arch/xtensa/lib/strnlen_user.S

   1 /*
   2  *  arch/xtensa/lib/strnlen_user.S
   3  *
   4  *  This file is subject to the terms and conditions of the GNU General
   5  *  Public License.  See the file "COPYING" in the main directory of
   6  *  this archive for more details.
   7  *
   8  *  Returns strnlen, including trailing zero terminator.
   9  *  Zero indicates error.
  10  *
  11  *  Copyright (C) 2002 Tensilica Inc.
  12  */
  13
  14 #include <variant/core.h>
  15
  16 /* Load or store instructions that may cause exceptions use the EX macro. */
  17
  18 #define EX(insn,reg1,reg2,offset,handler)       \
  19 9:      insn    reg1, reg2, offset;             \
  20         .section __ex_table, "a";               \
  21         .word   9b, handler;                    \
  22         .previous
  23
  24 /*
  25  * size_t __strnlen_user(const char *s, size_t len)
  26  */
  27
  28 #ifdef __XTENSA_EB__
  29 # define MASK0 0xff000000
  30 # define MASK1 0x00ff0000
  31 # define MASK2 0x0000ff00
  32 # define MASK3 0x000000ff
  33 #else
  34 # define MASK0 0x000000ff
  35 # define MASK1 0x0000ff00
  36 # define MASK2 0x00ff0000
  37 # define MASK3 0xff000000
  38 #endif
  39
  40 # Register use:
  41 #   a2/ src
  42 #   a3/ len
  43 #   a4/ tmp
  44 #   a5/ mask0
  45 #   a6/ mask1
  46 #   a7/ mask2
  47 #   a8/ mask3
  48 #   a9/ tmp
  49 #   a10/ tmp
  50
  51 .text
  52 .align  4
  53 .global __strnlen_user
  54 .type   __strnlen_user,@function
  55 __strnlen_user:
  56         entry   sp, 16          # minimal stack frame
  57         # a2/ s, a3/ len
  58         addi    a4, a2, -4      # because we overincrement at the end;
  59                                 # we compensate with load offsets of 4
  60         movi    a5, MASK0       # mask for byte 0
  61         movi    a6, MASK1       # mask for byte 1
  62         movi    a7, MASK2       # mask for byte 2
  63         movi    a8, MASK3       # mask for byte 3
  64         bbsi.l  a2, 0, .L1mod2  # if only  8-bit aligned
  65         bbsi.l  a2, 1, .L2mod4  # if only 16-bit aligned
  66
  67 /*
  68  * String is word-aligned.
  69  */
  70 .Laligned:
  71         srli    a10, a3, 2      # number of loop iterations with 4B per loop
  72 #if XCHAL_HAVE_LOOPS
  73         loopnez a10, .Ldone
  74 #else
  75         beqz    a10, .Ldone
  76         slli    a10, a10, 2
  77         add     a10, a10, a4    # a10 = end of last 4B chunk
  78 #endif /* XCHAL_HAVE_LOOPS */
  79 .Loop:
  80         EX(l32i, a9, a4, 4, lenfixup)   # get next word of string
  81         addi    a4, a4, 4               # advance string pointer
  82         bnone   a9, a5, .Lz0            # if byte 0 is zero
  83         bnone   a9, a6, .Lz1            # if byte 1 is zero
  84         bnone   a9, a7, .Lz2            # if byte 2 is zero
  85         bnone   a9, a8, .Lz3            # if byte 3 is zero
  86 #if !XCHAL_HAVE_LOOPS
  87         blt     a4, a10, .Loop
  88 #endif
  89
  90 .Ldone:
  91         EX(l32i, a9, a4, 4, lenfixup)   # load 4 bytes for remaining checks
  92
  93         bbci.l  a3, 1, .L100
  94         # check two more bytes (bytes 0, 1 of word)
  95         addi    a4, a4, 2       # advance string pointer
  96         bnone   a9, a5, .Lz0    # if byte 0 is zero
  97         bnone   a9, a6, .Lz1    # if byte 1 is zero
  98 .L100:
  99         bbci.l  a3, 0, .L101
 100         # check one more byte (byte 2 of word)
 101         # Actually, we don't need to check.  Zero or nonzero, we'll add one.
 102         # Do not add an extra one for the NULL terminator since we have
 103         #  exhausted the original len parameter.
 104         addi    a4, a4, 1       # advance string pointer
 105 .L101:
 106         sub     a2, a4, a2      # compute length
 107         retw
 108
 109 # NOTE that in several places below, we point to the byte just after
 110 # the zero byte in order to include the NULL terminator in the count.
 111
 112 .Lz3:   # byte 3 is zero
 113         addi    a4, a4, 3       # point to zero byte
 114 .Lz0:   # byte 0 is zero
 115         addi    a4, a4, 1       # point just beyond zero byte
 116         sub     a2, a4, a2      # subtract to get length
 117         retw
 118 .Lz1:   # byte 1 is zero
 119         addi    a4, a4, 1+1     # point just beyond zero byte
 120         sub     a2, a4, a2      # subtract to get length
 121         retw
 122 .Lz2:   # byte 2 is zero
 123         addi    a4, a4, 2+1     # point just beyond zero byte
 124         sub     a2, a4, a2      # subtract to get length
 125         retw
 126
 127 .L1mod2:        # address is odd
 128         EX(l8ui, a9, a4, 4, lenfixup)   # get byte 0
 129         addi    a4, a4, 1               # advance string pointer
 130         beqz    a9, .Lz3                # if byte 0 is zero
 131         bbci.l  a4, 1, .Laligned        # if string pointer is now word-aligned
 132
 133 .L2mod4:        # address is 2 mod 4
 134         addi    a4, a4, 2       # advance ptr for aligned access
 135         EX(l32i, a9, a4, 0, lenfixup)   # get word with first two bytes of string
 136         bnone   a9, a7, .Lz2    # if byte 2 (of word, not string) is zero
 137         bany    a9, a8, .Laligned # if byte 3 (of word, not string) is nonzero
 138         # byte 3 is zero
 139         addi    a4, a4, 3+1     # point just beyond zero byte
 140         sub     a2, a4, a2      # subtract to get length
 141         retw
 142
 143         .section .fixup, "ax"
 144         .align  4
 145 lenfixup:
 146         movi    a2, 0
 147         retw