arch/arm/lib/uaccess.S

   1 /*
   2  *  linux/arch/arm/lib/uaccess.S
   3  *
   4  *  Copyright (C) 1995, 1996,1997,1998 Russell King
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  *  Routines to block copy data to/from user memory
  11  *   These are highly optimised both for the 4k page size
  12  *   and for various alignments.
  13  */
  14 #include <linux/linkage.h>
  15 #include <asm/assembler.h>
  16 #include <asm/errno.h>
  17
  18                 .text
  19
  20 #define PAGE_SHIFT 12
  21
  22 /* Prototype: int __arch_copy_to_user(void *to, const char *from, size_t n)
  23  * Purpose  : copy a block to user memory from kernel memory
  24  * Params   : to   - user memory
  25  *          : from - kernel memory
  26  *          : n    - number of bytes to copy
  27  * Returns  : Number of bytes NOT copied.
  28  */
  29
  30 .c2u_dest_not_aligned:
  31                 rsb     ip, ip, #4
  32                 cmp     ip, #2
  33                 ldrb    r3, [r1], #1
  34 USER(           strbt   r3, [r0], #1)                   @ May fault
  35                 ldrgeb  r3, [r1], #1
  36 USER(           strgebt r3, [r0], #1)                   @ May fault
  37                 ldrgtb  r3, [r1], #1
  38 USER(           strgtbt r3, [r0], #1)                   @ May fault
  39                 sub     r2, r2, ip
  40                 b       .c2u_dest_aligned
  41
  42 ENTRY(__arch_copy_to_user)
  43                 stmfd   sp!, {r2, r4 - r7, lr}
  44                 cmp     r2, #4
  45                 blt     .c2u_not_enough
  46                 ands    ip, r0, #3
  47                 bne     .c2u_dest_not_aligned
  48 .c2u_dest_aligned:
  49
  50                 ands    ip, r1, #3
  51                 bne     .c2u_src_not_aligned
  52 /*
  53  * Seeing as there has to be at least 8 bytes to copy, we can
  54  * copy one word, and force a user-mode page fault...
  55  */
  56
  57 .c2u_0fupi:     subs    r2, r2, #4
  58                 addmi   ip, r2, #4
  59                 bmi     .c2u_0nowords
  60                 ldr     r3, [r1], #4
  61 USER(           strt    r3, [r0], #4)                   @ May fault
  62                 mov     ip, r0, lsl #32 - PAGE_SHIFT    @ On each page, use a ld/st??t instruction
  63                 rsb     ip, ip, #0
  64                 movs    ip, ip, lsr #32 - PAGE_SHIFT
  65                 beq     .c2u_0fupi
  66 /*
  67  * ip = max no. of bytes to copy before needing another "strt" insn
  68  */
  69                 cmp     r2, ip
  70                 movlt   ip, r2
  71                 sub     r2, r2, ip
  72                 subs    ip, ip, #32
  73                 blt     .c2u_0rem8lp
  74
  75 .c2u_0cpy8lp:   ldmia   r1!, {r3 - r6}
  76                 stmia   r0!, {r3 - r6}                  @ Shouldnt fault
  77                 ldmia   r1!, {r3 - r6}
  78                 subs    ip, ip, #32
  79                 stmia   r0!, {r3 - r6}                  @ Shouldnt fault
  80                 bpl     .c2u_0cpy8lp
  81
  82 .c2u_0rem8lp:   cmn     ip, #16
  83                 ldmgeia r1!, {r3 - r6}
  84                 stmgeia r0!, {r3 - r6}                  @ Shouldnt fault
  85                 tst     ip, #8
  86                 ldmneia r1!, {r3 - r4}
  87                 stmneia r0!, {r3 - r4}                  @ Shouldnt fault
  88                 tst     ip, #4
  89                 ldrne   r3, [r1], #4
  90                 strnet  r3, [r0], #4                    @ Shouldnt fault
  91                 ands    ip, ip, #3
  92                 beq     .c2u_0fupi
  93 .c2u_0nowords:  teq     ip, #0
  94                 beq     .c2u_finished
  95 .c2u_nowords:   cmp     ip, #2
  96                 ldrb    r3, [r1], #1
  97 USER(           strbt   r3, [r0], #1)                   @ May fault
  98                 ldrgeb  r3, [r1], #1
  99 USER(           strgebt r3, [r0], #1)                   @ May fault
 100                 ldrgtb  r3, [r1], #1
 101 USER(           strgtbt r3, [r0], #1)                   @ May fault
 102                 b       .c2u_finished
 103
 104 .c2u_not_enough:
 105                 movs    ip, r2
 106                 bne     .c2u_nowords
