add-year-lseek.s

.include "linux.s"
.include "record-def.s"

.section .data
file_name:
.ascii "test.dat\0"

.section .bss
.lcomm record_buffer, RECORD_SIZE

#Stack offsets of local variables
.equ ST_FILE_DESCRIPTOR, -4

.section .text
.globl _start
_start:
#Copy stack pointer and make room for local variables
movl  %esp, %ebp
subl  $4, %esp

# Open file for writing and reading
movl  $SYS_OPEN, %eax
movl  $file_name, %ebx
movl  $2, %ecx
movl  $0666, %edx
int   $LINUX_SYSCALL

movl  %eax, ST_FILE_DESCRIPTOR(%ebp)

loop_begin:
pushl ST_FILE_DESCRIPTOR(%ebp)
pushl $record_buffer
call  read_record
addl  $8, %esp

#Returns the number of bytes read.
#If it isn't the same number we
#requested, then it's either an
#end-of-file, or an error, so we're
#quitting
cmpl  $RECORD_SIZE, %eax
jne   loop_end

#Increment the age
incl  record_buffer + RECORD_AGE

# Reposition the offset of the open file
movl $SYS_LSEEK, %eax
movl ST_FILE_DESCRIPTOR(%ebp), %ebx
movl $RECORD_AGE, %ecx
movl $0, %edx
int $LINUX_SYSCALL

# TODO...Not sure how to write the year now.
movl $SYS_WRITE, %eax
movl ST_FILE_DESCRIPTOR(%ebp), %ebx
movl record_buffer + RECORD_AGE, %ecx
movl $4, %edx
int $LINUX_SYSCALL

jmp loop_begin

loop_end:
movl $SYS_EXIT, %eax
movl $0, %ebx
int $LINUX_SYSCALL

linux.s

#Common Linux Definitions

#System Call Numbers
.equ SYS_EXIT, 1
.equ SYS_READ, 3
.equ SYS_WRITE, 4
.equ SYS_OPEN, 5
.equ SYS_CLOSE, 6
.equ SYS_BRK, 45
.equ SYS_LSEEK, 19

#System Call Interrupt Number
.equ LINUX_SYSCALL, 0x80

#Standard File Descriptors
.equ STDIN, 0
.equ STDOUT, 1
.equ STDERR, 2

#Common Status Codes
.equ END_OF_FILE, 0

record-def.s

.equ RECORD_FIRSTNAME, 0
.equ RECORD_LASTNAME, 40
.equ RECORD_ADDRESS, 80
.equ RECORD_NICK, 320
.equ RECORD_AGE, 360

.equ RECORD_SIZE, 364