linux/arch/arm64/lib/strncmp.S
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   1/* SPDX-License-Identifier: GPL-2.0-only */
   2/*
   3 * Copyright (C) 2013 ARM Ltd.
   4 * Copyright (C) 2013 Linaro.
   5 *
   6 * This code is based on glibc cortex strings work originally authored by Linaro
   7 * be found @
   8 *
   9 * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
  10 * files/head:/src/aarch64/
  11 */
  12
  13#include <linux/linkage.h>
  14#include <asm/assembler.h>
  15
  16/*
  17 * compare two strings
  18 *
  19 * Parameters:
  20 *  x0 - const string 1 pointer
  21 *  x1 - const string 2 pointer
  22 *  x2 - the maximal length to be compared
  23 * Returns:
  24 *  x0 - an integer less than, equal to, or greater than zero if s1 is found,
  25 *     respectively, to be less than, to match, or be greater than s2.
  26 */
  27
  28#define REP8_01 0x0101010101010101
  29#define REP8_7f 0x7f7f7f7f7f7f7f7f
  30#define REP8_80 0x8080808080808080
  31
  32/* Parameters and result.  */
  33src1            .req    x0
  34src2            .req    x1
  35limit           .req    x2
  36result          .req    x0
  37
  38/* Internal variables.  */
  39data1           .req    x3
  40data1w          .req    w3
  41data2           .req    x4
  42data2w          .req    w4
  43has_nul         .req    x5
  44diff            .req    x6
  45syndrome        .req    x7
  46tmp1            .req    x8
  47tmp2            .req    x9
  48tmp3            .req    x10
  49zeroones        .req    x11
  50pos             .req    x12
  51limit_wd        .req    x13
  52mask            .req    x14
  53endloop         .req    x15
  54
  55WEAK(strncmp)
  56        cbz     limit, .Lret0
  57        eor     tmp1, src1, src2
  58        mov     zeroones, #REP8_01
  59        tst     tmp1, #7
  60        b.ne    .Lmisaligned8
  61        ands    tmp1, src1, #7
  62        b.ne    .Lmutual_align
  63        /* Calculate the number of full and partial words -1.  */
  64        /*
  65        * when limit is mulitply of 8, if not sub 1,
  66        * the judgement of last dword will wrong.
  67        */
  68        sub     limit_wd, limit, #1 /* limit != 0, so no underflow.  */
  69        lsr     limit_wd, limit_wd, #3  /* Convert to Dwords.  */
  70
  71        /*
  72        * NUL detection works on the principle that (X - 1) & (~X) & 0x80
  73        * (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
  74        * can be done in parallel across the entire word.
  75        */
  76.Lloop_aligned:
  77        ldr     data1, [src1], #8
  78        ldr     data2, [src2], #8
  79.Lstart_realigned:
  80        subs    limit_wd, limit_wd, #1
  81        sub     tmp1, data1, zeroones
  82        orr     tmp2, data1, #REP8_7f
  83        eor     diff, data1, data2  /* Non-zero if differences found.  */
  84        csinv   endloop, diff, xzr, pl  /* Last Dword or differences.*/
  85        bics    has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
  86        ccmp    endloop, #0, #0, eq
  87        b.eq    .Lloop_aligned
  88
  89        /*Not reached the limit, must have found the end or a diff.  */
  90        tbz     limit_wd, #63, .Lnot_limit
  91
  92        /* Limit % 8 == 0 => all bytes significant.  */
  93        ands    limit, limit, #7
  94        b.eq    .Lnot_limit
  95
  96        lsl     limit, limit, #3    /* Bits -> bytes.  */
  97        mov     mask, #~0
  98CPU_BE( lsr     mask, mask, limit )
  99CPU_LE( lsl     mask, mask, limit )
 100        bic     data1, data1, mask
 101        bic     data2, data2, mask
 102
 103        /* Make sure that the NUL byte is marked in the syndrome.  */
 104        orr     has_nul, has_nul, mask
 105
 106.Lnot_limit:
 107        orr     syndrome, diff, has_nul
 108        b       .Lcal_cmpresult
 109
 110.Lmutual_align:
 111        /*
 112        * Sources are mutually aligned, but are not currently at an
 113        * alignment boundary.  Round down the addresses and then mask off
 114        * the bytes that precede the start point.
