CS 213 Fall 2000 Homework Assignment H1 Part A Assigned Sept 12 Due Mon Sept 18 11 59PM Randy Bryant Randy Bryant cs cmu edu is the lead person for this assignment The purpose of this assignment is to learn IA32 Linux assembly language and to become familiar with how C code is translated into assembly You will do this by looking at a series of assembly language functions and decompiling them to find the C source code that produced them Reverse engineering this code will improve your understanding of both the C constructs and the assembly code Introduction In this assignment you will be given the assembly code file for a set of functions Your task is to derive C source code that compiles into code that is functionally equivalent In fact you should strive to make your code produce assembly code that is identical to the supplied assembly code None of the functions requires more than a few lines of code When you are trying to figure out what a given functions does try creating a small example to see what code the compiler emits If you can create a series of small functions that produce part of the answer you can then piece them together to create a solution Logistics You must work alone on this assignment The only hand in will be electronic Any clarifications and revisions to the assignment will be posted on Web page assigns html in the class WWW directory All files for this assignment are in the directory afs cs cmu edu academic class 15213 f00 H1a You will want to do your work on one of the class fish machines to be sure that you are using the correct version of the GCC compiler See the class WWW pages for more information on these machines First create a protected directory to work in and copy our template code using the command tar xvf afs cs cmu edu academic class 15213 f00 H1a H1a tar 1 This will create a variety of files including one named probs c In this assignment you will only modify this file Your first step should be to fill in your name and Andrew ID in the structure at the beginning of this file Your task is to fill in the bodies of six functions in probs c named arith mem optarith ifcode whilecode and forcode respectively Your goal is to make them have the same functionality as the corresponding functions in the file probs solve s The original C code for these functions has the following characteristics arith Some simple arithmetic operations mem Some memory referencing through pointers optarith Some arithmetic operations that get optimized by the compiler ifcode A conditional expression whilecode A while loop forcode A for loop Although you could brute force your solution by writing C code that uses goto s and things like that try to write the cleanest and most abstract C code you can Evaluation You will only get credit for problems in which you are able to exactly match the functionality of the assembly code versions The six problems count one point apiece Use the command make atest to generate a program that will run your functions against the original functions on some test data See the file README for documentation on this program Hand In Hand in your solution using the command make handin NAME yourname VERSION XX where yourname is your Andrew ID and XX is the version number i e 2 3 Only your highest numbered version submitted before the deadline will be graded 2
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