Re: [PATCH 1/8] arm64: Import latest version of Cortex Strings' memcmp

[Mark Rutland <mark.rutland@arm.com>]

Hi Robin,

On Tue, May 11, 2021 at 05:12:31PM +0100, Robin Murphy wrote:
> From: Sam Tebbs <sam.tebbs@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

What's the licensing/copyright situation here?

Because below...

> 
> 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/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 */

... this says 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
>   */

... but this referenced file says "SPDX-License-Identifier: MIT", and I
don't know when this relicensing is legitimate.

Thanks,
Mark.

>  
>  #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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