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# Modify records in a file and write them to the output file
.include "linux.s"
.include "record-def.s"
.section .data
input_filename:
.ascii "test.dat\0"
output_filename:
.ascii "modified.dat\0"
.section .bss
.lcomm record_buffer, RECORD_SIZE
.section .text
.globl _start
_start:
# Stack local vars
.equ ST_INPUT_DESCRIPTOR, -8
.equ ST_OUTPUT_DESCRIPTOR, -16
# Copy stack pointer and make room for local variables
movq %rsp, %rbp
subq $16, %rsp
# Open file for reading
movq $SYS_OPEN, %rax
movq $input_filename, %rdi
movq $0, %rsi
movq $0666, %rdx
syscall
cmpq $0, %rax
jl continue_processing
# We've got an error...
continue_processing:
movq %rax, ST_INPUT_DESCRIPTOR(%rbp)
.section .data
no_open_file_code:
.ascii "0001: \0"
no_open_file_msg:
.ascii "Can't open input file\0"
.section .text
pushq $no_open_file_msg
pushq $no_open_file_code
call error_exit
# Open file for writing
movq $SYS_OPEN, %rax
movq $output_filename, %rdi
movq $0101, %rsi
movq $0666, %rdx
syscall
movq %rax, ST_OUTPUT_DESCRIPTOR(%rbp)
loop_begin:
pushq ST_INPUT_DESCRIPTOR(%rbp)
pushq $record_buffer
call read_record
addq $16, %rsp
# Return number of bytes read. If it's not the same as
# $RECORD_SIZE, then we are either at EOF or we hit an error.
cmpq $RECORD_SIZE, %rax
jne loop_end
# Increment age...
incq record_buffer + RECORD_AGE
# Write record to the output file
pushq ST_OUTPUT_DESCRIPTOR(%rbp)
pushq $record_buffer
call write_record
addq $16, %rsp
jmp loop_begin
loop_end:
movq $SYS_EXIT, %rax
movq $0, %rbx
syscall
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