arm64: Import updated version of Cortex Strings' strlen
Import an updated version of the former Cortex Strings - now Arm Optimized Routines - strcmp function. The latest version introduces Advanced SIMD usage which rules it out for our purposes, but we can still pick an intermediate improvement from the previous version, namely string/aarch64/strlen.S at commit 98e4d6a from https://github.com/ARM-software/optimized-routines Note that for simplicity Arm have chosen to contribute this code to Linux under GPLv2 rather than the original MIT license. Signed-off-by: Sam Tebbs <sam.tebbs@arm.com> [ rm: update attribution and commit message ] Signed-off-by: Robin Murphy <robin.murphy@arm.com> Link: https://lore.kernel.org/r/32e3489398a24b23ae6e996935ac4818f8fd9dfd.1622128527.git.robin.murphy@arm.com Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Sam Tebbs
Will Deacon
parent
758602c044
commit
325a1de812
@ -1,115 +1,203 @@
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/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2013 ARM Ltd.
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* Copyright (C) 2013 Linaro.
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* Copyright (c) 2013, Arm Limited.
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*
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* This code is based on glibc cortex strings work originally authored by Linaro
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* be found @
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*
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* http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
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* files/head:/src/aarch64/
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* Adapted from the original at:
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* https://github.com/ARM-software/optimized-routines/blob/master/string/aarch64/strlen.S
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*/
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#include <linux/linkage.h>
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#include <asm/assembler.h>
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/*
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* calculate the length of a string
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/* Assumptions:
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*
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* Parameters:
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* x0 - const string pointer
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* Returns:
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* x0 - the return length of specific string
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* ARMv8-a, AArch64, unaligned accesses, min page size 4k.
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*/
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#define L(label) .L ## label
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/* Arguments and results. */
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srcin .req x0
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len .req x0
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#define srcin x0
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#define len x0
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/* Locals and temporaries. */
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src .req x1
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data1 .req x2
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data2 .req x3
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data2a .req x4
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has_nul1 .req x5
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has_nul2 .req x6
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tmp1 .req x7
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tmp2 .req x8
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tmp3 .req x9
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tmp4 .req x10
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zeroones .req x11
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pos .req x12
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#define src x1
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#define data1 x2
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#define data2 x3
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#define has_nul1 x4
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#define has_nul2 x5
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#define tmp1 x4
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#define tmp2 x5
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#define tmp3 x6
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#define tmp4 x7
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#define zeroones x8
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/* NUL detection works on the principle that (X - 1) & (~X) & 0x80
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(=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
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can be done in parallel across the entire word. A faster check
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(X - 1) & 0x80 is zero for non-NUL ASCII characters, but gives
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false hits for characters 129..255. */
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#define REP8_01 0x0101010101010101
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#define REP8_7f 0x7f7f7f7f7f7f7f7f
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#define REP8_80 0x8080808080808080
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#define MIN_PAGE_SIZE 4096
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/* Since strings are short on average, we check the first 16 bytes
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of the string for a NUL character. In order to do an unaligned ldp
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safely we have to do a page cross check first. If there is a NUL
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byte we calculate the length from the 2 8-byte words using
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conditional select to reduce branch mispredictions (it is unlikely
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strlen will be repeatedly called on strings with the same length).
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If the string is longer than 16 bytes, we align src so don't need
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further page cross checks, and process 32 bytes per iteration
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using the fast NUL check. If we encounter non-ASCII characters,
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fallback to a second loop using the full NUL check.
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If the page cross check fails, we read 16 bytes from an aligned
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address, remove any characters before the string, and continue
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in the main loop using aligned loads. Since strings crossing a
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page in the first 16 bytes are rare (probability of
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16/MIN_PAGE_SIZE ~= 0.4%), this case does not need to be optimized.
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AArch64 systems have a minimum page size of 4k. We don't bother
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checking for larger page sizes - the cost of setting up the correct
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page size is just not worth the extra gain from a small reduction in
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the cases taking the slow path. Note that we only care about
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whether the first fetch, which may be misaligned, crosses a page
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boundary. */
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SYM_FUNC_START_WEAK_PI(strlen)
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mov zeroones, #REP8_01
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bic src, srcin, #15
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ands tmp1, srcin, #15
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b.ne .Lmisaligned
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/*
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* NUL detection works on the principle that (X - 1) & (~X) & 0x80
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* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
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* can be done in parallel across the entire word.
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*/
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/*
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* The inner loop deals with two Dwords at a time. This has a
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* slightly higher start-up cost, but we should win quite quickly,
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* especially on cores with a high number of issue slots per
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* cycle, as we get much better parallelism out of the operations.
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*/
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.Lloop:
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ldp data1, data2, [src], #16
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.Lrealigned:
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and tmp1, srcin, MIN_PAGE_SIZE - 1
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mov zeroones, REP8_01
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cmp tmp1, MIN_PAGE_SIZE - 16
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b.gt L(page_cross)
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ldp data1, data2, [srcin]
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#ifdef __AARCH64EB__
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/* For big-endian, carry propagation (if the final byte in the
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string is 0x01) means we cannot use has_nul1/2 directly.
