[PATCH v2 1/8] arm64: Import latest version of Cortex Strings' memcmp
Robin Murphy
robin.murphy at arm.com
Thu May 27 08:34:41 PDT 2021
From: Sam Tebbs <sam.tebbs at arm.com>
Import the latest version of the former Cortex Strings - now
Arm Optimized Routines - memcmp function based on the upstream
code of string/aarch64/memcmp.S at commit e823e3a from
https://github.com/ARM-software/optimized-routines
Note that for simplicity Arm have chosen to contribute this code
to Linux under GPLv2 rather than the original MIT license.
Signed-off-by: Sam Tebbs <sam.tebbs at arm.com>
[ rm: update attribution and commit message ]
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---
arch/arm64/lib/memcmp.S | 330 ++++++++++++++--------------------------
1 file changed, 111 insertions(+), 219 deletions(-)
diff --git a/arch/arm64/lib/memcmp.S b/arch/arm64/lib/memcmp.S
index c0671e793ea9..498f0d9941d9 100644
--- a/arch/arm64/lib/memcmp.S
+++ b/arch/arm64/lib/memcmp.S
@@ -1,247 +1,139 @@
/* SPDX-License-Identifier: GPL-2.0-only */
/*
- * Copyright (C) 2013 ARM Ltd.
- * Copyright (C) 2013 Linaro.
+ * Copyright (c) 2013-2020, Arm Limited.
*
- * This code is based on glibc cortex strings work originally authored by Linaro
- * be found @
- *
- * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
- * files/head:/src/aarch64/
+ * Adapted from the original at:
+ * https://github.com/ARM-software/optimized-routines/blob/master/string/aarch64/memcmp.S
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
-/*
-* compare memory areas(when two memory areas' offset are different,
-* alignment handled by the hardware)
-*
-* Parameters:
-* x0 - const memory area 1 pointer
-* x1 - const memory area 2 pointer
-* x2 - the maximal compare byte length
-* Returns:
-* x0 - a compare result, maybe less than, equal to, or greater than ZERO
-*/
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64, unaligned accesses.
+ */
+
+#define L(label) .L ## label
/* Parameters and result. */
-src1 .req x0
-src2 .req x1
-limit .req x2
-result .req x0
+#define src1 x0
+#define src2 x1
+#define limit x2
+#define result w0
/* Internal variables. */
-data1 .req x3
-data1w .req w3
-data2 .req x4
-data2w .req w4
-has_nul .req x5
-diff .req x6
-endloop .req x7
-tmp1 .req x8
-tmp2 .req x9
-tmp3 .req x10
-pos .req x11
-limit_wd .req x12
-mask .req x13
+#define data1 x3
+#define data1w w3
+#define data1h x4
+#define data2 x5
+#define data2w w5
+#define data2h x6
+#define tmp1 x7
+#define tmp2 x8
SYM_FUNC_START_WEAK_PI(memcmp)
- cbz limit, .Lret0
- eor tmp1, src1, src2
- tst tmp1, #7
- b.ne .Lmisaligned8
- ands tmp1, src1, #7
- b.ne .Lmutual_align
- sub limit_wd, limit, #1 /* limit != 0, so no underflow. */
- lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */
- /*
- * The input source addresses are at alignment boundary.
- * Directly compare eight bytes each time.
- */
-.Lloop_aligned:
- ldr data1, [src1], #8
- ldr data2, [src2], #8
-.Lstart_realigned:
- subs limit_wd, limit_wd, #1
- eor diff, data1, data2 /* Non-zero if differences found. */
- csinv endloop, diff, xzr, cs /* Last Dword or differences. */
- cbz endloop, .Lloop_aligned
+ subs limit, limit, 8
+ b.lo L(less8)
- /* Not reached the limit, must have found a diff. */
- tbz limit_wd, #63, .Lnot_limit
+ ldr data1, [src1], 8
+ ldr data2, [src2], 8
+ cmp data1, data2
+ b.ne L(return)
- /* Limit % 8 == 0 => the diff is in the last 8 bytes. */
- ands limit, limit, #7
- b.eq .Lnot_limit
- /*
- * The remained bytes less than 8. It is needed to extract valid data
- * from last eight bytes of the intended memory range.
