bunch of these conflict with #defines in asm/termbits.h */
-#define		TANDEM		0x00000001	/* send stopc on out q full */
-#define		CBREAK		0x00000002	/* half-cooked mode */
-#define		LCASE		0x00000004	/* simulate lower case */
-#define		ECHO		0x00000008	/* enable echoing */
-#define		CRMOD		0x00000010	/* map \r to \r\n on output */
-#define		RAW		0x00000020	/* no i/o processing */
-#define		ODDP		0x00000040	/* get/send odd parity */
-#define		EVENP		0x00000080	/* get/send even parity */
-#define		ANYP		0x000000c0	/* get any parity/send none */
-#define		NLDELAY		0x00000300	/* \n delay */
-#define			NL0	0x00000000
-#define			NL1	0x00000100	/* tty 37 */
-#define			NL2	0x00000200	/* vt05 */
-#define			NL3	0x00000300
-#define		TBDELAY		0x00000c00	/* horizontal tab delay */
-#define			TAB0	0x00000000
-#define			TAB1	0x00000400	/* tty 37 */
-#define			TAB2	0x00000800
-#define		XTABS		0x00000c00	/* expand tabs on output */
-#define		CRDELAY		0x00003000	/* \r delay */
-#define			CR0	0x00000000
-#define			CR1	0x00001000	/* tn 300 */
-#define			CR2	0x00002000	/* tty 37 */
-#define			CR3	0x00003000	/* concept 100 */
-#define		VTDELAY		0x00004000	/* vertical tab delay */
-#define			FF0	0x00000000
-#define			FF1	0x00004000	/* tty 37 */
-#define		BSDELAY		0x00008000	/* \b delay */
-#define			BS0	0x00000000
-#define			BS1	0x00008000
-#define		ALLDELAY	(NLDELAY|TBDELAY|CRDELAY|VTDELAY|BSDELAY)
-#define		CRTBS		0x00010000	/* do backspacing for crt */
-#define		PRTERA		0x00020000	/* \ ... / erase */
-#define		CRTERA		0x00040000	/* " \b " to wipe out char */
-#define		TILDE		0x00080000	/* hazeltine tilde kludge */
-#define		MDMBUF		0x00100000	/* DTR/DCD hardware flow control */
-#define		LITOUT		0x00200000	/* literal output */
-#define		TOSTOP		0x00400000	/* stop background jobs on output */
-#define		FLUSHO		0x00800000	/* output being flushed (state) */
-#define		NOHANG		0x01000000	/* (no-op) was no SIGHUP on carrier drop */
-#define		L001000		0x02000000
-#define		CRTKIL		0x04000000	/* kill line with " \b " */
-#define		PASS8		0x08000000
-#define		CTLECH		0x10000000	/* echo control chars as ^X */
-#define		PENDIN		0x20000000	/* re-echo input buffer at next read */
-#define		DECCTQ		0x40000000	/* only ^Q starts after ^S */
-#define		NOFLSH		0x80000000	/* don't flush output on signal */
-#endif
-#define	TIOCLBIS	_IOW('t', 127, int)	/* bis local mode bits */
-#define	TIOCLBIC	_IOW('t', 126, int)	/* bic local mode bits */
-#define	TIOCLSET	_IOW('t', 125, int)	/* set entire local mode word */
-#define	TIOCLGET	_IOR('t', 124, int)	/* get local modes */
-#define		LCRTBS		(CRTBS>>16)
-#define		LPRTERA		(PRTERA>>16)
-#define		LCRTERA		(CRTERA>>16)
-#define		LTILDE		(TILDE>>16)
-#define		LMDMBUF		(MDMBUF>>16)
-#define		LLITOUT		(LITOUT>>16)
-#define		LTOSTOP		(TOSTOP>>16)
-#define		LFLUSHO		(FLUSHO>>16)
-#define		LNOHANG		(NOHANG>>16)
-#define		LCRTKIL		(CRTKIL>>16)
-#define		LPASS8		(PASS8>>16)
-#define		LCTLECH		(CTLECH>>16)
-#define		LPENDIN		(PENDIN>>16)
-#define		LDECCTQ		(DECCTQ>>16)
-#define		LNOFLSH		(NOFLSH>>16)
-#if !defined(__mips__)
-#define	TIOCSLTC	_IOW('t',117,struct ltchars)/* set local special chars*/
-#define	TIOCGLTC	_IOR('t',116,struct ltchars)/* get local special chars*/
-#endif
-#define OTIOCCONS	_IO('t', 98)	/* for hp300 -- sans int arg */
-#define	OTTYDISC	0
-#define	NETLDISC	1
-#define	NTTYDISC	2
-
-#endif /* !_SYS_IOCTL_COMPAT_H_ */
diff --git a/libc/include/sys/mman.h b/libc/include/sys/mman.h
index 170300a..af96eff 100644
--- a/libc/include/sys/mman.h
+++ b/libc/include/sys/mman.h
@@ -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);
+extern 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);
 #endif
-extern void* mmap64(void*, size_t, int, int, int, off64_t);
+extern 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, ...);
 
-extern int mlockall(int);
-extern int munlockall(void);
+extern int mlockall(int) __INTRODUCED_IN(21);
+extern int munlockall(void) __INTRODUCED_IN(21);
 extern int mlock(const void*, size_t);
 extern int munlock(const void*, size_t);
 
 extern int mincore(void*, size_t, unsigned char*);
 
 extern int madvise(void*, size_t, int);
-extern int posix_madvise(void*, size_t, int);
+extern int posix_madvise(void*, size_t, int) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/sys/personality.h b/libc/include/sys/personality.h
index 7764468..68ae77c 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);
+extern int personality(unsigned int persona) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/quota.h b/libc/include/sys/quota.h
index f4f6447..08ca982 100644
--- a/libc/include/sys/quota.h
+++ b/libc/include/sys/quota.h
@@ -40,7 +40,7 @@
 
 __BEGIN_DECLS
 
-int quotactl(int, const char*, int, char*);
+int quotactl(int, const char*, int, char*) __INTRODUCED_IN_FUTURE;
 
