diff --git a/include/dlfcn.h b/include/dlfcn.h
--- a/include/dlfcn.h
+++ b/include/dlfcn.h
@@ -80,6 +80,9 @@
 	const char	*dli_sname;	/* Name of nearest symbol. */
 	void		*dli_saddr;	/* Address of nearest symbol. */
 } Dl_info;
+#if __POSIX_VISIBLE >= 202405
+typedef struct dl_info Dl_info_t;
+#endif
 
 /*-
  * The actual type declared by this typedef is immaterial, provided that
@@ -119,9 +122,12 @@
 void	*dlopen(const char *, int);
 void	*dlsym(void * __restrict, const char * __restrict);
 
+#if __POSIX_VISIBLE >= 202405
+int	 dladdr(const void * __restrict, Dl_info * __restrict);
+#endif
+
 #if __BSD_VISIBLE
 void	*fdlopen(int, int);
-int	 dladdr(const void * __restrict, Dl_info * __restrict);
 dlfunc_t dlfunc(void * __restrict, const char * __restrict);
 int	 dlinfo(void * __restrict, int, void * __restrict);
 void	 dllockinit(void *_context,
diff --git a/include/stdlib.h b/include/stdlib.h
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -157,7 +157,7 @@
 /*
  * If we're in a mode greater than C99, expose C11 functions.
  */
-#if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L
+#if __ISO_C_VISIBLE >= 2011 || __cplusplus >= 201103L || __POSIX_VISIBLE >= 202405
 void *	aligned_alloc(size_t, size_t) __malloc_like __alloc_align(1)
 	    __alloc_size(2);
 int	at_quick_exit(void (*)(void)) __noexcept;
@@ -236,6 +236,13 @@
 int	 ptsname_r(int, char *, size_t);
 #endif
 
+#if __POSIX_VISIBLE >= 202405
+void	 qsort_r(void *, size_t, size_t,
+	    int (*)(const void *, const void *, void *), void *);
+void	*reallocarray(void *, size_t, size_t) __result_use_check
+	    __alloc_size2(2, 3);
+#endif
+
 #if __BSD_VISIBLE
 extern const char *malloc_conf;
 extern void (*malloc_message)(void *, const char *);
@@ -305,12 +312,8 @@
 int	 mkostemp(char *, int);
 int	 mkostemps(char *, int, int);
 int	 mkostempsat(int, char *, int, int);
-void	 qsort_r(void *, size_t, size_t,
-	    int (*)(const void *, const void *, void *), void *);
 int	 radixsort(const unsigned char **, int, const unsigned char *,
 	    unsigned);
-void	*reallocarray(void *, size_t, size_t) __result_use_check
-	    __alloc_size2(2, 3);
 void	*reallocf(void *, size_t) __result_use_check __alloc_size(2);
 int	 rpmatch(const char *);
 char	*secure_getenv(const char *);
diff --git a/include/string.h b/include/string.h
--- a/include/string.h
+++ b/include/string.h
@@ -63,8 +63,8 @@
 #endif
 int	 memcmp(const void *, const void *, size_t) __pure;
 void	*(memcpy)(void * __restrict, const void * __restrict, size_t);
-#if __BSD_VISIBLE
-void	*memmem(const void *, size_t, const void *, size_t) __pure;
+#if __POSIX_VISIBLE >= 202405
+void	*(memmem)(const void *, size_t, const void *, size_t) __pure;
 #endif
 void	*(memmove)(void *, const void *, size_t);
 #if __BSD_VISIBLE
@@ -98,7 +98,7 @@
 #if __POSIX_VISIBLE >= 200112
 int	 strerror_r(int, char *, size_t);
 #endif
-#if __BSD_VISIBLE
+#if __POSIX_VISIBLE >= 202405
 size_t	 (strlcat)(char * __restrict, const char * __restrict, size_t);
 size_t	 (strlcpy)(char * __restrict, const char * __restrict, size_t);
 #endif
diff --git a/include/time.h b/include/time.h
--- a/include/time.h
+++ b/include/time.h
@@ -180,15 +180,17 @@
 #include <xlocale/_time.h>
 #endif
 
-#if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2011 || \
+#if __ISO_C_VISIBLE >= 2011 || __POSIX_VISIBLE >= 202405 || \
     (defined(__cplusplus) && __cplusplus >= 201703)
 #include <sys/_timespec.h>
 /* ISO/IEC 9899:2011 7.27.2.5 The timespec_get function */
 #define TIME_UTC	1	/* time elapsed since epoch */
-int timespec_get(struct timespec *ts, int base);
-#if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2023
+#if __ISO_C_VISIBLE >= 2023 || __POSIX_VISIBLE >= 202405
 /* ISO/IEC 9899:2024 7.29.1 Components of time */
 #define TIME_MONOTONIC	2	/* monotonic time */
+#endif
+int timespec_get(struct timespec *ts, int base);
+#if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2023
 /* ISO/IEC 9899:2024 7.29.2.7 The timespec_getres function */
 int timespec_getres(struct timespec *, int);
 #endif
diff --git a/include/unistd.h b/include/unistd.h
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -483,6 +483,16 @@
 pid_t	 vfork(void) __returns_twice;
 #endif
 