- */
- lsl limit, limit, #3 /* bytes-> bits. */
- mov mask, #~0
-CPU_BE( lsr mask, mask, limit )
-CPU_LE( lsl mask, mask, limit )
- bic data1, data1, mask
- bic data2, data2, mask
+ subs limit, limit, 8
+ b.gt L(more16)
- orr diff, diff, mask
- b .Lnot_limit
+ ldr data1, [src1, limit]
+ ldr data2, [src2, limit]
+ b L(return)
-.Lmutual_align:
- /*
- * Sources are mutually aligned, but are not currently at an
- * alignment boundary. Round down the addresses and then mask off
- * the bytes that precede the start point.
- */
- bic src1, src1, #7
- bic src2, src2, #7
- ldr data1, [src1], #8
- ldr data2, [src2], #8
- /*
- * We can not add limit with alignment offset(tmp1) here. Since the
- * addition probably make the limit overflown.
- */
- sub limit_wd, limit, #1/*limit != 0, so no underflow.*/
- and tmp3, limit_wd, #7
- lsr limit_wd, limit_wd, #3
- add tmp3, tmp3, tmp1
- add limit_wd, limit_wd, tmp3, lsr #3
- add limit, limit, tmp1/* Adjust the limit for the extra. */
+L(more16):
+ ldr data1, [src1], 8
+ ldr data2, [src2], 8
+ cmp data1, data2
+ bne L(return)
- lsl tmp1, tmp1, #3/* Bytes beyond alignment -> bits.*/
- neg tmp1, tmp1/* Bits to alignment -64. */
- mov tmp2, #~0
- /*mask off the non-intended bytes before the start address.*/
-CPU_BE( lsl tmp2, tmp2, tmp1 )/*Big-endian.Early bytes are at MSB*/
- /* Little-endian. Early bytes are at LSB. */
-CPU_LE( lsr tmp2, tmp2, tmp1 )
+ /* Jump directly to comparing the last 16 bytes for 32 byte (or less)
+ strings. */
+ subs limit, limit, 16
+ b.ls L(last_bytes)
- orr data1, data1, tmp2
- orr data2, data2, tmp2
- b .Lstart_realigned
+ /* We overlap loads between 0-32 bytes at either side of SRC1 when we
+ try to align, so limit it only to strings larger than 128 bytes. */
+ cmp limit, 96
+ b.ls L(loop16)
- /*src1 and src2 have different alignment offset.*/
-.Lmisaligned8:
- cmp limit, #8
- b.lo .Ltiny8proc /*limit < 8: compare byte by byte*/
+ /* Align src1 and adjust src2 with bytes not yet done. */
+ and tmp1, src1, 15
+ add limit, limit, tmp1
+ sub src1, src1, tmp1
+ sub src2, src2, tmp1
- and tmp1, src1, #7
- neg tmp1, tmp1
- add tmp1, tmp1, #8/*valid length in the first 8 bytes of src1*/
- and tmp2, src2, #7
- neg tmp2, tmp2
- add tmp2, tmp2, #8/*valid length in the first 8 bytes of src2*/
- subs tmp3, tmp1, tmp2
- csel pos, tmp1, tmp2, hi /*Choose the maximum.*/
+ /* Loop performing 16 bytes per iteration using aligned src1.
+ Limit is pre-decremented by 16 and must be larger than zero.
+ Exit if <= 16 bytes left to do or if the data is not equal. */
+ .p2align 4
+L(loop16):
+ ldp data1, data1h, [src1], 16
+ ldp data2, data2h, [src2], 16
+ subs limit, limit, 16
+ ccmp data1, data2, 0, hi
+ ccmp data1h, data2h, 0, eq
+ b.eq L(loop16)
- sub limit, limit, pos
- /*compare the proceeding bytes in the first 8 byte segment.*/
-.Ltinycmp:
- ldrb data1w, [src1], #1
- ldrb data2w, [src2], #1
- subs pos, pos, #1
- ccmp data1w, data2w, #0, ne /* NZCV = 0b0000. */
- b.eq .Ltinycmp
- cbnz pos, 1f /*diff occurred before the last byte.*/
+ cmp data1, data2
+ bne L(return)
+ mov data1, data1h
+ mov data2, data2h
+ cmp data1, data2
+ bne L(return)
+
+ /* Compare last 1-16 bytes using unaligned access. */
+L(last_bytes):
+ add src1, src1, limit
+ add src2, src2, limit
+ ldp data1, data1h, [src1]
+ ldp data2, data2h, [src2]
+ cmp data1, data2
+ bne L(return)
+ mov data1, data1h
+ mov data2, data2h
+ cmp data1, data2
+
+ /* Compare data bytes and set return value to 0, -1 or 1. */