 107 .c2u_finished:  mov     r0, #0
 108                 LOADREGS(fd,sp!,{r2, r4 - r7, pc})
 109
 110 .c2u_src_not_aligned:
 111                 bic     r1, r1, #3
 112                 ldr     r7, [r1], #4
 113                 cmp     ip, #2
 114                 bgt     .c2u_3fupi
 115                 beq     .c2u_2fupi
 116 .c2u_1fupi:     subs    r2, r2, #4
 117                 addmi   ip, r2, #4
 118                 bmi     .c2u_1nowords
 119                 mov     r3, r7, pull #8
 120                 ldr     r7, [r1], #4
 121                 orr     r3, r3, r7, push #24
 122 USER(           strt    r3, [r0], #4)                   @ May fault
 123                 mov     ip, r0, lsl #32 - PAGE_SHIFT
 124                 rsb     ip, ip, #0
 125                 movs    ip, ip, lsr #32 - PAGE_SHIFT
 126                 beq     .c2u_1fupi
 127                 cmp     r2, ip
 128                 movlt   ip, r2
 129                 sub     r2, r2, ip
 130                 subs    ip, ip, #16
 131                 blt     .c2u_1rem8lp
 132
 133 .c2u_1cpy8lp:   mov     r3, r7, pull #8
 134                 ldmia   r1!, {r4 - r7}
 135                 subs    ip, ip, #16
 136                 orr     r3, r3, r4, push #24
 137                 mov     r4, r4, pull #8
 138                 orr     r4, r4, r5, push #24
 139                 mov     r5, r5, pull #8
 140                 orr     r5, r5, r6, push #24
 141                 mov     r6, r6, pull #8
 142                 orr     r6, r6, r7, push #24
 143                 stmia   r0!, {r3 - r6}                  @ Shouldnt fault
 144                 bpl     .c2u_1cpy8lp
 145
 146 .c2u_1rem8lp:   tst     ip, #8
 147                 movne   r3, r7, pull #8
 148                 ldmneia r1!, {r4, r7}
 149                 orrne   r3, r3, r4, push #24
 150                 movne   r4, r4, pull #8
 151                 orrne   r4, r4, r7, push #24
 152                 stmneia r0!, {r3 - r4}                  @ Shouldnt fault
 153                 tst     ip, #4
 154                 movne   r3, r7, pull #8
 155                 ldrne   r7, [r1], #4
 156                 orrne   r3, r3, r7, push #24
 157                 strnet  r3, [r0], #4                    @ Shouldnt fault
 158                 ands    ip, ip, #3
 159                 beq     .c2u_1fupi
 160 .c2u_1nowords:  mov     r3, r7, get_byte_1
 161                 teq     ip, #0
 162                 beq     .c2u_finished
 163                 cmp     ip, #2
 164 USER(           strbt   r3, [r0], #1)                   @ May fault
 165                 movge   r3, r7, get_byte_2
 166 USER(           strgebt r3, [r0], #1)                   @ May fault
 167                 movgt   r3, r7, get_byte_3
 168 USER(           strgtbt r3, [r0], #1)                   @ May fault
 169                 b       .c2u_finished
 170
 171 .c2u_2fupi:     subs    r2, r2, #4
 172                 addmi   ip, r2, #4
 173                 bmi     .c2u_2nowords
 174                 mov     r3, r7, pull #16
 175                 ldr     r7, [r1], #4
 176                 orr     r3, r3, r7, push #16
 177 USER(           strt    r3, [r0], #4)                   @ May fault
 178                 mov     ip, r0, lsl #32 - PAGE_SHIFT
 179                 rsb     ip, ip, #0
 180                 movs    ip, ip, lsr #32 - PAGE_SHIFT
 181                 beq     .c2u_2fupi
 182                 cmp     r2, ip
 183                 movlt   ip, r2
 184                 sub     r2, r2, ip
 185                 subs    ip, ip, #16
 186                 blt     .c2u_2rem8lp
 187
 188 .c2u_2cpy8lp:   mov     r3, r7, pull #16
 189                 ldmia   r1!, {r4 - r7}
 190                 subs    ip, ip, #16
 191                 orr     r3, r3, r4, push #16
 192                 mov     r4, r4, pull #16
 193                 orr     r4, r4, r5, push #16
 194                 mov     r5, r5, pull #16
 195                 orr     r5, r5, r6, push #16
 196                 mov     r6, r6, pull #16
 197                 orr     r6, r6, r7, push #16
 198                 stmia   r0!, {r3 - r6}                  @ Shouldnt fault
 199                 bpl     .c2u_2cpy8lp
 200
 201 .c2u_2rem8lp:   tst     ip, #8