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Since we expect strings to be small and early-exit,
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byte-swap the data now so has_null1/2 will be correct. */
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rev data1, data1
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rev data2, data2
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#endif
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sub tmp1, data1, zeroones
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orr tmp2, data1, #REP8_7f
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orr tmp2, data1, REP8_7f
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sub tmp3, data2, zeroones
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orr tmp4, data2, #REP8_7f
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bic has_nul1, tmp1, tmp2
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bics has_nul2, tmp3, tmp4
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ccmp has_nul1, #0, #0, eq /* NZCV = 0000 */
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b.eq .Lloop
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orr tmp4, data2, REP8_7f
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bics has_nul1, tmp1, tmp2
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bic has_nul2, tmp3, tmp4
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ccmp has_nul2, 0, 0, eq
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beq L(main_loop_entry)
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sub len, src, srcin
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cbz has_nul1, .Lnul_in_data2
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CPU_BE( mov data2, data1 ) /*prepare data to re-calculate the syndrome*/
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sub len, len, #8
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mov has_nul2, has_nul1
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.Lnul_in_data2:
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/*
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* For big-endian, carry propagation (if the final byte in the
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* string is 0x01) means we cannot use has_nul directly. The
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* easiest way to get the correct byte is to byte-swap the data
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* and calculate the syndrome a second time.
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*/
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CPU_BE( rev data2, data2 )
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CPU_BE( sub tmp1, data2, zeroones )
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CPU_BE( orr tmp2, data2, #REP8_7f )
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CPU_BE( bic has_nul2, tmp1, tmp2 )
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sub len, len, #8
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rev has_nul2, has_nul2
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clz pos, has_nul2
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add len, len, pos, lsr #3 /* Bits to bytes. */
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/* Enter with C = has_nul1 == 0. */
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csel has_nul1, has_nul1, has_nul2, cc
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mov len, 8
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rev has_nul1, has_nul1
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clz tmp1, has_nul1
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csel len, xzr, len, cc
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add len, len, tmp1, lsr 3
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ret
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.Lmisaligned:
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cmp tmp1, #8
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neg tmp1, tmp1
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ldp data1, data2, [src], #16
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lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */
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mov tmp2, #~0
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/* Big-endian. Early bytes are at MSB. */
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CPU_BE( lsl tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */
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/* Little-endian. Early bytes are at LSB. */
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CPU_LE( lsr tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */
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/* The inner loop processes 32 bytes per iteration and uses the fast
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NUL check. If we encounter non-ASCII characters, use a second
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loop with the accurate NUL check. */
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.p2align 4
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L(main_loop_entry):
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bic src, srcin, 15
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sub src, src, 16
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L(main_loop):
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ldp data1, data2, [src, 32]!
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L(page_cross_entry):
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sub tmp1, data1, zeroones
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sub tmp3, data2, zeroones
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orr tmp2, tmp1, tmp3
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tst tmp2, zeroones, lsl 7
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bne 1f
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ldp data1, data2, [src, 16]
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sub tmp1, data1, zeroones
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sub tmp3, data2, zeroones
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orr tmp2, tmp1, tmp3
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tst tmp2, zeroones, lsl 7
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beq L(main_loop)
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add src, src, 16
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1:
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/* The fast check failed, so do the slower, accurate NUL check. */
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orr tmp2, data1, REP8_7f
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orr tmp4, data2, REP8_7f
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bics has_nul1, tmp1, tmp2
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bic has_nul2, tmp3, tmp4
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ccmp has_nul2, 0, 0, eq
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beq L(nonascii_loop)
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/* Enter with C = has_nul1 == 0. */
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L(tail):
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#ifdef __AARCH64EB__
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/* For big-endian, carry propagation (if the final byte in the
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string is 0x01) means we cannot use has_nul1/2 directly. The
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easiest way to get the correct byte is to byte-swap the data
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and calculate the syndrome a second time. */
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csel data1, data1, data2, cc
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rev data1, data1
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sub tmp1, data1, zeroones
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orr tmp2, data1, REP8_7f
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bic has_nul1, tmp1, tmp2
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#else
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csel has_nul1, has_nul1, has_nul2, cc
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#endif
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sub len, src, srcin
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rev has_nul1, has_nul1
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add tmp2, len, 8
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clz tmp1, has_nul1
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csel len, len, tmp2, cc
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add len, len, tmp1, lsr 3
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ret
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L(nonascii_loop):
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ldp data1, data2, [src, 16]!
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sub tmp1, data1, zeroones
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orr tmp2, data1, REP8_7f
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sub tmp3, data2, zeroones
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orr tmp4, data2, REP8_7f
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bics has_nul1, tmp1, tmp2
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bic has_nul2, tmp3, tmp4
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ccmp has_nul2, 0, 0, eq
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bne L(tail)
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ldp data1, data2, [src, 16]!
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sub tmp1, data1, zeroones
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orr tmp2, data1, REP8_7f
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sub tmp3, data2, zeroones
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orr tmp4, data2, REP8_7f
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bics has_nul1, tmp1, tmp2
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bic has_nul2, tmp3, tmp4
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ccmp has_nul2, 0, 0, eq
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beq L(nonascii_loop)
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b L(tail)
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/* Load 16 bytes from [srcin & ~15] and force the bytes that precede
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srcin to 0x7f, so we ignore any NUL bytes before the string.
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Then continue in the aligned loop. */
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L(page_cross):
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bic src, srcin, 15
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ldp data1, data2, [src]
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lsl tmp1, srcin, 3
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mov tmp4, -1
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#ifdef __AARCH64EB__
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/* Big-endian. Early bytes are at MSB. */
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lsr tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */
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#else
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/* Little-endian. Early bytes are at LSB. */
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lsl tmp1, tmp4, tmp1 /* Shift (tmp1 & 63). */
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#endif
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orr tmp1, tmp1, REP8_80
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orn data1, data1, tmp1
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orn tmp2, data2, tmp1
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tst srcin, 8
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csel data1, data1, tmp4, eq
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csel data2, data2, tmp2, eq
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b L(page_cross_entry)
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orr data1, data1, tmp2
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orr data2a, data2, tmp2
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csinv data1, data1, xzr, le
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csel data2, data2, data2a, le
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b .Lrealigned
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SYM_FUNC_END_PI(strlen)
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EXPORT_SYMBOL_NOKASAN(strlen)
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