/* SPDX-License-Identifier: GPL-2.0-only */ /* * Copyright (C) 2013 ARM Ltd. * Copyright (C) 2013 Linaro. * * This code is based on glibc cortex strings work originally authored by Linaro * be found @ * * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/ * files/head:/src/aarch64/ */ #include #include /* * compare two strings * * Parameters: * x0 - const string 1 pointer * x1 - const string 2 pointer * Returns: * x0 - an integer less than, equal to, or greater than zero * if s1 is found, respectively, to be less than, to match, * or be greater than s2. */ #define REP8_01 0x0101010101010101 #define REP8_7f 0x7f7f7f7f7f7f7f7f #define REP8_80 0x8080808080808080 /* Parameters and result. */ src1 .req x0 src2 .req x1 result .req x0 /* Internal variables. */ data1 .req x2 data1w .req w2 data2 .req x3 data2w .req w3 has_nul .req x4 diff .req x5 syndrome .req x6 tmp1 .req x7 tmp2 .req x8 tmp3 .req x9 zeroones .req x10 pos .req x11 SYM_FUNC_START_WEAK_PI(strcmp) eor tmp1, src1, src2 mov zeroones, #REP8_01 tst tmp1, #7 b.ne .Lmisaligned8 ands tmp1, src1, #7 b.ne .Lmutual_align /* * 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. */ .Lloop_aligned: ldr data1, [src1], #8 ldr data2, [src2], #8 .Lstart_realigned: sub tmp1, data1, zeroones orr tmp2, data1, #REP8_7f eor diff, data1, data2 /* Non-zero if differences found. */ bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */ orr syndrome, diff, has_nul cbz syndrome, .Lloop_aligned b .Lcal_cmpresult .Lmutual_align: /* * Sources are mutually aligned, but are not currently at an * alignment boundary. Round down the addresses and then mask off * the bytes that preceed the start point. */ bic src1, src1, #7 bic src2, src2, #7 lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */ ldr data1, [src1], #8 neg tmp1, tmp1 /* Bits to alignment -64. */ ldr data2, [src2], #8 mov tmp2, #~0 /* Big-endian. Early bytes are at MSB. */ CPU_BE( lsl tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */ /* Little-endian. Early bytes are at LSB. */ CPU_LE( lsr tmp2, tmp2, tmp1 ) /* Shift (tmp1 & 63). */ orr data1, data1, tmp2 orr data2, data2, tmp2 b .Lstart_realigned .Lmisaligned8: /* * Get the align offset length to compare per byte first. * After this process, one string's address will be aligned. */ and tmp1, src1, #7 neg tmp1, tmp1 add tmp1, tmp1, #8 and tmp2, src2, #7 neg tmp2, tmp2 add tmp2, tmp2, #8 subs tmp3, tmp1, tmp2 csel pos, tmp1, tmp2, hi /*Choose the maximum. */ .Ltinycmp: ldrb data1w, [src1], #1 ldrb data2w, [src2], #1 subs pos, pos, #1 ccmp data1w, #1, #0, ne /* NZCV = 0b0000. */ ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */ b.eq .Ltinycmp cbnz pos, 1f /*find the null or unequal...*/ cmp data1w, #1 ccmp data1w, data2w, #0, cs b.eq .Lstart_align /*the last bytes are equal....*/ 1: sub result, data1, data2 ret .Lstart_align: ands xzr, src1, #7 b.eq .Lrecal_offset /*process more leading bytes to make str1 aligned...*/ add src1, src1, tmp3 add src2, src2, tmp3 /*load 8 bytes from aligned str1 and non-aligned str2..*/ ldr data1, [src1], #8 ldr data2, [src2], #8 sub tmp1, data1, zeroones orr tmp2, data1, #REP8_7f bic has_nul, tmp1, tmp2 eor diff, data1, data2 /* Non-zero if differences found. */ orr syndrome, diff, has_nul cbnz syndrome, .Lcal_cmpresult /*How far is the current str2 from the alignment boundary...*/ and tmp3, tmp3, #7 .Lrecal_offset: neg pos, tmp3 .Lloopcmp_proc: /* * Divide the eight bytes into two parts. First,backwards the src2 * to an alignment boundary,load eight bytes from the SRC2 alignment * boundary,then compare with the relative bytes from SRC1. * If all 8 bytes are equal,then start the second part's comparison. * Otherwise finish the comparison. * This special handle can garantee all the accesses are in the * thread/task space in avoid to overrange access. */ ldr data1, [src1,pos] ldr data2, [src2,pos] sub tmp1, data1, zeroones orr tmp2, data1, #REP8_7f bic has_nul, tmp1, tmp2 eor diff, data1, data2 /* Non-zero if differences found. */ orr syndrome, diff, has_nul cbnz syndrome, .Lcal_cmpresult /*The second part process*/ ldr data1, [src1], #8 ldr data2, [src2], #8 sub tmp1, data1, zeroones orr tmp2, data1, #REP8_7f bic has_nul, tmp1, tmp2 eor diff, data1, data2 /* Non-zero if differences found. */ orr syndrome, diff, has_nul cbz syndrome, .Lloopcmp_proc .Lcal_cmpresult: /* * reversed the byte-order as big-endian,then CLZ can find the most * significant zero bits. */ CPU_LE( rev syndrome, syndrome ) CPU_LE( rev data1, data1 ) CPU_LE( rev data2, data2 ) /* * For big-endian we cannot use the trick with the syndrome value * as carry-propagation can corrupt the upper bits if the trailing * bytes in the string contain 0x01. * However, if there is no NUL byte in the dword, we can generate * the result directly. We cannot just subtract the bytes as the * MSB might be significant. */ CPU_BE( cbnz has_nul, 1f ) CPU_BE( cmp data1, data2 ) CPU_BE( cset result, ne ) CPU_BE( cneg result, result, lo ) CPU_BE( ret ) CPU_BE( 1: ) /*Re-compute the NUL-byte detection, using a byte-reversed value. */ CPU_BE( rev tmp3, data1 ) CPU_BE( sub tmp1, tmp3, zeroones ) CPU_BE( orr tmp2, tmp3, #REP8_7f ) CPU_BE( bic has_nul, tmp1, tmp2 ) CPU_BE( rev has_nul, has_nul ) CPU_BE( orr syndrome, diff, has_nul ) clz pos, syndrome /* * The MS-non-zero bit of the syndrome marks either the first bit * that is different, or the top bit of the first zero byte. * Shifting left now will bring the critical information into the * top bits. */ lsl data1, data1, pos lsl data2, data2, pos /* * But we need to zero-extend (char is unsigned) the value and then * perform a signed 32-bit subtraction. */ lsr data1, data1, #56 sub result, data1, data2, lsr #56 ret SYM_FUNC_END_PI(strcmp) EXPORT_SYMBOL_NOKASAN(strcmp)