 202                 movne   r3, r7, pull #16
 203                 ldmneia r1!, {r4, r7}
 204                 orrne   r3, r3, r4, push #16
 205                 movne   r4, r4, pull #16
 206                 orrne   r4, r4, r7, push #16
 207                 stmneia r0!, {r3 - r4}                  @ Shouldnt fault
 208                 tst     ip, #4
 209                 movne   r3, r7, pull #16
 210                 ldrne   r7, [r1], #4
 211                 orrne   r3, r3, r7, push #16
 212                 strnet  r3, [r0], #4                    @ Shouldnt fault
 213                 ands    ip, ip, #3
 214                 beq     .c2u_2fupi
 215 .c2u_2nowords:  mov     r3, r7, get_byte_2
 216                 teq     ip, #0
 217                 beq     .c2u_finished
 218                 cmp     ip, #2
 219 USER(           strbt   r3, [r0], #1)                   @ May fault
 220                 movge   r3, r7, get_byte_3
 221 USER(           strgebt r3, [r0], #1)                   @ May fault
 222                 ldrgtb  r3, [r1], #0
 223 USER(           strgtbt r3, [r0], #1)                   @ May fault
 224                 b       .c2u_finished
 225
 226 .c2u_3fupi:     subs    r2, r2, #4
 227                 addmi   ip, r2, #4
 228                 bmi     .c2u_3nowords
 229                 mov     r3, r7, pull #24
 230                 ldr     r7, [r1], #4
 231                 orr     r3, r3, r7, push #8
 232 USER(           strt    r3, [r0], #4)                   @ May fault
 233                 mov     ip, r0, lsl #32 - PAGE_SHIFT
 234                 rsb     ip, ip, #0
 235                 movs    ip, ip, lsr #32 - PAGE_SHIFT
 236                 beq     .c2u_3fupi
 237                 cmp     r2, ip
 238                 movlt   ip, r2
 239                 sub     r2, r2, ip
 240                 subs    ip, ip, #16
 241                 blt     .c2u_3rem8lp
 242
 243 .c2u_3cpy8lp:   mov     r3, r7, pull #24
 244                 ldmia   r1!, {r4 - r7}
 245                 subs    ip, ip, #16
 246                 orr     r3, r3, r4, push #8
 247                 mov     r4, r4, pull #24
 248                 orr     r4, r4, r5, push #8
 249                 mov     r5, r5, pull #24
 250                 orr     r5, r5, r6, push #8
 251                 mov     r6, r6, pull #24
 252                 orr     r6, r6, r7, push #8
 253                 stmia   r0!, {r3 - r6}                  @ Shouldnt fault
 254                 bpl     .c2u_3cpy8lp
 255
 256 .c2u_3rem8lp:   tst     ip, #8
 257                 movne   r3, r7, pull #24
 258                 ldmneia r1!, {r4, r7}
 259                 orrne   r3, r3, r4, push #8
 260                 movne   r4, r4, pull #24
 261                 orrne   r4, r4, r7, push #8
 262                 stmneia r0!, {r3 - r4}                  @ Shouldnt fault
 263                 tst     ip, #4
 264                 movne   r3, r7, pull #24
 265                 ldrne   r7, [r1], #4
 266                 orrne   r3, r3, r7, push #8
 267                 strnet  r3, [r0], #4                    @ Shouldnt fault
 268                 ands    ip, ip, #3
 269                 beq     .c2u_3fupi
 270 .c2u_3nowords:  mov     r3, r7, get_byte_3
 271                 teq     ip, #0
 272                 beq     .c2u_finished
 273                 cmp     ip, #2
 274 USER(           strbt   r3, [r0], #1)                   @ May fault
 275                 ldrgeb  r3, [r1], #1
 276 USER(           strgebt r3, [r0], #1)                   @ May fault
 277                 ldrgtb  r3, [r1], #0
 278 USER(           strgtbt r3, [r0], #1)                   @ May fault
 279                 b       .c2u_finished
 280
 281                 .section .fixup,"ax"
 282                 .align  0
 283 9001:           LOADREGS(fd,sp!, {r0, r4 - r7, pc})
 284                 .previous
 285
 286 /* Prototype: unsigned long __arch_copy_from_user(void *to,const void *from,unsigned long n);
 287  * Purpose  : copy a block from user memory to kernel memory
 288  * Params   : to   - kernel memory
 289  *          : from - user memory
 290  *          : n    - number of bytes to copy
 291  * Returns  : Number of bytes NOT copied.
