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 arg
12   68/push  0x1000/imm32
13     # call
14   e8/call  new_segment/disp32
15     # discard arg
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                         .               .             .           .             .           .           .               1/imm32/exit            # copy to EAX
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                         .               .             .           .             .           .           .               mmap_new_segment/imm32  # copy to EBX
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                         .               .             .           .             .           .           .               mmap_new_segment/imm32  # copy to EBX
38   b8/copy                         .               .             .           .             .           .           .               0x5a/imm32/mmap         # copy to EAX
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:ft=subx:nowrap:tw&