# Mu - subx/053new_segment.subx

     1 # Create a new segment (for data) using mmap().
     2
     3 == code
     4
     5 # instruction                     effective address                                                   operand     displacement    immediate
     6 # op          subop               mod             rm32          base        index         scale       r32
     7 # 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
     8
     9 # main:  (manual test if this is the last file loaded)
    10   # EAX = new-segment(0x1000)
    11     # push args
    12   68/push  0x1000/imm32
    13     # call
    14   e8/call  new-segment/disp32
    15     # discard args
    16   81          0/subop/add         3/mod/direct    4/rm32/ESP    .           .             .           .           .               4/imm32                 # add to ESP
    17
    18   # store to *EAX
    19   c7/copy                         0/mod/direct    0/rm32/EAX    .           .             .           .           .               0x34/imm32              # copy to *EAX
    20
    21   # exit(EAX)
    22   89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                       # copy EAX to EBX
    23   b8/copy-to-EAX  1/imm32/exit
    24   cd/syscall  0x80/imm8
    25
    26 new-segment:  # len : int -> address
    27   # prolog
    28   55/push-EBP
    29   89/copy                         3/mod/direct    5/rm32/EBP    .           .             .           4/r32/ESP   .               .                       # copy ESP to EBP
    30   53/push-EBX
    31   # copy len to mmap-new-segment.len
    32   # TODO: compute mmap-new-segment+4 before runtime
    33   8b/copy                         1/mod/*+disp8   4/rm32/sib    5/base/EBP  4/index/none  .           0/r32/EAX   8/disp8         .                       # copy *(EBP+8) to EAX
    34   bb/copy-to-EBX  mmap-new-segment/imm32
    35   89/copy                         1/mod/*+disp8   3/rm32/EBX    .           .             .           0/r32/EAX   4/disp8         .                       # copy EAX to *(EBX+4)
    36   # mmap(mmap-new-segment)
    37   bb/copy-to-EBX  mmap-new-segment/imm32
    38   b8/copy-to-EAX  0x5a/imm32/mmap
    39   cd/syscall  0x80/imm8
    40   # epilog
    41   5b/pop-to-EBX
    42   89/copy                         3/mod/direct    4/rm32/ESP    .           .             .           5/r32/EBP   .               .                       # copy EBP to ESP
    43   5d/pop-to-EBP
    44   c3/return
    45
    46 == data
    47 # various constants used here were found in the Linux sources (search for file mman-common.h)
    48 mmap-new-segment:  # type mmap_arg_struct
    49   # addr
    50   00 00 00 00  # null
    51   # len
    52   00 00 00 00  # 0x1000
    53   # protection flags
    54   03 00 00 00  # PROT_READ | PROT_WRITE
    55   # sharing flags
    56   22 00 00 00  # MAP_PRIVATE | MAP_ANONYMOUS
    57   # fd
    58   ff ff ff ff  # -1 since MAP_ANONYMOUS is specified
    59   # offset
    60   00 00 00 00  # 0 since MAP_ANONYMOUS is specified
    61
    62 # vim:nowrap:textwidth=0