+/* 1003.1-2024 */
+#if __POSIX_VISIBLE >= 202405
+pid_t	 _Fork(void);
+int	 getentropy(void *, size_t);
+int	 getresgid(gid_t *, gid_t *, gid_t *);
+int	 getresuid(uid_t *, uid_t *, uid_t *);
+int	 setresgid(gid_t, gid_t, gid_t);
+int	 setresuid(uid_t, uid_t, uid_t);
+#endif
+
 #if __BSD_VISIBLE
 struct timeval;				/* select(2) */
 
@@ -510,14 +520,11 @@
 int	 fchroot(int);
 char	*fflagstostr(u_long);
 int	 getdomainname(char *, int);
-int	 getentropy(void *, size_t);
 int	 getgrouplist(const char *, gid_t, gid_t *, int *);
 int	 getloginclass(char *, size_t);
 mode_t	 getmode(const void *, mode_t);
 int	 getosreldate(void);
 int	 getpeereid(int, uid_t *, gid_t *);
-int	 getresgid(gid_t *, gid_t *, gid_t *);
-int	 getresuid(uid_t *, uid_t *, uid_t *);
 char	*getusershell(void);
 int	 initgroups(const char *, gid_t);
 int	 iruserok(unsigned long, int, const char *, const char *);
@@ -575,8 +582,6 @@
 int	 setpgrp(pid_t, pid_t);			/* obsoleted by setpgid() */
 void	 setproctitle(const char *_fmt, ...) __printf0like(1, 2);
 void	 setproctitle_fast(const char *_fmt, ...) __printf0like(1, 2);
-int	 setresgid(gid_t, gid_t, gid_t);
-int	 setresuid(uid_t, uid_t, uid_t);
 int	 setrgid(gid_t);
 int	 setruid(uid_t);
 void	 setusershell(void);
@@ -589,7 +594,6 @@
 int	 unwhiteout(const char *);
 void	*valloc(size_t);			/* obsoleted by malloc() */
 int	 funlinkat(int, const char *, int, int);
-pid_t	 _Fork(void);
 
 #ifndef _OPTRESET_DECLARED
 #define	_OPTRESET_DECLARED
diff --git a/include/wchar.h b/include/wchar.h
--- a/include/wchar.h
+++ b/include/wchar.h
@@ -235,12 +235,15 @@
 	    size_t, mbstate_t * __restrict);
 #endif
 
-#if __BSD_VISIBLE
-wchar_t	*fgetwln(FILE * __restrict, size_t * __restrict);
+#if __POSIX_VISIBLE >= 202405
 size_t	wcslcat(wchar_t *, const wchar_t *, size_t);
 size_t	wcslcpy(wchar_t *, const wchar_t *, size_t);
 #endif
 
+#if __BSD_VISIBLE
+wchar_t	*fgetwln(FILE * __restrict, size_t * __restrict);
+#endif
+
 #if __POSIX_VISIBLE >= 200809 || defined(_XLOCALE_H_)
 #include <xlocale/_wchar.h>
 #endif
diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -468,6 +468,176 @@
 #define	__RENAME(x)	no renaming in kernel/standalone environment
 #endif
 
