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arch/arm64: import arm64 strlen from glibc
Change-Id: I50182df06951bc3d124017bf5fe4dda21b7de47a Signed-off-by: Vaisakh Murali <[email protected]>
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| /* SPDX-License-Identifier: GPL-2.0-only */ | ||
| /* | ||
| * Copyright (c) 2013, Arm Limited. | ||
| * | ||
| * Adapted from the original at: | ||
| * https://github.com/ARM-software/optimized-routines/blob/master/string/aarch64/strlen.S | ||
| */ | ||
| /* Copyright (C) 2012-2023 Free Software Foundation, Inc. | ||
| This file is part of the GNU C Library. | ||
| The GNU C Library is free software; you can redistribute it and/or | ||
| modify it under the terms of the GNU Lesser General Public | ||
| License as published by the Free Software Foundation; either | ||
| version 2.1 of the License, or (at your option) any later version. | ||
| The GNU C Library is distributed in the hope that it will be useful, | ||
| but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
| Lesser General Public License for more details. | ||
| You should have received a copy of the GNU Lesser General Public | ||
| License along with the GNU C Library. If not, see | ||
| <https://www.gnu.org/licenses/>. */ | ||
|
|
||
| #include <linux/linkage.h> | ||
| #include <asm/assembler.h> | ||
|
|
||
| /* Assumptions: | ||
| * | ||
| * ARMv8-a, AArch64, unaligned accesses, min page size 4k. | ||
| * ARMv8-a, AArch64, Advanced SIMD. | ||
| * MTE compatible. | ||
| */ | ||
|
|
||
| #define L(label) .L ## label | ||
| #define PTR_ARG(n) mov w##n, w##n | ||
| #define SIZE_ARG(n) mov w##n, w##n | ||
|
|
||
| #ifndef STRLEN | ||
| # define STRLEN __strlen | ||
| #endif | ||
|
|
||
| /* Arguments and results. */ | ||
| #define srcin x0 | ||
| #define len x0 | ||
| #define result x0 | ||
|
|
||
| /* Locals and temporaries. */ | ||
| #define src x1 | ||
| #define data1 x2 | ||
| #define data2 x3 | ||
| #define has_nul1 x4 | ||
| #define has_nul2 x5 | ||
| #define tmp1 x4 | ||
| #define tmp2 x5 | ||
| #define tmp3 x6 | ||
| #define tmp4 x7 | ||
| #define zeroones x8 | ||
|
|
||
| /* 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. A faster check | ||
| (X - 1) & 0x80 is zero for non-NUL ASCII characters, but gives | ||
| false hits for characters 129..255. */ | ||
|
|
||
| #define REP8_01 0x0101010101010101 | ||
| #define REP8_7f 0x7f7f7f7f7f7f7f7f | ||
| #define REP8_80 0x8080808080808080 | ||
|
|
||
| #define MIN_PAGE_SIZE 4096 | ||
| #define synd x2 | ||
| #define tmp x3 | ||
| #define shift x4 | ||
|
|
||
| /* Since strings are short on average, we check the first 16 bytes | ||
| of the string for a NUL character. In order to do an unaligned ldp | ||
| safely we have to do a page cross check first. If there is a NUL | ||
| byte we calculate the length from the 2 8-byte words using | ||
| conditional select to reduce branch mispredictions (it is unlikely | ||
| strlen will be repeatedly called on strings with the same length). | ||
| #define data q0 | ||
| #define vdata v0 | ||
| #define vhas_nul v1 | ||
| #define vend v2 | ||
| #define dend d2 | ||
|
|
||
| If the string is longer than 16 bytes, we align src so don't need | ||
| further page cross checks, and process 32 bytes per iteration | ||
