[PATCH v2 2/8] arm64: Import latest version of Cortex Strings' strcmp

[Robin Murphy <robin.murphy@arm.com>]

From: Sam Tebbs <sam.tebbs@arm.com>

Import the latest version of the former Cortex Strings - now
Arm Optimized Routines - strcmp function based on the upstream
code of string/aarch64/strcmp.S at commit afd6244 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@arm.com>
[ rm: update attribution and commit message ]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 arch/arm64/lib/strcmp.S | 295 +++++++++++++++++-----------------------
 1 file changed, 124 insertions(+), 171 deletions(-)

diff --git a/arch/arm64/lib/strcmp.S b/arch/arm64/lib/strcmp.S
index 4e79566726c8..e82ccb6c2f93 100644
--- a/arch/arm64/lib/strcmp.S
+++ b/arch/arm64/lib/strcmp.S
@@ -1,84 +1,123 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
- * Copyright (C) 2013 ARM Ltd.
- * Copyright (C) 2013 Linaro.
+ * Copyright (c) 2012-2020, 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/strcmp.S
  */
 
 #include <linux/linkage.h>
 #include <asm/assembler.h>
 
-/*
- * compare two strings
+/* Assumptions:
  *
- * Parameters:
- *	x0 - const string 1 pointer
- *    x1 - const string 2 pointer
- * Returns:
- * x0 - an integer less than, equal to, or greater than zero
- * if  s1  is  found, respectively, to be less than, to match,
- * or be greater than s2.
+ * ARMv8-a, AArch64
  */
 
+#define L(label) .L ## label
+
 #define REP8_01 0x0101010101010101
 #define REP8_7f 0x7f7f7f7f7f7f7f7f
 #define REP8_80 0x8080808080808080
 
 /* Parameters and result.  */
-src1		.req	x0
-src2		.req	x1
-result		.req	x0
+#define src1		x0
+#define src2		x1
+#define result		x0
 
 /* Internal variables.  */
-data1		.req	x2
-data1w		.req	w2
-data2		.req	x3
-data2w		.req	w3
-has_nul		.req	x4
-diff		.req	x5
-syndrome	.req	x6
-tmp1		.req	x7
-tmp2		.req	x8
-tmp3		.req	x9
-zeroones	.req	x10
-pos		.req	x11
+#define data1		x2
+#define data1w		w2
+#define data2		x3
+#define data2w		w3
+#define has_nul		x4
+#define diff		x5
+#define syndrome	x6
+#define tmp1		x7
+#define tmp2		x8
+#define tmp3		x9
+#define zeroones	x10
+#define pos		x11
 
+	/* Start of performance-critical section  -- one 64B cache line.  */
+	.align 6
 SYM_FUNC_START_WEAK_PI(strcmp)
 	eor	tmp1, src1, src2
 	mov	zeroones, #REP8_01
 	tst	tmp1, #7
-	b.ne	.Lmisaligned8
+	b.ne	L(misaligned8)
 	ands	tmp1, src1, #7
-	b.ne	.Lmutual_align
-
-	/*
-	* NUL detection works on the principle that (X - 1) & (~X) & 0x80
-	* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
-	* can be done in parallel across the entire word.
-	*/
-.Lloop_aligned:
+	b.ne	L(mutual_align)
+	/* NUL detection works on the principle that (X - 1) & (~X) & 0x80
+	   (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+	   can be done in parallel across the entire word.  */
+L(loop_aligned):
 	ldr	data1, [src1], #8
 	ldr	data2, [src2], #8
-.Lstart_realigned:
+L(start_realigned):
 	sub	tmp1, data1, zeroones
 	orr	tmp2, data1, #REP8_7f
 	eor	diff, data1, data2	/* Non-zero if differences found.  */
 	bic	has_nul, tmp1, tmp2	/* Non-zero if NUL terminator.  */
 	orr	syndrome, diff, has_nul
-	cbz	syndrome, .Lloop_aligned
-	b	.Lcal_cmpresult
+	cbz	syndrome, L(loop_aligned)
+	/* End of performance-critical section  -- one 64B cache line.  */
 
