diff --git a/lib/libc/amd64/string/Makefile.inc b/lib/libc/amd64/string/Makefile.inc
index d982061e080b..03bca498e116 100644
--- a/lib/libc/amd64/string/Makefile.inc
+++ b/lib/libc/amd64/string/Makefile.inc
@@ -1,25 +1,26 @@
 MDSRCS+= \
 	amd64_archlevel.c \
 	bcmp.S \
 	memchr.S \
 	memcmp.S \
 	memcpy.S \
 	memmove.S \
 	memset.S \
 	stpcpy.S \
 	stpncpy.S \
 	strcat.S \
 	strchrnul.S \
 	strcmp.S \
 	strcpy.c \
 	strcspn.S \
+	strlcpy.S \
 	strlen.S \
 	strncmp.S \
 	strncpy.c \
 	strnlen.c \
 	strpbrk.c \
 	strrchr.S \
 	strsep.c \
 	strspn.S \
 	timingsafe_bcmp.S \
 	timingsafe_memcmp.S
diff --git a/lib/libc/amd64/string/strlcpy.S b/lib/libc/amd64/string/strlcpy.S
new file mode 100644
index 000000000000..2b32c6c78047
--- /dev/null
+++ b/lib/libc/amd64/string/strlcpy.S
@@ -0,0 +1,281 @@
+/*
+ * Copyright (c) 2023 The FreeBSD Foundation
+ *
+ * This software was developed by Robert Clausecker <fuz@FreeBSD.org>
+ * under sponsorship from the FreeBSD Foundation.
+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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
+ */
+
+#include <machine/asm.h>
+
+#include "amd64_archlevel.h"
+
+#define ALIGN_TEXT	.p2align 4, 0x90
+
+	.weak strlcpy
+	.set strlcpy, __strlcpy
+ARCHFUNCS(__strlcpy)
+	ARCHFUNC(__strlcpy, scalar)
+	ARCHFUNC(__strlcpy, baseline)
+ENDARCHFUNCS(__strlcpy)
+
+ARCHENTRY(__strlcpy, scalar)
+	push	%rbp		# establish stack frame
+	mov	%rsp, %rbp
+	push	%rsi
+	push	%rbx
+	push	%rdi
+	push	%rdx
+	mov	%rsi, %rdi
+	call	CNAME(strlen)	# strlen(src)
+	pop	%rdx
+	pop	%rdi
+	mov	-8(%rbp), %rsi
+	mov	%rax, %rbx	# remember string length for return value
+	sub	$1, %rdx	# do not copy into the final byte of the buffer
+	jc	0f		# skip copying altogether if buffer was empty
+	cmp	%rax, %rdx	# is the buffer longer than the input?
+	cmova	%rax, %rdx	# if yes, only copy the part that fits
+	movb	$0, (%rdi, %rdx, 1) # NUL-terminate output buffer
+	call	CNAME(memcpy)	# copy string to output
+0:	mov	%rbx, %rax	# restore return value
+	pop	%rbx
+	leave
+	ret
+ARCHEND(__strlcpy, scalar)
+
+ARCHENTRY(__strlcpy, baseline)
+	sub		$1, %rdx		# do not count NUL byte in buffer length
+	jb		.L0			# go to special code path if len was 0
+
+	mov		%esi, %ecx
+	pxor		%xmm1, %xmm1
+	mov		%rsi, %r9		# stash a copy of the source pointer for later
+	and		$~0xf, %rsi
+	pcmpeqb		(%rsi), %xmm1		# NUL found in head?
+	mov		$-1, %r8d
+	and		$0xf, %ecx
+	shl		%cl, %r8d		# mask of bytes in the string
+	pmovmskb	%xmm1, %eax
+	and		%r8d, %eax
+	jnz		.Lhead_nul
+
+	movdqa		16(%rsi), %xmm3		# load second string chunk
+	movdqu		(%r9), %xmm2		# load unaligned string head
+	mov		$32, %r8d
+	sub		%ecx, %r8d		# head length + length of second chunk
+	pxor		%xmm1, %xmm1
+	pcmpeqb		%xmm3, %xmm1		# NUL found in second chunk?
+
+	sub		%r8, %rdx		# enough space left for the second chunk?