 __END_DECLS
 
diff --git a/libc/include/sys/resource.h b/libc/include/sys/resource.h
index 8209dfb..3187420 100644
--- a/libc/include/sys/resource.h
+++ b/libc/include/sys/resource.h
@@ -45,16 +45,17 @@
 extern int getrlimit(int, struct rlimit*);
 extern int setrlimit(int, const struct rlimit*);
 
-extern int getrlimit64(int, struct rlimit64*);
-extern int setrlimit64(int, const struct rlimit64*);
+extern int getrlimit64(int, struct rlimit64*) __INTRODUCED_IN(21);
+extern int setrlimit64(int, const struct rlimit64*) __INTRODUCED_IN(21);
 
 extern int getpriority(int, int);
 extern int setpriority(int, int, int);
 
 extern int getrusage(int, struct rusage*);
 
-extern int prlimit(pid_t, int, const struct rlimit*, struct rlimit*);
-extern int prlimit64(pid_t, int, const struct rlimit64*, struct rlimit64*);
+extern int prlimit(pid_t, int, const struct rlimit*, struct rlimit*) __INTRODUCED_IN_32(24)
+  __INTRODUCED_IN_64(21);
+extern int prlimit64(pid_t, int, const struct rlimit64*, struct rlimit64*) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/select.h b/libc/include/sys/select.h
index 0c4a823..06c1c72 100644
--- a/libc/include/sys/select.h
+++ b/libc/include/sys/select.h
@@ -57,9 +57,9 @@
     } \
   } while (0)
 
-extern void __FD_CLR_chk(int, fd_set*, size_t);
-extern void __FD_SET_chk(int, fd_set*, size_t);
-extern int  __FD_ISSET_chk(int, fd_set*, size_t);
+extern void __FD_CLR_chk(int, fd_set*, size_t) __INTRODUCED_IN(21);
+extern void __FD_SET_chk(int, fd_set*, size_t) __INTRODUCED_IN(21);
+extern int __FD_ISSET_chk(int, fd_set*, size_t) __INTRODUCED_IN(21);
 
 #if defined(__BIONIC_FORTIFY)
 #define FD_CLR(fd, set) __FD_CLR_chk(fd, set, __bos(set))
diff --git a/libc/include/sys/sendfile.h b/libc/include/sys/sendfile.h
index c588e68..f90498a 100644
--- a/libc/include/sys/sendfile.h
+++ b/libc/include/sys/sendfile.h
@@ -35,11 +35,12 @@
 __BEGIN_DECLS
 
 #if defined(__USE_FILE_OFFSET64)
-extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count) __RENAME(sendfile64);
+extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count) __RENAME(sendfile64)
+  __INTRODUCED_IN(21);
 #else
 extern ssize_t sendfile(int out_fd, int in_fd, off_t* offset, size_t count);
 #endif
-extern ssize_t sendfile64(int out_fd, int in_fd, off64_t* offset, size_t count);
+extern ssize_t sendfile64(int out_fd, int in_fd, off64_t* offset, size_t count) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/signalfd.h b/libc/include/sys/signalfd.h
index 2537ab9..5b67822 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* mask, int flags) __nonnull((2));
+extern int signalfd(int fd, const sigset_t* mask, int flags) __nonnull((2)) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/socket.h b/libc/include/sys/socket.h
index c7e9acc..85999f3 100644
--- a/libc/include/sys/socket.h
+++ b/libc/include/sys/socket.h
@@ -113,7 +113,7 @@
    ? (struct cmsghdr*) (msg)->msg_control : (struct cmsghdr*) NULL)
 #define CMSG_OK(mhdr, cmsg) ((cmsg)->cmsg_len >= sizeof(struct cmsghdr) &&   (cmsg)->cmsg_len <= (unsigned long)   ((mhdr)->msg_controllen -   ((char*)(cmsg) - (char*)(mhdr)->msg_control)))
 
-struct cmsghdr* __cmsg_nxthdr(struct msghdr*, struct cmsghdr*);
+struct cmsghdr* __cmsg_nxthdr(struct msghdr*, struct cmsghdr*) __INTRODUCED_IN(21);
 
 #define SCM_RIGHTS 0x01
 #define SCM_CREDENTIALS 0x02
@@ -269,16 +269,17 @@
 #endif
 
 __socketcall int accept(int, struct sockaddr*, socklen_t*);
-__socketcall int accept4(int, struct sockaddr*, socklen_t*, int);
+__socketcall int accept4(int, struct sockaddr*, socklen_t*, int) __INTRODUCED_IN(21);
 __socketcall int bind(int, const struct sockaddr*, int);
 __socketcall int connect(int, const struct sockaddr*, socklen_t);
 __socketcall int getpeername(int, struct sockaddr*, socklen_t*);
 __socketcall int getsockname(int, struct sockaddr*, socklen_t*);
 __socketcall int getsockopt(int, int, int, void*, socklen_t*);
 __socketcall int listen(int, int);
-__socketcall int recvmmsg(int, struct mmsghdr*, unsigned int, int, const struct timespec*);
+__socketcall int recvmmsg(int, struct mmsghdr*, unsigned int, int, const struct timespec*)
+  __INTRODUCED_IN(21);
 __socketcall int recvmsg(int, struct msghdr*, int);
-__socketcall int sendmmsg(int, const struct mmsghdr*, unsigned int, int);
+__socketcall int sendmmsg(int, const struct mmsghdr*, unsigned int, int) __INTRODUCED_IN(21);
 __socketcall int sendmsg(int, const struct msghdr*, int);
 __socketcall int setsockopt(int, int, int, const void*, socklen_t);
 __socketcall int shutdown(int, int);
@@ -292,7 +293,8 @@
 __socketcall ssize_t recvfrom(int, void*, size_t, int, const struct sockaddr*, socklen_t*);
 
 __errordecl(__recvfrom_error, "recvfrom called with size bigger than buffer");
-extern ssize_t __recvfrom_chk(int, void*, size_t, size_t, int, const struct sockaddr*, socklen_t*);
+extern ssize_t __recvfrom_chk(int, void*, size_t, size_t, int, const struct sockaddr*, socklen_t*)
+  __INTRODUCED_IN(21);
 extern ssize_t __recvfrom_real(int, void*, size_t, int, const struct sockaddr*, socklen_t*) __RENAME(recvfrom);
 
