Unnamed

 .section .data
 mode_write:
  .ascii "w\0"
 mode_read:
  .ascii "r\0"
  #.equ stores numerical data, don't know if we could use those for these modes ie r0
 .section .text
 .globl _start
 .equ ST_ARGC, 0
 .equ ST_ARGV_0, 4
 .equ ST_ARGV_1, 8
 .equ ST_ARGV_2, 12
 #we'll take an input/output file as arguements
_start:
 movl %esp, %ebp
 subl $8, %esp      #local file descriptor variables
 pushl $mode_read
 pushl ST_ARGV_1(%ebp)
 call fopen         #not too interested in error checking stuff now :p
 addl $8, %esp
 movl %eax, -4(%ebp)
 
 pushl $mode_write
 pushl ST_ARGV_2(%ebp)
 call fopen
 addl $8, %esp
 movl %eax, -8(%ebp)
 
 .equ LOWERCASE_A, 'a'    #I don't know why i put these, just keeping to an example i seen :)
 .equ LOWERCASE_Z, 'z'
 .equ TO_UPPER_CONVERT, 'A' - LOWERCASE_A
 convert_loop:
 pushl -4(%ebp)
 call fgetc
 addl $4, %esp
 cmpl $0, %eax    #returns EOF/0 or error.. whatever works :)
 jle done_convert
 cmpl $LOWERCASE_A, %eax
 jl convert_loop
 cmpl $LOWERCASE_Z, %eax
 jg convert_loop
 
 #convert the character
 addl $TO_UPPER_CONVERT, %eax
 
 pushl -8(%ebp)     #push descriptor or FILE struct pointer
 pushl %eax         #push the character code
 call fputc
 continue:          #just a marker
  jmp convert_loop
 done_convert:
  pushl -8(%ebp)
  call fclose
  pushl -4(%ebp)
  call fclose
  pushl $0
  call exit