arch/xtensa/lib/usercopy.S

   1 /*
   2  *  arch/xtensa/lib/usercopy.S
   3  *
   4  *  Copy to/from user space (derived from arch/xtensa/lib/hal/memcopy.S)
   5  *
   6  *  DO NOT COMBINE this function with <arch/xtensa/lib/hal/memcopy.S>.
   7  *  It needs to remain separate and distinct.  The hal files are part
   8  *  of the Xtensa link-time HAL, and those files may differ per
   9  *  processor configuration.  Patching the kernel for another
  10  *  processor configuration includes replacing the hal files, and we
  11  *  could lose the special functionality for accessing user-space
  12  *  memory during such a patch.  We sacrifice a little code space here
  13  *  in favor to simplify code maintenance.
  14  *
  15  *  This file is subject to the terms and conditions of the GNU General
  16  *  Public License.  See the file "COPYING" in the main directory of
  17  *  this archive for more details.
  18  *
  19  *  Copyright (C) 2002 Tensilica Inc.
  20  */
  21
  22
  23 /*
  24  * size_t __xtensa_copy_user (void *dst, const void *src, size_t len);
  25  *
  26  * The returned value is the number of bytes not copied.  Implies zero
  27  * is success.
  28  *
  29  * The general case algorithm is as follows:
  30  *   If the destination and source are both aligned,
  31  *     do 16B chunks with a loop, and then finish up with
  32  *     8B, 4B, 2B, and 1B copies conditional on the length.
  33  *   If destination is aligned and source unaligned,
  34  *     do the same, but use SRC to align the source data.
  35  *   If destination is unaligned, align it by conditionally
  36  *     copying 1B and 2B and then retest.
  37  *   This code tries to use fall-through braches for the common
  38  *     case of aligned destinations (except for the branches to
  39  *     the alignment label).
  40  *
  41  * Register use:
  42  *      a0/ return address
  43  *      a1/ stack pointer
  44  *      a2/ return value
  45  *      a3/ src
  46  *      a4/ length
  47  *      a5/ dst
  48  *      a6/ tmp
  49  *      a7/ tmp
  50  *      a8/ tmp
  51  *      a9/ tmp
  52  *      a10/ tmp
  53  *      a11/ original length
  54  */
  55
  56 #include <variant/core.h>
  57
  58 #ifdef __XTENSA_EB__
  59 #define ALIGN(R, W0, W1) src    R, W0, W1
  60 #define SSA8(R) ssa8b R
  61 #else
  62 #define ALIGN(R, W0, W1) src    R, W1, W0
  63 #define SSA8(R) ssa8l R
  64 #endif
  65
  66 /* Load or store instructions that may cause exceptions use the EX macro. */
  67
  68 #define EX(insn,reg1,reg2,offset,handler)       \
  69 9:      insn    reg1, reg2, offset;             \
  70         .section __ex_table, "a";               \
  71         .word   9b, handler;                    \
  72         .previous
  73
  74
  75         .text
  76         .align  4
  77         .global __xtensa_copy_user
  78         .type   __xtensa_copy_user,@function
  79 __xtensa_copy_user:
  80         entry   sp, 16          # minimal stack frame
  81         # a2/ dst, a3/ src, a4/ len
  82         mov     a5, a2          # copy dst so that a2 is return value
  83         mov     a11, a4         # preserve original len for error case
  84 .Lcommon:
  85         bbsi.l  a2, 0, .Ldst1mod2 # if dst is 1 mod 2
  86         bbsi.l  a2, 1, .Ldst2mod4 # if dst is 2 mod 4
  87 .Ldstaligned:   # return here from .Ldstunaligned when dst is aligned
  88         srli    a7, a4, 4       # number of loop iterations with 16B
  89                                 # per iteration
  90         movi    a8, 3             # if source is also aligned,
  91         bnone   a3, a8, .Laligned # then use word copy
  92         SSA8(   a3)             # set shift amount from byte offset
  93         bnez    a4, .Lsrcunaligned
  94         movi    a2, 0           # return success for len==0
  95         retw
  96
  97 /*
  98  * Destination is unaligned
  99  */
 100
 101 .Ldst1mod2:     # dst is only byte aligned
