358 lines
14 KiB
TeX
358 lines
14 KiB
TeX
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\documentclass[a4paper]{article}
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\usepackage{graphicx}
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\usepackage{tabularx}
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\usepackage{enumitem}
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\usepackage{chngpage}
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\usepackage{calc}
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\usepackage[hidelinks]{hyperref}
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\usepackage[english]{babel}
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\usepackage{fancyvrb}
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\usepackage{tikz}
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\usepackage{forest}
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\usepackage[utf8]{inputenc}
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\usepackage{commath}
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\usepackage{minted}
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\usepackage{quotes}
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\usepackage{listings}
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\usepackage{graphicx}
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\usepackage{minted}
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\def\infinity{\rotatebox{90}{8}}
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\usepackage[shortlabels]{enumitem}
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\usepackage{caption}
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\usepackage{float}
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\usepackage{amssymb}
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\usepackage{amsmath}
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\usepackage{diagbox}
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\usepackage{slashbox}
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\usepackage{geometry} % For page dimensions and margins
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\geometry{
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paper=a4paper,
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top=2.5cm, % Top margin
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bottom=3cm, % Bottom margin
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left=2cm, % Left margin
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right=2cm, % Right margin
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}
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\usepackage{pgfplots}
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\pgfplotsset{width=15cm, height=10cm}
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\setminted{
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autogobble
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}
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\begin{document}
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\begin{titlepage}
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\scshape
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\centering
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\includegraphics[width=3cm, keepaspectratio]{logo_usi.png}
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\par
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\vspace{0.1cm}
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\texttt{FACULTY OF INFORMATICS}
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\vspace{1cm}
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\raisebox{-\baselineskip}{\rule{\textwidth}{1px}}
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\rule{\textwidth}{1px}
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\vspace{0.2cm}
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{\LARGE{{Advanced java programming}}}\par \vspace{0.1cm}
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Assignment 4
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\rule{\textwidth}{2px}
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\vspace{1cm}
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\begin{tabular}{lp{1cm}l}
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Author & \rule{0pt}{3ex} & FEDERICO \mbox{LAGRASTA}\\
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&&\\
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& \rule{0pt}{3ex} & CLAUDIO \mbox{MAGGIONI}
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\end{tabular}
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\vspace{1.3cm}
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\vfill
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\today
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\end{titlepage}
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\section*{Exercise A: Concurrency}
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As no synchronization b[Oetween the started threads exists, all the possible permutations of ``tX'' where $x$ is 1, 2 or 3 are valid outputs. Namely, all possible combinations are: \marginpar[right
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text]{\color{white}\url{https://youtu.be/4U_06LuzwJY}}
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\begin{itemize}
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\item ``t1 t2 t3 ``
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\item ``t1 t2 t3 ``
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\item ``t2 t1 t3 ``
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\item ``t2 t3 t1 ``
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\item ``t3 t1 t2 ``
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\item ``t3 t2 t1 ``
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\end{itemize}
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\section*{Exercise B: Concurrency}
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\begin{enumerate}
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\item No, as the method is \texttt{synchronized} and requires a mutually exclusive lock to be acquired to execute it, therefore only one thread at a time can execute;
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\item Yes, as \textit{getCounter()} is not marked with the \texttt{synchronized} keyword;
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\item Yes, as one thread may acquire the lock for \textit{incrementCounter()} while the other just released it and is executing \textit{getCounter()};
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\item Yes, as the updates to the \textit{count} variable in \textit{Counter} are atomic and safe,
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therefore the count will always be exact;
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\item The object will acquire and release the intrinsic lock of the \textit{counter} object defined at line 17.
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\end{enumerate}
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\section*{Exercise C: Concurrency}
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No, as the foreach loops may indeed run simultaneously. According to the Java 17 standard library documentation for \texttt{Collections.synchronizedList(...)}\footnote{\url{https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/Collections.html\#synchronizedList(java.util.List)}}, in order to obtain such access behaviour we would need to use the intrinsic lock of the list object wrapping the foreach loop with a \texttt{synchronized (integerList)} block.
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\section*{Exercise D: JVM Architecture}
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\begin{enumerate}
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\item As invoking \texttt{javap Secret} reports:
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\begin{verbatim}
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Warning: File ./Secret.class does not contain class Secret
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Compiled from "Login.java"\end{verbatim}
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the name of the original Java file is \texttt{Login.java};
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\item According to the output of \texttt{javap -c -l Secret}, specifically these lines:
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\begin{verbatim}
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0: ldc #55 // String Hello, try to find the username and the password [...]
