# Mu - 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                                                   operand     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 # main:
    13   # allocate x on the stack
    14   81          5/subop/subtract    3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32           # subtract from ESP
    15
    16   # syscall(read, stdin, x, 1)
    17     # fd = 0 (stdin)
    18   bb/copy-to-EBX  0/imm32
    19     # initialize x (location to write result to)
    20   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
    21     # size = 1 character
    22   ba/copy-to-EDX  1/imm32
    23     # syscall
    24   b8/copy-to-EAX  3/imm32/read
    25   cd/syscall  0x80/imm8
    26
    27   # syscall(write, stdout, x, 1)
    28     # fd = 1 (stdout)
    29   bb/copy-to-EBX  1/imm32
    30     # initialize x (location to read from)
    31   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
    32     # size = 1 character
    33   ba/copy-to-EDX  1/imm32
    34     # syscall
    35   b8/copy-to-EAX  4/imm32/write
    36   cd/syscall  0x80/imm8
    37
    38   # syscall(exit, EBX)
    39   b8/copy-to-EAX  1/imm32/exit
    40   cd/syscall  0x80/imm8
    41
    42 # vim:nowrap:textwidth=0