 #if defined(__BIONIC_FORTIFY)
diff --git a/libc/include/sys/socketcalls.h b/libc/include/sys/socketcalls.h
deleted file mode 100644
index 131e0bb..0000000
--- a/libc/include/sys/socketcalls.h
+++ /dev/null
@@ -1,54 +0,0 @@
-/*
- * Copyright (C) 2008 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 _SYS_SOCKETCALLS_H_
-#define _SYS_SOCKETCALLS_H_
-
-/* socketcalls by number */
-
-#define SYS_SOCKET      1               /* sys_socket(2)                */
-#define SYS_BIND        2               /* sys_bind(2)                  */
-#define SYS_CONNECT     3               /* sys_connect(2)               */
-#define SYS_LISTEN      4               /* sys_listen(2)                */
-#define SYS_ACCEPT      5               /* sys_accept(2)                */
-#define SYS_GETSOCKNAME 6               /* sys_getsockname(2)           */
-#define SYS_GETPEERNAME 7               /* sys_getpeername(2)           */
-#define SYS_SOCKETPAIR  8               /* sys_socketpair(2)            */
-#define SYS_SEND        9               /* sys_send(2)                  */
-#define SYS_RECV        10              /* sys_recv(2)                  */
-#define SYS_SENDTO      11              /* sys_sendto(2)                */
-#define SYS_RECVFROM    12              /* sys_recvfrom(2)              */
-#define SYS_SHUTDOWN    13              /* sys_shutdown(2)              */
-#define SYS_SETSOCKOPT  14              /* sys_setsockopt(2)            */
-#define SYS_GETSOCKOPT  15              /* sys_getsockopt(2)            */
-#define SYS_SENDMSG     16              /* sys_sendmsg(2)               */
-#define SYS_RECVMSG     17              /* sys_recvmsg(2)               */
-#define SYS_ACCEPT4     18              /* sys_accept4(2)               */
-#define SYS_RECVMMSG    19              /* sys_recvmmsg(2)              */
-#define SYS_SENDMMSG    20              /* sys_sendmmsg(2)              */
-
-#endif /* _SYS_SOCKETCALLS_H_ */
diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index ae85f62..46eec96 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -146,18 +146,18 @@
 extern int mkdir(const char*, mode_t);
 
 extern int fstat(int, struct stat*);
-extern int fstat64(int, struct stat64*);
+extern int fstat64(int, struct stat64*) __INTRODUCED_IN(21);
 extern int fstatat(int, const char*, struct stat*, int);
-extern int fstatat64(int, const char*, struct stat64*, int);
+extern int fstatat64(int, const char*, struct stat64*, int) __INTRODUCED_IN(21);
 extern int lstat(const char*, struct stat*);
-extern int lstat64(const char*, struct stat64*);
+extern int lstat64(const char*, struct stat64*) __INTRODUCED_IN(21);
 extern int stat(const char*, struct stat*);
-extern int stat64(const char*, struct stat64*);
+extern int stat64(const char*, struct stat64*) __INTRODUCED_IN(21);
 
 extern int mknod(const char*, mode_t, dev_t);
 extern mode_t umask(mode_t);
 
-extern mode_t __umask_chk(mode_t);
+extern mode_t __umask_chk(mode_t) __INTRODUCED_IN(21);
 extern mode_t __umask_real(mode_t) __RENAME(umask);
 __errordecl(__umask_invalid_mode, "umask called with invalid mode");
 
@@ -178,16 +178,17 @@
 #endif /* defined(__BIONIC_FORTIFY) */
 
 __BIONIC_LEGACY_INLINE int mkfifo(const char*, mode_t);
-extern int mkfifoat(int, const char*, mode_t);
+extern int mkfifoat(int, const char*, mode_t) __INTRODUCED_IN(23);
 
 extern int fchmodat(int, const char*, mode_t, int);
 extern int mkdirat(int, const char*, mode_t);
-extern int mknodat(int, const char*, mode_t, dev_t);
+extern int mknodat(int, const char*, mode_t, dev_t) __INTRODUCED_IN(21);
 
 #define UTIME_NOW  ((1L << 30) - 1L)
 #define UTIME_OMIT ((1L << 30) - 2L)
-extern int utimensat(int fd, const char *path, const struct timespec times[2], int flags);
-extern int futimens(int fd, const struct timespec times[2]);
+extern int utimensat(int fd, const char* path, const struct timespec times[2], int flags)
+  __INTRODUCED_IN(12);
+extern int futimens(int fd, const struct timespec times[2]) __INTRODUCED_IN(19);
 
 __END_DECLS
 
diff --git a/libc/include/sys/statvfs.h b/libc/include/sys/statvfs.h
index 3495546..e12f069 100644
--- a/libc/include/sys/statvfs.h
+++ b/libc/include/sys/statvfs.h
@@ -59,10 +59,12 @@
 #define ST_NODIRATIME  0x0800
 #define ST_RELATIME    0x1000
 
-extern int statvfs(const char* __restrict, struct statvfs* __restrict) __nonnull((1, 2));
-extern int statvfs64(const char* __restrict, struct statvfs64* __restrict) __nonnull((1, 2));
-extern int fstatvfs(int, struct statvfs*) __nonnull((2));
-extern int fstatvfs64(int, struct statvfs64*) __nonnull((2));
+extern int statvfs(const char* __restrict, struct statvfs* __restrict) __nonnull((1, 2))
+  __INTRODUCED_IN(21);
+extern int statvfs64(const char* __restrict, struct statvfs64* __restrict) __nonnull((1, 2))
+  __INTRODUCED_IN(21);
+extern int fstatvfs(int, struct statvfs*) __nonnull((2)) __INTRODUCED_IN(21);
+extern int fstatvfs64(int, struct statvfs64*) __nonnull((2)) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/swap.h b/libc/include/sys/swap.h
index e4c1819..b1f9295 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*, int) __nonnull((1));
-extern int swapoff(const char*) __nonnull((1));
+extern int swapon(const char*, int) __nonnull((1)) __INTRODUCED_IN(21);
+extern int swapoff(const char*) __nonnull((1)) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/sysinfo.h b/libc/include/sys/sysinfo.h
index b66bc8e..9a10d64 100644
--- a/libc/include/sys/sysinfo.h
+++ b/libc/include/sys/sysinfo.h
@@ -35,13 +35,13 @@
 
 int sysinfo(struct sysinfo* info);
 
