arch/arm/lib/memzero.S

   1 /*
   2  *  linux/arch/arm/lib/memzero.S
   3  *
   4  *  Copyright (C) 1995-2000 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 #include <linux/linkage.h>
  11 #include <asm/assembler.h>
  12
  13         .text
  14         .align  5
  15         .word   0
  16 /*
  17  * Align the pointer in r0.  r3 contains the number of bytes that we are
  18  * mis-aligned by, and r1 is the number of bytes.  If r1 < 4, then we
  19  * don't bother; we use byte stores instead.
  20  */
  21 1:      subs    r1, r1, #4              @ 1 do we have enough
  22         blt     5f                      @ 1 bytes to align with?
  23         cmp     r3, #2                  @ 1
  24         strltb  r2, [r0], #1            @ 1
  25         strleb  r2, [r0], #1            @ 1
  26         strb    r2, [r0], #1            @ 1
  27         add     r1, r1, r3              @ 1 (r1 = r1 - (4 - r3))
  28 /*
  29  * The pointer is now aligned and the length is adjusted.  Try doing the
  30  * memzero again.
  31  */
  32
  33 ENTRY(__memzero)
  34         mov     r2, #0                  @ 1
  35         ands    r3, r0, #3              @ 1 unaligned?
  36         bne     1b                      @ 1
  37 /*
  38  * r3 = 0, and we know that the pointer in r0 is aligned to a word boundary.
  39  */
  40         cmp     r1, #16                 @ 1 we can skip this chunk if we
  41         blt     4f                      @ 1 have < 16 bytes
  42 /*
  43  * We need an extra register for this loop - save the return address and
  44  * use the LR
  45  */
  46         str     lr, [sp, #-4]!          @ 1
  47         mov     ip, r2                  @ 1
  48         mov     lr, r2                  @ 1
  49
  50 3:      subs    r1, r1, #64             @ 1 write 32 bytes out per loop
  51         stmgeia r0!, {r2, r3, ip, lr}   @ 4
  52         stmgeia r0!, {r2, r3, ip, lr}   @ 4
  53         stmgeia r0!, {r2, r3, ip, lr}   @ 4
  54         stmgeia r0!, {r2, r3, ip, lr}   @ 4
  55         bgt     3b                      @ 1
  56         LOADREGS(eqfd, sp!, {pc})       @ 1/2 quick exit
  57 /*
  58  * No need to correct the count; we're only testing bits from now on
  59  */
  60         tst     r1, #32                 @ 1
  61         stmneia r0!, {r2, r3, ip, lr}   @ 4
  62         stmneia r0!, {r2, r3, ip, lr}   @ 4
  63         tst     r1, #16                 @ 1 16 bytes or more?
  64         stmneia r0!, {r2, r3, ip, lr}   @ 4
  65         ldr     lr, [sp], #4            @ 1
  66
  67 4:      tst     r1, #8                  @ 1 8 bytes or more?
  68         stmneia r0!, {r2, r3}           @ 2
  69         tst     r1, #4                  @ 1 4 bytes or more?
  70         strne   r2, [r0], #4            @ 1
  71 /*
  72  * When we get here, we've got less than 4 bytes to zero.  We
  73  * may have an unaligned pointer as well.
  74  */
  75 5:      tst     r1, #2                  @ 1 2 bytes or more?
  76         strneb  r2, [r0], #1            @ 1
  77         strneb  r2, [r0], #1            @ 1
  78         tst     r1, #1                  @ 1 a byte left over
  79         strneb  r2, [r0], #1            @ 1
  80         RETINSTR(mov,pc,lr)             @ 1