+/*
+ * Verify that zero or one of the environment selection macros are defined.
+ * See cdefs(9)
+ */
+#if __BSD_VISIBLE
+/*
+ * The error is preferred... if we can get away with it, move it to be with
+ * the rest of the __*_VISIBLE checks after the _*_SOURCE checks
+ */
+#error "__BSD_VISIBLE defined by user - exp-run"
+#warning "__BSD_VISIBLE defined by user, forcing _BSD_SOURCE see cdefs(9)"
+#ifndef _BSD_SOURCE
+#define _BSD_SOURCE
+#endif
+#endif
+
+/*
+ * The priority is _BSD_SOURCE, _XOPEN_SOURCE, _POSIX_C_SOURCE, _CXX_SOURCE
+ * _CXX_SOURCE can upgrade the C version for _XOPEN_SOURCE and _POSIX_C_SOURCE
+ * but cannot downgrade it.
+ */
+
+#if defined(_BSD_SOURCE)
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 9999
+#endif
+
+#ifdef _XOPEN_SOURCE
+# ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#  warning "_XOPEN_SOURCE undefined due to conflict - see cdefs(9)"
+# else
+#  if _XOPEN_SOURCE - 0 >= 800
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 2017
+#  elif _XOPEN_SOURCE - 0 >= 700
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1999
+#  elif _XOPEN_SOURCE - 0 >= 600
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1999
+#  elif _XOPEN_SOURCE - 0 >= 500
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1990
+#  else
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1
+#  endif
+# endif
+#endif
+
+#ifdef _POSIX_C_SOURCE
+# ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#  warning "_POSIX_C_SOURCE undefined due to conflict - see cdefs(9)"
+# else
+#  if _POSIX_C_SOURCE >= 202405
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 2017
+#  elif _POSIX_C_SOURCE >= 200809
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1999
+#  elif _POSIX_C_SOURCE >= 200112
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1999
+#  elif _POSIX_C_SOURCE >= 199506
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1990
+#  elif _POSIX_C_SOURCE >= 199309
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1990
+#  elif _POSIX_C_SOURCE >= 199209
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1990
+#  elif _POSIX_C_SOURCE >= 199009
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1990
+#  else
+#   define __PROGRAMMING_ENVIRONMENT_SELECTED 1
+#  endif
+# endif
+#endif
+
+#ifdef _POSIX_SOURCE
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#warning "_POSIX_SOURCE undefined due to conflict - see cdefs(9)"
+#else
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 1
+#endif
+#endif
+
+#ifdef _C23_SOURCE
+#if __PROGRAMMING_ENVIRONMENT_SELECTED > 2023
+#warning "_C23_SOURCE undefined due to conflict - see cdefs(9)"
+#else
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#undef __PROGRAMMING_ENVIRONMENT_SELECTED
+#endif
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 2023
+#endif
+#endif
+
+#ifdef _C11_SOURCE
+#if __PROGRAMMING_ENVIRONMENT_SELECTED > 2011
+#warning "_C11_SOURCE undefined due to conflict - see cdefs(9)"
+#else
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#undef __PROGRAMMING_ENVIRONMENT_SELECTED
+#endif
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 2011
+#endif
+#endif
+
+#ifdef _ISOC11_SOURCE
+#if __PROGRAMMING_ENVIRONMENT_SELECTED > 2011
+#warning "_ISOC11_SOURCE undefined due to conflict - see cdefs(9)"
+#else
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#undef __PROGRAMMING_ENVIRONMENT_SELECTED
+#endif
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 2011
+#endif
+#endif
+
+#ifdef _C99_SOURCE
+#if __PROGRAMMING_ENVIRONMENT_SELECTED > 1999
+#warning "_C99_SOURCE undefined due to conflict - see cdefs(9)"
+#else
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#undef __PROGRAMMING_ENVIRONMENT_SELECTED
+#endif
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 1999
+#endif
+#endif
+
+#ifdef _ISOC99_SOURCE
+#if __PROGRAMMING_ENVIRONMENT_SELECTED > 1999
+#warning "_ISOC99_SOURCE undefined due to conflict - see cdefs(9)"
+#else
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#undef __PROGRAMMING_ENVIRONMENT_SELECTED
+#endif
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 1999
+#endif
+#endif
+
+#ifdef _ANSI_SOURCE
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#warning "_ANSI_SOURCE undefined due to conflict - see cdefs(9)"
+#else
+#define __PROGRAMMING_ENVIRONMENT_SELECTED 1990
+#endif
+#endif
+
+#ifdef __PROGRAMMING_ENVIRONMENT_SELECTED
+#undef __PROGRAMMING_ENVIRONMENT_SELECTED
+#else
+#define _BSD_SOURCE
+#undef
+
+#if __BSD_VISIBLE
+// NOTE: We already got a warning about this when we defined _BSD_SOURCE
+#undef __BSD_VISIBLE
+#endif
+
+#if defined(__POSIX_VISIBLE)
+#error "Implementation reserved __POSIX_VISIBLE defined by user see cdefs(9)"
+#endif
+
+#if defined(__XSI_VISIBLE)
+#error "Implementation reserved __XSI_VISIBLE defined by user see cdefs(9)"
+#endif
+
+#if defined(__ISO_C_VISIBLE)
+#error "Implementation reserved __ISO_C_VISIBLE defined by user see cdefs(9)"
+#endif
+
+#if defined(__ISO_C_VISIBLE)
+#error "Implementation reserved __EXT1_VISIBLE defined by user see cdefs(9)"
+#endif
+
+/* 
+ * TODO shurd@: This is the end of the exp-run chunk
+ */
+
 /*-
  * The following definitions are an extension of the behavior originally
  * implemented in <sys/_posix.h>, but with a different level of granularity.