Linux_Assembly_Primer/StringBasics.s at master · 0x90shell/Linux_Assembly_Primer · GitHub

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
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
.data
	HelloWorldString:
		.asciz "Hello World of Assembly!"
	H3110:
		.asciz "H3110"
.bss

	.lcomm Destination, 100
	.lcomm DestinationUsingRep, 100
	.lcomm DestinationUsingStos, 100

.text

	.globl _start

	_start:
		nop
		# 1. Simple copying using movsb, movsw, movsl

		movl $HelloWorldString, %esi
		movl $Destination, %edi

		movsb
		movsw
		movsl

		# 2. Setting / Clearing the DF flag

		std # set the DF flag
		cld # clear the DF flag

		# 3. Using Rep

		movl $HelloWorldString, %esi
		movl $DestinationUsingRep, %edi
		movl $25, %ecx # set the string length in ECX
		cld # clear the DF
		rep movsb
		std

		# 4. Loading string from memory into EAX register

		cld
		leal HelloWorldString, %esi
		lodsb
		movb $0, %al

		dec %esi
		lodsw
		movw $0, %ax

		subl $2, %esi # Make ESI point back to the original string
		lodsl

		# 5. Storing strings from EAX to memory

		leal DestinationUsingStos, %edi
		stosb
		stosw
		stosl

		# 6. Comparing Strings

		cld
		leal HelloWorldString, %esi
		leal H3110, %edi
		cmpsb

		dec %esi
		dec %edi
		cmpsw

		subl $2, %esi
		subl $2, %edi
		cmpsl


		# The exit() routine

		movl $1, %eax
		movl $10, %ebx
		int $0x80