| using the fast NUL check. If we encounter non-ASCII characters, | ||
| fallback to a second loop using the full NUL check. | ||
| If the page cross check fails, we read 16 bytes from an aligned | ||
| address, remove any characters before the string, and continue | ||
| in the main loop using aligned loads. Since strings crossing a | ||
| page in the first 16 bytes are rare (probability of | ||
| 16/MIN_PAGE_SIZE ~= 0.4%), this case does not need to be optimized. | ||
| AArch64 systems have a minimum page size of 4k. We don't bother | ||
| checking for larger page sizes - the cost of setting up the correct | ||
| page size is just not worth the extra gain from a small reduction in | ||
| the cases taking the slow path. Note that we only care about | ||
| whether the first fetch, which may be misaligned, crosses a page | ||
| boundary. */ | ||
| /* Core algorithm: | ||
| Process the string in 16-byte aligned chunks. Compute a 64-bit mask with | ||
| four bits per byte using the shrn instruction. A count trailing zeros then | ||
| identifies the first zero byte. */ | ||
|
|
||
| SYM_FUNC_START_WEAK_PI(strlen) | ||
| and tmp1, srcin, MIN_PAGE_SIZE - 1 | ||
| mov zeroones, REP8_01 | ||
| cmp tmp1, MIN_PAGE_SIZE - 16 | ||
| b.gt L(page_cross) | ||
| ldp data1, data2, [srcin] | ||
| #ifdef __AARCH64EB__ | ||
| /* For big-endian, carry propagation (if the final byte in the | ||
| string is 0x01) means we cannot use has_nul1/2 directly. | ||
| Since we expect strings to be small and early-exit, | ||
| byte-swap the data now so has_null1/2 will be correct. */ | ||
| rev data1, data1 | ||
| rev data2, data2 | ||
| #endif | ||
| sub tmp1, data1, zeroones | ||
| orr tmp2, data1, REP8_7f | ||
| sub tmp3, data2, zeroones | ||
| orr tmp4, data2, REP8_7f | ||
| bics has_nul1, tmp1, tmp2 | ||
| bic has_nul2, tmp3, tmp4 | ||
| ccmp has_nul2, 0, 0, eq | ||
| beq L(main_loop_entry) | ||
|
|
||
| /* Enter with C = has_nul1 == 0. */ | ||
| csel has_nul1, has_nul1, has_nul2, cc | ||
| mov len, 8 | ||
| rev has_nul1, has_nul1 | ||
| clz tmp1, has_nul1 | ||
| csel len, xzr, len, cc | ||
| add len, len, tmp1, lsr 3 | ||
| PTR_ARG (0) | ||
| bic src, srcin, 15 | ||
| ld1 {vdata.16b}, [src] | ||
| cmeq vhas_nul.16b, vdata.16b, 0 | ||
| lsl shift, srcin, 2 | ||
| shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */ | ||
| fmov synd, dend | ||
| lsr synd, synd, shift | ||
| cbz synd, L(loop) | ||
|
|
||
| rbit synd, synd | ||
| clz result, synd | ||
| lsr result, result, 2 | ||
| ret | ||
|
|
||
| /* The inner loop processes 32 bytes per iteration and uses the fast | ||
| NUL check. If we encounter non-ASCII characters, use a second | ||
| loop with the accurate NUL check. */ | ||
| .p2align 4 | ||
| L(main_loop_entry): | ||
| bic src, srcin, 15 | ||
| .p2align 5 | ||
| L(loop): | ||
| ldr data, [src, 16] | ||
| cmeq vhas_nul.16b, vdata.16b, 0 | ||
| umaxp vend.16b, vhas_nul.16b, vhas_nul.16b | ||
| fmov synd, dend | ||
| cbnz synd, L(loop_end) | ||
| ldr data, [src, 32]! | ||
| cmeq vhas_nul.16b, vdata.16b, 0 | ||
| umaxp vend.16b, vhas_nul.16b, vhas_nul.16b | ||
| fmov synd, dend | ||
| cbz synd, L(loop) | ||
| sub src, src, 16 | ||
| L(main_loop): | ||
| ldp data1, data2, [src, 32]! | ||
