diff --git a/libc/arch-arm64/denver64/bionic/memcpy.S b/libc/arch-arm64/denver64/bionic/memcpy.S
index 700f0d0..85129fe 100644
--- a/libc/arch-arm64/denver64/bionic/memcpy.S
+++ b/libc/arch-arm64/denver64/bionic/memcpy.S
@@ -1,205 +1,63 @@
-/* Copyright (c) 2012, Linaro Limited
-   All rights reserved.
-   Copyright (c) 2014, NVIDIA Corporation.  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.
-       * Neither the name of the Linaro 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 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
-   HOLDER 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.
-*/
-
-/* Assumptions:
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
  *
- * denver, ARMv8-a, AArch64
- * Unaligned accesses
+ * 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.
  */
 
+// Prototype: void *memcpy (void *dst, const void *src, size_t count).
+
 #include <private/bionic_asm.h>
+#include <private/libc_events.h>
 
-#define dstin	x0
-#define src	x1
-#define count	x2
-#define tmp1	x3
-#define tmp1w	w3
-#define tmp2	x4
-#define tmp2w	w4
-#define tmp3	x5
-#define tmp3w	w5
-#define dst	x6
+ENTRY(__memcpy_chk)
+  cmp   x2, x3
+  b.hi  __memcpy_chk_fail
 
-#define A_l	x7
-#define A_h	x8
-#define B_l	x9
-#define B_h	x10
-#define C_l	x11
-#define C_h	x12
-#define D_l	x13
-#define D_h	x14
-
-#define QA_l	q0
-#define QA_h	q1
-#define QB_l	q2
-#define QB_h	q3
+  // Fall through to memcpy...
+END(__memcpy_chk)
 
