CIT 593代做、代写Dynamic Memory、代写C++设计、C/C++编程语言调试

日期：2019-12-09 10:13

CIT 593 | Assignment: Dynamic Memory & File I/O | 1

Setting up Codio for this HW:

1) Open the Codio assignment via Coursera

2) From the Codio File-Tree click on: lc4_memory.h and lc4_memory.c

Overview:

The goal of this HW is for you to write a program that can open and read in a .OBJ file created

by PennSim, parse it, and load it into a linked list that will represent the LC4’s program and data

memories (similar to what PennSim’s “loader” does). In the last HW, you created a .OBJ file. In

this HW, you will be able to read in a .OBJ file and convert it back to the assembly it came from!

This is known as reverse assembling (sometimes a disassembler).

RECALL: OBJECT FILE FORMAT

The following is the format for the binary .OBJ files created by PennSim from your .ASM files. It

represents the contents of memory (both program and data) for your assembled LC-4

Assembly programs. In a .OBJ file, there are 3 basic sections indicated by 3 header “types” =

CODE, DATA, SYMBOL.

● Code: 3-word header (xCADE, <address>, <n>), n-word body comprising the instructions.

This corresponds to the .CODE directive in assembly.

● Data: 3-word header (xDADA, <address>, <n>), n-word body comprising the initial data

values. This corresponds to the .DATA directive in assembly.

● Symbol: 3-word header (xC3B7, <address>, <n>), n-character body comprising the

symbol string. Note, each character in the file is 1 byte, not 2. There is no null

terminator. Each symbol is its own section. These are generated when you create labels

(such as “END”) in assembly.

LINKED LIST NODE STRUCTURE:

In the file: lc4_memory.h, you’ll see the following structure defined:

The structure is meant to model a row of the LC4’s memory: a 16-bit address, & its 16-bit

contents. As you know, an address may also have a label associated with it. You will also recall

that PennSim always shows the contents of memory in its “assembly” form. So PennSim

reverse-assembles the contents and displays the assembly instruction itself (instead of the

binary contents).

CIT 593 | Assignment: Dynamic Memory & File I/O | 2

As part of this assignment, you will read in a .OBJ file and store each instruction in a NODE of

the type above. Since they’ll be an unknown # of instructions in the file, you’ll create a linked

list of the nodes above to hold all the instructions that are in the .OBJ file.

The details of how to implement all of this will be discussed in the sections of this document

that follow.

FLOW CHART: Overview of Program Operation

CIT 593 | Assignment: Dynamic Memory & File I/O | 3

IMPLEMENTATION DETAILS:

The first files to view in the helper file are lc4_memory.h and lc4_memory.c. In these files you

will notice the structure that represents a row_of_memory as referenced above (see the

section: LINKED_LIST_NODE_STRUCTURE above for the node’s layout). You will also see

several helper functions that will serve to manage a linked list of “rows_of_memory” nodes.

Your job will be to implement these simple linked list helper functions using your knowledge

from the last HW assignment.

Next, you will modify the file called: lc4.c It serves as the “main” for the entire program. The

head of the linked list must be stored in main(), you will see in the provided lc4.c file a pointer

named: memory will do just that. Main() will then extract the name of the .OBJ file the user has

passed in when they ran your program from the argv[] parameter passed in from the user.

Upon parsing that, it will call lc4_loader.c’s open_file() and hold a pointer to the open file. It

will then ask call lc4_loader.c’s parse_file() to interpret the .OBJ file the user wishes to have

your program process. Lastly it will reverse assemble the file, print the linked list, and finally

delete it when the program ends. These functions are described in greater detail below. The

order of the function calls and their purpose is shown in commends in the lc4.c file that you will

implement as part of this assignment.

Once you have properly implemented lc4.c and have it accept input from the command line, a

user should be able to run your program as follows:

./lc4 my_file.obj

Where “my_file.obj” can be replaced with any file name the user desires as long as it is a valid

.OBJ file that was created by PennSim. If no file is passed in, your program should generate an

error telling the user what went wrong, like this:

error1: usage: ./lc4 <object_file.obj>

CIT 593 | Assignment: Dynamic Memory & File I/O | 4

Problem 1) Implementing the LC4 Loader

Most of the work of your program will take place in the file: called: lc4_loader.c. In this file, you

will start by implementing the function: open_file() to take in the name of the file the user of

your program has specified on the command line (see lc4_loader.h for the definition of

open_file()). If the file exists, the function should return a handle to that open file, otherwise a

NULL should be returned.

