Linux GCC compiler options

-g option enables use of extra debugging information that GDB can use. Here's example of C code:

int main() {
    int x = 1/0;    
}

let's compile it without -g option and see gdb output:

$ gcc test.c -o test
test.c: In function ‘main’:
test.c:2:11: warning: division by zero [-Wdiv-by-zero]
$ gdb -q ./test
Reading symbols from /home/mariusz/Dokumenty/Projekty/Testy/test...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/mariusz/Dokumenty/Projekty/Testy/test 

Program received signal SIGFPE, Arithmetic exception.
0x080483cb in main ()

And now with -g option:

$ gcc -g test.c -o test
test.c: In function ‘main’:
test.c:2:11: warning: division by zero [-Wdiv-by-zero]
$ gdb -q ./test
Reading symbols from /home/mariusz/Dokumenty/Projekty/Testy/test...done.
(gdb) run
Starting program: /home/mariusz/Dokumenty/Projekty/Testy/test 

Program received signal SIGFPE, Arithmetic exception.
0x080483cb in main () at test.c:2
2       int x = 1/0;    

As you can see, now there is information about line with error.

It is related to debugging:

(from man gcc)

-g Produce debugging information in the operating system's native format (stabs, COFF, XCOFF, or DWARF 2). GDB can work with this debugging information.

You can run a debugger on a program without debugging symbols in it, but it is like trying to find your keys in the dark. Eg, you cannot set breakpoints:

(gdb) break 6
No symbol table is loaded.

That's a big hassle.