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