p1 2025/2026

doc/z1.tex

@@ -0,0 +1,171 @@
+\documentclass[a4paper,12pt]{article}
+\usepackage[utf8]{inputenc}
+\usepackage{listings}
+\usepackage{xcolor}
+\usepackage{geometry}
+\geometry{margin=1in}
+
+% Configure listings for C code
+\lstset{
+    language=C,
+    basicstyle=\ttfamily\small,
+    keywordstyle=\color{blue}\bfseries,
+    stringstyle=\color{red},
+    commentstyle=\color{green!50!black},
+    numbers=left,
+    numberstyle=\tiny,
+    stepnumber=1,
+    numbersep=5pt,
+    showspaces=false,
+    showstringspaces=false,
+    frame=single,
+    breaklines=true,
+    breakatwhitespace=true,
+    tabsize=4
+}
+
+% Configure listings for GDB commands
+\lstdefinestyle{gdb}{
+    basicstyle=\ttfamily\small,
+    numbers=left,
+    numberstyle=\tiny,
+    stepnumber=1,
+    numbersep=5pt,
+    showspaces=false,
+    showstringspaces=false,
+    frame=single,
+    breaklines=true,
+    breakatwhitespace=true
+}
+
+\title{Debugging the \texttt{slen} Function with GDB}
+\author{}
+\date{May 22, 2025}
+
+\begin{document}
+
+\maketitle
+
+\section{Introduction}
+This document describes the \texttt{slen} function, a C function that calculates the length of a null-terminated string, and details the debugging process using GDB on an embedded target. The debugging session history is included to illustrate the steps taken to verify the function's correctness.
+
+\section{The \texttt{slen} Function}
+The \texttt{slen} function takes a string pointer and returns the number of characters until the null terminator (\texttt{\textbackslash 0}). Below is the source code:
+
+\begin{lstlisting}
+#include <stdint.h>
+
+const char * ptr = "informatyk mpabi 0\n";
+
+int slen ( char *s ) {
+    int n;
+    for (n = 0; *s != '\0'; s++)
+        n++;
+    return n;
+}
+
+int main () {
+    int x = slen (ptr);
+    return 0;
+}
+\end{lstlisting}
+
+The string \texttt{ptr} points to \texttt{"informatyk mpabi 0\textbackslash n"}, and \texttt{slen} is called to compute its length, stored in \texttt{x}.
+
+\section{Debugging Strategy}
+The debugging process uses GDB with a remote target (port 3333) to verify the \texttt{slen} function. The strategy includes:
+\begin{itemize}
+    \item \textbf{Setup}: Connect to the target, load the program, and set breakpoints.
+    \item \textbf{Execution Control}: Step through instructions and continue to breakpoints to inspect \texttt{slen}'s execution.
+    \item \textbf{Memory Inspection}: Verify the string pointer and memory contents.
+    \item \textbf{State Monitoring}: Use the GDB dashboard to track registers, stack, and memory.
+    \item \textbf{Iterative Testing}: Reset and reload the program to ensure consistent behavior.
+\end{itemize}
+
+\section{GDB Command History}
+The following GDB commands were executed to debug \texttt{slen}:
+
+\begin{lstlisting}[style=gdb]
+target extended-remote :3333
+file prog
+load
+si
+b main
+dashboard -layout registers stack memory
+c
+si
+c
+si
+c
+laod  % typo, likely meant load
+load
+c
+c
+c
+radix 16
+set radix 16
+p/x ptr
+p/x *ptr
+p/c *ptr
+p/s *ptr
+print &ptr
+p ptr
+dashboard memory set 0x800000c0 32
+dashboard memory watch 0x800000c0 32
+dash
+p/x &ptr
+p/x ptr
+p/x *ptr
+dash
+dash
+clear
+dash
+si
+monitor reset halt
+si
+si
+exit
+target extended-remote :3333
+dash
+dashboard -layout registers stack memory breakpoints
+file prog
+load
+si
+exit
+dashboard -layout registers stack memory breakpoints
+exit
+dashboard -layout registers memory breakpoints stack
+file prog
+load
+si
+exit
+\end{lstlisting}
+
+\subsection{Explanation of Commands}
+\begin{itemize}
+    \item \texttt{target extended-remote :3333}: Connects to the embedded target on port 3333.
+    \item \texttt{file prog}, \texttt{load}: Loads the executable \texttt{prog} onto the target.
+    \item \texttt{b main}, \texttt{c}: Sets a breakpoint at \texttt{main} and continues execution to it.
+    \item \texttt{si}: Steps through instructions, allowing inspection of \texttt{slen}'s loop.
+    \item \texttt{p/x ptr}, \texttt{p/x *ptr}, \texttt{p/c *ptr}, \texttt{p/s *ptr}: Inspects the \texttt{ptr} address, its first character (hex and char), and the full string.
+    \item \texttt{print \&ptr}, \texttt{p/x \&ptr}: Checks the address of \texttt{ptr} itself.
+    \item \texttt{dashboard memory set 0x800000c0 32}, \texttt{dashboard memory watch 0x800000c0 32}: Monitors 32 bytes at address \texttt{0x800000c0}, likely where the string resides.
+    \item \texttt{dashboard -layout ...}: Configures the GDB dashboard to show registers, stack, memory, and breakpoints.
+    \item \texttt{monitor reset halt}: Resets the target and halts execution.
+    \item \texttt{clear}, \texttt{exit}: Clears breakpoints and exits GDB sessions.
+    \item \texttt{radix 16}, \texttt{set radix 16}: Sets hexadecimal output for memory and values.
+    \item \texttt{dash}: Likely a custom alias or typo, possibly for dashboard commands.
+\end{itemize}
+
+\section{Key Checks for \texttt{slen}}
+The debugging process verifies:
+\begin{itemize}
+    \item \textbf{Pointer Validity}: \texttt{ptr} points to the correct string (checked via \texttt{p/s *ptr}).
+    \item \textbf{Loop Correctness}: The loop in \texttt{slen} increments \texttt{n} and stops at \texttt{\textbackslash 0} (inspected via \texttt{si}).
+    \item \textbf{Memory Access}: Memory at \texttt{0x800000c0} is valid and uncorrupted (via \texttt{dashboard memory watch}).
+\end{itemize}
+
+\section{Conclusion}
+The GDB command history provides a detailed view of the debugging process, ensuring \texttt{slen} correctly computes the string length. The iterative use of stepping, memory inspection, and state monitoring confirms the function's behavior on the embedded target.
+
+\end{document}

main.c

@@ -1,29 +1,24 @@
+// p26.9 -z1
 #include <stdint.h>
 
-uint32_t x = 1, y =2, z[10];
-uint32_t *ip;
+const char * ptr = "informatyk mpabi 0\n";
+const char * ptr2 = "indwed mpabi 0\n";
 
-char * ptr = "informatyk\0";
+int slen ( char *s ) {
 
-int strlen ( char *s ) {
     int n;
 
-    for (n = 0; *s != '\0'; s++) {
+    for (n = 0; *s != '\0'; s++)
         n++;
-    }
 
   return n;
 }
 
 int main () {
 
-    ip =&x;
-    y = *ip;
-    *ip = 0;
 
-    ip = &z[0];
-
-    x = strlen (ptr) ;   
+    int x = slen (ptr) ;   
+    int x2 = slen (ptr2) ;   
 
   return 0;
 }