-.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 preceed the start point.
-	*/
+L(end):
+#ifndef	__AARCH64EB__
+	rev	syndrome, syndrome
+	rev	data1, data1
+	/* The MS-non-zero bit of the syndrome marks either the first bit
+	   that is different, or the top bit of the first zero byte.
+	   Shifting left now will bring the critical information into the
+	   top bits.  */
+	clz	pos, syndrome
+	rev	data2, data2
+	lsl	data1, data1, pos
+	lsl	data2, data2, pos
+	/* But we need to zero-extend (char is unsigned) the value and then
+	   perform a signed 32-bit subtraction.  */
+	lsr	data1, data1, #56
+	sub	result, data1, data2, lsr #56
+	ret
+#else
+	/* For big-endian we cannot use the trick with the syndrome value
+	   as carry-propagation can corrupt the upper bits if the trailing
+	   bytes in the string contain 0x01.  */
+	/* However, if there is no NUL byte in the dword, we can generate
+	   the result directly.  We can't just subtract the bytes as the
+	   MSB might be significant.  */
+	cbnz	has_nul, 1f
+	cmp	data1, data2
+	cset	result, ne
+	cneg	result, result, lo
+	ret
+1:
+	/* Re-compute the NUL-byte detection, using a byte-reversed value.  */
+	rev	tmp3, data1
+	sub	tmp1, tmp3, zeroones
+	orr	tmp2, tmp3, #REP8_7f
+	bic	has_nul, tmp1, tmp2
+	rev	has_nul, has_nul
+	orr	syndrome, diff, has_nul
+	clz	pos, syndrome
+	/* The MS-non-zero bit of the syndrome marks either the first bit
+	   that is different, or the top bit of the first zero byte.
+	   Shifting left now will bring the critical information into the
+	   top bits.  */
+	lsl	data1, data1, pos
+	lsl	data2, data2, pos
+	/* But we need to zero-extend (char is unsigned) the value and then
+	   perform a signed 32-bit subtraction.  */
+	lsr	data1, data1, #56
+	sub	result, data1, data2, lsr #56
+	ret
+#endif
+
+L(mutual_align):
+	/* Sources are mutually aligned, but are not currently at an
+	   alignment boundary.  Round down the addresses and then mask off
+	   the bytes that preceed the start point.  */
 	bic	src1, src1, #7
 	bic	src2, src2, #7
 	lsl	tmp1, tmp1, #3		/* Bytes beyond alignment -> bits.  */
@@ -86,138 +125,52 @@ SYM_FUNC_START_WEAK_PI(strcmp)
 	neg	tmp1, tmp1		/* Bits to alignment -64.  */
 	ldr	data2, [src2], #8
 	mov	tmp2, #~0
+#ifdef __AARCH64EB__
 	/* Big-endian.  Early bytes are at MSB.  */
-CPU_BE( lsl	tmp2, tmp2, tmp1 )	/* Shift (tmp1 & 63).  */
+	lsl	tmp2, tmp2, tmp1	/* Shift (tmp1 & 63).  */
+#else
 	/* Little-endian.  Early bytes are at LSB.  */
-CPU_LE( lsr	tmp2, tmp2, tmp1 )	/* Shift (tmp1 & 63).  */
-
+	lsr	tmp2, tmp2, tmp1	/* Shift (tmp1 & 63).  */
+#endif
 	orr	data1, data1, tmp2
 	orr	data2, data2, tmp2
-	b	.Lstart_realigned
+	b	L(start_realigned)
 
-.Lmisaligned8:
-	/*
-	* Get the align offset length to compare per byte first.
-	* After this process, one string's address will be aligned.
-	*/
-	and	tmp1, src1, #7
-	neg	tmp1, tmp1
-	add	tmp1, tmp1, #8
-	and	tmp2, src2, #7
-	neg	tmp2, tmp2
-	add	tmp2, tmp2, #8
-	subs	tmp3, tmp1, tmp2
-	csel	pos, tmp1, tmp2, hi /*Choose the maximum. */
-.Ltinycmp:
+L(misaligned8):
+	/* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always
+	   checking to make sure that we don't access beyond page boundary in
+	   SRC2.  */
+	tst	src1, #7
+	b.eq	L(loop_misaligned)
+L(do_misaligned):
 	ldrb	data1w, [src1], #1
 	ldrb	data2w, [src2], #1
-	subs	pos, pos, #1
-	ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
-	ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
-	b.eq	.Ltinycmp
-	cbnz	pos, 1f /*find the null or unequal...*/
 	cmp	data1w, #1
-	ccmp	data1w, data2w, #0, cs
-	b.eq	.Lstart_align /*the last bytes are equal....*/
-1:
+	ccmp	data1w, data2w, #0, cs	/* NZCV = 0b0000.  */
+	b.ne	L(done)
+	tst	src1, #7
+	b.ne	L(do_misaligned)
+
+L(loop_misaligned):
+	/* Test if we are within the last dword of the end of a 4K page.  If
+	   yes then jump back to the misaligned loop to copy a byte at a time.  */
+	and	tmp1, src2, #0xff8
+	eor	tmp1, tmp1, #0xff8
+	cbz	tmp1, L(do_misaligned)
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	eor	diff, data1, data2	/* Non-zero if differences found.  */
+	bic	has_nul, tmp1, tmp2	/* Non-zero if NUL terminator.  */
+	orr	syndrome, diff, has_nul
+	cbz	syndrome, L(loop_misaligned)
+	b	L(end)
+
+L(done):
 	sub	result, data1, data2
 	ret
 
