blob: 6d17a39fa8a459681c62089738e5a7a7232df138 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
# Example showing mmap syscall.
# Create a new segment using mmap, save the address, write to it.
#
# To run (from the subx directory):
# $ subx translate examples/ex12.subx -o examples/ex12
# $ subx run examples/ex12
# You shouldn't get a segmentation fault.
== code
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 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
# syscall(mmap, 0x1000)
bb/copy-to-EBX Mmap-new-segment/imm32
b8/copy-to-EAX 0x5a/imm32/mmap
cd/syscall 0x80/imm8
# write to *EAX to check that we have access to the newly-allocated segment
c7/copy 0/mod/direct 0/rm32/EAX . . . . . 0x34/imm32 # copy to *EAX
# syscall(exit, EAX)
89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX
b8/copy-to-EAX 1/imm32/exit
cd/syscall 0x80/imm8
== data
# various constants used here were found in the Linux sources (search for file mman-common.h)
Mmap-new-segment: # type mmap_arg_struct
# addr
00 00 00 00 # null
# len
00 01 00 00 # 0x1000
# protection flags
03 00 00 00 # PROT_READ | PROT_WRITE
# sharing flags
22 00 00 00 # MAP_PRIVATE | MAP_ANONYMOUS
# fd
ff ff ff ff # -1 since MAP_ANONYMOUS is specified
# offset
00 00 00 00 # 0 since MAP_ANONYMOUS is specified
# . . vim:nowrap:textwidth=0
|