https://github.com/akkartik/mu/blob/master/subx/examples/ex10.subx

     1 # String comparison: return 1 iff the two args passed in at the commandline are equal.
     2 #
     3 # To run (from the subx directory):
     4 #   $ ./subx translate examples/ex10.subx -o examples/ex10
     5 #   $ ./subx run examples/ex10 abc abd
     6 # Expected result:
     7 #   $ echo $?
     8 #   0  # false
     9
    10 == code
    11 #   instruction                     effective address                                                   register    displacement    immediate
    12 # . op          subop               mod             rm32          base        index         scale       r32
    13 # . 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
    14
    15 Entry:  # return argv-equal(argv[1], argv[2])
    16 #       At the start of a SubX program:
    17 #         argc: *ESP
    18 #         argv[0]: *(ESP+4)
    19 #         argv[1]: *(ESP+8)
    20 #         ...
    21     # . prolog
    22     89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                 # copy ESP to EBP
    23     # argv-equal(argv[1], argv[2])
    24     # . . push argv[2]
    25     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           0xc/disp8       .                 # push *(EBP+12)
    26     # . . push argv[1]
    27     ff          6/subop/push        1/mod/*+disp8   5/rm32/EBP    .           .             .           .           8/disp8         .                 # push *(EBP+8)
    28     # . . call
    29     e8/call argv-equal/disp32
    30     # syscall(exit, EAX)
    31     89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                 # copy EAX to EBX
    32     b8/copy-to-EAX  1/imm32/exit
    33     cd/syscall  0x80/imm8
    34
    35 # compare two null-terminated ascii strings
    36 # reason for the name: the only place we should have null-terminated ascii strings is from commandline args
    37 argv-equal:  # (s1, s2) : null-terminated ascii strings -> EAX : boolean
    38     # initialize s1 (ECX) and s2 (EDX)
    39     8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           1/r32/ECX   4/disp8         .                 # copy *(ESP+4) to ECX
    40     8b/copy                         1/mod/*+disp8   4/rm32/sib    4/base/ESP  4/index/none  .           2/r32/EDX   8/disp8         .                 # copy *(ESP+8) to EDX
    41 $argv-equal:loop:
    42     # c1/EAX, c2/EBX = *s1, *s2
    43     b8/copy-to-EAX  0/imm32
    44     8a/copy-byte                    0/mod/indirect  1/rm32/ECX    .           .             .           0/r32/AL    .               .                 # copy byte at *ECX to AL
    45     bb/copy-to-EBX  0/imm32
    46     8a/copy-byte                    0/mod/indirect  2/rm32/EDX    .           .             .           3/r32/BL    .               .                 # copy byte at *EDX to BL
    47     # if (c1 == 0) break
    48     3d/compare-EAX  0/imm32
    49     74/jump-if-equal  $argv-equal:break/disp8
    50     # if (c1 != c2) return false
    51     39/compare                      3/mod/direct    0/rm32/EAX    .           .             .           3/r32/EBX   .               .                 # compare EAX and EBX
    52     75/jump-if-not-equal  $argv-equal:false/disp8
    53     # ++s1, ++s2
    54     41/inc-ECX
    55     42/inc-EDX
    56     # end while
    57     eb/jump  $argv-equal:loop/disp8
    58 $argv-equal:break:
    59     # if (c2 == 0) return true
    60     81          7/subop/compare     3/mod/direct    3/rm32/EBX    .           .             .           .           .               0/imm32           # compare EBX
    61     75/jump-if-not-equal  $argv-equal:false/disp8
    62 $argv-equal:success:
    63     b8/copy-to-EAX  1/imm32
    64     c3/return
    65     # return false
    66 $argv-equal:false:
    67     b8/copy-to-EAX  0/imm32
    68     c3/return
    69
    70 # . . vim:nowrap:textwidth=0