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/*

 * arch/alpha/lib/clear_user.S

 * Contributed by Richard Henderson 

 *

 * 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