Weekly Notes for Week 07

• In the lecture on February, 11th I will finish with the Chapter “Introduction” and will start the discussion of System Structures (Chapter 2).
• The 1st mandatory assignment will be made available on the course homepage during week 8.
• The following voluntary reading material will augment my presentation of DTrace, bpftrace, and perf. It might only be needed for week 08.
  • Dynamic Instrumentation of Production Systems, Bryan M. Cantrill, Michael W. Shapiro and Adam H. Leventhal, Solaris Kernel Development Sun Microsystems link
  • bpftrace and its bpftrace Tutorial
  • DTrace Intro, pdf and Brandan Gregg’s page on dtrace
  • The examples that were shown in the lecture can already be downloaded here, and will very likely be updated in week 8.
• Voluntary reading for SystemTap
• Voluntary reading on Linux kernel profiling with perf
• Note: The slides used in the lecture for the second chapter differ significantly from the original slides provided by Wiley.

Tutorial Session Week 07

• Prepare for the Tutorial Session in Week 07 from Chapter 1 the following exercises
  • 1.1, 1.3, 1.4, 1.5, 1.6, 1.8, 1.10, 1.11 (Practice Exercises)
  • 1.12, 1.14, 1.16, 1.19, 1.24 (Exercises)

C Programming (refresh)

• Which of the following is the proper declaration of a pointer?
  • int x;
  • int &x;
  • ptr x;
  • int *x;
• Which of the following gives the memory address of integer variable a?
  • *a;
  • a;
  • &a;
  • address(a);
• Which of the following gives the memory address of a variable pointed to by pointer a?
  • a;
  • *a;
  • &a;
  • address(a);
• Which of the following gives the value stored at the address pointed to by pointer a?
  • a;
  • val(a);
  • *a;
  • &a;
• Which of the following is the proper keyword or function to allocate memory in C?
  • new
  • malloc
  • create
  • value
• Which of the following is the proper keyword or function to deallocate memory?
  • free
  • delete
  • clear
  • remove
• Repeat the discussion of the four following examples to swap the content of two variables. Which of the examples are correct, which are wrong?

  • Swap Version 1

  • Swap Version 2

  • Swap Version 3

  • Swap Version 4

• Analyse the following C source code. Discuss what it does (this prepares you for the 1st mandatory assignment).

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#include "dm510_msgbox.h"
#include <stdlib.h>
#include <string.h>

typedef struct _msg_t msg_t;

struct _msg_t{
  msg_t* previous;
  int length;
  char* message;
};

static msg_t *bottom = NULL;
static msg_t *top = NULL;

int dm510_msgbox_put( char *buffer, int length ) {
  msg_t* msg = malloc(sizeof(msg_t));
  msg->previous = NULL;
  msg->length = length;
  msg->message = malloc(length);
  memcpy(msg->message, buffer, length);

  if (bottom == NULL) {
    bottom = msg;
    top = msg;
  } else {
    /* not empty stack */
    msg->previous = top;
    top = msg;
  }
  return 0;
}

int dm510_msgbox_get( char* buffer, int length ) {
  if (top != NULL) {
    msg_t* msg = top;
    int mlength = msg->length;
    top = msg->previous;

    /* copy message */
    memcpy(buffer, msg->message, mlength);

    /* free memory */
    free(msg->message);
    free(msg);

    return mlength;
  }
  return -1;
}

int main(int argc, char** argv) {
  char *in = "This is a stupid message.";
  char msg[50];
  int msglen;
 
  /* Send a message containing 'in' */
  dm510_msgbox_put(in, strlen(in)+1);
 
  /* Read a message */
  msglen = dm510_msgbox_get(msg, 50);

  return 0;
}