arm汇编代写 CMP-5013A Architectures

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School of Computing Sciences

CMP-5013A Architectures and Operating Systems Simple cipher in ARMv-7 assesmbly language.

Michal Mackiewicz M.Mackiewicz@uea.ac.uk 12th October 2018
25%

14th November 2018 3pm week 8 12th December 2018
Blackboard

Learning outcomes

To become familiar with the basic ARMv7-A instruction set architecture. Improved low-level programming skills with a focus on creating efficient solutions.

Specification Overview

In this assignment you will implement a simple cipher in the ARMv7-A assembly language.

Description

The algorithm you will implement is based on letter transpositions according to the scheme illustrated in Table 1.

The cipher requires a secret private key, which needs to be known to both parties to encrypt and decrypt any messages. The key can be represented by a string of characters.

Table 1: A table containing the private key and the message.

Let’s assume that we want to encrypt the string attack at five past four tomorrow with the private key string dragon. First, you enter the message into a table, row by row as shown in Ta- ble 1. If there is any space left in the last row, we fill it with one of the rare letters e.g. x. In order to encrypt the message, we need to change the order of the columns in the table according to the alphabetic order of the letters in the private key as shown in Table 2. Then, the enciphered

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Table 2: A table with the reordered columns. Cipher text can be read columnwise.

message is read columnwise. In this case, it would be tfstoaapuraitowkeooxcvfmxttarr. Note, to make the deciphering operation harder, you need to strip any message from all white spaces and punctuation and convert any upper case letters to lower case.

Message decryption is a reverse process utilising the same table. The cipher text is written into the columns of Table 2 and later read according to the private key letter order.

Your ARM assembly program, which you must name cw1, must accept two command line arguments. First argument must be 0 or 1 denoting encrypt/decrypt. The second argument must be a string representing the private key. The actual text to be encrypted/decrypted must be passed to the program using standard input. Your program must first convert the upper case letters to lower case before encryption. Further, it must strip the input text from any characters and whitespaces other than the 26 lower case English alphabet letters. The program must return its output i.e. depending on the first argument encrypted/decrypted text using standard output. You should test your program with the following syntax:

cat textfile.txt | ./cw1 0 privatekeystring | ./cw1 1 privatekeystring

This should return the original text from textfile.txt, albeit lower case and without white spaces and punctuation.

You are allowed to assume that the program input will not be longer than 1000 letter char- acters.

Relationship to formative assessment

The formative tests, which are available on Blackboard, should be helpful in learning the ARMv7 ISA. You should complete labsheets 5-7 before attempting this coursework.

Deliverables

This is an exercise that can be done in pairs. If you choose to work in a pair you must notify me about your pair members by email by Wed 24th Oct 5pm. If you don’t, you must complete your work individually.

The source code must be zipped into a file with the name containing Student IDs of both members of the group or your student ID if you worked individually. Both members of the group must then submit this (same) file to the digital dropbox located on the module Blackboard page. Make sure you test your solutions on a PiCluster machine BEFORE you submit.

Late submissions need to follow the appropriate late hand-in procedure. You can find out this information from the Hub.

If you have medical or other problems you can seek extensions to coursework deadlines. However, it is essential you obtain proper documentation in such cases (i.e. a medical certifi- cate).

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If one of the pair members is granted an extension, the other member of the pair also receives an extension. However, remember that this will apply only to those pairs who notified me that they will work in pairs, as explained above.

If you choose to work in a pair, both members of the pair are equally responsible for the joint work. In case of any breakdown of co-operation, you should complete your work individually and notify me by email. You will not receive any extra marks in such a case or for the fact that you chose or had to work individually. To make this very clear, you should treat this coursework as an individual exercise, which you are allowed to do in pairs.

If you cannot find your pair and would like me to help you find one, then please send me an email with your details by Monday 22nd Oct 6pm and I will try to pair you with another student. I strongly encourage everyone to engage in pair work.

Resources

You should do the Labsheets 5-7 which are available on BB. Labsheet 7 will contain exercises which will be particularly relevant from the point of view of this coursework. You should also consult the lecture notes on ARMv7 ISA.

Please also note the list of references below. In particular, I would encourage you to go through the relevant chapters in references [2] and [3].

You should attend all the lab sessions and discuss your progress with the teaching staff who will be able to provide you formative feedback.

My general advice on attempting this exercise as well as any other exercise in any assembly language would be to break the problem into small tasks and tackle them one by one. For each of these tasks, write a pseudo-code or the C code before you start writing in the assembly language.

Marking Scheme

This coursework carries 25% of the module weight so you will receive up to 25 marks. We will use the following marking scheme to award marks:

• All functionality implemented as requested. (up to 13 marks) • Code quality. (up to 6 marks).
• Quality of the code comments. (up to 6 marks).

We will judge the code quality based on the following criteria. You should follow the AAPCS Procedure Call Standard. The use of stack as well as frequent load/store instructions should be avoided if possible. Try to keep your variables in registers to make your program more effi- cient. Use ARM advanced addressing modes in cases when this can reduce the number of in- structions. Moreover, try to avoid short branches by using conditional execution of non-branch instructions.

The comments need to be extensive and they might take more space than the assembly code. The cw1.s you will need to submit should have a header with the usual information you find in the file headers such as the authors, dates and short descriptions. All variable to register mappings should be made clear. For each section you could attach a commented-out pseudo-code or C code. You should have both section and line comments.

Finally, you must not attempt to be ‘clever’ and submit the code that was produced by the C compiler. The requested program is simple enough to be written in assembly language from scratch. Any suspicious code will be thoroughly investigated and may result in 0 (zero) marks

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awarded for this assignment. We also reserve the right to quiz both members of the pair about any part of the code.

You should supplement your code with a brief commentary describing the individual con- tributions of both members of the pair.

References

1. [1]  ARM,TheARMv7ARreferencemanual,https://static.docs.arm.com/ddi0406/c/DDI0406C C arm architecture reference manual.pdf Last Accessed, Oct 2018.
2. [2]  Roger Ferrer Ibanez, Think in geek – ARM assembler in Rasberry Pi, http://thinkingeek.com/arm- assembler-raspberry-pi/
   Last Accessed, Oct 2018.
3. [3]  Robert G. Plantz, Introduction to Computer Organization: ARM Assembly Language Using the Raspberry Pi, http://bob.cs.sonoma.edu/IntroCompOrg-RPi/intro-co-rpi.html
   Last Accessed, Oct 2018.

4. [4]  ARM, Procedure call standard for http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042f/IHI0042F aapcs.pdf Last Accessed, Oct 2018.
5. [5]  ARM, ARM and Thumb-2 Instruction Set http://infocenter.arm.com/help/topic/com.arm.doc.qrc0001m/QRC0001 UAL.pdf Last Accessed, Oct 2018.

the ARM architecture,

Quick Reference

Card,

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