Also in lc4_loader.c, you will implement a second function: parse_file() that will read in and

parse the contents of the open .OBJ file as well as populate the linked_list as it reads the .OBJ

file. The format of the .OBJ input file has been in lecture, but its layout has been reprinted

above (see section: INPUT_FILE_FORMAT). As shown in the flowchart above, have the function

read in the 3-word header from the file. You’ll notice that all of the LC4 .OBJ file headers

consist of 3 fields: header type, <address>, <n>. As you read in the first header in the file, store

the address field and the <n> field into local variables. Then determine the type of header you

have read in: CODE/DATA/SYMBOL.

If you have read in a CODE header in the .OBJ file, from the file format for a .OBJ file, you’ll

recall the body of the CODE section is <n>-words long. As an example, see the hex listed below,

this is a sample CODE section, notice the field we should correlate with n=0x000C, or decimal:

12. This indicates that the next 12-words in the .OBJ file are in fact 12 LC-4 instructions. Recall

each instruction in LC4 is 1 word long.

CA DE 00 00 00 0C 90 00 D1 40 92 00 94 0A 25 00 0C 0C 66 00 48

01 72 00 10 21 14 BF 0F F8

From the example above, we see that the first LC-4 instruction in the 12-word body is: 9000.

(that happens to be a CONST assembly instruction if you convert to binary). Allocate memory

for a new node in your linked list to correspond to the first instruction (the section above:

LINKED LIST NODE STRUCTURE, declares a structure that will serve as a blue-print for all your

linked list nodes called: “row_of_memory”). As it is the first instruction in the body, and the

address has been listed as 0000, you would populate the row_of_memory structure as follows.

address 0000

label NULL

contents 9000

assembly NULL

next NULL

CIT 593 | Assignment: Dynamic Memory & File I/O | 5

In a loop, read in the remaining instructions from the .OBJ file; allocate memory for a

corresponding row_of_memory node for each instruction. As you create each

row_of_memory add these nodes to your linked list (you should use the functions you’ve

created in lc4_memory.c to help you with this). For the first 3 instructions listed in the sample

above, your linked list would look like this:

The procedure for reading in the DATA sections would be identical to reading in the CODE

sections. These would become part of the same linked list, as we remember PROGRAM and

DATA are all in one “memory” on the LC-4, they just have different addresses.

For the following SYMBOL header/body:

C3 B7 00 00 00 04 49 4E 49 54

The address field is: 0x0000. The symbol field itself is: 0x0004 bytes long. The next 4 bytes: 49

4E 49 54 are ASCII for: INIT. This means that the label for address: 0000 is INIT. Your

program must search the linked list: memory, find the appropriate address that this label is

referring to and populate the “label” field for the node. Note: the field: <n> tells us exactly how

much memory to malloc() to hold the string, however you must add a byte to hold the NULL. 5

bytes in the case of: INIT. For the example above, the node: 0000 in your linked list, would be

updated as follows:

address 0000

label INIT

contents 9000

assembly NULL

next

Once you have read the entire file; created and added the corresponding nodes to your linked

list, close the file and return to main(). If you encounter an error in closing the file, before

exiting, print an error, but also free() all the memory associated with the linked list prior to

exiting the program.

CIT 593 | Assignment: Dynamic Memory & File I/O | 6

Problem 2) Implementing the Reverse Assembler

In a new file: lc4_disassembler.c: write a third function (reverse_assemble) that will take as

input the populated “memory” linked list (that parse_file() populated) – it will now contain the

.OBJ’s contents. reverse_assemble() must translate the hex representation of some of the

instructions in the LC4 memory’s linked list into their assembly equivalent. You will need to

reference the LC4’s ISA to author this function. To simplify this problem a little, you DO NOT

need to translate every single HEX instruction into its assembly equivalent. Only translate

instructions with the OPCODE: 0001 (ADD REG, MUL, SUB, DIV, ADD IMM)

As shown in the flowchart, this function will call your linked list’s “search_by_opcode()” helper

function. Your search_by_opcode() function should take as input an OPCODE and return the

first node in the linked list that matches the OPCODE passed in, but also has a NULL assembly

field. When/if a node in your linked list is returned, you’ll need to examine the “contents” field

of the node and translate the instruction into its assembly equivalent. Once you have

translated the contents filed into its ASCII Assembly equivalent, allocate memory for and store

this as string in the “assembly’ field of the node. Repeat this process until all the nodes in the

linked list with an OPCODE=0001 have their assembly fields properly translated.

As an example, the figure below shows a node on your list that has been “found” and returned

when the search_by_opcode() function was called. From the contents field, we can see that

the HEX code: 128B is 0001 001 010 001 011 in binary. From the ISA, we realize the sub-opcode

reveals that this is actually a MULTIPLY instruction. We can then generate the string MUL R1,

R2, R3 and store it back in the node in the assembly field. For this work, I strongly encourage

you to investigate the switch() statement in C (any good book on C will help you understand

how this works and why it is more practical than multiple if/else/else/else statements). I also

remind you that you must allocate memory strings before calling strcpy()!

