GDB Debug C Program

Debugging a program with GDB

GDB Overview
————

GDB is a powerful UNIX program debugging tool released by the GNU Open source organization. Perhaps, you prefer that graphical interface, such as VC, BCB and other IDE debugging, but if you are in the UNIX platform to do software, you will find GDB this debugging tool than VC, BCB graphical debugger more powerful features. The so-called "inch, the ruler is short" is this truth.

In general, GDB is the main help you complete the following four aspects of the function:

1, start your program, you can follow your custom requirements to run the program at will.
2. Allow the program to be debugged to stop at the breakpoint where you have specified the adjustment. (Breakpoint can be a conditional expression)
3. When the program is stopped, you can check what happened in your program at this time.
4. Dynamically change the execution environment of your program.

From the above, GDB and the General debugging tool is not the same, basically is to complete these functions, but in the details, you will find GDB this debugging tool is powerful, you may be more accustomed to the graphical debugging tools, but sometimes, the command line debugging tools have a graphical tool can not be done. Let's see.

A debugging example
——————

SOURCE program: TST.C

1 #include <stdio.h>
2
3 int func (int n)
4 {
5 int sum=0,i;
6 for (i=0; i<n; i++)
7 {
8 sum+=i;
9}
Sum of ten return;
11}
12
13
Main ()
15 {
int i;
A long result = 0;
for (I=1; i<=100; i++)
19 {
result + = i;
21}
22
printf ("result[1-100] =%d/n", result);
printf ("result[1-250] =%d/n", func (250));
25}

Compile Build Execution file: (under Linux)
hchen/test> cc-g Tst.c-o TST

Debugging with GDB:

hchen/test> gdb TST <----------start GDB
GNU gdb 5.1.1
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, covered by the GNU general public License, and you are
Welcome to change it and/or distribute copies of it under certain.
Type "Show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "Show warranty" for details.
This GDB is configured as "I386-suse-linux" ...
(GDB) L <--------------------l command is equivalent to list, starting from the first line of the original code.
1 #include <stdio.h>
2
3 int func (int n)
4 {
5 int sum=0,i;
6 for (i=0; i<n; i++)
7 {
8 sum+=i;
9}
Sum of ten return;
(GDB) <--------------------direct return, repeat the last command
11}
12
13
Main ()
15 {
int i;
A long result = 0;
for (I=1; i<=100; i++)
19 {
result + = i;
(GDB) Break <--------------------set breakpoints at line 16th of the source program.
Breakpoint 1 at 0x8048496:file tst.c, line 16.
(GDB) Break Func <--------------------set breakpoints at the entrance of function func ().
Breakpoint 2 at 0x8048456:file tst.c, line 5.
(GDB) Info Break <--------------------view breakpoint information.
Num Type Disp Enb Address What
1 breakpoint Keep Y 0x08048496 in main at tst.c:16
2 Breakpoint Keep Y 0x08048456 in func at Tst.c:5
(GDB) R <---------------------running program, shorthand for Run command
Starting program:/HOME/HCHEN/TEST/TST

Breakpoint 1, Main () at Tst.c:17 <----------stop at the breakpoint.
A long result = 0;
(GDB) n <---------------------single statement execution, next command shorthand.
for (I=1; i<=100; i++)
(GDB) n
result + = i;
(GDB) n
for (I=1; i<=100; i++)
(GDB) n
result + = i;
(GDB) C <---------------------continue to run the program, continue command shorthand.
Continuing.
RESULT[1-100] = 5050 <----------program output.

Breakpoint 2, func (n=250) at Tst.c:5
5 int sum=0,i;
(GDB) n
6 for (i=1; i<=n; i++)
(GDB) P i <---------------------print the value of the variable i, the Print command shorthand.
$ = 134513808
(GDB) n
8 sum+=i;
(GDB) n
6 for (i=1; i<=n; i++)
(GDB) P sum
$ = 1
(GDB) n
8 sum+=i;
(GDB) P I
$2
(GDB) n
6 for (i=1; i<=n; i++)
(GDB) P sum
$4 = 3
(GDB) bt <---------------------view the function stack.
#0 func (n=250) at Tst.c:5
#1 0x080484e4 in Main () at tst.c:24
#2 0x400409ed in __libc_start_main () from/lib/libc.so.6
(GDB) Finish <---------------------Exit function.
Run till exit from #0 func (n=250) at Tst.c:5
0x080484e4 in Main () at tst.c:24
printf ("result[1-250] =%d/n", func (250));
Value returned is $6 = 31375
(GDB) C <---------------------continue to run.
Continuing.
RESULT[1-250] = 31375 <----------program output.

Program exited with code 027. <--------program exit, Debug end.
(GDB) Q <---------------------exit gdb.
Hchen/test>

Well, with the above perceptual knowledge, or let us have a systematic understanding of gdb it.

Using GDB
————

In general, GDB is mainly debugging the C + + program. In order to debug a C + + program, first at compile time, we have to add debug information to the executable file. This can be done using the-g parameter of the compiler (cc/gcc/g++). Such as:

> cc-g hello.c-o Hello
> g++-G hello.cpp-o Hello

Without-G, you will not see the program's function name, variable name, instead of the memory address of the runtime. After you have added the debug information with-G and successfully compiled the target code, let's look at how to debug it with GDB.

There are several ways to start gdb:

1. GDB <program>
Program is your execution file, usually under the catalogue of course.

2. GDB <program> Core
Using GDB to debug a running program and core file at the same time, the core is the file generated after core dump is executed illegally.

3. GDB <program> <PID>
If your program is a service program, you can specify the process ID at which the service program runs. GDB will automatically attach up and debug him. The program should be searched in the PATH environment variable.

GDB start, you can add some gdb start switch, the detailed switch can be viewed with gdb-help. I'll just cite some of the more commonly used parameters below:

-symbols <file>
-S <file>
Reads the symbol table from the specified file.

-se file
Reads the symbol table information from the specified file and uses it in the executable file.

-core <file>
-C <file>
Core file of core dump when debugging.

-directory <directory>
-D <directory>
Add a search path to a source file. The default search path is the path defined by path in the environment variable.

Transfer from http://blog.csdn.net/haoel/article/details/2879