Let us write a program which will generate a core dump.
#include <iostream>
using namespace std;
int divint(int, int);
int main() {
int x = 5, y = 2;
cout << divint(x, y);
x =3; y = 0;
cout << divint(x, y);
return 0;
}
int divint(int a, int b)
{
return a / b;
}
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To enable debugging, the program must be compiled with the -g option.
$g++ -g crash.cc -o crash
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NOTE: We are using g++ compiler because we have used C++ source code.
Now, when run this program on your linux machine, it produces the result:
Floating point exception (core dumped)
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You will find a core file in your current directory.
Now to debug the problem, start gdb debugger at command prompt:
$gdb crash
# Gdb prints summary information and then the (gdb) prompt
(gdb) r
Program received signal SIGFPE, Arithmetic exception.
0x08048681 in divint(int, int) (a=3, b=0) at crash.cc:21
21 return a / b;
# 'r' runs the program inside the debugger
# In this case the program crashed and gdb prints out some
# relevant information. In particular, it crashed trying
# to execute line 21 of crash.cc. The function parameters
# 'a' and 'b' had values 3 and 0 respectively.
(gdb) l
# l is short for 'list'. Useful for seeing the context of
# the crash, lists code lines near around 21 of crash.cc
(gdb) where
#0 0x08048681 in divint(int, int) (a=3, b=0) at crash.cc:21
#1 0x08048654 in main () at crash.cc:13
# Equivalent to 'bt' or backtrace. Produces what is known
# as a 'stack trace'. Read this as follows: The crash occurred
# in the function divint at line 21 of crash.cc. This, in turn,
# was called from the function main at line 13 of crash.cc
(gdb) up
# Move from the default level '0' of the stack trace up one level
# to level 1.
(gdb) list
# list now lists the code lines near line 13 of crash.cc
(gdb) p x
# print the value of the local (to main) variable x
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In this example, it is fairly obvious that the crash occurs because of the attempt to divide an integer by 0.
To debug a program 'crash' that has crashed and produced a core file named 'core', type the following at the command line:
As this is mostly equivalent to starting gdb and typing the 'r' command, all of the commands above could now be used to debug the file.
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