-int get_nprocs_conf(void);
+int get_nprocs_conf(void) __INTRODUCED_IN(23);
 
-int get_nprocs(void);
+int get_nprocs(void) __INTRODUCED_IN(23);
 
-long get_phys_pages(void);
+long get_phys_pages(void) __INTRODUCED_IN(23);
 
-long get_avphys_pages(void);
+long get_avphys_pages(void) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/sys/system_properties.h b/libc/include/sys/system_properties.h
index 01c3db3..99a6e59 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);
+int __system_property_set(const char* key, const char* value) __INTRODUCED_IN(21);
 
 /* Return a pointer to the system property named name, if it
 ** exists, or NULL if there is no such property.  Use 
@@ -93,9 +93,8 @@
 ** Order of results may change from call to call.  This is
 ** not a bug.
 */
-int __system_property_foreach(
-        void (*propfn)(const prop_info *pi, void *cookie),
-        void *cookie);
+int __system_property_foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie)
+  __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/timerfd.h b/libc/include/sys/timerfd.h
index 1aa97b4..a189742 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);
-extern int timerfd_settime(int, int, const struct itimerspec*,
-                           struct itimerspec*);
-extern int timerfd_gettime(int, struct itimerspec*);
+extern int timerfd_create(clockid_t, int) __INTRODUCED_IN(21);
+extern int timerfd_settime(int, int, const struct itimerspec*, struct itimerspec*)
+  __INTRODUCED_IN(21);
+extern int timerfd_gettime(int, struct itimerspec*) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/timex.h b/libc/include/sys/timex.h
index fade5c3..f704ce8 100644
--- a/libc/include/sys/timex.h
+++ b/libc/include/sys/timex.h
@@ -35,8 +35,8 @@
 
 __BEGIN_DECLS
 
-int adjtimex(struct timex*);
-int clock_adjtime(clockid_t, struct timex*);
+int adjtimex(struct timex*) __INTRODUCED_IN(24);
+int clock_adjtime(clockid_t, struct timex*) __INTRODUCED_IN(24);
 
 __END_DECLS
 
diff --git a/libc/include/sys/uio.h b/libc/include/sys/uio.h
index 72675d1..7a009b4 100644
--- a/libc/include/sys/uio.h
+++ b/libc/include/sys/uio.h
@@ -42,16 +42,18 @@
 ssize_t preadv(int, const struct iovec*, int, off_t) __RENAME(preadv64);
 ssize_t pwritev(int, const struct iovec*, int, off_t) __RENAME(pwritev64);
 #else
-ssize_t preadv(int, const struct iovec*, int, off_t);
-ssize_t pwritev(int, const struct iovec*, int, off_t);
+ssize_t preadv(int, const struct iovec*, int, off_t) __INTRODUCED_IN(24);
+ssize_t pwritev(int, const struct iovec*, int, off_t) __INTRODUCED_IN(24);
 #endif
-ssize_t preadv64(int, const struct iovec*, int, off64_t);
-ssize_t pwritev64(int, const struct iovec*, int, off64_t);
+ssize_t preadv64(int, const struct iovec*, int, off64_t) __INTRODUCED_IN(24);
+ssize_t pwritev64(int, const struct iovec*, int, off64_t) __INTRODUCED_IN(24);
 #endif
 
 #if defined(__USE_GNU)
-ssize_t process_vm_readv(pid_t, const struct iovec*, unsigned long, const struct iovec*, unsigned long, unsigned long);
-ssize_t process_vm_writev(pid_t, const struct iovec*, unsigned long, const struct iovec*, unsigned long, unsigned long);
+ssize_t process_vm_readv(pid_t, const struct iovec*, unsigned long, const struct iovec*,
+                         unsigned long, unsigned long) __INTRODUCED_IN(23);
+ssize_t process_vm_writev(pid_t, const struct iovec*, unsigned long, const struct iovec*,
+                          unsigned long, unsigned long) __INTRODUCED_IN(23);
 #endif
 
 __END_DECLS
diff --git a/libc/include/sys/vfs.h b/libc/include/sys/vfs.h
index 1fbc8be..9f04b28 100644
--- a/libc/include/sys/vfs.h
+++ b/libc/include/sys/vfs.h
@@ -138,9 +138,9 @@
 #define XFS_SUPER_MAGIC       0x58465342
 
 extern int statfs(const char*, struct statfs*) __nonnull((1, 2));
-extern int statfs64(const char*, struct statfs64*) __nonnull((1, 2));
+extern int statfs64(const char*, struct statfs64*) __nonnull((1, 2)) __INTRODUCED_IN(21);
 extern int fstatfs(int, struct statfs*) __nonnull((2));
-extern int fstatfs64(int, struct statfs64*) __nonnull((2));
+extern int fstatfs64(int, struct statfs64*) __nonnull((2)) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/sys/wait.h b/libc/include/sys/wait.h
index 2317b02..aba20e5 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 *);
+extern pid_t wait4(pid_t, int*, int, struct rusage*) __INTRODUCED_IN(19);
 
 /* 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 39b25b1..070913f 100644
--- a/libc/include/sys/xattr.h
+++ b/libc/include/sys/xattr.h
@@ -35,21 +35,26 @@
 #define XATTR_CREATE 1
 #define XATTR_REPLACE 2
 