| L(page_cross_entry): | ||
| sub tmp1, data1, zeroones | ||
| sub tmp3, data2, zeroones | ||
| orr tmp2, tmp1, tmp3 | ||
| tst tmp2, zeroones, lsl 7 | ||
| bne 1f | ||
| ldp data1, data2, [src, 16] | ||
| sub tmp1, data1, zeroones | ||
| sub tmp3, data2, zeroones | ||
| orr tmp2, tmp1, tmp3 | ||
| tst tmp2, zeroones, lsl 7 | ||
| beq L(main_loop) | ||
| add src, src, 16 | ||
| 1: | ||
| /* The fast check failed, so do the slower, accurate NUL check. */ | ||
| orr tmp2, data1, REP8_7f | ||
| orr tmp4, data2, REP8_7f | ||
| bics has_nul1, tmp1, tmp2 | ||
| bic has_nul2, tmp3, tmp4 | ||
| ccmp has_nul2, 0, 0, eq | ||
| beq L(nonascii_loop) | ||
|
|
||
| /* Enter with C = has_nul1 == 0. */ | ||
| L(tail): | ||
| #ifdef __AARCH64EB__ | ||
| /* For big-endian, carry propagation (if the final byte in the | ||
| string is 0x01) means we cannot use has_nul1/2 directly. The | ||
| easiest way to get the correct byte is to byte-swap the data | ||
| and calculate the syndrome a second time. */ | ||
| csel data1, data1, data2, cc | ||
| rev data1, data1 | ||
| sub tmp1, data1, zeroones | ||
| orr tmp2, data1, REP8_7f | ||
| bic has_nul1, tmp1, tmp2 | ||
| #else | ||
| csel has_nul1, has_nul1, has_nul2, cc | ||
| L(loop_end): | ||
| shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */ | ||
| sub result, src, srcin | ||
| fmov synd, dend | ||
| #ifndef __AARCH64EB__ | ||
| rbit synd, synd | ||
| #endif | ||
| sub len, src, srcin | ||
| rev has_nul1, has_nul1 | ||
| add tmp2, len, 8 | ||
| clz tmp1, has_nul1 | ||
| csel len, len, tmp2, cc | ||
| add len, len, tmp1, lsr 3 | ||
| add result, result, 16 | ||
| clz tmp, synd | ||
| add result, result, tmp, lsr 2 | ||
| ret | ||
|
|
||
| L(nonascii_loop): | ||
| ldp data1, data2, [src, 16]! | ||
| sub tmp1, data1, zeroones | ||
| orr tmp2, data1, REP8_7f | ||
| sub tmp3, data2, zeroones | ||
| orr tmp4, data2, REP8_7f | ||
| bics has_nul1, tmp1, tmp2 | ||
| bic has_nul2, tmp3, tmp4 | ||
| ccmp has_nul2, 0, 0, eq | ||
| bne L(tail) | ||
| ldp data1, data2, [src, 16]! | ||
| sub tmp1, data1, zeroones | ||
| orr tmp2, data1, REP8_7f | ||
| sub tmp3, data2, zeroones | ||
| orr tmp4, data2, REP8_7f | ||
| bics has_nul1, tmp1, tmp2 | ||
| bic has_nul2, tmp3, tmp4 | ||
| ccmp has_nul2, 0, 0, eq | ||
| beq L(nonascii_loop) | ||
| b L(tail) | ||
|
|
||
| /* Load 16 bytes from [srcin & ~15] and force the bytes that precede | ||
| srcin to 0x7f, so we ignore any NUL bytes before the string. | ||
| Then continue in the aligned loop. */ | ||
| L(page_cross): | ||
| bic src, srcin, 15 | ||
| ldp data1, data2, [src] | ||
| lsl tmp1, srcin, 3 | ||
| mov tmp4, -1 | ||
| #ifdef __AARCH64EB__ | ||
| /* Big-endian. Early bytes are at MSB. */ | ||
| lsr tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */ | ||
| #else | ||
| /* Little-endian. Early bytes are at LSB. */ | ||
| lsl tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */ | ||
| #endif | ||
| orr tmp1, tmp1, REP8_80 | ||
| orn data1, data1, tmp1 | ||
| orn tmp2, data2, tmp1 | ||
| tst srcin, 8 | ||
| csel data1, data1, tmp4, eq | ||
| csel data2, data2, tmp2, eq | ||
| b L(page_cross_entry) | ||
|
|
||
| SYM_FUNC_END_PI(strlen) | ||
| EXPORT_SYMBOL_NOKASAN(strlen) | ||
| EXPORT_SYMBOL_NOKASAN(strlen) |