 102         bltui   a4, 7, .Lbytecopy       # do short copies byte by byte
 103
 104         # copy 1 byte
 105         EX(l8ui, a6, a3, 0, l_fixup)
 106         addi    a3, a3,  1
 107         EX(s8i, a6, a5,  0, s_fixup)
 108         addi    a5, a5,  1
 109         addi    a4, a4, -1
 110         bbci.l  a5, 1, .Ldstaligned     # if dst is now aligned, then
 111                                         # return to main algorithm
 112 .Ldst2mod4:     # dst 16-bit aligned
 113         # copy 2 bytes
 114         bltui   a4, 6, .Lbytecopy       # do short copies byte by byte
 115         EX(l8ui, a6, a3, 0, l_fixup)
 116         EX(l8ui, a7, a3, 1, l_fixup)
 117         addi    a3, a3,  2
 118         EX(s8i, a6, a5,  0, s_fixup)
 119         EX(s8i, a7, a5,  1, s_fixup)
 120         addi    a5, a5,  2
 121         addi    a4, a4, -2
 122         j       .Ldstaligned    # dst is now aligned, return to main algorithm
 123
 124 /*
 125  * Byte by byte copy
 126  */
 127         .align  4
 128         .byte   0               # 1 mod 4 alignment for LOOPNEZ
 129                                 # (0 mod 4 alignment for LBEG)
 130 .Lbytecopy:
 131 #if XCHAL_HAVE_LOOPS
 132         loopnez a4, .Lbytecopydone
 133 #else /* !XCHAL_HAVE_LOOPS */
 134         beqz    a4, .Lbytecopydone
 135         add     a7, a3, a4      # a7 = end address for source
 136 #endif /* !XCHAL_HAVE_LOOPS */
 137 .Lnextbyte:
 138         EX(l8ui, a6, a3, 0, l_fixup)
 139         addi    a3, a3, 1
 140         EX(s8i, a6, a5, 0, s_fixup)
 141         addi    a5, a5, 1
 142 #if !XCHAL_HAVE_LOOPS
 143         blt     a3, a7, .Lnextbyte
 144 #endif /* !XCHAL_HAVE_LOOPS */
 145 .Lbytecopydone:
 146         movi    a2, 0           # return success for len bytes copied
 147         retw
 148
 149 /*
 150  * Destination and source are word-aligned.
 151  */
 152         # copy 16 bytes per iteration for word-aligned dst and word-aligned src
 153         .align  4               # 1 mod 4 alignment for LOOPNEZ
 154         .byte   0               # (0 mod 4 alignment for LBEG)
 155 .Laligned:
 156 #if XCHAL_HAVE_LOOPS
 157         loopnez a7, .Loop1done
 158 #else /* !XCHAL_HAVE_LOOPS */
 159         beqz    a7, .Loop1done
 160         slli    a8, a7, 4
 161         add     a8, a8, a3      # a8 = end of last 16B source chunk
 162 #endif /* !XCHAL_HAVE_LOOPS */
 163 .Loop1:
 164         EX(l32i, a6, a3,  0, l_fixup)
 165         EX(l32i, a7, a3,  4, l_fixup)
 166         EX(s32i, a6, a5,  0, s_fixup)
 167         EX(l32i, a6, a3,  8, l_fixup)
 168         EX(s32i, a7, a5,  4, s_fixup)
 169         EX(l32i, a7, a3, 12, l_fixup)
 170         EX(s32i, a6, a5,  8, s_fixup)
 171         addi    a3, a3, 16
 172         EX(s32i, a7, a5, 12, s_fixup)
 173         addi    a5, a5, 16
 174 #if !XCHAL_HAVE_LOOPS
 175         blt     a3, a8, .Loop1
 176 #endif /* !XCHAL_HAVE_LOOPS */
 177 .Loop1done:
 178         bbci.l  a4, 3, .L2
 179         # copy 8 bytes
 180         EX(l32i, a6, a3,  0, l_fixup)
 181         EX(l32i, a7, a3,  4, l_fixup)
 182         addi    a3, a3,  8
 183         EX(s32i, a6, a5,  0, s_fixup)
 184         EX(s32i, a7, a5,  4, s_fixup)
 185         addi    a5, a5,  8
 186 .L2:
 187         bbci.l  a4, 2, .L3
 188         # copy 4 bytes
 189         EX(l32i, a6, a3,  0, l_fixup)
 190         addi    a3, a3,  4
 191         EX(s32i, a6, a5,  0, s_fixup)
 192         addi    a5, a5,  4
 193 .L3:
 194         bbci.l  a4, 1, .L4
 195         # copy 2 bytes
 196         EX(l16ui, a6, a3,  0, l_fixup)
 197         addi    a3, a3,  2
 198         EX(s16i,  a6, a5,  0, s_fixup)
 199         addi    a5, a5,  2
 200 .L4:
 201         bbci.l  a4, 0, .L5
 202         # copy 1 byte
 203         EX(l8ui, a6, a3,  0, l_fixup)
 204         EX(s8i,  a6, a5,  0, s_fixup)
 205 .L5:
 206         movi    a2, 0           # return success for len bytes copied
 207         retw
 208
 209 /*
 210  * Destination is aligned, Source is unaligned
 211  */
 212
 213         .align  4
