# Mu - subx/050_write.subx

     1 # _write: write to a file descriptor
     2
     3 == code
     4
     5 # instruction                     effective address                                                   operand     displacement    immediate
     6 # op          subop               mod             rm32          base        index         scale       r32
     7 # 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes
     8
     9 # main:  (manual test if this is the last file loaded)
    10   # syscall(exit, 0) -- can't test these functions just yet
    11   bb/copy-to-EBX  0/imm32
    12   b8/copy-to-EAX  1/imm32
    13   cd/syscall  0x80/imm8
    14
    15 _write:  # fd : int, s : (address array byte) -> <void>
    16   # prolog
    17   55/push-EBP
    18   89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    19   # save registers
    20   50/push-EAX
    21   51/push-ECX
    22   52/push-EDX
    23   53/push-EBX
    24   # syscall(write, fd, (data) s+4, (size) *s)
    25     # fd : EBX
    26   8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           3/r32/EBX   8/disp8         .                 # copy *(EBP+8) to EBX
    27     # data : ECX = s+4
    28   8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           1/r32/ECX   0xc/disp8       .                 # copy *(EBP+12) to ECX
    29   81          0/subop/add         3/mod/direct    1/rm32/ECX    .           .             .           .           .               4/imm32           # add to ECX
    30     # size : EDX = *s
    31   8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           2/r32/EDX   0xc/disp8       .                 # copy *(EBP+12) to EDX
    32   8b/copy                         0/mod/indirect  2/rm32/EDX    .           .             .           2/r32/EDX   .               .                 # copy *EDX to EDX
    33     # syscall
    34   b8/copy-to-EAX  4/imm32/write
    35   cd/syscall  0x80/imm8
    36   # restore registers
    37   5b/pop-to-EBX
    38   5a/pop-to-EDX
    39   59/pop-to-ECX
    40   58/pop-to-EAX
    41   # epilog
    42   89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
    43   5d/pop-to-EBP
    44   c3/return
    45
    46 # vim:nowrap:textwidth=0