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
|
# Read records previously written in file.dat, by write-records software
.include "linux.s"
.include "record-def.s"
.section .data
filename:
.ascii "test.dat\0"
record_buffer_ptr:
.long 0
.section .text
.globl _start
_start:
# Stack locations for INPUT and OUTPUT FDs
.equ ST_INPUT_DESCRIPTOR, -8
.equ ST_OUTPUT_DESCRIPTOR, -16
movq %rsp, %rbp
subq $16, %rsp # Save space in the stack for FDs
call allocate_init # Initialize our memory
# allocate buffer
pushq $RECORD_SIZE
call allocate
movq %rax, record_buffer_ptr
# Open data file
movq $SYS_OPEN, %rax
movq $filename, %rdi
movq $0, %rsi # Open for read only
movq $0666, %rdx
syscall
# Save FD
movq %rax, ST_INPUT_DESCRIPTOR(%rbp)
# Yes, STDOUT is always 1, but if I want to change the output location
# later, I don't need to change everywhere...
movq $STDOUT, ST_OUTPUT_DESCRIPTOR(%rbp)
record_read_loop:
pushq ST_INPUT_DESCRIPTOR(%rbp)
pushq record_buffer_ptr
call read_record
addq $16, %rsp # Cleanup stack
# All records are RECORD_SIZE size, if we didn't get this amount of
# bytes from read function, we either are at EOF or we hit an error.
cmpq $RECORD_SIZE, %rax
jne finished_reading
# We are ok, so print the first name in the record
movq record_buffer_ptr, %rax
addq $RECORD_FIRSTNAME, %rax # Seek offset of the firstname in the
# buffer
pushq %rax
call count_chars
addq $8, %rsp # Cleanup stack
# Write name to OUTPUT
movq %rax, %rdx # Returned record size, used as argument to
# write()
movq record_buffer_ptr, %rsi
addq $RECORD_FIRSTNAME, %rsi
movq ST_OUTPUT_DESCRIPTOR(%rbp), %rdi
movq $SYS_WRITE, %rax
syscall
pushq ST_OUTPUT_DESCRIPTOR(%rbp)
call write_newline
addq $8, %rsp
jmp record_read_loop
# Free buffer
pushq record_buffer_ptr
call deallocate
finished_reading:
movq $SYS_EXIT, %rax
movq $0, %rdi
syscall
|
