https://github.com/akkartik/mu/blob/main/linux/ex12.subx

     1 # Example showing mmap syscall.
     2 # Create a new segment using mmap, save the address, write to it.
     3 #
     4 # To run:
     5 #   $ bootstrap/bootstrap translate ex12.subx -o ex12
     6 #   $ bootstrap/bootstrap run 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 Entry:
    15     # mmap(Mmap-new-segment->len)
    16     bb/copy-to-ebx  Mmap-new-segment/imm32
    17     e8/call  syscall_mmap/disp32
    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     # exit(eax)
    23     89/copy                         3/mod/direct    3/rm32/ebx    .           .             .           0/r32/eax   .               .                 # copy eax to ebx
    24     e8/call  syscall_exit/disp32
    25
    26 == data
    27
    28 # various constants used here were found in the Linux sources (search for file mman-common.h)
    29 Mmap-new-segment:  # type mmap_arg_struct
    30     # addr
    31     0/imm32
    32     # len
    33     0x100/imm32
    34     # protection flags
    35     3/imm32  # PROT_READ | PROT_WRITE
    36     # sharing flags
    37     0x22/imm32  # MAP_PRIVATE | MAP_ANONYMOUS
    38     # fd
    39     -1/imm32  # since MAP_ANONYMOUS is specified
    40     # offset
    41     0/imm32  # since MAP_ANONYMOUS is specified
    42
    43 # . . vim:nowrap:textwidth=0