diff --git a/include/string.h b/include/string.h
index a362dc9e0f3f..e7fd3db0f0fd 100644
--- a/include/string.h
+++ b/include/string.h
@@ -1,175 +1,203 @@
 /*-
  * SPDX-License-Identifier: BSD-3-Clause
  *
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 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.
  *
  *	@(#)string.h	8.1 (Berkeley) 6/2/93
  */
 
 #ifndef _STRING_H_
 #define	_STRING_H_
 
 #include <sys/cdefs.h>
 #include <sys/_null.h>
 #include <sys/_types.h>
 
 /*
  * Prototype functions which were historically defined in <string.h>, but
  * are required by POSIX to be prototyped in <strings.h>.
  */
 #if __BSD_VISIBLE
 #include <strings.h>
 #endif
 
 #ifndef _SIZE_T_DECLARED
 typedef	__size_t	size_t;
 #define	_SIZE_T_DECLARED
 #endif
 
 __BEGIN_DECLS
 #if __XSI_VISIBLE >= 600 || __ISO_C_VISIBLE >= 2023
 void	*memccpy(void * __restrict, const void * __restrict, int, size_t);
 #endif
 void	*memchr(const void *, int, size_t) __pure;
 #if __BSD_VISIBLE
 void	*memrchr(const void *, int, size_t) __pure;
 #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;
 #endif
 void	*memmove(void *, const void *, size_t);
 #if __BSD_VISIBLE
 void	*mempcpy(void * __restrict, const void * __restrict, size_t);
 #endif
 void	*memset(void *, int, size_t);
 #if __POSIX_VISIBLE >= 200809
 char	*stpcpy(char * __restrict, const char * __restrict);
 char	*stpncpy(char * __restrict, const char * __restrict, size_t);
 #endif
 #if __BSD_VISIBLE
 char	*strcasestr(const char *, const char *) __pure;
 #endif
 char	*strcat(char * __restrict, const char * __restrict);
 char	*strchr(const char *, int) __pure;
 #if __BSD_VISIBLE
 char	*strchrnul(const char*, int) __pure;
 int	 strverscmp(const char *, const char *) __pure;
 #endif
 int	 strcmp(const char *, const char *) __pure;
 int	 strcoll(const char *, const char *);
 char	*strcpy(char * __restrict, const char * __restrict);
 size_t	 strcspn(const char *, const char *) __pure;
 #if __POSIX_VISIBLE >= 200112 || __XSI_VISIBLE || __ISO_C_VISIBLE >= 2023
 char	*strdup(const char *) __malloc_like;
 #endif
 char	*strerror(int);
 #if __POSIX_VISIBLE >= 200112
 int	 strerror_r(int, char *, size_t);
 #endif
 #if __BSD_VISIBLE
 size_t	 strlcat(char * __restrict, const char * __restrict, size_t);
 size_t	 strlcpy(char * __restrict, const char * __restrict, size_t);
 #endif
 size_t	 strlen(const char *) __pure;
 #if __BSD_VISIBLE
 
 #ifndef _MODE_T_DECLARED
 typedef	__mode_t	mode_t;
 #define	_MODE_T_DECLARED
 #endif
 
 void	 strmode(mode_t, char *);
 #endif
 char	*strncat(char * __restrict, const char * __restrict, size_t);
 int	 strncmp(const char *, const char *, size_t) __pure;
 char	*strncpy(char * __restrict, const char * __restrict, size_t);
 #if __POSIX_VISIBLE >= 200809 || __ISO_C_VISIBLE >= 2023
 char	*strndup(const char *, size_t) __malloc_like;
 #endif
 #if __POSIX_VISIBLE >= 200809
 size_t	 strnlen(const char *, size_t) __pure;
 #endif
 #if __BSD_VISIBLE
 char	*strnstr(const char *, const char *, size_t) __pure;
 #endif
 char	*strpbrk(const char *, const char *) __pure;
 char	*strrchr(const char *, int) __pure;
 #if __BSD_VISIBLE
 char	*strsep(char **, const char *);
 #endif
 #if __POSIX_VISIBLE >= 200809
 char	*strsignal(int);
 #endif
 size_t	 strspn(const char *, const char *) __pure;
 char	*strstr(const char *, const char *) __pure;
 char	*strtok(char * __restrict, const char * __restrict);
 #if __POSIX_VISIBLE >= 199506 || __XSI_VISIBLE >= 500
 char	*strtok_r(char *, const char *, char **);
 #endif
 size_t	 strxfrm(char * __restrict, const char * __restrict, size_t);
 #if __BSD_VISIBLE
 
