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/*
 * arch/alpha/lib/clear_user.S
 * Contributed by Richard Henderson <rth@tamu.edu>
 *
 * Zero user space, handling exceptions as we go.
 *
 * We have to make sure that $0 is always up-to-date and contains the
 * right "bytes left to zero" value (and that it is updated only _after_
 * a successful copy).  There is also some rather minor exception setup
 * stuff.
 *
 * NOTE! This is not directly C-callable, because the calling semantics
 * are different:
 *
 * Inputs:
 *      length in $0
 *      destination address in $6
 *      exception pointer in $7
 *      return address in $28 (exceptions expect it there)
 *
 * Outputs:
 *      bytes left to copy in $0
 *
 * Clobbers:
 *      $1,$2,$3,$4,$5,$6
 */

/* Allow an exception for an insn; exit if we get one.  */
#define EX(x,y...)                      \
        99: x,##y;                      \
        .section __ex_table,"a";        \
        .gprel32 99b;                   \
        lda $31, $exception-99b($31);   \
        .previous

        .set noat
        .set noreorder
        .align 4

        .globl __do_clear_user
        .ent __do_clear_user
        .frame  $30, 0, $28
        .prologue 0

$loop:
        and     $1, 3, $4       # e0    :
        beq     $4, 1f          # .. e1 :

0:      EX( stq_u $31, 0($6) )  # e0    : zero one word
        subq    $0, 8, $0       # .. e1 :
        subq    $4, 1, $4       # e0    :
        addq    $6, 8, $6       # .. e1 :
        bne     $4, 0b          # e1    :
        unop                    #       :

1:      bic     $1, 3, $1       # e0    :
        beq     $1, $tail       # .. e1 :

2:      EX( stq_u $31, 0($6) )  # e0    : zero four words
        subq    $0, 8, $0       # .. e1 :
        EX( stq_u $31, 8($6) )  # e0    :
        subq    $0, 8, $0       # .. e1 :
        EX( stq_u $31, 16($6) ) # e0    :
        subq    $0, 8, $0       # .. e1 :
        EX( stq_u $31, 24($6) ) # e0    :
        subq    $0, 8, $0       # .. e1 :
        subq    $1, 4, $1       # e0    :
        addq    $6, 32, $6      # .. e1 :
        bne     $1, 2b          # e1    :

$tail:
        bne     $2, 1f          # e1    : is there a tail to do?
        ret     $31, ($28), 1   # .. e1 :

1:      EX( ldq_u $5, 0($6) )   # e0    :
        clr     $0              # .. e1 :
        nop                     # e1    :
        mskqh   $5, $0, $5      # e0    :
        EX( stq_u $5, 0($6) )   # e0    :
        ret     $31, ($28), 1   # .. e1 :

__do_clear_user:
        ldgp    $29,0($27)      # we do exceptions -- we need the gp.
        and     $6, 7, $4       # e0    : find dest misalignment
        beq     $0, $zerolength # .. e1 :
        addq    $0, $4, $1      # e0    : bias counter
        and     $1, 7, $2       # e1    : number of bytes in tail
        srl     $1, 3, $1       # e0    :
        beq     $4, $loop       # .. e1 :

        EX( ldq_u $5, 0($6) )   # e0    : load dst word to mask back in
        beq     $1, $oneword    # .. e1 : sub-word store?

        mskql   $5, $6, $5      # e0    : take care of misaligned head
        addq    $6, 8, $6       # .. e1 :
        EX( stq_u $5, -8($6) )  # e0    :
        addq    $0, $4, $0      # .. e1 : bytes left -= 8 - misalignment
        subq    $1, 1, $1       # e0    :
        subq    $0, 8, $0       # .. e1 :
        br      $loop           # e1    :
        unop                    #       :

$oneword:
        mskql   $5, $6, $4      # e0    :
        mskqh   $5, $2, $5      # e0    :
        or      $5, $4, $5      # e1    :
        EX( stq_u $5, 0($6) )   # e0    :
        clr     $0              # .. e1 :

$zerolength:
$exception:
        ret     $31, ($28), 1   # .. e1 :

        .end __do_clear_user