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7ff899969f
Add support for MTE to memchr. Regression tested with xcheck and benchmarked with glibc's benchtests on the Cortex-A53, Cortex-A72, and Neoverse N1. The existing implementation assumes that any access to the pages in which the string resides is safe. This assumption is not true when MTE is enabled. This patch updates the algorithm to ensure that accesses remain within the bounds of an MTE tag (16-byte chunks) and improves overall performance. Co-authored-by: Gabor Kertesz <gabor.kertesz@arm.com>
135 lines
3.3 KiB
ArmAsm
135 lines
3.3 KiB
ArmAsm
/* memchr - find a character in a memory zone
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Copyright (C) 2015-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<https://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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/* Assumptions:
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*
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* ARMv8-a, AArch64, Advanced SIMD.
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* MTE compatible.
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*/
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#ifndef MEMCHR
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# define MEMCHR __memchr
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#endif
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/* Arguments and results. */
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#define srcin x0
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#define chrin w1
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#define cntin x2
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#define result x0
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#define src x3
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#define cntrem x4
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#define synd x5
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#define shift x6
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#define tmp x7
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#define wtmp w7
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#define vrepchr v0
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#define qdata q1
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#define vdata v1
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#define vhas_chr v2
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#define vrepmask v3
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#define vend v4
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#define dend d4
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/*
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Core algorithm:
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For each 16-byte chunk we calculate a 64-bit syndrome value with four bits
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per byte. For even bytes, bits 0-3 are set if the relevant byte matched the
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requested character or the byte is NUL. Bits 4-7 must be zero. Bits 4-7 are
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set likewise for odd bytes so that adjacent bytes can be merged. Since the
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bits in the syndrome reflect the order in which things occur in the original
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string, counting trailing zeros identifies exactly which byte matched. */
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ENTRY (MEMCHR)
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DELOUSE (0)
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DELOUSE (2)
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bic src, srcin, 15
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cbz cntin, L(nomatch)
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ld1 {vdata.16b}, [src]
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dup vrepchr.16b, chrin
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mov wtmp, 0xf00f
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dup vrepmask.8h, wtmp
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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lsl shift, srcin, 2
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and vhas_chr.16b, vhas_chr.16b, vrepmask.16b
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addp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
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fmov synd, dend
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lsr synd, synd, shift
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cbz synd, L(start_loop)
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rbit synd, synd
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clz synd, synd
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add result, srcin, synd, lsr 2
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cmp cntin, synd, lsr 2
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csel result, result, xzr, hi
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ret
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L(start_loop):
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sub tmp, src, srcin
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add tmp, tmp, 16
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subs cntrem, cntin, tmp
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b.ls L(nomatch)
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/* Make sure that it won't overread by a 16-byte chunk */
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add tmp, cntrem, 15
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tbnz tmp, 4, L(loop32_2)
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.p2align 4
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L(loop32):
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ldr qdata, [src, 16]!
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
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fmov synd, dend
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cbnz synd, L(end)
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L(loop32_2):
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ldr qdata, [src, 16]!
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subs cntrem, cntrem, 32
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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b.ls L(end)
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umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
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fmov synd, dend
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cbz synd, L(loop32)
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L(end):
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and vhas_chr.16b, vhas_chr.16b, vrepmask.16b
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addp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
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fmov synd, dend
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add tmp, srcin, cntin
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sub cntrem, tmp, src
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#ifndef __AARCH64EB__
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rbit synd, synd
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#endif
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clz synd, synd
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cmp cntrem, synd, lsr 2
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add result, src, synd, lsr 2
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csel result, result, xzr, hi
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ret
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L(nomatch):
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mov result, 0
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ret
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END (MEMCHR)
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weak_alias (MEMCHR, memchr)
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libc_hidden_builtin_def (memchr)
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