 #ifndef _SWAB_DECLARED
 #define _SWAB_DECLARED
 
 #ifndef _SSIZE_T_DECLARED
 typedef	__ssize_t	ssize_t;
 #define	_SSIZE_T_DECLARED
 #endif /* _SIZE_T_DECLARED */
 
 void	 swab(const void * __restrict, void * __restrict, ssize_t);
 #endif /* _SWAB_DECLARED */
 
 int	 timingsafe_bcmp(const void *, const void *, size_t);
 int	 timingsafe_memcmp(const void *, const void *, size_t);
+
+#if __has_builtin(__builtin_alloca)
+#define	strdupa(_Str) (__extension__({				\
+	const char *_Str1;					\
+	size_t _Len;						\
+	char *_Copy;						\
+								\
+	_Str1 = (_Str);						\
+	_Len = strlen(_Str1) + 1;				\
+	_Copy = (char *)__builtin_alloca(_Len);			\
+	memcpy(_Copy, _Str1, _Len);				\
+	_Copy;							\
+}))
+
+#define	strndupa(_Str, _Maxlen) (__extension__({		\
+	const char *_Str1;					\
+	char *_Copy;						\
+	size_t _Len;						\
+								\
+	_Str1 = (_Str);						\
+	_Len = strnlen((_Str1), (_Maxlen));			\
+	_Copy = __builtin_alloca(_Len + 1);			\
+	(void)memcpy(_Copy, _Str1, _Len);			\
+	_Copy[_Len] = '\0';					\
+	_Copy;							\
+}))
+#endif
+
 #endif /* __BSD_VISIBLE */
 
 #if __POSIX_VISIBLE >= 200112 || defined(_XLOCALE_H_)
 #include <xlocale/_string.h>
 #endif
 
 #if __EXT1_VISIBLE
 
 #ifndef _RSIZE_T_DEFINED
 #define _RSIZE_T_DEFINED
 typedef size_t rsize_t;
 #endif
 
 #ifndef _ERRNO_T_DEFINED
 #define _ERRNO_T_DEFINED
 typedef int errno_t;
 #endif
 
 /* ISO/IEC 9899:2011 K.3.7.4.1.1 */
 errno_t memset_s(void *, rsize_t, int, rsize_t);
 #endif /* __EXT1_VISIBLE */
 __END_DECLS
 
 #endif /* _STRING_H_ */
diff --git a/lib/libc/string/Makefile.inc b/lib/libc/string/Makefile.inc
index a18eb62fddb8..689af376ec07 100644
--- a/lib/libc/string/Makefile.inc
+++ b/lib/libc/string/Makefile.inc
@@ -1,119 +1,121 @@
 #	@(#)Makefile.inc	8.1 (Berkeley) 6/4/93
 
 .if ${MK_MACHDEP_OPTIMIZATIONS} != "no"
 .PATH: ${LIBC_SRCTOP}/${LIBC_ARCH}/string
 .endif
 .PATH: ${LIBC_SRCTOP}/string
 .PATH: ${SRCTOP}/sys/libkern
 