 ENTRY(memcpy)
-
-	mov	dst, dstin
-	cmp	count, #64
-	b.ge	.Lcpy_not_short
-	cmp	count, #15
-	b.le	.Ltail15tiny
-
-	/* Deal with small copies quickly by dropping straight into the
-	 * exit block.  */
-.Ltail63:
-	/* Copy up to 48 bytes of data.  At this point we only need the
-	 * bottom 6 bits of count to be accurate.  */
-	ands	tmp1, count, #0x30
-	b.eq	.Ltail15
-	add	dst, dst, tmp1
-	add	src, src, tmp1
-	cmp	tmp1w, #0x20
-	b.eq	1f
-	b.lt	2f
-	ldp	A_l, A_h, [src, #-48]
-	stp	A_l, A_h, [dst, #-48]
-1:
-	ldp	A_l, A_h, [src, #-32]
-	stp	A_l, A_h, [dst, #-32]
-2:
-	ldp	A_l, A_h, [src, #-16]
-	stp	A_l, A_h, [dst, #-16]
-
-.Ltail15:
-	ands	count, count, #15
-	beq	1f
-	add	src, src, count
-	ldp	A_l, A_h, [src, #-16]
-	add	dst, dst, count
-	stp	A_l, A_h, [dst, #-16]
-1:
-	ret
-
-.Ltail15tiny:
-	/* Copy up to 15 bytes of data.  Does not assume additional data
-	   being copied.  */
-	tbz	count, #3, 1f
-	ldr	tmp1, [src], #8
-	str	tmp1, [dst], #8
-1:
-	tbz	count, #2, 1f
-	ldr	tmp1w, [src], #4
-	str	tmp1w, [dst], #4
-1:
-	tbz	count, #1, 1f
-	ldrh	tmp1w, [src], #2
-	strh	tmp1w, [dst], #2
-1:
-	tbz	count, #0, 1f
-	ldrb	tmp1w, [src]
-	strb	tmp1w, [dst]
-1:
-	ret
-
-.Lcpy_not_short:
-	/* We don't much care about the alignment of DST, but we want SRC
-	 * to be 128-bit (16 byte) aligned so that we don't cross cache line
-	 * boundaries on both loads and stores.  */
-	neg	tmp2, src
-	ands	tmp2, tmp2, #15		/* Bytes to reach alignment.  */
-	b.eq	2f
-	sub	count, count, tmp2
-	/* Copy more data than needed; it's faster than jumping
-	 * around copying sub-Quadword quantities.  We know that
-	 * it can't overrun.  */
-	ldp	A_l, A_h, [src]
-	add	src, src, tmp2
-	stp	A_l, A_h, [dst]
-	add	dst, dst, tmp2
-	/* There may be less than 63 bytes to go now.  */
-	cmp	count, #63
-	b.le	.Ltail63
-2:
-	subs	count, count, #128
-	b.ge	.Lcpy_body_large
-	/* Less than 128 bytes to copy, so handle 64 here and then jump
-	 * to the tail.  */
-	ldp	QA_l, QA_h, [src]
-	ldp	QB_l, QB_h, [src, #32]
-	stp	QA_l, QA_h, [dst]
-	stp	QB_l, QB_h, [dst, #32]
-	tst	count, #0x3f
-	add	src, src, #64
-	add	dst, dst, #64
-	b.ne	.Ltail63
-	ret
-
-	/* Critical loop.  Start at a new cache line boundary.  Assuming
-	 * 64 bytes per line this ensures the entire loop is in one line.  */
-	.p2align 6
-.Lcpy_body_large:
-	cmp	count, 65536
-	bhi	.Lcpy_body_huge
-	/* There are at least 128 bytes to copy.  */
-	ldp	QA_l, QA_h, [src, #0]
-	sub	dst, dst, #32		/* Pre-bias.  */
-	ldp	QB_l, QB_h, [src, #32]!	/* src += 64 - Pre-bias.  */
-1:
-	stp	QA_l, QA_h, [dst, #32]
-	ldp	QA_l, QA_h, [src, #32]
-	stp	QB_l, QB_h, [dst, #64]!
-	ldp	QB_l, QB_h, [src, #64]!
-
-	subs	count, count, #64
-	b.ge	1b
-
-	stp	QA_l, QA_h, [dst, #32]
-	stp	QB_l, QB_h, [dst, #64]
-	add	src, src, #32
-	add	dst, dst, #64 + 32
-	tst	count, #0x3f
-	b.ne	.Ltail63
-	ret
-.Lcpy_body_huge:
-	/* There are at least 128 bytes to copy.  */
-	ldp	QA_l, QA_h, [src, #0]
-	sub	dst, dst, #32		/* Pre-bias.  */
-	ldp	QB_l, QB_h, [src, #32]!
-1:
-	stnp	QA_l, QA_h, [dst, #32]
-	stnp	QB_l, QB_h, [dst, #64]
-	ldp	QA_l, QA_h, [src, #32]
-	ldp	QB_l, QB_h, [src, #64]!
-	add	dst, dst, #64
-
-	subs	count, count, #64
-	b.ge	1b
-
-	stnp	QA_l, QA_h, [dst, #32]
-	stnp	QB_l, QB_h, [dst, #64]
-	add	src, src, #32
-	add	dst, dst, #64 + 32
-	tst	count, #0x3f
-	b.ne	.Ltail63
-	ret
-
+  #include "memcpy_base.S"
 END(memcpy)
+
+ENTRY_PRIVATE(__memcpy_chk_fail)
+  // Preserve for accurate backtrace.
+  stp  x29, x30, [sp, -16]!
+  .cfi_def_cfa_offset 16
+  .cfi_rel_offset x29, 0
+  .cfi_rel_offset x30, 8
+
+  adrp  x0, error_string
+  add   x0, x0, :lo12:error_string
+  ldr   x1, error_code
+  bl    __fortify_chk_fail
+error_code:
+  .word   BIONIC_EVENT_MEMCPY_BUFFER_OVERFLOW
+END(__memcpy_chk_fail)
+
+  .data
+  .align 2
+error_string:
+  .string "memcpy: prevented write past end of buffer"