+	jbe		.Lhead_buf_end
+
+	/* process second chunk */
+	pmovmskb	%xmm1, %eax
+	test		%eax, %eax
+	jnz		.Lsecond_nul
+
+	/* string didn't end in second chunk and neither did buffer -- not a runt! */
+	movdqa		32(%rsi), %xmm0		# load next string chunk
+	pxor		%xmm1, %xmm1
+	movdqu		%xmm2, (%rdi)		# deposit head into buffer
+	sub		%rcx, %rdi		# adjust RDI to correspond to RSI
+	movdqu		%xmm3, 16(%rdi)		# deposit second chunk
+	sub		%rsi, %rdi		# express RDI as distance from RSI
+	add		$32, %rsi		# advance RSI past first two chunks
+	sub		$16, %rdx		# enough left for another round?
+	jbe		1f
+
+	/* main loop unrolled twice */
+	ALIGN_TEXT
+0:	pcmpeqb		%xmm0, %xmm1		# NUL byte encountered?
+	pmovmskb	%xmm1, %eax
+	test		%eax, %eax
+	jnz		3f
+
+	movdqu		%xmm0, (%rsi, %rdi)
+	movdqa		16(%rsi), %xmm0		# load next string chunk
+	pxor		%xmm1, %xmm1
+	cmp		$16, %rdx		# more than a full chunk left?
+	jbe		2f
+
+	add		$32, %rsi		# advance pointers to next chunk
+	pcmpeqb		%xmm0, %xmm1		# NUL byte encountered?
+	pmovmskb	%xmm1, %eax
+	test		%eax, %eax
+	jnz		4f
+
+	movdqu		%xmm0, -16(%rsi, %rdi)
+	movdqa		(%rsi), %xmm0		# load next string chunk
+	pxor		%xmm1, %xmm1
+	sub		$32, %rdx
+	ja		0b
+
+1:	sub		$16, %rsi		# undo second advancement
+	add		$16, %edx
+
+	/* 1--16 bytes left in the buffer but string has not ended yet */
+2:	pcmpeqb		%xmm1, %xmm0		# NUL byte encountered?
+	pmovmskb	%xmm0, %r8d
+	mov		%r8d, %eax
+	bts		%edx, %r8d		# treat end of buffer as end of string
+	tzcnt		%r8d, %r8d		# find tail length
+	add		%rsi, %rdi		# restore RDI
+	movdqu		(%rsi, %r8, 1), %xmm0	# load string tail
+	movdqu		%xmm0, (%rdi, %r8, 1)	# store string tail
+	movb		$0, 16(%rdi, %r8, 1)	# NUL terminate
+
+	/* continue to find the end of the string */
+	test		%eax, %eax		# end of string already reached?
+	jnz		1f
+
+	ALIGN_TEXT
+0:	pcmpeqb		32(%rsi), %xmm1
+	pmovmskb	%xmm1, %eax
+	pxor		%xmm1, %xmm1
+	test		%eax, %eax
+	jnz		2f
+
+	pcmpeqb		48(%rsi), %xmm1
+	pmovmskb	%xmm1, %eax
+	add		$32, %rsi
+	pxor		%xmm1, %xmm1
+	test		%eax, %eax
+	jz		0b
+
+1:	sub		$16, %rsi		# undo second advancement
+2:	tzcnt		%eax, %eax		# where is the NUL byte?
+	sub		%r9, %rsi
+	lea		32(%rsi, %rax, 1), %rax	# return string length
+	ret
+
+4:	sub		$16, %rsi		# undo second advancement
+	add		$16, %rdx		# restore number of remaining bytes
+
+	/* string has ended but buffer has not */
+3:	tzcnt		%eax, %eax		# find length of string tail
+	movdqu		-15(%rsi, %rax, 1), %xmm0 # load string tail (incl. NUL)
+	add		%rsi, %rdi		# restore destination pointer
+	movdqu		%xmm0, -15(%rdi, %rax, 1) # store string tail (incl. NUL)
+	sub		%r9, %rsi		# string length to current chunk
+	add		%rsi, %rax		# plus length of current chunk
+	ret
+
+.Lhead_buf_end:
+	pmovmskb	%xmm1, %r8d
+	add		$32, %edx		# restore edx to (len-1) + ecx
+	mov		%r8d, %eax
+	shl		$16, %r8d		# place 2nd chunk NUL mask into bits 16--31
+	bts		%rdx, %r8		# treat end of buffer as end of string
+	tzcnt		%r8, %rdx		# find string/bufer len from alignment boundary
+	sub		%ecx, %edx		# find actual string/buffer len
+	movb		$0, (%rdi, %rdx, 1)	# write NUL terminator
+
+	/* continue to find the end of the string */
+	test		%eax, %eax		# end of string already reached?
