https://github.com/akkartik/mu/blob/master/subx/examples/ex5.subx

     1 # Read a character from stdin, save it to a local on the stack, write it to stdout.
     2 #
     3 # To run (from the subx directory):
     4 #   $ ./subx translate examples/ex5.subx -o examples/ex5
     5 #   $ ./subx run examples/ex5
     6
     7 == code
     8 #   instruction                     effective address                                                   register    displacement    immediate
     9 # . op          subop               mod             rm32          base        index         scale       r32
    10 # . 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
    11
    12 Entry:
    13
    14     # allocate x on the stack
    15     81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # subtract from ESP
    16
    17     # syscall(read, stdin, x, 1)
    18     # . fd = 0 (stdin)
    19     bb/copy-to-EBX  0/imm32
    20     # . data = x (location to write result to)
    21     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              1/r32/ECX   4/disp8         .                 # copy ESP+4 to ECX
    22     # . size = 1 character
    23     ba/copy-to-EDX  1/imm32
    24     # . syscall
    25     b8/copy-to-EAX  3/imm32/read
    26     cd/syscall  0x80/imm8
    27
    28     # syscall(write, stdout, x, 1)
    29     # . fd = 1 (stdout)
    30     bb/copy-to-EBX  1/imm32
    31     # . data = x (location to read from)
    32     8d/copy-address                 1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none              1/r32/ECX   4/disp8         .                 # copy ESP+4 to ECX
    33     # . size = 1 character
    34     ba/copy-to-EDX  1/imm32
    35     # . syscall
    36     b8/copy-to-EAX  4/imm32/write
    37     cd/syscall  0x80/imm8
    38
    39     # syscall(exit, EBX)
    40     b8/copy-to-EAX  1/imm32/exit
    41     cd/syscall  0x80/imm8
    42
    43 # . . vim:nowrap:textwidth=0