 292  */
 293 .cfu_dest_not_aligned:
 294                 rsb     ip, ip, #4
 295                 cmp     ip, #2
 296 USER(           ldrbt   r3, [r1], #1)                   @ May fault
 297                 strb    r3, [r0], #1
 298 USER(           ldrgebt r3, [r1], #1)                   @ May fault
 299                 strgeb  r3, [r0], #1
 300 USER(           ldrgtbt r3, [r1], #1)                   @ May fault
 301                 strgtb  r3, [r0], #1
 302                 sub     r2, r2, ip
 303                 b       .cfu_dest_aligned
 304
 305 ENTRY(__arch_copy_from_user)
 306                 stmfd   sp!, {r0, r2, r4 - r7, lr}
 307                 cmp     r2, #4
 308                 blt     .cfu_not_enough
 309                 ands    ip, r0, #3
 310                 bne     .cfu_dest_not_aligned
 311 .cfu_dest_aligned:
 312                 ands    ip, r1, #3
 313                 bne     .cfu_src_not_aligned
 314 /*
 315  * Seeing as there has to be at least 8 bytes to copy, we can
 316  * copy one word, and force a user-mode page fault...
 317  */
 318
 319 .cfu_0fupi:     subs    r2, r2, #4
 320                 addmi   ip, r2, #4
 321                 bmi     .cfu_0nowords
 322 USER(           ldrt    r3, [r1], #4)
 323                 str     r3, [r0], #4
 324                 mov     ip, r1, lsl #32 - PAGE_SHIFT    @ On each page, use a ld/st??t instruction
 325                 rsb     ip, ip, #0
 326                 movs    ip, ip, lsr #32 - PAGE_SHIFT
 327                 beq     .cfu_0fupi
 328 /*
 329  * ip = max no. of bytes to copy before needing another "strt" insn
 330  */
 331                 cmp     r2, ip
 332                 movlt   ip, r2
 333                 sub     r2, r2, ip
 334                 subs    ip, ip, #32
 335                 blt     .cfu_0rem8lp
 336
 337 .cfu_0cpy8lp:   ldmia   r1!, {r3 - r6}                  @ Shouldnt fault
 338                 stmia   r0!, {r3 - r6}
 339                 ldmia   r1!, {r3 - r6}                  @ Shouldnt fault
 340                 subs    ip, ip, #32
 341                 stmia   r0!, {r3 - r6}
 342                 bpl     .cfu_0cpy8lp
 343
 344 .cfu_0rem8lp:   cmn     ip, #16
 345                 ldmgeia r1!, {r3 - r6}                  @ Shouldnt fault
 346                 stmgeia r0!, {r3 - r6}
 347                 tst     ip, #8
 348                 ldmneia r1!, {r3 - r4}                  @ Shouldnt fault
 349                 stmneia r0!, {r3 - r4}
 350                 tst     ip, #4
 351                 ldrnet  r3, [r1], #4                    @ Shouldnt fault
 352                 strne   r3, [r0], #4
 353                 ands    ip, ip, #3
 354                 beq     .cfu_0fupi
 355 .cfu_0nowords:  teq     ip, #0
 356                 beq     .cfu_finished
 357 .cfu_nowords:   cmp     ip, #2
 358 USER(           ldrbt   r3, [r1], #1)                   @ May fault
 359                 strb    r3, [r0], #1
 360 USER(           ldrgebt r3, [r1], #1)                   @ May fault
 361                 strgeb  r3, [r0], #1
 362 USER(           ldrgtbt r3, [r1], #1)                   @ May fault
 363                 strgtb  r3, [r0], #1
 364                 b       .cfu_finished
 365
 366 .cfu_not_enough:
 367                 movs    ip, r2
 368                 bne     .cfu_nowords
 369 .cfu_finished:  mov     r0, #0
 370                 add     sp, sp, #8
 371                 LOADREGS(fd,sp!,{r4 - r7, pc})
 372
 373 .cfu_src_not_aligned:
 374                 bic     r1, r1, #3
 375 USER(           ldrt    r7, [r1], #4)                   @ May fault
 376                 cmp     ip, #2
 377                 bgt     .cfu_3fupi
 378                 beq     .cfu_2fupi
 379 .cfu_1fupi:     subs    r2, r2, #4
 380                 addmi   ip, r2, #4
 381                 bmi     .cfu_1nowords
 382                 mov     r3, r7, pull #8
 383 USER(           ldrt    r7, [r1], #4)                   @ May fault