+	jnz		1f
+
+	ALIGN_TEXT
+0:	pcmpeqb		32(%rsi), %xmm1
+	pmovmskb	%xmm1, %eax
+	pxor		%xmm1, %xmm1
+	test		%eax, %eax
+	jnz		2f
+
+	pcmpeqb		48(%rsi), %xmm1
+	pmovmskb	%xmm1, %eax
+	add		$32, %rsi
+	pxor		%xmm1, %xmm1
+	test		%eax, %eax
+	jz		0b
+
+1:	sub		$16, %rsi
+2:	tzcnt		%eax, %eax
+	sub		%r9, %rsi
+	lea		32(%rsi, %rax, 1), %rax	# return string length
+	jmp		.L0031
+
+.Lsecond_nul:
+	add		%r8, %rdx		# restore buffer length
+	tzcnt		%eax, %eax		# where is the NUL byte?
+	lea		-16(%rcx), %r8d
+	sub		%r8d, %eax		# string length
+	cmp		%rax, %rdx		# is the string shorter than the buffer?
+	cmova		%rax, %rdx		# copy only min(buflen, srclen) bytes
+	movb		$0, (%rdi, %rdx, 1)	# write NUL terminator
+.L0031:	cmp		$16, %rdx		# at least 16 bytes to copy (not incl NUL)?
+	jb		.L0015
+
+	/* copy 16--31 bytes */
+	movdqu		(%r9), %xmm0		# load first 16 bytes
+	movdqu		-16(%r9, %rdx, 1), %xmm1 # load last 16 bytes
+	movdqu		%xmm0, (%rdi)
+	movdqu		%xmm1, -16(%rdi, %rdx, 1)
+	ret
+
+.Lhead_nul:
+	tzcnt		%eax, %eax		# where is the NUL byte?
+	sub		%ecx, %eax		# ... from the beginning of the string?
+	cmp		%rax, %rdx		# is the string shorter than the buffer?
+	cmova		%rax, %rdx		# copy only min(buflen, srclen) bytes
+	movb		$0, (%rdi, %rdx, 1)	# write NUL terminator
+
+	/* process strings of 0--15 bytes (rdx: min(buflen, srclen), rax: srclen) */
+.L0015:	cmp		$8, %rdx		# at least 8 bytes to copy?
+	jae		.L0815
+
+	cmp		$4, %rdx		# at least 4 bytes to copy?
+	jae		.L0407
+
+	cmp		$2, %rdx		# at least 2 bytes to copy?
+	jae		.L0203
+
+	movzbl		(%r9), %ecx		# load first byte from src
+	mov		%cl, (%rdi)		# deposit into destination
+	movb		$0, (%rdi, %rdx, 1)	# add NUL terminator (again)
+	ret
+
+.L0203:	movzwl		(%r9), %ecx
+	movzwl		-2(%r9, %rdx, 1), %esi
+	mov		%cx, (%rdi)
+	mov		%si, -2(%rdi, %rdx, 1)
+	ret
+
+.L0407:	mov		(%r9), %ecx
+	mov		-4(%r9, %rdx, 1), %esi
+	mov		%ecx, (%rdi)
+	mov		%esi, -4(%rdi, %rdx, 1)
+	ret
+
+.L0815:	mov		(%r9), %rcx
+	mov		-8(%r9, %rdx, 1), %rsi
+	mov		%rcx, (%rdi)
+	mov		%rsi, -8(%rdi, %rdx, 1)
+	ret
+
+	/* length zero destination: just return the string length */
+.L0:	mov		%rsi, %rdi
+	jmp		CNAME(strlen)
+ARCHEND(__strlcpy, baseline)
+
+	.section .note.GNU-stack,"",%progbits