-extern int fsetxattr(int fd, const char *name, const void *value, size_t size, int flags);
-extern int setxattr(const char *path, const char *name, const void *value, size_t size, int flags);
-extern int lsetxattr(const char *path, const char *name, const void *value, size_t size, int flags);
+extern int fsetxattr(int fd, const char* name, const void* value, size_t size, int flags)
+  __INTRODUCED_IN(21);
+extern int setxattr(const char* path, const char* name, const void* value, size_t size, int flags)
+  __INTRODUCED_IN(21);
+extern int lsetxattr(const char* path, const char* name, const void* value, size_t size, int flags)
+  __INTRODUCED_IN(21);
 
-extern ssize_t fgetxattr(int fd, const char *name, void *value, size_t size);
-extern ssize_t getxattr(const char *path, const char *name, void *value, size_t size);
-extern ssize_t lgetxattr(const char *path, const char *name, void *value, size_t size);
+extern ssize_t fgetxattr(int fd, const char* name, void* value, size_t size) __INTRODUCED_IN(21);
+extern ssize_t getxattr(const char* path, const char* name, void* value, size_t size)
+  __INTRODUCED_IN(21);
+extern ssize_t lgetxattr(const char* path, const char* name, void* value, size_t size)
+  __INTRODUCED_IN(21);
 
-extern ssize_t listxattr(const char *path, char *list, size_t size);
-extern ssize_t llistxattr(const char *path, char *list, size_t size);
-extern ssize_t flistxattr(int fd, char *list, size_t size);
+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 int removexattr(const char *path, const char *name);
-extern int lremovexattr(const char *path, const char *name);
-extern int fremovexattr(int fd, const char *name);
+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);
 
 __END_DECLS
 
diff --git a/libc/include/termios.h b/libc/include/termios.h
index e604747..15a7b32 100644
--- a/libc/include/termios.h
+++ b/libc/include/termios.h
@@ -40,8 +40,8 @@
 __BIONIC_LEGACY_INLINE void cfmakeraw(struct termios*);
 __BIONIC_LEGACY_INLINE int cfsetispeed(struct termios*, speed_t);
 __BIONIC_LEGACY_INLINE int cfsetospeed(struct termios*, speed_t);
-__BIONIC_LEGACY_INLINE int cfsetspeed(struct termios*, speed_t);
-__BIONIC_LEGACY_INLINE int tcdrain(int);
+__BIONIC_LEGACY_INLINE int cfsetspeed(struct termios*, speed_t) __INTRODUCED_IN(21);
+__BIONIC_LEGACY_INLINE int tcdrain(int) __INTRODUCED_IN(21);
 __BIONIC_LEGACY_INLINE int tcflow(int, int);
 __BIONIC_LEGACY_INLINE int tcflush(int, int);
 __BIONIC_LEGACY_INLINE int tcgetattr(int, struct termios*);
diff --git a/libc/include/time.h b/libc/include/time.h
index 1b0f6a1..039608b 100644
--- a/libc/include/time.h
+++ b/libc/include/time.h
@@ -76,7 +76,8 @@
 
 extern char* strptime(const char*, const char*, struct tm*) __LIBC_ABI_PUBLIC__;
 extern size_t strftime(char*, size_t, const char*, const struct tm*) __LIBC_ABI_PUBLIC__;
-extern size_t strftime_l(char *, size_t, const char *, const struct tm *, locale_t) __LIBC_ABI_PUBLIC__;
+extern size_t strftime_l(char*, size_t, const char*, const struct tm*, locale_t) __LIBC_ABI_PUBLIC__
+  __INTRODUCED_IN(21);
 
 extern char* ctime(const time_t*) __LIBC_ABI_PUBLIC__;
 extern char* ctime_r(const time_t*, char*) __LIBC_ABI_PUBLIC__;
@@ -85,7 +86,7 @@
 
 extern clock_t clock(void) __LIBC_ABI_PUBLIC__;
 
-extern int clock_getcpuclockid(pid_t, clockid_t*) __LIBC_ABI_PUBLIC__;
+extern int clock_getcpuclockid(pid_t, clockid_t*) __LIBC_ABI_PUBLIC__ __INTRODUCED_IN(23);
 
 extern int clock_getres(clockid_t, struct timespec*) __LIBC_ABI_PUBLIC__;
 extern int clock_gettime(clockid_t, struct timespec*) __LIBC_ABI_PUBLIC__;
@@ -99,8 +100,8 @@
 extern int timer_getoverrun(timer_t) __LIBC_ABI_PUBLIC__;
 
 /* Non-standard extensions that are in the BSDs and glibc. */
-extern time_t timelocal(struct tm*) __LIBC_ABI_PUBLIC__;
-extern time_t timegm(struct tm*) __LIBC_ABI_PUBLIC__;
+extern time_t timelocal(struct tm*) __LIBC_ABI_PUBLIC__ __INTRODUCED_IN(21);
+extern time_t timegm(struct tm*) __LIBC_ABI_PUBLIC__ __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/uchar.h b/libc/include/uchar.h
index a5e72ea..9a0e2f8 100644
--- a/libc/include/uchar.h
+++ b/libc/include/uchar.h
@@ -42,16 +42,12 @@
 #define __STD_UTF_16__ 1
 #define __STD_UTF_32__ 1
 
-size_t c16rtomb(char* __restrict, char16_t, mbstate_t* __restrict);
-size_t c32rtomb(char* __restrict, char32_t, mbstate_t* __restrict);
-size_t mbrtoc16(char16_t* __restrict,
-                const char* __restrict,
-                size_t,
-                mbstate_t* __restrict);
-size_t mbrtoc32(char32_t* __restrict,
-                const char* __restrict,
-                size_t,
-                mbstate_t* __restrict);
+size_t c16rtomb(char* __restrict, char16_t, mbstate_t* __restrict) __INTRODUCED_IN(21);
+size_t c32rtomb(char* __restrict, char32_t, mbstate_t* __restrict) __INTRODUCED_IN(21);
+size_t mbrtoc16(char16_t* __restrict, const char* __restrict, size_t, mbstate_t* __restrict)
+  __INTRODUCED_IN(21);
+size_t mbrtoc32(char32_t* __restrict, const char* __restrict, size_t, mbstate_t* __restrict)
+  __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index ea6c8a1..6b5ef76 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -176,12 +176,12 @@
 extern off64_t lseek64(int __fd, off64_t __offset, int __whence);
 