 384                 orr     r3, r3, r7, push #24
 385                 str     r3, [r0], #4
 386                 mov     ip, r1, lsl #32 - PAGE_SHIFT
 387                 rsb     ip, ip, #0
 388                 movs    ip, ip, lsr #32 - PAGE_SHIFT
 389                 beq     .cfu_1fupi
 390                 cmp     r2, ip
 391                 movlt   ip, r2
 392                 sub     r2, r2, ip
 393                 subs    ip, ip, #16
 394                 blt     .cfu_1rem8lp
 395
 396 .cfu_1cpy8lp:   mov     r3, r7, pull #8
 397                 ldmia   r1!, {r4 - r7}                  @ Shouldnt fault
 398                 subs    ip, ip, #16
 399                 orr     r3, r3, r4, push #24
 400                 mov     r4, r4, pull #8
 401                 orr     r4, r4, r5, push #24
 402                 mov     r5, r5, pull #8
 403                 orr     r5, r5, r6, push #24
 404                 mov     r6, r6, pull #8
 405                 orr     r6, r6, r7, push #24
 406                 stmia   r0!, {r3 - r6}
 407                 bpl     .cfu_1cpy8lp
 408
 409 .cfu_1rem8lp:   tst     ip, #8
 410                 movne   r3, r7, pull #8
 411                 ldmneia r1!, {r4, r7}                   @ Shouldnt fault
 412                 orrne   r3, r3, r4, push #24
 413                 movne   r4, r4, pull #8
 414                 orrne   r4, r4, r7, push #24
 415                 stmneia r0!, {r3 - r4}
 416                 tst     ip, #4
 417                 movne   r3, r7, pull #8
 418 USER(           ldrnet  r7, [r1], #4)                   @ May fault
 419                 orrne   r3, r3, r7, push #24
 420                 strne   r3, [r0], #4
 421                 ands    ip, ip, #3
 422                 beq     .cfu_1fupi
 423 .cfu_1nowords:  mov     r3, r7, get_byte_1
 424                 teq     ip, #0
 425                 beq     .cfu_finished
 426                 cmp     ip, #2
 427                 strb    r3, [r0], #1
 428                 movge   r3, r7, get_byte_2
 429                 strgeb  r3, [r0], #1
 430                 movgt   r3, r7, get_byte_3
 431                 strgtb  r3, [r0], #1
 432                 b       .cfu_finished
 433
 434 .cfu_2fupi:     subs    r2, r2, #4
 435                 addmi   ip, r2, #4
 436                 bmi     .cfu_2nowords
 437                 mov     r3, r7, pull #16
 438 USER(           ldrt    r7, [r1], #4)                   @ May fault
 439                 orr     r3, r3, r7, push #16
 440                 str     r3, [r0], #4
 441                 mov     ip, r1, lsl #32 - PAGE_SHIFT
 442                 rsb     ip, ip, #0
 443                 movs    ip, ip, lsr #32 - PAGE_SHIFT
 444                 beq     .cfu_2fupi
 445                 cmp     r2, ip
 446                 movlt   ip, r2
 447                 sub     r2, r2, ip
 448                 subs    ip, ip, #16
 449                 blt     .cfu_2rem8lp
 450
 451 .cfu_2cpy8lp:   mov     r3, r7, pull #16
 452                 ldmia   r1!, {r4 - r7}                  @ Shouldnt fault
 453                 subs    ip, ip, #16
 454                 orr     r3, r3, r4, push #16
 455                 mov     r4, r4, pull #16
 456                 orr     r4, r4, r5, push #16
 457                 mov     r5, r5, pull #16
 458                 orr     r5, r5, r6, push #16
 459                 mov     r6, r6, pull #16
 460                 orr     r6, r6, r7, push #16
 461                 stmia   r0!, {r3 - r6}
 462                 bpl     .cfu_2cpy8lp
 463
 464 .cfu_2rem8lp:   tst     ip, #8
 465                 movne   r3, r7, pull #16
 466                 ldmneia r1!, {r4, r7}                   @ Shouldnt fault
 467                 orrne   r3, r3, r4, push #16
 468                 movne   r4, r4, pull #16
 469                 orrne   r4, r4, r7, push #16
 470                 stmneia r0!, {r3 - r4}
 471                 tst     ip, #4
 472                 movne   r3, r7, pull #16
