Red Hat ENTERPRISE LINUX 3 - DEVELOPER TOOLS GUIDE Guide de l'utilisateur télécharger pdf (Page 66)

Chapter 5. Debugging

Ensure that the resulting binary hello is in the same directory as hello.c.

2. Run gdb on the hello binary, i.e. gdb hello.

3. After several introductory comments, gdb will display the default GDB prompt:

(gdb)

4. Some things can be done even before execution is started. The variable hello is global, so it can

be seen even before the main procedure starts:

gdb) p hello

$1 = "Hello, World!"

(gdb) p hello[0]

$2 = 72 'H'

(gdb) p *hello

$3 = 72 'H'

(gdb)

Note that the print targets hello[0] and *hello require the evaluation of an expression, as

does, for example, *(hello + 1):

(gdb) p *(hello + 1)

$4 = 101 'e'

5. Next, list the source:

(gdb) l

1 #include <stdio.h>

3 char hello[] = { "Hello, World!" };

5 int

6 main()

7 {

8 fprintf (stdout, "%s\n", hello);

9 return (0);

10 }

The list reveals that the fprintf call is on line 8. Apply a breakpoint on that line and resume

the code:

(gdb) br 8

Breakpoint 1 at 0x80483ed: file hello.c, line 8.

(gdb) r

Starting program: /home/moller/tinkering/gdb-manual/hello

Breakpoint 1, main () at hello.c:8

8 fprintf (stdout, "%s\n", hello);

6. Finally, use the “next” command to step past the fprintf call, executing it:

1 2 ... 61 62 63 64 65 66 67 68 69 70 71 ... 99 100

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Red Hat ENTERPRISE LINUX 3 - DEVELOPER TOOLS GUIDE Guide de l'utilisateur Page 66