 CFLAGS+= -I${LIBC_SRCTOP}/locale
 
 # machine-independent string sources
 MISRCS+=bcmp.c bcopy.c bzero.c explicit_bzero.c \
 	ffs.c ffsl.c ffsll.c fls.c flsl.c flsll.c \
 	memccpy.c memchr.c memrchr.c memcmp.c \
 	memcpy.c memmem.c memmove.c mempcpy.c memset.c memset_s.c \
 	stpcpy.c stpncpy.c strcasecmp.c \
 	strcat.c strcasestr.c strchr.c strchrnul.c strcmp.c strcoll.c strcpy.c\
 	strcspn.c strdup.c strerror.c strlcat.c strlcpy.c strlen.c strmode.c \
 	strncat.c strncmp.c strncpy.c strndup.c strnlen.c strnstr.c \
 	strpbrk.c strrchr.c strsep.c strsignal.c strspn.c strstr.c strtok.c \
 	strverscmp.c strxfrm.c swab.c \
 	timingsafe_bcmp.c \
 	timingsafe_memcmp.c \
 	wcpcpy.c wcpncpy.c wcscasecmp.c wcscat.c \
 	wcschr.c wcscmp.c wcscoll.c wcscpy.c wcscspn.c wcsdup.c \
 	wcslcat.c wcslcpy.c wcslen.c wcsncasecmp.c wcsncat.c wcsncmp.c \
 	wcsncpy.c wcsnlen.c wcspbrk.c \
 	wcsrchr.c wcsspn.c wcsstr.c wcstok.c wcswidth.c wcsxfrm.c wmemchr.c \
 	wmemcmp.c \
 	wmemcpy.c wmemmove.c wmempcpy.c wmemset.c
 
 SYM_MAPS+=	${LIBC_SRCTOP}/string/Symbol.map
 
 .if ${MK_ASAN} != "no"
 # These source files deliberately read out of bounds since they assume that
 # out-of-bounds memory accesses that don't cross pages are always legal.
 # Note: While this is fine on x86, it does break when running with CHERI.
 CFLAGS.strlen.c+=		-fno-sanitize=address
 CFLAGS.strchrnul.c+=	-fno-sanitize=address
 CFLAGS.memchr.c+=		-fno-sanitize=address
 .endif
 
 
 .if ${MK_MACHDEP_OPTIMIZATIONS} != "no"
 # machine-dependent string sources
 .sinclude "${LIBC_SRCTOP}/${LIBC_ARCH}/string/Makefile.inc"
 .endif
 
 MAN+=	bcmp.3 bcopy.3 bstring.3 bzero.3 ffs.3 index.3 memccpy.3 memchr.3 \
 	memcmp.3 memcpy.3 memmem.3 memmove.3 memset.3 strcasecmp.3 strcat.3 \
 	strchr.3 strcmp.3 strcoll.3 strcpy.3 strdup.3 strerror.3 \
 	string.3 strlcpy.3 strlen.3 strmode.3 strpbrk.3 strsep.3 \
 	strspn.3 strstr.3 strtok.3 strverscmp.3 strxfrm.3 swab.3 \
 	timingsafe_bcmp.3 \
 	wcscoll.3 wcstok.3 \
 	wcswidth.3 wcsxfrm.3 wmemchr.3
 
