LXR linux/arch/alpha/lib/clear

   1/*
   2 * arch/alpha/lib/clear_user.S
   3 * Contributed by Richard Henderson <rth@tamu.edu>
   4 *
   5 * Zero user space, handling exceptions as we go.
   6 *
   7 * We have to make sure that $0 is always up-to-date and contains the
   8 * right "bytes left to zero" value (and that it is updated only _after_
   9 * a successful copy).  There is also some rather minor exception setup
  10 * stuff.
  11 *
  12 * NOTE! This is not directly C-callable, because the calling semantics
  13 * are different:
  14 *
  15 * Inputs:
  16 *      length in $0
  17 *      destination address in $6
  18 *      exception pointer in $7
  19 *      return address in $28 (exceptions expect it there)
  20 *
  21 * Outputs:
  22 *      bytes left to copy in $0
  23 *
  24 * Clobbers:
  25 *      $1,$2,$3,$4,$5,$6
  26 */
  27
  28/* Allow an exception for an insn; exit if we get one.  */
  29#define EX(x,y...)                      \
  30        99: x,##y;                      \
  31        .section __ex_table,"a";        \
  32        .long 99b - .;                  \
  33        lda $31, $exception-99b($31);   \
  34        .previous
  35
  36        .set noat
  37        .set noreorder
  38        .align 4
  39
  40        .globl __do_clear_user
  41        .ent __do_clear_user
  42        .frame  $30, 0, $28
  43        .prologue 0
  44
  45$loop:
  46        and     $1, 3, $4       # e0    :
  47        beq     $4, 1f          # .. e1 :
  48
  490:      EX( stq_u $31, 0($6) )  # e0    : zero one word
  50        subq    $0, 8, $0       # .. e1 :
  51        subq    $4, 1, $4       # e0    :
  52        addq    $6, 8, $6       # .. e1 :
  53        bne     $4, 0b          # e1    :
  54        unop                    #       :
  55
  561:      bic     $1, 3, $1       # e0    :
  57        beq     $1, $tail       # .. e1 :
  58
  592:      EX( stq_u $31, 0($6) )  # e0    : zero four words
  60        subq    $0, 8, $0       # .. e1 :
  61        EX( stq_u $31, 8($6) )  # e0    :
  62        subq    $0, 8, $0       # .. e1 :
  63        EX( stq_u $31, 16($6) ) # e0    :
  64        subq    $0, 8, $0       # .. e1 :
  65        EX( stq_u $31, 24($6) ) # e0    :
  66        subq    $0, 8, $0       # .. e1 :
  67        subq    $1, 4, $1       # e0    :
  68        addq    $6, 32, $6      # .. e1 :
  69        bne     $1, 2b          # e1    :
  70
  71$tail:
  72        bne     $2, 1f          # e1    : is there a tail to do?
  73        ret     $31, ($28), 1   # .. e1 :
  74
  751:      EX( ldq_u $5, 0($6) )   # e0    :
  76        clr     $0              # .. e1 :
  77        nop                     # e1    :
  78        mskqh   $5, $0, $5      # e0    :
  79        EX( stq_u $5, 0($6) )   # e0    :
  80        ret     $31, ($28), 1   # .. e1 :
  81
  82__do_clear_user:
  83        and     $6, 7, $4       # e0    : find dest misalignment
  84        beq     $0, $zerolength # .. e1 :
  85        addq    $0, $4, $1      # e0    : bias counter
  86        and     $1, 7, $2       # e1    : number of bytes in tail
  87        srl     $1, 3, $1       # e0    :
  88        beq     $4, $loop       # .. e1 :
  89
  90        EX( ldq_u $5, 0($6) )   # e0    : load dst word to mask back in
  91        beq     $1, $oneword    # .. e1 : sub-word store?
  92
  93        mskql   $5, $6, $5      # e0    : take care of misaligned head
  94        addq    $6, 8, $6       # .. e1 :
  95        EX( stq_u $5, -8($6) )  # e0    :
  96        addq    $0, $4, $0      # .. e1 : bytes left -= 8 - misalignment
  97        subq    $1, 1, $1       # e0    :
  98        subq    $0, 8, $0       # .. e1 :
  99        br      $loop           # e1    :
 100        unop                    #       :
 101
 102$oneword:
 103        mskql   $5, $6, $4      # e0    :
 104        mskqh   $5, $2, $5      # e0    :
 105        or      $5, $4, $5      # e1    :
 106        EX( stq_u $5, 0($6) )   # e0    :
 107        clr     $0              # .. e1 :
 108
 109$zerolength:
 110$exception:
 111        ret     $31, ($28), 1   # .. e1 :
 112
 113        .end __do_clear_user
 114