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71: ldc #79 // String Congratulations, now write the username and the [...]
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[...]
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LineNumberTable:
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line 27: 0
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[...]
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line 41: 68
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line 42: 76
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[...]\end{verbatim}
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the string starting with ``Hello'' is stored in tag 55 of the constant pool and is loaded at line 27. The string starting with ``Congratulations'' is stored in tag 79 of the constant pool and is loaded at line 42.
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\item According to the output of \texttt{javap Secret} showing the class's interface:
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\begin{verbatim}
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public class Login {
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public Login();
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public static char transform(char);
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public static boolean access(java.lang.String, java.lang.String);
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public static void main(java.lang.String...);
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}\end{verbatim}
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there are three \texttt{public static} methods in the class.
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\end{enumerate}
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To aid the explanation of how we found the secret password we report the full output of
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\textit{javap -c -l Secret}:
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\begin{minted}{java}
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public class Login {
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public Login();
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Code:
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0: aload_0
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1: invokespecial #1 // Method java/lang/Object."<init>":()V
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4: return
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public static char transform(char);
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Code:
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0: iload_0
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1: bipush 97
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3: isub
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4: istore_1
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5: iload_1
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6: iconst_1
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7: isub
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8: bipush 26
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10: irem
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11: bipush 97
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13: iadd
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14: istore_2
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15: iload_2
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16: i2c
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17: ireturn
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public static boolean access(java.lang.String, java.lang.String);
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Code:
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0: ldc #7 // String tvvvvqfstuspohqbttxpse
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2: astore_2
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3: ldc #9 // String
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5: astore_3
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6: iconst_0
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7: istore 4
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9: iload 4
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11: aload_2
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12: invokevirtual #11 // Method java/lang/String.length:()I
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15: if_icmpge 40
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18: aload_3
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19: aload_2
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20: iload 4
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22: invokevirtual #17 // Method java/lang/String.charAt:(I)C
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25: invokestatic #21 // Method transform:(C)C
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28: invokedynamic #27, 0 // InvokeDynamic #0:makeConcatWithConstants:
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// (Ljava/lang/String;)Ljava/lang/String;
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33: astore_3
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34: iinc 4, 1
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37: goto 9
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40: aload_0
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41: ldc #31 // String admin
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43: invokevirtual #33 // Method java/lang/String.equals:(Ljava/lang/Object;)Z
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46: ifeq 70
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49: aload_1
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50: aload_3
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51: invokevirtual #37 // Method java/lang/String.toString:()Ljava/lang/String;
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54: invokevirtual #33 // Method java/lang/String.equals:(Ljava/lang/Object;)Z
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57: ifeq 70
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60: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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63: ldc #47 // String Success!! Access granted
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65: invokevirtual #49 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
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68: iconst_1
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69: ireturn
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70: iconst_0
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71: ireturn
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public static void main(java.lang.String...);
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Code:
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0: ldc #55 // String Hello, try to find the username and the [...]
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2: astore_1
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3: aload_1
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4: invokedynamic #57, 0 // InvokeDynamic #1:makeConcatWithConstants:
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// (Ljava/lang/String;)Ljava/lang/String;
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9: astore_1
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10: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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13: aload_1
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14: iconst_0
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15: anewarray #2 // class java/lang/Object
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18: invokevirtual #60 // Method java/io/PrintStream.printf:(Ljava/lang/String;
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// [Ljava/lang/Object;)Ljava/io/PrintStream;
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21: pop
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22: aload_0
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23: arraylength
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24: iconst_2
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25: if_icmpeq 48
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28: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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31: ldc #64 // String Usage:
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33: invokevirtual #49 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
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36: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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39: ldc #66 // String java Login username password
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41: invokevirtual #49 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
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44: iconst_m1
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45: invokestatic #68 // Method java/lang/System.exit:(I)V
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48: aload_0
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49: iconst_0
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50: aaload
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51: aload_0
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52: iconst_1
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53: aaload
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54: invokestatic #72 // Method access:(Ljava/lang/String;Ljava/lang/String;)Z
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57: ifne 68
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60: new #76 // class java/lang/RuntimeException
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63: dup
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64: invokespecial #78 // Method java/lang/RuntimeException."<init>":()V
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67: athrow
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68: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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71: ldc #79 // String Congratulations, now write the username and [...]
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73: invokevirtual #49 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
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76: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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79: ldc #81 // String Provide an explanation on how you discover it.
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81: invokevirtual #49 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
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84: goto 113
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87: astore_2
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88: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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91: ldc #83 // String Wrong username and/or password.
