https://github.com/akkartik/mu/blob/master/subx/068error-byte.subx
  1 # Print an error message followed by the text representation of a byte. Then exit.
  2 
  3 == code
  4 #   instruction                     effective address                                                   register    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     # manual test
 10 #?     # . var ed/EAX : exit-descriptor
 11 #?     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # subtract from ESP
 12 #?     89/copy                         3/mod/direct    0/rm32/EAX    .           .             .           4/r32/ESP   .               .                 # copy ESP to EAX
 13 #?     # . configure ed to really exit()
 14 #?     # . . ed->target = 0
 15 #?     c7          0/subop/copy        0/mod/direct    0/rm32/EAX    .           .             .           .           .               0/imm32           # copy to *EAX
 16 #?     # . error-byte(ed, Stdout, msg, 34)
 17 #?     68/push  0x34/imm32
 18 #?     68/push  "abc"/imm32
 19 #?     68/push  Stderr/imm32
 20 #?     50/push-EAX
 21 #?     e8/call  error-byte/disp32
 22     # automatic test
 23     e8/call  run-tests/disp32  # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'.
 24     # . syscall(exit, Num-test-failures)
 25     8b/copy                         0/mod/indirect  5/rm32/.disp32            .             .           3/r32/EBX   Num-test-failures/disp32          # copy *Num-test-failures to EBX
 26     b8/copy-to-EAX  1/imm32/exit
 27     cd/syscall  0x80/imm8
 28 
 29 # write(out, "Error: "+msg+": "+byte) then stop(ed, 1)
 30 error-byte:  # ed : (address exit-descriptor), out : (address buffered-file), msg : (address array byte), n : byte -> <void>
 31     # . prolog
 32     55/push-EBP
 33     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
 34     # write-buffered(out, "Error: ")
 35     # . . push args
 36     68/push  "Error: "/imm32
 37     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
 38     # . . call
 39     e8/call  write-buffered/disp32
 40     # . . discard args
 41     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
 42     # write-buffered(out, msg)
 43     # . . push args
 44     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x10/disp8      .                 # push *(EBP+16)
 45     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
 46     # . . call
 47     e8/call  write-buffered/disp32
 48     # . . discard args
 49     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
 50     # write-buffered(out, ": ")
 51     # . . push args
 52     68/push  ": "/imm32
 53     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
 54     # . . call
 55     e8/call  write-buffered/disp32
 56     # . . discard args
 57     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
 58     # print-byte(out, byte)
 59     # . . push args
 60     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0x14/disp8      .                 # push *(EBP+20)
 61     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
 62     # . . call
 63     e8/call  print-byte/disp32
 64     # . . discard args
 65     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
 66     # write-buffered(out, Newline)
 67     # . . push args
 68     68/push  Newline/imm32
 69     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
 70     # . . call
 71     e8/call  write-buffered/disp32
 72     # . . discard args
 73     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               8/imm32           # add to ESP
 74     # . flush(out)
 75     # . . push args
 76     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
 77     # . . call
 78     e8/call  flush/disp32
 79     # . . discard args
 80     81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # add to ESP
 81     # stop(ed, 1)
 82     # . . push args
 83     68/push  1/imm32
 84     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
 85     # . . call
 86     e8/call  stop/disp32
 87     # should never get past this point
 88 $error-byte:dead-end:
 89     # . epilog
 90     89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                 # copy EBP to ESP
 91     5d/pop-to-EBP
 92     c3/return
 93 
 94 == data
 95 
 96 # The buffered file for standard error.
 97 Stderr:
 98     # file descriptor or (address stream)
 99     02 00 00 00  # 1 = standard error
100     # current write index
101     00 00 00 00
102     # current read index
103     00 00 00 00
104     # length (8)
105     08 00 00 00
106     # data
107     00 00 00 00 00 00 00 00  # 8 bytes
108 
109 # TODO: 8 bytes is too small. We'll need to grow the buffer for efficiency. But
110 # I don't want to type in 1024 bytes here.
111 
112 # . . vim:nowrap:textwidth=0