 473 USER(           ldrnet  r7, [r1], #4)                   @ May fault
 474                 orrne   r3, r3, r7, push #16
 475                 strne   r3, [r0], #4
 476                 ands    ip, ip, #3
 477                 beq     .cfu_2fupi
 478 .cfu_2nowords:  mov     r3, r7, get_byte_2
 479                 teq     ip, #0
 480                 beq     .cfu_finished
 481                 cmp     ip, #2
 482                 strb    r3, [r0], #1
 483                 movge   r3, r7, get_byte_3
 484                 strgeb  r3, [r0], #1
 485 USER(           ldrgtbt r3, [r1], #0)                   @ May fault
 486                 strgtb  r3, [r0], #1
 487                 b       .cfu_finished
 488
 489 .cfu_3fupi:     subs    r2, r2, #4
 490                 addmi   ip, r2, #4
 491                 bmi     .cfu_3nowords
 492                 mov     r3, r7, pull #24
 493 USER(           ldrt    r7, [r1], #4)                   @ May fault
 494                 orr     r3, r3, r7, push #8
 495                 str     r3, [r0], #4
 496                 mov     ip, r1, lsl #32 - PAGE_SHIFT
 497                 rsb     ip, ip, #0
 498                 movs    ip, ip, lsr #32 - PAGE_SHIFT
 499                 beq     .cfu_3fupi
 500                 cmp     r2, ip
 501                 movlt   ip, r2
 502                 sub     r2, r2, ip
 503                 subs    ip, ip, #16
 504                 blt     .cfu_3rem8lp
 505
 506 .cfu_3cpy8lp:   mov     r3, r7, pull #24
 507                 ldmia   r1!, {r4 - r7}                  @ Shouldnt fault
 508                 orr     r3, r3, r4, push #8
 509                 mov     r4, r4, pull #24
 510                 orr     r4, r4, r5, push #8
 511                 mov     r5, r5, pull #24
 512                 orr     r5, r5, r6, push #8
 513                 mov     r6, r6, pull #24
 514                 orr     r6, r6, r7, push #8
 515                 stmia   r0!, {r3 - r6}
 516                 subs    ip, ip, #16
 517                 bpl     .cfu_3cpy8lp
 518
 519 .cfu_3rem8lp:   tst     ip, #8
 520                 movne   r3, r7, pull #24
 521                 ldmneia r1!, {r4, r7}                   @ Shouldnt fault
 522                 orrne   r3, r3, r4, push #8
 523                 movne   r4, r4, pull #24
 524                 orrne   r4, r4, r7, push #8
 525                 stmneia r0!, {r3 - r4}
 526                 tst     ip, #4
 527                 movne   r3, r7, pull #24
 528 USER(           ldrnet  r7, [r1], #4)                   @ May fault
 529                 orrne   r3, r3, r7, push #8
 530                 strne   r3, [r0], #4
 531                 ands    ip, ip, #3
 532                 beq     .cfu_3fupi
 533 .cfu_3nowords:  mov     r3, r7, get_byte_3
 534                 teq     ip, #0
 535                 beq     .cfu_finished
 536                 cmp     ip, #2
 537                 strb    r3, [r0], #1
 538 USER(           ldrgebt r3, [r1], #1)                   @ May fault
 539                 strgeb  r3, [r0], #1
 540 USER(           ldrgtbt r3, [r1], #1)                   @ May fault
 541                 strgtb  r3, [r0], #1
 542                 b       .cfu_finished
 543
 544                 .section .fixup,"ax"
 545                 .align  0
 546                 /*
 547                  * We took an exception.  r0 contains a pointer to
 548                  * the byte not copied.
 549                  */
 550 9001:           ldr     r2, [sp], #4                    @ void *to
 551                 sub     r2, r0, r2                      @ bytes copied
 552                 ldr     r1, [sp], #4                    @ unsigned long count
 553                 subs    r4, r1, r2                      @ bytes left to copy
 554                 movne   r1, r4
 555                 blne    __memzero
 556                 mov     r0, r4
 557                 LOADREGS(fd,sp!, {r4 - r7, pc})
 558                 .previous
 559