+L(return):
+#ifndef __AARCH64EB__
+ rev data1, data1
+ rev data2, data2
+#endif
+ cmp data1, data2
+L(ret_eq):
+ cset result, ne
+ cneg result, result, lo
+ ret
+
+ .p2align 4
+ /* Compare up to 8 bytes. Limit is [-8..-1]. */
+L(less8):
+ adds limit, limit, 4
+ b.lo L(less4)
+ ldr data1w, [src1], 4
+ ldr data2w, [src2], 4
cmp data1w, data2w
- b.eq .Lstart_align
-1:
- sub result, data1, data2
+ b.ne L(return)
+ sub limit, limit, 4
+L(less4):
+ adds limit, limit, 4
+ beq L(ret_eq)
+L(byte_loop):
+ ldrb data1w, [src1], 1
+ ldrb data2w, [src2], 1
+ subs limit, limit, 1
+ ccmp data1w, data2w, 0, ne /* NZCV = 0b0000. */
+ b.eq L(byte_loop)
+ sub result, data1w, data2w
ret
-.Lstart_align:
- lsr limit_wd, limit, #3
- cbz limit_wd, .Lremain8
-
- ands xzr, src1, #7
- b.eq .Lrecal_offset
- /*process more leading bytes to make src1 aligned...*/
- add src1, src1, tmp3 /*backwards src1 to alignment boundary*/
- add src2, src2, tmp3
- sub limit, limit, tmp3
- lsr limit_wd, limit, #3
- cbz limit_wd, .Lremain8
- /*load 8 bytes from aligned SRC1..*/
- ldr data1, [src1], #8
- ldr data2, [src2], #8
-
- subs limit_wd, limit_wd, #1
- eor diff, data1, data2 /*Non-zero if differences found.*/
- csinv endloop, diff, xzr, ne
- cbnz endloop, .Lunequal_proc
- /*How far is the current SRC2 from the alignment boundary...*/
- and tmp3, tmp3, #7
-
-.Lrecal_offset:/*src1 is aligned now..*/
- neg pos, tmp3
-.Lloopcmp_proc:
- /*
- * Divide the eight bytes into two parts. First,backwards the src2
- * to an alignment boundary,load eight bytes and compare from
- * the SRC2 alignment boundary. If all 8 bytes are equal,then start
- * the second part's comparison. Otherwise finish the comparison.
- * This special handle can garantee all the accesses are in the
- * thread/task space in avoid to overrange access.
- */
- ldr data1, [src1,pos]
- ldr data2, [src2,pos]
- eor diff, data1, data2 /* Non-zero if differences found. */
- cbnz diff, .Lnot_limit
-
- /*The second part process*/
- ldr data1, [src1], #8
- ldr data2, [src2], #8
- eor diff, data1, data2 /* Non-zero if differences found. */
- subs limit_wd, limit_wd, #1
- csinv endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
- cbz endloop, .Lloopcmp_proc
-.Lunequal_proc:
- cbz diff, .Lremain8
-
-/* There is difference occurred in the latest comparison. */
-.Lnot_limit:
-/*
-* For little endian,reverse the low significant equal bits into MSB,then
-* following CLZ can find how many equal bits exist.
-*/
-CPU_LE( rev diff, diff )
-CPU_LE( rev data1, data1 )
-CPU_LE( rev data2, data2 )
-
- /*
- * The MS-non-zero bit of DIFF marks either the first bit
- * that is different, or the end of the significant data.
- * Shifting left now will bring the critical information into the
- * top bits.
- */
- clz pos, diff
- lsl data1, data1, pos
- lsl data2, data2, pos
- /*
- * We need to zero-extend (char is unsigned) the value and then
- * perform a signed subtraction.
- */
- lsr data1, data1, #56
- sub result, data1, data2, lsr #56
- ret
-
-.Lremain8:
- /* Limit % 8 == 0 =>. all data are equal.*/
- ands limit, limit, #7
- b.eq .Lret0
-
-.Ltiny8proc:
- ldrb data1w, [src1], #1
- ldrb data2w, [src2], #1
- subs limit, limit, #1
-
- ccmp data1w, data2w, #0, ne /* NZCV = 0b0000. */
- b.eq .Ltiny8proc
- sub result, data1, data2
- ret
-.Lret0:
- mov result, #0
- ret
SYM_FUNC_END_PI(memcmp)
EXPORT_SYMBOL_NOKASAN(memcmp)
--
2.21.0.dirty
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