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