 #if defined(__USE_FILE_OFFSET64) && __ANDROID_API__ >= 21
-extern int truncate(const char* __path, off_t __length) __RENAME(truncate64);
-extern ssize_t pread(int __fd, void* __buf, size_t __count, off_t __offset)
-  __RENAME(pread64);
-extern ssize_t pwrite(int __fd, const void* __buf, size_t __count,
-                      off_t __offset) __RENAME(pwrite64);
-extern int ftruncate(int __fd, off_t __length) __RENAME(ftruncate64);
+extern int truncate(const char* __path, off_t __length) __RENAME(truncate64) __INTRODUCED_IN(21);
+extern ssize_t pread(int __fd, void* __buf, size_t __count, off_t __offset) __RENAME(pread64)
+  __INTRODUCED_IN(12);
+extern ssize_t pwrite(int __fd, const void* __buf, size_t __count, off_t __offset)
+  __RENAME(pwrite64) __INTRODUCED_IN(12);
+extern int ftruncate(int __fd, off_t __length) __RENAME(ftruncate64) __INTRODUCED_IN(12);
 #else
 extern int truncate(const char* __path, off_t __length);
 extern ssize_t pread(int __fd, void* __buf, size_t __count, off_t __offset);
@@ -191,10 +191,10 @@
 #endif
 
 extern int truncate64(const char* __path, off64_t __length) __INTRODUCED_IN(21);
-extern ssize_t pread64(int __fd, void* __buf, size_t __count, off64_t __offset) __INTRODUCED_IN(21);
-extern ssize_t pwrite64(int __fd, const void* __buf, size_t __count,
-                        off64_t __offset) __INTRODUCED_IN(21);
-extern int ftruncate64(int __fd, off64_t __length) __INTRODUCED_IN(21);
+extern ssize_t pread64(int __fd, void* __buf, size_t __count, off64_t __offset) __INTRODUCED_IN(12);
+extern ssize_t pwrite64(int __fd, const void* __buf, size_t __count, off64_t __offset)
+  __INTRODUCED_IN(12);
+extern int ftruncate64(int __fd, off64_t __length) __INTRODUCED_IN(12);
 
 extern int pause(void);
 extern unsigned int alarm(unsigned int __seconds);
@@ -202,7 +202,7 @@
 extern int usleep(useconds_t __usec);
 
 int gethostname(char* __name, size_t __len);
-int sethostname(const char* __name, size_t __len);
+int sethostname(const char* __name, size_t __len) __INTRODUCED_IN(23);
 
 extern void* __brk(void* __addr);
 extern int brk(void* __addr);
@@ -243,52 +243,53 @@
     _rc; })
 
 /* TODO(unified-headers): Factor out all the FORTIFY features. */
-extern char* __getcwd_chk(char*, size_t, size_t);
+extern char* __getcwd_chk(char*, size_t, size_t) __INTRODUCED_IN(24);
 __errordecl(__getcwd_dest_size_error, "getcwd called with size bigger than destination");
 extern char* __getcwd_real(char*, size_t) __RENAME(getcwd);
 
-extern ssize_t __pread_chk(int, void*, size_t, off_t, size_t);
+extern ssize_t __pread_chk(int, void*, size_t, off_t, size_t) __INTRODUCED_IN(23);
 __errordecl(__pread_dest_size_error, "pread called with size bigger than destination");
 __errordecl(__pread_count_toobig_error, "pread called with count > SSIZE_MAX");
 extern ssize_t __pread_real(int, void*, size_t, off_t) __RENAME(pread);
 
-extern ssize_t __pread64_chk(int, void*, size_t, off64_t, size_t);
+extern ssize_t __pread64_chk(int, void*, size_t, off64_t, size_t) __INTRODUCED_IN(23);
 __errordecl(__pread64_dest_size_error, "pread64 called with size bigger than destination");
 __errordecl(__pread64_count_toobig_error, "pread64 called with count > SSIZE_MAX");
-extern ssize_t __pread64_real(int, void*, size_t, off64_t) __RENAME(pread64);
+extern ssize_t __pread64_real(int, void*, size_t, off64_t) __RENAME(pread64) __INTRODUCED_IN(12);
 
-extern ssize_t __pwrite_chk(int, const void*, size_t, off_t, size_t);
+extern ssize_t __pwrite_chk(int, const void*, size_t, off_t, size_t) __INTRODUCED_IN(24);
 __errordecl(__pwrite_dest_size_error, "pwrite called with size bigger than destination");
 __errordecl(__pwrite_count_toobig_error, "pwrite called with count > SSIZE_MAX");
 extern ssize_t __pwrite_real(int, const void*, size_t, off_t) __RENAME(pwrite);
 
-extern ssize_t __pwrite64_chk(int, const void*, size_t, off64_t, size_t);
+extern ssize_t __pwrite64_chk(int, const void*, size_t, off64_t, size_t) __INTRODUCED_IN(24);
 __errordecl(__pwrite64_dest_size_error, "pwrite64 called with size bigger than destination");
 __errordecl(__pwrite64_count_toobig_error, "pwrite64 called with count > SSIZE_MAX");
-extern ssize_t __pwrite64_real(int, const void*, size_t, off64_t) __RENAME(pwrite64);
+extern ssize_t __pwrite64_real(int, const void*, size_t, off64_t) __RENAME(pwrite64)
+  __INTRODUCED_IN(12);
 
-extern ssize_t __read_chk(int, void*, size_t, size_t);
+extern ssize_t __read_chk(int, void*, size_t, size_t) __INTRODUCED_IN(21);
 __errordecl(__read_dest_size_error, "read called with size bigger than destination");
 __errordecl(__read_count_toobig_error, "read called with count > SSIZE_MAX");
 extern ssize_t __read_real(int, void*, size_t) __RENAME(read);
 
-extern ssize_t __write_chk(int, const void*, size_t, size_t);
+extern ssize_t __write_chk(int, const void*, size_t, size_t) __INTRODUCED_IN(24);
 __errordecl(__write_dest_size_error, "write called with size bigger than destination");
 __errordecl(__write_count_toobig_error, "write called with count > SSIZE_MAX");
 extern ssize_t __write_real(int, const void*, size_t) __RENAME(write);
 
