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Tue, 1 Mar 2022 10:14:43 +0000 From: Joey Gouly To: CC: , , , , , Subject: [PATCH v2 2/3] arm64: lib: Import latest version of Arm Optimized Routines' strncmp Date: Tue, 1 Mar 2022 10:14:34 +0000 Message-ID: <20220301101435.19327-3-joey.gouly@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20220301101435.19327-1-joey.gouly@arm.com> References: <20220301101435.19327-1-joey.gouly@arm.com> MIME-Version: 1.0 X-EOPAttributedMessage: 1 X-MS-Office365-Filtering-Correlation-Id: a145402a-c932-497f-0412-08d9fb6c526c X-MS-TrafficTypeDiagnostic: DBBPR08MB5993:EE_|AM5EUR03FT042:EE_|DB6PR0801MB1768:EE_ X-Microsoft-Antispam-PRVS: x-checkrecipientrouted: true NoDisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; X-Microsoft-Antispam-Message-Info-Original: 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 X-Forefront-Antispam-Report-Untrusted: CIP:40.67.248.234; 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Note that for simplicity Arm have chosen to contribute this code to Linux under GPLv2 rather than the original MIT OR Apache-2.0 WITH LLVM-exception license. Arm is the sole copyright holder for this code. Signed-off-by: Joey Gouly Cc: Robin Murphy Cc: Mark Rutland Cc: Catalin Marinas Cc: Will Deacon Acked-by: Mark Rutland --- arch/arm64/lib/strncmp.S | 234 +++++++++++++++++++++++---------------- 1 file changed, 141 insertions(+), 93 deletions(-) diff --git a/arch/arm64/lib/strncmp.S b/arch/arm64/lib/strncmp.S index e42bcfcd37e6..a4884b97e9a8 100644 --- a/arch/arm64/lib/strncmp.S +++ b/arch/arm64/lib/strncmp.S @@ -1,9 +1,9 @@ /* SPDX-License-Identifier: GPL-2.0-only */ /* - * Copyright (c) 2013-2021, Arm Limited. + * Copyright (c) 2013-2022, Arm Limited. * * Adapted from the original at: - * https://github.com/ARM-software/optimized-routines/blob/e823e3abf5f89ecb/string/aarch64/strncmp.S + * https://github.com/ARM-software/optimized-routines/blob/189dfefe37d54c5b/string/aarch64/strncmp.S */ #include @@ -11,14 +11,14 @@ /* Assumptions: * - * ARMv8-a, AArch64 + * ARMv8-a, AArch64. + * MTE compatible. */ #define L(label) .L ## label #define REP8_01 0x0101010101010101 #define REP8_7f 0x7f7f7f7f7f7f7f7f -#define REP8_80 0x8080808080808080 /* Parameters and result. */ #define src1 x0 @@ -39,10 +39,24 @@ #define tmp3 x10 #define zeroones x11 #define pos x12 -#define limit_wd x13 -#define mask x14 -#define endloop x15 +#define mask x13 +#define endloop x14 #define count mask +#define offset pos +#define neg_offset x15 + +/* Define endian dependent shift operations. + On big-endian early bytes are at MSB and on little-endian LSB. + LS_FW means shifting towards early bytes. + LS_BK means shifting towards later bytes. + */ +#ifdef __AARCH64EB__ +#define LS_FW lsl +#define LS_BK lsr +#else +#define LS_FW lsr +#define LS_BK lsl +#endif SYM_FUNC_START_WEAK_PI(strncmp) cbz limit, L(ret0) @@ -52,9 +66,6 @@ SYM_FUNC_START_WEAK_PI(strncmp) and count, src1, #7 b.ne L(misaligned8) cbnz count, L(mutual_align) - /* Calculate the number of full and partial words -1. */ - sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ - lsr limit_wd, limit_wd, #3 /* Convert to Dwords. */ /* NUL detection works on the principle that (X - 1) & (~X) & 0x80 (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and @@ -64,56 +75,52 @@ L(loop_aligned): ldr data1, [src1], #8 ldr data2, [src2], #8 L(start_realigned): - subs limit_wd, limit_wd, #1 + subs limit, limit, #8 sub tmp1, data1, zeroones orr tmp2, data1, #REP8_7f eor diff, data1, data2 /* Non-zero if differences found. */ - csinv endloop, diff, xzr, pl /* Last Dword or differences. */ + csinv endloop, diff, xzr, hi /* Last Dword or differences. */ bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ ccmp endloop, #0, #0, eq b.eq L(loop_aligned) /* End of main loop */ - /* Not reached the limit, must have found the end or a diff. */ - tbz limit_wd, #63, L(not_limit) - - /* Limit % 8 == 0 => all bytes significant. */ - ands limit, limit, #7 - b.eq L(not_limit) - - lsl limit, limit, #3 /* Bits -> bytes. */ - mov mask, #~0 -#ifdef __AARCH64EB__ - lsr mask, mask, limit -#else - lsl mask, mask, limit -#endif - bic data1, data1, mask - bic data2, data2, mask - - /* Make sure that the NUL byte is marked in the syndrome. */ - orr has_nul, has_nul, mask - -L(not_limit): +L(full_check): +#ifndef __AARCH64EB__ orr syndrome, diff, has_nul - -#ifndef __AARCH64EB__ + add limit, limit, 8 /* Rewind limit to before last subs. */ +L(syndrome_check): + /* Limit was reached. Check if the NUL byte or the difference + is before the limit. */ 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 + cmp limit, pos, lsr #3 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 + csel result, result, xzr, hi ret #else + /* Not reached the limit, must have found the end or a diff. */ + tbz limit, #63, L(not_limit) + add tmp1, limit, 8 + cbz limit, L(not_limit) + + lsl limit, tmp1, #3 /* Bits -> bytes. */ + mov mask, #~0 + lsr mask, mask, limit + bic data1, data1, mask + bic data2, data2, mask + + /* Make sure that the NUL byte is marked in the syndrome. */ + orr has_nul, has_nul, mask + +L(not_limit): /* 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. */ @@ -134,10 +141,11 @@ L(not_limit): 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. + /* The most-significant-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. */ +L(end_quick): lsl data1, data1, pos lsl data2, data2, pos /* But we need to zero-extend (char is unsigned) the value and then @@ -159,22 +167,12 @@ L(mutual_align): neg tmp3, count, lsl #3 /* 64 - bits(bytes beyond align). */ ldr data2, [src2], #8 mov tmp2, #~0 - sub limit_wd, limit, #1 /* limit != 0, so no underflow. */ -#ifdef __AARCH64EB__ - /* Big-endian. Early bytes are at MSB. */ - lsl tmp2, tmp2, tmp3 /* Shift (count & 63). */ -#else - /* Little-endian. Early bytes are at LSB. */ - lsr tmp2, tmp2, tmp3 /* Shift (count & 63). */ -#endif - and tmp3, limit_wd, #7 - lsr limit_wd, limit_wd, #3 - /* Adjust the limit. Only low 3 bits used, so overflow irrelevant. */ - add limit, limit, count - add tmp3, tmp3, count + LS_FW tmp2, tmp2, tmp3 /* Shift (count & 63). */ + /* Adjust the limit and ensure it doesn't overflow. */ + adds limit, limit, count + csinv limit, limit, xzr, lo orr data1, data1, tmp2 orr data2, data2, tmp2 - add limit_wd, limit_wd, tmp3, lsr #3 b L(start_realigned) .p2align 4 @@ -197,13 +195,11 @@ L(done): /* Align the SRC1 to a dword by doing a bytewise compare and then do the dword loop. */ L(try_misaligned_words): - lsr limit_wd, limit, #3 - cbz count, L(do_misaligned) + cbz count, L(src1_aligned) neg count, count and count, count, #7 sub limit, limit, count - lsr limit_wd, limit, #3 L(page_end_loop): ldrb data1w, [src1], #1 @@ -214,48 +210,100 @@ L(page_end_loop): subs count, count, #1 b.hi L(page_end_loop) -L(do_misaligned): - /* Prepare ourselves for the next page crossing. Unlike the aligned - loop, we fetch 1 less dword because we risk crossing bounds on - SRC2. */ - mov count, #8 - subs limit_wd, limit_wd, #1 - b.lo L(done_loop) -L(loop_misaligned): - and tmp2, src2, #0xff8 - eor tmp2, tmp2, #0xff8 - cbz tmp2, L(page_end_loop) + /* The following diagram explains the comparison of misaligned strings. + The bytes are shown in natural order. For little-endian, it is + reversed in the registers. The "x" bytes are before the string. + The "|" separates data that is loaded at one time. + src1 | a a a a a a a a | b b b c c c c c | . . . + src2 | x x x x