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176 lines
4.9 KiB
176 lines
4.9 KiB
/* SPDX-License-Identifier: GPL-2.0-only */ |
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/* |
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* Copyright (c) 2012-2021, Arm Limited. |
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* |
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* Adapted from the original at: |
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* https://github.com/ARM-software/optimized-routines/blob/afd6244a1f8d9229/string/aarch64/strcmp.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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/* Assumptions: |
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* |
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* ARMv8-a, AArch64 |
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*/ |
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#define L(label) .L ## label |
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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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/* Parameters and result. */ |
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#define src1 x0 |
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#define src2 x1 |
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#define result x0 |
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/* Internal variables. */ |
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#define data1 x2 |
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#define data1w w2 |
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#define data2 x3 |
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#define data2w w3 |
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#define has_nul x4 |
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#define diff x5 |
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#define syndrome x6 |
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#define tmp1 x7 |
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#define tmp2 x8 |
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#define tmp3 x9 |
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#define zeroones x10 |
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#define pos x11 |
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/* Start of performance-critical section -- one 64B cache line. */ |
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.align 6 |
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SYM_FUNC_START_WEAK_PI(strcmp) |
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eor tmp1, src1, src2 |
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mov zeroones, #REP8_01 |
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tst tmp1, #7 |
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b.ne L(misaligned8) |
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ands tmp1, src1, #7 |
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b.ne L(mutual_align) |
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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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L(loop_aligned): |
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ldr data1, [src1], #8 |
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ldr data2, [src2], #8 |
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L(start_realigned): |
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sub tmp1, data1, zeroones |
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orr tmp2, data1, #REP8_7f |
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eor diff, data1, data2 /* Non-zero if differences found. */ |
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bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ |
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orr syndrome, diff, has_nul |
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cbz syndrome, L(loop_aligned) |
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/* End of performance-critical section -- one 64B cache line. */ |
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L(end): |
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#ifndef __AARCH64EB__ |
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rev syndrome, syndrome |
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rev data1, data1 |
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/* The MS-non-zero bit of the syndrome marks either the first bit |
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that is different, or the top bit of the first zero byte. |
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Shifting left now will bring the critical information into the |
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top bits. */ |
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clz pos, syndrome |
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rev data2, data2 |
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lsl data1, data1, pos |
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lsl data2, data2, pos |
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/* But we need to zero-extend (char is unsigned) the value and then |
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perform a signed 32-bit subtraction. */ |
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lsr data1, data1, #56 |
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sub result, data1, data2, lsr #56 |
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ret |
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#else |
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/* For big-endian we cannot use the trick with the syndrome value |
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as carry-propagation can corrupt the upper bits if the trailing |
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bytes in the string contain 0x01. */ |
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/* However, if there is no NUL byte in the dword, we can generate |
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the result directly. We can't just subtract the bytes as the |
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MSB might be significant. */ |
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cbnz has_nul, 1f |
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cmp data1, data2 |
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cset result, ne |
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cneg result, result, lo |
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ret |
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1: |
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/* Re-compute the NUL-byte detection, using a byte-reversed value. */ |
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rev tmp3, data1 |
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sub tmp1, tmp3, zeroones |
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orr tmp2, tmp3, #REP8_7f |
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bic has_nul, tmp1, tmp2 |
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rev has_nul, has_nul |
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orr syndrome, diff, has_nul |
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clz pos, syndrome |
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/* The MS-non-zero bit of the syndrome marks either the first bit |
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that is different, or the top bit of the first zero byte. |
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Shifting left now will bring the critical information into the |
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top bits. */ |
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lsl data1, data1, pos |
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lsl data2, data2, pos |
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/* But we need to zero-extend (char is unsigned) the value and then |
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perform a signed 32-bit subtraction. */ |
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lsr data1, data1, #56 |
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sub result, data1, data2, lsr #56 |
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ret |
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#endif |
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L(mutual_align): |
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/* Sources are mutually aligned, but are not currently at an |
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alignment boundary. Round down the addresses and then mask off |
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the bytes that preceed the start point. */ |
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bic src1, src1, #7 |
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bic src2, src2, #7 |
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lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ |
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ldr data1, [src1], #8 |
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neg tmp1, tmp1 /* Bits to alignment -64. */ |
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ldr data2, [src2], #8 |
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mov tmp2, #~0 |
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#ifdef __AARCH64EB__ |
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/* Big-endian. Early bytes are at MSB. */ |
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lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ |
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#else |
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/* Little-endian. Early bytes are at LSB. */ |
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lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */ |
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#endif |
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orr data1, data1, tmp2 |
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orr data2, data2, tmp2 |
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b L(start_realigned) |
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L(misaligned8): |
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/* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always |
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checking to make sure that we don't access beyond page boundary in |
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SRC2. */ |
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tst src1, #7 |
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b.eq L(loop_misaligned) |
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L(do_misaligned): |
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ldrb data1w, [src1], #1 |
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ldrb data2w, [src2], #1 |
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cmp data1w, #1 |
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ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ |
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b.ne L(done) |
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tst src1, #7 |
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b.ne L(do_misaligned) |
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L(loop_misaligned): |
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/* Test if we are within the last dword of the end of a 4K page. If |
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yes then jump back to the misaligned loop to copy a byte at a time. */ |
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and tmp1, src2, #0xff8 |
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eor tmp1, tmp1, #0xff8 |
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cbz tmp1, L(do_misaligned) |
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ldr data1, [src1], #8 |
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ldr data2, [src2], #8 |
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sub tmp1, data1, zeroones |
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orr tmp2, data1, #REP8_7f |
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eor diff, data1, data2 /* Non-zero if differences found. */ |
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bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ |
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orr syndrome, diff, has_nul |
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cbz syndrome, L(loop_misaligned) |
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b L(end) |
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L(done): |
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sub result, data1, data2 |
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ret |
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SYM_FUNC_END_PI(strcmp) |
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EXPORT_SYMBOL_NOHWKASAN(strcmp)
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