-extern ssize_t __readlink_chk(const char*, char*, size_t, size_t);
+extern ssize_t __readlink_chk(const char*, char*, size_t, size_t) __INTRODUCED_IN(23);
 __errordecl(__readlink_dest_size_error, "readlink called with size bigger than destination");
 __errordecl(__readlink_size_toobig_error, "readlink called with size > SSIZE_MAX");
 extern ssize_t __readlink_real(const char*, char*, size_t) __RENAME(readlink);
 
-extern ssize_t __readlinkat_chk(int dirfd, const char*, char*, size_t, size_t);
+extern ssize_t __readlinkat_chk(int dirfd, const char*, char*, size_t, size_t) __INTRODUCED_IN(23);
 __errordecl(__readlinkat_dest_size_error, "readlinkat called with size bigger than destination");
 __errordecl(__readlinkat_size_toobig_error, "readlinkat called with size > SSIZE_MAX");
 extern ssize_t __readlinkat_real(int dirfd, const char*, char*, size_t) __RENAME(readlinkat);
 
-extern int getdomainname(char*, size_t);
-extern int setdomainname(const char*, size_t);
+extern int getdomainname(char*, size_t) __INTRODUCED_IN_FUTURE;
+extern int setdomainname(const char*, size_t) __INTRODUCED_IN_FUTURE;
 
 #if defined(__BIONIC_FORTIFY)
 
diff --git a/libc/include/utmp.h b/libc/include/utmp.h
index c6f22a5..62e8d59 100644
--- a/libc/include/utmp.h
+++ b/libc/include/utmp.h
@@ -101,7 +101,7 @@
 struct utmp* getutent(void);
 void endutent(void);
 
-int login_tty(int);
+int login_tty(int) __INTRODUCED_IN(23);
 
 __END_DECLS
 
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 625097e..91d6f24 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -81,23 +81,23 @@
 extern size_t            mbrlen(const char *, size_t, mbstate_t *);
 extern size_t            mbrtowc(wchar_t *, const char *, size_t, mbstate_t *);
 extern size_t mbsrtowcs(wchar_t*, const char**, size_t, mbstate_t*);
-extern size_t mbsnrtowcs(wchar_t*, const char**, size_t, size_t, mbstate_t*);
+extern size_t mbsnrtowcs(wchar_t*, const char**, size_t, size_t, mbstate_t*) __INTRODUCED_IN(21);
 extern wint_t            putwc(wchar_t, FILE *);
 extern wint_t            putwchar(wchar_t);
 extern int               swprintf(wchar_t *, size_t, const wchar_t *, ...);
 extern int               swscanf(const wchar_t *, const wchar_t *, ...);
 extern wint_t            ungetwc(wint_t, FILE *);
 extern int vfwprintf(FILE*, const wchar_t*, va_list);
-extern int vfwscanf(FILE*, const wchar_t*, va_list);
+extern int vfwscanf(FILE*, const wchar_t*, va_list) __INTRODUCED_IN(21);
 extern int vswprintf(wchar_t*, size_t, const wchar_t*, va_list);
-extern int vswscanf(const wchar_t*, const wchar_t*, va_list);
+extern int vswscanf(const wchar_t*, const wchar_t*, va_list) __INTRODUCED_IN(21);
 extern int vwprintf(const wchar_t*, va_list);
-extern int vwscanf(const wchar_t*, va_list);
+extern int vwscanf(const wchar_t*, va_list) __INTRODUCED_IN(21);
 extern wchar_t* wcpcpy (wchar_t*, const wchar_t *);
 extern wchar_t* wcpncpy (wchar_t*, const wchar_t *, size_t);
 extern size_t            wcrtomb(char *, wchar_t, mbstate_t *);
 extern int               wcscasecmp(const wchar_t *, const wchar_t *);
-extern int               wcscasecmp_l(const wchar_t *, const wchar_t *, locale_t);
+extern int wcscasecmp_l(const wchar_t*, const wchar_t*, locale_t) __INTRODUCED_IN(23);
 extern wchar_t          *wcscat(wchar_t *, const wchar_t *);
 extern wchar_t          *wcschr(const wchar_t *, wchar_t);
 extern int               wcscmp(const wchar_t *, const wchar_t *);
@@ -107,24 +107,24 @@
 extern size_t            wcsftime(wchar_t *, size_t, const wchar_t *, const struct tm *) __LIBC_ABI_PUBLIC__;
 extern size_t            wcslen(const wchar_t *);
 extern int               wcsncasecmp(const wchar_t *, const wchar_t *, size_t);
-extern int               wcsncasecmp_l(const wchar_t *, const wchar_t *, size_t, locale_t);
+extern int wcsncasecmp_l(const wchar_t*, const wchar_t*, size_t, locale_t) __INTRODUCED_IN(23);
 extern wchar_t          *wcsncat(wchar_t *, const wchar_t *, size_t);
 extern int               wcsncmp(const wchar_t *, const wchar_t *, size_t);
 extern wchar_t          *wcsncpy(wchar_t *, const wchar_t *, size_t);
-extern size_t wcsnrtombs(char*, const wchar_t**, size_t, size_t, mbstate_t*);
+extern size_t wcsnrtombs(char*, const wchar_t**, size_t, size_t, mbstate_t*) __INTRODUCED_IN(21);
 extern wchar_t          *wcspbrk(const wchar_t *, const wchar_t *);
 extern wchar_t          *wcsrchr(const wchar_t *, wchar_t);
 extern size_t wcsrtombs(char*, const wchar_t**, size_t, mbstate_t*);
 extern size_t            wcsspn(const wchar_t *, const wchar_t *);
 extern wchar_t          *wcsstr(const wchar_t *, const wchar_t *);
 extern double wcstod(const wchar_t*, wchar_t**);
-extern float wcstof(const wchar_t*, wchar_t**);
+extern float wcstof(const wchar_t*, wchar_t**) __INTRODUCED_IN(21);
 extern wchar_t* wcstok(wchar_t*, const wchar_t*, wchar_t**);
 extern long wcstol(const wchar_t*, wchar_t**, int);
-extern long long wcstoll(const wchar_t*, wchar_t**, int);
-extern long double wcstold(const wchar_t*, wchar_t**);
+extern long long wcstoll(const wchar_t*, wchar_t**, int) __INTRODUCED_IN(21);
+extern long double wcstold(const wchar_t*, wchar_t**) __INTRODUCED_IN(21);
 extern unsigned long wcstoul(const wchar_t*, wchar_t**, int);
-extern unsigned long long wcstoull(const wchar_t*, wchar_t**, int);
+extern unsigned long long wcstoull(const wchar_t*, wchar_t**, int) __INTRODUCED_IN(21);
 extern int               wcswidth(const wchar_t *, size_t);
 extern size_t            wcsxfrm(wchar_t *, const wchar_t *, size_t);
 extern int               wctob(wint_t);
@@ -133,25 +133,25 @@
 extern int               wmemcmp(const wchar_t *, const wchar_t *, size_t);
 extern wchar_t          *wmemcpy(wchar_t *, const wchar_t *, size_t);
 #if defined(__USE_GNU)
-extern wchar_t          *wmempcpy(wchar_t *, const wchar_t *, size_t);
+extern wchar_t* wmempcpy(wchar_t*, const wchar_t*, size_t) __INTRODUCED_IN(23);
 #endif
 extern wchar_t          *wmemmove(wchar_t *, const wchar_t *, size_t);
 extern wchar_t          *wmemset(wchar_t *, wchar_t, size_t);
 extern int               wprintf(const wchar_t *, ...);
 extern int               wscanf(const wchar_t *, ...);
 