 115        * We also need to adjust the limit calculations, but without
 116        * overflowing if the limit is near ULONG_MAX.
 117        */
 118        bic     src1, src1, #7
 119        bic     src2, src2, #7
 120        ldr     data1, [src1], #8
 121        neg     tmp3, tmp1, lsl #3  /* 64 - bits(bytes beyond align). */
 122        ldr     data2, [src2], #8
 123        mov     tmp2, #~0
 124        sub     limit_wd, limit, #1 /* limit != 0, so no underflow.  */
 125        /* Big-endian.  Early bytes are at MSB.  */
 126CPU_BE( lsl     tmp2, tmp2, tmp3 )      /* Shift (tmp1 & 63).  */
 127        /* Little-endian.  Early bytes are at LSB.  */
 128CPU_LE( lsr     tmp2, tmp2, tmp3 )      /* Shift (tmp1 & 63).  */
 129
 130        and     tmp3, limit_wd, #7
 131        lsr     limit_wd, limit_wd, #3
 132        /* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
 133        add     limit, limit, tmp1
 134        add     tmp3, tmp3, tmp1
 135        orr     data1, data1, tmp2
 136        orr     data2, data2, tmp2
 137        add     limit_wd, limit_wd, tmp3, lsr #3
 138        b       .Lstart_realigned
 139
 140/*when src1 offset is not equal to src2 offset...*/
 141.Lmisaligned8:
 142        cmp     limit, #8
 143        b.lo    .Ltiny8proc /*limit < 8... */
 144        /*
 145        * Get the align offset length to compare per byte first.
 146        * After this process, one string's address will be aligned.*/
 147        and     tmp1, src1, #7
 148        neg     tmp1, tmp1
 149        add     tmp1, tmp1, #8
 150        and     tmp2, src2, #7
 151        neg     tmp2, tmp2
 152        add     tmp2, tmp2, #8
 153        subs    tmp3, tmp1, tmp2
 154        csel    pos, tmp1, tmp2, hi /*Choose the maximum. */
 155        /*
 156        * Here, limit is not less than 8, so directly run .Ltinycmp
 157        * without checking the limit.*/
 158        sub     limit, limit, pos
 159.Ltinycmp:
 160        ldrb    data1w, [src1], #1
 161        ldrb    data2w, [src2], #1
 162        subs    pos, pos, #1
 163        ccmp    data1w, #1, #0, ne  /* NZCV = 0b0000.  */
 164        ccmp    data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
 165        b.eq    .Ltinycmp
 166        cbnz    pos, 1f /*find the null or unequal...*/
 167        cmp     data1w, #1
 168        ccmp    data1w, data2w, #0, cs
 169        b.eq    .Lstart_align /*the last bytes are equal....*/
 1701:
 171        sub     result, data1, data2
 172        ret
 173
 174.Lstart_align:
 175        lsr     limit_wd, limit, #3
 176        cbz     limit_wd, .Lremain8
 177        /*process more leading bytes to make str1 aligned...*/
 178        ands    xzr, src1, #7
 179        b.eq    .Lrecal_offset
 180        add     src1, src1, tmp3        /*tmp3 is positive in this branch.*/
 181        add     src2, src2, tmp3
 182        ldr     data1, [src1], #8
 183        ldr     data2, [src2], #8
 184
 185        sub     limit, limit, tmp3
 186        lsr     limit_wd, limit, #3
 187        subs    limit_wd, limit_wd, #1
 188
 189        sub     tmp1, data1, zeroones
 190        orr     tmp2, data1, #REP8_7f
 191        eor     diff, data1, data2  /* Non-zero if differences found.  */
 192        csinv   endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
 193        bics    has_nul, tmp1, tmp2
 194        ccmp    endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
 195        b.ne    .Lunequal_proc
 196        /*How far is the current str2 from the alignment boundary...*/
 197        and     tmp3, tmp3, #7
 198.Lrecal_offset:
 199        neg     pos, tmp3
 200.Lloopcmp_proc:
 201        /*
 202        * Divide the eight bytes into two parts. First,backwards the src2
 203        * to an alignment boundary,load eight bytes from the SRC2 alignment
 204        * boundary,then compare with the relative bytes from SRC1.
