Problem in debugging with "GDB"?

jeremy28 · 07-07-2010, 12:20 AM

Hi all;

I'm using ubuntu 9.04.

I've started using "gdb" to debug my project line by line and have not worked with command
line debugger yet. So, I'm not familiar with this type of debugging!

When I write "gdb ./myprogram" in terminal, I see:

Code:

GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...

And when I write "b 20" to set a breakpoint at 20th line of code, I see:

Code:

Breakpoint 1 at 0x8048150: file ../sysdeps/i386/elf/start.S, line 20.

Afterwards, when I run "r" command, I expect that the program runs till 20th line and then I can write "n" command line by line to see the parameters' values and memory contents, but I face with the program's complete running without any stop on line 20!!

What is the solution please?!

TIA.

zirias · 07-07-2010, 12:57 AM

Wrong file ... your binary does not consist only of your own source file but also of some parts of the GCC runtime. When you don't specify a file for your breakpoint, the first one encountered is used, in that case start.S, which is common startup code in assembly language.

Just write "b foobar.c:20" or use a symbol (aka function name) for defining the breakpoint.

murugesan · 07-07-2010, 06:19 AM

Compile the program with the option:
-g

Prefered option not to use while debugging
-O

More information with gdb:
http://geocities.ws/murugesan/technical/gdb/
or
http://murugesan.webnode.com/technical/gdb/

If the statement where the break is given, is inside a conditional loop, it may not enter that location.
Try to give the location before that line.

To start from main use
gdb) break main

jeremy28 · 07-18-2010, 12:07 AM

Hi and thanks of your help!

When I write "b myprogram.cpp:20" in gdb, I see the result:
(while, I'm in myprogram.cpp directory, of course!)

Code:

No source file named myprogram.cpp.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (myprogram.cpp:20) pending.

And then, I type the "r" command, but the program runs completely without any stop on line 20!

What is the reason please?!

THX.

murugesan · 07-19-2010, 02:59 AM

An example:

Assume that the source file myprogram.cpp is in the following directory:
/home/murugesandins/.Murugesan/src/myprogram.cpp
Compile the program using the following commands:

murugesan · 07-19-2010, 03:08 AM

An example:

Assume that the source file myprogram.cpp is in the following directory:

Code:

/home/murugesandins/.Murugesan/src/myprogram.cpp
Compile the program using the following commands:
cd /home/murugesandins/.Murugesan/src/
g++ -g myprogram.cpp
cd /home/murugesandins/.Murugesan/
(gdb) /home/murugesandins/.Murugesan/src/a.out --directory=/home/avay/.Murugesan/tcp/src
(gdb) break myprogram.cpp:20
(gdb) run
Starting program: /home/murugesandins/.Murugesan/src/a.out
line1:1
line2:1
line3:1
line4:1
line5:1
line6:1
line7:1
line8:1
line9:1
line10:1
line11:1
line20 is not set to 20:6
Program exited normally.

The reason is because of the following source code:

Code:

$ grep -n $ /home/murugesandins/.Murugesan/src/myprogram.cpp
1:#include <iostream>
2:using namespace std ;
3:int main()
4:{
5: int line1=1, line2=2, line3=3, line4=4, line5=5, line6=6, line7=7, line8=8, line9=9, line10=10, line11=11, line20=06 ;
6: cout << "line1:" << line1 << "\n" ;
7: cout << "line2:" << line1 << "\n" ;
8: cout << "line3:" << line1 << "\n" ;
9: cout << "line4:" << line1 << "\n" ;
10: cout << "line5:" << line1 << "\n" ;
11: cout << "line6:" << line1 << "\n" ;
12: cout << "line7:" << line1 << "\n" ;
13: cout << "line8:" << line1 << "\n" ;
14: cout << "line9:" << line1 << "\n" ;
15: cout << "line10:" << line1 << "\n" ;
16: cout << "line11:" << line1 << "\n" ;
17:
18: if ( 20 == line20 )
19: {
20: cout << "line20:" << line20 << "\n" ;
21: }
22: else
23: {
24: cout << "line20 is not set to 20:" << line20 << "\n" ;
25: }
26: return 0 ;
27:}

Hence set the break point at specified location.

When you get the following error:

Code:

No source file named myprogram.cpp.

It means the gdb is not able to find the location of source code. Hence it is assuming to take it while loading the shared library.

Kindly read the manual of gdb/ use the following command:

Code:

gdb --help

Aquarius_Girl · 07-19-2010, 03:09 AM

Quote:

Originally Posted by zirias

Wrong file ... your binary does not consist only of your own source file but also of some parts of the GCC runtime. When you don't specify a file for your breakpoint, the first one encountered is used, in that case start.S, which is common startup code in assembly language.

Just write "b foobar.c:20" or use a symbol (aka function name) for defining the breakpoint.

But simple b 7 works for me !
See the below code:

Code:

anisha@linux-uitj:~/junk> cat r.c
#include <stdio.h>

int main ()
{
     int i = 98;
        // HD, Figure 3-1
        i |= (i >>  1);
        i |= (i >>  2);
        i |= (i >>  4);
        i |= (i >>  8);
        i |= (i >> 16);

        printf ("%d", (i - (i >> 1)));
        //return i - (i >> 1);


}
anisha@linux-uitj:~/junk> gcc -g r.c
anisha@linux-uitj:~/junk> gdb a.out
GNU gdb (GDB) SUSE (6.8.91.20090930-2.4)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-suse-linux".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /home/anisha/junk/a.out...done.
(gdb) b 7
Breakpoint 1 at 0x400543: file r.c, line 7.
(gdb) r
Starting program: /home/anisha/junk/a.out
Missing separate debuginfo for /lib64/ld-linux-x86-64.so.2
Try: zypper install -C "debuginfo(build-id)=591af1afa33f255704fb6a60859b93d00e205302"
Missing separate debuginfo for /lib64/libc.so.6
Try: zypper install -C "debuginfo(build-id)=c5a3dfd66bf61fcdec9bc22153b2fbd0d6697960"

Breakpoint 1, main () at r.c:7
7               i |= (i >>  1);
(gdb)

Aquarius_Girl · 07-19-2010, 03:19 AM

Quote:

Originally Posted by jeremy28

When I write "gdb ./myprogram" in terminal, I see:

And when I write "b 20" to set a breakpoint at 20th line of code, I see:

Code:

Breakpoint 1 at 0x8048150: file ../sysdeps/i386/elf/start.S, line 20.

Afterwards, when I run "r" command, I expect that the program runs till 20th line and then I can write "n" command line by line to see the parameters' values and memory contents, but I face with the program's complete running without any stop on line 20!!

What is the solution please?!

TIA.

May be you did not compile your program like :

Code:

gcc -g myprogram.c

Notice the -g option ?

Aquarius_Girl · 07-19-2010, 03:26 AM

murugesan

Read the following link to make life easier for others:
http://www.linuxquestions.org/questi....php?do=bbcode

I couldn't read you post !

murugesan · 07-19-2010, 04:03 AM

Using BB Code List.

Aquarius_Girl · 07-19-2010, 04:09 AM

murugesan

One more gentle suggestion:

You could have modified your post number 6 by clicking the Edit button rather than posting it again