Sergeant's Website Assembly Language

HW08: Macros and The Stack due Mon 28 Oct 23:59

Purpose

This assignment gives practice writing x86_64 assembly code that:

uses the system stack to save and restore registers
uses a macro to perform a useful function without destroying register contents
views a string as a null-terminated array of individual characters

Allowed and Disallowed Resources

In completing this assignment you MAY use/access the following resources:

The assembly command cheat sheet (2 pages) handed out in class. https://josephus.sergeantservices.com/classes/al/source/pdf/IntelCodeTable.pdf
The ASCII chart handed out in class. https://josephus.sergeantservices.com/classes/al/source/pdf/ASCII-Conversion-Chart.pdf
Examples and sample code found here: https://josephus.sergeantservices.com/classes/al/source/. NOTE: The same examples can be cloned from this repository: https://tsergeant@bitbucket.org/tsergeant/al_examples.git
All files provided by the instructor in the al_homework repository.
Video instructions provided in Canvas as part of this course. You MAY NOT USE any other video resources.
The course notes that accompany the video instructions which can be found here: https://docs.google.com/presentation/d/1LLOiiKOPDwjEiQ4QDcC9pO59gUcud04ireg_4jbLs3w/edit#slide=id.p
The resources listed here: https://josephus.sergeantservices.com/classes/al/onlinesources.php which include the Intel Developer's Manual (https://josephus.sergeantservices.com/classes/al/source/pdf/intel_assembly_manual.pdf)
Any handouts provided by the instructor as part of this course.
Your own course notes
Your instructor
Discussions about the assignment with other students as long as you never look at the code produced by another student and you never receive instructions about solving the homework. That is, discussions need to be about concepts and understanding the technologies and not about how to solve the particular problem posed in this assignment.

You may NOT use/access:

Resources not expressly listed above, including, but not limited to, the following ...
Source code not provided as part of this assignment. (Obviously, this includes, but is not limited to, source code written by other students whether current or in the past).
Code-generating tools (of which ChatGPT is one of many examples).
Any web sites not directly linked to from the homework assignment.

Failure to abide by these guidelines will result in a zero for the assignment and the incident will be reported to the university provost as a violation of the university academic integrity policy. A second incident of academic dishonesty (whether from this course or another computer science course) will result in an F in the course.

Problem Description

In a separate source file (i.e., not in labday.asm) write a macro called cmp_str that accepts two arguments. Both arguments should be 64-bit addresses of null-terminated strings. The macro should work whether the addresses are stored in registers or in labels.

The macro should perform a byte-wise comparison of the individual bytes of the two strings and should finish with the status flags set so that the conditional jump commands will work properly if issued directly after the macro call.

The macro should preserve registers with the possible exception of one register that you may destroy.

Your program should allow the user to enter two strings and then should use the macro to determine whether the the strings are equal or if the first is less than the second or if the first is greater than the second. The input and output should be performed in the main program (not in the macro).

Examples

Suppose your program contains the following statements:

   cmp_str  A,B
   jl	      fun
   jmp      superfun

This table shows expected results for various values of A and B. REMEMBER: A and B could be labels or registers containing the address of a string. NOTE: This is NOT a complete list of test value, but rather some examples to illustrate what is expected.

A	B	Comparison	Result
ABE	LINCOLN	ABE LINCOLN	jump to fun
ABE	AB	ABE AB	jump to superfun
ZZTOP	abe	ZZTOP abe	jump to fun
(empty string)	A	`' A	jump to fun
SUPERFUN	SUPERFUNNY	SUPERFUN SUPERFUNNY	jump to fun
ABE	ABE	ABE ABE	jump to superfun