-.Lstart_align:
-	ands	xzr, src1, #7
-	b.eq	.Lrecal_offset
-	/*process more leading bytes to make str1 aligned...*/
-	add	src1, src1, tmp3
-	add	src2, src2, tmp3
-	/*load 8 bytes from aligned str1 and non-aligned str2..*/
-	ldr	data1, [src1], #8
-	ldr	data2, [src2], #8
-
-	sub	tmp1, data1, zeroones
-	orr	tmp2, data1, #REP8_7f
-	bic	has_nul, tmp1, tmp2
-	eor	diff, data1, data2 /* Non-zero if differences found.  */
-	orr	syndrome, diff, has_nul
-	cbnz	syndrome, .Lcal_cmpresult
-	/*How far is the current str2 from the alignment boundary...*/
-	and	tmp3, tmp3, #7
-.Lrecal_offset:
-	neg	pos, tmp3
-.Lloopcmp_proc:
-	/*
-	* Divide the eight bytes into two parts. First,backwards the src2
-	* to an alignment boundary,load eight bytes from the SRC2 alignment
-	* boundary,then compare with the relative bytes from SRC1.
-	* 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]
-	sub	tmp1, data1, zeroones
-	orr	tmp2, data1, #REP8_7f
-	bic	has_nul, tmp1, tmp2
-	eor	diff, data1, data2  /* Non-zero if differences found.  */
-	orr	syndrome, diff, has_nul
-	cbnz	syndrome, .Lcal_cmpresult
-
-	/*The second part process*/
-	ldr	data1, [src1], #8
-	ldr	data2, [src2], #8
-	sub	tmp1, data1, zeroones
-	orr	tmp2, data1, #REP8_7f
-	bic	has_nul, tmp1, tmp2
-	eor	diff, data1, data2  /* Non-zero if differences found.  */
-	orr	syndrome, diff, has_nul
-	cbz	syndrome, .Lloopcmp_proc
-
-.Lcal_cmpresult:
-	/*
-	* reversed the byte-order as big-endian,then CLZ can find the most
-	* significant zero bits.
-	*/
-CPU_LE( rev	syndrome, syndrome )
-CPU_LE( rev	data1, data1 )
-CPU_LE( rev	data2, data2 )
-
-	/*
-	* For big-endian we cannot use the trick with the syndrome value
-	* as carry-propagation can corrupt the upper bits if the trailing
-	* bytes in the string contain 0x01.
-	* However, if there is no NUL byte in the dword, we can generate
-	* the result directly.  We cannot just subtract the bytes as the
-	* MSB might be significant.
-	*/
-CPU_BE( cbnz	has_nul, 1f )
-CPU_BE( cmp	data1, data2 )
-CPU_BE( cset	result, ne )
-CPU_BE( cneg	result, result, lo )
-CPU_BE( ret )
-CPU_BE( 1: )
-	/*Re-compute the NUL-byte detection, using a byte-reversed value. */
-CPU_BE(	rev	tmp3, data1 )
-CPU_BE(	sub	tmp1, tmp3, zeroones )
-CPU_BE(	orr	tmp2, tmp3, #REP8_7f )
-CPU_BE(	bic	has_nul, tmp1, tmp2 )
-CPU_BE(	rev	has_nul, has_nul )
-CPU_BE(	orr	syndrome, diff, has_nul )
-
-	clz	pos, syndrome
-	/*
-	* The MS-non-zero bit of the syndrome marks either the first bit
-	* that is different, or the top bit of the first zero byte.
-	* Shifting left now will bring the critical information into the
-	* top bits.
-	*/
-	lsl	data1, data1, pos
-	lsl	data2, data2, pos
-	/*
-	* But we need to zero-extend (char is unsigned) the value and then
-	* perform a signed 32-bit subtraction.
-	*/
-	lsr	data1, data1, #56
-	sub	result, data1, data2, lsr #56
-	ret
 SYM_FUNC_END_PI(strcmp)
 EXPORT_SYMBOL_NOKASAN(strcmp)
-- 
2.21.0.dirty


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel