arch/alpha/lib/ev6-copy_user.S

   1 /*
   2  * arch/alpha/lib/ev6-copy_user.S
   3  *
   4  * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
   5  *
   6  * Copy to/from user space, handling exceptions as we go..  This
   7  * isn't exactly pretty.
   8  *
   9  * This is essentially the same as "memcpy()", but with a few twists.
  10  * Notably, we have to make sure that $0 is always up-to-date and
  11  * contains the right "bytes left to copy" value (and that it is updated
  12  * only _after_ a successful copy). There is also some rather minor
  13  * exception setup stuff..
  14  *
  15  * NOTE! This is not directly C-callable, because the calling semantics are
  16  * different:
  17  *
  18  * Inputs:
  19  *      length in $0
  20  *      destination address in $6
  21  *      source address in $7
  22  *      return address in $28
  23  *
  24  * Outputs:
  25  *      bytes left to copy in $0
  26  *
  27  * Clobbers:
  28  *      $1,$2,$3,$4,$5,$6,$7
  29  *
  30  * Much of the information about 21264 scheduling/coding comes from:
  31  *      Compiler Writer's Guide for the Alpha 21264
  32  *      abbreviated as 'CWG' in other comments here
  33  *      ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
  34  * Scheduling notation:
  35  *      E       - either cluster
  36  *      U       - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
  37  *      L       - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
  38  */
  39
  40 /* Allow an exception for an insn; exit if we get one.  */
  41 #define EXI(x,y...)                     \
  42         99: x,##y;                      \
  43         .section __ex_table,"a";        \
  44         .long 99b - .;                  \
  45         lda $31, $exitin-99b($31);      \
  46         .previous
  47
  48 #define EXO(x,y...)                     \
  49         99: x,##y;                      \
  50         .section __ex_table,"a";        \
  51         .long 99b - .;                  \
  52         lda $31, $exitout-99b($31);     \
  53         .previous
  54
  55         .set noat
  56         .align 4
  57         .globl __copy_user
  58         .ent __copy_user
  59                                 # Pipeline info: Slotting & Comments
  60 __copy_user:
  61         .prologue 0
  62         subq $0, 32, $1         # .. E  .. ..   : Is this going to be a small copy?
  63         beq $0, $zerolength     # U  .. .. ..   : U L U L
  64
  65         and $6,7,$3             # .. .. .. E    : is leading dest misalignment
  66         ble $1, $onebyteloop    # .. .. U  ..   : 1st branch : small amount of data
  67         beq $3, $destaligned    # .. U  .. ..   : 2nd (one cycle fetcher stall)
  68         subq $3, 8, $3          # E  .. .. ..   : L U U L : trip counter
  69 /*
  70  * The fetcher stall also hides the 1 cycle cross-cluster stall for $3 (L --> U)
  71  * This loop aligns the destination a byte at a time
  72  * We know we have at least one trip through this loop
  73  */
  74 $aligndest:
  75         EXI( ldbu $1,0($7) )    # .. .. .. L    : Keep loads separate from stores
  76         addq $6,1,$6            # .. .. E  ..   : Section 3.8 in the CWG
  77         addq $3,1,$3            # .. E  .. ..   :
  78         nop                     # E  .. .. ..   : U L U L
  79
  80 /*
  81  * the -1 is to compensate for the inc($6) done in a previous quadpack
  82  * which allows us zero dependencies within either quadpack in the loop
  83  */
  84         EXO( stb $1,-1($6) )    # .. .. .. L    :
  85         addq $7,1,$7            # .. .. E  ..   : Section 3.8 in the CWG
  86         subq $0,1,$0            # .. E  .. ..   :
  87         bne $3, $aligndest      # U  .. .. ..   : U L U L
  88
  89 /*
  90  * If we fell through into here, we have a minimum of 33 - 7 bytes
  91  * If we arrived via branch, we have a minimum of 32 bytes
  92  */
  93 $destaligned:
  94         and $7,7,$1             # .. .. .. E    : Check _current_ source alignment
  95         bic $0,7,$4             # .. .. E  ..   : number bytes as a quadword loop
  96         EXI( ldq_u $3,0($7) )   # .. L  .. ..   : Forward fetch for fallthrough code
  97         beq $1,$quadaligned     # U  .. .. ..   : U L U L
  98
  99 /*
 100  * In the worst case, we've just executed an ldq_u here from 0($7)
 101  * and we'll repeat it once if we take the branch
 102  */
 103
 104 /* Misaligned quadword loop - not unrolled.  Leave it that way. */
 105 $misquad:
 106         EXI( ldq_u $2,8($7) )   # .. .. .. L    :
 107         subq $4,8,$4            # .. .. E  ..   :
 108         extql $3,$7,$3          # .. U  .. ..   :
 109         extqh $2,$7,$1          # U  .. .. ..   : U U L L
 110
 111         bis $3,$1,$1            # .. .. .. E    :
 112         EXO( stq $1,0($6) )     # .. .. L  ..   :
 113         addq $7,8,$7            # .. E  .. ..   :
 114         subq $0,8,$0            # E  .. .. ..   : U L L U
 115
 116         addq $6,8,$6            # .. .. .. E    :
 117         bis $2,$2,$3            # .. .. E  ..   :
 118         nop                     # .. E  .. ..   :
 119         bne $4,$misquad         # U  .. .. ..   : U L U L
 120
 121         nop                     # .. .. .. E
 122         nop                     # .. .. E  ..
 123         nop                     # .. E  .. ..
