https://github.com/akkartik/mu/blob/master/subx/examples/ex12.subx

     1 # Example showing mmap syscall.
     2 # Create a new segment using mmap, save the address, write to it.
     3 #
     4 # To run (from the subx directory):
     5 #   $ ./subx translate examples/ex12.subx -o examples/ex12
     6 #   $ ./subx run examples/ex12
     7 # You shouldn't get a segmentation fault.
     8
     9 == code
    10 #   instruction                     effective address                                                   register    displacement    immediate
    11 # . op          subop               mod             rm32          base        index         scale       r32
    12 # . 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
    13
    14     # syscall(mmap, 0x1000)
    15     bb/copy-to-EBX  Mmap-new-segment/imm32
    16     b8/copy-to-EAX  0x5a/imm32/mmap
    17     cd/syscall  0x80/imm8
    18
    19     # write to *EAX to check that we have access to the newly-allocated segment
    20     c7          0/subop/copy        0/mod/direct    0/rm32/EAX    .           .             .           .           .               0x34/imm32        # copy to *EAX
    21
    22     # syscall(exit, EAX)
    23     89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                 # copy EAX to EBX
    24     b8/copy-to-EAX  1/imm32/exit
    25     cd/syscall  0x80/imm8
    26
    27 == data
    28
    29 # various constants used here were found in the Linux sources (search for file mman-common.h)
    30 Mmap-new-segment:  # type mmap_arg_struct
    31     # addr
    32     0/imm32
    33     # len
    34     0x100/imm32
    35     # protection flags
    36     3/imm32  # PROT_READ | PROT_WRITE
    37     # sharing flags
    38     0x22/imm32  # MAP_PRIVATE | MAP_ANONYMOUS
    39     # fd
    40     -1/imm32  # since MAP_ANONYMOUS is specified
    41     # offset
    42     0/imm32  # since MAP_ANONYMOUS is specified
    43
    44 # . . vim:nowrap:textwidth=0