 205        * If all 8 bytes are equal,then start the second part's comparison.
 206        * Otherwise finish the comparison.
 207        * This special handle can garantee all the accesses are in the
 208        * thread/task space in avoid to overrange access.
 209        */
 210        ldr     data1, [src1,pos]
 211        ldr     data2, [src2,pos]
 212        sub     tmp1, data1, zeroones
 213        orr     tmp2, data1, #REP8_7f
 214        bics    has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
 215        eor     diff, data1, data2  /* Non-zero if differences found.  */
 216        csinv   endloop, diff, xzr, eq
 217        cbnz    endloop, .Lunequal_proc
 218
 219        /*The second part process*/
 220        ldr     data1, [src1], #8
 221        ldr     data2, [src2], #8
 222        subs    limit_wd, limit_wd, #1
 223        sub     tmp1, data1, zeroones
 224        orr     tmp2, data1, #REP8_7f
 225        eor     diff, data1, data2  /* Non-zero if differences found.  */
 226        csinv   endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
 227        bics    has_nul, tmp1, tmp2
 228        ccmp    endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
 229        b.eq    .Lloopcmp_proc
 230
 231.Lunequal_proc:
 232        orr     syndrome, diff, has_nul
 233        cbz     syndrome, .Lremain8
 234.Lcal_cmpresult:
 235        /*
 236        * reversed the byte-order as big-endian,then CLZ can find the most
 237        * significant zero bits.
 238        */
 239CPU_LE( rev     syndrome, syndrome )
 240CPU_LE( rev     data1, data1 )
 241CPU_LE( rev     data2, data2 )
 242        /*
 243        * For big-endian we cannot use the trick with the syndrome value
 244        * as carry-propagation can corrupt the upper bits if the trailing
 245        * bytes in the string contain 0x01.
 246        * However, if there is no NUL byte in the dword, we can generate
 247        * the result directly.  We can't just subtract the bytes as the
 248        * MSB might be significant.
 249        */
 250CPU_BE( cbnz    has_nul, 1f )
 251CPU_BE( cmp     data1, data2 )
 252CPU_BE( cset    result, ne )
 253CPU_BE( cneg    result, result, lo )
 254CPU_BE( ret )
 255CPU_BE( 1: )
 256        /* Re-compute the NUL-byte detection, using a byte-reversed value.*/
 257CPU_BE( rev     tmp3, data1 )
 258CPU_BE( sub     tmp1, tmp3, zeroones )
 259CPU_BE( orr     tmp2, tmp3, #REP8_7f )
 260CPU_BE( bic     has_nul, tmp1, tmp2 )
 261CPU_BE( rev     has_nul, has_nul )
 262CPU_BE( orr     syndrome, diff, has_nul )
 263        /*
 264        * The MS-non-zero bit of the syndrome marks either the first bit
 265        * that is different, or the top bit of the first zero byte.
 266        * Shifting left now will bring the critical information into the
 267        * top bits.
 268        */
 269        clz     pos, syndrome
 270        lsl     data1, data1, pos
 271        lsl     data2, data2, pos
 272        /*
 273        * But we need to zero-extend (char is unsigned) the value and then
 274        * perform a signed 32-bit subtraction.
 275        */
 276        lsr     data1, data1, #56
 277        sub     result, data1, data2, lsr #56
 278        ret
 279
 280.Lremain8:
 281        /* Limit % 8 == 0 => all bytes significant.  */
 282        ands    limit, limit, #7
 283        b.eq    .Lret0
 284.Ltiny8proc:
 285        ldrb    data1w, [src1], #1
 286        ldrb    data2w, [src2], #1
 287        subs    limit, limit, #1
 288
 289        ccmp    data1w, #1, #0, ne  /* NZCV = 0b0000.  */
 290        ccmp    data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
 291        b.eq    .Ltiny8proc
 292        sub     result, data1, data2
 293        ret
 294
 295.Lret0:
 296        mov     result, #0
 297        ret
 298ENDPIPROC(strncmp)
 299EXPORT_SYMBOL_NOKASAN(strncmp)
 300
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