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
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
|
.global _start
.data
v_elf_header:
.byte 0x7f # Magic Number
.ascii "ELF" #
.byte 0x2 # 64-Bit
.byte 0x1 # little-endian
.byte 0x1 # ELFv1
.byte 0x0 # System V ABI
.quad 0x0 #
.hword 0x02 # Executable
.hword 0x3e # AMD x86-64
.int 0x1 # ELFv1
.quad 0x401000 # Entry
.quad 0x40 # Program Header Offset
.quad 0x100 # TODO: Section Header Offset
.int 0x0 #
.hword 0x40 # ELF Header Size
.hword 0x38 # Program Header Table Entry Size
.hword 0x3 # TODO: Number Of Entries in Program Header Table
.hword 0x40 # Section Header Table Entry Size
.hword 0x3 # TODO: Number Of Entries in Section Header Table
.hword 0x2 # TODO: Index of Section Header Table Entry containing section names
v_usage_message:
.asciz "bfc [input file] [output file]\n"
v_input_fd:
.int 0x0
v_output_fd:
.int 0x0
v_buffer_start:
.quad 0x0
v_buffer_end:
.quad 0x0
v_buffer_cursor:
.quad 0x0
.text
_start:
mov %rsp, %rbp
call f_check_args
call f_open_files
call f_init_buffer
mov $v_buffer_cursor, %rbx
mov (%rbx), %rsi
add $0x300, %rsi
mov %rsi, (%rbx)
call f_check_buffer
mov $v_buffer_cursor, %rsi
mov (%rbx), %rsi
add $0x300, %rsi
mov %rsi, (%rbx)
call f_check_buffer
# ----
mov $1, %rax
mov %rcx, %rdi
mov $v_elf_header, %rsi
mov $0x40, %rdx
syscall
# ----
call f_close_files
mov $0, %rdi
jmp f_exit
f_exit:
mov $60, %rax
syscall
f_check_args:
mov (%rbp), %rax
cmp $3, %rax
je l_check_args_success
mov $1, %rax
mov $2, %rdi
mov $v_usage_message, %rsi
mov $32, %rdx
syscall
mov $-1, %rdi
jmp f_exit
l_check_args_success:
ret
f_open_files:
mov $2, %rax
mov 16(%rbp), %rdi
mov $0, %rsi
mov $0, %rdx
syscall
mov $v_input_fd, %rbx
mov %eax, (%rbx)
mov $2, %rax
mov 24(%rbp), %rdi
mov $0x41, %rsi
mov $0744, %rdx
syscall
mov $v_output_fd, %rbx
mov %eax, (%rbx)
ret
f_close_files:
mov $3, %rax
mov %rbx, %rsi
syscall
mov $3, %rax
mov %rcx, %rsi
syscall
ret
f_init_buffer:
mov $12, %rax
mov $0, %rdi
syscall
mov $v_buffer_start, %rbx
mov %rax, (%rbx)
mov $v_buffer_end, %rbx
mov %rax, (%rbx)
mov $v_buffer_cursor, %rbx
mov %rax, (%rbx)
/*
* We directly skip to f_resize_buffer
* since we want to resize it to a usable amount
*/
f_resize_buffer:
mov $12, %rax
mov $v_buffer_end, %rbx
mov (%rbx), %rdi
add $0x400, %rdi
syscall
mov %rax, (%rbx)
ret
/* %rsi = needed end */
f_check_buffer:
mov $v_buffer_end, %rbx
mov (%rbx), %rax
cmp %rax, %rsi
jl l_check_buffer_large_enough
call f_resize_buffer
l_check_buffer_large_enough:
ret
|