CIT 593 | Assignment: Dynamic Memory & File I/O | 7

Problem 3) Putting it all together

As you may have realized main() should do only 3 things: 1) create and hold the pointer to your

memory linked list. 2) Call the parsing function in lc4_loader.c. 3) Call the disassembling

function in lc4_dissassembler.c. One last thing to do in main() is to call a function to print the

contents of your linked list to the screen. Call the print_list() function In lc4_memory.c; you will

need to implement the printing helper function to display the contents of your lc4’s memory

list like this:

<label> <address> <contents> <assembly>

INIT 0000 9000

0001 D140

0002 9200

…

0009 128B MUL R1, R2, R3

(and so on…)

Several things to note: There can be multiple CODE/DATA/SYMBOL sections in one .OBJ file. If

there is more than one CODE section in a file, there is no guarantee that they are in order in

terms of the address. In the file shown above, the CODE section starting at address 0000, came

before the CODE section starting at address: 0010; there is no guarantee that this will always

happen, your code must be able to handle that variation. Also, SYMBOL sections can come

before CODE sections! What all of this means is that before one creates/allocates memory for

a new node in the memory list, one should “search” the list to make certain it does not already

exist. If it exists, update it, if not, create it and add it to the list!

Prior to exiting your program, you must properly “free” any memory that you allocated. We

will be using a memory checking program known as valgrind to ensure your code properly

releases all memory allocated on the heap! Simply run your program: lc4 as follows:

valgrind –leak-check=full lc4

Valgrind should report 0 errors AND there should be no memory leaks prior to

submission.

Note: we will run Valgrind on your submission, if it leaks memory, you will lose many

points on this assignment. So watch the VIDEO, learn how to use Valgrind!!

Also note: If your code doesn’t compile or even run, you will lose most of the points of

this assignment!

CIT 593 | Assignment: Dynamic Memory & File I/O | 8

TESTING YOUR CODE

When writing such a large program, it is a good strategy to “unit test.” This means, as you

create a small bit of working code, compile it and create a simple test for it. As an example,

once you create your very first function: add_to_list(), write a simple “main()” and test it out.

Call it, print out your “test” list, see if this function even works. Run Valgrind on the code, see if

it leaks memory. Once you are certain it works, and doesn’t leak memory, go on to the next

function: “search_address()”; implement that, test it out.

DO NOT write the entire program, compile it, and then start testing it. You will never resolve all

of your errors this way. You need to unit test your program as you go along or it will be

impossible to debug.

Where to get input files?

In the last assignment, you created a .OBJ file. Try loading that file into Codio, and use your

program on it. You know exactly how that program should disassemble. To test further, bring

up PennSim, write a simple program in it, output a .OBJ from PennSim, then read into your

program and see if you can disassemble it. You can create a bunch of test cases very easily with

PennSim.

CIT 593 | Assignment: Dynamic Memory & File I/O | 9

STRUCTURING YOUR CODE:

Preloaded in Codio, you’ll find some of the files named below. For the ones you don’t see on

Codio, you must create them and implement them as described in the assignment above.

lc4.c - must contain your main() function.

lc4_memory.c - must contain your linked list helper functions.

lc4_memory.h - must contain the declaration of your row_of_memory

structure & linked list helper functions

lc4_loader.h - contains your loader function declarations.

lc4_loader.c - must contain your .OBJ parsing function.

lc4_disasembler.h - contains your disassembler function declarations.

lc4_disasembler.c - must contain your disassembling function.

Makefile - must contain the targets:

lc4_memory.o

lc4_loader.o

lc4_disassembler.o

lc4

All, clean and clobber

You cannot alter any of the existing functions in the .h files.

EXTRA CREDIT: A complete reverse assembler:

Finish the disassembler to translate any/all instructions in the ISA. Have you program print the

linked list to the screen still, but also create a new output file: <users_input>.asm. In that file it

should contain only the assembly program that you disassembled. If it works, I should be able

to load it into PennSim , assemble it, and reproduce the identical .OBJ file that your .ASM file

was derived from! Don’t forget to add in the directives (.CODE, .DATA)…the ultimate test of

your program will be getting it to assemble using PennSim!

Important Note on Plagiarism:

o We will scan your HW files for plagiarism using an automatic plagiarism detection tool.

o If you are unaware of the plagiarism policy, make certain to check the syllabus to see the

possible repercussions of submitting plagiarized work (or letting someone submit yours).