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bb2c12aecb
Add support for MTE to strcpy. 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: Wilco Dijkstra <wilco.dijkstra@arm.com>
188 lines
4.4 KiB
ArmAsm
188 lines
4.4 KiB
ArmAsm
/* strcpy/stpcpy - copy a string returning pointer to start/end.
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Copyright (C) 2013-2020 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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/* To build as stpcpy, define BUILD_STPCPY before compiling this file.
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To test the page crossing code path more thoroughly, compile with
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-DSTRCPY_TEST_PAGE_CROSS - this will force all unaligned copies through
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the slower entry path. This option is not intended for production use. */
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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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/* Arguments and results. */
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#define dstin x0
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#define srcin x1
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#define result x0
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#define src x2
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#define dst x3
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#define len x4
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#define synd x4
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#define tmp x5
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#define wtmp w5
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#define shift x5
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#define data1 x6
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#define dataw1 w6
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#define data2 x7
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#define dataw2 w7
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#define dataq q0
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#define vdata v0
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#define vhas_nul v1
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#define vrepmask v2
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#define vend v3
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#define dend d3
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#define dataq2 q1
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#ifdef BUILD_STPCPY
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# define STRCPY __stpcpy
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# define IFSTPCPY(X,...) X,__VA_ARGS__
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#else
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# define STRCPY strcpy
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# define IFSTPCPY(X,...)
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#endif
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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 (STRCPY)
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DELOUSE (0)
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DELOUSE (1)
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bic src, srcin, 15
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mov wtmp, 0xf00f
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ld1 {vdata.16b}, [src]
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dup vrepmask.8h, wtmp
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cmeq vhas_nul.16b, vdata.16b, 0
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lsl shift, srcin, 2
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and vhas_nul.16b, vhas_nul.16b, vrepmask.16b
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addp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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lsr synd, synd, shift
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cbnz synd, L(tail)
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ldr dataq, [src, 16]!
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cmeq vhas_nul.16b, vdata.16b, 0
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and vhas_nul.16b, vhas_nul.16b, vrepmask.16b
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addp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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cbz synd, L(start_loop)
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#ifndef __AARCH64EB__
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rbit synd, synd
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#endif
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sub tmp, src, srcin
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clz len, synd
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add len, tmp, len, lsr 2
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tbz len, 4, L(less16)
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sub tmp, len, 15
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ldr dataq, [srcin]
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ldr dataq2, [srcin, tmp]
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str dataq, [dstin]
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str dataq2, [dstin, tmp]
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IFSTPCPY (add result, dstin, len)
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ret
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.p2align 4,,8
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L(tail):
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rbit synd, synd
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clz len, synd
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lsr len, len, 2
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.p2align 4
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L(less16):
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tbz len, 3, L(less8)
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sub tmp, len, 7
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ldr data1, [srcin]
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ldr data2, [srcin, tmp]
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str data1, [dstin]
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str data2, [dstin, tmp]
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IFSTPCPY (add result, dstin, len)
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ret
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.p2align 4
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L(less8):
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subs tmp, len, 3
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b.lo L(less4)
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ldr dataw1, [srcin]
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ldr dataw2, [srcin, tmp]
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str dataw1, [dstin]
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str dataw2, [dstin, tmp]
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IFSTPCPY (add result, dstin, len)
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ret
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L(less4):
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cbz len, L(zerobyte)
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ldrh dataw1, [srcin]
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strh dataw1, [dstin]
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L(zerobyte):
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strb wzr, [dstin, len]
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IFSTPCPY (add result, dstin, len)
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ret
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.p2align 4
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L(start_loop):
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sub len, src, srcin
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ldr dataq2, [srcin]
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add dst, dstin, len
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str dataq2, [dstin]
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.p2align 5
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L(loop):
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str dataq, [dst], 16
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ldr dataq, [src, 16]!
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cmeq vhas_nul.16b, vdata.16b, 0
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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cbz synd, L(loop)
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and vhas_nul.16b, vhas_nul.16b, vrepmask.16b
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addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */
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fmov synd, dend
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#ifndef __AARCH64EB__
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rbit synd, synd
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#endif
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clz len, synd
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lsr len, len, 2
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sub tmp, len, 15
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ldr dataq, [src, tmp]
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str dataq, [dst, tmp]
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IFSTPCPY (add result, dst, len)
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ret
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END (STRCPY)
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#ifdef BUILD_STPCPY
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weak_alias (__stpcpy, stpcpy)
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libc_hidden_def (__stpcpy)
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libc_hidden_builtin_def (stpcpy)
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#else
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libc_hidden_builtin_def (strcpy)
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#endif
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