Binary Lab作业代做、代写C/C++编程语言作业、代做bin-lab-ref作业、C/C++程序作业代写
Binary Lab
Description
The main aim of this lab is to understand provided assembly code and generate C code that
corresponds to that assembly. You are provided with a C file (bin-lab.c) that contains a filled
main() function and empty five functions f1(), f2(), f3(), f4(), and f5(). Your job is to read the
object files (more on this shortly), understand the assembly of each function, and write the
corresponding C code of each of the 5 functions in the 5 C files. The main goal is that if we
compile and execute your code, it must generate the same output as the original executable ./binlab-ref
(provided).
Note: The fact that you have one function in each of the provided empty C files does not mean
that this function does not call another function. For example, when you examine the code for
f1() you may find that f1() calls another function b1(). In this case, you need to include b1() in
your code too.
Steps:
1. Download the file bin-lab.c
2. Download the executable bin-lab-ref
3. Execute bin-lab-ref to see the different outputs. You just need to type: ./bin-lab-ref
4. You need to fill-in the blanks of file bin-lab.c such that when executed, its output is similar to
./bin-lab-ref
5. You compile your code with the following command:
gcc -o bin-lab -fomit-frame-pointer bin-lab.c
How to work on this lab?
Your main source of help is a tool called objdump. Type:
objdump - d ./bin-lab-ref > output.txt
Open the file output.txt with any text editor and you will find the assembly of the code. Your
best starting point is to look for the labels f1, f2, f3, f4, and f5 on at a time and read the assembly
of each corresponding function. There may be extra assembly code, related to other libraries; you
do not need to worry about them.
Note: The aim is to make your executable generate the same output as ./bin-lab-ref but the
assembly generated from your code does NOT need to match the assembly generated from
the original code as this is not easily achievable.
Grading
There are 5 functions to implement. Each one is worth 20 points, for a total of 100 points.
Submission
You just need to submit bin-lab.c through NYU classes.
Important Notes
If, by trying to execute ./bin-lab-ref you receive “command not found” or the like, then type:
chmod 777 ./bin-lab-ref
and then re-try to execute./bin-lab-ref
Some instructions that we did not cover in class but you may find in the object files (not included
in the exam though):http://www.daixie0.com/contents/13/2080.html
repz: This is used due to some strange behavior with old AMD K8 regarding its branch
prediction. To make long story short, neglect it! So if you see, for example, repz retq
assume it is retq only.
nopl: this is a no-operation instruction. That is, do nothing instruction. It can take
argument but does nothing with it. It is mainly used as a delay instruction waiting for an
event to happen, such as incrementing rip register (more in-depth explanation will take us
a bit deeper into hardware). Also, it is used as “padding” in the code to make following
instruction start at specific address.
Enjoy!
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