Master of Science in Computer Science - Computer Science Introductory Course

Laboratory Work 4: Makefile

Translated from a French version designed by Bertrand Dupouy

1. Introduction to the program to be studied

Sword strikes are simulated by sending a signal to the opponent. Each fighter protects himself by ignoring the corresponding signal. When they attack their opponent, the fighters become sensitive to signals and can receive strikes. The program is divided into 3 functions:

• main contains global variables, a few #define and typedef statements and simulates the fight.
• Touche processes a received sword strike.
• Fin is called when a child process terminates

mkdir tp_chprod
cd tp_chprod

1.1 Question 1

• signal(sig, fonc) specifies that the fonc function should be called if a signal number sig is received
• kill(pid, sig) sends signal number sig to the process identified by pid,
• Read the comments at the beginning of starwars.c

while (PointsDeVie[Moi] > 0)
 {
 signal (Sabre[Lui], SIG_IGN); /* Comment 30 */
 sleep (random() % 3);
 sleep (TempsDefense[Moi] - 1); /* Comment 35 */
 signal (Sabre[Lui], Touche); /* Comment 40 */
 sleep (TempsAttaque[Moi]);
 if (kill(Pids[Lui], Sabre[Moi]) < 0) break; /* Comment 45 */
 }

• What does a process do when it executes instructions between comment 30 and comment 35 ? What behaviour is simulated by these instructions ?
• What does a process do when it executes instructions between comment 40 and comment 45 ? What behaviour is simulated by these instructions ?
  
• What happens for each process when signal Sabre[Lui] is processed by function Touche ?

1.2 Question 2

• - main.c that contains only main, the global variables and their initialization
• - foncs.c that contains only Touche and Fin,
• - foncs.h that contains the prototypes of functions Touche and Fin,
• - utils.h that contains only typdef and #define statements
• - globals.h that contains only the extern declarations relative to the global variables,

1. Cut the file as specified.
2. Include the required .h files in the appropriate .c files
   
3. Recompile each file as indicated below. You should not get any  "warnings". If there are, go back to step 2.
   • gcc -Wall -c main.c
   • gcc -Wall -c foncs.c

2. Makefile file

2.1 Question 1

gmake all
starwars

to verify that it works fine.

2.2 Question 2

gmake all

• use the -I option to tell the compiler where to find the include files,
• for the make command to find these files, use a variable that gives the name of the directory where the include files are stored.

2.3 Question 3

2.4 Question 4

1. Do again gmake starwars.
   If gmake recompiles good ! jump to next step.
   Otherwise, if nothing happens then something is missing as utils.h concerns foncs.c and main.c. Explain why nothing has been recompiled  ?
   Modify Makefile to solve this problem.
   
2. Do again gmake starwars, there may be a warning that we are going to ignore for NOW.
   Execute gmake starwars
   The values displayed are relative to life points (points de vie) in main and in touche ( ... Pts DV : ... ) and are surprising.
   correct program, error in printf !!!!
   
3. Correct the cause of  warning.
   Be careful when using printf to debug

3. Debugging

If you want to use  gdb with starwars, do :

gdb starwars

We can now execute starwars under gdb control and try the following commands :

(gdb) break main
Breakpoint 1 at 0x10900: file main.c, line 36.
(gdb) run
Starting program: starwars 
Breakpoint 1, main () at main.c:36
36 int TempsDefense[] = {5, 3};
(gdb) step
37 int TempsAttaque[] = {3, 1};
(gdb) step
41 printf ("PointsDeVie : SkyWalker %d DarkVador : %d\n",
(gdb) step
PointsDeVie : SkyWalker 1076101120 DarkVador : 0
44 pid = fork();
(gdb) print PointsDeVie[0]
$1 = 10
(gdb) print PointsDeVie[1]
$2 = 10
(gdb)

• break sets a breakpoint
• run restarts execution until another breakpoint is encountered.
• step executes the next instruction and stops.
• print visualizes the variable values.
• variable values can be modified using the set command, etc.