 MLINKS+=bzero.3 explicit_bzero.3
 MLINKS+=ffs.3 ffsl.3 \
 	ffs.3 ffsll.3 \
 	ffs.3 fls.3 \
 	ffs.3 flsl.3 \
 	ffs.3 flsll.3
 MLINKS+=index.3 rindex.3
 MLINKS+=memchr.3 memrchr.3
 MLINKS+=memcpy.3 mempcpy.3
 MLINKS+=memset.3 memset_s.3
 MLINKS+=strcasecmp.3 strncasecmp.3 \
 	strcasecmp.3 strcasecmp_l.3 \
 	strcasecmp.3 strncasecmp_l.3
 MLINKS+=strcat.3 strncat.3
 MLINKS+=strchr.3 strrchr.3 \
 	strchr.3 strchrnul.3
 MLINKS+=strcmp.3 strncmp.3
 MLINKS+=strcoll.3 strcoll_l.3
 MLINKS+=strcpy.3 stpcpy.3 \
 	strcpy.3 stpncpy.3 \
 	strcpy.3 strncpy.3
-MLINKS+=strdup.3 strndup.3
+MLINKS+=strdup.3 strndup.3 \
+	strdup.3 strdupa.3 \
+	strdup.3 strndupa.3
 MLINKS+=strerror.3 perror.3 \
 	strerror.3 strerror_l.3 \
 	strerror.3 strerror_r.3 \
 	strerror.3 sys_errlist.3 \
 	strerror.3 sys_nerr.3
 MLINKS+=strlcpy.3 strlcat.3
 MLINKS+=strlen.3 strnlen.3
 MLINKS+=strspn.3 strcspn.3
 MLINKS+=strstr.3 strcasestr.3 \
 	strstr.3 strnstr.3 \
 	strstr.3 strcasestr_l.3
 MLINKS+=strtok.3 strtok_r.3
 MLINKS+=strxfrm.3 strxfrm_l.3
 MLINKS+=timingsafe_bcmp.3 timingsafe_memcmp.3
 MLINKS+=wmemchr.3 wcpcpy.3 \
 	wmemchr.3 wcpncpy.3 \
 	wmemchr.3 wcscasecmp.3 \
 	wmemchr.3 wcscat.3 \
 	wmemchr.3 wcschr.3 \
 	wmemchr.3 wcscmp.3 \
 	wmemchr.3 wcscpy.3 \
 	wmemchr.3 wcscspn.3 \
 	wmemchr.3 wcsdup.3 \
 	wmemchr.3 wcslcat.3 \
 	wmemchr.3 wcslcpy.3 \
 	wmemchr.3 wcslen.3 \
 	wmemchr.3 wcsncasecmp.3 \
 	wmemchr.3 wcsncat.3 \
 	wmemchr.3 wcsncmp.3 \
 	wmemchr.3 wcsncpy.3 \
 	wmemchr.3 wcsnlen.3 \
 	wmemchr.3 wcspbrk.3 \
 	wmemchr.3 wcsrchr.3 \
 	wmemchr.3 wcsspn.3 \
 	wmemchr.3 wcsstr.3 \
 	wmemchr.3 wmemcmp.3 \
 	wmemchr.3 wmemcpy.3 \
 	wmemchr.3 wmemmove.3 \
 	wmemchr.3 wmempcpy.3 \
 	wmemchr.3 wmemset.3
diff --git a/lib/libc/string/strdup.3 b/lib/libc/string/strdup.3
index a19a00f5430b..b48d88d4bac2 100644
--- a/lib/libc/string/strdup.3
+++ b/lib/libc/string/strdup.3
@@ -1,97 +1,129 @@
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
 .\" 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.
 .\"
 .\"     @(#)strdup.3	8.1 (Berkeley) 6/9/93
 .\"
 .Dd May 5, 2020
 .Dt STRDUP 3
 .Os
 .Sh NAME
 .Nm strdup ,
-.Nm strndup
+.Nm strdupa ,
+.Nm strndup ,
+.Nm strndupa
 .Nd save a copy of a string
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In string.h
 .Ft char *
 .Fn strdup "const char *str"
 .Ft char *
+.Fn strdupa "const char *str"
+.Ft char *
 .Fn strndup "const char *str" "size_t len"
+.Ft char *
+.Fn strndupa "const char *str" "size_t len"
 .Sh DESCRIPTION
 The
 .Fn strdup
 function
 allocates sufficient memory for a copy
 of the string
 .Fa str ,
 does the copy, and returns a pointer to it.
 The memory is allocated with
 .Xr malloc 3
 and should be released with
 .Xr free 3
 when no longer needed.
 .Pp
 The
 .Fn strndup
 function copies at most
 .Fa len
 characters from the string
 .Fa str
 always
 .Dv NUL
 terminating the copied string.
+.Pp
+The
+.Fn strdupa
+function is identical to
+.Fn strdup
+but allocates the memory with
+.Xr alloca 3 .
+Similarly, the
+.Fn strndupa
+function is identical to
+.Fn strndup ,
+but allocates the memory with
+.Xr alloca 3 .
 .Sh RETURN VALUES
 If insufficient memory is available, NULL is returned and
 .Va errno
 is set to
 .Er ENOMEM .
 Otherwise, the
 .Fn strdup
 family of functions return a pointer to the copied string.
 .Sh SEE ALSO
+.Xr alloca 3 ,
 .Xr free 3 ,
 .Xr malloc 3 ,
 .Xr wcsdup 3
 .Sh STANDARDS
 The
 .Fn strdup
 function is specified by
 .St -p1003.1-2001 .
 The
 .Fn strndup
 function is specified by
 .St -p1003.1-2008 .
+The
+.Fn strdupa
+and
+.Fn strndupa
+functions are extensions,
+taken from glibc.
 .Sh HISTORY
 The
 .Fn strdup
 function first appeared in
 .Bx 4.3 Reno .
 The
 .Fn strndup
 function was added in
 .Fx 7.2 .
+The
+.Fn strdupa
+and
+.Fn strndupa
+functions were added in
+.Fx 15.1 .