blob: 4a48e825c0f1068d0d23315bb451472a38dd645c (
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
45
46
47
48
49
50
51
52
53
54
55
56
57
|
# _write: write to a file descriptor (fd)
== 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
Entry: # just exit; can't test _write just yet
# . syscall(exit, 0)
bb/copy-to-ebx 0/imm32
b8/copy-to-eax 1/imm32/exit
cd/syscall 0x80/imm8
_write: # fd : int, s : (address array byte)
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
50/push-eax
51/push-ecx
52/push-edx
53/push-ebx
# syscall(write, fd, (data) s+4, (size) *s)
# . fd : ebx
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 3/r32/ebx 8/disp8 . # copy *(ebp+8) to ebx
# . data : ecx = s+4
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 1/r32/ecx 0xc/disp8 . # copy *(ebp+12) to ecx
81 0/subop/add 3/mod/direct 1/rm32/ecx . . . . . 4/imm32 # add to ecx
# . size : edx = *s
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 2/r32/edx 0xc/disp8 . # copy *(ebp+12) to edx
8b/copy 0/mod/indirect 2/rm32/edx . . . 2/r32/edx . . # copy *edx to edx
# . syscall
b8/copy-to-eax 4/imm32/write
cd/syscall 0x80/imm8
# if (eax < 0) abort
3d/compare-eax-with 0/imm32
0f 8c/jump-if-lesser $_write:abort/disp32
$_write:end:
# . restore registers
5b/pop-to-ebx
5a/pop-to-edx
59/pop-to-ecx
58/pop-to-eax
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
$_write:abort:
# can't write a message here for risk of an infinite loop, so we'll use a special exit code instead
# . syscall(exit, 255)
bb/copy-to-ebx 0xff/imm32
b8/copy-to-eax 1/imm32/exit
cd/syscall 0x80/imm8
# never gets here
# . . vim:nowrap:textwidth=0
|