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                                                   operand     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   # store to *EAX
20   c7/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   00 00 00 00  # null
33   # len
34   00 01 00 00  # 0x1000
35   # protection flags
36   03 00 00 00  # PROT_READ | PROT_WRITE
37   # sharing flags
38   22 00 00 00  # MAP_PRIVATE | MAP_ANONYMOUS
39   # fd
40   ff ff ff ff  # -1 since MAP_ANONYMOUS is specified
41   # offset
42   00 00 00 00  # 0 since MAP_ANONYMOUS is specified
43 
44 # vim:nowrap:textwidth=0