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93: invokevirtual #49 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
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96: getstatic #41 // Field java/lang/System.out:Ljava/io/PrintStream;
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99: aload_0
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100: iconst_0
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101: aaload
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102: aload_0
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103: iconst_1
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104: aaload
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105: invokedynamic #85, 0 // InvokeDynamic #2:makeConcatWithConstants:
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// (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
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110: invokevirtual #49 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
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113: return
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Exception table:
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from to target type
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48 84 87 Class java/lang/RuntimeException
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}
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\end{minted}
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We first understand from instructions 28 to 45 of the \textit{main} method that
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the class is meant to be launched with two parameters, which are namely the
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username and the password.
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We see that from instructions 48 to 54 the \textit{access} static method is
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invoked with the first command line argument as the first parameter and the
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second command line argument as the second parameter, which are namely the
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username and the password provided for login. Then the \textit{access} method
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checks if its first parameter is equal to the string ``admin'' at instructions
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40 to 46, returning \texttt{false} if not. Therefore we can say the the right
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username is ``admin''.
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We then analyze the \textit{transform} method. Instructions 0 to 4 subtract the
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constant 97 (the character code of a lowercase ``a'') to the character given as
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argument, storing the result in the stack variable position 1. Then,
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instructions 5 to 7 subtract the constant 1 to the saved variable, instructions
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7 to 10 compute the modulo 26 (\texttt{\% 26}, where 26 is the number of ASCII
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lowercase letters) of the result and instructions 11 to 13 increment the final
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result with the constant 97 and returns the result as a character. Instructions
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14 to 17 in order store what the method computed in variable 2, loads variable 2
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and returns a copy cast to type \texttt{char}. Therefore, an equivalent Java
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source for the method is:
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\begin{minted}{java}
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public static char transform(char c) {
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return (char) (((c - ((int) 'a') - 1) % 26) + ((int) 'a'));
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}
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\end{minted}
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Instructions 0 to 37 show that a string with value ``tvvvvqfstuspohqbttxpse'' is
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read character by character the method \textit{transform} is applied, forming a
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new String. Given the reverse engineered \textit{transform} method and the fact
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that the string is composed only of lowercase letters starting from ``b'', both
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adding and subtracting ``a'' and computing a modulo 26 of each character are
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operations that lead to the same character. Indeed, the only change
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\textit{transform} applies to every single character is to subtract 1, or return
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the preceding character of each given character. Therefore, given this, we
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determine the decoded password to be the string ``suuuuperstrongpassword''.
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\section*{Exercise E: Monitoring JIT}
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\begin{enumerate}
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\item \begin{enumerate}[(a)]
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\item \texttt{-XX:-PrintCompilation}
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\item \texttt{-XX:+UnlockDiagnosticVMOptions -XX:+PrintInlining}
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\item \texttt{-XX:NativeMemoryTracking=summary}
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\end{enumerate}
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\item The output of the command \texttt{java -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlining Inlining} is the following:
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\begin{verbatim}
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@ 17 java.lang.String::isLatin1 (19 bytes) inline
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@ 27 java.lang.StringLatin1::hashCode (42 bytes) callee is too large
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@ 37 java/lang/StringUTF16::hashCode (not loaded) not inlineable
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@ 6 java.lang.String::coder (15 bytes) inline
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@ 6 Point::<init> (15 bytes) inline
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@ 1 java.lang.Object::<init> (1 bytes) inline
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@ 20 Point::getY (5 bytes) inline
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@ 25 Point::setX (6 bytes) inline
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@ 30 Point::setY (6 bytes) inline
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@ 6 Point::<init> (15 bytes) inline
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@ 1 java.lang.Object::<init> (1 bytes) inline
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@ 20 Point::getY (5 bytes) inline
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@ 25 Point::setX (6 bytes) inline
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@ 30 Point::setY (6 bytes) inline
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@ 20 Point::getY (5 bytes) accessor
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@ 25 Point::setX (6 bytes) accessor
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@ 30 Point::setY (6 bytes) accessor\end{verbatim}
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Therefore we can confirm that all methods listed were inlined while executing class \textit{Inlining}.
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\end{enumerate}
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\section*{Exercise F: Java Agent}
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\begin{enumerate}
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\item The compiled code given cannot be executed as-is as the class \textit{ch.usi.inf.ajp22.Point} contains an invalid java class file format version of 255 (where e.g. for Java 17 the correct value is 61).
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\item Please find the relevant source code in folder \texttt{ExcerciseF}.
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\end{enumerate}
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\end{document}
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