 214         .byte   0               # 1 mod 4 alignement for LOOPNEZ
 215                                 # (0 mod 4 alignment for LBEG)
 216 .Lsrcunaligned:
 217         # copy 16 bytes per iteration for word-aligned dst and unaligned src
 218         and     a10, a3, a8     # save unalignment offset for below
 219         sub     a3, a3, a10     # align a3 (to avoid sim warnings only; not needed for hardware)
 220         EX(l32i, a6, a3, 0, l_fixup)    # load first word
 221 #if XCHAL_HAVE_LOOPS
 222         loopnez a7, .Loop2done
 223 #else /* !XCHAL_HAVE_LOOPS */
 224         beqz    a7, .Loop2done
 225         slli    a10, a7, 4
 226         add     a10, a10, a3    # a10 = end of last 16B source chunk
 227 #endif /* !XCHAL_HAVE_LOOPS */
 228 .Loop2:
 229         EX(l32i, a7, a3,  4, l_fixup)
 230         EX(l32i, a8, a3,  8, l_fixup)
 231         ALIGN(  a6, a6, a7)
 232         EX(s32i, a6, a5,  0, s_fixup)
 233         EX(l32i, a9, a3, 12, l_fixup)
 234         ALIGN(  a7, a7, a8)
 235         EX(s32i, a7, a5,  4, s_fixup)
 236         EX(l32i, a6, a3, 16, l_fixup)
 237         ALIGN(  a8, a8, a9)
 238         EX(s32i, a8, a5,  8, s_fixup)
 239         addi    a3, a3, 16
 240         ALIGN(  a9, a9, a6)
 241         EX(s32i, a9, a5, 12, s_fixup)
 242         addi    a5, a5, 16
 243 #if !XCHAL_HAVE_LOOPS
 244         blt     a3, a10, .Loop2
 245 #endif /* !XCHAL_HAVE_LOOPS */
 246 .Loop2done:
 247         bbci.l  a4, 3, .L12
 248         # copy 8 bytes
 249         EX(l32i, a7, a3,  4, l_fixup)
 250         EX(l32i, a8, a3,  8, l_fixup)
 251         ALIGN(  a6, a6, a7)
 252         EX(s32i, a6, a5,  0, s_fixup)
 253         addi    a3, a3,  8
 254         ALIGN(  a7, a7, a8)
 255         EX(s32i, a7, a5,  4, s_fixup)
 256         addi    a5, a5,  8
 257         mov     a6, a8
 258 .L12:
 259         bbci.l  a4, 2, .L13
 260         # copy 4 bytes
 261         EX(l32i, a7, a3,  4, l_fixup)
 262         addi    a3, a3,  4
 263         ALIGN(  a6, a6, a7)
 264         EX(s32i, a6, a5,  0, s_fixup)
 265         addi    a5, a5,  4
 266         mov     a6, a7
 267 .L13:
 268         add     a3, a3, a10     # readjust a3 with correct misalignment
 269         bbci.l  a4, 1, .L14
 270         # copy 2 bytes
 271         EX(l8ui, a6, a3,  0, l_fixup)
 272         EX(l8ui, a7, a3,  1, l_fixup)
 273         addi    a3, a3,  2
 274         EX(s8i, a6, a5,  0, s_fixup)
 275         EX(s8i, a7, a5,  1, s_fixup)
 276         addi    a5, a5,  2
 277 .L14:
 278         bbci.l  a4, 0, .L15
 279         # copy 1 byte
 280         EX(l8ui, a6, a3,  0, l_fixup)
 281         EX(s8i,  a6, a5,  0, s_fixup)
 282 .L15:
 283         movi    a2, 0           # return success for len bytes copied
 284         retw
 285
 286
 287         .section .fixup, "ax"
 288         .align  4
 289
 290 /* a2 = original dst; a5 = current dst; a11= original len
 291  * bytes_copied = a5 - a2
 292  * retval = bytes_not_copied = original len - bytes_copied
 293  * retval = a11 - (a5 - a2)
 294  *
 295  * Clearing the remaining pieces of kernel memory plugs security
 296  * holes.  This functionality is the equivalent of the *_zeroing
 297  * functions that some architectures provide.
 298  */
 299
 300 .Lmemset:
 301         .word   memset
 302
 303 s_fixup:
 304         sub     a2, a5, a2      /* a2 <-- bytes copied */
 305         sub     a2, a11, a2     /* a2 <-- bytes not copied */
 306         retw
 307
 308 l_fixup:
 309         sub     a2, a5, a2      /* a2 <-- bytes copied */
 310         sub     a2, a11, a2     /* a2 <-- bytes not copied == return value */
 311
 312         /* void *memset(void *s, int c, size_t n); */
 313         mov     a6, a5          /* s */
 314         movi    a7, 0           /* c */
 315         mov     a8, a2          /* n */
 316         l32r    a4, .Lmemset
 317         callx4  a4
 318         /* Ignore memset return value in a6. */
 319         /* a2 still contains bytes not copied. */
 320         retw