I found a pdf file called: ProgrammingGroundUp-1-0-booksize.pdf, and one of the projects is to make an assembly program that takes in files and converts them to uppercase, `
.section .data
#######CONSTANTS########
#system call numbers
.equ SYS_OPEN, 5
.equ SYS_WRITE, 4
.equ SYS_READ, 3
.equ SYS_CLOSE, 6
.equ SYS_EXIT, 1
#options for open (look at
#/usr/include/asm/fcntl.h for
#various values. You can combine them
#by adding them or ORing them)
#This is discussed at greater length
#in "Counting Like a Computer"
.equ O_RDONLY, 0
.equ O_CREAT_WRONLY_TRUNC, 03101
#standard file descriptors
.equ STDIN, 0
.equ STDOUT, 1
.equ STDERR, 2
#system call interrupt
.equ LINUX_SYSCALL, 0x80
.equ END_OF_FILE, 0
#This is the return value
#of read which means we’ve
#hit the end of the file
.equ NUMBER_ARGUMENTS, 2
.section .bss
.equ BUFFER_SIZE, 500
.lcomm BUFFER_DATA, BUFFER_SIZE
.section .text
#STACK POSITIONS
.equ ST_SIZE_RESERVE, 8
.equ ST_FD_IN, -4
.equ ST_FD_OUT, -8
.equ ST_ARGC, 0
#Number of arguments
.equ ST_ARGV_0, 4
#Name of program
.equ ST_ARGV_1, 8
#Input file name
.equ ST_ARGV_2, 12
#Output file name
.globl _start
_start:
###INITIALIZE PROGRAM###
#save the stack pointer
movl %esp, %ebp
#Allocate space for our file descriptors
#on the stack
subl $ST_SIZE_RESERVE, %esp
open_files:
open_fd_in:
###OPEN INPUT FILE###
#open syscall
movl $SYS_OPEN, %eax
#input filename into %ebx
movl ST_ARGV_1(%ebp), %ebx
#read-only flag
movl $O_RDONLY, %ecx
#this doesn’t really matter for reading
movl $0666, %edx
#call Linux
int $LINUX_SYSCALL
store_fd_in:
#save the given file descriptor
movl %eax, ST_FD_IN(%ebp)
open_fd_out:
###OPEN OUTPUT FILE###
#open the file
movl $SYS_OPEN, %eax
#output filename into %ebx
movl ST_ARGV_2(%ebp), %ebx
#flags for writing to the file
movl $O_CREAT_WRONLY_TRUNC, %ecx
#mode for new file (if it’s created)
movl $0666, %edx
#call Linux
int
$LINUX_SYSCALL
store_fd_out:
#store the file descriptor here
movl %eax, ST_FD_OUT(%ebp)
###BEGIN MAIN LOOP###
read_loop_begin:
###READ IN A BLOCK FROM THE INPUT FILE###
movl $SYS_READ, %eax
#get the input file descriptor
movl ST_FD_IN(%ebp), %ebx
#the location to read into
movl $BUFFER_DATA, %ecx
#the size of the buffer
movl $BUFFER_SIZE, %edx
#Size of buffer read is returned in %eax
int
$LINUX_SYSCALL
###EXIT IF WE’VE REACHED THE END###
#check for end of file marker
cmpl $END_OF_FILE, %eax
#if found or on error, go to the end
jle end_loop
continue_read_loop:
###CONVERT THE BLOCK TO UPPER CASE###
pushl $BUFFER_DATA
#location of buffer
pushl %eax
#size of the buffer
call convert_to_upper
popl %eax
#get the size back
addl $4, %esp
#restore %esp
###WRITE THE BLOCK OUT TO THE OUTPUT FILE###
#size of the buffer
movl %eax, %edx
movl $SYS_WRITE, %eax
#file to use
movl ST_FD_OUT(%ebp), %ebx
#location of the buffer
movl $BUFFER_DATA, %ecx
int $LINUX_SYSCALL
###CONTINUE THE LOOP###
jmp read_loop_begin
end_loop:
###CLOSE THE FILES###
#NOTE - we don’t need to do error checking
movl $SYS_CLOSE, %eax
movl ST_FD_OUT(%ebp), %ebx
int $LINUX_SYSCALL
movl ST_FD_IN(%ebp), %ebx
movl $SYS_CLOSE, %eax
int $LINUX_SYSCALL
###EXIT###
movl $SYS_EXIT, %eax
movl $0, %ebx
int $LINUX_SYSCALL
###CONSTANTS##
#The lower boundary of our search
.equ LOWERCASE_A, ’a’
#The upper boundary of our search
.equ LOWERCASE_Z, ’z’
#Conversion between upper and lower case
.equ UPPER_CONVERSION, ’A’ - ’a’
###STACK STUFF###
.equ ST_BUFFER_LEN, 8 #Length of buffer
.equ ST_BUFFER, 12
#actual buffer
convert_to_upper:
pushl %ebp
movl %esp, %ebp
###SET UP VARIABLES###
movl ST_BUFFER(%ebp), %eax
movl ST_BUFFER_LEN(%ebp), %ebx
movl $0, %edi
#if a buffer with zero length was given
#to us, just leave
cmpl $0, %ebx
je end_convert_loop
convert_loop:
#get the current byte
movb (%eax,%edi,1), %cl
#go to the next byte unless it is between
#’a’ and ’z’
cmpb $LOWERCASE_A, %cl
jl next_byte
cmpb $LOWERCASE_Z, %cl
jg next_byte
#otherwise convert the byte to uppercase
addb $UPPER_CONVERSION, %cl
#and store it back
movb %cl, (%eax,%edi,1)
next_byte:
incl %edi
#next byte
cmpl %edi, %ebx
#continue unless
#we’ve reached the
#end
jne convert_loop
end_convert_loop:
#no return value, just leave
movl %ebp, %esp
popl %ebp
ret
`
the assembler is called "as", and the code is on page 87 of the file, you can easily get if you look it up on google, also the code doesn't copy and paste correctly for some reason, so you might sometimes see things like: jmp to_another_point
I tried to get rid of as many of those as I could, but there still might be some, and some of the comments were probably lost in the process, so I would suggest opening the original pdf file. I am running Ubuntu linux version 10.04.1, I am using as version 2.20.1, and the problem is that it creates the file, but the file is always empty.