-extern long long          wcstoll_l(const wchar_t *, wchar_t **, int, locale_t);
-extern unsigned long long wcstoull_l(const wchar_t *, wchar_t **, int, locale_t);
-extern long double        wcstold_l(const wchar_t *, wchar_t **, locale_t );
+extern long long wcstoll_l(const wchar_t*, wchar_t**, int, locale_t) __INTRODUCED_IN(21);
+extern unsigned long long wcstoull_l(const wchar_t*, wchar_t**, int, locale_t) __INTRODUCED_IN(21);
+extern long double wcstold_l(const wchar_t*, wchar_t**, locale_t) __INTRODUCED_IN(21);
 
-extern int    wcscoll_l(const wchar_t *, const wchar_t *, locale_t);
-extern size_t wcsxfrm_l(wchar_t *, const wchar_t *, size_t, locale_t);
+extern int wcscoll_l(const wchar_t*, const wchar_t*, locale_t) __INTRODUCED_IN(21);
+extern size_t wcsxfrm_l(wchar_t*, const wchar_t*, size_t, locale_t) __INTRODUCED_IN(21);
 
 extern size_t wcslcat(wchar_t*, const wchar_t*, size_t);
 extern size_t wcslcpy(wchar_t*, const wchar_t*, size_t);
 
 #if __POSIX_VISIBLE >= 200809
-FILE* open_wmemstream(wchar_t**, size_t*);
+FILE* open_wmemstream(wchar_t**, size_t*) __INTRODUCED_IN(23);
 wchar_t* wcsdup(const wchar_t*);
 size_t wcsnlen(const wchar_t*, size_t);
 #endif
diff --git a/libc/include/wctype.h b/libc/include/wctype.h
index 12ef7cd..41e0ec3 100644
--- a/libc/include/wctype.h
+++ b/libc/include/wctype.h
@@ -35,27 +35,27 @@
 
 __BEGIN_DECLS
 
-int iswalnum_l(wint_t, locale_t);
-int iswalpha_l(wint_t, locale_t);
-int iswblank_l(wint_t, locale_t);
-int iswcntrl_l(wint_t, locale_t);
-int iswdigit_l(wint_t, locale_t);
-int iswgraph_l(wint_t, locale_t);
-int iswlower_l(wint_t, locale_t);
-int iswprint_l(wint_t, locale_t);
-int iswpunct_l(wint_t, locale_t);
-int iswspace_l(wint_t, locale_t);
-int iswupper_l(wint_t, locale_t);
-int iswxdigit_l(wint_t, locale_t);
+int iswalnum_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswalpha_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswblank_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswcntrl_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswdigit_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswgraph_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswlower_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswprint_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswpunct_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswspace_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswupper_l(wint_t, locale_t) __INTRODUCED_IN(21);
+int iswxdigit_l(wint_t, locale_t) __INTRODUCED_IN(21);
 
-wint_t towlower_l(int, locale_t);
-wint_t towupper_l(int, locale_t);
+wint_t towlower_l(int, locale_t) __INTRODUCED_IN(21);
+wint_t towupper_l(int, locale_t) __INTRODUCED_IN(21);
 
-wint_t towctrans_l(wint_t, wctrans_t, locale_t);
-wctrans_t wctrans_l(const char*, locale_t);
+wint_t towctrans_l(wint_t, wctrans_t, locale_t) __INTRODUCED_IN_FUTURE;
+wctrans_t wctrans_l(const char*, locale_t) __INTRODUCED_IN_FUTURE;
 
-wctype_t wctype_l(const char*, locale_t);
-int iswctype_l(wint_t, wctype_t, locale_t);
+wctype_t wctype_l(const char*, locale_t) __INTRODUCED_IN(21);
+int iswctype_l(wint_t, wctype_t, locale_t) __INTRODUCED_IN(21);
 
 __END_DECLS
 
diff --git a/tests/complex_test.cpp b/tests/complex_test.cpp
index 746c0be..a8f6777 100644
--- a/tests/complex_test.cpp
+++ b/tests/complex_test.cpp
@@ -23,6 +23,7 @@
 #define __INTRODUCED_IN(x)
 #define __INTRODUCED_IN_32(x)
 #define __INTRODUCED_IN_64(x)
+#define __INTRODUCED_IN_FUTURE
 #endif
 
 // libc++ actively gets in the way of including <complex.h> from C++, so we