x a a a a a a a a b b b | c c c c c . . . + + After shifting in each step, the data looks like this: + STEP_A STEP_B STEP_C + data1 a a a a a a a a b b b c c c c c b b b c c c c c + data2 a a a a a a a a b b b 0 0 0 0 0 0 0 0 c c c c c + The bytes with "0" are eliminated from the syndrome via mask. + + Align SRC2 down to 16 bytes. This way we can read 16 bytes at a + time from SRC2. The comparison happens in 3 steps. After each step + the loop can exit, or read from SRC1 or SRC2. */ +L(src1_aligned): + /* Calculate offset from 8 byte alignment to string start in bits. No + need to mask offset since shifts are ignoring upper bits. */ + lsl offset, src2, #3 + bic src2, src2, #0xf + mov mask, -1 + neg neg_offset, offset 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. */ - bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ - ccmp diff, #0, #0, eq - b.ne L(not_limit) - subs limit_wd, limit_wd, #1 - b.pl L(loop_misaligned) + ldp tmp1, tmp2, [src2], #16 + LS_BK mask, mask, neg_offset + and neg_offset, neg_offset, #63 /* Need actual value for cmp later. */ + /* Skip the first compare if data in tmp1 is irrelevant. */ + tbnz offset, 6, L(misaligned_mid_loop) -L(done_loop): - /* We found a difference or a NULL before the limit was reached. */ - and limit, limit, #7 - cbz limit, L(not_limit) - /* Read the last word. */ - sub src1, src1, 8 - sub src2, src2, 8 - ldr data1, [src1, limit] - ldr data2, [src2, limit] - sub tmp1, data1, zeroones - orr tmp2, data1, #REP8_7f +L(loop_misaligned): + /* STEP_A: Compare full 8 bytes when there is enough data from SRC2.*/ + LS_FW data2, tmp1, offset + LS_BK tmp1, tmp2, neg_offset + subs limit, limit, #8 + orr data2, data2, tmp1 /* 8 bytes from SRC2 combined from two regs.*/ + sub has_nul, data1, zeroones eor diff, data1, data2 /* Non-zero if differences found. */ - bics has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ - ccmp diff, #0, #0, eq - b.ne L(not_limit) + orr tmp3, data1, #REP8_7f + csinv endloop, diff, xzr, hi /* If limit, set to all ones. */ + bic has_nul, has_nul, tmp3 /* Non-zero if NUL byte found in SRC1. */ + orr tmp3, endloop, has_nul + cbnz tmp3, L(full_check) + + ldr data1, [src1], #8 +L(misaligned_mid_loop): + /* STEP_B: Compare first part of data1 to second part of tmp2. */ + LS_FW data2, tmp2, offset +#ifdef __AARCH64EB__ + /* For big-endian we do a byte reverse to avoid carry-propagation + problem described above. This way we can reuse the has_nul in the + next step and also use syndrome value trick at the end. */ + rev tmp3, data1 + #define data1_fixed tmp3 +#else + #define data1_fixed data1 +#endif + sub has_nul, data1_fixed, zeroones + orr tmp3, data1_fixed, #REP8_7f + eor diff, data2, data1 /* Non-zero if differences found. */ + bic has_nul, has_nul, tmp3 /* Non-zero if NUL terminator. */ +#ifdef __AARCH64EB__ + rev has_nul, has_nul +#endif + cmp limit, neg_offset, lsr #3 + orr syndrome, diff, has_nul + bic syndrome, syndrome, mask /* Ignore later bytes. */ + csinv tmp3, syndrome, xzr, hi /* If limit, set to all ones. */ + cbnz tmp3, L(syndrome_check) + + /* STEP_C: Compare second part of data1 to first part of tmp1. */ + ldp tmp1, tmp2, [src2], #16 + cmp limit, #8 + LS_BK data2, tmp1, neg_offset + eor diff, data2, data1 /* Non-zero if differences found. */ + orr syndrome, diff, has_nul + and syndrome, syndrome, mask /* Ignore earlier bytes. */ + csinv tmp3, syndrome, xzr, hi /* If limit, set to all ones. */ + cbnz tmp3, L(syndrome_check) + + ldr data1, [src1], #8 + sub limit, limit, #8 + b L(loop_misaligned) + +#ifdef __AARCH64EB__ +L(syndrome_check): + clz pos, syndrome + cmp pos, limit, lsl #3 + b.lo L(end_quick) +#endif L(ret0): mov result, #0 ret - SYM_FUNC_END_PI(strncmp) EXPORT_SYMBOL_NOHWKASAN(strncmp)