 124         beq $0,$zerolength      # U  .. .. ..   : U L U L
 125
 126 /* We know we have at least one trip through the byte loop */
 127         EXI ( ldbu $2,0($7) )   # .. .. .. L    : No loads in the same quad
 128         addq $6,1,$6            # .. .. E  ..   : as the store (Section 3.8 in CWG)
 129         nop                     # .. E  .. ..   :
 130         br $31, $dirtyentry     # L0 .. .. ..   : L U U L
 131 /* Do the trailing byte loop load, then hop into the store part of the loop */
 132
 133 /*
 134  * A minimum of (33 - 7) bytes to do a quad at a time.
 135  * Based upon the usage context, it's worth the effort to unroll this loop
 136  * $0 - number of bytes to be moved
 137  * $4 - number of bytes to move as quadwords
 138  * $6 is current destination address
 139  * $7 is current source address
 140  */
 141 $quadaligned:
 142         subq    $4, 32, $2      # .. .. .. E    : do not unroll for small stuff
 143         nop                     # .. .. E  ..
 144         nop                     # .. E  .. ..
 145         blt     $2, $onequad    # U  .. .. ..   : U L U L
 146
 147 /*
 148  * There is a significant assumption here that the source and destination
 149  * addresses differ by more than 32 bytes.  In this particular case, a
 150  * sparsity of registers further bounds this to be a minimum of 8 bytes.
 151  * But if this isn't met, then the output result will be incorrect.
 152  * Furthermore, due to a lack of available registers, we really can't
 153  * unroll this to be an 8x loop (which would enable us to use the wh64
 154  * instruction memory hint instruction).
 155  */
 156 $unroll4:
 157         EXI( ldq $1,0($7) )     # .. .. .. L
 158         EXI( ldq $2,8($7) )     # .. .. L  ..
 159         subq    $4,32,$4        # .. E  .. ..
 160         nop                     # E  .. .. ..   : U U L L
 161
 162         addq    $7,16,$7        # .. .. .. E
 163         EXO( stq $1,0($6) )     # .. .. L  ..
 164         EXO( stq $2,8($6) )     # .. L  .. ..
 165         subq    $0,16,$0        # E  .. .. ..   : U L L U
 166
 167         addq    $6,16,$6        # .. .. .. E
 168         EXI( ldq $1,0($7) )     # .. .. L  ..
 169         EXI( ldq $2,8($7) )     # .. L  .. ..
 170         subq    $4, 32, $3      # E  .. .. ..   : U U L L : is there enough for another trip?
 171
 172         EXO( stq $1,0($6) )     # .. .. .. L
 173         EXO( stq $2,8($6) )     # .. .. L  ..
 174         subq    $0,16,$0        # .. E  .. ..
 175         addq    $7,16,$7        # E  .. .. ..   : U L L U
 176
 177         nop                     # .. .. .. E
 178         nop                     # .. .. E  ..
 179         addq    $6,16,$6        # .. E  .. ..
 180         bgt     $3,$unroll4     # U  .. .. ..   : U L U L
 181
 182         nop
 183         nop
 184         nop
 185         beq     $4, $noquads
 186
 187 $onequad:
 188         EXI( ldq $1,0($7) )
 189         subq    $4,8,$4
 190         addq    $7,8,$7
 191         nop
 192
 193         EXO( stq $1,0($6) )
 194         subq    $0,8,$0
 195         addq    $6,8,$6
 196         bne     $4,$onequad
 197
 198 $noquads:
 199         nop
 200         nop
 201         nop
 202         beq $0,$zerolength
 203
 204 /*
 205  * For small copies (or the tail of a larger copy), do a very simple byte loop.
 206  * There's no point in doing a lot of complex alignment calculations to try to
 207  * to quadword stuff for a small amount of data.
 208  *      $0 - remaining number of bytes left to copy
 209  *      $6 - current dest addr
 210  *      $7 - current source addr
 211  */
 212
 213 $onebyteloop:
 214         EXI ( ldbu $2,0($7) )   # .. .. .. L    : No loads in the same quad
 215         addq $6,1,$6            # .. .. E  ..   : as the store (Section 3.8 in CWG)
 216         nop                     # .. E  .. ..   :
 217         nop                     # E  .. .. ..   : U L U L
 218
 219 $dirtyentry:
 220 /*
 221  * the -1 is to compensate for the inc($6) done in a previous quadpack
 222  * which allows us zero dependencies within either quadpack in the loop
 223  */
 224         EXO ( stb $2,-1($6) )   # .. .. .. L    :
 225         addq $7,1,$7            # .. .. E  ..   : quadpack as the load
 226         subq $0,1,$0            # .. E  .. ..   : change count _after_ copy
 227         bgt $0,$onebyteloop     # U  .. .. ..   : U L U L
 228
 229 $zerolength:
 230 $exitout:                       # Destination for exception recovery(?)
 231         nop                     # .. .. .. E
 232         nop                     # .. .. E  ..
 233         nop                     # .. E  .. ..
 234         ret $31,($28),1         # L0 .. .. ..   : L U L U
 235
 236 $exitin:
 237
 238         /* A stupid byte-by-byte zeroing of the rest of the output
 239            buffer.  This cures security holes by never leaving
 240            random kernel data around to be copied elsewhere.  */
 241
 242         nop
 243         nop
 244         nop
 245         mov     $0,$1
 246
 247 $101:
 248         EXO ( stb $31,0($6) )   # L
 249         subq $1,1,$1            # E
 250         addq $6,1,$6            # E
 251         bgt $1,$101             # U
 252
 253         nop
 254         nop
 255         nop
 256         ret $31,($28),1         # L0
 257
 258         .end __copy_user
 259